This:
https://www.masdefense.com/7-5-300-BLK-BARRELED-UPPER-MAS-SQUADRON-9-87-p/mas-073b1-mdsq-10.htm

Who makes the 7.5 A1 upper?

No one (that I know of) unfortunately.

The reciever is Brownells retro slick side A1, Doublestar pistol tube, and Faxon barrel.

ADCO pinned the FSB for me.

That.

The Gold Dot 75 grain performs poorly  from 7.5" barrel -



but GD 55 did well -

Lol if you’re building a 7.5”, most sane people aren’t looking to reach out and touch someone. I’d assume he’s building a CQB pistol. Throw on a can and it still compact, and the bullets still have enough energy at close range to do serious damage.

Your comparison to the Vette is silly. He’s not trying to build a Vette. He wants a Smart Car with some ass to it. A 7.5” build in 5.56 covers that.

I had a 7.5" AR pistol and most of the hate spewed here is incorrect.  Was NOT loud as fuck, nor did it spew a massive fireball, nor did it have uncontrollable recoil, unreliability or poor accuracy.  The barrel was a no name (probably Bear Creek Arsenal I would guess) stainless .223 Wylde and was accurate as fuck.  Never once, in hundreds of rounds, did I ever have any sort of malfunction.  I used a KAK flash can and it was no louder, at my end, than a regular AR.  Downrange is a different story but I'm not downrange.  With a Holosun red dot, LaRue MBT trigger and a SBA3 brace it was awesome to shoot.  Used a Mlok 10" rail with flip up Magpul sights along with the Holosun and a standard carbine spring with an H2 buffer.  I did run a heavy duty extractor spring but it worked fine with the standard spring too.  I ended up trading it and a rifle for a Colt 6920 that I built into a SOPMOD Block 1 clone.  I still have another pistol, a 10.5" Commando style on a machined out 80% ghost gun lower.  With the A2 flash hider the 10.5" is much louder than the 7.5" with flash can ever was.

Reminds me of a small town PD (five officers) back in North Carolina. The chief had left so the acting chief went on a spending spree.  He didn't want to drive the sedan the previous chief drove so he got a new SUV.  He got himself a loaded 14.5" ar15 with optic and light.

He didn't forget the patrol officers, so he got them 7.5" 5.56s complete with happy switch (no lights, no optics)  He neglected to order them spare magazines so my friend on the department asked if he could borrow some so they could qualify.  The ban had recently ended while I didn't have an AR yet, I did have some mags.

They were issued ball (green tip IIRC) and I never saw my mags again

This is what I run.

110 grain vmax or Barnes with 7.5 blackout.

They do. It's called .22 LR.

Just use 55 grain soft points.

I had a 7.5" 5.56 pistol years ago (before braces were a thing) and I sold it fairly fast. It was too loud and the fireballs got old. I currently have a 7.5" 300blk and I love that thing. It's definitely a great length for hunting hogs from a truck cab. Ammo is twice as expensive, but if you're buying premium 5.56 it's not as big a leap in cost to decent .300. uppers and barrels are so cheap right now, get both?

Don't let them scare you OP, the fireball isn't that bad especially if you're using a light with it. I don't know why you would take a shot without using a light. And wouldn't you rather be deaf than dead?

That said, anything more then 20 yards and during daylight and the AR is going to beat the pistol every time. You can kiss your soft armor goodbye.

Best to go with a 22lr conversation kit.

M193 coming out of a 7.5 inch barrel at 2500 fps still has 750+ ft-lb of energy.

CCi Stinger (one of the fastest 22 rounds out there) per their website is only 191 ft-lb at the muzzle (32 grain at 1640 ft/s).

9mm +P ammo is in the 400-450 ft-lb range.

...

Even with only 7.5 inches, you are still better off with the 5.56.

the .25-20 killed the biggest racked deer ever killed by a man, and out of a rifle it has 150 foot pounds less energy than m193 from a 7.5" barrel.

Does anyone have experience with the 55 grain Hornady TAP 223 REM ammunition out of a 7.5 inch barrel? Label gives the muzzle velocity of 3240 FPS, I'm guessing that is out of a 20 inch barrel.  I say guessing since they don't list the barrel length of the test rifle.  My question is if the TAP ammo expands out of a 7.5 inch barrel AR15 pistol.

At 7.5", I'd go .300BO. Wait, I did.