Barrel Temperature and Accuracy?

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physikal

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My buddies and I were having a debate all day today about barrel heat. I have a pretty nice custom Rem 700 in .308 with a bull barrel and all that.

We shot probably 20+ rounds through it in about 10-15 minutes at targets ranging from 130yrds to 320 yrds. We made no adjustments to the scope to hit the targets. We started with a tannerite target at 130 yards and ended with one at 130 yards, dead on every time.

I for one don't believe the barrel accuracy is effected enough to worry about it, MAYBE when shooting out 1000+ yards, but I dunno.

Does anyone know of some well documented testing to prove this theory/myth true? If so could you please provide links. Thanks so much!
 
Well, the bull barrel is certainly going to help. Try that with a sporter barrel and I think you'll see some interesting things going on.
 
i too have the heavy barrel on my .308. shooting about 10 shots quickly, i do not see a change in accuracy. i do however see the barrels heat signature through my scope. ( the heat waves)
 
Heat affects the barrel in as much it allows it to swell and make contact with the stock. When you change the contact it changes the way the bullet comes out of the barrel.

Think of the barrel as a water hose. As the water comes out the hose flops around. If you put something in contact with the hose, it will change the direction the water comes out.

If the barrel is not allowed to come in contact with the stock (do to swelling) then it shouldn't change the impact.

What matters more is the temperature of the ammo itself. As an average, every 15 degrees of temp changes the impact 1 MOA. Lets say your chamber and barrel are hot from firing several rounds inside a minute. If the round is taken from the shade and put in the gun and fired instantly it doesn't have the opportunity to heat up, therefore shouldn't change impact. (free floating the barrel).

However, you stick the same round in chamber and let it set before shooting, the round heats up............same thing, every 15 degrees changes the impact 1 MOA. Trouble is you don't know the temp of the round so you can't make adjustments.

If you were to go to the firing line and watch competitors fire a 600 or 1000 yard match, you'll notice they don't chamber a round until the instant before they shoot. You'll see some, inexperienced shooters chamber a round and wait until the target comes up, then check the wind, and shoot.

If you compare the targets you'll see those who chamber the round and wait, have vertical groups, those who wait until they are ready to shoot don't.
 
Is this something noticeable at 100-300 yards as well? Or is it mostly when shooting 600+ yards out?

Also, does it make a difference on how the stock is mounted? I have a "free floating barrel" but I noticed that the space between the barrel and the stock on the left is a bit larger of a gap than on the right, the tip of the stock almost touches the barrel on the right. (I think the stock is somewhat bent?)

Thanks!
 
Yes its something you notice at 100 as well as 1000. MOA being MOA.

As to gap bigger on one side then the other, it doesn't matter the size of the gap as long as the stock isn't contacting the barrel.

Thinking about this, something else you have to look at is "is the action moving around in the stock? How's your betting?
 
Depends on the gun and the barrel. A heavier, thicker barrrel is stiffer and takes more shots to get it hot enough to matter. Thinner, hunting barrels are meant to be carried and only shot 1-3 times at most in a hunting situation.

I used to own a Remington Mt rifle with the pencil thin barrel. Shots #1 and #2 from a cold barrel were always dead on and usually touching. A 3rd shot would always open up the group to at least 1", usually a bit more. The few times I ever tried a 5 shot group with that rifle shots #4 and #5 would open up the groups to 2 or 3 inches.

That never concerned me, because I knew I'd never use that rifle for more than 2-3 shots at a time.
 
Kriagwy, your explanation makes sense. But does heat change the harmonics especially with a "sport" barrel. I notice my Rem 700 in .223 start to string vertically after 10-15 shots when shooting prairie dogs, confirmed when shooting 10 shot groups back to back. It has the factory stock with the built in barrel contact Remington uses near the tip of the fore end. Do you think the vertical climbing group is caused by the expanding barrel creating more pressure against the barrel rather than change in barrel harmonics? Guess I could free float it and see what happens then.
 
First let me say: there is no such thing as "always" in shooting. Some guns don't need to be free floated at all, I have a Rem 700 BDL in 223 I used as a LE counter sniper rifle. It doesn't change and I don't recall ever taking it out of the stock. Granted its a heavy barrel.

I have two Winchester Feather Weights (Pencil barrels) that will walk after 5-7 rounds but its a hunting rifle so it don't matter.

However, I took one of the actions (don't remember if it was the 257 or 270) out of the stock and put it in the stock of my Model 70 1000 yard gun. The action set in the glass, but the barrel didn't come close to touching the stock.

I fired 5 rounds as fast as I could to get it to seat in the stock then fired 20 rounds and it didn't walk with it got warm.

They say if you can get the barrel free floated you'll have a better chance of it not walking. Some say get it to the point where you can slide a dollar from the front to the action would be good enough. I double the dollar just to be safe.

I like heavy barrels on target rifles because it dampens the movement caused by my heart and such. I like light barrels on hunting rifles because I'm wimpy and too lazy to pack a heavy rifle.
 
Barrel harmonics is simply defined as the flexing or whipping of the barrel when the rifle is fired.

The critical objective is to have the barrel do this the same way, every time it is fired. This is best defined as consistency- and consistency, translates directly to accuracy.

When the barrel "whips" around, the muzzle is going to be at a certain point in space when the bullet exits. You want this "release point" to be the same. If it is, the point of impact will be identical if all other factors are the same.

Long, and thin, barrels "whip" more easily than thicker, shorter barrels.
Heavier, "bull" or "varmint" contours take longer to heat up(which changes the harmonics), and whip less for obvious reasons. They're generally more consistent when hot.

Harmonics are a subtle thing, just like some rifles shoot everything well, and others are picky as hell about what they like.

More importantly, as mentioned above, the receiver MUST be properly bedded with action pillars to eliminate movement of the receiver under recoil. This goes to what I said above about the muzzle being at the same point in space when the bullet exits...if the receiver has moved from a prior shot and is resting in a slightly different position that the shot before, guess what happens?
 
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