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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:
 
#30 ·
I've still got some wobble between the cartridge and chamber even after dropping the cartridge and not changing the taper.

Seems to me that for all these cases to split the chambers have to be cut big.
 
#31 ·
well all of you got me in the chicken mode. Im working on 3 pps43 trunions at this time. the barrels I got from omega wepons are off of 43'. so do I need to ream the chamber's or get the boldt (home made) slightly over on the LBS ? on all of the barrels the case does stick out farther than I like. muttman
 
#32 ·
Muttman -- it was a surprisingly easy job to ream the other .030 out.

I'm sure, as everyone has said, the sub gun operation was not effected by a split case. I think with just an AK cover between me and it though, I'll be a little more careful.:scared:
 
#34 ·
I have built a few x25 conversions and shoot a lot of surplus ammo. I agree with most everything said and will just add a couple points.

The split necks are completely normal for much of the surplus ammo and are not dangerous. The cracks are often present before firing the ammo and were present at the time they left the factory. They were not adequately annealed during forming but perform their purpose fine. My bulgarian and Yugo surplus show many cracks and the importer (CAI) even puts a disclaimer on their web site. This ammo will exhibit splits in many rounds regardless of how tight a chamber you have. So yes it is not suitable for reloading but it is for many cheaper than reloading.

Any bulged or ruptured cases are not normal and indicate there is something seriously wrong. It usually does go back to insufficient bolt weight. The surplus x25 is on the hot side for simple blowback operation. I prefer to use gas operation on all but the tube guns. Many believe you can look at the weight of a factory bolt such as a PPS43 and say thats the correct weight because it works in a factory gun. Thats not correct. Most open bolt designs rely on advanced primer ignition to give the effect of a heavier bolt. If you convert the weapon to closed bolt the weight may need to be increased. If you add a longer barrel the weight may need to be increased. The simple blowback operation is sensitive to ammo changes so you should settle on a type of ammo and tune the weapon to it.

I think the x25 is ideal for kids or new shooters in a well designed weapon. I built a gas operated AR15 in x25 for my daughter and she and I love it. She likes the cool muzzle blast and low recoil and I like the cheap price of ammo and more range time together. I encourage all my friends to build in x25 and stock up on surplus ammo while it is still cheap.
 
#35 ·
hey DOUBLETAPME! are we chasing each other around from forum to forum? LMAO


WInnR: glad to hear the reaming went good. :-0

and i noticed even more people mentioning that the split necks and case's are just how it goes for this round...

notice the DTM also agrees on the bolt weight being heavier for 16" subby conversions?

and yes lots of this does depend on the spring or if you went to a striker with a double inline spring instead of a hammer with a single inline spring.. not that any of that matters in your style of AK build.

it is a great cartridge but DTM & me differ on it for the younger crowd. thats what makes this so much fun.

sdk
 
#36 ·
2xTM -- Good to see you here. I appreciate your input on this and am more confident in being able to make a safe gun in x25. I've put alot of rounds through CZ52's, had to bump recoil spring weight but never noticed a blast from a ruptured case. That's all I'm trying for here.

I know the roller lock works, maybe there's something we can do on the AK. Supporting the cartridge seems to me to be a logical first step. Eliminating the .040" gap between the '74 bolt and PPS43 breech turns out to be easy.

VD -- I held the reamers out, I'll go out and get a measurement in just a minute. Sean, I also believe the other element, beyond headspace, is delayed extraction. Weight, spring, lock, semi lock, roller, gas --- I dunno man.:confused: edit -- I'm not so sure I want a rep for a good ream job!!
 
#45 ·
2xTM -- Sean, I also believe the other element, beyond headspace, is delayed extraction. Weight, spring, lock, semi lock, roller, gas --- I dunno man.:confused: edit -- I'm not so sure I want a rep for a good ream job!!
LMFAO yeah i figured you'd catch that.....




now if you think back a few pages in this thread i mentioned that some of the guys use that "other" reamer but they have to "feel' it in there...

and you promptly told me "you werent that good".............................. uh huh and just how did you wind up doing it? :) you "felt" it right in there after all didnt ya?

now that is FUNNY and ironic.



ok now back to the stupid question for you and the other "fancy" reamer guys..

im a bit confused here and you guys can probably sort htis out pretty quick..

