GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on December 17, 2014, 05:32:43 PM
-
About 2 years ago I bought a BAM B-51 in .22 cal from sniper when he got a crate of the last of them.... I knew they should be cleaned before shooting them, and I had other projects on the go, so hung it on the wall until "later".... Well, "later" finally arrived this week, so I read "The Book" (which I had previously downloaded), and stripped the barrel and breech off and pulled the hammer out to clean and deburr them and the tube.... The barrel was filthy, and the bolt was very stiff, so I removed the bolt, deburred all the holes and slots in the breech, and cleaned the barrel thoroughly, and gave the breech bore and the barrel a polish with Bore Brite.... The bolt was still stiff and I suspected it was bent, so over to the lathe, chucked the front, and spun it around to watch the handle wobble around nearly 1/16" off center.... No wonder it was stiff.... I spent quite a bit of time straightening it, and that freed it up nicely.... A thin smear of Moly paste and a new O-ring (the original was shredded from the sharp edges I had to remove) and it was ready to reinstall....
I had read about the hammer, and decided that the most suitable mod from "The Book" was to remove the threaded striker, cut a slot in the back end so that it could be adjusted with a long thin screwdriver through the rear plug, and reinstall it, being careful to put it back to the factory length.... I also put a small piece of plastic under the locking screw for the striker, and tightened the locking screw up to compress it against the threads to provide a "brake" so that the striker won't "self-adjust" and yet I can change the setting from the back.... The hammer is VERY heavy, and has a heavy steel spring shim and guide (top hat) inside, with the total weight being 148 grams, of which the top hat is 38.... This is extremely heavy, and is compensated for in the design by having a stiff spring and very short travel.... The normal method of tuning is to screw in the striker from the back (clockwise from the rear) which makes it protrude even further, shortening the stroke even more.... This moves the hammer back, increasing the preload on the spring, and making the cocking stroke shorter but even harder.... I wasn't too sure about the whole concept, but decided that I needed to test it in stock form and make the normal adjustments to get a baseline for further experiments....
I reinstalled the hammer, leaving the safety off so that I could adjust the hammer travel through the end plug with a long thin screwdriver.... The first tests were conducted at the stock travel setting, filling to 1000 psi for a shot, then 1500, then 2000 (velocity increasing), then 2500, 2800, and finally 3000, which resulted in the highest velocity (938 fps) with JSB Express 14.3 gr. pellets.... So, I knew I was in for a falling velocity shot string, at least with the lighter pellets.... I hooked up my Chrony to my Netbook using Chrony Connect, and starter shooting strings.... I then saved them into Excel to create the following graphs....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51Stock_zps204ef877.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51Stock_zps204ef877.jpg.html)
The initial tests, at stock hammer travel, showed a pretty powerful gun, 27-30 FPE (heavy pellets giving more FPE, as usual), but only 17-19 shots within my normal 4% ES.... The efficiency wasn't bad, considering the way the gun was tuned, from 0.89-0.95 FPE/CI, with the heaviest pellet having the best efficiency.... So far, no surprises, including the excess hammer strike, I expected that from what I had read about the gun, it was tuned for maximum velocity from the factory, not a proper bell-curve.... I removed the stock and cranked the striker in three turns, grabbed the middle-weight JSB 15.9 gr. Exact pellets, and found out I had gone too far.... The velocity at 3000 psi fell to the mid 700s, and took a dozen shots before it got to within 4% of what ended up being the peak at 874 fps.... After recording the string, I turned the striker out a turn, repeated the process, then once more, and the four strings with the 15.9 gr Exacts are all shown on the second graph above.... Here is a summary....
Stock setting.... decreasing string from 909 fps, averaging 894 fps (28.2 FPE), 17 shots at 0.90 FPE/CI, 3000 psi down to 2320....
In 1 turn.... normal bell-curve, 884-909-873, averaging 895 fps (28.3 FPE), 24 shots at 1.19 FPE/CI, 3000 psi down to 2280....
In 2 turns.... normal bell-curve, 862-896-861, averaging 878 fps (27.2 FPE), 25 shots at 1.20 FPE/CI, 2900 psi down to 2180....
In 3 turns.... normal bell-curve, 840-872-842, averaging 861 fps (26.2 FPE), 28 shots at 1.36 FPE/CI, 2700 psi down to 1980....
This confirmed that the factory hammer strike was too much, turning it out a turn gave more power and more shots at greater efficiency.... After that, turning the adjuster in more just dropped the pressure range and power.... The "proper" setting would be about 2 turns out from stock, using the factory rated 200 bar (2900 psi) fill pressure.... My gun was leaking down slowly during testing, so in fact the efficiency is actually better than what I recorded above.... I did NOT like the feel of cocking the gun at 3 turns out on the striker, and it was barely acceptable at 2.... The bolt pulls back a long way before engaging the hammer, and the cocking stroke is short and requires a very hard pull at that setting.... I think I will concentrate on lengthening the hammer stroke, reducing the preload, and reducing the hammer weight for the first round of mods.... The latter two will be done by replacing the top hat with a shorter unit (to reduce the preload) made from Delrin (to lighten it).... I will likely also fit a preload adjuster into the end cap to revert the adjustment to what I consider to be superior to the current setup.... Here is a photo of the gun, with a Leapers 3-9 x 32AO scope installed....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51_zpsb269773d.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51_zpsb269773d.jpg.html)
Bob
-
Looking forward to what combination you come up with…suspect it will be a different one than most.
Made me read over my notes. Remembering my first impressions of the BAM 51.
1. That’s one heavy spring/cocking stroke. No wonder they put that odd looking cocking piece on the rifle, it took a good firm grip and a firm pull to get the SOB cocked.
2. Why do we have a +3oz striker assembly? My first deduction was that the valve stem seal was a wide one. Larger area= more holding force from air pressure = harder hit to get it to open. Don’t know if I was wrong about thator not as I went with less air pressure rather than changing the valve stem seal.
3. Not enough difference in energy when cranked “up” to make up for the shot count when slightly cranked “down”. In your tests, believe 26 foot pounds X 28 shots is a lot better than 28 foot pounds X 17 shots (basically 728 foot pounds out of a tank full vs. 476 foot pounds).
Hat trend doesn’t continue forever. Someplace about 23-25 foot pounds it seems to reverse itself (getting less energy per tank full than at higher energy). This also points to a pretty large air passage from valve to pellet.
4. That air tube really seems thick walled! Guess I got use to the thin tubed PCP’s and thought the BAM’s tube unusually thick (thick enough that threading the actual air tube for the breech screws works fine).
5. Really suspicious of the small diameter bolt and the bolt locking screw diameter. Haven’t had a problem, but seems like that bolt locking screw really doesn’t leave a whole lot of the bolt diameter. Hasn’t given a bit of trouble, it just looks weak.
Have no idea what the gas tube contributes to the overall weifght,but have to expect an all wood and metal rifle to have a bit of weight.
6. Why is the trigger so curled and in the middle of the trigger guard? Should be a bit less curled and more towards the rear of the guard-space for a better visual (and a less long reach to the trigger).
It’s a minor thing, but did have to get that trigger a bit straighter and working more towards the rear of the trigger than the middle.
7. Whatever that device is on the muzzle, an LDC it is not. The barrel diameter isn’t a real common one (would be if more rifles were built in imperial measure than in metrics).
-
Hey Bob,
Nothing like a new project to lift your Holiday spirits :D
I have a stock B50 (.22 cal) & B51 (.177) that need some tinkering, it will be very interesting watching the "professor" in his workshop. It will be fun seeing what a great, unregulated (.22 cal.) string could look like.
If you went with a regulator, I think you should be able to get 40 shots at 875 fps using 15.99 JSB's; 45 shots at 850 fps using the same JSB's would be something!
Cheers,
Kirk
-
The valve throat may be large, I haven't got in there yet, but the ports are tiny.... I assume sized for a .177.... The transfer and barrel ports are under 3mm.... On a .22 cal I would normally use just over 4mm.... It looks like there is enough meat in the brass transfer port to drill it to 4mm (5/32").... barely.... and likewise the barrel port.... but no point in doing that until I pull the valve and have a look at the ports in there.... Hogging out the ports is the route to more power, but usually at the expense of a shorter, peakier power curve.... I agree the hooked trigger is a disaster, especially for my big fingers.... I plan to anneal it and straighten it some.... That bolt looks weak where the cocking pin goes through it.... one of the reasons I want to reduce the spring load, using more hammer travel to get the lost hammer energy back....
Bob
-
If you think the gun was dirty, pull the end cap off and look in the air tube. I stripped all three of mine , for regulator install, and found the air tube to be absolutely nasty. Tried to wash tube in parts washer and the crud just laughed at me. Cut a slot in a piece of 5/8" 7075 rod and used 240 paper saturated with parts cleaning liquid, in battery drill, to get it all out and then polished with 400. Can't believe they don't clean them after machining.
-
I gently straightened my triggers in a vise, with brass jaws. They straightened very easy without any heat.
-
With no changes, it looks like the gun takes about 2300-2400 psi to get 875 fps with the 15.9 gr. JSBs.... That's 27 FPE, so we need 27cc for the plenum, plus the volume taken up by the regulator (maybe 20cc?).... That would only leave 150cc (9.1 CI) of reservoir remaining, and from 2900 psi down to 2400 is only 34.5 bar, so you only have 314 CI of air to play with.... If you could get the same 1.20 FPE/CI, that is only 377 FPE, which works out to just 14 shots.... I would go on record as saying there is no way you can get 40 shots at that power with the porting the gun has now.... if ever....
Bob
-
You have a “carp load” of posts to look though, and what I’ve found is not new news, but will list it anyway (just to get your mind going)
The only things I learned about the trigger:
1. The trigger housing is held onto the air tube by two little screws. If it gets loose, your trigger will either be variable or just refuse to hold.
You can ”cheat” the sear by manually flipping it and get all the internal air tube “guts” out without taking the trigger apart. Can take the trigger apart without having to take the air tube guts out.
SO the trigger housing has no real need to be detachable. Can get the “guts” out of either one (air tube or trigger unit) and leave the housing in place.
So I more permanently attached the housing to avoid those screws lossening and screwing up the trigger pull. Could tack weld it for all the difference it would make, but silver solder, epoxy, or red lock tite will work.
