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PostPosted: Sat Jan 17, 2015 2:03 am 
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So ive got this old CPS sport and a stock 2240 barrel. I was looking at the idea of trying to convert
it to a .22 and it looks like a promising idea. Was hoping to pick up the accuracy with the longer barrel
but am left wondering if there is enough power. I drilled out a spare cartridge and thinned out the walls,
the .22's fit and line up which is good..

I was thinking of building a rifle around this and have a nice repeater, but the trigger is so tough on this thing.
So is this a good idea or bad?


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PostPosted: Sat Jan 17, 2015 1:38 pm 
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How thick are the walls between the chambers at the thinnest point? Just a bit worried they might let go and turn into shrapnel.


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PostPosted: Sat Jan 17, 2015 4:17 pm 
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Location: Waterloo, Ontario
Quote:
JWFX wrote
Was hoping to pick up the accuracy with the longer barrel but am left wondering if there is enough power.


For your info, the Umarex Walther CP Sport is nearly identical to the Walther CP99 which I have. Both of them have exactly the same mechanics and muzzle velocities. With 7gr .177 lead pellets mine shoots max. 356 and min. 322 fps for an 8-shot string at 19C. Assuming the same .22 cal barrel length as the original one (3.3"), with 14gr .22 lead pellets you can expect approximately 230-250fps at the same temperature and a bit higher at, say, 25-30C. If you install a stock 2240 barrel (7.5") you could roughly get to 300-310 fps?
IMHO even if you succeed with that conversion, it is not worth your time.


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PostPosted: Sat Jan 17, 2015 5:58 pm 
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EverHopeful wrote:
How thick are the walls between the chambers at the thinnest point? Just a bit worried they might let go and turn into shrapnel.


I was also thinking this... Drilling took out 1mm which is not that much, but doesn't leave a lot of material id say
approx 1/2 of the original wall thickness. Maybe before I start cutting barrels, I will fire it without the barrel in
place and see how it responds to the stress. I'll just wrap the outside with a thick cloth to catch any debris,
should anything break loose..



rav wrote:

For your info, the Umarex Walther CP Sport is nearly identical to the Walther CP99 which I have. Both of them have exactly the same mechanics and muzzle velocities. With 7gr .177 lead pellets mine shoots max. 356 and min. 322 fps for an 8-shot string at 19C. Assuming the same .22 cal barrel length as the original one (3.3"), with 14gr .22 lead pellets you can expect approximately 230-250fps at the same temperature and a bit higher at, say, 25-30C. If you install a stock 2240 barrel (7.5") you could roughly get to 300-310 fps?
IMHO even if you succeed with that conversion, it is not worth your time.


Thanks for the info.. I would imagine the super short barrel also contributes to such a low FPS. I dont have a chrony
yet but am making one. If all the other parts hold up in conversion, I would then be looking at a tighter hammer spring
and altering the valve with a goal of at least 400fps. I read somewhere about a similar setup getting a good improvement
with a longer barrel alone. If I cant get 400 ~ 420 FPS id be more than happy :D


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PostPosted: Sat Jan 17, 2015 6:54 pm 
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Yes, increasing the barrel length will get a good improvement. I went down this path with a PT-85. It's currently using the barrel from a P17 which is about 7" I think. I was getting pretty dismal fps with the factory barrel, low 300s for a few shots then quickly falling to a little below 300 for most of the cartridge. The longer barrel bumped that to around 400 with no other changes. I also tried converting to 22, but I couldn't get a decent seal between the magazine and the barrel, so I put that project on hold. The best I managed with 22 was a little over 200 fps :(

I'm also planning on turning the PT-85 into a semi-auto rifle, so I'm with you on that idea :) I figure a 13" barrel should work nicely - I might even be able to back off the hammer a little and get a few more shots per cylinder. Need to work out some way of operating the safety once most of the gun is buried inside a stock.

Jim


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PostPosted: Sat Jan 17, 2015 8:10 pm 
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EverHopeful wrote:
Yes, increasing the barrel length will get a good improvement. I went down this path with a PT-85. It's currently using the barrel from a P17 which is about 7" I think. I was getting pretty dismal fps with the factory barrel, low 300s for a few shots then quickly falling to a little below 300 for most of the cartridge. The longer barrel bumped that to around 400 with no other changes. I also tried converting to 22, but I couldn't get a decent seal between the magazine and the barrel, so I put that project on hold. The best I managed with 22 was a little over 200 fps :(

I'm also planning on turning the PT-85 into a semi-auto rifle, so I'm with you on that idea :) I figure a 13" barrel should work nicely - I might even be able to back off the hammer a little and get a few more shots per cylinder. Need to work out some way of operating the safety once most of the gun is buried inside a stock.

