So I got a stupid good deal on an AR lower locally, so good that I couldn't pass it up. I ordered an LPK and stock from PSA tonight, so that is pretty well covered. Problem is, I haven't decided what I want to build it into.

I currently own a 16" 5.56 AR that is set up as my patrol rifle. I also have a 16" 9mm AR for plinking fun, and for practice on my club's "pistol caliber only" bays. I was hoping to do something different with this one. I do reload, so I don't mind considering an oddball caliber...in fact, that's half the fun.

I've considered a .300 blackout. Don't have one yet, and it would be deer legal in my state. Also a 6.5 Grendel, as my buddy and I like shooting steel out beyond 600 yards, and that caliber looks like it might be more suitable than my .223. I've also looked at .458 SOCOM and .224 Valkyrie.

I'm not dead set on any of these...just some calibers I've considered. I'd like to hear your favorite AR cartridge and why...I need ideas!

I have too many 5.56 and 300blks. I also have a 9mm and 22 AR so I recently built a 6.5 Grendel.
Just because it was something different.

I doubt I will shoot it past 600 yards so I got a 12” barrel. It’s fun and accurate. I can’t wait for summer to try it outdoors.

If you do Grendel make sure your bolt and barrel match. I have a type 2 barrel and bolt.

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If you do Grendel make sure your bolt and barrel match. I have a type 2 barrel and bolt.

Good to know...thanks for the heads up!

I vote for a 20" upper in .223 / 5.56.

I'm not real keen on adding to calibers I have to keep on-hand.

.223, 7.62x39, 12ga, 20ga, .22, .38, .357, 45-70, 9mm, etc etc...

20" really makes use of the velocity / range the caliber was designed around. Yes bullets are better nowadays but 20" is a nice variety to have.

Plus with a scope you may be quite happy.

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Go big or small. 18"-20" precision build or a 14.5" permed lightweight compact build or even a pistol (300 BLK or 5.56, use the stock/rifle RE on the next build).

.50 Beowulf

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Originally posted by Oz_Shadow:
.50 Beowulf

I think I'll do one of these myself. I shot one back when it was the new hotness, and it's been on my mind since.

Yeah, I could definitely pick one up.

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Originally posted by arcwelder76:

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Originally posted by Oz_Shadow:
.50 Beowulf

I think I'll do one of these myself. I shot one back when it was the new hotness, and it's been on my mind since.

Yeah, I could definitely pick one up.

This will likely be my next some day as well.
SBR just because.

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Originally posted by Black92LX:

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Originally posted by arcwelder76:

quote:

Originally posted by Oz_Shadow:
.50 Beowulf

I think I'll do one of these myself. I shot one back when it was the new hotness, and it's been on my mind since.

Yeah, I could definitely pick one up.

This will likely be my next some day as well.
SBR just because.

Well, then you'll have to suppress it.

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Originally posted by 92fstech:
Problem is, I haven't decided what I want to build it into.

If you want to end up with a rifle you will enjoy shooting regularly, you must first determine its primary use.

Hunting needs will lean towards bigger bores. Bigger bores produce more kinetic energy and lower muzzle velocities. Therefore they tend to be used for shorter distances. Larger bores often work pretty well with short-ish and mid-length barrels.

Long distance target needs means a bullet with a good ballistics coefficient. Generally this means a smaller bore, although the Grendel bucks this trend. Long distance shooting demands a little higher muzzle velocity, so in concert with the properties of fluid dynamics, a longer barrel is preferred.

Some of the AR chamberings require bolts and magazines that are different than the normal ones used by 223/5.56.

Consider the cost of the entire system, especially if you're changing calibers. This includes magazines, initial ammo investment, sights/optics. And maybe other items such as light, sling, bipod.

Allow me to throw 6.8 SPC into the mix. Deer & hog harvesting round with decent ammo support from Federal and Hornady.

My very first AR build was a 16" rifle using Aero Precision upper, AR Performance Scout barrel and BCG, Seekins Precision hand guard & adjustable gas block. Rifle runs sub-MOA with factory ammo. With some fine tuning on the ASC mags, it runs like a sewing machine.

My second build a was an AR pistol in 6.8 SPC, also built on an Aero Precision upper, Bison Armory 8.5" barrel and BCG, Pantheon Arms Dolos kit, and Seekins Precision adjustable gas block. Serious firepower from a short barrel AR pistol.

Investing in 6.8 SPC hardware will help in future 224 Valkyrie builds, as the 224V uses the 6.8 SPC case, so mags and bolts will be interchangeable.

^^ 6.8 is an awesome round. Have a 12.5" noveske barrel. Shoots lights out.

Has anybody built a .300 blackout specifically geared towards running supersonic ammo through it? I know that blackout is really popular for it's subsonic/suppressed capabilities, but I'm not at a point where I can afford a tax stamp and suppressor. I do like the idea of a .30 caliber round that uses standard mags and a regular bolt, though. While I know it's never going to be avery1000 yard round, I imagine the lighter bullets will give me quite a bit more range over the subsonics, while still giving me more than twice the mass of a 5.56. is this a viable concept, or am I barking up the wrong tree?