2. The design supplies at least a little sear drag. The sear itself is spring loaded ”flip” sear, and will drag a little on the striker no matter what you do. Making sure that the striker is polished smooth and the sear spring is no stronger than it has to be seems to help.
4. Is a bit of a &^^& shoot getting the cat’s tail out of the trigger. Is possible to break it; being brass makes it tend towards cracking. Annelaing (and as you know, brass anneals the opposite of steel) and bending will work better than just bending.
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/DSCF1752.jpg)
5. By changing the settings of the trigger adjustments, can get the trigger to sit a bit more back in the trigger guard. This almost always makes the manual safety inoperable. Simple system, and if you just have to have it, can make the safety work.
6. If you give up on the manual safety (and most will as it seems to work bass-ackwards for right handed shooters) the threaded hole for the safety makes a dandy threaded hole for a spring adjuster (or even reaching in for the stroke adjustment if the back of that “striker nose” screw is slotted and the adjuster hollow).
SUSPCIOUS about the two main faults reported over the years:
1. Suspect leaks are due to the age of the o-rings. Last ones were imported awhile ago, and no telling how long before that they sat around. The o-rings are getting old even if the gun hasn’t been used. I kind of expect one to shrink/get hard/crack by now. It doesn’t seem to be a design flaw, just old o-rings (that probably started off life sub standard).
2. The valve stem seal has been know to break. It has a sharp edge at the reduction for the return spring, and sharp edges focus stress.
The return spring is both stiff and likely to become coil bound if the valve stem is depressed very far.
So am going to guess the combination of a sharp edge at the rebated section of the seal, a coil bound return spring, a major-weight striker weight, a strong striker spring, and shooting at too LOW a pressure are the main causes of valve stem seal failure.
-
I think Ribbonstone is correct on the O-rings. I had to replace the O-rings on the fill probe on all three rifles. They were rather hard and broke when removing. I bought a pack of each size o-ring for the gun and have replaced them all, some more than once as the regulator and valve has been pulled several times. As stated it would probably be better to anneal the brass triggers before bend but I did three, being very gentle and had no issues.
-
Hey Bob,
That sure was a pipe dream -> wasn't it ::)
With your current tinkering, do you have the data to make a chart graphing Velocity (Y axis) and PSI on the X? This would be using 14.3 or 15.99 JSB's. This would inform folks like me, what possible setpoints might be picked when using a regulator!
If not, I will do it and post !!!
-
Ribbonstone I'm aware of the O-ring and poppet problems, I'll be looking for them when I pull the valve, also the brass filter.... plus a major clean on the tube.... Hopefully I should know enough by then to decide what to do with the valve ports, if anything, when I'm in there.... I already gave the trigger a little squeeze (took a chance and didn't heat it) will try it again to see if I can live with it before annealing it if I decide to have another go....
Unless I'm being fussy for some reason I usually only take pressure readings at the beginning and end of the string.... You can assume the pressure drop is a straight line, and in a regulated gun it should be.... but unregulated it is usually a slight curve, using less psi per shot at high pressure and more at low pressure.... It's pretty easy to plot velocity vs. pressure, I may do that later if I get bored....
Bob
-
Will be interested in what you find and what direction you go with that rifle.
-
SpiralGroove.... Here is the plot of Velocity vs. Pressure for the 15.9 gr. Exacts....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51VelocityvsPressure_zps2539dc62.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51VelocityvsPressure_zps2539dc62.jpg.html)
I added a trendline joining the lowest velocity and highest velocity recorded and the (estimated) pressures they occurred at.... basically a trendline for all the curves, so I would use that.... Note that 875 fps occurs at 2400 psi.... This is actually a very informative way to look at the data.... particularly if you want to make a decision on a regulator setpoint.... Note that it basically takes hammer strike out of the picture....
Bob
-
In this photo you can see the stock hammer, guide, spring, and end cap.... Notice that the striker is sticking out about 2 turns from the nose of the hammer (stock setting was 0.75mm), and also notice the distance from the front of the hammer to the lock screw....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/StockHammerParts_zpsb0770d9c.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/StockHammerParts_zpsb0770d9c.jpg.html)
I shortened the front of the hammer by 2mm and made a flush striker to increase the hammer throw by 2.75mm (0.108") over stock.... I also made a very light plastic spring guide that adds only 1/4" of preload to the spring instead of 1/2".... Here are those parts....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/NewGuideandShortenedHammer_zpsdd424231.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/NewGuideandShortenedHammer_zpsdd424231.jpg.html)
I also removed the screw that prevents the hammer from rotating.... It is only necessary if you want to adjust the striker (I don't) and with it removed the hammer can be withdrawn out the back of the tube by lifting up the trigger sear without having to remove the breech.... I reassembled the gun, hoping that the extra hammer travel would mean it would still work about the same with less preload.... It didn't.... I had to put 4 washers under the back end of the hammer spring, and shorten the spring guide because it hit them.... I ended up making the guide the same length as the guide portion on the original metal one because I ended up needing more than stock preload with the much lighter guide.... In other words, I lost more hammer strike by reducing the weight than I gained by increasing the travel.... I shot strings with both 4 and 5 washers, and then put back the original metal guide with no washers, so I had stock preload minus 2.75mm but the spring was still at the same length when cocked as a stock gun.... This combination actually increased the power over stock.... The shot strings, using 15.9 gr. JSB Exacts, are shown below....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51MoreHammerTravel_zps55d09ca4.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51MoreHammerTravel_zps55d09ca4.jpg.html)
The interesting thing is that I gained in efficiency and shot count with the additional hammer travel.... In addition, I ended up with more power when I went back to the stock metal guide (top hat) but with the extra 2.75mm of hammer travel.... Strangely, I also ended up with a bell-curve with that setup, even though the hammer strike was greater than before (when I didn't have one).... Here is a summary of the three strings....
Light Guide, 4 washers.... normal bell-curve, 856-892-856, averaging 878 fps (27.2 FPE), 32 shots at 1.41 FPE/CI, 2900 psi down to 2140....
Light Guide, 5 washers.... normal bell-curve, 870-905-871, averaging 889 fps (27.9 FPE), 28 shots at 1.29 FPE/CI, 3000 psi down to 2270....
Heavy Guide, stock preload.... bell-curve missing some shots at the beginning, 903-924-887, averaging 908 fps (29.1 FPE), 20 shots at 1.27 FPE/CI, 3000 psi down to 2420....
The first string is directly comparable to the first tests at 2 turns out, same power (27.2 FPE), but now 32 shots instead of 25, 1.41 FPE/CI instead of 1.20.... It looks like the additional hammer travel is worthwhile.... I need to fit a preload adjuster to the rear end cap and do some more tests, so that is next....
Bob
-
Wow :o Bob, 1.41 FPE/CI looks pretty amazing ;D
Just tested my BAM 50 (.22 cal.) and it repeatedly get 850+ fps using 15.99 JSB's at 1450 psi (100 bar).
Hence, given Lloyd's calculator, I should be able to get 50 shots at 850 fps going from 200 bar to 100 bar using the same pellet.
This of course assumes I can maintain a 1.31 FPE/CI. So this is a worthy goal for my tune looking at a setpoint of about 1500 psi.
I'm very interested on your efficiency tweaks (porting/preload mods)................Thanks ;D ----->>>Kirk
-
SpiralGroove.... You are unlikely to get 1.31 FPE/CI at 1500 psi, don't forget the average pressure of my strings was nearly 2600 psi.... Of course if you back the power down, that will help maintain the efficiency....
Bob
-
Doninva, I think the problem with the O-ring on the check valve of fill port is that the gap between the sealing surfaces is too large. Thus the O-ring extrudes and shreds. New replacements don't last that long for most people. A hard 90 durometer should last longer.
My B51 was one of the "new old stock" rifles that Mike got a couple of years ago and, despite getting lots of use, that is the only high pressure O-ring I have had to replace. The original O-rings even survived a teardown and rebuild.
-
Hey Bob,
One last question :P:
Generally speaking, what is the slope of the efficiency curve moving going from 100 bar to 200 bar (Pressure on X, E on Y)?
Kirk
-
nervoustrigger, good info. Next time I order some o-ring, will get some good for abrasion.
-
Well, just PM me your address. I have a whole bag and can never use them all.
-
This afternoon I made an RVA (rear velocity adjuster / power adjuster / preload adjuster) and shortened the spring guide to compensate for it.... Here are the parts....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/RVAParts_zps0501ed8a.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/RVAParts_zps0501ed8a.jpg.html)
On the left is the guide, shortened 1/4".... In the middle is the B-51 end cap.... I milled a 3/8" diameter recess into it leaving 1/4" of the threads remaining, and then milled a 1/8" slot on the bottom side of the spring seat area.... On the right is the 8-32 adjusting screw, with a thinned nut and the adjuster with pin to prevent rotation.... You insert the screw through the threaded hole in the end cap (it just clears and can rotate) and then install the nut and tighten it against the shank of the screw, which leaves just enough space the screw can rotate but only have about 0.010" end float.... Then screw on the adjuster with the pin the slot in the end cap so it can't rotate....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/RVA_zps79075d78.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/RVA_zps79075d78.jpg.html)
Once assembled, there is 8 turns (1/4") of adjustment, and the only modification necessary on the stock was to file a small angled notch to clear the ball-end hex driver used to adjust it.... In the photo, it is roughly in the middle of its adjustment range.... When fully out, the adjuster takes up 0.10" of room in the spring seat, so I shortened the guide 1/4" to allow adjustment in both directions from the stock preload.... It is at the stock setting when 3 turns out from maximum preload.... I then tethered the gun to a tank through a regulator set to 200 bar (2900 psi) and shot 5 shots at each setting (1 turn increments) and plotted the average velocity as shown in the top graph below....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51WithRVA_zps68f129c3.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51WithRVA_zps68f129c3.jpg.html)
Since the stock preload was 3 turns out, and it was on the lower end of the knee of the velocity curve at 200 bar, I thought that would be a good place to shoot my first string.... The results are in the bottom graph above.... I was extremely pleased, as the first shot at 3000 psi ended up exactly 4% below the peak of 904 fps, and I got 32 shots averaging 888 fps (27.9 FPE) from 3000 psi down to 2220, which works out to 1.38 FPE/CI.... That is a great number at that power, one that few PCPs can match in my experience.... The question is why is this gun so efficient?....
