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All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: JPSAXNC on June 14, 2021, 05:43:48 PM

Title: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 14, 2021, 05:43:48 PM
I wanted something more practical, so I put a 19 inch 30 cal. barrel on it. The gun uses two carts. the velocity with 30 cal. 44 grain JSB's is 550 fps.  I have to wind a softer hammer spring for it, right now the valve dwell is way longer than it needs to be.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: GarthThomas on June 15, 2021, 12:39:44 PM
Does it sound like a spit wad
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 15, 2021, 03:58:24 PM
Hi Garth, It's sounding pretty crisp now. I had made a Peek toilet plunger poppet for it and a SS. transfer port. The gun was burping though and I didn't have a plan to deal with that, I going to wind a softer hammer spring for it but decided to lighten the hammer instead. The hammer was pretty heavy and the hammer spring is very strong, lightening the hammer shortened the valve dwell and pretty much cured the burp, so it's close to being tuned, then I'll test it for shot count. This is a Crosman made gun that uses two co2 carts, but the tube is a little longer than other two cart guns, because they made the valve a little longer, I guessing to hold more pre warmed gas.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Nvreloader on June 16, 2021, 11:52:00 AM
James
What hammer is used in this rifle?
What is the inside diameter and the O/S dimensions of the spring?

Reason for the questions is,
you might be able to use a Flat Wire spring along with a SSG to get the best tune possible.
These type of springs provide the power needed, but also provide a lighter pull weight of the bolt etc.

Tia,
Don
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 16, 2021, 12:03:54 PM
any pictures James ? whats the barrel length
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 17, 2021, 04:21:08 PM
Hi Don, I haven't seen this hammer in any other Crosman gun. The hammer is 1.970" long and probably weighed 1.5-2 ounces before I lightened it. The spring is 3.789" long, it's wound from .045 wire, the od. is .333". I'm real happy with this spring, it gives me a good power range.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 17, 2021, 04:35:38 PM
I'll see if I can get a pic and email it. the barrel is 19" long. I'm pleased with the power so far, I had drilled the hole in the hammer deeper to help lighten it which reduced the preload on the spring, I fired the gun this morning when it was about 72 degrees, and got 544fps. then I put the gun in the sun and let it warm up till it felt very warm but not hot, and got the same 544fps. So wondering if there was valve lock, I put a spacer in the hammer to increase the preload, let the gun warm back up in the sun, and got 575fps. I Think the same performance can be gotten with any Crosman two cart gun and valve work. I thought of mounting the barrel on a Crosman 400 tube, but I would have had to machine a custom receiver, So I sawed the 50 cal. barrel off about 3/4" ahead of the transfer port, made a sleeve, and pressed the 30 cal. barrel in.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 17, 2021, 09:18:37 PM
nice.. i never did a 30 co2.. I did do a 9mm, a 25, and a 50... In 9mm i was able to get 46 fpe. which thinking back was about 500 fps.. I was getting 6 shots per co2.the slightest adjustment in tuning led to snow firing out the barrel on a humid day.. So there was always a very sweert spot for tuning.. Whats nice about co2 , and why i love it , Is you really dont have to worry soo much about cracking force needed to open the valve. I was running massive ports on the 9mm and a stock hammer / spring combo...
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 23, 2021, 11:29:53 AM
(https://live.staticflickr.com/65535/51266155363_66140bf76e_z.jpg) (https://flic.kr/p/2m7drUp)DSCF0712 (https://flic.kr/p/2m7drUp) by murphyrobert9 (https://www.flickr.com/photos/56743574@N07/), on Flickr

(https://live.staticflickr.com/65535/51267009140_1a0f3b30e4_z.jpg) (https://flic.kr/p/2m7hPGG)DSCF0713 (1) (https://flic.kr/p/2m7hPGG) by murphyrobert9 (https://www.flickr.com/photos/56743574@N07/), on Flickr

(https://live.staticflickr.com/65535/51266158323_da39866f27_z.jpg) (https://flic.kr/p/2m7dsMr)DSCF0715 (1) (https://flic.kr/p/2m7dsMr) by murphyrobert9 (https://www.flickr.com/photos/56743574@N07/), on Flickr

(https://live.staticflickr.com/65535/51265236292_50fa1d03ec_z.jpg) (https://flic.kr/p/2m78JGm)DSCF0716 (https://flic.kr/p/2m78JGm) by murphyrobert9 (https://www.flickr.com/photos/56743574@N07/), on Flickr

