Hole from a drill press in an AK chamber


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TrekkieFromHell
July 21, 2006, 10:00 PM
I'll keep it simple. We made some AK's from kits, and a hole was overdrilled and made it into the chamber. Not realizing this as I didn't do the drilling and everything looked fine to me, we test fired it today. All the casings come out with a nice round hole on the side of them. So does anyone know how I would fix the hole?

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Jim K
July 21, 2006, 10:28 PM
Yep, replace the barrel. Any other method would not be ideal and could lead to trouble further down the line.

Jim

P95Carry
July 21, 2006, 10:54 PM
Jim is spot on - as to the chosen method.

However - I would if my own gun and not one to be fired by a third party - consider fitting an interference fit pin (about 1/2 thou oversize) - and once a just visible show inside chamber - take a few light cuts with a chamber reamer and plenty of lube.

Any external plussage can be removed however desired and surface touched up. If the fit is good and tight then the pressure on that area from expanding case should be insuffient to cause any backing out. Assuming we are talking about a hole no bigger than about 3/32.

Malapai
July 22, 2006, 07:28 PM
wow you had to really get busy with the drill to overdrill into the chamber. The trunnion thickness is only about 1/8" to 5/32" at best and will hold about 4 threads of a 10-32 screw. I assume your doing a screw build as drilling the trunion for rivets here involves pressing out the barrel to begin with.

P95Carry is correct with his fix and this method is what I would. Good luck

Jim K
July 22, 2006, 10:13 PM
Well, folks, I can't say that won't work, but I suspect that at some point that plug would become a projectile, with unpredictable and possibly dangeous results.

It might be better to tap the hole and then plug it with a screw; threads should give more support than just an interference fit.

The correct fix is still the one I recommended; IMHO anything else is risky.

Jim

P95Carry
July 22, 2006, 10:26 PM
Jim - I would still agree for sure - your way is best - no probs there. True also a thread formed and then insertion of small machine screw (chamber still to be smoothed) is better than my interference fit approach - which is just the simpler route.

However - and being too lazy right now to do the math - if we take the ''footprint'' of the pin in chamber - and divide that into the surface area of the whole case - I would expect local pressure on that to be way below what might be needed to blow it out. Plus .......

If the hole itself only resulted in local case bulge then we can probably assume no case blowout likely - which would be needed IMO to place higher pressures on a pin.

Not trying to be argumentative - just playing with the other option :)

carpettbaggerr
July 22, 2006, 10:37 PM
What about MIG welding? I think I'd weld it before I'd use a pin or screw.

P95Carry
July 22, 2006, 10:42 PM
Not sure of wall thickness in the area but penetration would I think be an issue - the weld would have to be deep enough to reach into chamber and a bit more - to allow for a reamer finish.

Stronger yes but much more disturbance to metalwork - as well as the refinishing.

RyanM
July 22, 2006, 11:24 PM
However - and being too lazy right now to do the math - if we take the ''footprint'' of the pin in chamber - and divide that into the surface area of the whole case - I would expect local pressure on that to be way below what might be needed to blow it out. Plus .......

If the hole itself only resulted in local case bulge then we can probably assume no case blowout likely - which would be needed IMO to place higher pressures on a pin.

I'm pretty sure TrekkieFromHell said there were holes in the fired cases, not "bulges."

And the force on the pin is a lot easier to calculate than that. The maximum chamber pressure of the 7.62x39mm cartridge is 50,000 CUP. That'd be around 40,000 to 45,000 PSI, given that .223 Remington has a max chamber pressure of 45,000 PSI/55,000 CUP.

So let's say it's 45,000 PSI to be on the safe side. That means there's 45,000 pounds pushing on every single square inch. The bigger the surface area, the more force. So that's why long, narrow cartridges have less of a problem with backforce on the bolt face than those fancy shmancy fat magnums.

Anyway, I dunno what width the hole is, but here's a table.

1/32" - 34.5 pounds
1/16" - 138.1 pounds
3/32" - 310.6 pounds
1/8" - 552.5 pounds

P95Carry
July 22, 2006, 11:29 PM
Oops - Ryan correct re the holes - sorry!

Thx for doing the math :)

As I said I still support Jim's advised method as best. And reiterate I'd only try this trick on my own gun - with some consideration also to where the actual hole was!

medmo
July 22, 2006, 11:31 PM
Safety First - REPLACE THE BBL!

I'm sure if you were on a deserted island and the only rifle on the deserted island had a hole drilled through the chamber that fixing it in the deserted machine shop on the deserted island by tapping, installing a machine screw, low temp silver soldering the machine screw threads and re-reaming the chamber would be okay.

So, that is probably not the case. Replacing the bbl with a non chamber perforated bbl type is the only really safe fix. There is enough pressure chamber going on there where it's not a good idea to go monkeying around with it.

barnetmill
July 24, 2006, 05:20 PM
For what it is worth I do know of drilled through chambers in bolt actions guns being repaired by insertion of a screw. I think that the high temp locktite was used. I assumed it worked out ok. A friend of mine usually has new customers bring him things that have been really messed up by other "gunsmiths". He is a good machinist. Pressure guns have holes drilled through their chambers, not sure if any gas leaks out or not. The chambers are often thicker which may give more length (strength) from the threads.

If the hole is through the top of the chamber and you wear glasses the worst case scenario with an AK is the gas pressure blows a small hole through the case and hole in the chamber. Your hands are out of the way so you should not lose any fingers. The gun will not blowup. I am guessing that it would jam or at least really stress the extractor although that is not clear from TrekkieFromHell's account. The trouble with an AK is that a lot rounds of will likely get fired through it and any repair had better be a good one.

cmidkiff
July 24, 2006, 05:56 PM
I'm thinkin' a little JB Weld...



(Yes, I'm joking! Please don't do this!)
Replace the BBL. Only way to do it right.

TrekkieFromHell
July 26, 2006, 02:12 PM
Thanks for all the replies! I'm still not sure what I'm going to do yet, but now I have some pretty good ideas to consider. Weirdest thing about it though, is it shoots just fine, just was worried about that screw a bit. Now the other AK kits came out alright, one came out damn near perfect! Just have to grind down something on it and its done :)

Here are some pics of them for who is interested...
The green one is the one with the problem, the black one just needs an adjustment, and the wood stock one works just fine. Even if it doesn look like its been laying on the side of the road for a while.
http://www.thehighroad.org/attachment.php?attachmentid=42740&d=1153937371

http://www.thehighroad.org/attachment.php?attachmentid=42741&d=1153937462

http://www.thehighroad.org/attachment.php?attachmentid=42742&d=1153937472

carpettbaggerr
July 27, 2006, 03:22 AM
Looks sharp. But I'd certainly replace the barrel on that Bullpup. Posthaste.

I would not want to mess around with a pin or screw right next to my face..........

:uhoh:

Malapai
July 28, 2006, 09:19 AM
Your builds look good, Where did you get the composite stocks for the black one?

Here is a few pics of my romanian builds The first pic below shows refinished stocks on two builds. I cut off the front handles.

http://i73.photobucket.com/albums/i232/rddown/AK-47/painpleasure001.jpg

Here is one bead blasted, range tested and ready for finishing :

http://i73.photobucket.com/albums/i232/rddown/AK-47/5-12-06003.jpg

Some detail on charging handle:

http://i73.photobucket.com/albums/i232/rddown/AK-47/Image3.jpg

Duracoated and all done:

http://i73.photobucket.com/albums/i232/rddown/AK-47/finished007.jpg

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