Weird AR15 300BLK-Out FTE/FTF

[Chuck R.]

Spent yesterday afternoon helping on of the guys put together a 16" AR15 in .300AAC for his son to deer hunt with. Parts were:

Aero upper and lower
Wilson Combat barrel & BCG
Geissele SSA-E trigger
Magpul Furniture

Assembly went smooth, test firing not so much.

The barrel and bolt passed head space check, Headspace is tight, but passed a "GO" gauge. The gun had multiple FTE and an occasional FTF where the bolt wouldn't go completely into battery, when sling shot-ted. It will when going using the bolt release. It would lock back on empty mag, ejection pattern was where it's supposed to be.

FTE's were with a round stripped from the mag, partially chambered, but with the spent case from the fired round hung up in the ejection port.

Tried another bolt, zero issues. Checked extractor and ejector..OK, but brass was very tight going into the bolt face. Tried another couple of pieces of brass, and I couldn't even get some of the brass into the bolt face. When leveraging in a piece of brass onto the bolt face with the ejector and extractor in place, it will partially eject, but hangs up. Pic is with ejector and extractor in place, extractor has the post and rubber "O" ring in place. Ejector has plenty of strength.



Try as I might I can't duplicate the above picture with one of my bolts. Honestly it's the 1st time I've ever seen anything like this. I measured on of my bolt's faces at .3830" and I measured the WC Bolt face at .3760".

It appears the bolt face is too small. He's going to get on the phone with Wilson Combat on Monday and see what they have to say.

Has anybody ever experienced similar??

 

[Gordon]

well with "zero Issues" with another bolt that kinda narrows it down, provided zero issues with all the different brass that seems "too tight"

 

[luzyfuerza]

Are you using only one brand/lot of 300 AAC brass? Try testing the WC bolt with some other 300 AAC or .223/5.56 (removed from the receiver of course) brass and see if the problem persists.

Your measurements do likely tell the story, though. SAAMI gives max rim diameter as 0.378 - 0.010". Depending on how you measured the bolt face, cases at SAAMI max diameter could interfere with bolt face ID.

(Sorry for the ugly link)

https://www.bing.com/images/search?view=detailV2&ccid=/sdHlnue&id=2C136E13C536C926EA5191220A8292F10D0DDC3A&thid=OIP._sdHlnueEDdBxDlTMsKISAHaFZ&mediaurl=https://uploads.tapatalk-cdn.com/20170525/b1594af2fd2b376e5f1b54f823d59b1a.jpg&cdnurl=https://th.bing.com/th/id/R.fec747967b9e103741c4395332c28848?rik=OtwNDfGSggoikQ&pid=ImgRaw&r=0&exph=1291&expw=1773&q=saami+brass+spec+300+aac+drawings&simid=608012312422007976&form=IRPRST&ck=AF7FD92FC40A726D94096C2CD5DCEBD4&selectedindex=4&pc=EMMX01&ajaxhist=0&ajaxserp=0&vt=4&sim=11&adlt=demote&shtp=GetUrl&shid=cce2354e-1545-4ce2-934b-081849fa43fc&shtk=SkFNTUVEIEJPTFQgLSAzMDAgQkxLIEFSLTE1IC0gUGFnZSAy&shdk=Rm91bmQgb24gQmluZyBmcm9tIHd3dy5ndW5zaXRlLmNvLnph&shhk=AYxal0aWdWCCXwBydCwJ9S2f57me+1P23UMYoKZBkcU=&shth=OIP._sdHlnueEDdBxDlTMsKISAHaFZ

 

[Chuck R.]

Are you using only one brand/lot of 300 AAC brass? Try testing the WC bolt with some other 300 AAC or .223/5.56 (removed from the receiver of course) brass and see if the problem persists.

Your measurements do likely tell the story, though. SAAMI gives max rim diameter as 0.378 - 0.10". Depending on how you measured the bolt face, cases at SAAMI max diameter could interfere with bolt face ID.

https://www.bing.com/images/search?view=detailV2&ccid=/sdHlnue&id=2C136E13C536C926EA5191220A8292F10D0DDC3A&thid=OIP._sdHlnueEDdBxDlTMsKISAHaFZ&mediaurl=https://uploads.tapatalk-cdn.com/20170525/b1594af2fd2b376e5f1b54f823d59b1a.jpg&cdnurl=https://th.bing.com/th/id/R.fec747967b9e103741c4395332c28848?rik=OtwNDfGSggoikQ&pid=ImgRaw&r=0&exph=1291&expw=1773&q=saami+brass+spec+300+aac+drawings&simid=608012312422007976&form=IRPRST&ck=AF7FD92FC40A726D94096C2CD5DCEBD4&selectedindex=4&pc=EMMX01&ajaxhist=0&ajaxserp=0&vt=4&sim=11&adlt=demote&shtp=GetUrl&shid=cce2354e-1545-4ce2-934b-081849fa43fc&shtk=SkFNTUVEIEJPTFQgLSAzMDAgQkxLIEFSLTE1IC0gUGFnZSAy&shdk=Rm91bmQgb24gQmluZyBmcm9tIHd3dy5ndW5zaXRlLmNvLnph&shhk=AYxal0aWdWCCXwBydCwJ9S2f57me+1P23UMYoKZBkcU=&shth=OIP._sdHlnueEDdBxDlTMsKISAHaFZ

I tried multiple makes of both .300AAC and .223/5.56 and in two of my bolts. It really does look like the WC bolt is out of spec. Even the brass I could get into the bolt were significantly tighter than my bolts, and they would hang up when ejecting just like in the picture above. Honestly I would have (and did) suspect anything else but that as I've never encountered in before, I've never even read about it or something similar before.

I did have one other bolt once that wouldn't headspace closed on a no-go and on a Colt Field gauge. Manufacturer replaced it

 

[luzyfuerza]

You might want to find a case or two on the small side of the 0.378 - 0.010" tolerance band and see if they work properly.

This would be pretty conclusive evidence for WC to consider.

 

[Chuck R.]

You might want to find a case or two on the small side of the 0.378 - 0.010" tolerance band and see if they work properly.

This would be pretty conclusive evidence for WC to consider.

Great idea!!!

 

[Chuck R.]

Guys, quick update.

My friend spent some time on the phone with WC this am explaining issue and steps taken to identify. WC rep said those bolts run a little "tight". They're sending him our a new upgraded BCG (Nickle Boron) today as a replacement, and he'll mail back the other so they can check it out.