How common is heat warp in ARs and can you do anything about it?

Hellgate

Hellgate

Member
I have a brand new upper with a 16" HBAR spiral fluted SS nitrided 1:8 free floated barrel. It looks to be shooting 1 MOA which is what I want. However, when shooting the first 5 shot group on a cold barrel I noticed that the first round was the highest and the rest trailed down to 2" lower than the first shot. Confession: I did not note the exact order of the POIs but it was a fairly narrow vertical string the lowest round being 2" lower than the first. Subsequent groups with a warm barrel behaved well as I was working up loads (i.e. some larger than others varying with the powder charge) but without vertical stringing and obvious fliers. I want this gun to be my calling rifle. If it turns out that the groups descend 2"@100yds from cold to warm is there anything I can do to correct it? Am I relegated to 3 shot groups and a long period of cool down while working up loads? It's the first 3 shots that are most critical for me because after the first 3 shots the rest are Hail Mary's on a runner. The rifle has approximately 100 rounds through it.
 
Originally Posted By: Hellgate It looks to be shooting 1 MOA which is what I want. However, when shooting the first 5 shot group on a cold barrel I noticed that the first round was the highest and the rest trailed down to 2" lower than the first shot.

maybe i am missing something. but how is that moa?

honestly, i would not be one bit happy with that barrel if it was mine. first 3 shots or first 10 shots it better shoot better than what you just explained.

can it be corrected? need to know the cause first. i have had a few nitrated barrels. was never happy with any of them.

good luck.
 
Hellgate,

This is a very common phenomenon.

Here is a link to a fella who can explain this stuff much better than me.

https://www.youtube.com/watch?v=_KRUAv3Byp4&list=PLJUaiRIEduNXoal2_PkBZi0vDCIcEPxUn&index=40

Glen Zediker talks about this stuff in detail in many of his great books also.

I like to clean my guns, shoot them in the back yard a few times, clean the chamber and put them away as ready to go. Some rifles shoot great right out of cleaning though.

It depends on the barrel etc.
 
I don't think its a heat issue - especially if its doing it on the first 5 shots. There are a number of things that can cause vertical stringing. If you do a google search on vertical stringing, you'll find a fairly long list of potential causes. Some of those items will apply to the AR platform, and some will not. If you use those applicable items as a checklist for diagnostics, there's a good chance you'll find a cure. I'm no expert but, from my understanding, stringing could come from things like ammo selection/load development, barrel nut tension, or even the barrel itself. Start with the easy stuff, and I'm sure you'll figure out whats going on.
 
Not to drift the thread, but I need to confess that I called Aero Precision about a stringing problem with a new upper. Problem solved when I noticed the front of the one piece mount was attached to the rail on the hand guard. Slaps forehead.
 
Doesn't sound like a heat issue. If it were it wouldn't hold a group at all. I agree with a lot of what was in the video. I have worked with metal my whole career. A bullet is going to leave material behind and that's going to change the interface between the rifling and bullet.
Clean it good. Shoot it. Clean chamber. If accuracy changes, clean barrel and repeat.
 
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