@ Turkish, half and half. You're not going to rock up with a gold plated desert eagle, it's got to be essentially practical and comfortable for the role at hand but over all kind of yes, any weapon that is practical. And sometimes it does not fit any rules of practicality and is used anyway, but that is rare.
They train with a huge variety of weaponary so it's not odd to see one in training, just in an overt mission, within a hot zone, it's unlikely but happens. They use the AK variants to fit in with the local populace, everyone has one. And with training too it allows them to train the way the host nation would train with standardised weaponary; it also makes them fit in a little easier. In a combat role it would normally be standardised but sometimes isn't, all kinds of reasons can be to why:- sometimes testing, operators choice, patrol commanders choice, logistics, whatever.
Everything must be mission related, some pieces of kit like this is mission essential.
All Special Forces units do it, from a SEAL using the Israeli Tavor TAR-21 in Iraq, Delta using G36's, G3's, MP5's and HK416's to SCAR-H's and M4A1's. Delta even used AK's in the initial invasion of Iraq and Afghanistan, some SEAL units using the AK in Vietnam as it was considered more reliable and left no sign of American presence. There is obvious problems with exchanging ammunition and parts, friendly fire and that's the operators choice and risk. Don't get me wrong, it is a rare event but one that does sometimes happen.
SOTG are really flexible because they have to be as a smaller unit in high risk situations, behind enemy lines or within known enemy areas and they try to keep practical, say a close combat mission; someone rocks up with a sawned off shotgun as back-up piece of kit. It may be odd and not conventional but it works. Knuckle dusters, knives, back-up back-up (back-up to secondary) .38 pistols, yes revolvers (six-shooters), you name it.
@ Viqs, internally with all kinds of stuff like filters, different lenses and cut-outs for certain pieces of kit. They are not stock.
Tactical Education and Motivation.http://www.cqb-team.com/cqbforum/