There are a few things I noticed that are consistent with many of the things in "The Book".... First of all the initial, upwards part of the shot strings are rather ragged, with significant shot to shot variation (although within the 4% ES), compared to the downward, low pressure side of the string.... Secondly, the pressure drop is almost perfectly linear instead of curved upwards in the middle, which is normal for unregulated PCPs (they usually use more air per shot at low pressure).... Third, I noticed no "burping" and very little increase in the volume of the muzzle blast towards the end of the string.... Fourth, the sear has quite a strong spring so that it drags on the hammer to a significant degree.... Here is what I think is happening.... I think the heavily sprung sear is dragging so hard on the heavy, slow moving hammer, that that friction prevents it from bouncing and wasting air at the low pressure end of the string, and indeed you can't hear any resulting "burrpppp" from hammer bounce.... However, this drag, being not completely identical shot to shot, causes the velocity swings in the first part of the string, exactly where you would expect to see that effect exaggerated.... On the latter part of the string, even large changes in hammer strike will not change the velocity, and we don't see any.... The (almost complete?) lack of hammer bounce shows up in reduced air usage and greater efficiency towards the low pressure end of the string.... I think a lot of that is due to the (what we would think was excessive) sear drag on the hammer....
Now I have a problem.... Should I leave well enough alone and be happy with a fairly powerful and very efficient gun?.... or should I hog out the tiny ports and see if there is a beast sleeping inside this gentle giant?.... I think we all know the answer to that.... *grin*....
Bob
-
SpiralGroove.... There is no simple answer to that question, it depends entirely on how where the valve is closing relative to barrel length.... In a MSP, with a dump valve, once you get to a reasonable power level the efficiency actually DROPS the higher the pressure because although you are increasing the velocity, you are dumping more and more air out the muzzle after Elvis has left the building, and the efficiency goes DOWN with increased pressure.... In an extremely efficient PCP, with the valve closing early (at 15-20% of barrel length or less) the efficiency may be almost directly proportional to the pressure.... double the pressure and double the efficiency.... Most PCPs will lie somewhere in between, about all you can say is that AT A GIVEN FPE LEVEL the efficiency is usually higher as you increase the pressure.... This is because to keep the same FPE you will reduce the valve dwell, using a shorter burst of higher pressure air, and using a greater percentage of the barrel to then expand that air....
Bob
-
Bob,
Very nice, can't wait until the next episode ------>>
Hail Caesar !!! ;)
-
Bob,
Just a piece of info that will help consistency .... VENT the backside of hammer by putting in a vent in rear cap ;)
Found coming into the side where cap rests within stock best. Small trough cut in the wood cut toward trigger mechanics gives path for air to come and go within this space as hammer strokes.
-
I noticed mention in "The Book" of the vent holes in the piston just behind the striker lock screw, I guess they are supposed to allow air from the front of the piston to the back.... I was thinking of making sure the tube was vented front and rear anyway, thanks for the confirmation, I'll try that.... Now that I have removed the safety I may just drill through the hole in the end of the cap where the detent spring was.... I'll have a look....
Bob
-
I noticed mention in "The Book" of the vent holes in the piston just behind the striker lock screw, I guess they are supposed to allow air from the front of the piston to the back.... I was thinking of making sure the tube was vented front and rear anyway, thanks for the confirmation, I'll try that.... Now that I have removed the safety I may just drill through the hole in the end of the cap where the detent spring was.... I'll have a look....
Bob
Sprialgroove will confirm this i'm sure ;)
-
Hey Guys,
This venting "tweak" is pretty advanced stuff for me as I just got into 7th grade on PCP tuning :P
I saw something in the book about the valve not opening if the hammer was sealed (w/lube), but that went right over my now sharpened Pin Head.
So, I have no holes in my delrin hammer, besides the one drilled & tapped for my a 1/4" hex bolt turned striker. No venting out the rear - what should I be noticing w/o? Regulated shot string <2% ES.
Sorry Motorhead, no help from the undergrad ::)
-
Lol ... have to go back into the PM's and re-read who it was then i was talking with about venting ... they did so with a LARGE gain in velocity and consistency.
My bad to insinuate such a thing !! :-[
Bob will get there ... he always does ;D
-
In "The Book" they talk about screwing the striker in too far and blocking the vent holes behind it, resulting in a drop from 900 fps to 200.... because a vacuum is created behind the hammer.... When I had my gun apart I confirmed that yes, there is a pair of holes just behind the striker that pass into the center of the hammer, through the hole in the guide and spring, and would allow air into the space behind the hammer on firing.... If you made your own hammer and omitted those holes, I can see a problem for sure.... I had already thought ahead to that possibility.... However, adding more venting MAY decrease the shot-to-shot variation with the stock hammer, I don't know.... Has anyone found a difference in a stock, vented hammer with adding more venting to the rear of it?.... Obviously if you removed the safety (as I did) and didn't fit an RVA screw that area is well vented, and I was still getting a ragged front half of the string that way, if anything it is better with the RVA in place but that may have nothing to do with the amount of venting.... Anybody notice a difference in velocity or variation just by removing the safety?....
Bob
-
Bob, the things you write go right over my head about 85% of the time..Mostly because i dont' understand how airguns work. However I love the end result of what you do! Keep up the good work..
-
Hey Bob/Scott,
So far I haven't gone with the rear velocity adjuster; trying to teach my Son the importance of a Safety (and to always use it before loading the gun). Have pulled the hammer to make striker adjustments (which is a pain), but pretty much have the striker "in" almost all the way creating a hammer very similar to your shortened one.
So for the vent hole (even though I haven't experienced a power/shot consistency issue), I was thinking of drilling a 1/8" hole in the front and rear (not the tip holding the striker) of delrin hammer to vent any pressure which could create THE vacuum issue.
This should solve any problems -> Right?
Here are some pics........
http://i113.photobucket.com/albums/n227/kirk_schwarz/Hammer001_zps1d545311.jpg (http://i113.photobucket.com/albums/n227/kirk_schwarz/Hammer001_zps1d545311.jpg)
http://i113.photobucket.com/albums/n227/kirk_schwarz/Hammer005_zps3a712c3a.jpg (http://i113.photobucket.com/albums/n227/kirk_schwarz/Hammer005_zps3a712c3a.jpg)
http://i113.photobucket.com/albums/n227/kirk_schwarz/Hammer006_zps1315492a.jpg (http://i113.photobucket.com/albums/n227/kirk_schwarz/Hammer006_zps1315492a.jpg)
-
Does the rifle loose a lot of weight when you replace the parts with Delrin parts, or not much?
-
Bob,
When i did all my work on the B51 a lighter hammer was indeed part of the rework.
Pulling off the safety rocker opened the rear screw hole in a sense adding a SMALL vent.
What came to my attention was the air movement against my face upon firing ( have a LOT of facial hair )
In the case of the BAM what I was feeling was air intake at the 4mm hole.
Shooting over the Chrony finger over the hole / finger off the hole gave a variance flagging me to the fact suction was happening and the factory means to create venting was insufficient.
Same thing happens within the Marauder rifle. Solid diameter hammer absolutely need the rear caps adjuster hole to remain open for venting.
On nearly ever hammer i have made for my personal use has longitudinal cuts down there length with a ball end mill. This allows transference of displaced air ahead of or behind the hammer. Doing so have vastly reduced compression losses on the valve side and suction losses on the spring side.
-
Scott,
So for hammer venting, you're saying the 1/8" hole through the hammer (I was suggesting will be inadequate), and to go with some kind of groove down the hammer length instead -> Right?
Kirk
-
Scott,
So for hammer venting, you're saying the 1/8" hole through the hammer (I was suggesting will be inadequate), and to go with some kind of groove down the hammer length instead -> Right?
Kirk
On a BAM because hammer is rotationally floating ( IIRC ) having sear able to hold anywhere around entire diameter that groove trick DOES NOT work :P
To get a sufficient vent took a 1/4" hole into side of end cap drilled on a diagonal angle intersecting the spring pocket area just behind shoulder. The 4mm threaded hole was not enough. Also end cap safety screw location was IMO too susceptible to debris getting in. Which is why I did the vent hole where covered by stock and cut a trough in the wood to the trigger mechanics area.
-
Hey Motorhead - Thanks !!
Hey Pellgunfun,
When I tuned my gun and reworked my stock, I probably lost 8 oz or 1/2 lb - a noticeable difference.
If I was to do the stock again, I would take more wood off the forearm which I left too bulky - also stain darker...
http://i113.photobucket.com/albums/n227/kirk_schwarz/BAMB50001_zps9996613a.jpg (http://i113.photobucket.com/albums/n227/kirk_schwarz/BAMB50001_zps9996613a.jpg)
http://i113.photobucket.com/albums/n227/kirk_schwarz/BAMB50-4_zps2f43e012.jpg (http://i113.photobucket.com/albums/n227/kirk_schwarz/BAMB50-4_zps2f43e012.jpg)
-
Have wondered about that vent hole. I had my doubts at first, seeing the large port that the blot’s locking screw makes, and that’s ahead of the striker aseembly. Thought that would vent any air being compressed ahead of the striker.
More going on that that.
Vent in the striker does seem to be needed (can plug it and find that out pretty quickly). IS it because it compresses air ahead of it (but the locking bolt port on the left side should take care of that) or is it because it wants to pull a vacuum behind it?
So long as I’m wondering, if you use a lighter striker assembly traveling faster, would it need a larger vent than the heavy slow striker assembly?
Or is my brain too work-fried to see something simple?
-
Absolutely in terms of air transfer, faster a displacement happens faster any captive air wants to escape.
As flow resistance rises within the compressed or vacuum sides, greater is damping effect this air has on the motion of hammer.
Sadly were not cycling these parts in a vacuum where air pressure differential would not matter, so if we do what we can in mitigating these air motion damping losses more consistent will be the motion created by the mechanics of the system.
-
ALMOST got me.
Was planning some tests with the vent open/vent closed/safety screw in place/safety screw removed.
Then I thought about it a little harder.
I like it the way it is and I’d better stop experimenting with it.
USUALLY, I’m the one to down tune a rifle for efficient air use, lower power, and a long shot count. I happened to pick my BAM to be one of my more powerful PCP and wanted a pretty simple goal: +30 foot pounds and +20 sweet spot shots.
It’s not a rifle I plink with a lot, or pound long strings of targets. Pretty much just a hunter that can keep energy up to about the 20 foot pound level at 50yards.
