Biggest influence overall length has on performance is on pressure due to available space for powder in the case but it also impacts feeding from the mag. I had mine seated out a bit longer but I had some failure to feed because it would hit the feed ramp and basically flip up into a stovepipe position. Seating projectiles back approximately 15-20 thou solved it.
I've been experimenting with different COLs, for the 135gn projectile they suggest a max COL of 1.168". I haven't had any issues with the actual operation of the gun but have been trying to isolate what is causing the issue with my dirty trigger finger!
I initially started loading at 3.2 (using AP70N) but that caused feed issues and my trigger finger was black after 100 rounds!
So I upped the charge gradually and ended up towards the top end of the range with 3.9gn, the max suggested by ADI is 4.2. This produced the least residue on my finger.
Then I started playing around with the COL which I hadn't considered before. (I'm new to this reloading business!)
So I ended up with a COL of 1.100" and this has given me the best results although the rounds are still not as 'clean' as factory ammo. I'm wondering if I should back off the charge a little and see what effect that has.
I have a theory that with the projectile seated further out, it is being ejected from the case at a lower pressure that is being reached before all the powder is burnt. Could be all bollocks though!
ps. My 'fascination' (as someone called it) with my dirty trigger finger is just because I don't get it with factory ammo.