GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: lloyd-ss on September 05, 2011, 11:36:45 AM
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Some of you guys do such beautiful work...... beautiful fits and finishes and design.... lots of patience and craftsmanship.
My stuff..... well, it is usually very functional. Let's leave it at that. Works like gang busters (or breaks), and looks good at 10 feet... no close-ups, please. Time to move on to the next project... somebody else finish up the details.
I'm glad we all make such a nice mix of styles on this gate. Everybody seems pretty comfortable with there skill level and everyone is very supportive and helpful, and that is very, very, cool. Thank you, everyone! ;)
So a short while ago I traded David some odds and ends for a used Disco stock because I wanted to keep my original intact for special reasons, but I wanted do some mods.
Here are some first pics. .437 O.D. x 30" long .25 cal barrel (barrel liner from Mike Sayers). Not sure how long the barrel will be in the end. An additional airtank of 4130 steel 1" O.D. x .063 wall x 19.75 long. Should give about 180 more cc's after deducting for threaded end plugs. (standard disco is about 135 cc's or so) I will connect the 2 tubes in the area of the gauge port. I might move the fill nipple to the lower tube and add a new triple barrel band, and LDC. Time will tell. I've modded the internals of the Disco to get 49fpe in .22 cal. rsterne has gone a little higher, so I guess i have to, too, sigh. ;) Gotta stay on your toes around here!! ;D
That big power was sucking the air up so this extra tube will more than double the tank volume.
I'll keep it coming, no promises on when, though. Lots of little parts and pieces to make.
Happy Labor Day everyone,
Lloyd
P.S. I haven't looked around, but someone might have already done this. :'(
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/DiscTank-1.jpg)
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/DiscTank-3.jpg)
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WOW!!!! Great idea Lloyd. On the same lines as the Careers air tube setup. More air to push them big chunks of lead out the barrel. Now we need to fix you up wiff real nice stock fer her...:) Never seen a mod like this one before Lloyd.
I love your comfort zone Lloyd. Wish I had that talent. More pics to come I hope. Keep us appraised buddy.
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Lloyd I must say your a man of many talents.
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Definately a project to keep an eye on. Great idea. Those discos seem to be a very popular building platform. Looks great so far. Good luck!
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WOW!!!! Great idea Lloyd. On the same lines as the Careers air tube setup. More air to push them big chunks of lead out the barrel. Now we need to fix you up wiff real nice stock fer her...:) Never seen a mod like this one before Lloyd.
I love your comfort zone Lloyd. Wish I had that talent. More pics to come I hope. Keep us appraised buddy.
Gene, I added the emphasis on your words in the quote. Actually in my opening sentence, your Beji Disco project was one of the nice ones I was thinking about. ;D
Lloyd
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Great project Lloyd!
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i have to, too, sigh. ;)
Happy Labor Day everyone,
Lloyd
Ha, you said to-to... :)
Looks great LLoyd! I'll definatly keep an eye on your progress.
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Great idea and will make a handy hunter for sure.... MuzzleMack was working on a dual tube Disco setup but I don't know if he ever finished and tested it.... it was just a "personal project" gun.... I believe he was going to build it as a .25 also....
There are pretty limited choices in .25 cal ammunition for medium to higher powered PCPs.... ranging in weights from the 25.3 gr. JSB Kings to the 43.2 gr. EunJin Pointeds.... Virtually everyone seems to have settled on the JSBs at between 950-1000 fps as the best long range pellet, although some barrels seem to work well with the .25 cal Predators and the 31 gr. Baracuda/Kodiaks.... Lots of guys use the EunJins for shorter distances, but they don't seem to have the accuracy/trajectory for the long ranges.... I know there are custom bulllets available that are heavier, they just aren't common....
The point of that last paragraph was to suggest that you aim for about 50-60 FPE for your project.... I got 58 FPE with my .25 cal Disco, but only about 8-9 shots.... so I detuned it to 45 FPE (11 shots).... With you having more than double the air, you should be able to hit the mid 50s and still have reasonable efficiency and shot count....
Have you thought of the possibility of a regulator between the two tubes?.... run the lower tube at 3000 psi and the upper at a regulated 2000?.... ;D
Bob
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now thats a great idea!
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Great idea and will make a handy hunter for sure.... MuzzleMack was working on a dual tube Disco setup but I don't know if he ever finished and tested it.... it was just a "personal project" gun.... I believe he was going to build it as a .25 also....
There are pretty limited choices in .25 cal ammunition for medium to higher powered PCPs.... ranging in weights from the 25.3 gr. JSB Kings to the 43.2 gr. EunJin Pointeds.... Virtually everyone seems to have settled on the JSBs at between 950-1000 fps as the best long range pellet, although some barrels seem to work well with the .25 cal Predators and the 31 gr. Baracuda/Kodiaks.... Lots of guys use the EunJins for shorter distances, but they don't seem to have the accuracy/trajectory for the long ranges.... I know there are custom bulllets available that are heavier, they just aren't common....
The point of that last paragraph was to suggest that you aim for about 50-60 FPE for your project.... I got 58 FPE with my .25 cal Disco, but only about 8-9 shots.... so I detuned it to 45 FPE (11 shots).... With you having more than double the air, you should be able to hit the mid 50s and still have reasonable efficiency and shot count....
Have you thought of the possibility of a regulator between the two tubes?.... run the lower tube at 3000 psi and the upper at a regulated 2000?.... ;D
Bob
Right now I have more questions than answers: barrel length, valve flow capacity, pellet vs bullet, valve chamber vol control vs regulator. I think I will just play and see what falls into place. The pellet and vel info is helpful. If I stick with the long barrel, the 31 gn barracudas might work out. Pellet vs bullet is a serious consideration at so many different levels, but I will at least have to try some bullets to see what they do. That really changes the nature of the Disco, though, probably in a direction that I do not care to go. I would like to avoid a regulator if I can and think I will try partitioning off the valve chamber first to see how that will affect velocity consistency and efficiency. For me, I think this disco will be a learning tool.
With the spring compression limited to about .500" and the actual hammer stroke being only about .660, I wonder how limiting that is for the total power of the set-up? Where is the true bottle neck? What about the little transfer port between the tank and barrel? Has anybody altered that, for better or worse? Do the tall breech blocks use the same dia port?? Many folks are using those. A delicate balance there. All that said, backing down from that max always yields such an improvement in shot count.
Thanks for the input. I am looking forward to this.
Lloyd
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Hi LLoyd
Looking good so far.
Let us know how the mod performs.
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go for it lloyd a .25 on a disco is a good idea even if it gets only 9 shots
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The transfer port on my .25 cal Disco is the same size as I use on a .22 cal.... 0.166" ID.... With a bottom fed barrel about teh biggest you can go is 3/4 of the bore or the pellet has trouble loading past it.... That would be 3/16" on a quarter bore.... That's what my Hayabusa uses, and yes the transfer port is taller because of the repeater breech....
Bob
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Wow, great idea! This will be interesting for sure.
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Book marked and eagerly awaiting updates
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Well, she's up and running!
I finished it up very late last night. Filled it with my shop compressor... no leaks. Filled it to 1000 psi... leaked at the gauge (o-ring fitting), tightened it up and the leak stopped. Filled it to 2200 psi and went to bed. This AM, still at 2200 psi. I have to tell you, that is very unusual for me, LOL. ;D
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/Extra_tank_installed-1.jpg)
The air transfer from tank to tank happens in the gauge fitting area. I had opened up the old gauge fitting (the one that fits in the tube with 2 o-rings) to get free flow from the front of the tank and 50fpe in the .22 version. With the new adapter I made, I bored it out most of the way, but just left a small hole to the front of the tank to start with it slightly choked down on power. Still, I just took one shot at 2200 psi with a .25 Barracuda (30.1 gn) and got 787 fps = 41.4 fpe. I think that's a good starting point.
I'll shot a string with this fill and then take it apart to get some detail pics. The new tank more than doubles the HPA volume, so I think I'll have to go for more power to make it seriously worthwhile. This could be a nice hunting set up, or worthy of a .25cal Marauder 8 shot clip. Even with the long barrel, hearing protection or a shroud are in order. So far, so good!
Lloyd
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Good first trial.... I'm watching over your shoulder.... ;D
Bob
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Sweet!
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Well, I think I got lucky on this one. There is a leak around the transfer port because I can feel a little puff of air every time the gun is fired.
I managed to shoot a 46 shot string with the .25 cal Disco with 310 cc of reservoir and 30" barrel.
30.1 Barracudas, 46 shots, starting at 2200 psi and shooting down to 1040 psi.
Average FPS = 768, Std Dev 15 FPS, Average FPE = 38.4 Std Dev 1.5 FPE.
The string is a little ragged because of the air leak, but overall, I am very happy with how flat the string is for a first pass, IMHO. I think fixing the air leak will smooth out the line.
Lloyd
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/25Disco_shot_string-1-1.jpg)
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Very nice, Lloyd.... Interesting the first couple of shots were a slightly higher velocity than usual.... otherwise a nice flat shot string.... What was the velocity range, about 8%?.... Excellent efficiency as well, 39.4 x 46 = 1812 FPE from 310/16.4=18.9 CI with an 80 Bar drop = 1512 CI for 1812/1512 = 1.20 FPE/CI....
What does the gun weigh?....
Bob
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Bob, 1.08 lbs for the tube (1" x .065 x 20", 4130-normalized- surprisingly easy to work with.) + about .3 lbs for the plugs. Total weight is about 7 lbs, but I don't have a good scale in that range.
Total spread is 8.2% of the average, and if you drop the last 2 shots it's 6.8%. I would think that fixing the air leak at the transfer port would improve that. What do you think?
I am surprised at how flat the string is, despite the bumpiness. I guess the chamber volume and spring and pellet, etc., must all be matched nicely. Luck. I am going to go for higher power, though.
Next time I think I have an easier way to join the tubes at the front..... maybe. I moved the fill nipple to the lower tube to make room for a shroud. But if I use a tall breech block for a 25 cal marauder mag, it might be a moot point. Thoughts? I'll email the spreadsheet.