So unless Bob comes up with something that will drastically change my view point, am going to leave it alone.
-
I think the air in front can vent just fine through that slot where the cocking pin rotates through, but SpiralGroove I can't believe you are getting away with Delrin against the trigger sear !!!.... Surely that can't last ?..... With no hole through the hammer and the safety installed, you will be getting a vacuum behind the hammer, particularly if it fits well....
I had removed the #26 screw to allow my hammer to rotate (as some said was OK in "The Book"), but have identified a problem with that.... If the hammer rotates to put that screw hole at the bottom (and it had) the hole can hit the sear on trigger release, and I think that was where my erratic velocities were coming from, at least to some extent.... I replaced that screw (so the hammer can't rotate) and when tested with the larger ports the erratic velocities had mostly gone away, and I am still just using the stock hole through the hammer to vent the area behind it....
Bob
-
Yeah,
When I started my B50 tune (.177 cal.) a few months ago, Scott suggested I use 100% Nylon instead of Delrin. However, I was in a hurry, couldn't find any nylon, so I bought a stick of delrin for the job. During the tune, having shot more strings than I care to remember (like a painful hangover), the hammer showed no sign of abrasion (I pulled it out many times to look)? I'll check the hammer for wear at the sear contact again. If it looks bad now :o, I may remove a little delrin and try replace the surface with something harder. During the tune I had lightly polished the sear facings (500 grit) while keeping its edges.
As far as pneumatic function, I was able to get 70 shots at 892 fps, hence I had no complaints. Some other members got 80 shots per fill and I wrote this off to the "Sail" I installed (yet to remove :P). So I had planned to remove it, and was hoping to get 10 more shots. On my AT44 tune, my test results showed the "Sail" hurt efficiency/performace rather than improve it.
Now it appears I may need to vent the hammer a little better too (I think my hammer is about 10 to 15 thousandths smaller than the original).
Thanks all!! ------------> Hey Ribbonstone "Go For It" ;) My prior tune (the pain part) is still with me, but you gotta move foreward ---> Kirk
-
NOPE…got enough problem rifles to spend my limited time/concentration on one that isn’t a problem. The BAM 51 isn’t a problem child.
All I wanted was +30 foot pounds, + 20 shots, and hopefully a decent air efficiency (as I pump fill, don’t like wasting my effort).
Had a problem with the #26 screw.
Evidently it got buggered. What I think I did was over tighten it (although I’m careful, so it could have been tweaked before it got in my grubby hands). Seems to be a soft screw and the slot got “spread” which made the head kind of out-of round.
Would work back and forth slicker-n-snot when the striker was tried with just the striker in the tube (no spring).
Was trying very low pressure operation at the time:
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/DSCF0421.jpg)
Took a bit of investigation to figure out that as the spring compressed, it somewhat torqued the striker to the side, which rubbed in the slot a little too hard/inconsistently, which gave those occasional way-slow shots. Rub marks on the screw head and rub marks on just one side of the slot it runs in were the big clue.
Quick and simple fix was to polish the slot and the screw head, and attempt to harden the screw head (KASE-KNIT).
Debated removing the #26 screw, but mine is an old rifle, and the striker/tube aren’t perfectly round. Never did bother to figure out which (or both) was at fault. Wouldn’t rotate more than about 40degrees without binding. May just have been the years of use, but considering how the trigger works, didn’t think increasing the “slack” by lapping was a good idea.
Polishing/hardening the screw and polishing the slot pretty much cured the wild velocity change problem.
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/DSCF0422.jpg)
Eventually, I worked my way up in power, but kept to the lower fill pressure (can tell I’m a hand-pump kind of guy by my liking for low pressure).
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/IMG_0068-1.jpg)
BUT…being prone to fooling around with what is already working, I screwed that up. After a good bit of resetting/retesting, managed to get close to the above setting.
(MORAL HERE: don’t fix what ain’t broke!...which is why I won’t be back inside this rifle until something breaks or leaks).
Posted last weekend for some testing at 20 yards (mostly looking at the difference in 1 shot. 3-shot, and 5-shot groups).
http://www.gatewaytoairguns.org/GTA/index.php?topic=79780.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=79780.0)
-
Today I removed the breech and drilled out the barrel port and milled the transfer port recess deeper, completely through the breech to put the flat that it seals against in the barrel itself.... That allowed me to change to a 5/16" OD x 5/16" long Teflon Rod transfer port.... The stock porting (valve, transfer port and barrel) was a very stingy 0.114" (likely made for a .177) and I went to my usual 75% of the bore for the barrel port, which is a #20 drill (0.162").... The transfer port was the next size up (0.166"), and when I did the valve exhaust port later in the day, I used an 11/64" drill (0.172").... Here is a photo of the breech after machining, and the new transfer port sitting on top of it.... Note the beautiful job on the leade where it tapers into the rifling, visible through the barrel port.... The stock bolt probe seats JSB pellets nicely ahead of the (now larger) port, so no problem there....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/NewTransferPort_zps29821e08.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/NewTransferPort_zps29821e08.jpg.html)
At this point I still had not modified the valve, but I wanted to see what I had gained (if anything) so I filled the gun and shot a string with the 15.9 gr. Exacts using the same 3 turns out on preload that I did on the last string for comparison.... It was shooting hotter, and I figured if I gained more when I drill out the valve port (and I should) I might be overpowering the Exacts, so I shot another string with the 18.1 gr. Heavies as well, same preload setting.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51BiggerPorts_zpsade5ad93.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51BiggerPorts_zpsade5ad93.jpg.html)
With the 15.9 gr. pellets I gained a solid 30 fps, lost a few shots, and the first shot at 3000 psi was more than 4% below the peak velocity, which had moved down from 2700 psi to 2600, but was now 935 fps.... I had 27 shots within my 4% ES, averaging 921 fps (30.0 FPE) at 1.35 FPE/CI.... With the 18.1 gr. pellets, the first two shots were too slow, and there was a nice long plateau from 2700 psi down to 2400 at just under 890 fps.... This was an exceptional string, I got 33 shots averaging 876 fps (30.8 FPE) from 2900 psi down to 2100, which works out to 1.45 FPE/CI.... That's pretty amazing in .22 cal at over 30 FPE, IMO....
Not wanting to stop there, I bled off the pressure and pulled the valve.... I was shocked when I saw the size of the valve spring, and how much preload it has, partly from the 1/8" thick brass spacer on the poppet.... The preload is so much I don't think the valve can even lift 0.1" without the spring going coil bound, which is likely the cause for the known poppet failures from shooting the gun at low pressure or dry-firing it.... The poppet was an interesting design, with a highly concave face that seals right around the outside edge, making the seal 0.41" OD.... At 3000 psi, that takes 396 lbs. to crack the valve, plus the force of that massive spring (another 20 lbs?).... so no wonder the hammer weighs a ton.... The throat of the valve is a generous 0.240", which seems totally out of place compared to the tiny 0.114" exhaust port.... The port is quite near the seat, but I determined there was lots of room to go to the size I wanted (in fact you could go to 3/16" for a .25 cal.), so I carefully positioned the valve in my milling attachment on my old Atlas lathe and drilled the exhaust port out, in 3 steps, to 11/64" (0.172").... I then eased the corners at the bottom to remove any sharp edges with a small spherical burr in the Dremel, cleaned everything up, (including the inside of the tube, it was filthy), replaced all the O-rings, added a small washer to prevent the check valve from damaging the brass filter in the fill fitting, and reassembled the gun.... I'm pretty sure I cured the leak, at least it's a LOT better.... Here is a photo of the drilled out valve and the poppet, valve spring, and spacer....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/ValveMod_zps5e3cdd3f.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/ValveMod_zps5e3cdd3f.jpg.html)
I am in the process of topping off my Great White tank with my Shoebox compressor, so shooting strings will have to wait, but I had enough air in my SCUBA tank to get one fill to 3000 psi.... I still had the preload at 3 turns out, grabbed the 18.1 gr. JSBs and took a shot.... Hmmmmmmmmm.... 772 fps.... Valve lock?.... I continued shooting and the gun came alive at about 2700 psi and peaked at 2400 at.... are you ready for this?.... 1013 fps (41.3 FPE).... I refilled to 2900 and cranked the preload in a turn at a time, and it was still increasing at 2900 psi even at maximum preload, where it was doing about 980 fps.... I will be shooting some strings when I have my tank topped up, but it looks like I will eventually need more hammer strike to find out what the maximum is at 3000 psi.... After the next round of tests I will either increase the hammer travel more, remove some of the preload on the valve spring (or use a weaker one), or both, as the gun is already hard to cock at maximum preload.... Who would have thought that a gun known for too much hammer strike would need even more once the beast inside was unleashed?....
Bob
-
Do think that short dwell/stiff spring/sharp corner on the valve stem is at least one of the reasons for valve seal breakage .
So which direction will you go…more spring tension (already hard to cock, and I keep thinking of that skinny bolt body and how much “meat” at the locking screw) or more striker weight?
Or, is the initial “slack” in the bolt opening an indication that there could be even more striker travel to be had?
-
Hey Ribbonstone,
Maybe the "Venting Tweak" can be added to your Bucket List? (for when your plate is clear).
Hey Bob,
With all the headaches associated with the (heavy duty) hammer and monster, valve spring, what are the "costs" in terms of goals (Max, efficient FPE) of using a different approach (delrin hammer/guide and lighter valve spring)? Less durability?
I think, all things being equal, the gun would operate easier (less mechanical brute force) and be lighter to boot. Why would one not go that direction, unless efficient -> maximum power cannot be obtained? I know it takes more time to make the parts and tinkering to tune, but that doesn't matter if it's the best approach.
Knowing what you know, isn't it pretty clear to you at this point?