7.62x25 TOK is what we all run in the subbys' and conversion...

that other reamer is for 7.63 x25 which is .30 mauser ..... ISNT IT?

so would that explain the loosness you guys are getting?

while they are close they are not the same....

or are they?


this is a great building conversation and im enjoying quite a bit. :)
 
#37 ·
VD -- I didn't go to the books so I've got no idea if these #'s are in keeping with those published. Also, the barrel is still unfired so I can't give a definitive "it works".

Some folks collect baseball cards, I collect reamers. They're like a well stocked coffee can of random nuts and bolts, you KNOW it's there if you look long enough.

I used a .362" on the casing edge ledge and a .376" on the shoulder. They both had standard beveled edges. I didn't touch side walls or taper.

By hand with a half dozen fits per cut. Did the lower edge first to make sure it was riding on the shoulder.
 
#38 ·
winn r,
I should of stated that the build is non AK, it will be for a non kit pps43, read scrach build type gun, but I'm still working on my 9mm ak. the 43 build's should "work out" in the long run but the 9mm is the one that conserns me with the boldt. the barrel is a uzi and a round will sink in the chamber farther than the x25 but still will not sink down to the extractor cut on the case like I think it should but Im new at this.
BTW what LBS spring did you go with on the 52? I when up one from OEM that wolfe seals but have not had the chance to give it a try. muttman
 
#42 ·
winn r,
but Im new at this.
BTW what LBS spring did you go with on the 52? I when up one from OEM that wolfe seals but have not had the chance to give it a try. muttman


You're not near as new at this as I!

I can't remember of course, what Wolfe spring worked in the CZ52. I'm tempted to say the heaviest they have but that may not be right. I found out long ago that, with springs, the full menu was worth the price -- I wouldn't be there unless I had a problem. In the package deals of different weight springs there was a solution somewhere.

My thanks to some unremembered on this board who advised the sharp recoil was fixable with a spring.



Thanks Winn R !!

VD PS: Your .376 inch reamer appears to be a letter "V". The .362 is very close to a 23/64 inch reamer (resharpened ?? or press fit reamer ??).
Most of these are like a lot of the women I've dated -- it doesn't pay to question their past too closely.
 
#39 ·
Thanks Winn R !!
I'll check the sizing vs standard reamer and drill sizes as well as metric sizes. I have used a 25/64 inch straight chucking reamer to create 9x19mm Luger chambers using a lathe. They fit rather well too !!

The 7.62x25 Tokarev (Mauser) uses the same dimensions plus the bottle neck and throating compared to the 9x19mm Luger. What a coincidence !!! Both rounds morphed from the American Borchardt

I will try a custom ground taper and throater to make the Tokarev chamber along with my 25/64 inch (9.921mm) straight chucking reamer.

VD PS: Your .376 inch reamer appears to be a letter "V". The .362 is very close to a 23/64 inch reamer (resharpened ?? or press fit reamer ??).
 
#41 ·
Hello mutman,
Yes. I used a standard 25/64 inch straight chucking reamer to make my 9x19mm Luger chambers. The reamer was not tapered nor did it have a pilot nose. It works well. No rougher is needed either. A lathe IS needed to ream the barrel properly.

I have done the same thing with a 31/64 inch straight chucking reamer (.481 inch or about 12.22 mm) to cut .45 ACP chambers. Granted there is supposed to be a tiny chamber taper of about 1/10mm in the .45 ACP but it doesn't affect the proper sealing of the gas pressure in the breach.

A taper to the reamers would be nice but is not mandatory.

Back to the 7.62x25 Tokarev... Since this is a bottleneck type cartridge a rougher is needed to remove the extra meat from the barrel. A new drill bit (NIB even) can rough cut a chamber IN A LATHE. A bit with a useful tip angle could likely carve the bottleneck shoulder taper which is about 33 degrees included angle. I would not hand grind this angle on a bit. The hand ground tip will NOT track properly into a barrel blank !!! Do this job on a tool and cutter grinder - carefully.

