Re: 338 Whisper
I've had over 5 years of trigger time with a custom built 300 Whisper that I bought from J.D. Jones. It's a short AR-15 with a supressor. I use it with 220 gr Sierra MK bullets at 1050 fps. This is one of the most interesting rifles that I have ever owned. This rifle will shoot MOA groups at 300 yards and it's a spectacular tactical rifle that makes less noise than a BB gun.
HOWEVER, it would be a terrible choice for deer hunting. This cartridge is designed to be a subsonic round and the trajectory is like launching a '52 Buick downrange. At 300 yards it drops almost 8 1/2 feet. It shoots very tight groups but delivers no significant punch beyond 100 yards. Hot loads with light weight bullets aren't much better.
If you're thinking about getting a 300 or 338 Whisper, I'd say go for it ... but don't use it for hunting. I've got more info about it on my website (one web page will even let you hear a few shots).