It's not to me, but I'm not Tony Stark :P
Kirk
-
I took some time this evening to shoot some strings with the modded valve at several preload settings.... I used the JSB Exact Heavy 18.1 gr. pellets for all tests, and only those shots within a 4% ES were recorded.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51ValveandPorts_zps9f58a6a0.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51ValveandPorts_zps9f58a6a0.jpg.html)
To say this thing came alive when I drilled the valve out would be an understatement.... The highest velocity recorded was 1028 fps (42.5 FPE) at about 2500 psi with the preload at maximum.... The string is near ideal for a 200 bar (2900 psi) fill, but I can't max. the gun out at that pressure, there isn't enough hammer strike to find out what it would do with the JSB Heavies, let alone heavier pellets.... That string averaged 1012 fps (41.2 FPE) for 22 shots from 2900 psi down to 2120, for an amazing 1.40 FPE/CI.... At 3 turns out, I got 24 shots at 982 fps (38.7 FPE) average, from 2700 psi down to 1930 for 1.46 FPE/CI.... At 5 turns out the fill pressure was 2500 psi, returning 25 shots at 960 fps average (37.1 FPE), down to 1760 psi, for an efficiency of 1.51 FPE/CI.... At the minimum preload, 8 turns out, I still got an average of 931 fps (34.8 FPE) for 23 shots from 2200 psi down to just 1600, with an astounding 1.61 FPE/CI, it only used 600 psi to do that....
I particularly like the string at 5 turns out, from 941-973-941 using a 2500 psi fill to get 25 shots, the longest string.... I know the JSB Heavies are accurate at that velocity in other guns, and they were shooting one-hole groups during the Chrony session, which certainly looks promising.... However, it seems I can never leave well enough alone, so I'm going to pull the valve apart and remove some of the preload by thinning out that brass collar on the poppet.... I can't shake the thought that I can get the same performance without beating the valve to death with such a heavy hammer strike, I would really like to reduce that....
Bob
-
Ribbonstone, after I reduce the valve spring preload I may look for more hammer travel to reduce the preload and cocking effort further.... I am convinced that the stiff spring going coil bound at low pressures or firing when empty is the main culprit for breaking the stem.... I think the heavy hammer is trying to drive the stem through the poppet after the spring stops it....
SpiralGroove, I can't see that light a hammer (eg Delrin) working at the high end of the pressure range to get the FPE I'm seeing now, although I could be wrong of course.... It appears that this gun could be regulated at about 1900-2000 psi and shoot at about 35 FPE with the 18 gr. pellets.... At that pressure level, I would think a much lighter hammer could be used, but at the expense of more spring of course (relative to what a heavy hammer needs).... UNLESS more travel can be found, which I think likely....
There also is the possibility of making a smaller OD poppet, which could drastically reduce the hammer strike required.... I can see that happening as well.... The valve, with opening the exhaust, transfer, and barrel ports out to 3/16", is plenty capable of powering a .25 cal. also.... Lots of possibilities here....
Bob
-
There does seem to be room for more stroke, but I'd have to check the length of the striker body. The way the sear works, can't have the rear edge of the striker ahead of the sear. Don't have my striker out, but memory has the sear close to the rear end of that striker (when the striker is down). Might be wrong about that, memory is a fickle mistress.
-
I was able to shorten the striker nose IIRC 1/4" there about or a tad more. Helped regain strike energy with the lighter hammer.
++ gain using a lighter hammer is the shock & thump of accelerating that massive factory hammer was much reduced while the Lock Time also sped up.
-
Hey Bob,
I understand we have different perspectives on what is THE "optimal" tune (I'm a target shooter). As you know, I'm looking to get a long shot string (50/45/40) at medium power -> 825 fps to 850 fps in .22 cal (25/26 FPE). Using a regulator, the deal breaker for me is increasing efficiency using porting/hammer/spring/venting tweaks to get there (1.25 to 1.31 FPE/CI at 1500 to 1700 psi).
Right now, I don't have the wherewithall to separate the wheat from the shaft when making very small adjustments w/o making time consuming or $$ costly setbacks.
I've experienced the Bliss and Painful "black holes" the dark side has to offer. Any help getting me to the promised land.......... is appreciated.
-
Shortening the nose of the factory striker 1/4" would eliminate the striker lock screw.... Not a problem if you glue (Loctite) the striker in place.... If you don't shorten it, it would block those two vent holes as well, but you vented the back of your tube to get around that anyway.... I haven't examined the striker and sear geometry to determine the maximum striker travel possible yet, but Ribbonstone is correct, the striker must keep the sear depressed or it will lock up....
Increasing stroke gains both energy (needed to overcome the large poppet area x pressure) and momentum (to create dwell for more FPE).... Decreasing the weight only reduces momentum without changing energy.... Therefore, if you do both (increase stroke and lighten the hammer) it is a good solution to overcome the large opening force without creating more dwell than you need.... Excellent solution for smaller calibers, lower FPE levels, and lower pressures.... For where I'm at now, not necessarily so, although I want to do as far in that direction as possible....
SpiralGroove, as you are aware, getting high efficiency at low pressures is more difficult.... In regulated guns, IMO, there is no better way to your goal than taking the time to find the best balance between setpoint and hammer strike so that you end up on the knee of the curve, and more specifically that portion of the knee where the velocity goes flat to slightly up below the setpoint, extending the string below it.... That achieves two things.... For the bulk of your shots, it puts you just on the high pressure (efficient) side of what would be the sweet spot in an unregulated gun.... Then when you come off the regulator, you push over the top of the sweet spot and down the other side slightly before the velocity drops off, extending the string even further.... I don't want to drag this thread off into regulated gun tuning, and I know you have read it, but for others who haven't, I go into that in detail in this thread.... http://www.gatewaytoairguns.org/GTA/index.php?topic=74919. (http://www.gatewaytoairguns.org/GTA/index.php?topic=74919.)
Bob
-
Almost there…keep it up and I’ll find myself back inside that old BAM.
My compromise was for easy cocking, +20 shots, +30 foot pounds. Really not too thrilled with increasing cocking effort, but it may be that with more striker stroke, I might not have to.
No time this week, solid work (including Christmas), but I’ll be following along with the thread
-
Today I pulled the valve apart again, and worked on the poppet and spring.... I ground the ends of the spring flat, which decreased the length by 0.030".... I made a washer that reduced the preload by 0.095", so I shortened the preload by 1/8" from 0.200" to 0.075".... I had a spare poppet, so I tapered the sides slightly to reduce the seat diameter from 0.41" to 0.36", which doesn't sound like much, but that reduced the force holding the valve closed form 396 lbs. to 305 lbs., so combined with the spring change I reduced the effort to open the valve by 25%.... The changes also meant that the valve could open a lot further without the spring hitting coil bind.... Here is a photo of the old and new poppets, shim, and the spring with the ends ground flat....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/Valves_zps56d28cbf.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/Valves_zps56d28cbf.jpg.html)
I reassembled the gun, and expecting it to need less hammer strike I set the preload to minimum, tethered the gun at 2900 psi, and fired a shot across the Chrony.... 1095 fps with 18.1 gr. JSB Heavies!.... REALLY !?!.... Wow, I guess it was driving the spring to coil bind before, I expected the same velocity at less preload, not another 60 fps!.... I tried all the hammer preload settings, and it really made no difference, the velocity was maxed even at minimum preload.... I stripped the back of the gun apart, took the plastic spring guide I had and turned 0.150" off the preload spacer and tried that instead of the metal one.... Now I could back off the velocity a little bit when I set the preload to minimum.... So, I went digging through my hammer springs and found a couple of likely candidates, and ended up with the ability to at least create a velocity curve.... I took that spring and "set" it by compressing it fully several times, and it lost about 0.1" in length, and I reinstalled it and ran one more test.... The results are in the graph below....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51HammerSprings_zpscd95b86c.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51HammerSprings_zpscd95b86c.jpg.html)
You can see that even with minimal preload the stock spring was too strong.... The new, set spring was still capable of getting the gun to maximum, so I tried a few heavier pellets, with the following results at 2900 psi:
JSB Heavy 18.1 gr.: 1100 fps (48.6 FPE)
H&N Baracuda 21.0 gr.: 1053 fps (51.7 FPE)
EunJin Dome 28.4 gr.: 956 fps (57.6 FPE)
EunJin Point 32.1 gr." 933 fps (62.1 FPE)
This gun was no slouch stock at nearly 30 FPE, but I have more than doubled that now, putting it amongst the highest powered .22 cal PCPs.... I then hooked my Chrony up to my Netbook using Chrony Connect, and shot three strings with the JSB 18.1 gr. pellets, as in the graph below....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51NewPoppetandSprings_zpse8dc90a3.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51NewPoppetandSprings_zpse8dc90a3.jpg.html)
At 4 turns out from my maximum preload setting (with the new lighter, set, spring) the string started nearly at the top and I only got 15 shots.... At 6 turns out, with a 3000 psi fill, I got a normal bell-curve 1004-1041-998 over 21 shots, averaging 1025 fps (42.2 FPE), at 1.19 FPE/CI.... and at 8 turns out (my minimum preload) I had to start the string at 2700 psi, and I got 20 shots ending at 1960 psi, 980-1015-979, averaging 1000 fps (40.2 FPE), at 1.31 FPE/CI.... The efficiency is down a bit, but still very good considering the power level.... I really like the MUCH lighter cocking force, it should be a lot easier on the gun.... If there is any drawback to the gun the way it is now, it is that I can't tune it down enough to get the JSB Heavies into the mid 900s.... There are two solutions, one is to fit a weaker hammer spring and drop the fill pressure down, the other is to fit a smaller transfer port and run the hammer spring at about 6 turns out, which gave me the 1025 fps string above.... From what I saw previously with this gun, dropping the power by dropping the fill pressure doesn't buy you many more shots, so I think I will try a smaller transfer port and see if that will flatten out the string.... I think something about 9/64" (0.140") should put me at about 35-36 FPE with those pellets, so I will start at 1/8", see what I get, and then try and work my way up until the gun is averaging ~ 950 fps where I know those Exact Heavies tend to still be accurate....
When I took a look at the diameter of the stock poppet I knew immediately why the B-50/51 had such a heavy hammer.... I figured that making it a bit smaller would ease the loads on everything, but I was surprised at just how effective it was.... The poppet could be made quite a bit smaller still, there is no reason the OD couldn't be reduced down to 5/16", maybe even 0.300", because the throat is "only" 0.240".... Doing that would, I think, necessitate making a much lighter hammer to compensate.... That's not a bad thing, but I have the idea in the back of my mind to convert my gun to a .25 cal, so the ability to flow lots of air isn't a bad thing, and I have the cocking effort under control just fine.... Oh, I also took some measurements on the hammer throw, and it can be nearly doubled over stock.... The way my gun was tuned from the factory the hammer travel was 0.52", and it is now 0.625".... I can go all the way to 1.00" by shortening the nose of the striker another 3/8", not that I plan to.... You can't machine off all of the nose right back to the shoulder, or that shoulder will hit the cocking pin when it rotates downwards when you rotate the bolt, but that is the limiting factor.... Even with that shoulder flush with the back of the side cocking slot, the back of the hammer is still behind the sear, so I see no reason that shouldn't work.... Increasing the travel to 1" would allow an even lighter striker and hammer spring.... You would just have to watch that with the valve fully open (to coil bind) that the sear didn't catch behind the hammer....