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Originally posted by 92fstech:
Has anybody built a .300 blackout specifically geared towards running supersonic ammo through it?

I imagine the lighter bullets will give me quite a bit more range over the subsonics

is this a viable concept, or am I barking up the wrong tree?

I have a 12" 300blk upper. So far I've only shot supersonic ammo, with a can. I also got a tax stamp so one of my lowers is an SBR. Other than I just wanted it, the primary purpose was to have a 223-ish recoil pulse carbine that I could use to practice on steel targets closer than 100 yards. Regardless of what ammo I use on my 16" barrel 223, I start dimpling my AR500 steel at distances less than 80 yards. With heavy (~ 150 grain) bullets and supersonic 300blk ammo, I should be able to shoot at targets of 25-50 yards without dimpling the steel.

What I'm seeing is bullet velocities of 2300 fps or more start to ding up my steel. The 140-150 grain ammo produces a little less than 2,000 fps at the muzzle, so I should be totally good to go.

So far I've shot a handful of factory loads with bullets from 110 to 150 grains. The heavier supersonic FMJ ammo exhibits decidedly unspectacular accuracy at 100 yards, but it should be fine for my closer steel targets.

My upper shows very nice accuracy at 100 yards with Hornady 110 Vmax, Sig Sauer 125 HPBT, and Corbon 125 MPR. I shot the Hornady and Sig Sauer rounds out to 450 yards with surprisingly good accuracy on a 10" steel plate. I didn't have longer distance dope (elevation or windage) on these rounds at the time, so I had to "walk" the rounds into the target. Supersonic 300blk ammo is capable at this range, as long as you are using good bullets and have a good barrel.

I have not yet shot subsonic ammo through my 300blk, but I can tell you the flight ballistics are pretty unspectacular past 100 yards.

I think supersonic 300blk is a very viable concept. One just needs to understand the ballistics differences between the 223 and 308 bullets when shot from a 223-ish capacity case.

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So far I've shot a handful of factory loads with bullets from 110 to 150 grains. The heavier supersonic FMJ ammo exhibits decidedly unspectacular accuracy at 100 yards, but it should be fine for my closer steel targets.

Yeah, I was thinking around a 125 grain bullet should be fine for what I'm considering...still about twice the weight of the 55-65 grain pills I'm shooting through my 5.56.

When comparing performance of 223 to 300blk, you should really look at 69-77 grain 223 bullets versus the 125 grain blackouts. The industry backers of the blackout have often shown the blackout's superior ballistics to the 223, but generally with modern & heavier bullets in the 300 versus 55 ball ammo in 223.

Well that's a no brainer. Compare modern 73-77 grain match/hunting bullets to 55 FMJ in a 223, and the 55's don't look very good at all.

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Originally posted by fritz:
When comparing performance of 223 to 300blk, you should really look at 69-77 grain 223 bullets versus the 125 grain blackouts. The industry backers of the blackout have often shown the blackout's superior ballistics to the 223, but generally with modern & heavier bullets in the 300 versus 55 ball ammo in 223.

Well that's a no brainer. Compare modern 73-77 grain match/hunting bullets to 55 FMJ in a 223, and the 55's don't look very good at all.

The problem with the heavier 223 bullets, though, is that you are really restricted in how you load them due to the longer OALs not fitting in the mag. This is not an issue with the .300.

I don't handload, so I rely on factory ammo. I can assure that 69-77 grain factory ammo shoots very well in my 1/8 through 1/7 twist barrels, both those chambered in 5.56 and .223. I just retired a 1/9 twist 5.56 barrel which shot factory 69 very well in all conditions, and did well with 75-77 in warmer temps.

My 18" 1/7 5.56 does best with Hornady 75 BTHP, my 20" 1/8 .223 does best with Hornady 73 ELD-M. This ammo fits all magazines without issues and cycles without fail. And I've shot both to distances of 700+ yards with excellent accuracy.

You shouldn't be running into magazine length issues until you jump to 80 or 90 grain 223 bullets.

For hunting, 6.8 is my favorite caliber.

Helps to compare apples to apples too, if you're talking about something like hunting. It does no good to compare a hunting bullet in one caliber to a match bullet in another, unless you're only going to shoot paper of things you don't care where it runs off and dies.


Some barrels on sale.. whats left anyway. https://truesportingarmsllc.co...oduct-category/ar15/

Crazy thing about uppers right now, I spent the weekend pricing out things and while it didn't work for me because I was after something specific, some of those Primary Arms deals are amazing. Even if it's not top shelf stuff, the prices are rock bottom. I was very temped to buy a complete upper and throw the barrel away juts because it was cheaper than buying the parts piece by piece.