Overpressure in .308 for gas guns

[knife edge]

Guys/Gals,

Very new to reloading. I've worked up in typical fashion to near, but under max loads per Hodgedon. I noticed that Hornady, Sierra and Hodgedon all report different maximum loads for the 175-180g bullets, with Hornady being VERY conservative. Again, this particular load is under per Hodgedon and over max per Hornady. On other forums I am getting mixed reviews as to whether I am approaching max or already past it, have also been referred to this site.

Currently using 45.0g BLC-2 in Federal brass with 178g Hornady Match bullets. MV 2494 ft/sec which is about 50 ft/sec faster than FGMM 175SMK. This is a load I would like to file away for later use as I move on to a new powder but feel that I may have an overpressure condition, again unknown. The primer is cratering and I am getting a shiny spot on the case head from the ejector however I cannot feel any indentation when I drag my nail across it. As a last check I measured the case heads against the body using once fired FGMM out of a bolt gun as the standard. The load in question is for a Larue OBR 18". Thoughts?

Once fired Federal GMM from a Savage .308 bolt gun:

.468" at the head:

.466" at the body:

3X fired Federal brass, 178g Hornady Match, 45.0g BLC-2, 18" OBR

.469" at the head (.001" larger than once fired)

.472" at the body (the body has expanded beyond the head)

A comparison of the two heads side by side:
The lettering on the once fired Federal brass out of the bolt gun has deeper lettering while the 3X fired handloaded brass appears to be flattening.

Any comments you guys have will be appreciated, just trying to keep it safe.

 

[Top Cat]

Re: Overpressure in .308 for gas guns

It would be more useful to compare the two cases fired from the same rifle. From what you have there, no real comparison can be made, but your fired case doesn't show any serious pressure signs to my eyes.

The optimum load for your gas gun is a load that approximates FED GMM. Fed GMM is not a max load, so if you are approximating GMM velocity as fired from the same rifle, you should be in the same pressure range.

Your primer isn't flattened at all, so I'm thinking that the primer cratering is more likely from an undersized firing pin, a large hole, and/or a soft primer. You didn't say what primer you are using, but a Win LR is a good match for BLC2.

Fed brass is soft, and gets battered more from repeated use in a gas gun. Lapua is harder, as is Win brass, and M118 LR brass is excellent in gas guns.

Anyway, I don't use BL-c2 anymore, I prefer 4895 or Varget, because they are more consistent in velocity spread and less temp sensitive, but TAC is also good if you like ball powder.

Your load looks ok to me.

TC

 

[bowslngr]

Re: Overpressure in .308 for gas guns

In my opinion, the ejecter mark and the primer cratering are most likely caused by an overgassed condition rather than an overpressure condition, per se.

That said, the flattening of the lettering in the case head suggests that you may be over the top in terms of max pressure as well.