Jim


I love my .22 air rifles, a true semi auto in .22 would be great for backyard shooting. I figured i'd start with a semi-auto
.22 pistol, but cant find anything within a reasonable price which I wouldn't mind sacrificing. Come to think of it, I don't
think I ever found a .22 pistol with a rotary clip. Do they even exist?


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PostPosted: Sat Jan 17, 2015 8:14 pm 
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JWFX wrote:

Come to think of it, I don't
think I ever found a .22 pistol with a rotary clip. Do they even exist?¸


Sure - the Daisy 622X uses a rotary plastic clip.

NLA - but you can sometimes find one used; Mr.Marvin often has one.

http://co2airguns.net/Collection/Daisy%20622X/index.htm


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PostPosted: Sat Jan 17, 2015 8:37 pm 
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wllm995 wrote:
JWFX wrote:

Come to think of it, I don't
think I ever found a .22 pistol with a rotary clip. Do they even exist?¸


Sure - the Daisy 622X uses a rotary plastic clip.

NLA - but you can sometimes find one used; Mr.Marvin often has one.

http://co2airguns.net/Collection/Daisy%20622X/index.htm



Seems it was a rare gun even back in 2007 topic15031.html

Why is there such a lack of this type of air pistol? One would figure that at least one of the big airgun companies
would have taken the opportunity to corner the market :shock:


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PostPosted: Sat Jan 17, 2015 8:42 pm 
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JWFX wrote:

Why is there such a lack of this type of air pistol? One would figure that at least one of the big airgun companies
would have taken the opportunity to corner the market :shock:


No idea - there would be a LOT of people who would buy one if it was available.

:?


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PostPosted: Sat Jan 17, 2015 8:45 pm 
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wllm995 wrote:
JWFX wrote:

Why is there such a lack of this type of air pistol? One would figure that at least one of the big airgun companies
would have taken the opportunity to corner the market :shock:


No idea - there would be a LOT of people who would buy one if it was available.

:?


I find it really strange because even in the USA there is nothing along these lines.. If it was something you
could not find in Canada only would be typical of our restrictions here, but the USA too? thats just odd.
I'd buy two, one to keep original, and one to make my repeater rifle!


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PostPosted: Sat Jan 17, 2015 11:10 pm 
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Odd isn't it. Same with semi-auto pellet rifles, there's just not a lot of choice, especially if you want something that actually cocks the hammer during the shot cycle which counts out the 1077.


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PostPosted: Sat Jan 17, 2015 11:47 pm 
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EverHopeful wrote:
Odd isn't it. Same with semi-auto pellet rifles, there's just not a lot of choice, especially if you want something that actually cocks the hammer during the shot cycle which counts out the 1077.


After reading on the few pistols that were produced, there seems to be a low shot count per co2 cylinder. Appears to be
about half the shots you see in .177. I wonder if this had anything to do with it? Might take a while, but im going to try and get
one of the discontinued models, and fingers crossed on a new release if that ever happens.


Regarding my CPS sport, after taking some measurements I will have to not only turn the barrel and take away
some of the O.D and groove to fit, but also rework the mount that holds it. Im thinking maybe keep this as a .177
but switch out the barrel for a longer .177 to pick up some FPS and accuracy.

The magazine when drilled out for a .22 is probably far too thin walled to make the pressure and send it down a longer
barrel should I convert to a rifle. I think the best bet is to get a hold of a proper .22 pistol and go from there. Its going to
take some searching and even more time waiting, but that appears to be my best bet on this idea.


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PostPosted: Sun Jan 18, 2015 6:31 am 
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The old catch 22, the blowback pistols are already gas hogs because of the gas requirements to run the action. If you then try and drive .22 pellets with a short barrel the situation gets worse and the shorts per 12g CO2 gets pretty poor. Shouldn't be quite so bad with rifle length barrels though, especially if the blowback action was designed just to cock the hammer and not to produce simulated recoil. I'm surprised there aren't more SA rifles on the market, I'm certain they'd sell well.


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