There are two issues, but let me stress that they are MINOR issues.

First, a 1:7 twist DOES considerably over-spin the bullets [b]compared to the OPTIMAL spin rate[/b].  But for practical purposes, this means very little.  In most cases, there will be a *slight* loss of accuracy.  By slight, I mean that your groups with M193 may be .2-.5MOA worse than with a 1:12 twist.  This is no where near enough to matter for shooting out to 200m, but if you are trying to shoot beyond 300m, it may be noticable.  But your bigger problem is that M193 isn't all that great a performer beyond 300m anyway.  What I'm trying to get at is that this small difference means nothing to a "combat shooter", but would be important to a target shooter (but who is using 55gr bullet for target shooting at 300m or more?).

The other issue is that 1:7 barrels wear faster than 1:9 barrels (which wear faster than 1:12 barrels, and so on).  Primarily, this is throat erosion.  Is this enough to notice?  Perhaps, but your shooting style will make a far bigger difference than the twist rate, IMO.

So, there are differences, but they are minor, and someone who feels the need to shoot bullets heavier than 72grs is likely to feel that capability far outweighs the downsides.  If you're shooting only bullets 72gr and less, including M193 and M855, then 1:7 offers you no advantages, and very minor penalties.

-Troy