Barrel Heating Affecting Accuracy?

[chp5]

Barrel heating affecting accuracy?

I shoot two different AR uppers in competition. The first one is a 20” Colt A1 “Pencil Barrel,” 1/12. The second one is a Bushmaster 20” Government profile barrel that my smith cut to 17”, 1/9. Both are lightweight barrels.

I don’t notice any stringing out of the barrels at long range when practicing. However, some shooters believe that even <20 rapid fire rounds will heat the barrel enough to adversely affect accuracy.

For example, Stage 11 at Ft. Benning had an array of 8-9 cardboard targets that were approximately 1-30 yards away, then 6 six-inch plates that ranged from 100-160 yards roughly.

IMO, the best way to shoot it was to shoot the paper offhand, standing, then drop to a knee and shoot the steel. I saw many shooters drop to a knee and shoot the steel first. When asked, each shooter stated that he wanted to shoot the longer-range steel first – before the barrel heated up.

Two questions:

1. What is your opinion?

2. If heating is an issue, will it more readily affect my two lightweight barrels?

[milanuk]

Hmm... here's some thoughts from a HP shooter... during the 'Rapid' Fire stages of an 80rd RMC, we shoot two sighters, slow fire, in two minutes either Sitting @ 200, or Prone @ 300yds. Then when the real fun begins we drop from Standing to position (Sitting or Prone) and fire 10 shots in 60 seconds (70 seconds for 300yd Prone), including getting situated, and mandatory magazine change. Then they score the targets, we stand, and do it again. So about 22 rds down range in probably less than 5 minutes. The X-ring is 3" in diameter, the 10 ring is 7" for both distances. For the really good shooters, scores of 100 with very high X counts are not uncommon... with standard A2 iron sights (some of these guys can shoot sub-MOA groups w/ irons)

If you've got noticeable change of point of impact due to barrel heating... and I mean you've really, no-kidding explored it and proven it to yourself... I'd almost say get your gun looked at, or get a heavier barrel. I'd imagine you guys are probably putting a lot more rounds down range in a shorter period of time, but w/ a Service Rifle HBAR contour (full 1+" behind the front sight, 0.750" out front) I'd be pretty surprised if you still saw enough 'drift' to be meaningful.

YMMV,

Monte

[kurtm]

On stage 11 I droped into a reverse kneeling while racking the rifle and shot the steel from right to left. I didn't do it that way because of the barrel heat, I did it that way because after the steel was hit the first set of targets was indexed on the left requiering just a slight depression of the barrel to engage, no swing neccessary, also it is much faster to shoot doubles accurately while in a nice braced position. I was 3rd on this stage in tactcal being beat only by Taran and my brother....but I shot it with iron I have never seen barrel heat to cause measurable accuracy problems for the targets we shoot at! KURTM

[George]

Agreed with Kurt. Barrel heat from 30+ fast rounds causing enough POI change to effect hitting steel targets at under 400 meters, hahahaha! ROTFLMAO

You need to get a new bbl if that happens to your rifle. No barrel should warp that much or it belongs out in back with the beer cans ;-)

[TommiF]

I made barrelheattest year ago. I have DPMS Bull-3 barrel what has been in transportation accident. It's bended, when in lathe, I measeured 0,3mm bending in middle of barrel. Also one gunsmith looked thru it and easily saw bending also inside the barrel. Couse the barrel was bended after finishing, I wanted to know, if it reacts to temperature changes and makes movement in POI. So I went to range, it was some degrees below zero(Celsius) and I shot with freezing barrel one five shot group. Ammo was 69SMK, what runs 40mm/200m. Then I shot 30 rounds fastfire and another five shot group with SMK. Movement of POI of those SMK groups was about 30mm to 200 meters and groupsize were similar. I don't worry about that. Actually, when I know little that movement of POI is,there is one thing less to worry

Tommi

Edited December 19, 2005 by TommiF

[Paule]

There are conditions that will cause stringing, and in a hurry. Primary cause is when the outer contour of the barrel is not concentric with the bore. This happens when they are turned too aggressively and without proper journaling. When one side of the barrel is thicker than the other, stringing is inevitable. How much depends on how small the contour gets and how much heat is applied.

I've seen and shot barrels that would put five into 2" at 300 yards but the next five needed a garbage can lid to cover them top to bottom. Relatively heavier contours like service rifle and HBars are much less susceptible to this. Lighter contours require much more care during contouring to avoid these problems.

[jm951]

At Ft. Benning, I shot steel first because I find that it's easier to speed up my cadence than slow it down. The thought was small targets first, big fast targets last. Also shot it from right to left for the same reason Kurt did, only an elevation change was necessary to make the transition.

Even so, if you shot the cardboard first, that shouldn't have heated your barrel up enough to cause stringing unless there is a structural problem like concentricity, mentioned earlier. If your barrel isn't concentric, it about doesn't matter what you do, past a couple of rounds, it will have problems.

[chp5]

There are conditions that will cause stringing, and in a hurry. Primary cause is when the outer contour of the barrel is not concentric with the bore. This happens when they are turned too aggressively and without proper journaling. When one side of the barrel is thicker than the other, stringing is inevitable. How much depends on how small the contour gets and how much heat is applied.

I've seen and shot barrels that would put five into 2" at 300 yards but the next five needed a garbage can lid to cover them top to bottom. Relatively heavier contours like service rifle and HBars are much less susceptible to this. Lighter contours require much more care during contouring to avoid these problems.

Paul,

Have you seen such problems with factory barrels (specifically Colt and BM)? Is this only a problem with re-contoured barrels? Thanks.