Best caliber for pistol/SBR under 10"?

[TomMontana]

I was thinking about a 7.5" 223 for range amusement. Talked to a guy at the range and he was building an 8" 300 AAC Blackout for range/hunting and was convinced it was the way to go. The shortest .223 I have is 10.3" and 9mm is 5.5". For those who have gone under 10", what is your caliber preference and what would you have done differently with the build?

Other than annoying other shooters, any reason to not build a 7.5" .223 upper? Talk me out of it.

 

[ChevyGuy91]

I have a 300blk in 8.5" and a 10.5" 556 gun. For 556, I wouldn't go much shorter then 10.5", unless there is a real niche reason like a PDW or something. Even then I would probably use 300blk instead, you lose too much velocity for 556 to do it's job. Unless it's a toy and because 556 is cheaper to shoot, then jam on.

Something to consider with shorter barrels, folks who go with 7.5" barrels usually add a large/long muzzle device to make the 7.5" barrel more user friendly, and by the time they are done, they are not much shorter then a 10.5" barrel with an A2 sized muzzle device and have a significant loss in velocity.

 

[Kevin_NH]

9mm: For a suppressor host, 135gr ammo can go supersonic even out of a 7.5" barrel, but most 147gr will stay subsonic with the short barrel.

22lr: Same consideration. In the winter even CCI-SV can go supersonic with a long barrel and the right weather.

 

[oldguy68]

50 BMG would be awsome in 7 1/2 inches!

I would be a one and done type of firearm.
But what a first and last shot it would be.

 

[icyclefar]

Pistol caliber, either 9mm or 45acp

 

[Asaltweapon]

I have a Phase 5 pistol 7.5" in 5.56. It's fun to shoot and reasonably cheap. 300BLK is not so cheap.

If I do another SBR it will be in 9mm.

 

[steve8140]

I have a 7.5” 5.56 and yes it is loud but it’s fun to shoot. I plan on making a 10.5” for it in the future too. I have a Gamma VG6 brake on it so people gate being near me on the range.

 

[67ray]

Have a 7.5" in 556 and it isn't the noise it is the compression and heat - you need a full face shield to shoot it comfortably!

 

[Al-Jim19]

If it’s strictly a toy I would go for a 5.56/9mm just because it would be most economical. Ballistically the 5.56 loses a lot through a short barrel, which others more knowledgeable than me can weigh in on. For range fun and MAYBE short range defense 9mm with uzi magazines would probably be my choice.

 

[1776]

Steyr 9x25

MP 34 - Wikipedia

 

[Bt74]

7" Marauder from PSA! Really pisses off the Fudds at the range!

 

[Shawnyc]

I have a 8.5 inch 300blk, subsonics cycle fine and is super smooth. I agree a short 9mm would be fun.

 

[Bt74]

Yeah, I have a suppressed 10'5" .300blk that runs flawlessly.

 

[Mass-diver]

I have an AA 7.5” in 5.56 - run great, super fun toy.

 

[Lxpony]

5.45x39 -- the only right answer. 8.5"barrel

 

[LuvDog]

My SBRs are 9mm, 223, 300blk and 22lr.

 

[TomMontana]

Saw a guy at the range today shoot a H&K MP5. He even had that eurotrash look. So awesome. Absolute match made in heaven.

 

[Frizzle Fry]

9x19mm, 45acp and 300BLK are all excellent. If you go the pistol route I'd go 300BLK it's not THAT pricy and performs great from my 7.5" pistol.

 

[groundscrapers]

300blk gets my vote for an AR build because it will stabilize the rounds and cycle reliably. In other hosts I would check out the micro scorpions from cz or the mpx for 9mm SBR's, for 22s I would chop a 15-22.

 

[E.Stoner]

300 Blk or 9mm.
5.56 doesnt really do anything good under 11" except make noise and beat the shit out of your gun.
300Blk does a lot and 9mm is cheap and fun as hell! Cant go wrong.

