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Master Endmill Breaker
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Discussion Starter · #1 ·
Okay, let's say someone has a 16" .45ACP barrel that needs to be turned down on the lathe so the various AK barrel blocks can be installed. What would be the minimum safe thickness that the walls of the barrel could be turned down to?

IIRC, the 1911 barrel O.D. is around 0.575". This would leave a wall thickness of about .063". That's fine for the short pistol barrel, but I am going to have about 14" of barrel hanging out past the receiver. I had planned on cutting the barrel blocks apart and welding them to custom sleeves to press onto the barrel. This may not be necessary if I can track down some of the larger variations of the AK parts...

The specs I have for European and Chinese 7.62 barrels is:

CHINESE BARREL: O. D. DIMENSIONS
Chamber .764" (19.25mm w/ .005 - .006" press fit)
Rear Sight Base .734" (18.5mm w/ .005 - .006" press fit)
Handguard Retainer .691"
Gas Block .634" (16mm w/ .003 - .004" press fit)
Front Sight Base .594" (15mm w/ .003 - .004" press fit)

EURO PATTERN BARREL:
Chamber .908" (23mm w/ .003 - .004" press fit)
Rear Sight Base .694" (17.5mm w/ .003 - .004" press fit)
Handguard Retainer .671"
Gas Block .594" (15mm w/ .003 - .004" press fit)
Front Sight Base .575" (14.5mm w/ .003 - .004" press fit)

Another option would be RPK parts. The only issue I have with the RPK parts is the sphincter-puckering price tag. The dimensions for those RPK parts would be:

RPK: O. D. DIMENSIONS
Chamber .908"
Rear Sight Base .885"
Handguard Retainer (unknown)
Gas Block (unknown)
Front Sight Base .608"

There are some varying dimensions on a few parts listed on K-Var and Global Trades.

Any suggestions on barrel wall thickness or parts variants to fit larger O.D. barrels would be appreciated.
 

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Premium Member
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5,980 Posts
The other RPK dimensions are:
handguard retainer .847
and gas block .758
There are several guys here with Thompsons. That would certainly have the classic dimension.

 

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Master Endmill Breaker
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1,367 Posts
Discussion Starter · #3 ·
My barrel is one of the Tommygunshop.com 16" replacement barrels for the semi-auto Thompsons. As it stands, the Thompson barrel will easily fit the standard European trunnion if I shave 0.080" off the chamber end diameter.

If I use the 0.730" rear sight block, that leaves me with a wall thickness of 0.140".

The 0.673" handguard retainer from K-var leaves me with a wall thickness of 0.112" (minus a couple more so the retainer can slide.

The 0.631" gas block leaves me with a wall thickness of 0.091".

The 0.591" front sight block leaves me with a wall thickness of 0.071".

There will be some variations in the dimensions because of press-fit and clearance fit, but that would basically leave me with this if I use larger AK parts:



If I go with the RPK parts, I'll pick up a substantial amount of wall thickness. The downside is the RPK parts will be an additional $120 over the AK parts!

I planned on turning the barrel to leave as much thickness as possible between lands. Most of the SMG barrels I've seen have pretty thick walls. I'm guessing this is more of a durability issue as the pressures from pistol loads will be lower than those of rifle loads.

I'm not building a machinegun, and I will not be rolling around on the ground with this rifle or throwing it around. Is the extra cost of RPK parts worth it?

Another option would be to use the RPK rsb and hg retainer, and then use the AK gasblock and fsb. This would only leave me with a section of barrel with thinner walls that is about 6" long. It will still be thicker than a 1911 barrel at that point.

I'm still considering making sleeves to weld to the AK parts, but buying parts would be a helluva lot easier...
 

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Happy Camper
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7,794 Posts
Remember those SAR-1's that had the threads removed? Those are reported to be 0.465" at the muzzle. OK, so subtract 0.3" for the bullet, leaves you 0.165" at the muzzle... /2 (need radius not diameter) and you have 0.0825" wall thickness... almost 0.1".


Keep in mind, that's at the MUZZLE end where pressures will be lowest.

Then again, you are looking for a considerably lower-velocity cartridge.



I would recommend reaming the RSB, GB, and FSB as large as possible... this will leave more space for the barrel. I have reamed an AK-74 GB for a Chinese AK-47 rifle for my AK-103 project and had real good luck with it.

http://pookieweb.dyndns.org:61129/AK/reaming/reaming.htm

I'll bet you can go pretty wide when reaming the RSB and FSB - the GB I would try to leave some material for the diameter, but the other parts are a no-brainer to ream out as thin as needed.
 

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Premium Member
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Ryan--I shipped off the rpk parts today to you.
Keep us plugged in on how it's going!
 

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As a mechancial engineer, I would consider the internal pressure, stress risers from cutting and rifling, bending, and more importantly fatigue. The pressure cycles with every shot. Get the dimensions off a few pistol barrels, there are reasons for those wall dimensions. 0.070-0.080" seems pretty thin to me for any long term use. It only takes one failure hear your head and eyes to make you wish you had the beef.
 

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Master Endmill Breaker
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1,367 Posts
Discussion Starter · #7 ·
I have made several posts with updates on the progress since this thread was last active.

This thread is OLD and OUTDATED. All barrel thickness issues were taken care of by the RPK barrel parts (BIG "Thank You" to Winn!!!). That's why the last post in this thread is more than a year old.

Other threads were started with updates to construction, in order that this thread would stay back in the past where it belongs!!!

FWIW, Typical 1911 barrels are around 0.580" O.D. at the muzzle. The majority of the barrel is 0.570" O.D. This leaves a barrel wall of 0.065" at the muzzle and 0.060" for the majority of the barrel.
 
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