I have an Olympic Arms AR15 with a 16" stainless heavy barrel.  Gun is usually a real tack driver (.75 MOA).  However, it seems that as the barrel heats up, my rounds start drifting to the right.  We're not talking full auto, 300 rounds in 2 minutes here.   Basically, if I shoot 20 rounds in under 5 minutes, the last 5-6 rounds seem to start pulling right, usually about 1-2 inches at 100 yards.  Is this common?  I assume its the gun, but maybe it's me and I'm starting to flinch a little or lose concentration.  (This is shooting prone).

Just wondering what others experience is.

The barrel heat isn't a factor. Chamber heat is. If the round sits in a hot chamber it will heat up. It will subsequently burn faster during ignition and combustion, leading to higher chamber pressures. This will in turn give you an increase in velocity.

Watch guys shooting LD and ULD. They will sit with the bolt open, round half or less into the chamber, so that the heat escapes past the round and not into it.

20 degrees of air temp is good for a minute of angle differemce. Imagine what the difference is for a really hot chamber.

I vote you


I've never noticed any drift, even with much hotter barrels.

tha air temp effect on a round has more to do with the density of thair than anything... if you can recreate what the gun is doing -- and have someone else experience the same thing, I would suggest that the barrel was not properly stress relieved.

Barrels are a funny beast... but if you are getting that much drift, with that little heat, I would hit up whoever made the barrel and ask them to relace it.

Well, looks like the majority thinks its me, which is definitely possible.  I guess it's always easier to blame the equipment.  What I really should do is experiment a little more.  Try shooting the rifle off a bench.  Load up a 30 round mag, and try to empty it in 3-4 minutes.  Try shooting 30 rounds, letting the barrel cool off for 10-15 minutes and then shooting another 30 rounds.

In any case, it's a great excuse to have some fun at the range.