In that regard, what CAN be done to sandproof a rifle, at the design phase?
In that regard, what CAN be done to sandproof a rifle, at the design phase?
Okay. In those designs that use a bolt housed within a reciprocating carrier, like the FAL, M16 and AK, you want the ratio of weight of carrier to bolt to be as high as possible without going overboard; that provided enough force to overcome any resistance from foreign matter debris, fouling, or the two in combination.
Either turnbolt locking, as per the M16, AK and Garand/M14 or locking *flaps* or tabs as per the Russian Tokarev and DP machinegun, the British L86A2 and BAR appear workable. Internal *sand cuts* as on the British Commonwealth L1A1 versions of the FAL may help, though the Israelis considered adding them to their rifles as an afterthought and came to the conclusion that it wasn't worth the effort; their concern was limited to a single theater, of course, and the Brits still had a worldwide interest at that time [mid-1950s] of course; Austrralia was still using the WWI-issue Number One Mark Three S.M.L.E. and something a bit more modern was needed, though the old SMLE and Bren served quite well in Korea for the Diggers.
And note that the Bren and Australian Owen, Austen and F1 submachineguns used top-mounted magazines as per the Japanese Type 96 and 99 and the French Mle 24/29. This allows any sand or grit to fall downwards and pass through the action of the weapon as recoil and vibration shake it free inside the magazine during firing, and it can then fall free through the ejection port or be carried out as empty brass is ejected; this also allows draining of water from magazines taped up to avoid sand or mud collecting in the bottoms of them. Top mounted magazines also allow large magazine capacities without interfering with a good prone position, and allow easy changing of magazines or fitting large capacity drums. The downside is the requirement for offset sights, probably not a problem as electro/optical sights are becoming more and more a standard fixture: that goes on one side and an adjustable iron sight backup goes on the other; ideally, the operator gets to decide which one goes where.
And as on the Bren, L1A1 and Robinson Arms M96, it can be helpful if there's an adjustable gas system, allowing additional gas to keep things operating should fouling or debris be slowing things up, and offering adjustment to compensate for variations between different manufacturing lots of ammunition, particularly with those with very wide distribution and differing bullet weights and powder charges, as per 7,62 NATO and 9mm parabellum- [7,62x39mm M43 Russian AK ammo is pretty much the same no matter what its source, though there are variations of brass and steel-cased versions and light bullet *training loads*, so it can apply to an AK, too.
Tolerances and fitting should take their cues from the AK47 and M1911A1 pistol, both particularly praised for their reliability and dependability, and construction can involve either milled or stamped/pressed sheetmetal components or plastics, as used in the Austrian Glock pistols and AUG rifle and Spanish Parinco 3C submachinegun. But they should be designed into the system rather than evolve by happy circumstance of machine wear following massive production, or careful armourer assembly.
That's far from an all-inclusive list, but it could make for a good starting place.
-archy-/-