Anyone do the 8 to 4 chamber bevel?

[into_the_knight 22]

So the bulgarian magazine was causing the bullet to hit just right at the edge of the chamber. Occasionally that caused fail to feed. As well as the times when it would feed the bullet would be a little loose. (I really ought to use snap caps for hand cycling. I know it's dangerous but I've actually got the trigger group out of the gun so I'm okay I think.)

 

So I was reading several pieces of information where a bevel was put into the chamber to help fix this. However, the problem is that the bullet case is not as supported. But this may not be a problem depending on if the bevel is minor. As well as this doesn't change the headspace of the gun.

 

So I saw a range of things out there.

 

On the gun wiki, the saiga being pictured had a severe feed ramp cut into the chamber.

 

 

Here's a picture of something Dinzag did.

 

 

And here's a picture of something from AIM surplus.

 

 

http://img119.imageshack.us/my.php?image=img0436ad1.jpg

 

So my mod is probably close to what Dinzag did but just a bit more material came off. I would hand cycle and then go back to removing material until I could tell the feed path was going to work with the bevel. Do you guys think what that Saiga up top has had done is dangerous for case expansion?

 

So has anyone else done this? Anyone had a Kaboom from this type of mod? Any advice tips info?

[nalioth 405]

First off, most of your KABOOMs come from ammunition that's been reloaded (and possibly resized) many times.

 

Second of all, if you have to grind that much of your breech face for functionality, you're doing something wrong.

 

 

Thirdly: AIM's picture taking skills suck.

 

[fxhart 14]

Do you have a bullet guide?

[into_the_knight 22]

First off, most of your KABOOMs come from ammunition that's been reloaded (and possibly resized) many times.

 

Second of all, if you have to grind that much of your breech face for functionality, you're doing something wrong.

 

 

Thirdly: AIM's picture taking skills suck.

 

 

Mine is much closer to the Dinzag example.

 

The AIM surplus rifle example and the one on the gun wiki are done without feed ramps I believe. So the feed ramp is the chamber bevel which intrudes into the chamber more than I'd be comfortable with. Especially the one at the very top. Again, I was having slight feed issues after installing the dinzag guide. And I think it comes down to the vagaries of magazine tolerances and Saiga tolerances. My Saiga has an 08 at the beginning of the serial number and I'm supposing that means 2008. It also has dimples but no Y.

 

The more I've thought about this the less surprised I am that there are slight issues with feed path. I bet that the trunnion lugs are used to be a guide left to right for feedpath. But I'll bet they're designed for the slightly fatter 7.62. So a 5.65 may not get as on track as a 7.62.

 

But I get different results with different mags. The cheap ass promags geometry works well and pushes the rounds to the center and then impacts the feed ramp at a good angle and feeds without any touching of the chamber face. Galil steel mags work well too. But the Bulgarian mag seems to keep the bullets just a little bit higher and they come out without being directed to the center quite as much (but still good enough), but it's not being forced up enough by the feedramp and is slightly impacting the chamber face occasionally. And I mean right on the damn corner. So it's really close.

 

Plus I got this out of Dinzag's instructions. a) A bullet guide needs to be added to the front trunnion. Also, depending on reliability, you may need to grind a slight bevel in the chamber face.

 

Back to the topic of Kabooms.

 

I was hearing that kabooms can be a combination of a "hot load" in the case and an unsupported case.

 

The only kaboom I've ever seen was in Glock .40 cal. I was standing behind the guy. Not too much damage to him, but we were both pretty startled to say the least. Now I'm just worried thinking about a 55K PSI Kaboom. Yikes.

[into_the_knight 22]

Do you have a bullet guide?

 

Yeah I'm using the Dinzag Bullet Guide.

 

I did find that instruction a from the i223 Magazine Options document was kind of necessary for mine.

 

Maybe it's a manufacturing tolerance issue?

 

Here's the doc.

 

http://www.dinzagarms.com/downloads/223_mag_options.pdf

 

a) A bullet guide needs to be added to the front trunnion. Also, depending on reliability, you may need to grind a slight bevel in the chamber face.

