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Old 07-12-2018, 07:29 AM   #1
JTM20
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Default Do I Need a New Barrel?

After screwing-up while headspacing my Tantal build, i need to replace the front trunnion and bolt (locking lugs are toast and it's a nonmatching kit). Problem is i already drilled the barrel pin channel on the barrel.

Do i need a new barrel once i replace these parts? I'm thinking yes since they probably won't headspace the same, but I'm wondering if i can save it.
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Old 07-12-2018, 07:42 AM   #2
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Install the barrel and then determine if it will headspace., or if an oversized pin or a weld bead in the pin channel will resolve any headspace issue.
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Old 07-12-2018, 10:44 AM   #3
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How did you manage to toast a bolt and trunnion?
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Old 07-12-2018, 11:45 AM   #4
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Quote:
Originally Posted by def90 View Post
How did you manage to toast a bolt and trunnion?
Ground off too much material trying to adjust headspace that was too tight after pinning the barrel. Turned out i just forgot to ream the barrel pin hole.

I probably went through the surface hardening and don't want to risk it.

Last edited by JTM20; 07-12-2018 at 11:51 AM.
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Old 07-12-2018, 12:19 PM   #5
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How did you manage to toast a bolt and trunnion?
Me. Dremil showed up
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Old 07-12-2018, 02:34 PM   #6
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You ground on the trunion and the bolt??
Ouch.

Post some pics to see how bad it really is.
Trunion might be fixable.

Yes the barrel pin slot is likely in the wrong place.

I don't weld those. A bunch of other guys will be along to say it's ok.
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Old 07-13-2018, 11:35 AM   #7
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I wouldn't show pics of that. You will get made fun of. Just learn not to do that again ;-)
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Old 07-13-2018, 11:59 AM   #8
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It has become an expensive environment to join the learning curve with AKs. It’s a dying hobby unfortunately. The files will become mostly news, politics and religion with prying eyes.

Sad days.
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Old 07-13-2018, 12:10 PM   #9
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Yea, can't imagine anyone grinding off the lugs to set headspace. No way there was any research done on that method. If I were you I would sell everything as a kit and recoup as much as you can then go buy an AK before you kill yourself. Make sure the pointy end faces away from you.
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Old 07-13-2018, 12:11 PM   #10
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Quote:
Originally Posted by JTM20 View Post
Ground off too much material trying to adjust headspace that was too tight after pinning the barrel. Turned out i just forgot to ream the barrel pin hole.

I probably went through the surface hardening and don't want to risk it.
Quote:
Originally Posted by 1biggun View Post
You ground on the trunion and the bolt??
Ouch.

Post some pics to see how bad it really is
.
Trunion might be fixable.

Yes the barrel pin slot is likely in the wrong place.

I don't weld those. A bunch of other guys will be along to say it's ok.
Oh... I'd like to see photos too.. Just for learning reference what not to do.. Please post photos!
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Old 07-13-2018, 01:00 PM   #11
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Dont grind on a bolt or breech block to even the lugs out. I assume they needed lapped in.
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Old 07-13-2018, 01:13 PM   #12
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Not overly relevant in this case, but giving the barrel a quick push forward has helped me slightly loosen headspace, and ensure the barrel is where it will be after firing some rounds.

How tight was the headspace?
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Old 07-13-2018, 01:39 PM   #13
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A trunion might be able to be remachined by some one depending how bad it is.

No point of making fun or insulting a guy. He's asking for help.

Post up some pics.
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Old 07-18-2018, 07:31 PM   #14
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I got the new trunnion riveted in and everything lined up ok. The headspace was a little tight, but was fine once I moved the barrel a nudge forward, ran a 7mm reamer through by hand, and pressed the original pin in.

There was a couple thousands gap between the front of the trunnion barrel pin hole and front of the barrel channel, should I oversize the barrel pin?

Also here's the pictures, old on the left. I probably could have kept the original trunnion, but the right lug just didn't look good to me.





Thanks for the advice, and for anyone reading, don't do what I did.

Last edited by JTM20; 07-18-2018 at 08:20 PM.
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Old 07-18-2018, 10:10 PM   #15
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I don't see much wrong with the trunion .

The bolt it a mess but it would be of use to some guys who could get the lugs back to were there making the correct contact and have the correct ramp and helix .