(https://live.staticflickr.com/65535/51267012500_29ace6c783_z.jpg) (https://flic.kr/p/2m7hQGC)DSCF0717 (https://flic.kr/p/2m7hQGC) by murphyrobert9 (https://www.flickr.com/photos/56743574@N07/), on Flickr
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 23, 2021, 11:30:17 AM
james' picturesd of the gun above
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JuryRigger on June 23, 2021, 01:15:17 PM
Cool gun!  :D
Jesse
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on June 23, 2021, 02:37:34 PM
Cool gun.  Was this a Crosman 160 that someone added a different hammer/system and obviously a different barrel?
What were the specs for the 50 cal?
Looks like either a really long valve stem or im not seeing all the hammer or the TP turns around and angles forward.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 25, 2021, 08:59:43 AM
Thanks for posting the picks Rob. Some answer's. The cocking slot on the gun is stock, the stock hammer is spool shaped. I turned down the nose of the bolt and cut a new o-ring groove in it to fit the .30 cal. barrel, I was getting some blow back from the breech so I added the green o-ring that seals against the back of the barrel and that fixed the problem. The sights came off an old b-3 springer, I had to cut dove tails to mount the rear sight. The gun does not say Crosman or anything else anywhere on it, the only marking was a serial # on the barrel, but the stock and trigger housing look like Crosman's.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 29, 2021, 03:16:40 PM
I'm thinking about getting a longer barrel blank, But I don't how much of a velocity increase I could get if the barrel was 24"-25" long over the 19" barrel. Would it be worth the work and cost?
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 29, 2021, 03:23:11 PM
I'm thinking about getting a longer barrel blank, But I don't how much of a velocity increase I could get if the barrel was 24"-25" long over the 19" barrel. Would it be worth the work and cost?

I tested this notion with 9mm and co2 .. I had built a 20 inch barrel co2 , and Bob Sterne had built a 28 incher..Our numbers were very similar, i think he had me by 1 or 2 FPE .. I made a reamed extension to test the gains from an extra 4 inches.. I didnt gain anything.. I think at 550 fps , you might be close to peak.. I think if all the stars aligned , 600 might be possible .
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 29, 2021, 03:27:06 PM
maybe Bob will jump in and apply LLoyds spreadsheet to know for sure.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 29, 2021, 05:32:07 PM
Hi Rob, the extension is a good idea, I bored out a 6" section of .22 barrel to .302, now I just have to make the sleeve,
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 29, 2021, 09:20:21 PM
nice.. should be interesting
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 30, 2021, 10:56:56 AM
First test in the basement @72 degrees, with the 6" extension 557 fps. without 519 fps.  39 fps. gain. I'll get another test in a little latter this morning.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 30, 2021, 12:00:50 PM
wow , serious fpe gain with those 40 plus grain pellets.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on June 30, 2021, 12:26:18 PM
Nice gains.
Just looking at this gun again.  Was the bolt slot cut all the way to the back of the breech so a longer projectile could be loaded from the rear?  If so, this appears to be a dart gun.  What is the bolt on this?About 3/4"?  Im still trying to figure out the TP on this.  How far is the TP inside the barrel?  Im just wondering how far the pellet is infront of the TP.  It may gain more fps with a longer bolt probe is what I am thinking.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on June 30, 2021, 12:31:37 PM
Ok now I see and understand "Capture gun" in the title.  Dont mind my stupidity.  The rest of the above applies.  I think this would gain more with an appropriate probe.  This one must have relied on the skirt pushing it past the TP.  Was the 50 caliber barrel smooth bore? 
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 30, 2021, 12:57:56 PM
More testing 519fps. and 550fps., so 30fps. with the 6" extension, @ 72 degrees F. 
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on June 30, 2021, 01:04:44 PM
Hi Dan, Yes, it was a tranquillizer dart gun, the 50cal. barrel was rifled. The transfer port is about a 1/4" ahead of the breech of the barrel, the probe pushes the pellet skirt just past the transfer port.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on June 30, 2021, 05:06:21 PM
whast your throat diameter ansd stem size?? that tiny stem we discussed might be a blessing here
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on June 30, 2021, 07:51:32 PM
Any specs on the barrel you took off?  Im wondering if it would also be useful for a big bore?  If rifled but I bet they used a pretty slow twist (1:66, etc) similar to a black powder gun.  If not these barrels might be good fodder for big bores.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 01, 2021, 08:07:24 AM
Hi Rob, I don't remember the original size of the valve throat and transfer port, but I'm pretty sure they were the same as the other 2 cart guns. I the stock valve stem is 1/8", The transfer port now is .211, and the valve throat was enlarged to match it.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 01, 2021, 08:11:13 AM
Hi Dan, the 50 cal barrel had a big flat cut out of the bottom side where the end cap screwed on to give the cap clearance, but it was way to deep creating a very thin spot in the barrel.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 01, 2021, 01:01:08 PM
I left the gun in the sun until it felt hot, and got 581fps. with the 19" barrel.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on July 01, 2021, 02:00:52 PM
I left the gun in the sun until it felt hot, and got 581fps. with the 19" barrel.

nice , approaching the 600 mark.. I do think its possible..
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 01, 2021, 04:41:32 PM
Hi Dan, the 50 cal barrel had a big flat cut out of the bottom side where the end cap screwed on to give the cap clearance, but it was way to deep creating a very thin spot in the barrel.
I see the poorly planned pressure plug placement portion.  Pitty.  Well the pressure probably is so low at that point in the shot it still would work as a bullet shooter. If you can find/make the right bullet.

