Barrel weight, what's the actual effect on accuracy.

[Ringer]

So I understand that a heavier barrel won't heat up as fast and that a heated barrel can/will effect the gun's accuracy. My questions are; how much, how fast and in what way?

Does it cause your groups to get larger? Does it cause your groups to move around moreso than get larger? Both? If you are firing from a bench where you are repositioning after each shot, so not rapid fire by any means, how many shots until you notice this impact? A couple? 5 or so? At a 100 yards are we talking an inch? More, less?

Any feedback in general appreciated.

 

[ZombiesAhead]

1. To answer quantitative questions, we need specs on the rifle/ammo/barrel weight/length/etc
2. probably
3. yes
4. yes
5. probably never if you go slow with a normal rifle
6. more
7. more
8. depends how accurate the rifle is, need more specs to quantify

Seriously, though, do you have a specific platform in mind? There's a good thread going right now in this very forum on AR-15 heavy vs. standard barrels.

One platform that people seem to really notice this is the Mini-14.

 

[Zak Smith]

I can shoot the match grade barrels on my bolt guns until they are too hot to touch. Accuracy and zero do not change.

It all depends on the rifle and the barrel.

 

[rockstar.esq]

As I understand it, the effect of heating is due to the barrel warping. I have seen situations where having it free floating did wonders so my guess is that it warps enough to contact the stock. Bear in mind that some cartridges seem to be fire breathers whereas others are relatively tame. A fine example of the fire breathing lot would be the 7.62x54R milsurp ammo. That stuff gets a gun blistering hot in five shots in ten seconds. In comparison, a .22 LR rifle barely warms from the same regimen. The added mass of a heavy barrel does slow the heating but bear in mind that it doesn't cool faster than a thin one.

My anecdotal experience has shown that groups open up with my Mosin Nagant to roughly double when the bore is hot. There doesn't seem to be much rhyme or reason to where the shots get dispersed. Slowing the shooting to five shots over fifteen seconds seems to help considerably (3"-4" average).

In comparison, my heavy barreled .308 will place five shots in ten seconds into less than an inch when I start with a cold bore. Admittedly, I try not to heat the barrel up since I'm after precision not speed. That being said, when I've run the bolt as fast as I can, the group size seems more influenced by me rushing than anything else. My guess is that the semi-auto folks have more insights into this. I can say that AR's seem far less likely to open up as a Mini-14 due to heat. There again, I think there's a strong argument towards thinking the stock is getting struck by the barrel.

 

[GarandOwner]

There are more reasons that just heat dissipation as to why a heavy barrel are inherently more accurate than standard barrels. But I will just address your questions:

1 Does it cause your groups to get larger?
How much - at the same temperature the size of the groups should not differ much from that of a cold barrel, the difference is the time in which it takes for the barrel to get to the same temperature. The heavy barrel will open up less due to the fact that it maintains its rigidity better when it heats since it takes more force to warp.

How fast - This depends on the size of the barrels you are comparing. a simple comparison would be a heavy barrel that is twice the size of a standard barrel. It would take twice as long to heat up to the same temperature. This is because since it has twice the mass it requires twice the amount of heat energy to change its temperature.

2. Does it cause your groups to move around moreso than get larger?

The answer is both, groups will move around a bit and get larger as the barrel expands.

3 If you are firing from a bench where you are repositioning after each shot, how many shots until you notice an impact?

If you are slow firing, especially at 100 yards you prob will not notice a difference in accuracy. This depends on how well you shoot the gun more than heat effects. What matters is the time between shots, if you take 2 minutes between each shot, than the barrel will take longer to heat up, so you will not notice a difference as fast. Once again it will take twice as long with the heavy barrel. However in the same respect, once a heavy barrel heats up, it will take twice as long to cool down.

 

[Ringer]

I'm talking bolt action rifle. Particularly the CZ 550 American in .308. It's a 7lb gun with about a 24" barrel. I'm not out to win any target shooting competitions. I am also talking about it taking say two minutes to get off 5 shots, not 10 or 15 seconds. For a multi purpose rifle I don't want any extra weight, but was just curious what the effect would be when punching paper.

Thanks for the replies!

 

[RugerOldArmy]

FWIW, heavier barrels had less change as they heat for me than pencil barrels.

In terms of the .308 / CZ-550, I can't speak for the American, but this is what the .308 550 Varmint did in my very first batch of .308 reloads for it. Shoots better than I can.

 

[rangerruck]

yes, basically , on all the above. now if you take a full 30 seconds between shots, you can keep sporter bbls, nice and tight groups; I do with my cz 527.
But my bull bbls, i can do a rapid fire session, and the groups will not open up.
thats a full 30 seconds, and then I start to settle in for the next shot. I keep the action open, and no cart in the chamber, for the bull 30 seconds.
The cz 550, will be an excellent choice.

 

[Anteater1717]

A fine example of the fire breathing lot would be the 7.62x54R milsurp ammo. That stuff gets a gun blistering hot in five shots in ten seconds.

Wierd I've had the complete opposite experience, it takes about 50rnds out of my Mosin (firing quickley) to get it hot.