hot or cold barrel


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zamboxl
December 24, 2006, 04:46 AM
Hey guys when sighting in a rifle is there a huge diference between hot, and cold barrel? If i sight the rifle with a hot barrel, will there be a big diference when let's say i go huting and the barrel is cold? will it trow my shot off by alot?

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kd7nqb
December 24, 2006, 04:54 AM
This is my two shots, I know when police snipers check the zero on their rifle they take a "cold barrell shot" and only retest it after it has cooled. Dont know how much difference it makes.

Ifishsum
December 24, 2006, 05:07 AM
I zero to a cold barrel because it's the first shot that counts in a hunting situation. With some rifles it will make a significant difference, and with some it may not, but zero your rifle for the most likely circumstance you'll encounter with that first shot, which is almost always a cold barrel.

Another consideration is the clean barrel - some rifles throw off the first shot by 2+ inches after they've been well cleaned, so once I've sighted in for the season I don't clean the barrel until after the hunt.

Jenrick
December 24, 2006, 05:40 AM
A lot is weapon and cartridge specific. My AR-180B (not something I would recomend as a hunting rifle normaly) shoots dead on (call it about 1MOA) for it's cold barrel shot. After that it opens up to about 6" at 100yds if I really let it heat up. Cool it all the way down, back on POA/POI.

Buddies Rem 700 shoots pretty much POA/POI cold or hot (though he can't rapid fire a 30 rd mag to really heat it up either).

YMMV. Test YOUR rifle and round to be sure.

-Jenrick

rangerruck
December 24, 2006, 06:04 AM
if it is a good made rifle, it shouldn't , but it proly will, the less the better.

zamboxl
December 24, 2006, 07:08 AM
o i forgot to add this is an old mn 91/30, it's in decent shape but it is far from a tack driver.

Grumulkin
December 24, 2006, 07:32 AM
It is important to know where the gun shoots on the first shot but, if I had a gun with widely varying impact points between cold and hot, I would be trying to find out what is wrong with it. Various things can cause this including improper bedding or a barrel that hasn't been properly stress relieved.

Cleaning can make a big difference if you leave a coating of oil in the bore. If you remove the oil before you shoot with solvent, this difference will probably go away.

dispatch55126
December 24, 2006, 12:12 PM
If you want to know the differance between a hot and cold barrel, shoot a Mini 30 at 50 yds. The first shot with an ambient temp barrel is/was dead on every time. The next 2 shots would have about a 1" rise and the 3rd shot on would hit approx 3" above first shot. There's nothing wrong with it, just a hot barrel allows for more flex when fired. High speed cameras show that barrels flex like an arrow when fired and they become more elastic as the barrel heats up.


BTW, to quell any accuracy arguments on the Mini 30, IT IS NOT MEANT TO BE A LONG RANGE TACK DRIVER! Its a semi auto that was designed for central/south american police where volume rules over accuracy.

Jim Watson
December 24, 2006, 01:11 PM
I doubt you could tell much difference with a surplus rifle in the woods.

But why not shoot the gun and find out?

And just to inject another variable that matters to hunters and snipers; where does your rifle shoot cold and clean, cold and fouled, warm and fouled? It takes a lot of work to get a real deal cold clean zero. Some people dodge the question by shooting slowly to get a cold fouled zero, clean the gun, and then fire a couple of fouling shots. Put it away with a little soot in the barrel so it will be predictable when needed. Of course that needs checking periodically to see if the fouling ages, doesn't it?

A target shooter will KNOW and either disregard his first sighter shot or know how much difference there is and allow for it so as to get started adjusting for the day's conditions.

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