Mike - I think the suggestion to identify your application comes into play here. If you're going for a long range, bull barreled, precise target shooter, then free-float will give you some accuracy gains. If this is going to be an M4-type carbine, (a fighting rifle), then there's little-to-no need to free float anything, unless you just like to spend money...Adding a Troy MRF or MRF-DI to your carbine will being the ability to add accessories and bridge forward optics without breaking the bank. Troy rails are over-built, light, (only adds 2oz to your rifle), affordable and most of all - highly regarded among people who actually use their rifles for their profession.
http://www.troyind.com/MRFDI.html
The debate over M4 feed ramps is not heated, but it is lengthly. There are points on both sides of the feed ramp aisle, but Grant from G&R put an exclamation point on the side for their use over on M4C. Their site is down, but head over there for some good information on the subject. Personally, I would not build a rifle without-them - especially in Massachusetts. Being relegated to pre-ban USGI mags makes use of the M4 ramps a reliability feature that I would not be without. The use of M4 feed ramps and new high reliability mags has taken the utility of modern carbine length rifle to a new level. Using the ramps in conjunction with properly maintained USGI mags can achieve near or the same level of reliability. Do M4-type rifles function without them? Sure - just look at Stag. I will make the point however, that adding them - especially to a short tube carbine, is a good safety net toward keeping the gun reliable.
I would also not build a short-tube M4 rifle without an M-16 bolt carrier group and an H-buffer on board. I would be willing to bet that most of the reliability issues related to M4-type rifles can be attributed to improper bolt and buffer combination. I have proven this point at the range last month, with a friend's carbine that was sensitive to reloads and was not holding the bolt back on the last round. It was thought to be a stiff buffer spring, too much material on the hammer, bad magazines, or just needing to be broken in. The problem evaporated when I dropped my BCM BCG into his rifle...gone.
So, in short - my suggestion for a fighting rifle is:
- Troy MRF-DI
- M4 Feed Ramps
- BCM or Colt M-16 BCG
- H-Buffer
Life will be good....
