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 Post subject: Big Bore Pistol Build
PostPosted: Sun Jan 19, 2014 12:04 am 
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Location: Coalmont BC
For those of you that have been following my development thread on the 2240 - 2550, with the Extended Valve, and have been wondering where it was leading.... here is the answer.... Now that I have a much larger valve, and the ability to develop enough power, I can get on with the project I had in mind originally.... a non-PAL pistol (ie under 500 fps) in .25 cal, followed by .300 cal and .357 cal until I run out of available power (which may very well be at .25 cal, only time will tell).... I wanted to incorporate the MRod self-indexing .25 cal magazine, which thanks to Lloyd at AirGunLab, is also available in .30 cal.... and because I'm right handed I wanted a left-hand bolt action so that I can maintain my grip while cocking the gun and feeding another pellet.... I also wanted to use a Center-Point 32mm Reflex Sight, but they fit on a Weaver rail, so having a Weaver mount on the breech was part of the project as well....

I spent about half a day designing and making the Weaver mount, which bolts on top of the forward section of the breech, and then two full days machining the breech and bolt.... Here is the result....

Image

The two holes right at the edges of the Weaver rail are to access the 4-40 screws that locate the front of the breech, and the hole behind them is to access one of the two barrel setscrews, so I never have to remove the Weaver rail from the breech.... The breech is made for a 1/2" OD barrel, and will accept a .25 ACP barrel, plus the .300 cal and .357 cal barrels that Sean Pero and I came up with and Sean is selling.... All the barrels will carry an internal O-ring, sealing on the caliber-sized straight nose of the bolt, which seats the pellet past the transfer port and then retracts into the "J" slot so that the transfer port is completely unobstructed.... I used this setup on my Disco Double, and I really like it, so I decided to incorporate it into this pistol build....

The main tube is from a Crosman 2250, using the Extended Valve and lightweight hammer, driven by a Disco hammer spring adjusted by a Challenger RVA.... The valve was opened up to a 1/4" throat, and the 5/16" OD Teflon transfer port is 7/32" ID, with barrel porting to match.... The main tube and the breech are drilled 5/16" to accept the transfer port, and I added a 6-32 tapped hole between the two 4-40 holes in the main tube for a larger central mounting screw to make the breech 100% rigid.... The MRod magazine will need a small clearance notch in the left side ridge on the bottom to clear the head of the screw which protrudes slightly.... Here is what the gun looks like, assembled but without a barrel....

Image

I'm pretty excited to see how far this project can proceed before running out of power just using a 12 gr. CO2 cartridge, and staying within the 500 fps Canadian non-PAL limits....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Jan 19, 2014 12:08 am 
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Location: Okanagan,BC
Looking forward to another unique and amazing build!


8)


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PostPosted: Sun Jan 19, 2014 4:02 am 
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Location: Victoria, BC and Clarkston, WA
Nice work Bob!
I have got a 22XX breach that I built with a built in Weaver rail that I still need to cut the slot for the bolt handle. All the other work is done. Thinking a .25 calibre rifle might be fun on a 2260 tube.

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-Rick
Pardini K10
Brocock Concept .22
3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
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PostPosted: Sun Jan 19, 2014 7:02 am 
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Location: Annapolis Valley, Nova Scotia
That is awesome! nice work! cant wait to see it complete, any chance you might bring this to life for us in a link to a short vid when its finished? to see it kill some targets or cans would be tops! 8)


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PostPosted: Sun Jan 19, 2014 7:39 am 
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Location: 123 gun street Nova Scotia
not sure the 9mm will work out , but even at .25 it could be a great gun


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PostPosted: Sun Jan 19, 2014 11:41 am 
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Yeah, kind of my feeling as well, jezX.... I'd be surprised if I can get it over 400 fps in .357.... but hey, all it costs is 1/2 a barrel and some work, right?....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Jan 19, 2014 11:43 am 
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Location: Northern Ontario
Awesome as always.

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PostPosted: Sun Jan 19, 2014 12:39 pm 
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great stuff Bob as usual :wink:

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PostPosted: Mon Jan 20, 2014 5:54 pm 
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Location: Hanover, On
Absolutely amazing! Is the bolt on the left side because you're a southpaw or because it allows you to maintain a right hand hold while cycling the bolt?


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PostPosted: Mon Jan 20, 2014 6:15 pm 
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owen wrote:
Absolutely amazing! Is the bolt on the left side because you're a southpaw or because it allows you to maintain a right hand hold while cycling the bolt?


Mostly for right handed people! Easier to maintain a proper grip.

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-Rick
Pardini K10
Brocock Concept .22
3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
Mrodair CP-1M .22 and .177


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PostPosted: Mon Jan 20, 2014 6:25 pm 
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Location: Northern Ontario
owen wrote:
Absolutely amazing! Is the bolt on the left side because you're a southpaw or because it allows you to maintain a right hand hold while cycling the bolt?

Bolt action pistols are often left side, as right handed shooters dont need to release their grip that way.
My 2260 carbine and 2240 pistol are set up that way.

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PostPosted: Mon Jan 20, 2014 6:36 pm 
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YEP!, right handed pistol shooter = left handed bolt.... especially with the self-indexing magazine, just cock and shoot....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Feb 27, 2014 9:40 pm 
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Location: Coalmont BC
I got my barrels from Sean last week, so it was time to get back to this project.... I ordered the barrels before the project even started, and I got three 12.5" barrels, in .250 cal, .300 cal, and .357 cal.... With the data I collected using a 24" barrel in .25 cal I now have my doubts if anything larger than the .25 cal makes sense on CO2, but it was time to fit the quarterbore barrel and see what happens.... I spent the day machining and fitting the barrel to the repeater breech I made and then proceeded to test the gun.... Here is a photo of the completed 2550 pistol....

Image

The breech functions flawlessly, I really like cocking the gun with my left hand, which the MRod magazine makes easy.... I wound the Disco spring all the way to coil bind, shot 2 shots through the Chrony, backed the adjuster out a turn and kept going, shooting pairs of shots until the adjuster was 12 turns out.... Here is the result....

Image

Instead of the velocity plateau only being above about 3 turns out (between there and coil bind), it was twice that long as a result of the shorter barrel.... In other words, you could reduce the preload a lot more without losing any velocity compared to the 24" barrel.... The maximum velocity was in the 470s with JSB Kings, just about perfect for a non-PAL pistol.... I adjusted the preload to 8 turns out, just on the knee of the curve, and put in a new cartridge and shot a string, taking 1 shot per minute, with the results as shown above.... The magazines are 8 shots, and the velocity started at 475 fps and gradually dropped to 461 fps at shot 17, staying above 450 at shot 21.... and the end of the 3rd magazine, at shot 24, was on the steep drop off but still above 400 fps....

I'm very pleased with the results, but it looks to me like there is little point in trying to go to a larger caliber.... No question it will work, but I think the velocity will drop significantly below the 500 fps goal.... With the Disco spring having lots of preload still available, generating the valve dwell for the larger calibers isn't the problem, but flowing enough CO2 to provide good velocity with only 850 psi likely is....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Feb 27, 2014 10:20 pm 
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Location: Alberta Canada
Good lookin pistol there Bob. Are you running a 22xx valve upon that?

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PostPosted: Fri Feb 28, 2014 12:00 am 
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Location: Coalmont BC
Here is the previous thread with details on the extended valve.... post406307.html

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
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