MR1 reloading question ... no replies in reloading forum so I'll try here

[Tikka223]

Folks,

I reload for the MR1 and have been using Winchester brass, 55gr VMAX, CCI BR-4s, and various loads of Varget. 26gr of Varget seems to be getting the best accuracy to date.

Once fired, I've been using a Redding full-length sizing die on the brass. The brass has been cleaned using an ultra-sonic cleaner.

My question:

Once fired, I find the brass comes out very dirty and "sooty". From what I understand, the MR1 is piston driven and thus there should be little gas blow-back into the chamber. Does this mean that I should only neck-size to get a better seal at the shoulder of the case?

Here is a pic of some fired cases:

 

[Rotaxpower]

Have you tried bumping your charge up? It may help the case fill out and seal the chamber a bit better, causing less of the soot on the cases.


BTW I am not sure if 26grns is the max charge. If it is don't go over

 

[fireball]

Neck size only and you run the risk of case feeding issues.

See if annealing the brass makes any differance.

 

[Tikka223]

I think I'll load a few and chance the feeding issues. I'll also check my full-length die, I'm pretty sure there's a way you can reduce how much it bumps the shoulder back on the case.

Not sure if I want to go higher in the powder range.

Is this common on other semis, like ARs?

 

[DaveMachine]

I ran into a problem with sooty cases like that with my 6.5x55 Tikka (using 142gr SMKs) because I wasn't seating the bullets deep enough (in order to reach the edge of that long throat designed for 160gr bullets). IIRC it was the lack of initial pressure that caused the dirty burning.

Seeing as your rounds have to fit into an AR15 magazine that would probably mean the bullets are likely seated in the case far enough already. Maybe you could try a Lee Factory Crimp Die or a different powder and see if you get the same results?

I've also heard of folks polishing their expander balls in order to size them down very very slightly (by about 0.001" if I recall) in order to get more neck tension.

By no means am I an expert so it's probably best to wait for some of the more experienced reloaders to chime in.