Thain said:
Yes, and no, it is my experience that sound rules for variant ammo adds realism to the game, when that variant ammo is introduced in a logical, true-to-life (or at least, true-to-genre) and above all balanced manner.
I would hazard a guess that any "extra attention to detail" rules add-on (whether we are talking about rules for ammo, poisons, magic, rituals, computers or whatever) implemented as well as you qualify this for ammo... logical, sound, true-to-genre AND balanced (all in one simple Kit!!!) ... would be an addition to any game that sees that aspect in general use.
I just so rarely see all four of those criteria met by a sub-element add-on that i rarely give it significant consideration.

As an example... i would much rather have a player say to me "Joshua will try and move to cover, someplace within pistol range" than have him say "Joshua will move to get 50% cover for the +2 to Ac so behind those crates since they are 3' tall and he wants to get to 32m so as to avoid the -2 more for being beyond 16" so he will take a round to push that crate 1 m closer."
FYI
I have the original UMF on a shelf. I picked it up back when i was buying Chameleon Eclectic's spy/agent/terrorism game... Millenium's End... if thats the right name. It was a real cool book as i recall. If i remember correctly it had a clear overlay for shot scatter that you would lay over your target's sil to see precisely where your shot landed.