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Posted: 5/17/2008 2:20:05 PM EDT
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So I picked up a set of "GO" and "NO-GO" gauges from brownells to check my new build and found out that my headspace is off. So i stripped the bolt and inserted the "go" gauge and this is what it looked like: http://i274.photobucket.com/albums/jj254/g2jap/headspace.jpg Then I tried it with the bolt carrier and this is what it looked like: http://i274.photobucket.com/albums/jj254/g2jap/headspace3.jpg So a little info about the build. The bolt and carrier and barrel match up but I had to change the front trunnion so its not matching. The barrel pin hole and everthing seemed to match up perfectly and the barrel pin went in without any problems. so what should I do now? How bad off is my headspace? am I going to need to drill a new barrel pin hole? I dont have any tools besides basic handtools (hand drill and punches) but I might be going to a build party next week to work on it. |
| If I read you correctly, the trunnion does not match your kit numbers. That is the cause of the HS problem. You will need to adjust the barrel depth in the trunnion to correct the HS, and then drill and pin the barrel in the correct position. You might have to use a larger pin to correct this as well. |
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I am in the process of building 2 aks at the same time one is a romy pistol turned down by Pat that is built on a flat (barrel not pressed in yet). the other is a romy built on a nds-3. between the two build I sent out the kit to Pat to be turned down to a pistol and mixed up the trunions (dumb mistake) between the two. The pistol flat has the trunion riveted in and no barrel and the NDS has the trunion and barrel installed. If that made sense, what would be the easiest way to go about this? Am I better off drilling a bigger hole for the barrel pin and get a larger barrel pin? If that is the easiest way then what size should I drill it out to and where can I get a barrel pin to fit it? Second, would it be better to demill the front trunions and install them on the correct reciever? If this is a better way how do you go about pressing out a barrel on a assembled rifle? Also I dont have access to any high powered tools for right now, I might be going to a build party next week but it isnt for sure. So I am pretty much limited to a dremill and hand drill. |
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So if I follow you . You are in possesion of the original trunnion but it is on another build and and that the recivers are the issue. One registered as a Pistol and the other a rifle. If that is the case,I would suck it up and dissasemble the kits and start over again. To me it would be be a smaller PITA to do that than trying to head space all over aagin. It is possible to do that with carefull drilling so you will not damage the recivers. This helps Trigger Guard Rivet Drilling Jig $25.00 |
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The bolt not closing on a go is common on even on matching kits. US made guage are SAMI spec which varies from the Euro CIP specs. See if the stripped bolt will close on a live round. If it does, try a live round with two pieces of masking tape on the primer end, if it still closes It it good. |
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I just tried 2 different live rounds with 2 pieces of masking tape on the back of the primer the first was remington umc brass cased and the second is some chinese st6eel case. The remington seems to set all the way but the chinese steel core stuff doesnt set. so does that mean my headspace is good even if the "go" gauge didnt set all the way? Here are some pics: In this pic it shows how the live round and bolt line up. It takes a little force to move the bolt to the correct position but it does set correctly. http://i274.photobucket.com/albums/jj254/g2jap/headspace6.jpg Here is the bolt and carrier group. Didnt really take any pressure to sit correctly with the live round. http://i274.photobucket.com/albums/jj254/g2jap/headspace5.jpg |
On Romanian rifles the bolt does not close all the way on a go gauge, but the carrier still closes. Your carrier does not close on a go gauge, Your headspace is not OK. Check headspace with go and no-go gauges, not with ammo and tape. |
| Your real close. Common commie method to fix this is to either tap the barrel in or out WITH THE BARREL PIN IN PLACE during first assembly after they had drilled for the barrel pin and something "moved" in the process . Hence the reason why some barrel pins are a pain to remove. The barrel has been bumped. In your case toss it in the press and bump the barrel back a hair. Pretty common problem you have with a pretty easy fix. Have a had a few pull this on me. 5 minute fix. People will swear up and down the barrel won't move with the pin in there but rest assure, it does. You'll hear it. |
Huh? No build should close on a no-go. How is masking tape going to tell you anything? You have no idea what measurement you are starting with. The difference between a go and a no-go is only .006 If you happen to start with a cartridge that is already on the long side (but still within spec) and add .006 to it (with tape or any other method) you can easily end up with too much headspace. You must start with the minimum spec (a go gage) and then add between .001 and .006 to it in order to achieve the proper headspacing. |