 

So I have a slight bevel. And if I didn't have a bullet guide, no way this puppy would even work. So I'm finding I had to do a little bit of clean up on top of the bullet guide. But that's kind of okay because even the instructions I got with the bullet guide said this might be the case.

 

I'm just looking to see if anyone else has done it.

 

I've also seen a lot of people being real cavalier on other sites where they say they just cut the feed ramp at 6 o clock in the chamber face and don't worry about it.

 

This 8 to 4 modification was also discussed at length on the Survivalist SKS boards. It's a sticky post at the top of their board.

 

But I still can't help but worry about case support. Although, I'm thinking it's prolly gonna be okay.

 

So I'm asking around. Seeing what other people's experiences are.

 

I know nalioth has had nothing but pleasant surprises with his. He didn't even have to modify the trunnion lugs to get his bulgy's to fit. He just cleaned up the interdiction tab and was rocking and rolling. I'm jealous.

[csspecs 1,987]

Mag is seating high if its hitting low on the chamber with a bullet guide. Have any scuffs on the top of the feed lips on the mags?

 

 

I have not had to do anything like that with my rifles.. I did do something like that with a .22 that had a sharp edge that would cut the lead bullets rather then chamber them. I guess if it solves the problem and does not explode its probably ok.

Edited June 17, 2009 by csspecs

[TonyRumore 1,332]

You can bevel the chamber a bit, but don't go too far. There was no way around it when I made the 5.45x39 Saiga.

The bolt hit the cartridge guide and the bullet tip lift was not quite there without a slight chamfer around the the chamber.

 

Tony

[into_the_knight 22]

Mag is seating high if its hitting low on the chamber with a bullet guide. Have any scuffs on the top of the feed lips on the mags?

 

 

I have not had to do anything like that with my rifles.. I did do something like that with a .22 that had a sharp edge that would cut the lead bullets rather then chamber them. I guess if it solves the problem and does not explode its probably ok.

 

Well. I haven't shot it yet. So I don't know if it is gonna explode. Funny. Really funny.

 

I think the mag sits high possibly. But I followed the mag lug modifications as I saw them on Sheik Yerbouti's site and Dinzag's site.

 

I've also wonder about whether it is the fact I have a flat trunnion versus the round trunnion. When you get the round trunnion with round bullet guide it would seem to stand to reason that the bullets hitting the curved part on the left or right would be deflected a bit higher and forced back into the center of the barrel.

 

Anyhoo, I'm enjoying this weapon still. I picked up an AR at the local shop and man it just feels wrong. The charging handle feels like opening a coke can or something.

 

It's neat working on your own weapon.

 

But I went back and read dinzag's guide for 7.62 and he says nothing of touching up the chamber with a bevel on the 7.62 instructions. He does mention it on the 223 page. Perhaps there's just a little more vagaries to magazine and rifle manufacture when using 223 versus 7.62.

 

So I'm guessing this is an uncommon 223 type of thing that happens from time to time after a build up of tolerances from Izmazh and Bulgaria's Circle 10 factory.

 

And I think dinzag's guide works very well, much better than anything I could make. It works great with Galils which are supposed to be the harder magazine to work with.

[into_the_knight 22]

You can bevel the chamber a bit, but don't go too far. There was no way around it when I made the 5.45x39 Saiga.

The bolt hit the cartridge guide and the bullet tip lift was not quite there without a slight chamfer around the the chamber.

 

Tony

 

Thanks. That's what I was hoping to hear. Yay! It's not just me. Have you fired a lot of rounds through it? Is the 5.45 a hot load like the 5.65?

 

I didn't go anywhere near as far as what the top picture showed. I was reading about feed ramp intrusion on the 1911 forums and those dudes got me freaked out. They had out their calipers and were talking about less than 1 hundredth of an inch and crap. Then I started thinking that hey these 223's have 55K psi making those guns look like poodles.

 

Thanks again.

[into_the_knight 22]

Mag is seating high if its hitting low on the chamber with a bullet guide. Have any scuffs on the top of the feed lips on the mags?

