In a COLT M4 16" 1-7 (fully chrome lined), will the bullets be overstabilized, and will it wear the barrel faster (increased velocity)than heavier bullets (70gr+)?  Basically, at 100yds (bench), will I notice a "substantial" difference in accuracy/groups using the 55gr vs. a 75gr?  I went to check the ammo oracle, but the search here didn't find it.  I'm still looking for it, but another link would be great, thanks

From the Ammo Oracle:

Q.Simple question: Can I fire M193 ammo in my 1:7 or 1:9 twist barrel?

Yes.

M193 is essentially a "universal" round; able to be stabilized by barrels with twists between 1:14 and 1:7.

Here's the Ammo Oracle link.

[url]http://www.ammo-oracle.com/[/url]

Out of my 20" Colt (same 1/7" twist as the 16" M4) my best groups so far are from 50gr. Winchester Ballistic Tips.  Granted this was at 100 yards, not 400 yards, but the point is 55gr. will work fine.

Another point to consider regarding the "extra velocity" is that those Winchester white box rounds (55gr FMJ) are much slower than M193. My experience with my 20" Bushmaster (and pretty mucy everybody who tests them) is that you get only about 3050-3100 fps out of them . Remington UMC 55gr FMJ also gives the same velocity, but Winchester Q3131a gives me the full 3250-3275 fps. The various SS109 loads I have tried give me about 3075-3100 fps, so the Winchester white box is slower than SS109.

It's good range ammo, try it. If your rifle likes it, shoot it with no fears.