.25 Disco fever.... add another project to the pile

[john]

www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cfluting.htm

[lloyd-ss]

www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cfluting.htm

John,
Thanks for that link.  That is a good explanation of what fluting does and does not do.  I wonder if most people opt for fluting because it looks wicked?

I bought two .50 cal barrel blanks a while ago, 1.125 dia x 28".  I have used one, and turned it down to .880 dia to make the weight manageable 'cause the blank weighs 6-1/2 lbs.
Fluting the second barrel to get it to the same weight would be very neat looking, but a ton of work.  My mill doesn't have power feed on the table.

[lloyd-ss]

I put the Disco back together after making the videos, but before doing that I copied Toolmakers Delrin valve head/stem idea.  Thanks Matt!
I had the gun blazing for the video, but wanted to see if it was now "too modified" to shot at velocities that are more in line with what a pellet wants for accuracy.  A true test.  Using Matt's valve head idea I actually made the valve seat dia .015 larger... again... opposite way for controllable low power.

All I really did for this test compared to the 80 FPE video was remove a .25 long shim from the hammer spring, and back the RVA off so that the hammer spring was preloaded only about one turn.

Well, I took 52 shots on one fill, using JSB Exact Kings, starting at 2300 psi and shooting down to 1150 psi.  Velocity ranged from 787 to 909 FPS, not too great, but that was 52 shots and the average FPE was 42.3.  The efficiency was a very good (IMHO) 1.46 FPE/cuin.

A few of observations:
1)  The jaggedness of the velocity curve was from the light hammer preload.
2)  The gun had a real sweet spot from about 1700 psi to 1250 psi; 18 shots from 889 to 909fps.  Seems to beg for a 1250 psi regulator for maximum shot consistency. ( I am pumping Bob S for info     )
3)  Conversion from max power to usable power was easy.
4) The light tap of the heavy hammer on this valve worked better than I expected.
5) Air efficiency was much better than I expected.
6) Despite all the nice "normal" power stuff, I think this thing is BEGGING for a .308 barrel and bullets instead of pellets.
IMO

Happy Thanksgiving,
Lloyd

[0351_Vet]

Llyod .....That is so cool. Man, I love it. If you go to .308, I'll buy your barrel and value set up.
52 shots, heck, that's more them my M-rood from 3000-2000PSI. (like 24).
Keep us informed Brotha....Way Cool.

[rsterne]

Looks like your sweet spot starts at about 1400 psi.... Since you will have a much lower average pressure with a regulator (depending on where you install it) I would reccommend you plan on at least 1400 psi for the setpoint.... maybe more....

You can get rid of the low spring preload by going to a weaker spring and more preload of course.... but then that .308 cal sounds inviting, doesn't it?....

Bob

[0351_Vet]

It all sounds inviting....... Great Stuff you Two.

[airpuffhunter]

Yes but
for .308 or 320, would you have to machine the inside of the breech for the bolt?
and also probably the outer diameter of the barrel will make you want to machine the inside of the breech, to fit it? (you don want the barrel to be too thin I think)
any way happy thanks giving to all

[Bandit_46]

That's a Good thing Lloyd, as something tells me you wouldn't be Content without an Ongoing project,he he! Have fun,


Troy

[lloyd-ss]

Yes but
for .308 or 320, would you have to machine the inside of the breech for the bolt?
and also probably the outer diameter of the barrel will make you want to machine the inside of the breech, to fit it? (you don want the barrel to be too thin I think)
any way happy thanks giving to all

Yes, you are exactly right.  You'd either have to buy (or make) an aftermarket breech, or bore the bolt end of the breech out to .312(approx), and then make a new bolt. For the barrel, I have a .308 barrel liner that is .500 O.D., so I'd most likely have to machine about .062 off it's O.D. for it to slide into the standard breech block.  Not too bad of a task, except that the set screw that normally secures the barrel into the breech probably isn't suitable for a thin barrel wall.  A more suitable method would be needed.

[airpuffhunter]

so a second barrel band or something like that is in your mind?
if you go with the thinning if the barrel, are you going to trim just the part that enters the breech, or are you going to go all the way along the barrel? if not carefull it will end inclined i supose.
wouldn't it be better  to install some sort of breech riser?

[lloyd-ss]

so a second barrel band or something like that is in your mind?
if you go with the thinning if the barrel, are you going to trim just the part that enters the breech, or are you going to go all the way along the barrel? if not carefull it will end inclined i supose.
wouldn't it be better  to install some sort of breech riser?

All very good points.  The Disco breech has about a .437 hole and the .308 barrel is .500 so I had thought about turning the barrel down just for the portion that goes in the breech.  If I did that the barrel would be about .005 above the air tube, so just barely enough clearance. 
But in the end, I opted to leave the disco breech alone and instead made a new breech for the .308 barrel.  A proof of concept thing.  I married the new breech to the disco disco double tube setup and am just about ready to do some test shooting.  The valve is already pretty well ported out and the hammer setup is strong enough to split rocks if needed.

