I've been having a good run with the .223 manually operated (no gas system) AR15 type pistols, but I have a little trouble with recoil using a rifle scope in US. And even more in flop using peep on peep. It beats my glasses up something fierce!

I'm not sure that my 77gr bullets will reliably take down Rams if I shorten the barrel enough to add a muzzle brake, so I got to wondering what a minimalist step up might be.

6,5 Grendel has been a consideration, even before I sent the first .223 round downrange. Seems a bit powerful, but it is available fairly readily. 6,5 TCU is rather too long to work out of an AR mag. .300 Blackout is a standby.

But I have a couple thousand 6,5mm bullets sitting about doing nothing! 80 to 140gr.

Went searching a little and found that Pacific Tool and Gage has reamers for something called 6.5 300 AAC Blackout, so no design work needs to be done, just the cubic money to buy multiple reamers.

And then there's the 6.5 PCC, which is a shortened .223. Available(?) barrels and dies. The very short neck probably isn't a drama in the manually operated pistol, but...

https://illirianengineeringc.ipage.com/index.html

Just spitballing ideas at this point. Anybody mad enough to have already travelled this path?

Most Reamers can be rented, helps save on project costs. Both sound interesting to me, keep us informed with your decision and progress.