7.62 NATO v. .308 brass: how important?

[boltstop]

I've done an audette ladder and worked up loads per TresMon - and have discovered loads which work pressure and accuracy wise with 7.62 NATO brass I have. I'm using 168-gr. SMK and Varget, and have found loads in the neighborhood of 40.7 gr. to 42.7 gr seated 10-thou into the lands. All bolt lifts were sticky with primer flowage only on the 42.7 gr. load (I think I failed to bump the shoulders back; it's my first time not fully resizing the cases). Closing the bolt with the bullet out that far was a BITCH!

So here's my question:

I used NATO Remington cases. The loads seem pretty light for Varget; I suspect the reduced interior space of the NATO case is responsible for the accuracy and eventual (when getting up near 42.7 gr.) pressure signs on the primers. When I put these loads in Remington .308 cases with the bullets seated 10 thousandths off the lands, will I see weak velocities and poor performance?

How important is case choice anyway?

 

[Greg Langelius *]

Re: 7.62 NATO v. .308 brass: how important?

In general, your suspicions are correct. Military brass is essentially reinforced in the base/web area, and internal volume is diminished.

Rather than making assumptions and arbitrarily altering loads, simply substitute the Rem brass with the existing load and see for yourself where that ends you up. Then you will have a benchmark against which to base alterations, which will likely turn out to be charge increases. Proceed from there with caution and you should do fine.

Seating into the lands can result in significant and perhaps unnecessary pressure spikes.

My experience is that such spikes often cloud the picture, and can show pressure indicators that do not properly correspond to actual velocities.

I would begin by immediately backing off the OAL from .010" into the lands to .010" <span style="font-style: italic">off</span> the lands, then proceed with the other load alterations. I think the first consequence you will notice will be a reduction or elimination of bolt force issues. My own personal preference is to jump, rather than jam.

Case choice is important because cases vary between makers, and often between individual production lots. The important thing is consistency.

Greg

 

[samnev]

Re: 7.62 NATO v. .308 brass: how important?

I would follow Greg's instructions. Very sound advice.

 

[boltstop]

Re: 7.62 NATO v. .308 brass: how important?

Thanks Greg.

I will be loading today and shooting tomorrow and will report back my findings with pictures.

 

[Grump]

Re: 7.62 NATO v. .308 brass: how important?

You don't know nuttin' until you know your fired cases' water capacity.

There are surprises sometimes.