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Discussion Starter · #1 · (Edited)
New build doesn't work UPDATED

UPDATE AND PICS IN POST 37

What a discouraging PITA.

I put together an AR, using an ARP 16" scout barrel with ARP chamber, superbolt, PSA premium BCG (removed bolt), Aero Precision upper, gun store gas block (nice fit and appeared to align well). Barrel and chamber were thoroughly cleaned before assembly.

Lower worked on previous build 100%.

From the first round, FTE. Only 2 or 3 rounds out of 30 ejected and fed. The bolt never once locked back. Plenty of bolt-over-base failures. Sometimes the bolt would leave the brass in the chamber.

I switched bolt carriers, no difference. Switched lowers (one carbine, one rifle), no difference.

Feeds, extracts by hand 100%, though sometimes the bolt has held on tour a case, not ejecting it. The rim was tight in the bolt face.

Using S&B 110 fmj ammo from PSA. All fired rims measure 0.418" - 0.420", less than 0.422". Spent bass does show signs of pressure; some faint ejector marks, a little swiping on about half, primers noticeably flattened and enough cratering to catch a fingernail. Yet, rims not chewed at all by extractor. Only one of the cases left in the chamber needed to be tapped out, all others fell out when rifle was tilted back.

ASC mags.

Cannot tell if undergassed or overgassed, or ammo problem.

Not thrilled about the tight bolt with a moderately offset FP hole either.

Oh well, have to load up some ammo and see if it was the S&B or not. Have some 95 gr Barnes on the way with H4198 and 322 powder. Hope I won't be wasting those next trip.
 

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My all new build is an ARP barrel and a bcg with BOTH being melonite coated. The first 5 rounds I had to bump the butt stock while pulling on the charging handle. After that, the action would function.

Not sure if this is your issue, but, on mine it appeared to be mostly a "break in process" for the new melonite barrel AND bcg. It functions fine now.
 

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A good place to start would be to pull the gas block and check that the residue suggests that the port is aligned with the blocks hole. This is the most likely of spots to be either mis-aligned or mis-installed and can be checked fairly quickly and easily.
 

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Feeds, extracts by hand 100%, though sometimes the bolt has held on tour a case, not ejecting it. The rim was tight in the bolt face.
This part has me wondering... have you tried using the PSA bolt instead of the Super Bolt? Are you saying the ejector is sticking down?
 

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What buffer and spring? Did you clean the bolt and chamber really well before firing? Dry cycling a couple hundred times by hand can help the action smooth out a bit. Double check the gas tube alignment with the hole in the gas block, also look for signs of major gas leakage. S&B ammo is sufficiently hot for function testing.

-Alexander
 

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Check you gas system. You are experiencing what what going on with my 450BM, changed ammo, and switched to an adjustable gas block and it worked with the occasional hiccup
 

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Discussion Starter · #7 ·
What buffer and spring? Did you clean the bolt and chamber really well before firing? Dry cycling a couple hundred times by hand can help the action smooth out a bit. Double check the gas tube alignment with the hole in the gas block, also look for signs of major gas leakage. S&B ammo is sufficiently hot for function testing.

-Alexander
Regular buffers and springs. 2 different lowers, one A2 that works fine, one new carbine. No difference between the 2.

Bolt looked clean, lubed ejector and extractor both before use. Both moved freely. Brand new superbolt I ordered with barrel.

Action is plenty smooth by hand, I cycled a few mags through it. The only hiccup was a few cartridges extracting, but not ejecting.

I cleaned the chamber and barrel thoroughly before firing.

What has me stumped is the possibility of over gassing without any exractor marks on the rims.

Will remove gas block tonight and verify alignment and port size.
 

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Discussion Starter · #8 · (Edited)
This part has me wondering... have you tried using the PSA bolt instead of the Super Bolt? Are you saying the ejector is sticking down?
The BGC was 5.56. I only have the one 6.8 bolt.

I don't think the ejector was sticking down, the cartridge felt stuck in the bolt. Like the rim was too big or the bolt face was too small.
 

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One thing to look for in the barrel port, and gas tube port is a large burr from drilling. That can obstruct both quite a bit. I had one barrel with a chip from drilling that blocked over 50% of the port.

Compressed air works well to test cycle the action and if you wipe some liquid soap on suspect leak areas you'll find them quick.