Lloyd
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It's possible that the air leak may be the cause of the slightly jagged shot string.... They are seldom perfect.... When I'm working on shot strings I use 4% for my cutoff point.... That is about 1/4" POI change from the velocity at 50 yards.... some people use 3%, and some (for 25 yards and under) use up to 10%.... I adjust my fill and refill pressures (and hammer hit) to achieve that 4% curve....
I've found that lightening the hammer helps even out the shot-to-shot variation.... The downside is that you lose velocity and energy and have to lean on the hammer spring to get it back.... Restricting the transfer port knocks down the maximum velocity which flattens the curve.... Opening up the ports tends to make the curve steeper, hence shortening the portion within the 4% window....
7 lbs. for an 1800 FPE total gun is pretty darn good, I think.... Do you have a small feed hole between the bottom and top tube so that the shot is only drawing from the upper tube?.... What are your port sizes right now?....
Bob
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Using PA's specified 31grain per Baracuda.25, instead of 30.1, get even better ave fpe...~40.6fpe?
I see that 2200psi -1040psi = 1160psi drop = 80Bar drop from a 310cc = 18.92cu in reservoir
but i don't understand where the 1512cu in came from...?...
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I assume Lloyd weighed the pellets, the manufacturers weights are often wrong.... If you multiply 18.9 CI by 80 Bar, you get 1512 CI of air at 1 Bar pressure, which we use for a standard to compute the efficiency....
Bob
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Bob, Thanks for the thoughts on the spread. The air leak will be the first thing I attack. The deburring in the spring and hammer area. We'll see how that helps and go on from there.
There is a .087 hole between the tubes, and that flows from the lower tube into the part that used to be the gauge adapter piece that has the 2 o-rings. There is also a .087 hole thru the end of the gauge adapter to the front of the original tube.
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Gotcha.... and what diameter are the valve, transfer, and barrel ports?....
Bob
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Using PA's specified 31grain per Baracuda.25, instead of 30.1, get even better ave fpe...~40.6fpe?
I see that 2200psi -1040psi = 1160psi drop = 80Bar drop from a 310cc = 18.92cu in reservoir
but i don't understand where the 1512cu in came from...?...
John,
Yes, I usually weigh a few pellets before testing. The heavier the pellet the farther off they are sometimes. I just weighed 6 more of the H&N Barracudas together and got an average of 30.3gn for those. The tin has 31.02 printed on it.
I think Bob explained where the cubic inches came from.... standardizing the volume of air used back to sea level pressure, kinda like air compressors are rated in standard cubic feet per minute (scfm).
There is a link to a shot efficiency calculator near the top of the page in the GTA Library that you might find interesting.
Lloyd
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Gotcha.... and what diameter are the valve, transfer, and barrel ports?....
Bob
Bob, I'll verify the dimensions when I tear it down for pics.
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??? ??? ??? You guys just kill me I look forward to your post but I understand about half of what you talk about but I am learning so keep it up. You 2 are in a league of your own no doubts about it . Thanks David
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??? ??? ??? You guys just kill me I look forward to your post but I understand about half of what you talk about but I am learning so keep it up. You 2 are in a league of your own no doubts about it . Thanks David
David, you aren't by any chance calling us airgun nerds, are you? LOL ;D Bob, what do you think? ;)
Lloyd
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Lloyd were did you get the .25", 30" long barrel?
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~lifting up the flap of my shirt pocket protector to expose the very worn badge underneath~
YUP, it says NERD alright!.... ;D
Bob
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Lloyd were did you get the .25", 30" long barrel?
It is a barrel liner I bought from Mike Sayers, TJ's Enterprises, in Alexandria KY. He does the actual hammer forging of the chrome moly barrel liners that various places sell, including Track of the Wolf, I believe. Bunches of different calibers and rifling configurations to choose from. Sells it cut to length by the inch. Easy guy to work with and I probably have 8 different barrels from him.
I posted a picture of a stock list of what he had a while ago. Maybe search under my name and Mike Sayers.
Bob, do you by any chance have a new price list that you could post? I am pretty sure mine is out of date.
Lloyd
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I don't have a new list, but I can tell you that the current price is $4.25 per inch.... Here are some of interest:
.25 Auto: .243 bore, .250 groove, 1 in 14 twist, 6 land, 7/16" OD (will fit Crosman breech to convert to .25 cal)
.30 cal: .300 bore, .308 groove, 1 in 20 twist, 4 land, 1/2" OD (he also has a 10" twist - 6 land)
.357 cal: .348 bore, .357 groove, 1 in 16 twist, 6 land, 1/2" OD
.40 cal: .400" bore, .408 groove, several twists 14-24", 6 land, 5/8" OD
.45 ACP: .444 bore, .452 groove, 1 in 16 twist, 6 land, 5/8" OD
.45 Colt: .440 bore, .452 groove, 1 in 16 twist, 6 land, 5/8" OD
.45-70: .450 bore, .457 to .458 groove, several twists 17-26", 3 to 6 lands, 5/8" OD
.50 cal: .500" bore, .510" groove, 1 in 20 twist, 6 land, 11/16" OD
I just purchased a .457 with a 1 in 26" twist.... It has very narrow lands and looks like a great airgun barrel.... You can contact Mike Sayers at:
T.J.'s
3652 Neltner Road,
Alexandria, KY, 41001
(859) 635-5560
mikeandsusansayers "at" fuse "dot" net
He isn't set up for plastic or PayPal, you will need to send him a money order.... Liners are well packed and shipped promptly.... and he will do custom ones if you want to pay for a Mandrel or purchase in quantity....
Bob
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thank you both
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I managed to shoot a 46 shot string with the .25 cal Disco with 310 cc of reservoir and 30" barrel.
30.1 Barracudas, 46 shots, starting at 2200 psi and shooting down to 1040 psi.
Average FPS = 768, 8.2% vel spread, Std Dev 15 FPS, Average FPE = 38.4 Std Dev 1.5 FPE.
The string is a little ragged because of the air leak, but...Lloyd
.... Excellent efficiency as well, 39.4 x 46 = 1812 FPE from 310/16.4=18.9 CI with an 80Bar drop = 1512 CI for 1812fpe/1512cu in = 1.20 FPE/CI....What does the gun weigh?....Bob
I see that 2200psi -1040psi = 1160psi drop = 80Bar drop from a 310cc = 18.92cu in reservoir...but I don't understand where the 1512cu in came from...?...
If you multiply 18.9 CI by 80 Bar, you get 1512 CI of air at 1 Bar pressure, which we use for a standard to compute the efficiency....Bob
As I read and reread that last sentence, I kept seeing "volume times pressure equals pressure" which of course is nonsense...what the...what is he...?... ???
But that's not what you're saying.
You're stating a proportionality...a:b = c:d...or...a is to b as c is to d...
You're saying "X IS TO 80Bar AS 18.9 IS TO 1Bar so solving for X...X = 18.9cu in * 80Bar = 1512cu in.
In math, X:80 = 18.9:1 or X/80 = 18.9/1 or X = 80*18.9/1 = 1512
But why is that proportionality meaningful? Because it answers the question "How much air IS TO the reservoir pressure drop AS the original unpressurized tank of air WAS TO atmospheric air pressure (which is 1Bar at sea level)?" or "How much air is pumped into this tank to raise the pressure in the tank from atmospheric pressure up to 80Bar?"
So you're saying "Before we pump up the tank, there is 18.9cu in of air in the tank at normal atmospheric pressure...because 18.9cu in is the physical volume of the tank. If we pump up the tank to 80Bar, there will be enough air in there to fill a 1512cu in volume when allowed to escape back into the atmosphere...which is exactly what Lloyd did when he allowed it to excape one shot at a time 46 times.
Of course Lloyd didn't start down from 80Bar. He started at 2200psi = 151.7Bar and dropped 80Bar down to 152-80=72Bar = 1040psi...same deal...shooting 46pellets released 1512cubic inches of air.
If only that were as clear as it is wordy, Everyone would understand what I think I said. :D
p.s. here is a pretty user-friendly Units Conversion website:
www.convert-me.com/en/ (http://www.convert-me.com/en/)
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John,
You've got the hardest part figured out, and that is "How much "room air" did I use for those 46 shots?"
So those 46 shots used 1512 cuin, which is less than one cubic foot. Total FPE for the 46 shots was 1814fpe, so that means that I got approx 1.2 fpe for each cubic inch of air used. Pretty amazing how these pcp's work, when you think about it. That 1.2 fpe per cubic inch is one measure of an airgun's efficiency.
Glad you are enjoying this! ;D
Lloyd
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shooting 46 pellets released 1512 cubic inches of air.
YUP, that's exactly what we are saying.... and that 1512 CI of air, as it expanded in the barrel, produced 1812 FPE of energy.... Hence the efficiency was 1.20 FPE/CI.... Here is a calculator you can play with....
http://calc.sikes.us/1/ (http://calc.sikes.us/1/)
HTHs....
Bob
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Bob,Lloyd,etal:john,etal = LXA:glahsshoppahs
Thanks for the priceless lessons, Guys, i'm hanging up for tonight, ...zzz...hammers springs ports...zzz...valves...regulation...zzz...
The League of Extraordinary Airgunners
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Well, some good news and not so good news on this project.
First off, I got the bumpiness of the velocities in the shot string really smoothed out nicely! It turned out to be mostly about some partial threads in the rear cap (velocity adjuster/spring length adjuster) that the spring was snagging on when the gun fired. I bored that out to give full clearance and then put a polished center guide for the spring to keep it straight during compression. Now the spring will compress and expand very smoothly. I also found some damage on the valve head so I made a new stem and head. Shot-to-shot consistency is now very good (I don't have a full string because I was trying different pellet weights but here are five 31.4 gns that I shot: 865,864,865,861,859).
The bad news for me right now is that I seem to be stuck at 53 FPE, and I had to use 42.7gn EunJins to get that. I opened up the passage to the front of main air tank to get good flow (previously it was a drilled .087 hole), but I have to figure out what the bottle neck is. I will read around on the GTA and see if someone else has gotten thru this barrier with a disco. I feel sure somebody has.
