Fixing AK Headspace

[JPurp]

I have searched all over and there are tons of posts on how to confirm headspace and info on why headspace is important but nothing clear on how to fix it.

I have a Romy G kit that I believe to be numbers matching. I have confirmed the front trunnion, bolt and bolt carrier do match but the barrel doesn't have a serial number (that I was able to locate). I am 99.99% confident it is in fact a numbers matching kit.

I have pressed the barrel back in and reinstalled the barrel pin. I have removed the firing pin and extractor from the bolt for my testing.


Bolt only - Nothing chambered - 100% lock
Bolt only - CIP Go - 50% lock
Bolt only - Snap cap - 50% lock
Bolt only - CIP No Go - no lock

Based on this foundation level test my conclusion is a headspace issue. I am guessing because the bolt will not give me 100% twist lock that the barrel must be moved out of the trunnion a small amount.

If I move the barrel out and it headspaces correctly what do I do from there?

Drill another barrel pin hole? What size? Should I use an oversized barrel pin? Is there any trick to this I should be aware of?

Am I looking at this all wrong? Is there something else I should be looking at?

Help!

Thanks,

-JP

[Cokebottle]

Oversized hole (through trunnion and barrel) and oversized pin.

Hopefully someone with actual experience will chime in with the proper procedure to actually do it without egging the holes, but you got a free BTT out of it

[SJgunguy24]

Looks like you just about nailed it, you could also do a search over at the AK files and see what pops up there.
If you need an over sized pin, I would go the drill bit route. It's heat treated and you are able to get just about any size you need.

[416stroker]

If your not a member check out gunco.net. There's a lot of good info there. How does it do with a live round and hows your bolt gap?

[marxdspot]

CIP and SAAMI are not military standards. According to Dave Manson the CIP should result in a longer measurement than SAAMI. CZ-USA also says this about their Czech-made 7.62x39 bolt action. Both CIP and SAAMI are measured to a datum point or line on the shoulder. The East German and Chinese military gauges are only listed by the total length of each gauge and can not be directly compared to civilian SAAMI and CIP gauges. The SAAMI gauge has a different shoulder angle than the CIP gauge. The Chinese chamber has a rounded shoulder but ammunition shape is standard and gauge length are similar to Soviet military gauges.

The East German gauges are most likely the closest to the correct gauges for AK's, which are MASSI guages.

Here are some measurements:
MASSI (East German) Military PKM GO Gauge=32.85mm (converts to 1.2933")

CIP GO Gauge=1.2271", CIP NO-GO Gauge=1.277", Field Gauge=1.281"

SAAMI GO Gauge=1.252", NO-GO Gauge=1.262"


I've had the same problem on some of my past builds. Have you tried test fitting a spent cartridge? If the bolt closes on the cartridge, that's a rough indicator that your headspace could be okay, since the NO-GO didn't close. If you're in doubt, get a set of MASSI Go/Field guages. You could find them at Sarco. Also, make sure you clean your chamber before you measure headspace.

Now with regards to correcting headspace in the event the seller switched barrels, I usually do the following:

After checking headspace and am confident that headspace is correct, drill a larger size hole and install bigger pin to compensate for the adjustment. You could buy a new pin from Brad at Gunthings.com. He's got a .281 size pin and all you would need is a J size drill bit to enlarge the barrel pin hole.

[Cokebottle]

After checking headspace and am confident that headspace is correct, drill a larger size hole and install bigger pin to compensate for the adjustment. You could buy a new pin from Brad at Gunthings.com. He's got a .281 size pin and all you would need is a J size drill bit to enlarge the barrel pin hole.

Is the hardness of the trunnion and barrel comparable? By that I mean, when running the drill through (of course, on a press), how much risk is there of the bit wandering into the original groove and egging the trunnion?

I'm assuming here... high speed, plenty of cutting fluid, and slow, gentle cuts.

[marxdspot]

Is the hardness of the trunnion and barrel comparable? By that I mean, when running the drill through (of course, on a press), how much risk is there of the bit wandering into the original groove and egging the trunnion?

I'm assuming here... high speed, plenty of cutting fluid, and slow, gentle cuts.

Well, actually slowest speed possible on your drill press would be best. At high speed, you could risk damaging/breaking your drill bit. Just take it slow. When drilling, make sure to let up after a couple of mill's. I've never egged the trunnion holes that I've drilled. I usually make sure everything is prepped and set. A drill vise is my best friend when it comes to drilling the barrel pin hole. Make sure the when you vise the trunnion down, it's at 90 degrees to the drill. Check your alignment by placing a drill bit into the hole and see if it aligns straight with you drilling bit. Egging isn't the biggest worry. My biggest worry is when that drill bit isn't aligned perpendicularly to the bit. If you're off a bit, man, that hole on the other side is gonna be twice as big. I think you know what I mean.

[Cokebottle]

the bit. If you're off a bit, man, that hole on the other side is gonna be twice as big. I think you know what I mean.

Been there done that welded up the holes and started over (not on a barrel).

[motorhead]

it's possible for the barrel to be installed "tight" and the pin to still go in. actually, tight is preferred, as long as the bolt locks completely. you should try reinstalling the barrel normally with the original pin while checking before going o/s. diddling with the bolt lugs is NOT recommended.

[ar15barrels]

You can often move the barrel forward without even removing the pin.
Just put it in the press and push the barrel against the pin.
It will move enough to make the difference between the bolt almost closing and the bolt actually closing on the go gauge.

[SVT-40]

You can often move the barrel forward without even removing the pin.
Just put it in the press and push the barrel against the pin.
It will move enough to make the difference between the bolt almost closing and the bolt actually closing on the go gauge.

Just what I was going to suggest. Give it a good press.
Since you have removed the firing pin have you checked to see if the bolt will close on a loaded round?

One other thing look on the underside of the rear sight leaf it should have a serial number. If the kit was matching it should match the rest of your parts. One way to confirm if the barrel is matching. That is as long as you did not remove the RSB or rear sight it's self.

[JPurp]

To answer as many questions as possible.

No I have not tried a spent shell casing as I do not currently have one. I will be trying that this weekend. The closest thing I have is a set of Snap Caps in 7.62.

I am going to try and press the barrel with the pin installed. Like I said the bolt turns about half way into the locked position with the Snap Cap and the Go Gauge. I am guessing it is close.

The underside of the sight also matches the rest of the numbers. At this point the following have matching numbers trunnion, bolt carrier, bolt, gas tube and sight. The only thing I can't confirm is the barrel.

Fingers crossed on pressing the barrel forward. The excitement factor on having to drill out a new barrel pin is about a -7 on a scale of 1 to 10.

Thanks for all the info.

[oldyeller]

All my matching builds close half way on a standard go gauge, and all the way on a live wolf round- sounds good to go to me. Correct me if I am wrong, but the design keeps the action from firing out of battery.(hammer hits nub on the back of the carrier instead of the firing pin until bolt lugs are fully engaged)

[JamesY]

The last two kits I built had all matching everything. When I checked the HS on both, the go gauge wouldn't go in but a live round would. I guess there's nothing wrong with being a little tight.

[ar15barrels]

The last two kits I built had all matching everything. When I checked the HS on both, the go gauge wouldn't go in but a live round would. I guess there's nothing wrong with being a little tight.

As long as ammo chambers, there's no problem being short.