Testing, testing...

[stanc]

I guess we're not on the same page...especially since "ho-ho" is the same as LOL and suggests my view that the senior folks would indeed laugh out loud if presented a "new" infantry cartridge producing a puny muzzle velocity.

Joe, we were clearly not on the same page in regard to a "ho-ho" test. :o

As for muzzle velocity needed for a 7.62 replacement, we're actually pretty close. I've thought all along that -- again, for psychological/emotional appeal -- an alternative cartridge should at least equal 7.62 muzzle velocities (in same length barrels), and said so in discussions on the old forum.

I don't know where your 2750 fps figure comes from, but for 7.62 M80 book velocity of 2800 fps from a 24" barrel, I estimate that a 20" tube would give ~2700 fps.

Wilson Combat lists MV of their 6.8 SPC 110gr loads as 2700 fps, from a 16" barrel. That would easily be ~2800 fps from a 20" tube. With a longer, more streamlined bullet, loaded to 2.4-2.5" OAL, it would have trajectory and wind drift comparable to 7.62 M80.

Due to its smaller diameter bullet, it'd be a bit tougher for 6.5mm (be it 6.5 Grendel or 6.5 HPI-SPC) to get muzzle velocities that high.

IMO, the .42" diameter SPC case can work, although "stretching" it a couple millimeters as Tony suggests might be worthwhile.

Using a .44" case, as per the 7x46 UIAC, would be less desirable, but still usable at that case length and cartridge OAL of 2.5 inches. Going to 2.8" OAL seems neither necessary nor desirable. Put a 6.5x52 Carcano and 7.62x51 NATO side-by-side; the difference in size is almost unnoticeable. I don't know if the difference in weight is significant.