the troubleshooting forum?  I got a doozy and I guess there is no other place to put it.

OK, I have some other posts about this sort of, but this is the main one after two days of experimentation.

Problem - AR carbine that goes into burst mode.  Only three times but that is enough.

Equipment -
Rifle 1 (the one with burst problem) is a frankengun.  Wilson 16" bull barrel, freefloat handguards. FN upper flattop, ASA bolt, bushy lower built with bushy parts, RRA NM trigger, buttstock & plunger/spring from SP1.

Rifle 2 is a spacegun 20" douglas barrel, freefloat, flattop, ASA lower and buttstock, Jewell trigger, NM bolt.

The problem started when I was breaking in Rifle 1.  I was shooting Federal Eagle ammo.  The rifle had two occasions where it burst about 3-4 rounds.  While bursting I could feel the trigger pulse with each shot fired.  I also fired Q3131A ammo and never had a burst.

Returned to the range a second time, and again, with Federal Eagle ammo it burst once in about 20 rounds.  Never again with Q3131A.

Soooo, I thought I would experiment.  I swapped lowers with Rifle 2.  Expecting that the problem was related to the trigger I tried shooting the Spacegun upper on the frankengun lower.  Except it would not cycle.  Short stroking.  I can only assume that the different tension in the buffer springs prevented a full cycle.  However, the Spacegun (which shot fine once reassembled) only eats Federal Match ammo.  So I don't know if it would have been a valid test.

At this point I was out of Federal Eagle ammo, and never had a burst again.

The conclusion I have (???) is that the carbine has a powerful buffer spring (can't cycle in spacegun) and that it is slamming the bolt back hard - into fairly soft Federal primers and the firing pin is actually extending when it closes to battery.

If this seems a valid conclusion, does anyone have any suggestions for fixing this?  I don't want to worry about which ammo I use in this gun so would prefer an answer other than "don't use Federal Eagle".

Thanks all.

James
 

That would'nt happen to be the gun that got thrown across the counter would it?[:)]

Garandshooter,

Thanks for the tips.  I am taking it to my gunsmith for a checkup.

CIB,

No.  Well, parts of it are.  Maybe the parts have a long memory???  :)

James