Guns & Outdoors Forum

This started out as a Crosman 1332, the one that you had to work up a sweat hand pumping it 10 times between shots. I put it on the chronograph beforehand and it hovered at around 390fps when pumped 10 times.

I always wanted to convert one to a PCP so I got started on it. Ended up making a housing/pressure tank that holds the valve and hammer. I also disassembled the valve, opened the passages and replaced the orings with harder teflon rings to take the higher pressures.

Had to come up with a barrel band for the front since the old one that incorporated the hand pump wouldn't work anymore so I got to take a crash course in CAD design for the 3d printer but it turned out fantastic. I also made a front sight blade into it.

Got it all assembled and hand pumped up to 2000psi which gave me a velocity of 638fps. Not bad out of an 8 inch barrel. I might throw a longer barrel on it later just for the velocity increase but this thing is fun! Not sure what the shot count will be but it's not using much pressure between shots.

What kind of pellets did you use? What weight? How big is the tank? Just wondering.

Looks nice! Does crosman still sell the good breech separate? Good meaning not plastic and with a scope base?

2.5 cubic inches for the tank volume. Not sure on the pellet weight but I used the same ones for before and after velocity. I cant remember if I stated that this is a 22 caliber.

CPJ 2.0 wrote: ↑Sat Jul 01, 2023 11:29 pm Looks nice! Does crosman still sell the good breech separate? Good meaning not plastic and with a scope base?

I dont know if crosman does but there's a seller on ebay, who's name is "Needfull things" and he's an absolute prìck. Long story on that but he won't ever get a dime from me. Thatll be the next thing I make.

You will likely have to order them, but the Crosman premier NON hollow points shoot better, or at least in all three of my .22 pellet guns. But aside from finding them in a Cabelas once, Ive had to amazon them.

If you have the opportunity, could you chronograph, at least, five pellets back to back? I'll have a better idea of how much pressure you're dropping per shot. I'm guessing not too much but measuring would be better than guessing.

I measured my own Crosman pellets, both the Flat Points and the kinda pointed RN, they both weighed 14.2 gr. If you don't know the weight of your own hollow point pellets, I'll use 14.2 gr as a guess, just to get started.

With those velocity numbers, along with barrel length, pressure, tank volume and pellet weight, I'll have enough to get started. I want to play with some numbers. You know, just for fun.

That pellet gun looks like good tree rat medicine

Turns out that you can buy the steel breech at Pyramidair so I ordered one of those and the 14 inch barrel. I'm going to make a threaded adapter so that I can put my can on this thing.

Justsomedude wrote: ↑Sun Jul 02, 2023 3:27 pm Turns out that you can buy the steel breech at Pyramidair so I ordered one of those and the 14 inch barrel. I'm going to make a threaded adapter so that I can put my can on this thing.

Sounds great, can't wait to see how it works out. I like the suppressor idea. Keep us updated.

Castle wrote: ↑Sun Jul 02, 2023 3:55 pm

Justsomedude wrote: ↑Sun Jul 02, 2023 3:27 pm Turns out that you can buy the steel breech at Pyramidair so I ordered one of those and the 14 inch barrel. I'm going to make a threaded adapter so that I can put my can on this thing.

Sounds great, can't wait to see how it works out. I like the suppressor idea. Keep us updated.

Oh, I will get some chronograph numbers for you as well when I get back in the shop. I'm curious to see the velocity drop also.

I know you've been busy but any updates on this project

I posted my project on a certain platform that pertains to these specific airguns and got such a large interest in them that I decided to go into a small production run to post on Amazon (who blocked my listing because they said they were assault rifle conversion kits ) so ended up posting them on ebay. I've not had a chance to do much else since then. I do plan on getting chronograph numbers though.

Justsomedude wrote: ↑Sat Jul 15, 2023 12:06 am I posted my project on a certain platform that pertains to these specific airguns and got such a large interest in them that I decided to go into a small production run to post on Amazon (who blocked my listing because they said they were assault rifle conversion kits ) so ended up posting them on ebay. I've not had a chance to do much else since then. I do plan on getting chronograph numbers though.