I might have to start a new .308 thread.  Sooner or later the Disco is going to run out of breath.
Lloyd

[0351_Vet]

This just keeps getter better and better Lloyd. Good stuff here. !!!!!!
Eyes glued to this thread... Keep us informed my Brotha.

Walt

[Jaymo]

Great thread. How'd I miss this?
Horizontal mill with convex cutters and dividing head with tailstock would be your best bet for fluting barrels.
However, that's a big, expensive setup.

"Cooling fins" could be cut with a lathe and parting tool. May even help with noise when combined with a barrel shroud.

I want to modify my twin tube Sam Yang 909 to take 2 of the larger dia tubes from a 909s, as well as a 909s valve.
I'd get the higher max velocity of a 909s, with more reservoir volume.
You have me thinking about making my home made big bore PCP as a twin tube design, when I get a "round tuit".
Where do you buy your 4130 tubing and the steel for your threaded end plugs?

I'm tempted to "twin tube" my B50.
I've been thinking about making a barrel shroud for the B50 that wouldn't necessitate a riser breech. It would have to have the end cap and baffles drilled off center, so it would have more air space above the barrel than below.
Essentially, the shroud would be installed above center on the barrel. It would be easier to make it that way and make a new barrel band, than to make a new, riser breech.
Then again, I'd love to have a riser breech for it that takes Mrod mags.
I've thought about making a toggle link straight pull or even a sidelever breech for it.

[lloyd-ss]

Jaymo,
No real plans to flute any barrels.  Definitely a lot of work.
I bought the 4130 tubing for my air tank from Mcmaster, 89955K63 for 1" O.D. x .065 wall.  A 6 foot piece is $31.  Mcmaster gets a lot of my money because they have virtually everything.  I use 303 stainless for a lot of my solid parts because it is the only real free machining stainless.  Actually, with a 28 pitch thread, aluminum end plugs have plenty of strength.   BTW, the 4130 tube in the normalized or annealed condition (as it is usually supplied) has a yield of about 75,000 psi.  So the 1" OD x .049 won't start to swell until it over 11,000 psi.  That gives a nice 3 to 1 safety factor for the tank. 

I like your idea of an off center shroud.  I've considered that but haven't come up with a fail safe way to keep the disks oriented properly in the barrel.  Maybe you've thought of a way?

The toggle link (for just the breech, or both breech and hammer?) sounds interesting.  Nice straight-line travel.

[0351_Vet]

I'm keeping my eyes open and my mouth shut..........
Lloyd, you just keep amazing me. Waiting quietly.

[gene_sc]

Lloyd do you thread your tube on your lathe?

[lloyd-ss]

Gene,
Yes, I do almost all of my threading on the lathe.  My headstock has  a 1" hole so I try and stay at 1" or below.  For bigger diameters, I will use a steady rest.  A pain, but it works ok.
I have also collected a fair selection of taps from Ebay, and sometimes I will single point an I.D. thread and get it close to size, and then use a tap to bring it into final size.  Then I can use that known good thread to gauge the fit on the mating part.

I enjoy single point cutting of threads on the lathe, especially when the fit comes out really nice.  But if I have a tap, I use it.

Lloyd

[rsterne]

Any more news on this thread, Lloyd?....

Bob

[lloyd-ss]

Bob,
Thanks very much for asking.
Yes, I fabricated a breech (not too pretty, but functional) and bolt for the .308/.312 barrel I have and installed that onto the dual tube set-up.  I tried some trial shots and the velocity was low.  Then I changed the de-bounce materials I had at the valve assembly.  That apparently was a major mistake as it created an unbelievable hammer bounce situation.  The resonance was perfect, and the thing sounded like a machine gun with linear amplitude decay!  That left me a little frustrated, but I think the valve closing spring might be too weak and I will look at the debounce materials again, if they are needed.  I use them to limit the max valve opening. 

So I temporarily put that gun aside and coincidentally was assigned a new project at work where all the start-up capital had to be planned, purchased and received by the end of the year.  (One item was a granite surface plate 3' x 14' x 1-1/2' thk.  That is a very cool 10,000 pound monster.)  So I have been slammed at work, but am on vacation now and am playing with the pcp pistol with it's different challenges.  I needed a different distraction, even if it was still an airgun.

So, I will be pulling the .308 disco out sometime in the not to distant future to see what it can do.  To be perfectly honest, because removing and reinstalling the valve in the disco is such a PITA (total disassembly, o-ring cutting, etc), I avoid doing it and will often find something else to do instead.  I know if I get into fiddling with the valve spring, the valve  might need to be in and out of the gun several times until I get it right.
Task avoidance.   
Lloyd

[rsterne]

I know what you mean RE the O-ring cutting.... I HATE that big hole for the gauge.... I'm making an extended valve front end to replace the gauge block tomorrow that moves the O-rings ahead of the gauge hole....

Bob