tdbru Wrote:...
7.62x39 is going to be quite different than what is needed in the 6.5 Grendel for 123gr. Grendel ammo.
...-tdbru
So as it turns out, not as much as you might think, which is pretty interesting. Of course, to remind, this is a hypothetical, and only a path for the desparate. And that buying Wolf Steel 6.5 Grendel to start with is a way better route - so long as you actually have that option.
But yea, I remember this from back when you could get AA2220 as a 7.62x39 powder surpluse, and run in .223 ammo, quite similarly to AA2230. And I ran over 16lb of that 7.62 powder. So that got me thinking, maybe those powders are close between the two cartridges. As most reloaders know, the bigger the diameter the bullet (iin relation to case capacity), the faster powder it needs, to replace the large increase in reaction chamber volume as the bullet starts down the barrel (bigger hole). Which means a .30 cal will need a faster powder than a .223 or Grendel. But the lower the pressure, the lower the charge. And the heavier the bullet, the slower the powder. As it turns out, those 3 variables seem to combine to give fairly similar charges across all 3 rounds. Taking a 123 gr 7.62x39 round, necking it down to 6.5, and putting a light 90 gr bullet actually can work (but I haven't done it, hence the post and question).
So looking it up, a typical 7.62x39 123 gr reload is:
26.5 gr H4198
31.5 gr H335
etc.
A typical 90 gr TNT Grendel reload:
26.8g H4198
31.7gr H335
Pretty much the exact same load. Obviously this is uncharted territory and caution is a must, but the base though that this is a route to cheap primed (and charged) cases that with processing in a press to neck down, is a cheap and readily available route, to start firing a Grendel to those desparate without options. And only, ,for those without options.
Also, my own experience with fire-forming has been that is way higher priority for people than it needs to be. I run 7.62 casings all the time, up to 5 cycles on some now, necks are doing fine. Once you find a load appropriate for those thicker walls, it doesn't matter if it's fire-formed or not. The brass flows out to full chamber dimensions before peak pressure hits, meaning peak pressure isn't any different fireformed or not. Just run that load, and it cycles fine, velocity is the same, and accuracy is surprisingly also the same. My only 1/2 MOA group I ever got was with PMC full-load blaster 7.62x39 brass I was shooting that wasn't evenfireformed yet (i.e. still 7.62x39 body tapered). Cycled fine, shot great. I don't anneal or any of that. Just adjust the die so that a resized casing fits in the chamber, and run with it.
Again, this is a technical hypothetical conversation, not a recommendation. Just an investigation on what back-up plans there are that one can keep in their back pocket. I suspect the biggest unknown really, is the resizing and necking down of a steel casing. It's easy with brass (with a crumple failure rate of around 5%, depending). With steel, I don't really know if that works or not.
Also, as noted above, while this route is currently only marginally cheaper than just buying Wolf Steel 6.5 Grendel (if you can find such), it will amost certainly be considerably more accurate, as well as pragmatic as a hunting round, since a .264 dia TNT 90 is a way more accurate and effective bullet than a 100 gr steel jacket .262" dia Wolf Steel FMJ bullet.
Thanks for all the replies, having fun with coversation

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