Assault Rifle Conversion kits?

Maybe I missed the boat but Amazon sees an assault rifle conversion kit?

It would be funny if it wasn't so stupid. I think I have an oil filter outside that could be construed as a silencer.

Well I did get some numbers today. Did the steel breach conversion with longer barrel and also made a PCP conversion for the 2240 model which actually works incredibly well. Pumped up to 2250psi, the SBR does 784, 792, 796, 792, 789. I think I hit the pressure that the valve was starting to have lockup at because as the pressure dropped, the velocity went up. Overall, not a bad velocity string. After that the shots were dropping by roughly 5 psi, then 10 psi.

Justsomedude wrote: ↑Sat Jul 15, 2023 9:00 pm 20230715_165345.jpgWell I did get some numbers today. Did the steel breach conversion with longer barrel and also made a PCP conversion for the 2240 model which actually works incredibly well. Pumped up to 2250psi, the SBR does 784, 792, 796, 792, 789. I think I hit the pressure that the valve was starting to have lockup at because as the pressure dropped, the velocity went up. Overall, not a bad velocity string. After that the shots were dropping by roughly 5 psi, then 10 psi.

Yeah, I agree on the lockup.

You used a longer barrel? How long?

BTW, those are good velocities from a pistol airgun.

"After that the shots were dropping by roughly 5 psi, then 10 psi."

You were measuring the tank pressure directly? Just wondering.

How many shots did you manage to fire before you were about 90% velocity?

Thanks for the update.

I definitely wasn't as thorough with testing as I could have been. I tried different tank pressures before I finally got to where I took these velocities because I tried 2500psi and it wouldn't even smack the valve open. That's when I backed off to 2250. It's also a 14.7" bbl. I'm not sure about the 90% velocity part but it hovered around 780 ish for quite a while. I should also add that I misspoke. It was dropping 5fps then later on 10fps with subsequent shots.

Justsomedude wrote: ↑Sat Jul 15, 2023 9:59 pm I definitely wasn't as thorough with testing as I could have been. I tried different tank pressures before I finally got to where I took these velocities because I tried 2500psi and it wouldn't even smack the valve open. That's when I backed off to 2250. It's also a 14.7" bbl. I'm not sure about the 90% velocity part but it hovered around 780 ish for quite a while. I should also add that I misspoke. It was dropping 5fps then later on 10fps with subsequent shots.

Ok, that makes sense... I wouldn't expect it to decrease linearly. I think I have enough info to start guessing at a few things.

Thanks

I looked at the Crosman website and the .22 cal HP pellets are listed as 14.3 gr so 14.2 would've been a reasonable guess.

Just out of curiosity, what kind of data are you trying to come up with?

If you can successfully model the technical/mathematical aspects of a design on paper that translate into an accurate working design on the bench, that performs as predicted, then you can make other small changes on paper with a reasonable expectation of success without actually having to build or change anything. Yes, the changes and the resulting performance characteristics would only exist on paper as theory but that's still better than a blind guess (Trial and Error) saying, "Well, let's do this and see what happens." At some point, you may become tired of the marginal progress of a design and give up on it, altogether, and that would be unfortunate.

For instance, let's say you successfully model your .22, .25 and .50 cal designs accurately and then a customer walks in and says, "I love your .25 cal model but I've always wanted one in .280... Can you build me one in that caliber? And at a regulated 3000 psi, what kind of velocity could I expect with my 140 grain bullets?" "Also, with my .45L carbon fiber tank filled at 4000 psi with a 2 in^3 plenum attached, how many shots can I get out of that?"
A technical/mathematical model might help you to better answer those questions. The alternative is to build it and see what happens and hope the customer buys it after you've already incurred the expense.

As for me, it's just for fun as I have no plans on building or selling anything. A lot of people make weird faces at what I call fun

Finally, there's been a few times I've visited websites that offered products and the claims were so often exaggerated or outright provably false. Either these folks didn't know any better or they were liars. In either case, it didn't look good for the folks behind the product making these claims.

Anyway, keep us updated. I have a few thoughts already but I'll save them for another day. I find airguns and black powder very interesting these days... don't ask why