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Author Topic: 50 cal. co2 capture gun converted to 30 cal.  (Read 566 times))

Online BigBird

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #40 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.
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Offline Rob M

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #41 on: July 20, 2021, 10:10:27 PM »
ive shot a lot of pellets through PB barrels on pcps , pretty decent accuracy actually
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Online BigBird

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #42 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).
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Offline Rob M

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #43 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
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Online rsterne

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #44 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
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Online BigBird

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #45 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.
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For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him.
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Offline JPSAXNC

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #46 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.
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Online rsterne

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #47 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....



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....



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

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).

Offline JPSAXNC

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #48 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.
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Online BigBird

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #49 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.
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Offline JPSAXNC

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #50 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.
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Online BigBird

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #51 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?
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Online rsterne

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Re: 50 cal. co2 capture gun converted to 30 cal.
« Reply #52 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
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).