VD
 
#43 · (Edited)
I have done the same thing with a 31/64 inch straight chucking reamer (.481 inch or about 12.22 mm) to cut .45 ACP chambers. Granted there is supposed to be a tiny chamber taper of about 1/10mm in the .45 ACP but it doesn't affect the proper sealing of the gas pressure in the breach.


VD
how did you know Im planing on a fal in .45 acp :).
the drill bit to ruffer you just made my day. thanks.
of the reamer is over sized as these would be are the cases reloadable?

muttman
 
#46 ·
lets see what these look like. Can't vouch for the source though. The lower is 7.62x25.
 

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#47 ·
well as you can see there are some differances. Differant shoulder angle. differant body angle differant overall length. Differant OD at the shoulder. Ill stick with the reamer made for the round. as I under stand it the tokerov will fit and fire in the mauser chamber but the mauser has problems in the tokerov chamber. I havent personaly tried it only read it. IMOO it would be wise just to use the correct reamer. There avaliable and guarentee a correct chamber. I not removable pilot reamer would be less than the one I bought likely around $100 or less. I got mine from pacific BTW
 
#48 ·
ok so they ARE a shade different.....

so that was part of my question back a few, were you guys using the TOK reamer or the Mauser reamer? ( in getting the "loose" chambers)

great info.
 
#49 ·
Im using a 7.62x25 reamer and its pretty tight like it should be IMOO. the loose chamber I referd to was in a used factory PPSH 41 barrel that a member sent me. it was considerably looser but one would expect that in a military full auto made to shoot in subzero temps and in the dirt. id say the side to side play was well over .005 there is deffinatly going to be a differance in how it extracts I wont know untill I get a gun built.

I relize that there will be no reloading of the surpluss stuff but commercial brass is avaliable and I like my stuff to shoot accuratly. There is not reason to think that good ammo in a good chamber and barrel would not be accurate. I have heard reports of 9mm Sunomies doing 1MOA or better it would be nice that a x25 with good ammo did the same. I suspose if you reload and have a 30 mauser chamber you could kust load so mauser for it. I have no issue using what every you have to make a chamber I plan on boring the chamber on my 444?????????? with a small boring bar. I see no reason it cant be done.
 
#50 ·
a 9mm soumi is a completely different shooting animal than a ppsh.....

soumis even in full auto are the absolute most accurate subby you will ever see... hands down. not even close.

ppsh41 is great to shoot but its more about practice and "feeling" them in to what works for accuracy, then actual "aiming" like you can a soumi.

soumi sites are real good and the weight just seems perfect for the round. ive ran some FA groups with a soumi that you would swear came from a longer barreled semi gun.

they really are quite impressive..... but that is a different thread. LMAO
 
#51 ·
a 9mm soumi is a completely different shooting animal than a ppsh.....

soumis even in full auto are the absolute most accurate subby you will ever see... hands down. not even close.

ppsh41 is great to shoot but its more about practice and "feeling" them in to what works for accuracy, then actual "aiming" like you can a soumi.

soumi sites are real good and the weight just seems perfect for the round. ive ran some FA groups with a soumi that you would swear came from a longer barreled semi gun.

they really are quite impressive..... but that is a different thread. LMAO
thanks for sharing Id love to shoot a full auto soumi or even get my SA project started for that matter. I get sad every time i look at my kits and see them all cut up and destroyed. what I was getting at was that if a good barrel and ammo was used the round should be accurate. Im planning a 16" AK with a decent barrel and expect it to shoot as good as my other builds with hand loads. a 7.62 Soumi would be neat.
 
#52 ·
I can tell why the splits are occurring in the neck of the rounds.

A .362 reamer doesn't touch the side walls where the case is .333. The case has an extra 30 thousands to split in. This is on three PPS43 barrels.
 
#53 ·
1biggun:

oh you'll be happy with it out of the 16" barrel.... for sure. its a great plinker! and its still my favorite caliber to shoot.

