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Posted: 6/12/2015 2:06:15 PM EDT
After taking my new build out and firing 60 rounds, I noticed that two of the bolt lugs had chips on them. They aren't on the face of the lugs and can't really even be seen from the front, but appear on the sides/corner when you look at an angle.
The two lugs between the chipped lugs have wear marks from the bolt catch. Red marks are the chipped lugs. 
The barrel extension is still dirty, but I see no real indicators that the lugs are making contact anywhere. Is it possible that the bolt catch is just hitting the bolt at just enough of an angle to cause an issue? It is a 308 build. |
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Can you provide any information as to the brand of bolt, barrel, etc? Could be related to the bolt catch, improper hardening, ammo, etc. Take a close look on the space between the barrel extension lugs and the barrel, where the bolt lugs make contact with the back end of the barrel, and look for any burrs that may be making contact with the front of the barrel lugs. What type of ammunition are you using, any steel case? On another note, take a look at the feed ramps from the upper receiver and the feed ramps on the barrel, do not exactly line up and may need a little clean up if there are any feeding related issues.
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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No feeding issues, no failures to eject, brass looked good. Everything functioned perfectly, I just noticed those imperfections on the bolt when I cleaned it.
PSA barrel, BCG, upper, etc. I was using Federal M80 for 40 rounds and ZQIs equivalent for 20. I did find one area on the extension that looks like it corresponds with the chip near the ejector. 
The rest appear to be fine. |
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Barrel rotated in the upper receiver barrel socket when the barrel nut was being tightened.
The top lug should be TDC of the receiver, while section between the two feed ramps should be BTD/ Center of the lower take down block. on your upper, the barrel extension top and bottom lugs are now clocked to the 11:45 position, instead of dead noon/straight up and down instead
So with the barrel extension not indexed correctly in the upper receiver, but instead slightly counter clockwise instead, this is mis-indexing the bolt to barrel lugs as the bolt lugs enter and exit the barrel lugs, and what is causing the knicks and burs If the barrel has a taper pin FSB installed, then the barrel can be slipped in the upper receiver barrel socket without having to loosen the barrel nut. If you have a gas block instead on the barrel, then the barrel will need to be reinstalled. Really, being a new rifle, just send the upper receiver back to have the barrel install/indexed corrected in the upper receiver. Also, send just the bolt to have it replaced as well. The bolt is probably fine, but since the nicks was caused by the barrel not being correctly index installed in the upper receiver, have them replace the bolt as well). |
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Quoted:
Barrel rotated in the upper receiver barrel socket when the barrel nut was being tightened. The top lug should be TDC of the receiver, while section between the two feed ramps should be BTD/ Center of the lower take down block. on your upper, the barrel extension top and bottom lugs are now clocked to the 11:45 position, instead of dead noon/straight up and down instead https://farm1.staticflickr.com/428/18553169249_903b57f79d_b.jpg So with the barrel extension not indexed correctly in the upper receiver, but instead slightly counter clockwise instead, this is mis-indexing the bolt to barrel lugs as the bolt lugs enter and exit the barrel lugs, and what is causing the knicks and burs If the barrel has a taper pin FSB installed, then the barrel can be slipped in the upper receiver barrel socket without having to loosen the barrel nut. If you have a gas block instead on the barrel, then the barrel will need to be reinstalled. Really, being a new rifle, just send the upper receiver back to have the barrel install/indexed corrected in the upper receiver. Also, send just the bolt to have it replaced as well. The bolt is probably fine, but since the nicks was caused by the barrel not being correctly index installed in the upper receiver, have them replace the bolt as well). VERY good observation. Could it be the picture angle making it look off? (similar to the gas tube not looking centered) I have another picture (not the best quality) and it looks to be lined up fairly well. Are those marks directly above the lug witness marks? or is it just a happy coincidence they line up perfectly 
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Just draw a line from the bottom center of the front take down lug, to the center of the gas tube channel above.
Center tip of the lug between the barrel feed ramps, and the center of the top lug should be on the same line, and not clocked off it instead. Granted that the tolerance for the bolt to barrel lugs allow for some light off indexing and no binding, its not much and a over clocked barrel is going to cause binding of the bolt to barrel lugs instead. As for the upper receiver socket pin indent, and the barrel extension pin, when a barrel nut bearing surfaces or barrel nut over tightened, the barrel extension pin will dent the side of the upper receiver barrel socket pin channel, or the barrel extension pin just bends, and what allows the barrel to twist in the upper barrel socket to end up with a incorrectly clocked barrel (barrel extension) in the upper receiver. 
As for the evil of possibilities, the upper receiver barrel socket was not produced square to the upper receiver line, or the extension pin is not TDC with the FSB index on the barrel, and the barrel extension had to be clocked out of correct index to get the rifle to bore sight zero instead. |
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http://www.ar15.com/forums/t_2_301/267120_Just_got_my_PA10_kit_yesterday__anyone_have_this_problem___update_OP_.html
The issue with my PA10 appeared to be too mostly due to too much play between the carrier and upper combined with something out of spec. Still a lot of play with what they sent back to me but I think it will work |
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Quoted:
http://www.ar15.com/forums/t_2_301/267120_Just_got_my_PA10_kit_yesterday__anyone_have_this_problem___update_OP_.html The issue with my PA10 appeared to be too mostly due to too much play between the carrier and upper combined with something out of spec. Still a lot of play with what they sent back to me but I think it will work That's what I thought too (I had posted in your thread) but after getting it to the range and putting some rounds down range I saw the chips. When it first arrived, there was nothing wrong other than it being dirty. |
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Quoted:
After taking my new build out and firing 60 rounds, I noticed that two of the bolt lugs had chips on them. They aren't on the face of the lugs and can't really even be seen from the front, but appear on the sides/corner when you look at an angle. https://farm1.staticflickr.com/356/18713054406_3a3e70ddd3_b.jpg The two lugs between the chipped lugs have wear marks from the bolt catch. Red marks are the chipped lugs. http://i234.photobucket.com/albums/ee75/Synyster06Gates/18553174789_4e2eedea97_b_zpsvbxq2ypj.jpg https://farm1.staticflickr.com/428/18553169249_903b57f79d_b.jpg The barrel extension is still dirty, but I see no real indicators that the lugs are making contact anywhere. Is it possible that the bolt catch is just hitting the bolt at just enough of an angle to cause an issue? It is a 308 build. I would just clean the bolt well and try it again. Perhaps they were there all along and you just didn't notice? If that's not to your likeing I would just get another bolt from Brownells (maybe a SS bolt) and give it a try. Impala |
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