No doubt you've done some good work on the paint job, that isn't the issue though.
The issue is that some people look down on custom mandos, some purists on these forums and other costuming groups. Now I know the mercs are really working hard to up the quality of those who costume in public, and I am sure that it is your intention to get the best out of your budget, your armour is looking fantastic at the moment, so, without trying to sound like a great big douche, I think you'd be letting your hard work so far down by sporting an M16 rifle.
Reach for the moon and settle for the stars, which basically means, strive for the best and only cut corners if you have to, that snub rifle you have with your armour on post 14 looks much more Starwarsy and with a few greeblies stuck to it would look fantastic.
I'm sorry if that sounded harsh at all, it was meant to be a constructive pep talk