Calico M950:
http://www.military-today.com/firearms/calico_m950.jpg
Possibly would use the P90 Anims, although I'm not sure how it'll look, I'm hoping similar to the Chang-Feng 06 SMG
Automag Pistol:
https://static1.squarespace.com/static/56311321e4b08236a1ddbbf7/t/587b8a986a4963fff6d13a48/1484491417595/AutoMag44Classic.jpg?format=1000w
Possibly could use the Desert Eagle anims, but the hands may clip through the gun or not touch it at all, the Parabellum might work too though.
PP90M1:
http://www.imfdb.org/images/thumb/b/bc/Pp90m1-2.jpg/350px-Pp90m1-2.jpg
Bizon Anims
IWI Tavor SAR:
http://cdn1.athlonoutdoors.com/wp-content/uploads/sites/8/2015/06/bullpup-swja15-iwi-682x383.1431968400.png
TKB 076:
https://qph.ec.quoracdn.net/main-qimg-c77024b65e13f76cc99225c2b00d9815-c
or https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQgdI3jUmDxXceeV_jD54wvH3hobSBi3jqzrfifxJXn0mb25Iki
I'm not sure if this one will work with current anims, the magazine might be positioned too far back
Kel-Tec RFB:
https://cdn3.volusion.com/ftmar.dfprg/v/vspfiles/photos/RFB18BLK-2.jpg?1435390667
Possibly could be a sniper rifle/DMR, and use the WA-2000 animations
Walther P99:
http://www.imfdb.org/images/thumb/7/70/WaltherP99_twotoneA.jpg/400px-WaltherP99_twotoneA.jpg
Colt CM901:
http://www.imfdb.org/images/thumb/d/d4/CM901.jpg/800px-CM901.jpg
Most likely would be an AR but might make a good DMR sniper rifle as well
Barrett M107:
http://www.imfdb.org/images/thumb/a/a2/Berrett_M107.jpg/400px-Berrett_M107.jpg
HK Mg4:
http://www.imfdb.org/images/thumb/1/1b/H%26KMG4.jpg/500px-H%26KMG4.jpg
A few too that I'm not sure are possible with given animations, considering the bizarre magazine placement:
HK G11:
https://static.giantbomb.com/uploads/scale_small/1/13313/1169189-g11_scope.jpg
MP412 REX:
http://www.imfdb.org/images/thumb/c/c7/Mp-412-1.jpg/400px-Mp-412-1.jpg
Now I've never done any requests like this before so if there is any proper formatting/guidelines I missed, please let me know in the comments.
Ah, I fogot REX revoler isn't a traditional cylinder mag.
Well, the only gun in Payday 2 that have break-action that fits with it are the M79 Grenade launcher, but then it won't have rotating cylinder anim during shot.