Here are pics of some of the parts and pieces. The transfer port from the lower tank to the upper is a .087 hole thru the modified phillips head screw that ties the tanks together. The actual hole under the valve head is .250. The transfer port bushing into the barrel is .156. Looking at the pics, one thing I haven't checked recently is whether the bolt probe is long enough to push the pellet fully past the transfer port.
Lloyd
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/parts4.jpg)
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/parts3.jpg)
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/parts8.jpg)
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/parts7.jpg)
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On my .25 cal Disco I have seen 58 FPE with an 0.040" wire x 1.75" long hammer spring just shy of coil bind and a 2400 psi fill.... The peak velocity was 919 fps with 30.9 gr. Baracudas and occurred at 2000 psi.... The barrel port was 0.169", the TP was 0.166" and the valve exhaust port was 0.161" at a 20* angle and then streamlined by hand with a dremel.... The valve throat was drilled out but was not a full 1/4" (IIRC it was 15/64").... but the valve stem was slimmed to 0.115" and it was shortened 0.060" to increase the hammer stroke.... The valve was also bored out to 0.60" ID and the threads shortened to 0.30" long on the male (front) and tapered from that depth into the 0.60" ID on the back half.... The valve inlet was tapered and streamlined and the gauge port was 5/16" ID (offset) and tapered both ends for better flow into the valve....
Bob
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Bob,
Thanks for those details. It looks I have a couple more "opportunities for improvement" (that's what they call it at work, LOL) between the valve head and the pellet. I've got the rest of it pretty well covered.
Lloyd
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Hi guys,
I've been following this post. I also like to build a lot of custom guns. Mostly Crosman. Any way I recently built a 32 cal. disco and came to a dead end with the power. I'd say right around the same 55 FPE with .310 RND ball. I did all the normal valve porting, transfer ports, .046 x 1.75 heavy hammer spring etc. I came to the conclusion that I was never going to get any were unless 1 had more hammer weight and 2 major valve mods. Any way I saw Don Cothran had made a rear cocker for some ones custom build. Don't know if he was trying to achieve the same thing as me but was the prefect way of adding more hammer weight. This is what I came up with. 4 oz hammer rear cocker. By doing this I gained about 10 FPE which put me up to 64/65 FPE. Still have some fine toning with the power adjuster.
Any way food for thought. Keep them coming.
(http://i667.photobucket.com/albums/vv36/seanjspictures/Air%20Gun%20Parts/IMG_1693.jpg)
(http://i667.photobucket.com/albums/vv36/seanjspictures/Air%20Gun%20Parts/IMG_1696.jpg)
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Nice setup.... That looks like a Crosman hammer.... how did you install the cocking rod?.... Press fit?.... I don't imagine you drilled and tapped it and put in a setscrew because they are (case?) hardened.... My RVA is almost identical I could easily adapt it if desired....
Incidently, I have a 9mm 2260 Carbine running only a 16.5" barrel.... I got it to over 63 FPE (606 fps with 77.8 gr. EunJins) with a modded Disco valve and a stock hammer.... So you CAN get over 60 FPE if you go to a big enough caliber.... ;D
Bob
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Workingman,
Mine is in pieces on the bench right now and ready to go back together. I like that hammer cocker. I am headed to the lathe right now!
Thanks,
Lloyd
P.S. I'll be back
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I had to machine a completely new hammer. Its made out of stainless steel. The rod is threaded on both ends and screws in to hammer and then into weight.
Those are really good # s on the 9mm.especially with such a short barrel. I think I ported the valve out to the max with out re designing the valve stem. Cut threads, stream line inlets, bored to .250, TP .190, angled exhaust port and that using stock valve spring. I had a light valve spring and was getting higher # s but was all over the place.
I don't want to high jack lloyds thread. But would like to talk more about some of your mods. I do have a 9mm 16.5 L barrel Hi pac carbine I built and currently building two more 32 cals 14.5L barrel and another Disco. ;D
TO BE CONTINUED
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Workingman,
Sounds like you have some neat projects going, I hope we get to see some pics and such.
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It's late, and I refined several of my mods this evening, and added the heavier hammer and cocker. Great timing.
Only took a handful of shots, but ....
.25 cal RWS superdome weighed 31.4 and I got 962 fps = 64.5 fpe
.25 cal EunJin weighed 42.7 , 855 fps = 69.3 fpe
Details tomorrow night.
Lloyd
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What an amazingly informative and interesting thread. Thanks Lloyd (& Bob, & WMinVA)
Totally in awe, at the knowledge you guys posses. Thanks for such a great posting.
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Incidently, Lloyd and workinmanVA.... you don't need the recessed "waist" in the Disco hammer.... and in fact if you make the hammer a simple cylinder it will not only be heavier but it will work better if you should decide to use an MRod trigger group.... The shoulder on the original style hammer crashes into the sear and can break it.... I had it happen on my Hayabusa.... The shoulder provides a "half cock" position which I have never seen the use of.... except maybe for filling from zero pressure if your hammer spring is holding the valve open....
Great numbers on the .25, Lloyd.... can't wait for the details....
Bob
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You know I wondered about making the recess. The first one I made I completely recessed the hammer and the one in the pic I made just like the stock Crosman one. I guess the reason I recessed them was that I was worried about sear drag across a larger area of the hammer. If sear drags not a deal breaker, it would defiantly be a lot easier to machine. I have two more I have to make. How did it damage the sear? That hammer must of been putting a real beating the that sear.
I've been following your Hayabusa project on here and the Canadian forum. Very impressive. Actually that thread on the Canadian forum is the reason I vented my tube close to valve to prevent hammer bounce. Some times building and tuning air gun re mines me of the guy who invented the planetary gear set used in automatic transmission (he went crazy). So many variables.
lloyd nice #s. Can't wait to see some more.
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The sear broke completely.... it was impacting the shoulder on the hammer, there was quite a mark there (I didn't harden the hammer)....
Bob
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Things are still in a flux, but I managed to get a few numbers.
After thinking about what I ended up with last night, I decided to increase the hammer weight and use a larger spring to see what will happen, like was mentioned above.
Here is the setup I have:
Valve opening is drilled out to .281 (seat dia)
Valve head .390 max dia , .356 dia at seal line
Valve stem .139 for about .15 of length under the head. Remainder is .156 dia.
Valve body exhaust .201 dia, but heavily beveled inside the valve body.
Used a very light return spring on the valve head, 1.75 lbs to open the valve. Normal spring must be at least 5 pounds.
Valve body bored out to .680 dia
Remainder of the valve body has been opened up significantly and streamlined.
Old gauge port area has been opened up to the front of the tube.
Transfer port between the lower tank and the upper tank is .156 dia.
Transfer passage from the valve, thru the tank wall and breech, and to the inside of the barrel is now .199
Barrel is 30" long.
The hammer spring I used this time is .388 dia x .060 wire x 2.1 long, 17 coils.
Hammer now has extension attached to it with another weight of approx 50 grams.
Special cocking device like in Workingman's picture above.
Total tank volume approx 310cc.
I filled it to 2000 psi and took a few high power shots:
1) 1001 fps, 31.4 gn, 69.9 fpe (eff .85 fpe/cuin)
2) 903 fps, 42.7 gn, 77.3 fpe (Holy &^^& !!) (eff .94 fpe/cuin)
3) 1027 fps, 25.4 gn, 59.5 fpe (eff .71 fpe/cuin)
4) 963 fps, 31.4 gn, 64.7 fpe (eff .78 fpe/cuin)
pressure ended at 1800 psi
Still needs lots of fine tuning, but I should be able to make it manageable.
Best regards, Lloyd
(edit- corrected the hammer weight)
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I wish I understood all of that Lloyd....but the numbers are looking real GOOD.
You have my attention. :)
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Well, you've taken your Disco beyond what I did with my Hayabusa, congratulations.... The valve I am using is 1/4" at the throat and 3/16" ports through all the way to the barrel.... I guess size is important!.... I got the following:
1061 fps JSB King 25.3 gr - 60.5 FPE @ 2000 psi
983 fps H&N Baracuda 30.9 gr. - 66.3 FPE @ 1900 psi
867 fps EunJin Pointed 43.2 gr. - 72.1 FPE @ 1800 psi
Note that the heavier pellets were peaking at less than 2000 psi, I didn't have enough hammer strike to dump 2000 properly....
How did you bore the valve out to 0.680" when it's only 0.740" OD?.... that's only a 0.030" wall thickness, pretty thin for 2000 psi, isn't it?.... or do you figure it's just expanding out against the tube?....
I get such a hoot out of bouncing ideas off each other and pushing each other to new levels of performance.... We are approaching Condor performance.... I wonder what we could do with some of those 60-80 gr. slugs?.... What REALLY tickles me is the level of performance we are getting at only 2000 psi.... or even less.... ;D
When I do my 9mm Disco I will likely be borrowing the weighted outside cocking hammer idea as well.... and it looks like I'm going to have to find some bigger hammer springs....
Bob
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All I know is I'm sending my PCP to you guys when it's tune-up time (And I haven't even got to shot it yet). Hoping for the weekend.
Man, I love this thread.....and .25 Go big or go home.
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Ha, ha, this really is quite a trip. Almost an obsession. My wife just shakes her head and calls me a sick f***. Terms of endearment.
It certainly does make it a lot more fun and worthwhile when there are other folks to exchange ideas with.
Thanks everyone!
Bob, I think it was the big hammer and spring, combined with the extra light return spring that gave it the final few fpe. I don't think I can get any sort of string at that power level, but who knows? I had to do a fast fill from my scuba tank to get the initial seal on the valve.
The .680 bore inside the valve might be off a few thousandths + or -. It's down inside the threads of the valve, so with the .280 hole at the valve seat, I laid a .201 drill blank in there to estimate the bore radius on either side. Yes, I am relying on the tank tube as a safety back up for the valve body. Still, with a .74 OD and .03 wall, a 28ksi yield strength wouldn't show any measurable movement until above 2500psi. And I know the yield of the valve material is above 28ksi, and tensile is way above that. I would not do that if it were not contained in the tank tube, though.
