IIRC the A1 actually ditched the tungsten core, it's a "lead free" round not AP, the M855 was supposed to be an "environmental friendly" round the tungsten isn't a penetrator really it's some sort of composite matrix but after studies showed that Tungsten is just as bad an even worse than lead as far as the environment goes they've redesigned the round.

The M855A1 is also lighter than the M855 so if my memory serves me correctly they've switched to a mild steel core.

The M955 does use a tungsten carbide penetrator and is classified as an AP round but the usual "green tip" (or well just "green" ammo now since the A1 doesn't have a tip color) ammo that is in use uses steel penetrators for the most part.

Interesting. I had assumed tungsten was environmentally friendly since it is permitted for waterfowl hunting:

http://www.cabelas.com/product/Non-Toxic-Shot-Buyers-Guide/5...

M885 was originally designed as basically a copper coated tungsten penetrator, but the M885A1 now is steel tipped with solid copper body. Turns out the tungsten core made it loose it's spin during flight and caused tumbling.

Not sure they saved themselves a lot of money, copper is $. I knew they were trying a tin alloy at one point, not sure what happened to that other than Google saying "Unstable at high temperatures", which is interesting.

The M855 was supposed to be a round that would leave less environmental impact both in actual use and in training.

Tungsten ended up being just as toxic ( The round also had stability and terminal ballistics issues but that is another topic) as lead so they've replaced that one in the M855A1 with mild steel.

Then they had a fancy jacket made out of bismuth and tin alloy that appeared to be both not exactly environmentally friendly especially for the users due to buildup of bismuth salts firearm and unstable at high temperatures which causes inconsistencies in accuracy when fired from a hot barrel.

So they've pretty much moved back to a copper alloy half jacket and an arrowhead steel tip insert, the M855A1 also didn't solve all balsitis issues and ended up being slightly longer which can cause feeding issues.

Ah... I'll have to lookup the bismuth salts forming. That was the missing piece I couldn't find.

Most of my barrels are ferritic nitrocarburized, so they should be impervious to anything... guessing that the US armed forces might have as fancy bore linings.

IIRC it was something to do with the bismuth interacting with powder and primer residue.

And don't be surprised if military guns are less decked out than yours they are built to costs.

Also remember that it's how often you clean your barrel and how many rounds you fire.

The M855A1 was designed to used in both assault rifles and LMGs so something like a SAW would fire 1000s of rounds before it can be properly cleaned up. Even an M4 would probably be much less cared for while on active duty than your match grade rifle.

>don't be surprised if military guns are less decked out than yours they are built to costs

A quick search suggests M16/4 barrels are chrome lined - just like a good AK