I saw that episode also, thought the same thing. I'm almost positive that Deadshot's rifle in the final encounter was an M1A Scout. More Hollywood "Ooops" I guess
The AR-7 super sniper rifles used in a variety of movies because they could have the actor assemble it just before taking that shot such as in Femme Nikita.
Richie's (Sam Elliott) LAR Grizzly .45 magnum from Shakedown. Also for pure fun, the awesome weapons used by the inter-galactic exterminators in Critters.
Maybe it was the cinematography, or the "do you feel lucky, punk" line, but the S&W Model 629. 44 Magnum 629 was pretty impressive, even more so for a non-revolver guy.
Everyone has already alluded to my favorites but I think for a diversity/plethora of weaponry (that really caught my eye as a kid) the movie "Magnum Force" definitely ranks among the best.
*edited to add: They should give a medal to whomever is responsible for creating the IMFDB web site--It is simply invaluable!
1 Smith & Wesson Model 29
2 Colt Python
3 Colt Diamondback
4 Smith & Wesson M76
5 Smith & Wesson Model 10
6 Beretta 951
7 Colt Detective Special
8 Smith & Wesson Model 10 Snub
9 M1 Thompson
10 Browning Auto-5
11 Browning Hi-Power
12 Winchester 1897
13 Ithaca 37
14 Winchester Model 70
15 M1911A1
16 Smith & Wesson Model 19 Snub