After the discussion of hammer design, I will probably make a new hammer to get all the weight inside the gun. I also will try slipping an o-ring onto the pull rod for the hammer cocker to see how much the valve is opening. The o-ring will act as a tell-tale for the actual movement. Modeling clay will do the same thing. My valve has a short stem and the travel is limited to about .140. I have NO idea how much it is actually opening.
This is fun!
Regards,
Lloyd
P.S. 0351-vet, you might enjoy this video for maximum power. Its a different gun.
http://www.gatewaytoairguns.org/GTA/index.php/topic,12886.0.html (http://www.gatewaytoairguns.org/GTA/index.php/topic,12886.0.html)
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Ha, ha, this really is quite a trip. Almost an obsession. My wife just shakes her head and calls me a sick f***. Terms of endearment.
It certainly does make it a lot more fun and worthwhile when there are other folks to exchange ideas with.
Thanks everyone!
P.S. 0351-vet, you might enjoy this video for maximum power. Its a different gun.
http://www.gatewaytoairguns.org/GTA/index.php/topic,12886.0.html (http://www.gatewaytoairguns.org/GTA/index.php/topic,12886.0.html)
Lloyd, Thanks Bud.......Great Video (You guys kill me). :) :) :) :)
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I'm thinking that the hammer and spring are most of the power difference compared to my Hayabusa.... especially since my FPE with the 25 gr. is slightly higher than yours at 2000 psi.... Have you ever bothered working out all the port areas to see where the greatest restriction is?.... When I did my Hayabusa I started from 75% of the barrel (ie 0.188") and worked back from there, just making sure nothing else was more restrictive than the barrel port.... That was easy with the transfer port and valve exhaust port (also 3/16").... The valve throat is 1/4" with a stock 5/32" stem.... That works out to 0.049 - 0.019 = 0.030 sq.in. and a 3/16" hole is 0.028 so no problem there.... I use a bolt probe that is 1/8" (smaller than the valve stem).... so again, less restriction than the barrel/transfer port....
Have you noticed any tendency for the pellet to hang up on the 0.199" port?.... just curious.... I wonder where the optimum is for diameter/flow compared to TP volume losses.... I know where that is on .177, it's a stock 0.140" port.... Even angling the port / streamlining seems to decrease velocity unless you are REALLY pushing the limits.... but then that's what we are doing, right?.... If you're not having pellet loading problems perhaps I should be looking at 80% of bore for the barrel port.... or maybe an elongated hole that is only 75% of the bore wide but as much as one caliber long (ie 0.188" x 0.25")?.... That should flow about the same as a 0.216" round hole.... let's call it 7/32".... Then again, I wonder if the increased TP volume would hurt?....
BTW, I gave the Condor owners a gentle "poke" on the CAF, telling them what you were doing and that you had achieved over 77 FPE with a 43 gr. EunJin.... and asking them what a Condor can do with that same pellet.... no answer so far.... Maybe somebody here will chime in.... I'm thinking we must be getting pretty close.... ;D
Regardless, I'm darned proud of what we are achieving on only 2000 psi.... pretty remarkable.... Really good idea using an O-ring to measure valve lift.... make SURE you tell us those results.... and you're right this is a BLAST, and it's what forums such as this are for.... sharing ideas in the best of possible ways....
Bob
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It is most definitely interesting reading what you are working on even if it is WAY OVER MY HEAD! I kinda understand what your doing but trying to understand exactly what your saying is a bit difficult.
A dual tube Disco 25 and and a higher riser to be able to use the MRod or PRod magazine would make a great hunting rifle. look forward to more post on this subject
Norm
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It is most definitely interesting reading what you are working on even if it is WAY OVER MY HEAD! I kinda understand what your doing but trying to understand exactly what your saying is a bit difficult.
A dual tube Disco 25 and and a higher riser to be able to use the MRod or PRod magazine would make a great hunting rifle. look forward to more post on this subject
Norm
Norm,
I hear what you are saying about a .25 MRod magazine! Why not put the power to good use, huh? It is in the plan!
I know the explanations get a little cryptic sometimes. It's often late at night or early int he AM and I don't take the time to explain it all. Or I will be on a roll and won't take the time to stop and take a few good pics. But, I do hope to add some more pics that more clearly show what the mods are. Many of them are pretty straight forward.
Glad you are enjoying it!
Lloyd
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I'm thinking that the hammer and spring are most of the power difference compared to my Hayabusa.... especially since my FPE with the 25 gr. is slightly higher than yours at 2000 psi.... Have you ever bothered working out all the port areas to see where the greatest restriction is?.... When I did my Hayabusa I started from 75% of the barrel (ie 0.188") and worked back from there, just making sure nothing else was more restrictive than the barrel port.... That was easy with the transfer port and valve exhaust port (also 3/16").... The valve throat is 1/4" with a stock 5/32" stem.... That works out to 0.049 - 0.019 = 0.030 sq.in. and a 3/16" hole is 0.028 so no problem there.... I use a bolt probe that is 1/8" (smaller than the valve stem).... so again, less restriction than the barrel/transfer port....
Have you noticed any tendency for the pellet to hang up on the 0.199" port?.... just curious.... I wonder where the optimum is for diameter/flow compared to TP volume losses.... I know where that is on .177, it's a stock 0.140" port.... Even angling the port / streamlining seems to decrease velocity unless you are REALLY pushing the limits.... but then that's what we are doing, right?.... If you're not having pellet loading problems perhaps I should be looking at 80% of bore for the barrel port.... or maybe an elongated hole that is only 75% of the bore wide but as much as one caliber long (ie 0.188" x 0.25")?.... That should flow about the same as a 0.216" round hole.... let's call it 7/32".... Then again, I wonder if the increased TP volume would hurt?....
BTW, I gave the Condor owners a gentle "poke" on the CAF, telling them what you were doing and that you had achieved over 77 FPE with a 43 gr. EunJin.... and asking them what a Condor can do with that same pellet.... no answer so far.... Maybe somebody here will chime in.... I'm thinking we must be getting pretty close.... ;D
Regardless, I'm darned proud of what we are achieving on only 2000 psi.... pretty remarkable.... Really good idea using an O-ring to measure valve lift.... make SURE you tell us those results.... and you're right this is a BLAST, and it's what forums such as this are for.... sharing ideas in the best of possible ways....
Bob
Bob, I'll answer as best as i can, from the beginning of your email.
Regarding the heavy hammer and spring, I think that made the biggest difference at the high end of the pressure range where the tank pressure works harder against the head of the valve. Now that all the porting is more or less maxed out, I can drop back on the spring and hammer and see what happens. I also think the extra light return spring helped.
With the various port restrictions I think streamlining the ports might be as important as port size. Trying to get the air to turn the corners and make an ugly U-turn. I have heard that contouring the bottom of the bolt probe can be helpful. With my current setup, I calculate that at 2000psi, I use 8 cc's of air out of the tank with each shot. 8 ccs will fill the 25 cal barrel for 10" of length. That's a lot of air at that pressure, so I am guessing that a little extra volume in the passages after the valve won't hurt too much. A tall breech block adds extra volume and I think those shoot just as fast as a short breech block??
I deburred the inside of the barrel where the .199 hole enters it such that the pellets go in easily. I haven't shot this gun for accuracy, so I don't know if I have a problem there or not.
This is good stuff!
Lloyd
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Great job lloyd. Those are some great #s. Smoken. Have you got to shoot a good shot string? I was lookin back through my notes and when I had the lite valve return spring I was getting higher #s but my standard deviation doubled. That was before I installed the rear cocker. I'm tempted to put the lite spring back in.
One of the nice things about the rear cocker is being able to fine tune the hammer weight ,screw one off and screw a lighter one on. I've been curios about the max travel of the valve stem. The stock valve stem length from the back of the valve to tip of the valve stem is around .330 +/-. My guess would be around .200 .. I like the o ring trick I'm going to have to try that.
Any way its exciting to see your accomplishments. Its a good feeling when thinks work out.
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I'd be really shocked if the valve stem travel is 0.200".... but I've been wrong before.... IIRC poppet valves flow 100% when the lift is 1/4 of the seat diameter....
Area = Pi R^2 = Pi x R x R
Circumference = Pi x 2 x R
Curtain Area = Circumference x Lift = Pi x 2 x R x L
For Curtain Area equals Seat Area.... Pi x R x R = Pi x 2 x R x L.... solve for L.... L= Pi x R x R / Pi x 2 x R.... L = R/2
If the seat diameter is 0.3" the lift only needs to be 0.075" for full flow.... After that additional lift only increases the duration not the flow rate.... at least in theory....
C'mon Lloyd, stick an O-ring on that hammer stem.... we're dyin' here.... ;D
Bob
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Bob,
Prepare to be shocked. I have to run to work in a few minutes, but I put an o-ring on the cocking rod to act as a tell tale. I think I had estimated my valve stem protrusion at about .140. Well, I think it is probably more like .160. I had shortened it at your suggestion to get more hammer travel distance. I took several dry fire shots at about 1400-1200 psi and the o-ring consistently showed about .160 of travel until I backed the spring preload out several turns. Then I was getting about .130 of valve travel. I cranked it back in a little and got a 51 ftlb shot (25.4 gn at 953 fps) with about .150 travel at 1200 psi. I think my valve stem might be too short and I am limiting the power to a measly 77 fpe at the higher pressures, LOL. I will have to spend more time with this tonight and get some accurate measurements!
Not a hint of hammer bounce, but that's another story.
So the extra travel distance is not necessary for the air flow, but it is what increases the dwell. Makes sense.
Lloyd
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Be interesting what you find when you fit a longer valve stem (or will you shorten the back of the valve like a 22XX?).... Mind you, I've never played with a 4 oz. hammer either.... :o
You greedy guy!.... I only told you I shortened the stem 0.060".... ;D
Bob
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OK, I have cleaned this thing up a little since last time, but she is still a mean one. Bob, yes, I did get greedy with the stem length, but that version has a home made valve stem and head that is about .100 shorter than stock.
