Quote Originally Posted by DWood View Post
Like everyone else here, I have a 10.5" SBR and don't have any experience with a 7.5" SBR.

I hope some who have run the 7.5" barrel will chime in here and relay some experience based on actual use.
I had a 7.5 DPMS kitty Kat upper. The first 100 rounds were a little unreliable, with 4-5 FTE and FTF each. Some of those issues were due to be breaking it in the dead of winter - air temperatures in the single digits. After adding a DFender on the extractor spring and running more ammo through reliability became a failure of 1:200 with cheap Wolf and Winchester White Box.

Frankly, I bought the DPMS as a proof of concept - I did not care for what it offered. I traded it off for a small profit and some conclusions.
1) 7.5 ballistics were underwhelming in theory, especially in cheap ammo and 1:9. Ammo options have improved and SOST type cartridges provide a more adequate option in a longer short barrel. I rarely shot beyond 50 yds and noticed no accuracy issues.
2) The 7.5 appears to be wasting much of propellant out of the front end in blast and light. It beats a sharp stick, but the cartridge was not designed for this barrel length.
3) the Kitty Cat had a jackassery of a heavy, thick aluminum fore end... Appreciated for the heat protection, but unnecessary heavy on the front end.
4) the simple mechanics of 7.5 barrel makes accurately holding a pistol with such a short fore end seemed a big compromise. I found the SAS sling method with Magazine well back pressure worked, but the heavy foreend moved the center of gravity too far forward. A longer fore end or lighter foreend would have been more valuable.

That all said, I am trying again with 10.5. Gabe Suarez has been talking up the 10.5 for years. He is contreversial, but the concepts seem mostly valid on a non-SBR platform. It might be worthwhile to check out his concepts especially with SIG brace on the scene now.