I have a complete AR-10 upper minus the BCG .I then bought a DPMS complete BCG and the bolt will not enter the barrel extension .I tried it in every position so its not the extension being not turned to the right spot .I'm guessing either the extension isn't a DPMS or the bolt head . Any other ideas ? I'm going to take it to a WW 2 rifle match Saturday and a bunch of Tactical shooters will be there to set up the range after we are done so maybe I can get some hints from them . Arnie
- Thread starter arnie19
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AR-10 = Armalite (although MANY use it to describe ANY AND ALL large-frame AR, but then you get into the sorts of trouble you are likely having) 
LR-308 = DPMS
DO NOT MIX AND MATCH PARTS BETWEEN THE PLATFORMS, ESPECIALLY BOLTS, AS THEY ARE NOT INTERCHANGEABLE!
LR-308 = DPMS
DO NOT MIX AND MATCH PARTS BETWEEN THE PLATFORMS, ESPECIALLY BOLTS, AS THEY ARE NOT INTERCHANGEABLE!
AR10 is an Armalite and I don't think a .308 DPMS bolt will work.
Edited to add ORD beat me to it, he is correct...
Pictures would be most helpful.
DPMS bolt will fit into Armalite extension and vice versa. However, there is a slight difference in bolt face recess and lug thickness between Armalite bolt and DPMS bolt that precludes headspace being "correct".
You have an Armalite AR-10 upper (DPMS is not an AR-10 but an LR) and a DPMS complete BCG?
You did make sure bolt was fully forward in BCG before inserting into upper, correct?
Again, pictures would be most helpful.
DPMS bolt will fit into Armalite extension and vice versa. However, there is a slight difference in bolt face recess and lug thickness between Armalite bolt and DPMS bolt that precludes headspace being "correct".
You have an Armalite AR-10 upper (DPMS is not an AR-10 but an LR) and a DPMS complete BCG?
You did make sure bolt was fully forward in BCG before inserting into upper, correct?
Again, pictures would be most helpful.
The upper is from Black thorn and the bolt is from Custom Built Arms .Both are supposed to be DPMS compatible .I ordered a BCG from Black thorn .If that doesn't work then there is something wrong on there end . None of it is Armalite ,and yes I said ar-10 but its a generic ar 308 .Arnie
Wait...STOP...say no more.
You had us at "Black thorn" (or Black Thorn or Blackthorne or...whatever the hell name they are going by this time). A Hesse by any other name would still wreak of $#!T. They are of notoriously poor quality in every respect. Heaven only knows what might be wrong with it, but suffice it to say...GOOD LUCK and God speed!
It was forward when I put it in .I even took the bolt head out of the carrier and it wont go in .To me the extension looks rough and needs cleaning up with a hard stone .I can see burrs and rough machine marks on it but I think it just was not finished properly .
I've owned four DPMS LR's, still have a 243. The bolt you show does not look like the bolt in my rifle. The locking lugs do not look the same to me.
have looked inside the gas key on top of the carrier for obstructions and make sure the gas tube fits inside and that its not flared out to much
You didn't happen to post about how you were buying a blackthorn AR10 upper awhile back on Calguns did you?
http://w.calguns.net/calgunforum/showthread.php?t=824333&page=2
Also that bolt is not factory DPMS I've had several of them. The machining is different and the extractor looks to be chromed? or something. However that does not mean the BCG is bad...just not DPMS factory unless they are doing something radically different now vs last year.
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No that wasn't me on Calguns .Any way I ordered a BCG from them and hopefully it will fit properly .If the bolt head I took pictures of isn't a DPMS ,I wonder what it is ? I got that BCG from a company called Custom Built Arms .Is there a picture of an Armalite bolt head any where ?
donws2 , I brought up your pictures and mine side by side and my bolt head looks like it was cast and also the angles on the sides of the lugs look different . I wonder if this was a cast head that missed a step in machining . Any way I will find out when the other BCG shows up or maybe Saturday or for sure Tuesday as one of the guys that shoots with us on Tuesday has a 308 AR of some kind . Arnie
Well my BCG came out of a factory .243 DPMS rifle, which is the same as the .308. I've owned three others factory DPMS .308 rifles but sold the others when things got crazy and made a few bucks. All four rifles BCG's looked just like the one above so my guess is what you have is not DPMS. That or in the crazy time they sent out a bolt that had not been finished milled like you said.
Brian and others .I tried the BCG from two other AR 308 rifles and they fit my upper just fine .I tried my BCG in those two AR's and it fit them just fine so what is the problem ?My guess is I have a bolt head that's made to maximum tolerances and the extension was made to the minimum tolerances .I now have a BCG from the maker of the upper and it works fine also. I got another barrel extension and that fat bolt head fits it but very tight . You can see looking from what would be the barrel end that the locking lugs are hitting in different places and also the maximum diameter of the head at the valleys of the lugs is hitting also .I measured that and the good fitting head is .020 smaller in diameter than the fat head .
Its the inside diameter that's too big not the outside .I would have to put it in an index head on a mill and take about .010 out of the bottom of each groove bottom between the locking lugs . I have a mill and a lathe so it wouldn't be a problem but I would like to find the proper blue prints of the bolt head before doing any modifying .Especially since that bolt head does fit two other rifles with no problems .Arnie