So what I have done recently is 1) increase the hammer stroke, 2) regain the original .250 (approx) max valve stroke, 3) incorporate a much stronger and adjustable spring, 4) incorporate a much heavier hammer that is adjustable in weight.
Here is what I came up with. Some of the ideas are new, some are copied from other folks, and some are variations of what others have already done. Can you imagine how hard it would be to do something like 20 years ago before the "information highway?"
This is a pic of most of the parts that go into a set up with a .770 hammer stroke. Stock is about .600. I also has room for a fatter and longer spring, and is adjustable for preloading the spring. It also has a big hammer, plus a cocking pull rod with the additional weight of the cocking knob.
Notable in this pic is the cocking rod that has a drawer pull as a cocking knob. The hammer and rod are 70 grams and the knob is 35 grams. Because the knob is tied directly to the hammer, changing the knob will change the hammer weight. We were discussing a similar situation on another gate earlier today.
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/hammer-spring-parts-1.jpg)
Here are all the pieces assembled together. The threaded insert that the cocking rod goes thru adjusts the spring preload. The drawer pull has a nice sharp edge to scrape the hide off your thumb when the hammer fires forward. Gotta fix that!
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/hammer-spring-assy-1.jpg)
Here is how I got the extra hammer stroke length. In the stock config, the sear catches on the bevel at the front of the hammer. In the new config, the sear catches at the same place. OK, no diff. BUT The new hammer has cup and the surface that contacts the valve stem is recessed in that pocket. That way, the hammer doesn't hit the valve stem until the front of the hammer is well past where it used to strike the stem. About .200 farther, but I have a little piece of dowel pin in there that will drive the valve stem down past flush at the end of the valve body. That is to compensate for a short valve stem (shut up) and I am again giving up a little hammer travel. If I make a new valve, I will make the stem longer so I don't have to jury-rig the hammer stroke.
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/hammer-faces-1.jpg)
More coming shortly!!
Lloyd
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Have you ever wondered how far the valve actually opens when it is struck by the hammer? Yea, me too.
I was able to do it with this setup by putting an o-ring around the cocking rod. You re-adjust it with each shot, and then, shooting the gun moves the cocking rod and hammer as a single unit. The o-ring is pushed back on the rod at the maximum valve stroke for that setup. Then the hammer bounces and the gap left at the o-ring shows how far the valve actually opened.
The picture sequence shows an interesting phenomenon that we had all heard about but probably didn't have any proof of.
The hole in the adjuster that the cocking rod slide thru is too small for the o-ring so it stops the movement of the o-ring.
Look at the last 2 pics. In the second from the bottom,
The air is at 2200psi and the valve has only gotten open to .076 of travel before the HPA forces it shut.
Then in the last pic, the gun has been fired at 1600 psi and the stroke stopped at .150
I also took at shot at around 1200 psi and the valve had opened up more than .200
I will be working on getting some shot strings that have some useful data. With the adjustability of the spring and hammer, it will be tough to zero in on a "best" setup, but there will be lots of "good" setups.
Lloyd
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/tell-5.jpg)
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Lloyd.... I gotta hand it to you.... You definitely think "outside the box".... I love the recessed hammer face (gonna steal that one for my Hayabusa).... For my "big-bore" Hayabusa I planned on moving the valve ahead to get more hammer fall.... With that idea, I may not need to....
The idea of using an O-ring on the cocking rod to measure valve lift is one of the best demonstrations of the KISS principle I have seen in a very long time.... BTW, remember I said that max flow on a poppet valve occurs when the lift = 1/4 diameter.... How big was the valve throat again?.... :P
Now you're gonna have the problem I have on my Hayabusa.... too many variables.... ;D
Bob
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Bob,
The recessed hammer face just kind of came to me when I was figuring out what I would have to move to get more hammer stroke. Definitely use it! When I re-make the valve stem with more sticking out, I can replace that little steel dowel pin in the hammer with a flush one, but I think the net result will be the same???
I stole the o-ring idea, but it is perfect for this. The hole in the valve is .281 and the valve stem is .139. But the front end of my valve is very un-areodynamic and needs to be redone, I think. It's all about chasing the bottle necks. HPA flows more like water than air, so I have opportunities for improvement.
Yes, I agree on the too many variable thing. And I have a hard time changing just one thing at a time, LOL.
Lloyd
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I have a hard time changing just one thing at a time
I noticed !!!
must resist.... mmuusstt rreessiisstt.... mmmuuusssttt rrreeesssiiisssttt.... ;D
Bob
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Here is the latest data, but I am not too thrilled. A lot of work, but not much additional gain. I know there are some bottle necks that I need to figure out. ???
So I took these shots with various pellets to get a feel for what might be there. I am starting to run out of pellets and need to order some.
The .25 Air Venturi has straight cylindrical sides and is just about impossible to load without hammering them into the breech. Has anybody used these Air Venturi .25 and do you have the same problem? My barrel is actually a barrel liner for firearms so might be working against me.
So the shots were with one Air Venturi 50gn, two eunJin 42.8 gn, and the rest were Barracuda 30.2 gn. My grain weights might look odd, but I weighed the pellets to get an accurate weight for the tests. The total hammer weight is about 105 grams. With a few of the adjacent shots, I removed the cocking knob, which cuts the hammer weight by about 35 grams. And to be honest, I dont think removing the extra hammer weight helped or hindered. There fore, it will probably be best to leave it off. Less wear and tear on everything. Still, the stock weight is about 53 gns, and even without the knob, the new hammer is 75 grams, so almost a 50% increase.
So, the power level seems to be stalled :'( ,it likes heavy pellets, but is really inefficient with light pellets :'( . It uses lots of air, but that is to be expected at these power levels. After all, that's why added the second tube, LOL. ;D
So what to do next? I think the valve head is like driving down the road with a sheet of plywood stuck flat against the front of your car. Not aerodynamic at all.
So, any suggestions from anyone? First thing is I need is more pellets, or maybe soft cast bullets. The thought of using bullets does turn this thing into something else, but for the sake of experimentation and knowledge, maybe I need to go there. Still, those big EunJins might be plenty of weight. What do you think ??? I know mellowroadman over on the Big Bore gate had cast some nice .25 bullets.
Thoughts anyone..... Please..... :-[
Thanks,
Lloyd
Various shots with heavy hammer and spring. Various pellet weights. Starting and ending pressures recorded, but the 63 psi per shot is just an average. Efficiency stinks, but that's what it costs. Actual valve openg was .085 with the first shot, and slowly crept up to about .200 with the last shot.
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/DblTubeDisco-w-Hammer.jpg)
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hmmmmmmmmm.... Interesting results.... My first comment is that unless you are going to regulate this beast, you either need to increase the fill pressure or reduce the hammer strike.... The velocity starts out high and declines from there.... That indicates you need to balance things better.... I am getting almost identical results from my Hayabusa with the Baracudas.... 66.3 FPE at 1900 psi.... but at a lot higher efficiency (~1.1 FPE/CI).... Like I was discussing in another thread, when the heavy pellets show a large advantage over the medium weight ones.... the gun is likely an air-hog.... Your efficiency numbers, from my experience, are showing that trend.... so I would back off on the hammer strike, lose a bit of power, and gain some efficiency.... If you can throw those Kodiaks downrange in the mid 900's you'll have a heck of a rifle.... Have a look at this graph....
(http://i378.photobucket.com/albums/oo221/rsterne/22%20PCP/22XXPCP82000psi.jpg)
Notice what happens with the last 2 turns on the hammer spring preload.... With the light pellets there is NO gain in velocity.... and even with the heavy pellets the gain is very small (~3%).... Then look at the efficiency curve.... You are using nearly 50% more air and gaining nothing.... Now check out this graph for an unregulated gun....
(http://i378.photobucket.com/albums/oo221/rsterne/Discovery/Disco1050FPE.jpg)
Notice that the lightest pellets start at their highest velocity, and as the weight increases, you begin to get a bell-curve.... By the time you get to EunJins, the bell-curve is well established.... For the curves on the left (at maximum hammer spring preload), here are the efficiencies....
Hobby 11.9 gr. - 0.78 FPE/CI
Express 14.3 gr. - 0.83 FPE/CI
Exact 15.9 gr. - 0.87 FPE/CI
Heavy 18.1 gr. - 0.90 FPE/CI
Kodiak 21 gr. - 0.95 FPE/CI
Rab. Magnum 24.8 gr. - 1.03 FPE/CI
EunJin Dome 28.7 gr. - 1.05 FPE/CI
EunJin Pointed 32.4 gr. - 0.94 FPE/CI (IIRC, they were a tight fit)
With 18.1 gr. Heavies at reduced hammer spring preload, the efficiency increased to 1.14 FPE/CI in the case of 2 turns out.... Your shot string looks like the ones for the light pellets in the above graph.... and the efficiencies are in that range as well (~0.8 FPE/CI).... When you look at shot count, if you set a 4% velocity variation as the standard.... using the Baracudas starting at 1013 fps.... you only have 7 shots above 972 fps (including the one 42.8 gr).... starting at 2137 psi and ending at 1693 psi.... IMO, better to lose a bit of velocity, and gain efficiency and shot count....
It's a hoot going for broke and seeing what your new toy will do.... and I'm as guilty as any of savouring that moment.... Then, unfortunately, you have to back the gun down to what is reasonable and practical.... With the power you are getting from the platform, the only way I can see to possibly take advantage of the potential FPE is to try much heavier "boolits".... A good fitting, aerodynamic 50-60 grain bullet might prove just the ticket.... but I have no experience to draw from on that....
Bob
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Yup, that's my style.... go for broke first, and get everything maxed out. Then back the velocity down to 80 or 90% of max, and that will cut the air usage almost in half. But a gun developed that way will never be efficient in the low power ranges because the air passages will all be over sized. But I could leave it stock if that's what I wanted, LOL.
