AR 15 upper calibers... Convince me...

[Ol` Joe]

The Grendel is an excellent choice and a step up if you plan on using it on deer over the 5.56 with its heavier bullets that offer a larger frontal area and increased energy. Accuracy is very good as well, although here are not many producers of it and a reliable supply may be a problem short of going online. The fact you don’t want to load your ammo or use a AR10 platform makes the choices you can go with quite limited, there are very few cartridges with a .378” rim diameter.

Handload and rounds like the 25x45 Sharps or 6x45 would make excellent alternative options. Both are fine on deer at average Michigan ranges and the accuracy of them is excellent, the 6x45 was one of the top favorites of benchrest shooters until the 6ppc came along and knock it off its perch. Components are plentiful and of high quality at reasonable prices.

[oldmann1967]

I vote ar10 in 6.5 PRC. Not exactly what you are asking, but very capable waaaaay out there.

[pscipio03]

I guess it depends on your flavor, but if ammo price is a concern, I'd get a CMMG 9mm upper and a Hahn Precision magwell adapter for your lower and rock 9mm out of it. Then you can swim in your excess 9mm for what some of the boutique rounds cost.

[joepistol]

Surprised that no one's mentioned a 7.62 X 39 upper.. while not a long range caliber,
ammo is east to find, relatively inexpensive, and having a 30 cal bullet is > than the smaller options,
(has more velocity than 300 BO) . Good mags are plentiful, reliable, & inexpensive as well

My Ar-15 PSA upper in this caliber is surprisingly accurate.

[UpNorthWOLF]

Surprised that no one's mentioned a 7.62 X 39 upper.. while not a long range caliber,
ammo is east to find, relatively inexpensive, and having a 30 cal bullet is > than the smaller options,
(has more velocity than 300 BO) . Good mags are plentiful, reliable, & inexpensive as well

My Ar-15 PSA upper in this caliber is surprisingly accurate.

I got out of the round a decade ago... Sold my Polytech Legend and everything I had for it.

[loki993]

Personally I don't see the attraction of the 65 Grendel if you aren't trying to stretch the legs of the Ar15...you have your bases covered with the BO and standard 556 anything else is just doing something slightly differently.

You ever think of going to a pistol caliber? Easy to shoot, easy to buy so you can stack it deep...a PCC is still going to be relatively effective at fighting ranges

[DP425]

IMO, .224 Valkyrie is prob the best round for the small frame AR. Gives you range, accuracy, and terminal performance in a combination that is hard to get with anything else.

[UpNorthWOLF]

Personally I don't see the attraction of the 65 Grendel if you aren't trying to stretch the legs of the Ar15...you have your bases covered with the BO and standard 556 anything else is just doing something slightly differently.

You ever think of going to a pistol caliber? Easy to shoot, easy to buy so you can stack it deep...a PCC is still going to be relatively effective at fighting ranges

Toyed with a 9MM, though would be better with a new lower and not an adapter. But since that would also be better with a longer barrel, I feel buying more Blackout ammo would be a better investment than a 9MM carbine.

[esq_stu]

Pistol caliber - whatever caliber and magazines you can share with of the pistols you might carry. Blowback, no gas tube/block to worry about. Cheap to shoot.

I have two ARs in 9mm using Glock magazines. Dedicated Glock mag lowers. They'll take G26 size and up. I've seen barrels and bolt carriers in .40 and .45 acp and I'm sure there are others.

[UpNorthWOLF]

Pistol caliber - whatever caliber and magazines you can share with of the pistols you might carry. Blowback, no gas tube/block to worry about. Cheap to shoot.

I have two ARs in 9mm using Glock magazines. Dedicated Glock mag lowers. They'll take G26 size and up. I've seen barrels and bolt carriers in .40 and .45 acp and I'm sure there are others.

No Glocks here