05-17-2011, 01:00 PM
JASmith Wrote:We should take a close look at one of Stan's long-time favorites -- the .25 Remington necked down to 6mm. One can think of it as a 6.8mm SPC stretched and necked down.Thanks for the plug, Joe.
We can analytically demonstrate that the heavier 6mm bullets will have potential from equal or better penetration than the 7.62 M80 round. The smaller diameter has an edge for getting equal sectional density bullets up to higher velocities than do the larger diameter pills. A 100-115 gr 6mm driven at the velocities this intermediate round can deliver will almost certainly be far more lethal that th 62 or 77 gr 5.56 round when similar bullet construction is used.
While the 6mm Optimum might be worth considering, my original proposal was somewhat flawed, if only because it was based on inadequate information. :o
The first error was in postulating a VLD bullet (to maximize BC). I think Gene has noted that a VLD is a poor choice for a military bullet.
The second flaw was in planning for a lead-core projectile. I didn't know at the time that the US Army was later going to switch to "green" bullets.
An M855A1-type 6mm bullet (with 5:1 L/D) would likely weigh less than 90 grains, and have a BC subtantially lower than the 95gr lead-core VLD on which I had based the 6mm Optimum's estimated performance.
I might be mistaken, but it appears that eco-friendly 6mm bullets of 100-115 grains may not be feasible. The Barnes banded solid in this caliber is only 75 grains, with a 4.4:1 L/D and an unspectacular 0.341 BC. http://www.midwayusa.com/viewproduct/?pr...ber=950050
BTW, NAMMO experimented with brass solids, and found them unsatisfactory. See page 7 of: http://www.dtic.mil/ndia/2006smallarms/mauritzson.pdf Might a design like the NAMMO BNT (page 9) be what the UK would require, being it's a FMJ?