.308 or .338?

[cysoto]

When this project is complete it will primarily be used for shooting steel from 200 to 500 meters.

Out to 500 meters? Between those two calibers, .308, hands down.

[Tim K]

If you ever had a desire to shoot in a competition, that 200g bullet will exceed the maximum allowed at some venues.

Personally, I'd go .260 Rem. Significantly better than .308 at long range, low recoil, less expensive (a tiny bit) to load. Since it's .308 based, I assume it should run in the AR-10.

It's on my list of toys to want.

[cysoto]

... I assume it should run in the AR-10.

It does but, in order to make it fit the magazine, you need to load the rounds to a short OAL which will increase the cartridge pressure.

[Gunner]

308 hands down.

The 338 Federal cant push any decent 338 bullets fast enough. Past a few hundred yards it would be like lobbing in artillery shells.

See this is whee the debate stops. Hoser chimed in and he knows what he is talking about.

[C Ward]

338 Fed is dying a slow uneventful death like all the other rounds that didn't catch the publics fancy .

This really is a no brainer , the bullet selection available in 30 cal is leaps and bounds better in 338 . Shooting to distance is all about BC and to get a good BC in 338 you got to go to a 250 grain projectile and the 338 Fed doesn't have the case capacity to take advantage of it .

This will be even more the case if this is an AR10 based rifle and being limited to mag length . AR10's are finicky bastards in 308 let alone other cartridges that it wasn't designed for . The further you stray from 308 and the powders associated with it the worse it gets .

[MarkCO]

See this is whee the debate stops. Hoser chimed in and he knows what he is talking about.

Should have been. .308 over .338 is good advice.

The .260 is a perfectly fine cartridge for the AR-10 platform and factory ammo does a very solid job. The 7mm-08 is also a consideration.

Of the .308 family, .243, .260, 7mm-08, .308 and .338 Federal, I might put the .338 ahead of the .243. Then between .260, 7mm-08 and .308, it is kind of preference if you toss out the prevalence and cost of factory ammo benefitting the .308.

[Delfuego]

I believe you are thinking of the wrong .338.

You know I am! I was thinking 338 Lapua! Not Federal. I thought you were gonna buy and build Glenski's 338 lapua stuff

308 hands down.

The 338 Federal cant push any decent 338 bullets fast enough. Past a few hundred yards it would be like lobbing in artillery shells.

I have had to opportunity to shoot, sight-in and play around with a 338 AR-10. The bullet drop at 600y was considerable; way, way more than 223 or 308.

[Tim K]

It does but, in order to make it fit the magazine, you need to load the rounds to a short OAL which will increase the cartridge pressure.

With 123g SMK's, you can easily load to 2.800" without pressure problems. A small compromise from the 142's, but not terrible.

[ray1970]

If you ever had a desire to shoot in a competition, that 200g bullet will exceed the maximum allowed at some venues.

Personally, I'd go .260 Rem. Significantly better than .308 at long range, low recoil, less expensive (a tiny bit) to load. Since it's .308 based, I assume it should run in the AR-10.

It's on my list of toys to want.

I briefly considered the 260 Remington but heard reports that it could be a bit rough on barrels. I suppose as little as I will probably realistically shoot it I might not wear a barrel out. Heck, even if I did wear one out every four or five years I guess the cost of a new barrel wouldn't be so bad. I'll have to do a little more research on it tonight.

Once again, thank you all for the helpful advice and information. That's why I posted this up here.

[cysoto]

With 123g SMK's, you can easily load to 2.800" without pressure problems. A small compromise from the 142's, but not terrible.

I have only seen it tested with 142 grainers and it was piercing primers left and right.