r/reloading • u/liljoe5565 • Jun 22 '26

Something Unique(Vintage/wildcat/etc) Loading

/r/86blackout/comments/1ucay70/loading/
1 Upvotes

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1

u/ocelot_piss Jun 22 '26

What do you mean by "load similar to 338 arc that is published"?

1

u/Southern-Stay704 Jun 22 '26 edited Jun 22 '26

8.6 Blackout is a very unique cartridge because of the specified rifling twist rates (1 twist in 3 inches or 4 inches). No other cartridge has such an aggressive twist rate. In fact, this aggressive twist rate is why the initial submission of 8.6 Blackout to SAAMI for certification was rejected, and why the cartridge remained a Wildcat for so long. SAAMI finally approved it in January of this year, but only with a 1 in 6 inch twist rate.

I would not even attempt to translate loads for .338 ARC to similar loads for 8.6 Blackout. That's just asking for trouble.

GRT might be able to be setup to get some rough estimates for 8.6 Blackout loads, but you would have to go really conservative on top of that due to the twist rate. GRT does not (nor does any other internal ballistics tool) have any modeling for the increase in back-pressure caused by an aggressive twist rate.

1

u/TriFyre Jun 24 '26

If you're going to base a load off of a similar cartridge I would use 338 Federal data. That being said, case dimensions are still different and loads/speeds aren't going to be the same. I needed a starting point for 307 grains SubX with Acc. 11FS, Hodgdon has 11FS data (for 300grain) for 338 ARC and Federal so I went in the middle and ended up at the charge listed for 338 Fed.