 

[MAGA99]

If you want to go short barrel, 300black is the ticket, especially when suppressed. Yess, the ammo ain’t cheap, but we pay to play, right. Plus 556 is crazy out of a short barrel. Firing an unsupprssed firearm, especially a rifle indoors is not good for my eardrums. This is why god gave us suppressors, it was like the 11th commandment!!! or something.

 

[thormx538]

8.5" 300BLK if you plan to suppress it. I see you're in MA though so you can go down to 7" and not lose a ton ballistically. The 7" guns are rough on suppressors.

7.5" 223 gives up a lot on ballistics.

From Quickload, napkin numbers:

300BLK: 125gr Hornady SST, 18.5gr Lil' Gun, 2.100" COAL
7" -- 98.65% burn, 1906fps (1367 J)
8.5" -- 99.57% burn, 2003fps (1510 J)
16" -- 100% burn, 2262fps (1925 J)

5.56mm: 77gr SMK, 24.4gr CFE223, 2.260" COAL
7.5" -- 83.34% burn, 2060fps (984 J)
10.3" -- 89.44% burn, 2313fps (1240 J)
16" -- 95% burn, 2621fps (1592 J)

You can see that an 8.5" 300BLK burns all of the powder, and gets you the same muzzle energy as a 16" 5.56mm loaded with 77gr bullets. The shorter 5.56 barrels don't burn enough of the powder.

If I switch to a 69gr SMK in 5.56mm, that is only 1542 J (2725 fps) out of a 16". If we run the classic M193 clone (26.5gr H335, 55gr FMJBT) we get 1606 J from a 16" (3114 fps) and only 972 J (2422 fps) from a 7.5" barrel, with only 86% of the powder being burnt.

So in short, on a pretty common supersonic load, a 7" 300BLK has nearly 40% more energy than most loads from a 7.5" 5.56mm, and that same 7" 300BLK retains about 70% of the energy that it's 16" counterpart has, where as a 7.5" 5.56mm only has about 60% of the energy that a 16" has.

Just to be complete, lets look at downrange numbers. At 300yd, here is the retained energy of the 125gr SST and 77gr SMK loads

125gr SST:
7" -- 429 J
8.5" -- 477 J
16" -- 631 J

77gr SMK:
7.5" -- 362 J
10.3" -- 475 J
16" -- 639 J

The 300BLK all loads retain about 32% of their energy at 300yd. The 5.56mm loads retain 36-40% (because of the different amount of powder burn in the different barrel lengths). At 300yd you can see how the 8.5" 300BLK matches a 10.3" 5.56mm very closely, and the 16" barrels match pretty well too.

So in closing, if you plan to keep it under 200yd or so, the 300BLK is the easy choice. Parts commonality with 5.56mm, availability of cheap coated bullets for plinking, complete powder burn, and a lot of oomph.

The 6.8SPC is another good choice for an SBR round that packs a punch at 200-400yd. I don't have the numbers in front of me, but IIRC, most common powders are burnt by 12.5", and that .277" projectile offers a better coefficient than the .308" in similar weights (110-130gr).

Or 10mm. The 10mm blowback guns are still tinkerer's toys at this point from what I understand, but KVP and Macon are making big strides towards getting them to be very reliable.

 

[Bando_Red]

If it's just a range toy than I would personally go with 7.62x39. More kick and more fireball, but the velocity loss is less of an issue with a .312 bullet that weighs 2-3 times as much as the .22 bullet if I ever did want to do something besides punch paper with it, even if thats just punching watermelons or steel plates. Plus who doesn't like fireballs?

.300 blackout is a cool round but like .357 sig the price of ammo relegates it strictly to reloaders and people who don't have to pay for their gun's diet.

 

[MSant]

I have an 11 inch 30 carb. Lots of grins. Ho blackoit

 

[widnerkj]

Have a 8" .300 blk. It's a hoot, I love plinking around the desert with it. Little bro's got a 7.5" .223, and it fireballs nicely. I'll dig for some pics.