Shipbucket

Thanks.
Caddaric might have done, but I'm not sure
And because I'm bored.

One of the more popular modifications

High Standard HS-10B
On the B model the integrated flashlight and fixed carry handle was replaced with a folding carry handle and improved sights.
Despite a capacity of only four shells and a rather dodgy firing mechanism it became quite popular among US police forces for a while, however it was soon retired and sold on to the civilian market.
Popular modifications includes replacing the carry handle with picatinny rails and a magazine tube extension.

Very interesting designs. Great work!

that is a lot of firepower!

I drew the AKS74U and AKS74L families but for versioning problems I have not posted yet.

Moving on from tacticool to the very old
Bergman-Bayard M1910/21 as used by the Danish Army in the interwar years

DISA Light Assault Rifle M/62

Same as above but with a tubular metal stock

United Defense Manufacturing Corporation PVAR (Penumatic Valve and Rod) rifle:

The PVAR rifle is a modification of the standard M4 carbine which has the traditional direct gas impingement system replaced by a short-stroke gas piston system. UDMC claims the PVAR system is superior to 'drop-in' gas piston conversion kits for AR-15 rifles sold by manufacturers such as Adams Arms. The version of the PVAR shown here goes with a built-in sight on the gas block.
manufacturer's website
PVAR test firing (includes underwater firing test!)

Great additions.