(https://i.imgur.com/h1QGUzE.jpg)
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 17, 2021, 10:11:28 PM
I bought a .30 airgun barrel blank  I made it 25" long, at 86 degrees f. it shot 604 fps. with the 44 grain JSB's. I can tell the hammer is bouncing now the report sounds very airy, oddly, the report with the 19" barrel was a nice crack. I don't know why it's different now.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on July 17, 2021, 10:24:57 PM
WOW , awesome.. the reason the report has gone down is your muzzle pressure is lower ( youre running super efficient using eevery last drop of the co2 energy.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 18, 2021, 01:00:14 AM
So looks like a lot more fps than your test extension..  Same size TP?  36 FPE is good.  Has your shot count remained about the same?
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 18, 2021, 07:58:17 AM
Hi Dan, Yes, it's shooting faster than it did with the extension. The 19" barrel and the extension both had bigger bore diameters than the new barrel, and were letting some of the gas blow by the pellet. The bore diameter of the new barrel is .298 the old barrel .305  I haven't tested it for shot count yet. I need to try to debounce the hammer first.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 18, 2021, 10:11:16 AM
Hi Rob, Yes, I think it's at about the limit of power, 578fps. @75 degrees.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 18, 2021, 06:48:10 PM
Have you tried some accuracy tests?  Some say a .30 pellet sometimes works in a PB barrel.  I hadn't used them in my 30 cal after putting a scope on mine, disadsembled and havent put it back together again.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 20, 2021, 11:32:25 AM
553 fps. @ 70 degrees,  560fps. with the hammer spring adjuster turned all the way in. 
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on July 20, 2021, 01:51:40 PM
James , arent you now using an LW barrel?
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 20, 2021, 05:04:21 PM
Hi Rob, Yes, the new barrel is an LW, the old 19" barrel was .30 powder burner barrel.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 20, 2021, 09:58:56 PM
Hi Rob, Yes, the new barrel is an LW, the old 19" barrel was .30 powder burner barrel.
Well don't discount the PB barrel. It just needs bullets and HPA.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on July 20, 2021, 10:10:27 PM
ive shot a lot of pellets through PB barrels on pcps , pretty decent accuracy actually
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 20, 2021, 10:32:13 PM
ive shot a lot of pellets through PB barrels on pcps , pretty decent accuracy actually
Rob. That's good to know.  I have a tight .305 PB military barrel that I need to turn down and use.  Maybe a .30 disco (some day).
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: Rob M on July 20, 2021, 10:41:28 PM
i just got old rem700 and other 30.06 barrels off ebay or gunbroker .. theyre about the perfect  diameter for the pellets
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: rsterne on July 21, 2021, 12:11:19 AM
I have a couple of .308 cal PB barrels, but one is a 12" twist and the other 10".... While pellets may fit OK (I found the head very loose), and fly reasonably at low velocities, IMO that is wayyyyyyyy too fast a twist rate.... For a pellet barrel I feel that the TJ's 26" twist in .300 cal is about as fast as I would want to go, and the 42" twist that Doug Pickard had them make up would be much more interesting to me....

Bob
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 21, 2021, 02:34:33 AM
Bob,
Not doubting you.  You'll have to check my math as I am not good.  In the last two columns I am trying to match the RPMs that a 26 and 42 twist have at 950 fps (last 2 RPMs in 2nd colum) by adjusting the FPS of a 10, 12, 16 twist barrel.  And I dont know if this even works or not.  However you can see the RPMs are huge in the first 3 = overstabilization??

MV.    Twist.  RPM@950.    Fps at.    Fps at
                                                16286.   26308
950   -   10   -   68400   -   226   -   365
950   -   12   -   57000   -   271   -   438
950   -   16   -   42750   -   362   -   585
950   -   20   -   34200   -   452   -   731
950   -   26   -   26308   -   588   -   950
950   -   42   -   16286   -   950   -   1535

Actually the 1:16 twist at 585 fps (what OP has) matches the 26 twist at 950 fps.  But yeah you'd have to really slow the 10 and 12 twists down.  So IF the pellets fit and you could slow them down (365 in a 10 twist) they may make good barn critter dispatch barrels (not punching holes in roofs).  Again, if you have any accuracy. THEN take the same gun and turn it up (somehow) to bullet shooting power for coyotes or hogs???

