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6/2/2020 2:34:59 PM
Posted: 12/28/2002 7:28:04 AM EDT
I have a Bushy 16" upper with a fluted HBAR.  I am still breaking it in, which according to Bushmaster takes about 300 rounds before cleaning for their chrome lined barrels.  Problem is that it failed to fully chamber some reloads last time out, and when I switched to factory SA it wouldn't chamber those either.  I cleaned it and it chambered everything OK.  I took it back to the range yesterday and after sighting in with 20 rounds of XM193 switched over to the reloads for plinking.  Same problem with jamming and failing to fully chamber again after only 20 rounds.  Cleaned it again and everthing chambers just fine at home.  I am used to going a couple of hundred rounds at least without cleaning my 20" Bushy and no problems.  I am using the same bolt and carrier with both uppers.  Does this sound like a non-mil spec chamber?  Has anyone else had this problem with a new upper or have any ideas on how to correct the problem?
Link Posted: 12/28/2002 8:11:30 AM EDT
[Last Edit: 12/28/2002 8:24:09 AM EDT by 7IDL]
It only jams/ftf after/durring the use of your reloads?

maybe a powder problem related to your reloads.

are your reloads properly resized? (ie: SB)

how about trim length?

are they neck sized?
Link Posted: 12/28/2002 8:16:48 AM EDT
If you are using a USED bolt in a new upper,
it may be a headspace issue.

Of course reloads just complicate the
Link Posted: 12/28/2002 9:58:40 AM EDT
The last time it would not chamber the first reload after using only twenty XM193 Federal rounds to sight in.  After cleaning again it would chamber the reloads.

I had been FL but not SB resizing for my 20" without a problem, but that was my first thought.  I have started SB sizing everything for my AR's now, but these were some of the "old" rounds loaded this past summer that I'm still shooting up.  Such a chore [:D]  

What really bothered me though was it not fully chambering the South African factory rounds that even work in my Fulton Armory match chamber upper.  That one has its own dedicated bolt and carrier, so the headspace issue is probably the next place to look.  

Bushmaster said a dedicated bolt wasn't necessary with their standard uppers, but it's probably a good idea in an upper you depend on to work every time.  I am thinking somebody decided to supply this upper with a match chamber since I specified a "fluted HBAR" and that it doesn't have the tolerance of the other Bushy.

Thanks for the replies!

Link Posted: 12/28/2002 11:35:46 AM EDT

You should be using a SB die, and make sure you have trimmed your cases. It's possible your chamber is a touch short in the throat.
Link Posted: 12/28/2002 12:22:04 PM EDT
Small base dies are seldom if ever needed in factory chambered rifles. It is only in tight chambered match rifles that small base dies are usually needed. Where the problem is is in the shoulder. In a gas gun the shoulder must be bumped back in order to function properly. Most reloaders do not know how to do this properly and unless you have a gauge, it is somewhat difficult to do. A RCBS Precision Mic is the way to go. It will tell you how to set up your die so as to size the brass enough, but not too much. Too little sizing and you have the problems you are having. Too much and case life is much shorter and having a premature case head seperation is increased. The AR is pretty versatile in its powder selection, so I really doubt that is the problem. Your current sizing die may more than likely be just fine, you just need to adjust the amount you bump back the shoulder.

Get the Mic, read the directions, set up your sizing die correctly and your problems should go away.
Link Posted: 12/29/2002 2:58:49 PM EDT
Thanks Rebel!

That sounds on point because the rounds that do chamber often have a smudge of sorts or bright ring in the shoulder area.  I'm still using the RCBS FL die and their instructions were to tighten until the shelholder seats against the die at the top of the press stroke and then 1/8 turn more to take out any slack.  

I'll check out the precision mic but I may need to get a shellholder set that allows the case to go further into the die.  It still bothers me that the first failure included not chambering the factory SA surplus that chambers OK in my match chambered gun.    
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