Bob
-
Bob,
when I had made a lighter hammer had used a marauder threaded striker within it. This gave stroke adjust even tho hammer spun within tube, if you wanted length of stroke changed it could still be manipulated by removing hammer and changing striker screw position.
-
Thanks Bob 8),
You gave me some nice guidelines for my tune ;D.
Kirk
-
Will file it away, hope to get to it after this week.
Longer stroke might allow a lighter cocking force, but I’ll be conservative about it and shorten the nose no more than can be made up for by the screw (so if I don’t like the results, could go back to the current stroke length).
-
Last night I made a 1/8" transfer port and installed it, and this morning I determined that 1 turn of preload (from my minimum) gave a great string at the power I wanted with the JSB 18.1 gr. Heavies, so I shot strings starting from 3000 psi with five different pellets from 18 gr. and up at that setting.... I shot them through the Chrony at a target at 20' using 5 shot groups, not taking huge care, but good enough to assess the accuracy of the different pellets to do a "first cut".... The 18.1 gr. JSBs didn't disappoint, both types of EunJins, although still one ragged hole at that range, were nearly twice the group size on average, the Baracudas were in between, and rivaling the 18 gr. Heavies for top dog were the 25.3 gr. JSB Monsters.... Usually they shoot visibly worse than the Heavies, but this barrel appears to like them, more on that later.... Anyway, here are the shot strings, starting at 3000 psi, but only including the shots within a 4% ES, so the heavier pellets are missing the high pressure shots, as usual....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-5122calShotStrings_zps312fd1c6.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-5122calShotStrings_zps312fd1c6.jpg.html)
Here is the summary....
JSB Heavy 18.1 gr.: 26 shots averaging 949 fps (36.3 FPE) at 1.31 FPE/CI
H&N Baracuda 21.0 gr.: 20 shots averaging 910 fps (38.7 FPE) at 1.37 FPE/CI
JSB Monster 25.3 gr.: 24 shots averaging 847 fps (40.3 FPE) at 1.37 FPE/CI
EunJin Dome 28.9 gr.: 22 shots averaging 811 fps (42.3 FPE) at 1.48 FPE/CI
EunJin Point 32.4 gr.: 22 shots averaging 772 fps (42.9 FPE) at 1.46 FPE/CI
This looks like a perfect tune for the JSB Heavies, and I have lots of preload available to get the Baracudas (and their cousins the Hunter and Hunter Extreme) up into the mid 900s with the small port.... I was quite interested in what I could get with the 25.3 gr. Monsters, and found that at maximum preload (8 turns in) I was getting 913 fps at 2900 psi.... I didn't test those pellets for maximum velocity yesterday when I had the big port in the gun, but I figured it should do closer to 1000 maxed out, so I pulled the gun apart yet again and put the 0.166" transfer port back in.... I tethered the gun at 2900 psi and added the preload data to the graph from yesterday as below....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51HammerSprings_zps9822539c.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51HammerSprings_zps9822539c.jpg.html)
As you can see, this hammer spring is not quite maxing out the velocity with the 25.3 gr. pellets, there might be another 10 fps in it before it plateaus with the big ports, but 980 fps works out to 54 FPE, so figure the maximum with the stock hammer spring would be 55 FPE.... However, that matters not, because I had to back the preload out half way to 4 turns in from minimum to get a proper string starting from 3000 psi, and here it is....
(http://i378.photobucket.com/albums/oo221/rsterne/BAM%20B-51/BAMB-51JSBMonster_zps9c02af8e.jpg) (http://s378.photobucket.com/user/rsterne/media/BAM%20B-51/BAMB-51JSBMonster_zps9c02af8e.jpg.html)
I'm impressed.... This is the strongest performance I've had from a .22 cal pellet shooter based on a production airgun, although I know there are stronger guns out there (eg. Condor).... I sure hope this pellet ends up being accurate downrange, it certainly is just making tiny ragged holes indoors.... From a 3000 psi fill I got a total of 17 shots averaging 935 fps (49.1 FPE) within a 4% ES, ending at 2180 psi for an efficiency of 1.23 FPE/CI, which I consider pretty amazing at nearly 50 FPE in .22 cal.... Not only that, but 12 shots were within a 2% ES (19 fps variation) averaging 941 fps (49.8 FPE), from 1950 psi down to 2350.... That would be plenty for a days hunt for nearly anything except ground squirrels, at least for me.... I'm pretty stoked that I have a .22 cal that does 50 FPE with a pellet that looks to have promising accuracy potential, and a good BC for great downrange performance.... It should deliver ~ 28 FPE at 100 yards....
With this thing shooting as well as it does, I'm shelving any plans to change it to .25 cal, at least until I have a chance to find out how accurate it is with these pellets this summer.... Unless I have a lightbulb moment, this project is done, at least for now....
Bob
-
Bob, have to give you a “thank you”. Without this post, might have lived with a problem with the BAM 51 unaware.
Nothing quite as blinding as ignorance.
PROBLEM: With the nose screw (#25 in the diagram) back flush with the nose of the bolt, was blocking ˝ the striker vent. Never thought to check that until now, but it explains some of the difficulties I’ve had with this rifle.
SOLUTION: So I ran the screw forward until I could pass a pin punch fully through the vent hole, and ground that screw and nose of the striker as close to the locking screw as I dared.
So here, I can actually SEE all the way across the vent, the striker nose is as short as I can make it and keep the setscrew, and the stroke is up to .70”.
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/9459eb4c-90b4-43c8-9f70-ce96f510f793.jpg)
Goal here is to say at the same +30 foot pounds, but make cocking a bit easier, so I hope to be able to reduce the striker spring tension even more than it is now.
RIGHT NOW, have no idea how the changes worked out, will have to do some testing once I have time and daylight.
The “wild card” might be that the vent is now fully open where as it was partly closed before.
Have been using a medium weight “top hat”, but have a few alternatives of various weights still hanging around.
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/DSCF0570.jpg)
Given a few hours of daylight this week, will see how light a striker spring I can go and still get +30 foot pounds of energy.
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/c5cd507c-1f03-444f-ae6b-5faeca9327f0.jpg)
-
Nice solution on the striker length.... I left enough meat on mine to keep it adjustable, but if you just want the striker fixed and flush, no reason not to do exactly what you did, crank the lock screw down and grind off all the extra.... Yes, about 0.70" would be the travel that way.... I tried lightening my top hat, but lost hammer strike, so was unable to do that until I slimmed the poppet down.... That made a HUGE difference, and was the reason I could (in fact had to) change to a lighter hammer spring with the plastic top-hat, thinned down to reduce the preload.... and get 50 FPE to boot....
BTW, I milled a 7/32" hole through the back bottom of the end plug to vent the area behind the hammer.... It lines up with my pin & slot for the RVA and there is some room around the RVA as well, so I have more area than the original 2 vent holes (and they are still open as well)....
Bob
-
Pretty much why I ended up with that medium weight top hat, needed the mass to pop open that issue valve stem.
Before these posts, didn't know that the vent was partly blocked by the nose-screw. Had adjusted it back to get more stroke, but never thought to check if it blocked the vent. It did. So I ran it FORWARD far enough to put a pin punch though the vent holes, then ground the screw and striker nose back to the set screw.
Not real sure what an "extra" stroke is going to do (looks roughly like about a 19-23% gain in stroke) , but in expectation I did reduce the striker spring a bit.
Suspect a .25 barrel is in your future, although a cast bullet .22 could put that "extra" air to good use without the expense of a new barrel.
-
If the JSB Monsters are accurate I think I'll leave it the way it is.... If not, then faced with detuning it from 50 FPE down to 36 then you are probably right.... With enlarging the ports to 3/16" I suspect 70ish FPE wouldn't be too difficult in .25 cal.... but then I'm faced with the same problem, too much power for the JSB Kings, so then detune it back to 50 FPE again to use them.... Not a lot of point if it shoots the 25 gr. Monsters well, they are the same weight, and being less frontal area will have a better BC than the Kings.... I hope it likes them at longer ranges....
On the other hand, if JSB ever bring out their 34ish gr. Super Kings.... hmmmmmmmmmmmmm....
BTW, I modded my striker the way you did, only took off about another 0.040" and it made NO difference, but I couldn't leave some (potential) on the table.... *LOL*.... I think the stroke is about 0.66"....
Bob
-
Great find Ribbonstone!
Nice job........... Hope it works out well for you ;)
Bob inspired me crack open my BAM B50 and check delrin hammer, remove valve sail, change valve spring and vent hammer as you did (different method). Got it all together, but my "old nemesis" (valve poppet) appears to be leaking at its seat. Will pull the whole sha...bang again tomorrow and hopefully get her going.
Kirk
-
Hey Bob,
Now that your tune is finished, what do you think about the quality of this rifle for $209 (B50) or $259 (B51) :D??
;D Is this a deal or what ??....................Kirk
-
DEFINITE DEAL !!! However, they are for those who like to play, as the way they are stock, they have too hard a hammer strike and need to be tamed down a bit.... much like the new Discos (whereas the old ones were about perfect).... Downloading "The Book" and reading through it BEFORE you purchase would be a good idea, just to let you know what you are in for....
Now that I have been inside and experimented on my B-51 first hand, there are some things I would do differently than "The Book".... For one thing, I dislike the hammer travel adjustment (on any rifle, IMO more is better), I would recommend that you set it to maximum (flush with the end of the hammer, even shorten the hammer if you can, but make certain you don't plug the vent holes).... Then fit a weaker spring (hoping you can find one that suits your tune) and tune using preload adjustments, either by fitting an RVA or making a selection of top hats and shims.... This allows you to use the least possible hammer spring tension, which given the design of the skinny bolt and the small amount of material around the cocking pin, may drastically increase the serviceability of that part.... Like Ribbonstone, that greatly concerns me, I really wish they had gone with a larger OD bolt....
