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Old 11-02-2007, 07:33 PM   #1
Random Chaos
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Default Headspace problem

Prior to firing a couple mags through my just built SA85 the HS was so tight that it would not even close on a GO gauge. Now after test firing 2 mags, it will now close on a NO-GO gauge. I'm thinking that I have to pull the barrel and re-headspace. This is a matching kit and the rifle was not hot when I tested it.
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Old 11-02-2007, 09:23 PM   #2
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Something is not right. There's no way you should have that much movement with that few rounds.

1. Is the cross pin in the barrel?

2. Do the bolt lugs or the trunion look messed up / bent / excessively worn / cracked?

3. Did you adjust anything after the first try with the GO gauge?

4. Did you pull the extractor when you did the GO test? It can potentially interfere.

5. Did you use one brand/type of GO gauge and another for the NO-GO?
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Old 11-02-2007, 10:18 PM   #3
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Quote:
Originally Posted by ronin
Something is not right. There's no way you should have that much movement with that few rounds.

1. Is the cross pin in the barrel?
yes

2. Do the bolt lugs or the trunion look messed up / bent / excessively worn / cracked?
no, everything looks fine. It was not an extremely worn kit. I got it from Centerfire

3. Did you adjust anything after the first try with the GO gauge?
no, I had wanted to test fire it but waited over the weekend until I got my gauges. I then tested my headspace with both gauges and it would not close on a NO-GO or GO but would close on a cartridge.

4. Did you pull the extractor when you did the GO test? It can potentially interfere.
yes

5. Did you use one brand/type of GO gauge and another for the NO-GO?
They are both Clymer
I've done some recent builds and have ran a couple mags through each. All the builds have had tight headspace, so I wanted to see if my HS had changed any on any of the builds, so I checked them on two they were still tight but on this one it dramatically increased.
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Old 11-02-2007, 11:26 PM   #4
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Wow. I have to say I'm not sure here. I hope some of the other guys can help out here.
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Old 11-02-2007, 11:29 PM   #5
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If you set the headspace originally with some schmutz or a chip in the chamber, you would get a false reading with your gages. If the cases look OK, test regularly with a field gage and don't sweat it until it fails that test too. Then you DEFINATELY would need to fix it.

-- Max

If your chamber was squeeky clean, that means metal has flowed in only 60 rounds. Check your lugs and locking recesses. I would think they are dead soft and the rifle is junked.
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Old 11-03-2007, 08:44 AM   #6
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This has me baffled. I guess there may have been some crap in the chamber but it would amaze me that it would be the exact same size to enable a positive headspace test as it did. I gonna pull the barrel today. I want to see how the barrel channel looks, just to make sure it is perfectly rounded. When I assembled it, I do not remember the channel being elongated but if it was elongated toward the breech end, it could result in this problem. I have tested the rifle with a couple other bolts. One from a Polish rifle and one from another SA85 kit I have AND BOTH FAIL!!! I just don't know.

Would Manson sell field guages for 7.62X?

Thanks for the help.
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Old 11-03-2007, 10:03 AM   #7
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I use Manson's gauges. I bought GO, NO-GO and FIELD direct from him last fall.

http://www.mansonreamers.com/NewTools.htm

I think Brownell's has them too.

What bothers me about what you are describing is that it went from tighter than "GO" to loose enough to fail NO-GO. That's a heck of a change.

Debris (metal shavings, dirt, rust, grease) could definitely have thrown off the first one.

If it were me, I'd very carefully check the bolt logs and the trunion for any wear, cracking or bending. I'd also check the face of the bolt.

All things being equal, I think it would be pretty hard for the barrel to move. Thus, I'd look at the other areas first.
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Old 11-03-2007, 11:20 AM   #8
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I bought the Manson guages - don't have a single rifle that will close on the go guage - anyone wanna buy an unused no go guage :-/
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Old 11-03-2007, 12:31 PM   #9
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It sounds like he needs the FIELD guage at this point. However, I was told not to mix brands. Either go all Clymer or Manson.
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Old 11-03-2007, 12:31 PM   #10
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BTW, I think it was Curtis (AK-Builder) who recommended Manson to me and I've been happy with them.
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Old 11-03-2007, 12:58 PM   #11
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Damn, this is FN aggravating!!! I have tried 4 different bolts and all of them close on a NO-GO in this rifle!!! I have inspected the B/C and compared them to the B/C out of 2 other SA85 kits and the B/C "appear" to be exactly as the other two. I could not see any cracks, breakage or really any heavy wear. The only thing about this build that stands out is that I did have to pull the barrel 3-4 times because I had a terrible time getting the barrel installed without any cant and the top wear it fits into the trunnion is somewhat galled but not badly. I'll prolly pull the barrel this afternoon. I don't know whether to cannabalize a romy kit for another barrel or try to re-headspace.
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Old 11-03-2007, 01:55 PM   #12
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My only thought would be, was the barrel pin jornal in the barrel dead nutz on when you drove it in or was it off a hair causing it to kinda cut a new jornal on the barrel or the pin when installed and it slid forward slightly. Before pulling the barrel put a muzzle nut on even with the crown and put a protective device in place (pennies or a block of wood) and give it a few whacks with a hammer and see if you headspace changes.
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Old 11-03-2007, 02:19 PM   #13
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check to see if your trunions cracked
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Old 11-04-2007, 11:45 AM   #14
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If there were cosmoline or other gunk in the chamber when initially headspaced it could have compressed allowing a perfect fit for the "GO" gauge,