-Alexander
 

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i'm guessing you have a gas block issue. i too fell prey to the 'gunshop' gas block. i replaced it with a Troy and problem solved. But rest assured their will be answers posted here.
 

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you may have multiple issues, so only try fixing one thing at a time--

you might need to tweak the mag feed lips and spring a little, also check the ejector for brass shavings, they can cause the ejector to stick in the bolt, might need to radius the ejector some to keep from causing "swipes" on your cases and shaving off brass pieces

also check your gas system to make sure its all lined up properly like the others said---- did you butt the gas block directly up on the shoulder of the barrel? or is it set off just a little?
 

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What a discouraging PITA.

I put together an AR, using an ARP 16" scout barrel with ARP chamber, superbolt, PSA premium BCG (removed bolt), Aero Precision upper, gun store gas block (nice fit and appeared to align well). Barrel and chamber were thoroughly cleaned before assembly.

Lower worked on previous build 100%.

From the first round, FTE. Only 2 or 3 rounds out of 30 ejected and fed. The bolt never once locked back. Plenty of bolt-over-base failures. Sometimes the bolt would leave the brass in the chamber.

I switched bolt carriers, no difference. Switched lowers (one carbine, one rifle), no difference.

Feeds, extracts by hand 100%, though sometimes the bolt has held on tour a case, not ejecting it. The rim was tight in the bolt face.

Using S&B 110 fmj ammo from PSA. All fired rims measure 0.418" - 0.420", less than 0.422". Spent bass does show signs of pressure; some faint ejector marks, a little swiping on about half, primers noticeably flattened and enough cratering to catch a fingernail. Yet, rims not chewed at all by extractor. Only one of the cases left in the chamber needed to be tapped out, all others fell out when rifle was tilted back.

ASC mags.

Cannot tell if undergassed or overgassed, or ammo problem.

Not thrilled about the tight bolt with a moderately offset FP hole either.

Oh well, have to load up some ammo and see if it was the S&B or not. Have some 95 gr Barnes on the way with H4198 and 322 powder. Hope I won't be wasting those next trip.
Did you place the rear set screw of the gas block in the dimple? Did you remove the rear set screw of the GB and look down through it to make sure the gas tube is not blocking some of the port/hole in the top of the gas block?
Highly unlikely over-gassed if the bolt would not lock back.
 

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Discussion Starter · #13 · (Edited)
Yes I carefully lined up the gas system during assy. The gas tube port was where it was supposed to be and yes I made sure the set screw was in the dimple.

I am home now, took another look at it, and I was likely mistaken about overgassing. I thought that might be the case because empties were left in the barrel. However, the extractor seems weakly sprung. It is much easier to move than with my other bolts.

Also, when assembling the bolt into the carrier, it was a much tighter fit than I recalled for other builds. I removed the bolt to inspect the gas rings, and they cannot by pushed below the shoulders of the groove all the way around. Another bolt I have is not like that.

So I believe I have a bolt with an extractor problem and a gas ring sealing problem. Along with the most off-center FP hole I have, among several AR15s.

I think I need to exchange the bolt for a serviceable unit.

Thank you Constructor for your reply.
 

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Discussion Starter · #14 · (Edited)
also check your gas system to make sure its all lined up properly like the others said---- did you butt the gas block directly up on the shoulder of the barrel? or is it set off just a little?
No shavings, I just cleaned it all.

Gas block butted up against shoulder.

ETA I just checked the gas port alignment, removed the gas block and soot formed a perfect circle around the barrel gas port.
 

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Bad Bolt?

Super bolts are notorious for being bad. I had same issues with a brand new bolt,(not Superbolt) and bought another and gun has never missed a beat since.
 

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I had a similar situation a few years ago . Took me a couple trips to the range to figure out if had the gas tube in upside-down. .

I've got several superbolts never herd of them being notoriously bad!!!
 

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i've got around a dozen or so superbolts, and have never had a problem
 

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Super bolts are notorious for being bad. I had same issues with a brand new bolt,(not Superbolt) and bought another and gun has never missed a beat since.
Notorious? I remember something from ~5 years ago, but those were dealt with. What else?
 

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Super bolts are notorious for being bad. I had same issues with a brand new bolt,(not Superbolt) and bought another and gun has never missed a beat since.
I hope this was a typo for you Dan. I've NEVER had an issue with a Super Bolt from ARP.
 
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