I think the fact that i was able to drop the hammer weight from 105 grams down to 70 grams with no appreciable change in velocity shows that the spring is overpowering the hammer and valve.
Like you said, I do want to try and get some more top end power out of this by going to a little higher fill pressure. I have done the calculations and I will replace the (3) 8-32 screws that hold the valve in place with (3) 10-32 screws. That should be a strength increase of about 40%. The tube and other components all calculate well within the desired safety factor.
Lloyd
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I have done the calculations and I will replace the (3) 8-32 screws that hold the valve in place with (3) 10-32 screws. That should be a strength increase of about 40%. The tube and other components all calculate well within the desired safety factor.
Lloyd
Lloyd, I love the progress you are making. I think I know what my winter project might be. Thanks to you and Bob for the ideas and information.
I highlighted the last paragraph from your post because I think it is important for someone thinking of undertaking a project that involves high pressure to understand that the math comes first. From the shear stress on the bolts to the stress on the thin walled cylinders there is a lot going on when a PCP is just sitting there fully charged.
I am not trying to discourage anyone. If someone cant find a formula or is uncertain of performing the calculations feel free to PM me. I am more than willing to help as are many here.
I took the time to do the calculations when I converted my 2260. Remember, safety FIRST, and happy shooting.
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Rescue35 is right on!!! As intersting as this thread is, ANYONE THINKING OF BUILDING THEIR OWN PCP NEED TO KNOW THE DANGERS. The pressures that are present in all PCPs, be it a custom built one or one you buy of the shelf can cause extreme harm if you do not pay attention to what you are doing. Things like being disturbed while filling your PCP and taking your eyes off the gauge even for several seconds can cause pressure to rise above safe levels. So everyone out there be safe and be careful we do not want to see anyone hurt or worse.
Norm
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Great Thread and Thanks for warning us all of the dangers involved with PCP's. I think this thread is a marvel of very firearms educated people pushing the envelope because THEY HAVE THE KNOWLEDGE. I personally wouldn't attempt any of the above myself, but it is certainly educating. Thanks Bob & Lloyd for the informative thread.....and Norm for the stern warning on PCP's.
Again....GREAT THREAD
Edited for bad grammar......
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Thanks guys for reinforcing the SAFETY aspect of PCPs. That always has to be number one in your mind.
The pcps we buy are well engineered with all the calculations to back up their safety. Many of us like to work on our guns, and there are plenty of great mods you can do that don't affect safety. But unless you can honestly say that you know exactly how a change will affect the safety, I would not do it. Rescue35 has graciously offered to take a look at folks ideas, but it all boils down to YOU doing the right thing.
Norm's comment about paying attention while filling your gun is EXTREMELY important now that 4500 psi is so available. Recommended fill on a disco is less than half that. Each time you overload a metal part, it is weaker the next time. Please be careful.
Lloyd
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I was thinking about the discussion on going for broke on a design (my style) and got to thinking I'd stop changing one thing after another and take a closer look at where I was right now.
Well, I am glad I did. In fact I am kinda tickled about it.
One thing I had noticed about the heavy hammer (and then only1harry had mentioned it elsewhere) was about beating things up with too much hammer. During one session, I had removed the 30 gram cocking knob, which left the hammer at a mere 75 grams, yeah. Bottom line was that removing the extra hammer weight didn't drop the velocity much at all.
So I replaced the cocking knob with a 10-32 wing nut, and used the long spring and backed the preload way off. I played with it to get the curve to start where i wanted and the velocity where I wanted it, and ended up with a very nice classic inverted bathtub velocity curve. And a very pretty one, I think. And the efficiency went way up, too.
Filled to 2250 psi, shot down to 1500 psi, 310cc dual tank
Barracuda 30.2 gn (weighed them)
23 shots between 903 fps and 960 fps.
18 shots with a 4% spread of 921 to 960 fps.
18 shots between 57.0 fpe and 61.8 fpe.
I was going to do some shooting for accuracy and was all set up to shoot in the woods behind my garage, but then got a long phone call and it was getting too dark to shoot. Got off 3 shots at 43 yards. 2 of them touched and one was 1-1/2 " away, so I have no idea what I've got. But I will find out. Was using a bug buster 6 x 32 which likes lots of light.
Lloyd
P.S. I am attaching the pics a different way, so I hope it works.
edit note- I took a total 5 psi readings for the string and averaged them in my table.
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Excellent results.... and the efficiency at ~1.4 FPE/CI is great as well.... If the Baracudas will group for you, you are in business.... I'd try the 25.4 gr. JSB Kings with the same tune for accuracy.... and also backed down into the mid 900's (~50 FPE).... Since those are the only pellets with a good BC and a .25 cal PCP is the king of long distance critter whacking.... you don't have a lot of other choices....
PS, if you plot the velocity and energy curves on an axis that starts at 0 fps it looks a lot flatter.... ;D
Bob
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I managed to get a tiny bit of shooting for accuracy done with the gun set up as in the chart above. I pushed my target a little farther into the woods to get a full measured 50 yards. It runs downhill pretty noticeably.
After it was all settled in, I did a 6 shot group with H&N Barracudas at about 940 fps for 59fpe. Leapers Bug Buster 6x 32 scope. The group was 1.25 c to c, so definitely not what I am looking for, but it's a start. And I have only tried the Barracudas.
50 yard lane down into the woods behind my garage. Target circled in red.
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/50_yd_lane.jpg)
This guy was trying to block the lane. Yes, those are antlers. The 2nd one had just trotted off.
Darn pests!
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/50_yd_blocking.jpg)
the 50 yard target
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/50_yd_1st.jpg)
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Actually not too bad at 50 yards for just the first pellet.... It will be interesting to see how it groups with JSB Kings and EunJin Domes.... My bet is on the Kings.... You can also try the 31 gr. RWS Superdomes and the 26 gr. Predator Polymags.... I have some of each but have never done any accuracy tests in .25 yet.... So far, everyone shooting a quarter-bore at the longer ranges raves about the accuracy of the JSB Kings....
BTW, how much velocity are you gaining from the 30" barrel compared to 24".... I know you can figure that out (and probably have).... Did you know that you can get a 23.8" long choked Lothar Walther barrel in .25 cal that is only 12mm OD? (special order).... just requires a skim off it to fit the breech and it still clears the main tube (barely).... That is what I have on my .25 Disco....
Bob
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Bob, yes, the diff between 25" and 30" calcs to be only 40 fps. I have a 16mm (.630) x 25" LW .25cal barrel in my stash. It's the one I used in the max velocity video from 2008. Not sure what I am going to do. ???
The 30 " barrel seems excessive and right now I have it secured and cushioned with some Sorbothane and I am not too confident in its stability, but it seems too whippy for free floating, I think. I ought to try and zero in on its accuracy capability in this long barrel configuration first. :P
I could see maybe going to a tall breech and a .25 cal rotary magazine, with the .630 dia .25 cal LW barrel and an LDC. That would probably be a sweet setup, ;D but it is really a $$ commitment, too.
But I have been neglecting the big bore stuff and that wants some $$ and hours, too. [Funny, that almost sounded like what I say at work, and I want to keep it fun. :'(] Anyway, got numerous directions to choose from, so I will just see how it evolves. :D Oh, and I have at least one more mod to make to the valve head configuration in this thing to see if I can wring any more out of it. :o
Lloyd
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This is the first of a series of 4 videos about how I did the modifications. Much of the info is already in this thread, but the videos tie it all together (and you don't have to read ;D ).
This first video is a demonstration of the .25 caliber power and is also ion the PCP gate, but I wanted to have all 4 videos in the same thread for continuity.
Video number 1.
.25 cal Disco Power Demo
http://www.youtube.com/watch?v=GVx8i4_VJVQ# (http://www.youtube.com/watch?v=GVx8i4_VJVQ#)
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Video number 2.
.25 cal Disco Pellets and Hammer Springs and Adjuster
http://www.youtube.com/watch?v=2pHTnw0ylrI# (http://www.youtube.com/watch?v=2pHTnw0ylrI#)
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Video number 3
Hammer assembly, breech, barrel, and the second air tube
http://www.youtube.com/watch?v=nPM2hapJ4xM# (http://www.youtube.com/watch?v=nPM2hapJ4xM#)
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Lloyd you da man! ;)
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Here we go! This is the last one.
Video number 4
Air Tube and Valve Assembly
http://www.youtube.com/watch?v=gWLiLxLQmMM# (http://www.youtube.com/watch?v=gWLiLxLQmMM#)
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Read 1449 times........Today at 01:34:48 PM
I rest my case, the Man is a Master. Great Video's Lloyd.
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Great videos, Lloyd.... Interesting how different your prototype valve is from the production Disco one.... with the screw in ends retaining the screen and the O-ring.... I even have one Disco valve without any O-ring seal on the stem!!!.... The production valves are aluminum, of course as well....
Bob
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Bob,
Yes, there have apparently been variations over the years. My Discos are older plus many of the parts in the video are my fabrication. With the exception of the barrel, someone with good shop skills and a lathe and mill, and lots of time, could build something similar from scratch. Or even better, as you have done.
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Bob,
Yes, there have apparently been variations over the years. My Discos are older plus many of the parts in the video are my fabrication. With the exception of the barrel, someone with good shop skills and a lathe and mill, and lots of time, could build something similar from scratch. Or even better, as you have done.
It is amazing how simple of a design these rifles are. Great example of the KISS philosophy at work.
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;) General Disclaimer ;)
Hey Everyone,
Thanks for all the comments and encouragement, but I do want to make just a few general comments on the subject of modifying airguns.
As I have said many times, if I couldn't work on airguns, I probably wouldn't own them. And by work on them, I mean try new and different things. Its about the creativity and the learning. I like to learn from what other people have done, but I usually dive in and try something my own way first. Later I might find out that it has already been tried, and that there is a better way. No big deal, I learned something anyway.
