Cold versus Hot Barrel Accuracy

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Thread: Cold versus Hot Barrel Accuracy

  1. #1
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    Cold versus Hot Barrel Accuracy

    Shooting my FN SCAR 17 - I've noticed that when I go to the range (after having sighted in my holographic sight with 3x scope combo awhile back) it seems to shoot larger groups until about 10 shots in. So it seems to group about 3 inches at 50 yards until the barrel warms up. After this I can hit bullseye 95% of the time. I chose 50 yards because I can see the target better with 3x and won't have to worry about too many outliars with a longer distance when "testing" things.

    I am using the same ammo the whole time and every time. I do not mess with the sight at all during the "testing".

    Is this me personally getting "warmed" up when I go to the range or is there proof that this gun shoots better hot?

    It bothers me knowing I might go deer or hog hunting with a very cold barrel and less accurate. Thanks as always FN Forum!
    Last edited by kalebk11; 06-16-2012 at 11:34 AM.


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    Senior Member HC015***'s Avatar
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    A barrel will open up as it gets hotter, but only after a certain temperature is reached and that takes more than 10-20 rounds. Personally, I have experienced the barrel opening up my groups when it gets hot, but then again I shoot anywhere from 250-500 each range trip. I can hit the bullseye at 50 yards every time, but when I shoot at 100 it seems to open up a bit, especially towards the end of the mag. I shoot a lot of silver and brown bear, as well as federal gold medal match when I can afford it. I experience 2 to 5 inch groups with the russian, and 1 to 2 inch groups with the FGMM. Possibly shooter error? Try keeping your POA steady and don't lose your sight picture. Hold that weapon tight to your chest, aim, and squeeze that trigger. That seems to help me when I was all over the target.

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    My SCAR shoots best when the barrel is cold (where it can shoot sub MOA). Once the barrel gets really hot, the grouping opens up for me, to something like 3 MOA (and it seems to shift a bit too, though I have to shoot it more to be certain). At the range I usually let the barrel cool when that happens and shoot my other guns. It seems odd that you're experiencing the opposite.

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    Senior Member Ferris2son's Avatar
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    Quote Originally Posted by Extra411 View Post
    My SCAR shoots best when the barrel is cold (where it can shoot sub MOA). Once the barrel gets really hot, the grouping opens up for me, to something like 3 MOA (and it seems to shift a bit too, though I have to shoot it more to be certain). At the range I usually let the barrel cool when that happens and shoot my other guns. It seems odd that you're experiencing the opposite.
    What he said.

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    Senior Member blueiron's Avatar
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    Every barrel is a law unto itself. Cartridges play a part as well. I have seen the rare rifle that shoots tighter as they heat up.

    Usually, a barrel's accuracy is measured from the initial shot through the third or fifth round. Most battle rifles are known for shifting points of impact as the round count increases.

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    Senior Member cetane's Avatar
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    You are just getting settled in nice when your groups tighten up. The cold barrel, first shot is without a doubt the most accurate a barrel can be. Your just getting better and better every round you shoot.

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    Of course I am compensating for something.... If I could kill something at 300 meters with my c*ck I would not need a gun!

    Originally Posted by Clyde
    and then they get to enjoy trying to ride the concussion wave....
    and start peppering them mercilessly with flying hot brass
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    As others have said, depends upon the number or rounds and speed at which you shoot. For accuracy purposes, I don't start testing loads until I put at least five rounds down the tube. This gets rid of any cleaning solvents or lubrication remaining in the bore that can change POI. My 17 is easily capable of 3/4 MOA or better with loads it likes. Once it gets past about 40 rounds or so and heats up, POI changes just a bit, but nothing major. If changing loads (powder type), I always let the rifle cool down and put a couple wet patches down the barrel followed by a dry one. Then shoot five rounds with the new load just as before. Sounds silly but I have seen this happen. Change powder or ammo, it coats the barrel with a slightly different residue. Any inconsistency down the bore in that coating can produce slight shot to shot velocity variances until it works itself out. This will not manifest itself at 100 yards. It can at longer ranges. If testing cold bore, I just run a single dry patch down the bore prior to going to the range with no cleaning after the previous outing.
    Last edited by 10auto; 06-16-2012 at 10:55 PM.
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    Group anomalies aren't unusual in piston guns as barrel heat increases to the threshold of not being able to rest bare fingers on the barrel. The amount of variable increases with the amount of heat, not only due to material expansion but the duration of time the cartridge sits in the heated chamber before being fired.

    -SS
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    To add to what SS said above, a case study regarding how sensitive ammunition is to heat -- especially at longer ranges. Used to do quite a bit of long range competition a while back at 1000 yards, bolt guns -- 300 WinMag match rifle in this scenario. On the average Summer day, we would keep our ammo in a small thermos cooler (just in the box, no ice, etc.) when not on the line. When it was time to shoot, we had a towel right next to the rifle and would drape a corner of it over the cartridges we were about to use in order to keep them out of the sun. Only when the live string started would we uncover them. A cartridge sitting in direct sunlight for a couple minutes would throw a foot of vertical (out of the main group) into the shot at 1000 yards. If there was an obvious condition change that I decided to wait out (600 yard flag went nuts all of a sudden after previous shots), I would immediately bring the round back out of the chamber so it didn't cook. Even mild heat from sun exposure over just a couple minutes was enough to introduce a very slight increase in pressure. But at long range, this translates abruptly on paper. Imagine a very hot chamber in a SCAR and a round sitting in there for several seconds.... it will change point of impact in a margin reflecting how far the shot has traveled.
    Last edited by 10auto; 06-16-2012 at 11:41 PM.
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    Senior Member HC015***'s Avatar
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    I remember the man with the longest recorded sniper kill said he referred to an "old sniper trick" where he would leave his ammo out in the sun and that would make the bullets fly farther. He was able to hit the guy way out there no problem, not exactly sure what science is going on here but I'm sure hotter bullets are better on paper than a bullet sitting in a very hot chamber. I assume the powder burns more evenly or faster? He did mention that he was using American made ammo which did act differently in the air, and they realized by leaving the ammo out in the sun it did help the trajectory or flight path if you will of the bullet to the target.

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