Range Report Overbore and keeping barrel cool

[Hawk45]

Looking for a new cartridge to do some longer range shooting (past 1200yds). Currently my .308 is my most potent round (I relaod). I'm trying to stay away from Magnums if I can (contrary to my original plan).

I've been thinking maybe .243, but all the factory offerings only have twists to shoot up to 105's at best. If I could shoot 115s I'd probably be all over it.

I also been thinking .260 w/ 139s and maybe a 30/06 w/ 208s.

Anyway, my questions are:
1. What is the least overbored LR (1200 - 1500yds) cartridge you'd recommend?
Edit: Found this which is pretty cool -
http://bulletin.accurateshooter.com/2011/04/overbore-cartridges-a-working-definition/

2. What is the proper definition of "keeping your barrel cool" or "over heating your barrel" for extended life? Since I've never had a "burner" round before I want to understand better.

Is it too hot to the touch? Or is even just warm to the hand too hot? Does length of strings matter if you keep the barrel at a lower temp? Is 50rds in 5rd strings over an hour too much? I've never shot fast enough to get the barrel of my .308 hotter than maybe warm to the touch, so never really thought about before.

 

[redbullitt]

Re: Overbore and keeping barrel cool

Barrels are disposable really, just like nice Lapua brass lol.

I like the 260 (with 140 amax and 142 smk) a lot. I havent done any long long range shooting with it, but lots of people have had good experience with it. Barrel life is markedly better than 243 supposedly. The 260 is much much easier to shoot the the 308 or 3006. Great ballistics, less recoil.

As far as barrel heat, I will usually shoot 5 or 6 shots at separate targets, then relax a bit. Barrel does not get too hot. As long as it does not feel too hot to my hand I dont really sweat it at all, especially on the 308. I don't shoot 20 round strings or anything like that though.

It seems like the 260 does heat up quicker than the 308. Both barrels of mine are similar contours.

 

[Greg Langelius *]

Re: Overbore and keeping barrel cool

The .260 Rem is a capable, adequate LR chambering; but it loses some performance ground to overbore chamberings like the 6.5-284.

I am coming around to an enhanced degree of respect for the .280 Rem (AKA 7mm Remington Express) as an LR chambering.

There's a somewhat complex tradeoff, but the keys to improved barrel heat dissipation are a larger barrel surface area, and enhanced barrel thermal conductivity. Steel is an excellent structural medium, but it sucks at heat transmission.

A more ideal approach is an aluminum jacketed barrel, which can conduct more heat to the surface in less time.

To my knowledge, only one barrel maker offers such a barrel, Lothar-Walther. It's not cheap, being a pair of nested barrels, and the price is proportionately more. But for barrel blistering chamberings, I consider it to be the only truly viable solution.

Greg

 

[DAVETOOLEY]

Re: Overbore and keeping barrel cool

You might consider the often ignored 7MM Rem Mag. They come with the twist to handle 168-180 gr. bullets.

 

[RobertB]

Re: Overbore and keeping barrel cool

.260 Fo Sho

 

[Greg Langelius *]

Re: Overbore and keeping barrel cool

The 7mm mag and 280 Rem come with the same rifling twist rate, and the 280's chamber/bore ratio would fall somewhere between the .30-'06 and the .25-'06 on that chart.

For comparison, my (not-LR) Match chambering is .30BR, and my C/F trainer/plinker is 7.62x39, which has an even lower expansion ratio than any cartridge on that list.

Greg