As I said at the beginning of video number 3, there are a lot of folks out there that know a lot more about airguns and have a lot more experience than I do. I have learned a lot from them. They have tried and true methods that not only work for them, but will work for other people, too. I am sure that some of my modifications make them shake their head. That's fine. My methods work for me and serve my purpose, but are definitely not for everyone. I like the results (mostly ;) ), but others might not have any use for them. It's about the challenge of making something better, and that is my interpretation of "better".
So take what you what you want from what I have presented.
A guy I used to work with did automotive work on the side. Mostly custom modifications and difficult repairs, special stuff. His guarantee was, "30 seconds or 30 feet," but he had a long waiting list of customers. And he never lost his love of working on cars.
I'm glad I have airguns, and all the good folks of the GTA.
Lloyd
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lloid thank you for the videos
lots of info in there
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lloid thank you for the videos
lots of info in there
^+1 really helps us newbies understand how these things work.
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Bob, yes, the diff between 25" and 30" calcs to be only 40 fps. I have a 16mm (.630) x 25" LW .25cal barrel in my stash. Not sure what I am going to do. ???
I could see maybe going to a tall breech and a .25 cal rotary magazine, with the .630 dia .25 cal LW barrel and an LDC. That would probably be a sweet setup, ;D but it is really a $$ commitment, too.
Lloyd
Lloyd,
I think you should just build it for me in the 25", (and apply that money to towards your BIG BORE projects that were put on hold, whilst perfecting this here beauty). :) :) :) I have a brand new (DOD) "Disco Organ Donor" just waiting for surgery from "Dr. Lloyd". :) :) :) Man, I love this thread.
Walt
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Hey Lloyd,
On your 30" inch barrel. If you want to lighten it up and let it free float, flute the barrel. Like the barrel on 0351_vet's signature photo.
Here is some more reading I looked up in a hurry. http://en.wikipedia.org/wiki/Fluting_(firearms) (http://en.wikipedia.org/wiki/Fluting_(firearms)) You will appreciate the first link in the references on why fluting does not stiffen barrels.
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I have always liked the look of a fluted barrel. My 30" .25 cal is really a barrel liner ans is only .437 O.D., so not too much extra. The other .25 is .630 dia, so plenty of material. I am wondering how barrel fluting is normally done: before or after rifling, by hobbing or grinding? I don't know but it looks like a lot of work unless you have the right equipment.
I know that when I thread the end of a thin barrel liner, it has the effect of choking the barrel, which is fine at the muzzle, but not at the breech. So I am thinking that getting too thin with the bottoms of the flutes might do something odd (as in - not good) to the rifling. Maybe a little localized decorative fluting, but nothing too serious.
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Hey Lloyd,
On your 30" inch barrel. If you want to lighten it up and let it free float, flute the barrel. Like the barrel on 0351_vet's signature photo.
Here is some more reading I looked up in a hurry. http://en.wikipedia.org/wiki/Fluting_(firearms) (http://en.wikipedia.org/wiki/Fluting_(firearms)) You will appreciate the first link in the references on why fluting does not stiffen barrels.
"Typically" the flutes are to increase surface area, to make the barrels less susceptible for overheating. And on most "Sniper" rifles to help prevent "mirage" due to barrel heat.
I too have several AR15/M16/M4 Heavy Barrels that too are fluted. They look Bithin, yet their function has (for me always) been for heat displacement.
The only Barrel Fluting I have seen machined was done on a Mill with a long bed (?) and it was drawn into the bit from one direction to the other. The bed was driven (power), then the barrel re-indexed to the next flute location and then another pass was made.
Sorry, I'm not a machinist so I am sure my terminology is weak. :)
Also....That was on a bull barrel. On a tapered barrel the setup gets a little more complicated as the bed has to be canted with the rank of the barrel, if that makes sense.
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You are spot on Vet. That is how I would do it. Set the barrel up in an indexer with the barrel running in the X axis. Cut the desired flute and then index by the number of flutes you want.
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thanks for posting this now i can pull the valve and gauge port out of my disco for repair
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www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cfluting.htm (http://www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cfluting.htm)
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www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cfluting.htm (http://www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cfluting.htm)
John,
Thanks for that link. That is a good explanation of what fluting does and does not do. I wonder if most people opt for fluting because it looks wicked?
I bought two .50 cal barrel blanks a while ago, 1.125 dia x 28". I have used one, and turned it down to .880 dia to make the weight manageable 'cause the blank weighs 6-1/2 lbs.
Fluting the second barrel to get it to the same weight would be very neat looking, but a ton of work. My mill doesn't have power feed on the table.
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I put the Disco back together after making the videos, but before doing that I copied Toolmakers Delrin valve head/stem idea. Thanks Matt!
I had the gun blazing for the video, but wanted to see if it was now "too modified" to shot at velocities that are more in line with what a pellet wants for accuracy. A true test. Using Matt's valve head idea I actually made the valve seat dia .015 larger... again... opposite way for controllable low power.
All I really did for this test compared to the 80 FPE video was remove a .25 long shim from the hammer spring, and back the RVA off so that the hammer spring was preloaded only about one turn.
Well, I took 52 shots on one fill, using JSB Exact Kings, starting at 2300 psi and shooting down to 1150 psi. Velocity ranged from 787 to 909 FPS, not too great, but that was 52 shots and the average FPE was 42.3. The efficiency was a very good (IMHO) 1.46 FPE/cuin.
A few of observations:
1) The jaggedness of the velocity curve was from the light hammer preload.
2) The gun had a real sweet spot from about 1700 psi to 1250 psi; 18 shots from 889 to 909fps. Seems to beg for a 1250 psi regulator for maximum shot consistency. ( I am pumping Bob S for info ;D )
3) Conversion from max power to usable power was easy.
4) The light tap of the heavy hammer on this valve worked better than I expected.
5) Air efficiency was much better than I expected.
6) Despite all the nice "normal" power stuff, I think this thing is BEGGING for a .308 barrel and bullets instead of pellets.
IMO
Happy Thanksgiving,
Lloyd
(http://i226.photobucket.com/albums/dd79/loyd500/Disco%20project/Disco52shotstringGraph.jpg)
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Llyod .....That is so cool. Man, I love it. If you go to .308, I'll buy your barrel and value set up.
52 shots, heck, that's more them my M-rood from 3000-2000PSI. (like 24).
Keep us informed Brotha....Way Cool.
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Looks like your sweet spot starts at about 1400 psi.... Since you will have a much lower average pressure with a regulator (depending on where you install it) I would reccommend you plan on at least 1400 psi for the setpoint.... maybe more....
You can get rid of the low spring preload by going to a weaker spring and more preload of course.... but then that .308 cal sounds inviting, doesn't it?....
Bob
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It all sounds inviting....... :) Great Stuff you Two.
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Yes but
for .308 or 320, would you have to machine the inside of the breech for the bolt?
and also probably the outer diameter of the barrel will make you want to machine the inside of the breech, to fit it? (you don want the barrel to be too thin I think)
any way happy thanks giving to all
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That's a Good thing Lloyd, as something tells me you wouldn't be Content without an Ongoing project,he he! Have fun,
Troy
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Yes but
for .308 or 320, would you have to machine the inside of the breech for the bolt?
and also probably the outer diameter of the barrel will make you want to machine the inside of the breech, to fit it? (you don want the barrel to be too thin I think)
any way happy thanks giving to all
Yes, you are exactly right. You'd either have to buy (or make) an aftermarket breech, or bore the bolt end of the breech out to .312(approx), and then make a new bolt. For the barrel, I have a .308 barrel liner that is .500 O.D., so I'd most likely have to machine about .062 off it's O.D. for it to slide into the standard breech block. Not too bad of a task, except that the set screw that normally secures the barrel into the breech probably isn't suitable for a thin barrel wall. A more suitable method would be needed.
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so a second barrel band or something like that is in your mind?
if you go with the thinning if the barrel, are you going to trim just the part that enters the breech, or are you going to go all the way along the barrel? if not carefull it will end inclined i supose.
wouldn't it be better to install some sort of breech riser?
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so a second barrel band or something like that is in your mind?
if you go with the thinning if the barrel, are you going to trim just the part that enters the breech, or are you going to go all the way along the barrel? if not carefull it will end inclined i supose.
wouldn't it be better to install some sort of breech riser?
All very good points. The Disco breech has about a .437 hole and the .308 barrel is .500 so I had thought about turning the barrel down just for the portion that goes in the breech. If I did that the barrel would be about .005 above the air tube, so just barely enough clearance.
But in the end, I opted to leave the disco breech alone and instead made a new breech for the .308 barrel. A proof of concept thing. I married the new breech to the disco disco double tube setup and am just about ready to do some test shooting. The valve is already pretty well ported out and the hammer setup is strong enough to split rocks if needed.
I might have to start a new .308 thread. Sooner or later the Disco is going to run out of breath.
Lloyd
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This just keeps getter better and better Lloyd. Good stuff here. !!!!!!
Eyes glued to this thread... :) Keep us informed my Brotha.
Walt
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Great thread. How'd I miss this?
Horizontal mill with convex cutters and dividing head with tailstock would be your best bet for fluting barrels.
However, that's a big, expensive setup.
"Cooling fins" could be cut with a lathe and parting tool. May even help with noise when combined with a barrel shroud.
I want to modify my twin tube Sam Yang 909 to take 2 of the larger dia tubes from a 909s, as well as a 909s valve.
I'd get the higher max velocity of a 909s, with more reservoir volume.
You have me thinking about making my home made big bore PCP as a twin tube design, when I get a "round tuit".
Where do you buy your 4130 tubing and the steel for your threaded end plugs?
I'm tempted to "twin tube" my B50.
I've been thinking about making a barrel shroud for the B50 that wouldn't necessitate a riser breech. It would have to have the end cap and baffles drilled off center, so it would have more air space above the barrel than below.
Essentially, the shroud would be installed above center on the barrel. It would be easier to make it that way and make a new barrel band, than to make a new, riser breech.
Then again, I'd love to have a riser breech for it that takes Mrod mags.
I've thought about making a toggle link straight pull or even a sidelever breech for it.
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Jaymo,
No real plans to flute any barrels. Definitely a lot of work.
