Here is my suggestion.

You guys like?

I don't see much use for these.

Bullets for other vendor and brickforge weapons?

Having some bullets and spent cartridges (not just for sniper rifles) could be kind of fun, if they were scaled to Brickforge and Brickarms weapons. But therein lies the problem, since that would make them tiny. Look at the barrels of some of those guns...

That and none of those rounds are all that big compared to people, like SV said, they'd be tiny in lego scale.

Some large artillery shells might be interesting.

The bigger they are, the more easily they can be brickbuilt.

True, though something like a 105mm shell is too small for brickbuilt.

I just have a hard time seeing myself buying extra "rounds" when I could buy another weapon or armor.

If I just have to have some spent rounds for a particular MOC, I will just cut down a little brass rod and toss it on at the end.