Originally Posted by
MistWolf
What are the case dimensions of the 7.62x40 and capacity compared to the 300 Blackout?
It is approximately .200" longer. I trim my BLK brass to 1.355" and my 7.62x40 brass to 1.555". The 7.62x40 also has a bit of the case taper taken out when fireformed (more on this later)
What pressures are both rounds loaded to?
Both can handle the same pressures as the .223 parent brass, which IIRC is 55,000 PSI.
How deeply does the 150 gr bullet intrude into the powder space? Which 150 gr bullet is used, is it a flat base or boat tail?
You could use just about any 150gr bullet, but in the 7.62x40 and the 300 BLK you are beyond the point of diminishing returns IMO. If you do it to make major power factor for competition, that's fine, but most 150gr .308" bullets won't do much at the velocities you can get in these smaller cases. That may change as bullets designed for the 300 BLK start coming out but for now, the bread and butter for supersonics in both will be 110-125gr.
With a twist of 1:11 or 1:12, does that mean this new round intended to run bullets of 150 gr & less?
Yes. From what I've read from the original designer, Kurt, it was intended as an improvement on the 300 Whisper for supersonic use.
Has the 7.62x40 been submitted to SAAMI? The blurb states that the factory ammo will be fire-formed upon firing to give an additional grain of capacity. Where does the factory case headspace? When fire-formed, what changes? Does the fire-formed case have less body taper and/or steeper shoulder angle?
I'm not at home or I'd post a picture of an unfireformed case next to a fireformed case but in short the case taper is straighter in the 7.62x40 and the shoulder angle is different. There isn't much of a shoulder, but I like the sharper shoulder for more positive headspacing so I usually fireform my cases before loading to full potential. It may not be necessary, but I feel better about it.
What has been posted is a lot of advertising hype with very little technical data
Info will come out with time and the right questions. I've been following alot of the threads on the 7.62x40 since I've had one of the early barrels for a while now. Bill and his employees have gone above and beyond providing info and being completely up front about what the cartridge is capable of. I think they are being a bit conservative about velocities, which I'm glad to see. Nothing more frustrating than being told something will perform to a certain spec and then being disappointed when it won't do it.
I'm glad to see it going mainstream since I've been very happy with mine. I'm anxious to get my hands on an 11.3" barrel. My current barrel is in the 16" flavor.
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