WinnR: just when i thought we were about to hijack and redirect this thing to another build.... you full circled it and got it back on topic again.

you dog! (i'll try to be slicker with the redirect next time.... lmao)

interesting discovery on your part.

s
 
#54 ·
One other quick note one of you guys may have the #'s to check me on-- The PPS43 mag looks like it rides .100" high in the AK measuring from the base of the receiver to the firing pin or nob.

Maybe why everyone's had to trim off the bottom of their bolt to keep from picking up two rounds.
 
#55 ·
The case has an extra 30 thousands to split in. This is on three PPS43 barrels.
Ya , they are really sloppy. Most have a .311 bore too which is not correct for the round. I guess thats why they are called bullet hoses and fed with a drum.:) Seriously though, if you are concerned with accuracy you should have a .308" blank turned and reamed with the correct Tok reamer. If you sold your factory barrel it would cover much of the cost. Im not sure if you have said yet what you are building.

I have to agree with sean the Suomi is in a different class than the bullet hoses.

I have experimented a little with the accuracy potential of the cheap surplus x25 ammo. The best I did was 2.75" at 50 yards with Yugo. The accuracy drops off fast at longer ranges. It was fired from a 16" .308" bore heavy profile free floated barrel with tight chamber on a dedicated AR platform. I was impressed it did that well concidering it was 6.5 cents a round and had split necks. I don't know what the results would be if you tried commercial or hand loads in an accurate barrel.

I machined the AR receiver from a billet of Fortal and it is fed with a CZ26 mag. This is her with an Eotech.

Sorry if I got off topic again.:)

 
#58 ·
Ya , they are really sloppy. .308" blank turned and reamed with the correct Tok reamer. If you sold your factory barrel it would cover much of the cost. Im not sure if you have said yet what you are building.
What I'm looking for is a fun center fire gun shooting cheap ammo with minimum recoil that doesn't come apart when it's fired. I think a x25 on an AK can fill the bill. But, as has been stated above, I may be kidding myself.

It may be that a rechambered .308 is required. There's no doubt that in the PPS43 barrel the necks will split, they're completely unsupported, but with the round at least seated in the chamber now perhaps there won't be blowback from ruptured cases.

Yes, these barrels are going for $90 up!!!

I have to agree with sean the Suomi is in a different class than the bullet hoses.
You know -- I haven't checked the ones I have but all these are in 9mm aren't they?

Sorry if I got off topic again.:)
I think the topic is sub gun conversions -- you're right on top of it!!





.030 is a ton of clearance there is no way your going to see any good accuracy with a neck that loose.
Plus all the comments about the case rupturing are easy to understand.

Yes, the commie burpguns have a great amount of slop in both the chambers and the bores. They were born of desperation not national matches.
VD
I think that's it. The other thing explained are the comments about fire balls. The unburned powder escaping around a neck thats unsealed :smilie_sc
 
#56 ·
A .362 reamer doesn't touch the side walls where the case is .333. The case has an extra 30 thousands to split in. This is on three PPS43 barrels.

Ill measure my reamer in the am but I dont think there is any were near that much clearance in my chambers I cut. I did however split a couple necks in my 45-70 addapter. I did notice the bullets are heavyly crimped with a demple that looks like it was done with a center punch . the splits I had on the romy stuff all had them were it was crimped.

I just measured some fired brass and the necks were only .335 and they rechamber so im pretty certain Im at around .336 or around .003 clearance . Im sure in a machine gun were accuracy is the least of one concernes and feeding and extraction were the top priority. if there going to split at that tight of a clearance there going to split no matter what. .030 is a ton of clearance there is no way your going to see any good accuracy with a neck that loose.
 
#57 ·
According to Frank C. Barnes in his epic book, Cartridges Of The World, DBI Books, Inc 1989... the .30 Mauser, the 7.62x25 Tokarev, and the .30 Borchardt all use the same size and shape case dimensions. Powder charges however vary greatly and should NOT be interchanged.

Yes, the commie burpguns have a great amount of slop in both the chambers and the bores. They were born of desperation not national matches.

Muttman, The straight chucking reemer will cut a non-tapered chamber. The brass (.45 ACP for example) will have a slight expansion at the front half of the case but is still reloadable if quality brass is used. Most military brass is junk compared to commercial brass these days. But we all knew that !!!

VD
 
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