[mountainlion]

What is a wall gun?., something that can shoot through a wall?

[W.]

I had a 50-round belt of .50 Browning ammo hanging on my wall. Cost a couple bucks to put it together, but it was cool!

[Kevmo]

The future of sniper rifles is the DARPA EXACTO laser guided rounds out of a smoothbore .50 caliber. Beginners can hit moving targets at 2 miles.

https://en.wikipedia.org/wiki/EXACTO

[Paal Gulli]

Barrett doesn't call it a "sniper" rifle, they call it an "anti-materiel" rifle. But in a classic case of under-promising and over-delivering, the M82/M107 happens also to be precise enough to do double-duty as a sniper rifle.

It bears mention that the M82 was the first weapon ever formally adopted by any military service that was designed, developed, marketed and mass-produced exclusively by the same company (the M-16 wasn't mass-produced for DoD until after Armalite sold the rifle to Colt).

All because it occurred to some professional photographer with no engineering credentials (named Ronnie Barrett) that there might be a market for a man-portable .50 BMG rifle. So he recruited a professional machinist pal to work with him in his garage nights and weekends, and the M82 was what they created.

It also bears mention that the US Militaries have only 'standardized' two long guns since adopting the M-16 in the early 1960s, and the both of them were Barrett products, the M82/M107 and the MRAD, which was created (by Ronnie's son, Chris) expressly as a 'sniper' rifle.