New Barrel "Settle In"

[Jetracer013]

I just finished building a new upper using a Wilson SS 1:9 16" lightweight barrel. I have taken it to the range twice now and have a concern about what I am seeing. I do want this to devolve into a argument about "break-in", because I did not do anything to break it in. I have fired 150rds now. and It seems as though the groups are shifting. I zeroed it at 50 then began shooting at 100. I shot a few 5 shot groups just to get data to zero for 100. After shooting several groups and getting a good zero, the groups began to drop. The next few groups settled around 2" lower than the previous groups. I am hoping that the barrel is "settling in" is this correct? or do I need to tear it down and check the barrel nut? Is it possible that the lightweight barrel is getting hot and deflecting?

I would appreciate input from anyone with experience.

Thanks,

ML

[co-exprs]

I'm no expert on building uppers, but in general I like to try simple solutions before trying complex ones. After 150rds, I'd hit the barrel with some JB compound and call the break in good. It's common for there to be some POI shift during the first few hundred rounds, so keep an eye on things during the next 100-200rds and if it doesn't settle in, then check the torque on the barrel nut. Personally, I don't see much POI shift during barrel heat up. I mean, there might be a little at distances of 400+ yds, but it isn't much and I gotta get the barrel hot enough to make holding the hand guard uncomfortable. Which isn't very often.

[Matt Cheely]

The face of the reciever may not be square. As the barrel heats up it grows and is now pushing your zero off. If you let it cool and the groups return to your initial zero you'll know if that could be the issue.

[caspian guy]

Also check your scope and mount.

Was the barrel a tight fit in the reciever or was there some play? (i have seen a really loose fit between the barrel extension and the upper exhibit this behavior). (Could probably exacerbate the issue matt mentioned above).

Is anything touching (or close to touching) under the float tube (gas block for instance)?

Edited August 24, 2012 by caspian guy