Bullet walk with brand new barrel.

[nwolf]

I just picked up a new upper at the KC gun show yesterday. It has a 24" black rain mediem contour barrel 1-8 twist .223, free float, dpms slick side reciever. I shot a few different loads through it yesterday and found it to shoot 40gr sierra varminters the best. My problem is that it walks down as it warms up, by that I mean after the first shot. If I fire two shots within 30 seconds, the 2nd shot will hit 2" low. If I fire a third, that one will hit lower still. After a few minutes of sitting, the poi will go back up. Shot group if I take my time is 3/8 wide, 1 1/2 tall.
Anybody ever seen a barrel walk after one shot?

 

[msalm]

Either there's an incredible amount of residual stress in the barrel steel OR my intuition would say the gas tube might be a tad too long and is bottoming out in the carrier key. Since the gas tube heats up instantly, it would lengthen a bit and if it is touching the bottom of the key, the carrier would be putting pressure on the tube and essentially pushing it forward from above, which would cam the barrel downward....just a hunch though. Otherwise I have had barrels walk as they heated up, but not after one round. That said, a cryo treatment solved the problem in those cases.

 

[woodnut]

nwolf, better listen to msalm! He KNOWS ARs. You might want to email him or PM a note to him. If anyone can help, Matt can.

 

[lamiglas]

Could it just be the bullet is to light/ short for your twist? Just throwing it out there

 

[msalm]

OK, one more thought, is your barrel nut tight??? Hold the upper receiver tight in one hand and try and twist/torque the barrel with the other. If there is any movement at all, your barrel is loose.