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Blowback Head Space x25 Conversions

9K views 80 replies 14 participants last post by  1biggun 
#1 ·
While there's not much away from the muzzle end that can hurt in this hobby, out of battery or extreme head space can make some blood. I may put a trunnion in with toothpicks but the thought of an unsupported round going off in my face makes my skin crawl.

The open bolt sub guns fire before the round is fully chambered. A 7.62x25 sits 140 thousandths out of the chamber when it's all the way in. The gap between an AK74 bolt and the chamber face with a fully chambered round is 40 thousandths on a PPS43 barrel.

I've see no mention in other threads of machining the bolt face deeper although I may have missed it.

I think in terms of the bolt being held a few thousandths off the cartridge by the carrier on the trunnion but that leaves alot of cartridge unsupported.

Am I missing something here? :help:
 
#59 ·
FWIW, regarding the Wolfe CZ-52 recoil springs.

I've been running the Wolfe 18.5 Lb CZ-52 recoil spring for years now. Never had a problem. Brass still ejects into the next county, but I was only concerned with reports of roller wear with light springs. It's the highest pound rate they sell.
 
#61 ·
CZ52 spring -- my dim memories also said the heaviest they had.

Another question for those who have been here before:
AK conversion to x25 -- the shorter cartridge length gives some space. Has anyone taken that out of the front of the receiver, moved the trunnion rearward? It would likely require shortening the bolt to let the hammer angle stay the same. Is there something else? Is this doable?
 
#62 ·
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the shorter cartridge length gives some space. Has anyone taken that out of the front of the receiver, moved the trunnion rearward? It would likely require shortening the bolt to let the hammer angle stay the same. Is there something else? Is this doable?
thats what im going to do on the plow back pistiol im working on. it will use a custom bolt. there is also recently posted here a build that has the trunion moved back (I think) moving the trunion back would allow the ejector to remain in the original location on a standard reciver. It would how ever be a issue on a NDS as the serial numbers are in the front making shortening a reciver impossa ble with out wrecking the numbers. the other option is to leave the reciver as is and add a filler piece. I calculated around a 1" to 1.5" lost inthe length of a pistol or rifle.
 
#63 ·
WINNR:

im gonna back up jsut a hair on you here...

Mike makes the 7.62 barrels and has plenty of them... 16.25 inches long and they are tight in the chamber...

you could just get one of those and chamber it as you mentioned to whatever depth you want and sell your regular barrel..

this would be much easier and they are pretty accurate as this is the barrel we are using in the P7 & the AR/ZK uppers..

the P7 chamber he is not leaving the overhang on, as he is using a 9mm AR bolt head on it...

he would probably tell you what that number is if you asked.

just a thought for you and an option to get another barrel/trunnion set up.

sdk
 
#64 · (Edited)
OK -- I'm in the market.

And just bought a reamer.

And I'll let go of one of my pps barrels. They all look perfect inside and pass a bullet test. Surely folks aren't really getting $90 for these? Is $75 and actual shipping a fair price?

What's the fun with out a little horse trading? pm me.

Edit: Well, that didn't last long -- evidently it is.
 
#69 ·
I'm following with interest as I want to have a "kid-friendly" plinker as well! :D

I didn't make a note of it at the time, but someone had done a conversion with the x39 barrel and reported no noticeable loss in accuracy, thus my *assumption* that it will be good enough to kill soda cans at the range :)
 
#70 ·
#71 ·
Jerry - I asked these guys to make one for the 7.62x25 in a 7.62x39 but didn't get a response.

So I make one myself but haven't fired it yet and can't report on it's performance.
 
#73 ·
Forgot to add this - has anyone purchased one of these?

CHAMBER ADAPTERS

Here's the discussion on .308 vs. .311 - AZHONKEY has used both successfully
I have a 7.62x39 to 30-06 addapter. I used it and the accuracy wasent that great around 3"- 4"at 100 yards or worse. I saw no signs of pressure with my brass cased hand loads. the same gun in 30-06 shot 3/4" with factory ammo. It was a pain out get out once its loctited in. I was able to save it for reuse and Im going to but it in old mauser with a so so barrel for my kid to practice with.
 
#79 ·
I'm gonna hafta figure out headspace for this x25 build that I'll be starting here soon. The headspace is one issue that concerns me since I am not totally sure on how to get it right on this build.

I've never really deal with headspace issue's in my 2 previous builds.
 
#80 ·
My thoughts on head spacing these is to let the carrier be stopped by the trunnion allowing 5 thousands between the bolt and breech.

Of course the pps 43 barrels have to be reamed to let this occur.
 
#81 ·
I'm gonna hafta figure out headspace for this x25 build that I'll be starting here soon. The headspace is one issue that concerns me since I am not totally sure on how to get it right on this build.

I've never really deal with headspace issue's in my 2 previous builds.
what the post above said.

If I recall correctly your barrel had the protrusion set to give the same bolt clearance as a regular AK bolt. so tere is pleanty of protrusion.on a blow back you set it up were the carrier hits the trunion just shy of the the bolt face hitting the barrrel face. On a gas op, You use the correct guage to set head space.
 
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