Shooting the 75 Tap you will need 7 or 8 twist barrels to stabilize the longer bullets.
Any brand MAY work for a weekend plinker but IMO you guys need to stick with professional grade rifles, I don't think you need a cold hammer forged barrel especially if it doesn't shoot as well as a 4140 or 4150 chromelined barrel but the overall quality/reliability of you weapons should be better than average. Colt and LMT would be 2 of the top choices, most companies do not make a 7 or 8 twist barrel so that eliminates many choices. There are several smaller custom shops that can build to suit with quality that exceeds large production companies.
Staked carrier keys, MPI/HP tested Carpenter alloy 158 bolts or better, chromelined or nitro-carburized barrel, M4 feed ramps and chrome silicon extractor springs in the bolt are required IMO, some of the other stuff not so much. The main thing is getting them operating correctly and reliably with the ammo you intend to use to start with and teaching maintenance, keeping the carrier, bolt, trigger parts and buffer spring lubed is very important. If you need a SSS Op (buffer) spring and H2 buffer to control an over gas issue then use it but they aren't always needed and can even cause short stroking on some weapons. If a McFarland gas ring is needed to stop gas blow by then use it but sometimes they are so tight they can restrict bolt movement in the carrier enough to cause short stroking. The black O ring on the extractor spring isn't always needed either, sometimes it can make the movement too stiff to allow the extractor to snap over the rim of the cartridge.
I am sure others will be along to give you their opinions.
5.56, 6.8, SIX5. The Nexgen of 308s
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Last edited by Constructor; 07-04-2010 at 01:37..