| so which way should I press the barrel out to adjust the headspacing. Should I press it out, barrel away from the trunion or should I press the barrel more into the trunion? in the previous posts I think it ways stated that I should press it towards the trunion but I think it should be pressed out of the trunion a little. right? |
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I would put the bolt from other kit and see if this will solve the problem. Remember - if this gun does not close on a gauge, the other one will probably have to much of head space if you indeed mixed the trunnions. Also, DO NOT "bump the barrel" if you "bump" it, it will be back after some firing. The proper way to adjust to small of head space is to grind bolt's locking lugs; to much of head space - match with other bolt or push the barrel in and drill for a bigger barrel pin. |
According to what armchair gunsmith? To the OP. never, never, never grind the bolt. Headspace is adjusted the exact same way whether it it too tight or too loose, namely an oversize barrel pin. |
According to Official Soviet AKM Medium Repair Manual... If you call it "armchair gunsmithing", I guess you know better.... |
| Considering everything you have said about your headspace I would argue you are just fine. The problem arises when there is too much space/play in the chamber and things don't encapsulate the case perfectly (i.e. too much space allows things to over expand or explode). In this case the fact that it is having problems with the one guage not closing the bolt completely but still capable of chambering a round tells me you are on the better side of headspace problems. Especially with the AK the way it was designed, if the bolt does not go all the way into battery the hammer will not strike the firing pin and therefore you will not have a round detonated while it is outside the chamber (which is also very bad). So you may need to see which rounds will and won't work, but I would say you should be fine. You could certainly try to move the barrel out a little bit, but I would not if it were mine. |
Arsenal Inc. headspace by grinding back of lugs. |
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The difference in the minimum and maximum length is .006. Most headspacing issues require only .001-.003 adjustment to bring into spec. Good luck trying to remove that amount of material accurately with a grinder and more importantly exactly the same amount from both lugs. A thousandth or two too much, and you'll be tossing the bolt or at the very least starting all over and doing it the right way. I don't believe that any arms manual would suggest attempting it unless it was some sort of life or death field operation. Anybody who attempts to adjust their headspace this way is a hack. |
If you like, I can e-mail you a scan of this manual, but it will be up to you to translate it from Russian. Also, let me ask you, how would you adjust for tight head space in rifles with treaded barrels (such as earlier AK's and Galils) assuming that the gasport is already drilled? |
| Anything with a threaded barrel (except for something that uses a distinct HS system like the FAL or a floating nut like the AR) is headspaced by turning down the barrel shoulder on a lathe before the gas port is drilled (or short chambered then finish reamed) Why do you suppose that new barrels come without the gas port or GB/FSB/RSB pin holes drilled? |
The AK does not have a threaded barrel. And in this case the barrel already has the gas port done which should not be a problem since the difference required to make it pass head space would not effect the gas port tolerences. The AK uses a pinned barrel which is why so many have suggested using an oversized barrel pin. The chamber is also already done, if you were to turn down the barrel you would need to ream out the chamber. That is what makes building AKs a non-gunsmith option. |
I think you missed the last couple of posts, try backing up a little. I was answering the question above my reply. |
I guess you are missing a big point here: we are not talking about building guns from "virgin" parts, rather "repairing" (or rebuilding) once assembled guns, some that seen a heavy use. As I stated above, the Soviet Ministry of Defence AK / AKM repair manual has a chapter on fitting new bolt to a BARRELED RECEIVER, and this chapter never mentioned of fitting a new barrel pin (in fact it is not mentioned nowhere in this manual), in contrast the procedure is given on grinding the locking lugs. I assume, that the barrel could be moved one way or other and oversized barrel pin installed, but this is not a factory approved method. |
There's the key words right there, repair manual. I said in the beginning that, that might be some sort of field repair method, but it is not the way they are built or an arsenal repair method. Here's an item from gunthings.com. AK Barrel pin, new, size .281, slightly oversize for situations where you are adjusting headspace or the hole is damaged and you need to redrill to a larger diameter. Use a J size drill. $4.00 |
to get back on subject, do this. |
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Why go to all that trouble demilling both guns and re assembling them when we're talking about moving your barrel probly no more than .005 either way? personally ,I would knock out the barrel pin, set the receiver up in some sort of good solid setup and with a BFH and soft punch, Smack that bad boy (probly out) and try the go gage till it goes. Run the letter J or whatever is the right size drill thru the hole and press the O/S pin in. Done............ But before doing this i would try swapping the bolts as someone already suggested |
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