I graphed out an assault rifle design following the P90 magazine orientation back in 2005, but ran into trouble with the exact problem stanc pointed out: case taper for longer cartridges. The 5.7x28 does in fact have zero case taper on the wall. The P90 uses a recoiling barrel to deal with pressure, which would not be conducive to accuracy for a modern assault rifle, so I looked into a rotary locking system in a larger bullpup profile with a longitudinal top-fed magazine, with bottom eject.
Another big constraint with that concept is the magazine width, as mentioned already. It would make a pretty bulky gun, especially if the COAL was increased to escape the limitations of the AR15 magwell. It is an interesting idea though. I toyed with several designs based off that system to include PDW's, DMR's, and grenade-launcher combos that pack a lot of firepower into a very small profile. One of the things I addressed was firing hand functioning of common controls: selector manipulation, bolt catch, mag release, and others I won't mention. The P90 requires two hands to operate when changing mags if you keep your firing hand on the grip.
If any of you have felt the FN2000, it is horribly bulky...to the point where you can't even get a good sight picture without canting the gun with iron sights. It also has no bolt hold-open device, and sucky mag change characteristics. There is another way of dealing with bullpups that has not been explored yet.
LRRPF52
Another big constraint with that concept is the magazine width, as mentioned already. It would make a pretty bulky gun, especially if the COAL was increased to escape the limitations of the AR15 magwell. It is an interesting idea though. I toyed with several designs based off that system to include PDW's, DMR's, and grenade-launcher combos that pack a lot of firepower into a very small profile. One of the things I addressed was firing hand functioning of common controls: selector manipulation, bolt catch, mag release, and others I won't mention. The P90 requires two hands to operate when changing mags if you keep your firing hand on the grip.
If any of you have felt the FN2000, it is horribly bulky...to the point where you can't even get a good sight picture without canting the gun with iron sights. It also has no bolt hold-open device, and sucky mag change characteristics. There is another way of dealing with bullpups that has not been explored yet.
LRRPF52
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