I just got a tin of 100 of the Hatsan .30 cal pellets for $8.99 on Amazon between previous posts  :D.
I still think you could somehow bump up the head of these and make a dimple on the front with a simple tool that hits center of bottom and top.  Haven't tried yet though.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 21, 2021, 08:52:44 AM
The barrel on my .30 cal. Mrodair Varmint conversion, has four lands and grooves a .299 bore and .309 groove depth, and a 1:28 twist. It's a power burner barrel but I have no idea from what, or where to get another one. It shoots the 44 grain JSB's very well.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: rsterne on July 21, 2021, 03:47:39 PM
You don't need the same RPM for stability at all velocities.... However, if the RPM is too high, the trend towards Dynamic Instability increases, particularly as the forward velocity slows going down range.... Pellets are primarily "flare stabilized", they only need a small amount of stability from spin, so you can get away with very slow twist rates, on the order of 100 to 200 calibers, depending on the pellet.... That means a 30-60" twist for a .30 cal....

I made a die for "bumping up" the diameter on JSB pellets back when I was playing with the .308 PB barrels.... The tapered anvil is adjustable for height, and the shoulder limits how far the die goes together when tapped with a hammer....

(https://hosting.photobucket.com/albums/oo221/rsterne/Big Bore/.highres/IMG_3180_zpsb4865488.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/1104e32d-26f0-43bb-a6d6-3e39ea94a17d/p/4bc8b7c4-9ed2-4117-ae00-5a440d81f451)

It created a Meplat on the nose, and as the length decreased, the diameter expanded.... On the right hand side of the photo, you can see the difference when a stock JSB pellet (R) and one that is bumped up to .308 cal (L) is pushed through a .308 barrel....

(https://hosting.photobucket.com/albums/oo221/rsterne/Big Bore/.highres/IMG_3181_zps5e712afb.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/1104e32d-26f0-43bb-a6d6-3e39ea94a17d/p/98a0765e-4aad-40f3-a7df-bd45b95e7bd5)

James, a 28" twist would work great with pellets in .30 cal.... I wonder what PB had such a slow twist rate?....

Bob
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 22, 2021, 12:13:14 AM
Hi Bob, That was a barrel blank that I had bought from Randy Mitchel when he was still in business.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 22, 2021, 12:51:25 AM
Nice set up Bob!  Wow that bumper is great!

I probably need to determine how to figure out when instability starts.  Is that something you can calculate?  I like shooting round balls in my .44 at about 950 fps and don't have access to a real range right now to figure it out.

Maybe that was a .32 ACP barrel liner made by someone who knew twist rates.  Or some .30 cal rimfire or gallery guns.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on July 22, 2021, 02:51:30 PM
I let the gun warm up in the sun, and shot 628 fps. for 38 fpe. having a barrel that fits the pellet gained some velocity.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on July 22, 2021, 05:09:34 PM
I think some paintballers have special heaters for their co2.  Not sure why this isnt implemented much in the airgun world.  I wonder if CO2 guns could be used in the winter with a heater?
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: rsterne on July 22, 2021, 06:00:44 PM
Pellet stability is not something you can calculate, unfortunately.... It's very much a trial and error thing.... However, as we gain knowledge, we are realizing that most airgun twist rates are too fast, and the current trend is to much slower twist for pellets.... An added advantage to lower twist rates is less aerodynamic jump (vertical deflection in a crosswind).... and of course less tendency to spiral (corkscrew) when shot faster to longer distances, which is the primary problem with too fast a twist.... I recently tried a 16" twist with the 34 gr. JSB Beasts in .22 cal, and couldn't hit the paper at 100 yds, they were spiralling so badly....  ::)

Bob
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on August 21, 2021, 09:40:56 AM
I enlarged the valve throat from .250 to .263, and the transfer port from .205 to .228, and shot 632 fps. @ 84 degrees with the 44 grain JSB's. The fastest shot so far was 660fps. with the JSB's.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on August 21, 2021, 06:47:38 PM
Hmm, did it go down or at a different temp?
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on October 05, 2021, 09:24:50 AM
I made a tapered transfer port. The transfer port is .3 long with about a 1.2 degree taper from .228 to .212 and shot 603fps. with the 44 grain jsb's @ 67 f.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: BigBird on October 05, 2021, 10:32:29 AM
Wonder what it will be with 84°?
Is there an oring on the lower part?  May not need with CO2 but how does it seal? Delrin TP?
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on October 05, 2021, 11:29:48 AM
Hi Dan, I'm not using seals, I just leave the transfer port a couple of thousandths proud, when the breech screw is tightened that seals the port.
Title: Re: 50 cal. co2 capture gun converted to 30 cal.
Post by: JPSAXNC on October 05, 2021, 05:24:57 PM
With the .228-.212 transfer port it shot 603@ 67f.  602@ 72f. 625@76f. I have three transfer ports I'll test.