Max Chamber Pressure

[English Rifleman]

Sort of like GRH post, I ran a sim with some of my data, on my 22" bolt action (with press kept below 52 ksi), which could show something similar to your case.  Couple of posts on Accurate shooter on RS52 powder ( another UK question) for 6mm dasher says your powder is similar to varget but has possibly more temperature sensitivity 68-90 *F.  My results (disclaimers about you have to work up in your gun), showed 22" results with 107 smk of ~50ksi and 2650 fps.  You will want to make sure that you don't run an over-compressed load, as results get dicey.

Having an AR frame but no gas line will perform much like a bolt action but you're still limited to 52 ksi to avoid excess stress on the unlocking lugs.

Primer flattening can be a sign of overpressure but imo not a good one to place a LOT of confidence in, since a little bit of excess headspace can also flatten primers during the shot.  I can't see the MV GRH's plot is showing, but my run yields 2650 fps approx. 

Mind your bolt lift... although for an "AR" style it could be stiff for lots of shots.  I have 1 kali-key which turns an AR into your style (although there is a little gas bleed off) and it seems to be "stiff" - more like sticky due to some fouling - for most every shot I took (it was an 18" 300 ham'r barrel).  So ymmv.  i didn't particularly enjoy the 300 hamr/kalikey combo by the way.

One final thought, Hornady has a chart of MV vs barrel length, for its 108-110 gr bullets/ barrel lengths.  That would tell you how much extra MV yo might see for a 22 vs 18" gas-type gun, which you could add to that page for any powder on there (gas gun is 18" data).  Those extra 4" give you a boost for sure.

Yes thanks
All good info.
I was talking to another shooter here in UK and hes told me to get "Quicklload" as it seems to cater for the European powders / bullets ETC.
As with GRH post of the Gordons Sim, i can see how this takes most of the guess work out.
I dont know anyone else currently shooting this caliber / platform (In UK), so i am kinda on my own at the moment.
Apart from everyone here ofcoarse.