Since the clones where all CG was there ever an actual prop made?
A long rifle is seen in behind-the-scenes images from Revenge of the Sith. I dunno about the short rifle.
There is a very detailed full-size ROTS clone statue from 2004 that carries a short rifle, but I think it is a promotional statue: not a prop.
The clones in the flashbacks in the recent OWK series were performers in armour, and they carry physical props: long and short rifles. The armour is slightly different from the movies.
There were also clones in a flashback in BOBF, with same armour as OWK, but I haven't seen any confirmation that those would have been live-action. There is this shot from BOBF though ... The helmet here looks CGI to me because the holes between the teeth in the helmet are black "decals" like the CGI models in ROTS and the visor is not recessed into the helmet more than a mm. Like the armour, the rifle here might differ a bit from ROTS.
Also since you have made a E-11, I would use that as a reference starting point on scale and just collect as many screen caps as possible and go from there.
There's a story that the long rifle had been designed from putting together parts of weapons for action figures. The back end was the back end of a DLT-19 (German MG-34), and the long barrel was an E-11 (Sterling)
but in a larger scale and upside-down.
Then the short carbine would have been designed by shortening the long rifle. I think the barrel is smaller in diameter than the long rifle's.
The grip is the same but the trigger guard is more rounded. The trigger looks like a two-scalloped trigger like the MG-34 and the long rifle but the CGI troopers in ROTS pull it in the middle...