Id happily give you $25 for the parts to use in a blow back if you think there junk .

glad you got the new trunnion in .

PM me if you want to recoupe some of your loss.
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Old 07-19-2018, 05:13 AM   #16
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lapping compound is your friend.
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Old 07-19-2018, 07:50 AM   #17
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Can’t see anything with those pics.
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Old 07-19-2018, 06:43 PM   #18
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Quote:
Originally Posted by 1biggun View Post
I don't see much wrong with the trunion.
If I'm seeing it correctly, there's a bunch of material missing from the right lug.
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Old 07-19-2018, 06:47 PM   #19
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You guys can flame all you want but I headspace with the bolt and go gage in. Push the barrel till I feel a little resistance and bam! Headspaced perfectly on the first try in about five minutes.
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Old 07-19-2018, 06:52 PM   #20
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Here's a thread about it.
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Old 07-19-2018, 07:38 PM   #21
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Quote:
Originally Posted by JerrySexton View Post
You guys can flame all you want but I headspace with the bolt and go gage in. Push the barrel till I feel a little resistance and bam! Headspaced perfectly on the first try in about five minutes.
No flaming here. That is very nearly the "factory" method for press and pin barrels and it's mine as well. Press to firm headspace, blacken the contact faces, and adjust with oilstone until acceptable closing force is obtained.
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Old 07-19-2018, 08:15 PM   #22
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Nothing wrong with that at all. It's a decent technique. As long as you don't over press.
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Old 07-19-2018, 08:16 PM   #23
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You need to get a new hobby before you kill yourself or someone else. Grinding on bolts and trunnions is Dangerous. It don't take a Rocket Scientist to figure it out. Not Flaming just the Facts like Joe Friday would say.
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Old 07-19-2018, 08:32 PM   #24
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Quote:
Originally Posted by Rforbus View Post
No flaming here. That is very nearly the "factory" method for press and pin barrels and it's mine as well. Press to firm headspace, blacken the contact faces, and adjust with oilstone until acceptable closing force is obtained.
That's fine untill you consider the number of guys who can't press a barrel in to even get the pin slot lined up will be the same guys
who end up getting the bolt stuck solid against the guage that's now pressing a ring into the chamber and no way to get it apart .
Seen it first hand guy sent me one like that.

I'm all for lapping the lugs in on mismatched parts and correcting misalignment
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Old 07-19-2018, 08:37 PM   #25
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Quote:
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If I'm seeing it correctly, there's a bunch of material missing from the right lug.
Looking really close, the top of RH lug looks rounded off.
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Old 07-19-2018, 08:47 PM   #26
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Quote:
Originally Posted by JerrySexton View Post
You guys can flame all you want but I headspace with the bolt and go gage in. Push the barrel till I feel a little resistance and bam! Headspaced perfectly on the first try in about five minutes.
Quote:
Originally Posted by Rforbus View Post
No flaming here. That is very nearly the "factory" method for press and pin barrels and it's mine as well. Press to firm headspace, blacken the contact faces, and adjust with oilstone until acceptable closing force is obtained.
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Nothing wrong with that at all. It's a decent technique. As long as you don't over press.
I started doing that about 5 years ago with perfect results every time.

All this time I thought I was Cave-Manning it...and embarrassed to admit it!!
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Old 07-19-2018, 10:50 PM   #27
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Quote:
Originally Posted by 1biggun View Post
That's fine untill you consider the number of guys who can't press a barrel in to even get the pin slot lined up will be the same guys
who end up getting the bolt stuck solid against the guage that's now pressing a ring into the chamber and no way to get it apart .
Seen it first hand guy sent me one like that.

I'm all for lapping the lugs in on mismatched parts and correcting misalignment
But that's "those guys" and not me. It's still fine.
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Old 07-19-2018, 10:55 PM   #28
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Quote:
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But that's "those guys" and not me. It's still fine.
Agreed
A man should know his limits and ability.
Beyond that thread carefully
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Old 07-19-2018, 11:06 PM   #29
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The factory method uses a Go gage but presses the barrel with a certain limited, measured amount of pressure.
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Old 07-19-2018, 11:43 PM   #30
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But that's "those guys" and not me. It's still fine.
No argument .
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Old 07-20-2018, 05:19 AM   #31
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i heard the romanian factory presses "until the light goes out".
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