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what is the most effective terminal performer out of a 10 inch ar15 barrel...762x39, 308, 300 black, something else? parameters are 0 to 150 yards...preferably 20 or 30 round mags. looking for foot pounds maybe
 

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They are all crap out of a 10.5 barrel. And there is nothing that you need to shoot at 150 yards that requires only a 10" barrel. Rifle rounds should be shot out of a rifle. Chopping a barrel off a AR and calling it a pistol doesn't make it a "pistol".

Besides my rant.... You are missing the one designed for short barrels... 6.8 SPC II. That was designed for more punch out of a short barrel... Meaning 14" carbine military barrels. And yes, it is the best at doing exactly that. 300 was designed to be suppressed. AK and 308 were designed for AKs and battle riffles. 6.8 performs best out of short barrels, and I would not want to shoot it out of a 10"
 

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.308 doesn't fit in an AR-15.

6.8 SPC wins out of an AR-15, I think. I've got a 12.5" and manage a 90 grain TNT at 2600 FPS with handloads and without pushing pressures. I DO have a stainless steel suppressor hanging off the end to manage noise.
 

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300bo is basically a pistol round, and does quite well out of a short barrel. now that their are plenty of bullets that will expand at lower speeds, 300bo is probably the reining AR 15 pistol champ. I would guess the 6.8 would top it's KE, but I think the 300 will perform better. 500 beowulf is actually a stretched 50ae, so that is going ton be the best one if you want to go thumper. 450 bushy is probably quite similar to 460sw, but haven't looked into it.
 

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I'll add the 6.5 Grendel...at least in a 12" pistol...mine will do easy 1.25" groups @ 100 yds, sometimes under an inch.

At the ranges you're looking at, the 6.5 Grendel, 6.8 SPC and the 300 blk are all good choices. If you don't reload, the 300 blk may be your best option due to the number of factory available loads.
 

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300bo is basically a pistol round, and does quite well out of a short barrel. now that their are plenty of bullets that will expand at lower speeds, 300bo is probably the reining AR 15 pistol champ. I would guess the 6.8 would top it's KE, but I think the 300 will perform better. 500 beowulf is actually a stretched 50ae, so that is going ton be the best one if you want to go thumper. 450 bushy is probably quite similar to 460sw, but haven't looked into it.
300 shoots out of a short barrel. A 110 Barnes does about 2000 out of a 9" barrel. A 115 10mm does about 1900. A 220 gr subsonic 300 is around 900 fps out of a 9".... A 45acp does that out a 1911.

It's not that any of that is bad... But shooting that round out of a short barrel turns it into pistol cartridge territory which... Why bother? With a rifle round, a short barrel still give more blast and flash for same ballistics... Where as using pistol cartridges in longer barrel doesn't. So why neuter rifle rounds, that are more expensive to achieve performance similar to pistol rounds?

The real plus is rifle rounds. A 14" carbine is well 5" longer.

Now there is a lot I could be missing. Have not looked much at true SBRs. But we haven't even mentioned shotguns....
 

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But we haven't even mentioned shotguns....
Why mention shotguns? The OP is wanting to build an AR-15 (pistol or SBR).

I DO like your idea of a PCC for this purpose. Make it a .45 ACP or 10mm and you shouldn't get NEARLY the blast that you would get with a rifle round and still get adequate performance at the 150 yard and shorter range. Unfortunately, I don't now the numbers for ft/lbs energy at those distances. It seems like the OP is looking for high energy transfer at relatively short distances with standard capacity for ARs.

mtnlvr, I thought about the 6.5 Grendel, but with a short barrel and relatively short distance the Grendel is just not intended for this purpose. The starting FPS isn't there and the BC capabilities of the 6.5 projectile that retains energy at longer ranges are wasted.
 

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Why mention shotguns? The OP is wanting to build an AR-15 (pistol or SBR).

I DO like your idea of a PCC for this purpose. Make it a .45 ACP or 10mm and you shouldn't get NEARLY the blast that you would get with a rifle round and still get adequate performance at the 150 yard and shorter range. Unfortunately, I don't now the numbers for ft/lbs energy at those distances. It seems like the OP is looking for high energy transfer at relatively short distances with standard capacity for ARs.

mtnlvr, I thought about the 6.5 Grendel, but with a short barrel and relatively short distance the Grendel is just not intended for this purpose. The starting FPS isn't there and the BC capabilities of the 6.5 projectile that retains energy at longer ranges are wasted.
Cause if we are talking punch at shorter ranges, it has it. Point being, what is a good weapon at short ranges... Well, SG isn't an AR, but it does have something to offer.

I'm not the anti-SBR. I know they are super popular. I know we have a massive love for ARs these days and nobody seems to be able to get over the fact we must have 10 in every possible configuration. I'm just more of a purpose kind of guy, and I don't really get the point.

I've been round and round over a compact package. I Get it. PCC/PDW/SBR... Higher capacity than pistol. You are either trying to push pistol bullets faster, or neutering rifle bullets going slower. At the end of it, you still have to have bullets designed to operate at the terminal ballistics of the setup. And then, when you look at terminal ballistics... Of what you end up with... What's comparable? Is the juice really worth the squeeze? Compact platforms are great in tight quarters, small flash/bangs not so much.... Especially 30 of them.
 

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What about that new Winchester (??) cartridge, the 350 legend. Due to the case design it should burn faster powders well and throw a larger diameter heavy bullet at shorter ranges. Even from a short barreled rifle/pistol.

And no, I'm not buying/building one. In AR15's I'm sticking with the .223. Up close even a 55 grain bullet is still hauling butt. I think the guys over at arfcom figure the 55 grain FMJ will still break apart/fragment out to 150 yds. before it's slow muzzle velocity causes it to be going too slow to act as it was designed to do.

Check out that new Winchester cartridge.

Found a link to some info on it.
Winchester .350 Legend

Some of those loads are still packing over 500 ft lbs of energy at 300 yds.
 

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Why mention shotguns? The OP is wanting to build an AR-15 (pistol or SBR).
Umm. Just to name a few

Rock Island VR80
Charles Daly 410 AR upper (yes it does exist) Charles Daly AR15 .410 Upper-SALE - AtlanticFirearms.com
Charles Daly AR12
Fedarm FR98
Fedarm FR99
Panzer AR12 Pro
Typhoon Defense X12

And there are also a bunch of AK looking shotguns too. Haven't seen the short barrels in an AR style form, though there are some shockwave style FIREARM with short barrels and semi auto like the emporer arms mogul and the mossberg and remington versions as well.

Slugs will work just fine at 150 yards.
 

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300 shoots out of a short barrel. A 110 Barnes does about 2000 out of a 9" barrel. A 115 10mm does about 1900. A 220 gr subsonic 300 is around 900 fps out of a 9".... A 45acp does that out a 1911.

It's not that any of that is bad... But shooting that round out of a short barrel turns it into pistol cartridge territory which... Why bother? With a rifle round, a short barrel still give more blast and flash for same ballistics... Where as using pistol cartridges in longer barrel doesn't. So why neuter rifle rounds, that are more expensive to achieve performance similar to pistol rounds?

The real plus is rifle rounds. A 14" carbine is well 5" longer.

Now there is a lot I could be missing. Have not looked much at true SBRs. But we haven't even mentioned shotguns....
The .30 cal rifle bullet has a very different ballistic coefficient compared to .40 cal bullet though.
 

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The .30 cal rifle bullet has a very different ballistic coefficient compared to .40 cal bullet though.
Definitely, but to 150 yds it won't make that much difference. Long rang... absolutely.
 
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