Tuning the gun for a lower pressure fill by using the McMaster Carr spring recommended in "The Book" is probably a really good idea, it just wasn't the direction I wanted to go.... I would be curious what fill pressure you would end up with setting the striker flush with the end of the hammer, installing the McMaster Carr spring, and no other changes, both in .177 and .22 cal.... That might be all you need to do to end up with a pretty nice setup....
Bob
-
Awesome stuff!!!!
Bob, would you be interested in producing your own "the book"? I think you may find that it quickly becomes the "holy grail" for all BAM owners, especially those in .22cal.
You could call it "Book 2: taking it to the next level and beyond".
-
Two problems with that.... upsetting those who did all the ground work and wrote "The Book", and finding the time to do it.... especially the latter.... If I wrote a book on airguns I wouldn't be able to do the development, that would have to stop.... On the other hand, maybe the book wouldn't be out of date when it was finished.... just a couple of years later after I started working on them again.... because ideas and methods are always changing.... A perfect example is my findings compared to "The Book"....
I've learned soooooooo much over the past 7 years since I got back into airguns I can't believe it.... Equally inspiring is that I'm still learning with every project.... with no end in sight, fortunately.... God I love this hobby.... ;D
Bob
-
It’s a little fast.
Shortest daylight hours of tye year, so only had time to run one shot string with one weight pellet.
Shortened the striker nose to increase stroke to something like .67-.70”.
Decreases striker string preload slightly (cocking effort is acceptable).
In doing so, found that previously the vent hole was mostly blocked. It’s now open.
Runs right at about 150-155BAR (call it 2300psi)
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/1a2fbaa3-6c6f-4e1d-81fc-0c2b129f0df5.jpg)
Efficiency seems good (will have to re-run those numbers as I might have fouled that up).
Probably will never know what made the difference, the longer stroke or the now completely clear vent hole.
BARELY got my 20 shot goal.
Really think it’s driving those 15.9’s a little fast, but should be good with 18.1’s or 21gr. pellets (and the heavy weights might add a shot or two to the count). If the past is any guide, those heavy weight pellets will also up the energy level a bit (probably to 33 foot pounds).
So I’ll be looking to trade 10% of the energy per shot for a bit more shot count; probably with a slightly smaller transfer port. With luck, might get 15-20% more shots for that 10% energy drop.
-
Three choices to get the velocity down.... heavier pellets, less preload and a lower fill, or smaller transfer port.... The choice depends on what you want to fill to.... but the smaller port may give you the most shots at lower FPE.... Congrats on getting a better all around setup, though.... That string looks similar to my lowest tune in Post #46 (the black line) except mine was 23 shots at 34.8 FPE with 18.1 gr. starting at 2200, but certainly very similar.... Me, I'd try the 18.1 gr. JSB Heavies, I haven't got a gun that doesn't like them, and you'd be shooting them in the low 900s.... but if you want less energy and more shots, then yeah, a smaller transfer port....
Bob
-
Will test the 18.1gr. JSBs and the 21gr. pellets as I find time this week and see if the energy gain for heavy pellets is still in proportion to the old tune. If it is, then I’d expect the 21gr. pellets to end up at about 33 foot pounds, which is a bit over my goal.
So I’ll trade that 10% “extra” energy for more shots one way or another.
Might decrease the spring tension a little and see how that plays out, but suspect that I’ll eventually try a slightly smaller transfer port.
Shot this last week with the old tune. Can tell I just glued the target to a cardboard Coke box, tossed a rock in the box, and set it out at the longer distance I could manage,
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/9b229d25-0bd4-42e7-9f01-275f5432da61.jpg)
So…1.4” at 45 yards is worth about 3.1MOA, so with 1/8MOA “clicks” on the scope, tried 25 clicks up. Not perfect, but for an old cheap scope, it works.
-
Good thread guys, my BAM work has come to a grinding halt and the reasons in this thread are why. There are twenty different ways to go and I don't have the time to work on it :(. High chance it is getting shipped to someone to do the work.
BZ
-
The big thing is to decide what you want and then focus on how to get there....
Bob
-
Wow, I'm very tempted to pull mine back apart and incorporate some of these changes. Seems like I was getting about 24 shots around 30fpe (JSB 18.1gr) with a velocity spread of 4% with the current tune but the energy levels you're getting, Bob, is just intoxicating :D. It shoots the JSB heavies so well and I just haven't had much luck with the Monsters or Eun Jins with this barrel so I'm torn on whether it would be worth the trouble. I'm tempted nonetheless because when I tuned it last time, I didn't know much about PCP internal workings so I was afraid to make any permanent changes. I'm over that hump now ;)
-
The big thing is to decide what you want and then focus on how to get there....
Bob
Bob:
That's easy. shoot a 10 grain pellet in the mid 800 to 900 fps range with little deviation for decent shot count using the BAM for FT shoots.
I am going to anneal the trigger and straighten it as you have noticed its big and clunky the way it sits now. But all the other stuff...that's the issue.
BZ
-
Correct me if I am wrong, but it does not seem there is a negative to turning down the O.D. of the poppet. I really like the direction this went. I had accepted that these guns just won't run on 3kpsi. I am wondering what if the poppet was turned down and the spring/ brass washer was left stock. I am sure the power would be less, but could it help level the shot string/ extend shot count?
-
Moorepower:
Mine will run at 2800 psi (I never pumped to 3000) and launches JSB 10 grainers at 960 fps.
BZ
-
BZ, 21fpe in .177 cal...that's a fast icepick! ;)
-
BZ, 21fpe in .177 cal...that's a fast icepick! ;)
Yes it is Jason LOL! That's also the problem for FT. I can get great accuracy with JSB's and H&N .4.51 Barracudas, but at those speeds I cannot use it for FT. And once I shoot down far enough on pressure my POI starts to shift too much. My BAM needs "smoothed out" just like everyone says.
Its also really LOUD at that pressure.
BZ
-
If I had it to do again, I would taper the OD of the poppet at the seat to 5/16".... I would still reduce the thickness of the washer on the spring seat because I think driving the spring to coil bind is the reason for breaking the poppets.... However, if you drastically reduce the hammer strike to compensate for the smaller poppet and NEVER shoot the gun at too low a pressure (what is that, I don't know) you could probably leave the spring and spacer alone.... When you do the above you MUST fit a weaker hammer spring to compensate, and you would be well advised to lighten the hammer as well, certainly replace the top hat with plastic, then it's easy to reduce the preload by reducing the thickness of the "brim" of the hat (mine is now 0.10" instead of 0.50")....
Like most mods to a PCP, change one thing, that leads to two, which lead to four, and pretty soon you are nearly starting from scratch.... It's just what happens when you start modding, no solution to it but dive in with your eyes WIDE open.... BTW, properly tuned a PCP should be QUIETER at high pressure at the same FPE level....
Bob
-
moorepower, your Inbox is full....
Bob
-
BZ, since you are doing FT, have you considered installing an in-tube regulator? In .177, you can get a ton of consistent shots with a moderate pressure setpoint. It would need some porting and a lightened striker as compared to stock.
My son's QB79 fitted with a 1000psi 13ci Ninja bottle gets over 100 15fpe shots on a fill. The volume is larger but I did not install an RVA to fine tune the striker preload so it's wasting air, so I would not be surprised if you could extract 60-70 shots from the B51 with some tuning.
-
moorepower, your Inbox is full....
Bob
Drained.
-
Always seems better for me to start out with some goal in mind. Could be power related, could be shot count related, or it could be both. Just figure out what you want it to do FIRST, then work in that direction.
Can’t have everything. Power works against shot count, increase one and you’ll decrease the other. A more efficient tune can give you more shots than an inefficient one, but there is no real magic here: energy in vs energy out, there isn’t going to be some magic formula to reverse that.
So pick what you want to do, read “The Book” and read the threads here on the BAM. Should be able to get where you’re going if it is in the rhelm of possibility.
Probably better to do a “gut-check” to see if you goal is likely. Use this calculator, putting in your fill pressures, 196cc’s as the air volume, etc.
http://www.calc.sikes.us/1/ (http://www.calc.sikes.us/1/)
By playing with the shot count, look at the fpe-cuin results. Stuff in the 1.4-1.5 area would be a good tune.
-
This is what I've done so far to the valve, I shaped a poppet to 5/16" and made the thinner washer as well I flattened the ends of the spring.
I drilled the hole in the valve body larger to 5/32"
(http://i1054.photobucket.com/albums/s483/Garth58/Dec232014004_zps53be6f69.jpg)
I made a thinner acetal spring guide for the hammer and installed the M-C spring. I screwed the threaded striker flush but I could see it was obstructing the vent hole so I ground a little off to clear the hole. Also to add to less than stock preload I had previously drilled the end cap larger so the MC spring could turn easily. I'll post the string later.
(http://i1054.photobucket.com/albums/s483/Garth58/Dec232014008_zps02bbc2b8.jpg)
So just some numbers ,I left the factory TP in but it looks like I will have to try a smaller one .
110bar/JSB18.1 Sot down to 62bar I stopped there because I was past 4%
702 756 775 776 749
706 756 782 772 740
695 761 777 769
720 767 777 765
699 760 773 761
727 753 778 755
735 763 778 757
752 759 772 753
755 767 773 747
749 771 773 745
It's also very easy to pull the bolt back now, I am going to take the hammer out and check for debris or a burr on screw #26 the string seemed a little erratic. What do you think?
-
By playing with the shot count, look at the fpe-cuin results. Stuff in the 1.4-1.5 area would be a good tune.
1.4 - 1.5 fpe-cuin at high power ( Yours & Bobs ) would be phenomenal !!
-
Bob tends to change things for best possible results. Modded valve stem, lightened strikers and top hats, modded transfer ports, various springs, spring adjusters, etc. All great stuff, and it works.
I tend to just fiddle around with the issue parts, doing minimal mods.
His results are better, either by power or by shot count.
Think the point is to decide ahead of time what it is you want.