If the top of the barrel/journal were galled enough it will allow the barrel to be pressed up enough in the journal to allow it to "ramp" the pin creating your headspace problem, now this is the wierd part because usually the headspacegets tighter UNLESS your using a AK 74 style muzzle brake which actually pulls forward on the barrel when fireing.......

An over sized pin journal will cause the same effect instead of actually removing the barrel try resettting the headspace so it will barelly close on a go gauge then drill out to a larger barrel pin diameter this will avoid disturbing the set the barrel has already made in the journal...
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Old 11-04-2007, 01:25 PM   #15
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Quote:
Originally Posted by dstorm1911

An over sized pin journal will cause the same effect instead of actually removing the barrel try resettting the headspace so it will barelly close on a go gauge then drill out to a larger barrel pin diameter this will avoid disturbing the set the barrel has already made in the journal...
Thanks to all for the help, I am not a noobie at this but I do have another question, how much should I drill out the journal? I know renuzit can furnish oversize pins but what size bit should I use and what size pin should I go with. Also in doing the re-headspacing, is that a press a little and then test and repeat until it is right procedure?
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Old 11-04-2007, 01:54 PM   #16
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Quote:
Originally Posted by JIGBALLS
Did you test fire the rifle with the very tight headspace ? just wondering if firing the rifle with the tight headspace might have put extra force on the receiver lugs and maybe moved the trunion in the receiver .
It was fired with tight headspace. The bolt would not close on GO or NO-GO, however it would close on a cartridge. I do not think the trunnion moved, all 6 rivets appear as they did when I set them. I going to take out the pin and re-headspace it this afternoon.

Rick
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Old 11-04-2007, 03:51 PM   #17
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Rick, check to see what oversize pin ya have access to that is as close as possible to the original 7 mm then drill .001 smaller than that pin, I've been workin out in a hot semi trailer all morning trying to sort out my stuff so my brain isn't working for numbers right now, Most folks just mic out drill bits then make a pin fron the chuck end of a bit using the next smaller to drill the hole out which works fine, I'd go a few thousandths over to start then visually inspect the hole to be sure its perfectly uniform if not go to the next bit then make a pin outa the next size up in a fraction/letter set.

As far as setting headspace ya got it, press and test untill its very tight on a GO gauge I personally get mine to barelly close on a Manson gauge then tighten it up a lil bit it'll still close on a round and after fireing 20-30 rnds will barelly close on the gauge as it will set in a lil bit.
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Old 11-05-2007, 11:20 AM   #18
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I pushed out the barrel pin yesterday. The channel in the barrel is wider than the hole in the trunnion. Looking through the trunnion, I can see that neither the forward side of the channel or the rearward side of the channel is truly flush with the trunnion hole. My barrel pin is dead nutz on .277. I'm going to re-headspace and see how bad it looks and then make a decision whether to drill out the hole or to cannabilize one of my romys.
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Old 11-05-2007, 02:59 PM   #19
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when ya re-drill ya just need to go large enough to give a clean hole the trunion will require a good bit and lots of oil but the barrel is soft and will go very fast then the other side of the trunion will be back to taking your time and again lots of oil, I've dealt with some that required as much as .020" oversize pins ya will need to see how far off your barrel cut is, if ya can measure the bottom of the cut in the barrel it will give ya an idea how much oversize ya will need to go...
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Old 11-08-2007, 11:10 AM   #20
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Default Fixed, I think...

This was one f'ed up barrel. I headspaced it so that it closes on a cartridge but will not close on my gauges, I figured it should expand some once I fire it. I then ordered a couple bits and a couple tool steel rods (drill blanks) from MC. I initially drilled the hole out to .2969 and I could still tell that the channel was wider than the hole in the trunnion, so much so that it "could " effect HS. I drilled again with a .311 bit and that was almost perfect. I then cut the tool steel rod (.3160) to make the barrrel pin. I put it in the freezer for a few hours, then pressed it in. I checked the HS after all this and it was fine. My only concern is that in drilling it to .311, did I go to deep? I'll prolly take it to the range over the weekend.

Thaks for all the help.

Rick
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Old 11-08-2007, 11:47 AM   #21
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Ya'll be fine at .311" ya really have plenty of material and with a proper tight fitting pin it will support the chamber etc...
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Old 11-08-2007, 02:14 PM   #22
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Glad to hear you figured it out Random Chaos. I wonder how they messed the groove up at the factory. We'll never know unfortunately.
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