I bought the 4130 tubing for my air tank from Mcmaster, 89955K63 for 1" O.D. x .065 wall. A 6 foot piece is $31. Mcmaster gets a lot of my money because they have virtually everything. I use 303 stainless for a lot of my solid parts because it is the only real free machining stainless. Actually, with a 28 pitch thread, aluminum end plugs have plenty of strength. BTW, the 4130 tube in the normalized or annealed condition (as it is usually supplied) has a yield of about 75,000 psi. So the 1" OD x .049 won't start to swell until it over 11,000 psi. That gives a nice 3 to 1 safety factor for the tank.
I like your idea of an off center shroud. I've considered that but haven't come up with a fail safe way to keep the disks oriented properly in the barrel. Maybe you've thought of a way?
The toggle link (for just the breech, or both breech and hammer?) sounds interesting. Nice straight-line travel.
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I'm keeping my eyes open and my mouth shut..........
Lloyd, you just keep amazing me. Waiting quietly. :)
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Lloyd do you thread your tube on your lathe?
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Gene,
Yes, I do almost all of my threading on the lathe. My headstock has a 1" hole so I try and stay at 1" or below. For bigger diameters, I will use a steady rest. A pain, but it works ok.
I have also collected a fair selection of taps from Ebay, and sometimes I will single point an I.D. thread and get it close to size, and then use a tap to bring it into final size. Then I can use that known good thread to gauge the fit on the mating part.
I enjoy single point cutting of threads on the lathe, especially when the fit comes out really nice. But if I have a tap, I use it.
Lloyd
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Any more news on this thread, Lloyd?....
Bob
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Bob,
Thanks very much for asking.
Yes, I fabricated a breech (not too pretty, but functional) and bolt for the .308/.312 barrel I have and installed that onto the dual tube set-up. I tried some trial shots and the velocity was low. Then I changed the de-bounce materials I had at the valve assembly. That apparently was a major mistake as it created an unbelievable hammer bounce situation. The resonance was perfect, and the thing sounded like a machine gun with linear amplitude decay! That left me a little frustrated, but I think the valve closing spring might be too weak and I will look at the debounce materials again, if they are needed. I use them to limit the max valve opening.
So I temporarily put that gun aside and coincidentally was assigned a new project at work where all the start-up capital had to be planned, purchased and received by the end of the year. (One item was a granite surface plate 3' x 14' x 1-1/2' thk. That is a very cool 10,000 pound monster.) So I have been slammed at work, but am on vacation now and am playing with the pcp pistol with it's different challenges. I needed a different distraction, even if it was still an airgun.
So, I will be pulling the .308 disco out sometime in the not to distant future to see what it can do. To be perfectly honest, because removing and reinstalling the valve in the disco is such a PITA (total disassembly, o-ring cutting, etc), I avoid doing it and will often find something else to do instead. I know if I get into fiddling with the valve spring, the valve might need to be in and out of the gun several times until I get it right.
Task avoidance. ;D
Lloyd
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I know what you mean RE the O-ring cutting.... I HATE that big hole for the gauge.... I'm making an extended valve front end to replace the gauge block tomorrow that moves the O-rings ahead of the gauge hole....
Bob
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I know what you mean RE the O-ring cutting.... I HATE that big hole for the gauge.... I'm making an extended valve front end to replace the gauge block tomorrow that moves the O-rings ahead of the gauge hole....
Bob
Bob, Excellent idea on that new extended front end and eliminating that o-ring cheese grater!
Lloyd
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I couldn't find any tapered springs anywhere, so I did a mod on the stock valve spring today.... I tapered it!!!
I slid/screwed a 17/64 drill inside about 3/4 of the way and tapped it with a hammer on an anvil until I could pull it straight out.... then I repeated with a 9/32" drill in about half way and then a 19/64" drill in about 2 coils.... I finished with a 5/16" drill in about 1.5 coils and ended up with a spring that is stock on one end (to fit the valve head) and it's 19/64" ID and 3/8" OD on the other end.... That will allow me to drill the new valve front out to 19/64 (0.297") instead of 1/4".... increasing the area of the inlet side of the valve by 41% over stock.... In addition, it will sit in a 3/8" drilled seat in the front end....
It is currently sitting in a 500*F oven for 1/2 hour to re-temper it and stress-relieve it after the pounding I gave it.... Hopefully that will allow it to live.... I'll post a photo of my valve front end in my 9mm/.308 Disco thread in the Big Bore Gate when finished....
Bob
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Hi Bob
wouldn't it be better to do a little longer valve body and then do the holes in the out side of the valve body like you did in the Tf 78 project
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The Disco valve seals to the tube at the front, not near the poppet where the valve comes apart like the QB78.... In addition, in a Disco tube, there is a 1/2" hole for the gauge about 3/4" ahead of the front of the valve.... that means that the air reservoir has to be sealed bridging that area as well.... That's where my extended valve front end will seal.... An additional problem is the hole for the front trigger mount, so even if you were using a 22XX or custom tube the seal would have to be ahead of that anyway (ie where the Disco valve seals)....
The way my QB valve is cut away will only work if that portion of the valve is ahead of the point where the valve seals the air reservoir....
Bob
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Great idea about fixing the issue with o'ring getting pinched in that big hole... :) I hated that also. Love Lloyds term "Cheese Grader".. That is a perfect description.... :)
I wanted to mention something. To adress the issue with the front breech mount hole in tube. To me that is the perfect place to put the breech hold down screw but gets in the way of multishop designs. I also thought of another ideas for my next Disco breech. The hole in top of breech that hold the barrel down. Drill through base of breech block. Of course the hole would be smaller than the actual hole at top for set screw that holds barrel in place. Locate, drill and tap into the valve body. Using a bottom tap. Or just drilling and tapping hole in tube. The o'ring on valve would be forward of the hole. At this location there should be plenty of meat to tap the valve body without going through. That would solve my issue with the front hole in tube for mounting the breech. Maurader's use two hold down screws that go through tube and into valve body.
Gene
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If I understand you correctly, you are talking about bolting the breech down directly above the front trigger screw?.... If you use a single bolt that would be under the barrel.... Since you have to slide the barrel into the breech before the breech is bolted down (so that the assembly can drop over the trasfer port).... then you have no way to access the head of the screw because the barrel is in the way.... or am I misunderstanding you?.... Two screws like the way the MRod is done would work, providing the breech is wide enough so the screws can miss the barrel....
Bob
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You would tighten the front breech screw to tube down before inserting the barrel and locking it down. Front breech hold down screw would be under barrel.
The hole would be in front of the port.
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I understood correctly, then.... so you must not have the transfer port coming up to the barrel or you wouldn't be able to slide the barrel in once the port is in place as normally the transfer port projects into a recess on the barrel.... I guess the port seals to the breech only?.... Do you use O-rings to seal to the barrel like a QB?.... or not bother?....
Bob
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Maybe this chicken scratch drawing would help understand what I am saying...:)
Gene
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I got it, Gene.... but I don't think you understand my concern.... With the front breech bolt UNDER the barrel you have to install the breech first, tighten the screws, THEN slide the barrel into place from the front....
HOWEVER, the transfer port and O-ring have to be installed into the breech AFTER the barrel is in place in the breech.... It looks to me like the top of the transfer port projects above the bottom of the breech and into the barrel.... or at least the O-ring presses against the barrel.... If you install the transfer port in the breech, and install the breech, the transfer port (or at least the O-ring on it) will prevent you from sliding the barrel into place....
How do you do both?....
Bob
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OK Bob, now I see what you mean.. Pretty thick head here. Guess I can scratch that idea unless I can find a majician in the house... :)
Gene
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Sorry....
Bob
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No problem Bob... I am here to learn. Thanks for you help.. Always welcome.
Gene
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I've been pondering this. Gene, I agree that the current disco breech attachment system leaves some improvement opportunities. The M-rod and P-rod more or less fixed that with the 4 outboard screws.
Bob, you mentioned that the QB uses o-ring to seal the barrel. Do they use two internal o-ring grooves, one on either side of the xfer port, that the barrel slips thru and thus stops leakage during firing. It certainly would be nice to be able to secure the breech first, and then slip in the barrel.
Lloyd
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Thats exactly what I did ! I made a multi breach for my Disco. & drilled & taped 8-32 threads directly across from the stock screw. I cut 0-ring groves on each side of the t.p. in the barrel just the same as the QB-78 set up. Used a 5/16 x 3/8 long set screw directly above to secure barrel & give access to mounting screw below. Gives a much more solid mounting & you can remove barrel without removing breach. At the time I was thinking of being able to do a quick caliber change. Used a simple 0-ring to seal breach to valve t.p. Shoots great & no leaks.
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Looks like you guys have solved the problem...:) Thanks a bunch.. still learning....:)
Gene
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Learning is what its all about...... and having fun.
Rocko thanks for the info. What kind of I.D. grooving tool did you use?
Thanks,
Lloyd
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I.D. grooving tool for what ? I cut o-ring grooves on the barrel with a parting tool in my lathe. Not sure what you are referring to. Thanks
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Rocko,
I thought you cut the grooves inside the breech where the barrel slides in, not on the O.D. of the barrel.
Lloyd
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No problem LLoyd,
I guess my original discription my not have been very clear. The only I.D. o-ring groove I cut was inside the breach end of the barrel to seal the bolt probe. I ground it from a standard 1/4" lathe tool. It was a tight fit in a .22 barrel but worked out OK. Don't know if I can do it with a .177 barrel or not. Will find out one of these days.
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The QB barrel uses three O-rings (why 3, I don't know) and seals both sides of the transfer port.... the grooves are in the barrel, which is about 1/2 OD where it slides into the breech.... The O-rings are 1/2" OD x 3/8" ID x 1/16" thick (standard size #012).... One problem with the QB barrel mounting is that the part that inserts into the breech is relatively short (less than 1.5"?) and is located by only a single set screw.... It can wiggle sideways in the breech.... It needs a 2nd set screw on top.... or two in from the sides just in front of the loading port.... to be made 100% rigid....
Bob