-
Yes, I was shocked to see 1.40 FPE/CI at 41.2 FPE average, 1.46 FPE/CI at 38.7 FPE average, 1.51 FPE/CI at 37.1 FPE average, and 1.61 FPE/CI at 34.8 FPE average, but that's what the gun got with the 18.1 gr. JSB Heavies.... Those kind of efficiency numbers are usually reserved for lower powered target rifles, and even then they aren't easy to obtain.... I still think part of the reason is the draggy sear design preventing hammer bounce from reopening the valve.... Heck, I'm even more amazed that I got 1.23 FPE/CI at 49.1 FPE average with the 25.4 gr. Monsters.... It's not easy to hit that kind of efficiency in .25 cal at 50 FPE, let alone with a .22 caliber....
Bob
-
Oh Ribbonstone,
You've got one of the nicest Bam B51 stocks out there! I think it's greatly improved with the longer forearm tip; it balances the gun much better than the OEM.
I still can't decide if I want to go two tone or not? I really wanted to re-do my stock because I felt it wasn't dark enough.
It got dented today somehow, so that's next for me. I had originally used a light maple stain, intentionally not wanting to overpower what little grain there was. But I don't like it. I bought some pre-stain and will use it so I can use something darker and not have to worry about totally overpowering the Blah...wood. Stock work is my favorite airgun, tinkering activity - I think?
http://i113.photobucket.com/albums/n227/kirk_schwarz/BAMB50-4_zps2f43e012.jpg (http://i113.photobucket.com/albums/n227/kirk_schwarz/BAMB50-4_zps2f43e012.jpg)
Sorry for going off topic :-\
-
Not my stock work, bought it used that way; previous owner had the talent.
Can tell the stock started off as an issue BAM51, but I’d never have gotten it to look like that.
-
BZ, since you are doing FT, have you considered installing an in-tube regulator? In .177, you can get a ton of consistent shots with a moderate pressure setpoint. It would need some porting and a lightened striker as compared to stock.
My son's QB79 fitted with a 1000psi 13ci Ninja bottle gets over 100 15fpe shots on a fill. The volume is larger but I did not install an RVA to fine tune the striker preload so it's wasting air, so I would not be surprised if you could extract 60-70 shots from the B51 with some tuning.
PM sent.
BZ
-
I posted my first string on my picture post above if you interested. More power than I need but the range of adjustment has opened up greatly. My goal is as many shots as possible around 15ftlbs. or less.
Thank you Bob for relighting the fire.
-
Hey GarthThomas,
If you spend $80 for a Milo74 regulator, you should be able to get 110 shots at 800 fps (14.9 fpe) using 10.5 grain CPUM. I'm estimating you would be using air from 3000 psi down to 750 psi. Make your setpoint about 800 psi (55 bar).
This assumes a 1.14% efficiency, which could a sticking point, also the regulator's pressure flexibility.
I'd go for it, but I've been labeled enthusiastic by the masses ;).
-
I skipped some different weight pellet testing as the daylight hours after work are real short this time of year.
Before this post, was happy with this tune:
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/6de2506b-67c7-4645-b226-b102b26c85ae.jpg)
Then I started reading these posts and started changing things.
1.Got back into the rifle and ground off part of the striker nose to lengthen the stroke.
2. In doing #1 discovered the vent was mostly blocked, so arranged for that to be clear as well.
3. Reduced the spring tension slightly.
With the above changes, shot this string:
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/1a2fbaa3-6c6f-4e1d-81fc-0c2b129f0df5.jpg)
Wanted to trade some of that “extra” energy for shot count, so partly took the rifle apart (just the top half, didn’t even have to destock the air tube) and measured the transfer port.
The transfer port measured .135”. I reduced it to .125” (basically roughened the inside, filled it with Devcon, let it cure, and drilled it to .125”).
Did do a couple of shots with the 15.9gre. pellets at the middle of the expected shot count. Those few shots averaged 911fps (about 29.3 foot pounds).
Did one full string of shots:
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/8326e877-4033-4eaf-b5af-0d9737fd1117.jpg)
So the end result of this was:
1. The longer stroke let me get away with a lighter striker spring tension, which makes cocking a little easier.
2. The +30 foot pound shot string increased by 10%.
3. The difference in efficienty is within normal variation, would have to keep track over several to get a reasonably good approximation.
Probably worth the trouble. The little extra in the shot count is a plus, the lower cocking force is a plus...am sure the amount of work it took will diminish in my mind over time, so will rate it a "win".
-
KEWL !!!
Bob
-
Hey GarthThomas,
If you spend $80 for a Milo74 regulator, you should be able to get 110 shots at 800 fps (14.9 fpe) using 10.5 grain CPUM. I'm estimating you would be using air from 3000 psi down to 750 psi. Make your setpoint about 800 psi (55 bar).
This assumes a 1.14% efficiency, which could a sticking point, also the regulator's pressure flexibility.
I'd go for it, but I've been labeled enthusiastic by the masses ;).
I was hoping to get as close to those numbers without spending anything, ;)
-
Can tell the smaller transfer port leveled off the "plateau" a little better (which is really waht restricting the port does), even though the shot count isn't drastically different from the first shot string. Looking at the 2% shots, first string got 14 shots and the last one 18, so while there isn't a whole lot more shots, they're a little more "level".
-
Hey GarthThomas,
I'm sure you could, just the regulator should give the whole string an ES of less than 3% :o
-
Hey Ribbonstone,
Yeah, "all in all", given our tweaks to our BAM set-ups (time spent vs change), I would put the results in the Marginal category.
Sure yours performs a little better and mine does too (mostly affected by the removal of the sail), but in hindsight, I would say the old addage "If it ain't broken, don't fix it" -> applies. OK, my trigger feels normal now too.......
In my case, working on a low pressure string (venting & shortening the hammer) pretty much gave me more hammer -> something I really didn't need. I needed more efficiency - period. So, what more hammer gave me was the ability, within the Delrin hammer/spring guide realm, to use the MC spring vs stock (clipped by 3 coils). So less wear and tear on the machine. To summarize, for those enthusiastic, perfectionists --> Go for It!!! Because you gotta find out ::) ------ otherwise --> Don't.
My Two Cents ................
-
Just tend to set a goal for each gun, either in terms of shot count, or power, and occasionally both.
Probably the only think I’ll try past this is going back to the original striker spring strength, up the fill to 170BAR, and reduce the transfer port a little more. Still want my upper energy limit to be 30 foot pounds, but I might eek out another couple of shots in a string that way.
-
Quite likely....but harder to cock, though....
Bob
-
True...might get a couple more shots per string, but enjoy it less.
-
I put a 3/32" transfer port this morning and I'm down to 18fpe the curve seems flatter but I started with too low a fill for the string and I haven't had time for another try but I may be up to 40 shots within 4%. 18fpe seems to be a threshold for using JSB18.1 to their best advantage, but I find the CPHPs are were to deliver some 1/2"groups at 45yds today in spite of the wind. I think I'll extend the threaded striker next. Its nice to be filling to 110bar, my muscles are getting sore from this tear down, I probably pumped 250 times before I realized I'd only finger tighten the fill nipple, I felt pretty stupid but was thankful I didn't need to tear down again.
Do you think I'm hijacking Bobs post here.
-
I would recommend leaving the striker screwed in flush with the front of the hammer.... If you need less power, reduce the preload on the spring by clipping part of a coil at a time or thinning out the shoulder on the top hat.... or smaller transfer port or higher pressure fill....
Bob
-
OK…tried another tune.
NOT in the spirit of careful experimentation, changed THREE THINGS all at once. Yes, if I were a careful/scientific kind of guy, would have changed each in isolation, but time/day light constraints made me go for all 3 changes at once.
1. Reduced the transfer port from .120” to about .110-.113”. Basically a 7/64ths inch drill, which could have wobbled a few 1/1000ths.
2. Increased the string tension by .08” (the thickness of the washer used on the striker spring). Cocking force seemed reasonable (just barely more than if felt like before if I consentrated on it.)
3. Filled to 170 BAR (about 2500psi) to match the increases spring tension.
End result was this:
(http://i157.photobucket.com/albums/t50/ribbonstone/9fa4d6db-0b9d-4ea0-8c0a-fd01ccc6374d.jpg)
1. Under 30 foot pounds. Goal was 30+, so I’ll have to speed it up by about 6%.
2. On an educated-guess, if I increase energy by 6%, am likely to decrease shot count by 12%.
3. If #2 holds true, then the 30 foot pound shot count might work out to about 29-30 shots. 30 shots at 30 foot pounds would have been nice, and may be possible, but right now it looks more like 28-29 shots at +30 foot pound will be the out-come.
4. The “improvements” are coming in small increments.
5. Is a little more efficient that it was.
-
Nice Ribbonstone,
So that's 2500 psi down to about 1700 psi, with 1.38 efficiency? Great that you can get 775 fps using a 21 grain pellet with transfer port at .120". That higher pressure is making a difference. My (.177) B50 has all ports increased to .1406 (9/64"). If you can get 30 shots at 30 FPE, that's about a 36% increase from your original shot count :D
I'd say THAT is mostly definitely worth your toil ;)
-
Still improving, I look forward to your final tune..... no doubt you will have a nice setup....
Bob
-
The thing about a definitive "goal" is that if even 6% off that goal, have to make the adjustment...and am likely to have to adjust things a 2nd or 3rd time to get it closer to (or a few 1/10ths either side) my 30 foot pound goal. Know that's kind of pedantic of me, but I set out for 30 foot pounds and will phart around until I get it.
-
I'm down to 5/64" TP and the top hat shoulder from 3/8" to 1/4" and about 14.5fpe avg. for 40 shots within 4%, I have one smaller TP left and a spare MC spring
-
Bump. Sorry.
-
Great thread, tons of amazing info. I've updated the reference site I put together to point to this and other recent posts as well.
-
Got side tracked by a BAM 50 in .177, so the work on the .22 51 got put in the “good enough” category.
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/0070394e-6620-4a84-b9db-a12e8efb3932.jpg) (http://s157.photobucket.com/user/ribbonstone/media/BAM51/0070394e-6620-4a84-b9db-a12e8efb3932.jpg.html)
(http://i157.photobucket.com/albums/t50/ribbonstone/BAM51/3b8d91ab-c131-4748-a87b-6e66195a8e34.jpg) (http://s157.photobucket.com/user/ribbonstone/media/BAM51/3b8d91ab-c131-4748-a87b-6e66195a8e34.jpg.html)
Same system with either of them, just playing with spring tension/striker weight/transfer port. Valve is as-issued.
-
Great motivation indeed. So far I've learned at least one very valuable lesson... I need different tools if I'm going to make my own replacement spring guide.