 

 

I have not had to do anything like that with my rifles.. I did do something like that with a .22 that had a sharp edge that would cut the lead bullets rather then chamber them. I guess if it solves the problem and does not explode its probably ok.

 

I do notice that when I hand cycle the bolt, I can feel it touching the top of the magazine. Should I bend the feed lips down?

[csspecs 1,987]

Uhh no.. Messing with the feed lips tends to make any mag all screwy.

 

I've never played with the other types of mags but I have a couple pro mags that would seat higher then others and jam the nose of a round into barrel. Since they are plastic and cheap enough that I did not really care, I just cut a little from the bottom side of the rear tab and melted a little back on the top to bring the mag down.

 

You could test that idea by putting a little card board on the top of the rear magazine tab to seat it lower (probably have to hold it in as it may not lock). If that fixes it then maybe add a little tab to the mags or to the rifle. If not you only wasted a little time and some cardboard and you can still bevel the chamber.

 

As for using live rounds to hand cycle... Its not the best but I do it all the time. Just have the barrel pointed at something solid that you don't like very much and have your FCG out or at the very least your firing pin or hammer.

 

I can't really say for sure its the mag sitting to high... But I have made a good number of mags and when puzzling out the design that was one thing that became VERY clear, you want it high so the bolt strips the round but to high will cause all sorts of problems with feeding, either to high causing an ejected live round or to flat a feed and it hits the side of the barrel. As the round is forced up by a feed ramp it also is aimed toward the middle by the pressure of the round below it in the magazine, so not enough upward angle and you also won't get the round pointing to the middle of the chamber.

 

 

EDIT:

DUH I see you already did it.... Ok well that little bit you shaved off is probably fine. I've seen a couple home built kit guns that had huge chunks ground out instead of using a feed ramp. My WASR-2 has a pretty big bevel in it as well, not something I would do myself but its had 4k down the tube and has not killed me yet.

Edited June 17, 2009 by csspecs

[dmadmooney 0]

Convert to AR mags. Works.

[Azrial 1,091]

Unsupported cartridges due to feed ramp modifications in hands guns is problematic with their comparatively low pressure.

 

In a RIFLE, no way.

[into_the_knight 22]

Unsupported cartridges due to feed ramp modifications in hands guns is problematic with their comparatively low pressure.

 

In a RIFLE, no way.

 

 

No way as in it won't matter?

 

Or no way as in don't do it, it's worse than problematic in a rifle?

[into_the_knight 22]

So I took it to the range today. I ran UMC brass, and Silver Bear. I'm alive and the weapon functioned fine. No FTF. No FTE. I used the black bulgy, the smoke bulgy, the promag ak a5 (ak 223 no feed ramp), and the galil steel mag. Not one of them failed to feed. However, I was somewhat sparing in my magazine loading. I loaded 5 shots in each magazine and cycled through them all a couple of times.

 

To begin the shooting, I extended by rifle stock to the last position and put one round in the chamber by hand. Pulled the trigger and I was still alive. After 60 rounds of ammunition, I was still alive and feeling fine.

 

Thanks all.

[avatar 4]

So I took it to the range today. I ran UMC brass, and Silver Bear. I'm alive and the weapon functioned fine. No FTF. No FTE. I used the black bulgy, the smoke bulgy, the promag ak a5 (ak 223 no feed ramp), and the galil steel mag. Not one of them failed to feed. However, I was somewhat sparing in my magazine loading. I loaded 5 shots in each magazine and cycled through them all a couple of times.

 

To begin the shooting, I extended by rifle stock to the last position and put one round in the chamber by hand. Pulled the trigger and I was still alive. After 60 rounds of ammunition, I was still alive and feeling fine.

 

Thanks all.

 

 

Too be more sure of safety check your brass. I seriously doubt you'd have any problems with new brass, but if you reload you may want to keep a close eye on your empties. From all my reloading experience any failures happened a bit further up the case. If you're gonna have a case separation it'll be your brass fault and would most likely go even if your chamber had no bevel. The case is still pretty thick in the area you bevelled (judging from your pic).

And a +1 to AR mags.

And by all means stay alive

Edited June 24, 2009 by avatar