I spent some time checking the Algore-web trying to find concrete info on XM193, and if it really is a hotter load than M193. I found one reference that said that XM193 is really M193 that the military rejected. I'm interested because this is what I keep in my 16", 1/9 twist M&P15T, and I'd like to know if this is the best FMJ round given my barrel length and twist. I also read that with the 55 gr. M/XM193 rounds, the twist rate really isn't that important, it's only when heavier bullets are used that the twist rate becomes important. I did find some good info discussing fragmentation of M193, and that velocities need to be above 2700 fps for fragmentation to realiably occur. From what I read, XM193 does about 3075 fps. from a 16" barrel, and keeps above 2700 fps out to about 150-200 yards. So my questions are: -Is X/M193 (55 gr.) the proper bullet weight ammo for my rifle (vrs. heavier 62 & 77 gr. rounds) given the twist rate and barrel length of my rifle? -What is the real difference between XM193 and M193 ammo? -Does barrel twist rate effect velocity to an appreciable degree? I hunted for answers to these questions before I posted this, but my google-fu was weak today!
http://ammo.ar15.com/ammo/ http://www.m4carbine.net/showthread.php?t=25709&highlight=xm193 http://www.thegunzone.com/556xm.html http://www.m4carbine.net/showthread.php?t=9511
Optimal twist/weight is: 1/9 - 55gr - M193 1/7 - 62gr - M855 77gr (MK 262 MOD 0/1) will not stabilize, and will most likely keyhole from a 1/9. XM193 didn't meet contract specs and it's better to recoup some cost and sell it off than throw it away or remanufacture. I think someone's told you a tale... No.
Winchester White Box is M193 for all practical purposes, works great in a 9 twist and available at Wally World cheap. Some times I run across the Malayisian M193, it's pretty good surplus and hits the required velocity from a 20" IMO the M193 55gr FMJ will have better terminal effects than M855 from a shorter barrel weapon.
as stated, XM193 is MIL contract ammo that did not meet final MIL inspection [for whatever reason], hence the X designator. I have a 1/7 twist and a 1/9. The M193 does shoot better in the 1/9 and my M855 [contract ammo] shoots better in the 1/7....marginally. Inside of the ranges I shoot at [generally <200m] I am still able to take care of my target quite well regardless of the ammo I use in either twist rate.
