07-09-2013, 05:52 PM
Guardsman26 Wrote:Reading this discussion convinces me that Bill Alexander and the team at Lapua did a truly excellent job with the 6.5 mm Grendel. To package that amount of performance in a cartridge the same length as a 5.56 mm M855 is truly impressive. The point that is well made here is what happens when you mass produce Grendel rounds, need to use an FMJ projectile or fire the round from a weapon with an excessively short barrel: you get a certain amount of performance degradation.
Then there is the need for a tracer, which eats away at case capacity.
Then there is a possible future need for a polymer cartridge, which also erodes case capacity by about 10%.
For all these reasons, giving the Grendel a longer case is the perfect start point for a GPC contender IMO. You don't need a wider case, like the 7.62 mm one, simply a slightly longer version of the existing Grendel 11.3 mm head diameter.
As soon as you extend the Grendel case length, however, you will need a weapon with a longer action length. You need an AR12.5. Once you accept that requirement, then you are on the road to a perfect GPC. The net result is a weapon that is about 1 lb / 500 g heavier than a 5.56 mm equivalent.
But, here comes the good news. When it comes to building a SAW variant, you can actually start with a 5.56 Minimi M249 rather than the 7.62 mm M240. So with the SAW, you can create a much lighter machine gun, but with much greater firepower.
I've looked at the cross-section of the 6.5mm Swede Tracer, and the existing sectional density and bullet profile of 130gr class 6.5mm pills would facilitate the tracer element without impacting case capacity like tracers do to 5.56 and 7.62 NATO. I don't think there's a need to affect case capacity at all really with an LMG using a 2.400" COAL.
A wider case is also a no-go because you just departed from the intermediate cartridge concept and weight parameters, falling into self-loading battle rifle territory-a system that shouldn't have progressed past WWII in my opinion.
If you were with me when I put 4 rounds on-target at 1200yds from my 16" Grendel as fast as I could index the reticle and pull the trigger, I think the words "performance degradation" would evaporate from your perspective on this cartridge in its existing form. That type of performance is currently exploitable by Machine Gunners and Snipers/DM's. A system built around a military projectile with a BC in the low-to-mid .5's G1 is easy to do. I think a 130gr would be the ticket, run at 2500-2600fps. An LMG will have a bolt/chamber/breech built around the cartridge. I still see no reason to increase the case length & weapon weight, especially for a DMC/SASS.