Hey everyone,

I have a bare aero m5 upper and lower I’m going to be building out over the next few months. I’m still in the in the planing stage and was 100% sure I was going with .308 win, but then I went and mind blanked myself just now while holding a 7mm-08 cartridge from one of my bolt guns. So now I’m indecisive on which I should go with, would love to hear any pros, cons and experiences. Thanks

NOT INTERESTED IN 6.5 Creed!

You said nothing about the intended use of this gun, that makes a big difference.

If you don't reload and want large amounts of cheapish ammo then go 308 otherwise I would go with 7-08.

It will be a hunting rig for deer and hogs, and a midrange hopefully one day a 1000 yard plinker. It won’t be my go to hunting rig because my main deer rifles are a 300 win mag and a 7mm-08 though that could change once I start shooting it. It will probably be more of a hog gun over a deer gun if I’m honest.

7mm-08 is a great cartridge, better than .308 win in every way except for 1 which is cost.

I'm a fan of keeping shit simple, since you already have a 7mm-08 go with that.

As a reloader I like the .308 for all the different bullet choices.

For your intended use, both .308 and 7mm-08 would be fine.
The real world differences in performance are just not that much.

I think it comes down to the following question:
Do you want the availability of cheaper .308 ammo or the compatibility with my existing 7mm-08 rifle?

Disclosure: I own .308 and 7mm-08 bolt guns and multiple .308 semis.

I was in a similar dilemma,  although I never considered the .308.  I was all set to build a 7mm-08. I really like that cartridge.  Problem is,  in an AR10 setup the magazine restricts the load length. Since I wanted to run heavier projectiles that was only possible by seating deeper into the case eating up capacity. 6.5 Creedmoor was relatively new and in the running. Ammo was a little expensive,  but not a killer. Loadings seemed pretty flexible.

With that I went with the 6.5 Creedmoor and have never regretted it. Great cartridge. Using heavier projectiles is not an issue and velocities show some decent capabilities. On a second build I did a 6mm Creedmoor.  Been really happy with it as well. For a 7mm-08 I'll eventually get a bolt gun.

Only advice I'd offer... build the one you initially/originally considered and wanted. By doing so you will probably not end up second guessing anything. If something other than a .308, look into adjustable gas blocks. Even on a .308 they may be advisable. Hopefully someone with a .308 will chime in.

Since you already have 7mm-08, I would do that.

Do you hand load by any chance?

I would echo this post, very well stated

I don’t reload although I have started doing some research on the subject.

Thanks for all the replies. I think I would regret not building it out in 308 so that’s what I’ll do, I could always build a 7mm-08 upper down the road.

Good way to go.  While something else may be nice,  unless you go with what you originally wanted the will always be that nagging little thought.  Sounds like you'll be avoiding that.

Keep us posted with posts and pics as you go.

I built a 7mm-08 AR with a BHW 16" barrel. Terrific deer slayer. Feeds all factory ammo, and Federal Fusion is my hunting round of choice for it. I find recoil to be noticeably lower, even though they aren't that different on paper.

BTW, Federal Fusion chronos as fast as Hornady Superformance. It's hot stuff.

-Stooxie

invest $150 and buy quick load

then sort cartridges and propellants that fit the output parameters you laid out

you're on there right track though, build to a purpose

you're going to end up reloading, and that's a good thing

you won't save any money,  but you'll shoot more

Quick load? Think I had that condition in middle school . Does that pertain to reloading equipment/ device?

Quickload is an "internal ballistics" program that gives you pressures for specific rounds and powders in specific barrel lengths

you can dork around with a simple ballistics calculator and see what external ballistics characteristics each round and rifle provide

of course it's software and not reality, so it's a rough estimate

even with a rough estimate, if you're working on a purpose-built gun, working backwards from the round you desire/require is probably the best way to go about determining the rifle features you're going to want

of course you're going to account for the style of shooting, and environments you prefer, but ballistic performance and terminal performance will always trump those

and to reach those desired or required end-states, you have to start with how to create those firing conditions at the gun

if you choose this route, you'll end up switching between quickloads and a simple ballistics application to determine the recipe for the round you'll want to fire (and probably a few dozen alternates) and then just build the gun to meet those parameters. then build the ammunition to match