06-10-2012, 04:42 AM
I've been photoshopping again 
Some thoughts on the options for a GPC (General Purpose Cartridge) which could replace the 7.62x51 in portable small arms carried by dismounted infantry with substantial reductions in weight and recoil (and could also replace the 5.56mm in the infantry squad, although that would stick around for a long time in non-infantry applications).
I start with the assumption that the ideal GPC cannot be accommodated in the AR-15 platform. The Grendel is by far the best attempt to do so but, as is being discussed on another thread on this forum, the case width limits the maximum safe pressure to around 50,000 psi, which I suspect isn't quite enough to extract the performance required to replace the 7.62mm. Particularly when the US Army's preference for lead-free bullets is taken into account (longer bullets = less room for propellant). So all of the proposals below exceed the overall length of the 5.56x45.
The first three on the left are based on the 6.8mm Rem only with the case extended slightly to 45mm and (more importantly) the overall length allowed to grow a lot more to use higher-BC bullets. The three versions show 6.35mm, 6.5mm and 6.8mm calibres. These were chosen because the ARDEC calibre survey tested cartridges in 6.35mm and 6.8mm (but not 6.5mm) and concluded that these two were both better than 5.56mm, 6mm or 7.62mm.
The next three (in the same calibres) are based on the Grendel, only with the case extended to 42mm. The longer OAL would ensure that they could not be chambered in modified AR-15 actions, so could be loaded to higher pressures. Maybe this could be designated something like 6.5GM (Grendel Maximum)? With the increasing availability of commercial rifles based on the AR-10 action, this could find plenty of good homes as a big brother to the Grendel (and being a bullpup supporter, I'd love to see one of these in a Kel-Tec RFB!). There is obviously room to extend the OAL to accommodate lead-free bullets. The aim would be to match the performance of the 6.5 Grendel in 24 inch barrels (in metric round figures, 8g at 800m/s, or 123 grains at 2,620 fps) only with longer, lead-free bullets in shorter barrels (20 inch, with decent performance maintained from carbine barrels).
The final cartridge is the 7.62x51 for comparison.
The cartridges shown in the pic are purely indicative and the designs would doubtless be amended by people who know more about the technicalities than I do.
Comments?
![[Image: GPC.jpg]](http://www.quarry.nildram.co.uk/GPC.jpg)
Some thoughts on the options for a GPC (General Purpose Cartridge) which could replace the 7.62x51 in portable small arms carried by dismounted infantry with substantial reductions in weight and recoil (and could also replace the 5.56mm in the infantry squad, although that would stick around for a long time in non-infantry applications).
I start with the assumption that the ideal GPC cannot be accommodated in the AR-15 platform. The Grendel is by far the best attempt to do so but, as is being discussed on another thread on this forum, the case width limits the maximum safe pressure to around 50,000 psi, which I suspect isn't quite enough to extract the performance required to replace the 7.62mm. Particularly when the US Army's preference for lead-free bullets is taken into account (longer bullets = less room for propellant). So all of the proposals below exceed the overall length of the 5.56x45.
The first three on the left are based on the 6.8mm Rem only with the case extended slightly to 45mm and (more importantly) the overall length allowed to grow a lot more to use higher-BC bullets. The three versions show 6.35mm, 6.5mm and 6.8mm calibres. These were chosen because the ARDEC calibre survey tested cartridges in 6.35mm and 6.8mm (but not 6.5mm) and concluded that these two were both better than 5.56mm, 6mm or 7.62mm.
The next three (in the same calibres) are based on the Grendel, only with the case extended to 42mm. The longer OAL would ensure that they could not be chambered in modified AR-15 actions, so could be loaded to higher pressures. Maybe this could be designated something like 6.5GM (Grendel Maximum)? With the increasing availability of commercial rifles based on the AR-10 action, this could find plenty of good homes as a big brother to the Grendel (and being a bullpup supporter, I'd love to see one of these in a Kel-Tec RFB!). There is obviously room to extend the OAL to accommodate lead-free bullets. The aim would be to match the performance of the 6.5 Grendel in 24 inch barrels (in metric round figures, 8g at 800m/s, or 123 grains at 2,620 fps) only with longer, lead-free bullets in shorter barrels (20 inch, with decent performance maintained from carbine barrels).
The final cartridge is the 7.62x51 for comparison.
The cartridges shown in the pic are purely indicative and the designs would doubtless be amended by people who know more about the technicalities than I do.
Comments?