Crap groups when barrel gets hot

[2hkusp]

I bought a BCM upper with the ELWF 14.5" barrel and an Aimpoint T1. Every time I've used it the barrel gets super hot after about 20 rounds and the groups open up from 1-2MOA to 10-12MOA. Attached a photo from today, shooting at 200yd target, holding same POA slowly firing each shot. I'm not this bad at shooting (I think) because I had my other AR today (LMT MRP 14.5") and was getting way tighter groups with a lot more rounds through it. Are lightweight barrels crap? Should I send back to BCM? Had a flash hider pinned/welded to the ELWF barrel too, so it's a sunk cost now.

IMG_4233.jpegIMG_4233.jpeg

[alx01]

Even a lightweight barrel should not do that. There is something wrong with one or more of the following:
- barrel
- pin and weld job (which might have caused some damage)
- barrel/rail install
- possibly a loose sights/mount
- ammo or barrel/ammo combination

In my experience lightweight barrels will lose accuracy/POI shift faster than a regular or a heavy barrel. I haven't done testing, but I imagine it would be after 60-120 very fast rounds (basically magdumps).
I don't think you would see a significant accuracy shift difference in a lightweight vs medium weight barrel if you're shooting a round every 1-2 seconds and in less than 90 rounds.

[Mike Miller]

If that's at 200 yards, I don't think those groups are 10-12 moa

[gaijin]

Have BCM look at their barrel.
I had a 300 BLK upper of theirs that was a 6 MOA+ barrel I sent back and they replaced it.

Shit happens, no one/nothing is infallible.

[ndmiller]

Looks like 1-2 MOA with 6 flyers.....Check Aimpoint mount, something could be loose.

[markm]

The bore diameter will open up with heat, and those barrels get hot quick. (they cool quick too). But at 200 yards, that looks like 4-5 MOA to me unless I'm nuts.

[Wake27]

Where is the target that you're basing 1-2 MOA off of? 200 yds with a red dot is not going to produce the tightest groups regardless of the barrel and a lot of other factors are coming into play.

[Clint]

Just talked to a customer the other day that mentioned a barrel from another mfg that had groups open up when hot.

That barrel was from a reputable mfg, but was also fluted.

[2hkusp]

Here's another photo from yesterday fromIMG_4231.jpeg shooting 30rnds in 5 minutes or so cold bore at the 200yd line. I've circled the initial grouping and it's tight when the barrel's cold.

Checked my scope mount, it's rock solid. No play in the rail. I'll take the gun out again and try grouping at 100yds today.

[TomMcC]

So, that target is 12" X 18"? And you're using a 4 moa dot T1? If so, that 4 moa dot is now 8 moa at 200 yds. Your group looks to be maybe 7" X 10". So I would ask, are you immobilizing the gun on a bench? Are you used to whatever trigger you are using? Will the gun actually shoot 1-2 moa cold at a 100 yds with that ammo? Are you being very careful with your dot placement at 200 yds...are you consistent in it's placement?