08-27-2011, 07:10 PM
Jaywalker Wrote:...Is there a power requirement inside 500 meters that would disadvantage the Grendel in favor of the more powerful M80 ball? I'm thinking about chewing up cinder block, or something the M80 could do better...This is the key point of a debate still in progress after months (possibly years) of discussions.
My own limited knowledge of penetration mechanics suggests that the Grendel can have very much the same potential for deep penetration or perforating barriers as does the 7.62X51 M80 round. The qualifier is important, because the M80 does not come close to exploiting the potential of the 7.62X51 cartridge.
While bullets from the Grendel won't carry as much kinetic energy, this metric is perhaps the least important measure of lethality. On the other hand, momentum and energy density are important measures of the potential for a bullet to get deep inside of something or to break through a barrier. (Divide momentum or kinetic energy by the area of the bullet -- in much the same manner as sectional density.) The Grendel can easily match or exceed the M80 in these two categories.
The additional qualifier is bullet construction. A bullet with, for example, the same style as the M855A1 (there are others too), but carrying the same momentum and energy density as the M80, will outperform it in all aspects but temporary wound cavity dimensions. One can debate the importance of this metric. Some of the literature suggests that the permanent wound cavity size (as measured in gel) is the better measure of lethality potential. Again, we can reasonably assert that the Grendel will be more lethal than the 5.56 when similar bullet construction is used. This would make it good enough while the 7.62X51 is more than needed at these shorter ranges.
What has not been done is live-fire testing to test the theory (or assertions depending on mindset). For this, we would need at least FMJ bullets in an appropriate weight category and preferably bullets with a penetrator core.
The Lapua 144 gr FMJ bullet is too long and too heavy for the Grendel. Their 100 grain offering is a round nose. I suspect the reason we haven't heard much said about the Norma 120 gr FMJ (Specifically called out as "6.5 Grendel" on the MidwayUSA website) is that it is too new for folks to play with much.
Some of us are reluctant to push testing with bullets we know are not representative of those that would be used for cat. Others would be happy to see any testing move forward.