Never used a bullpup in combat.
I never found a way to do this satisfactorily with a bull pup.
From the US Army training manual.
“ g. Run to the next position —
(1) Keep the distance short to avoid accurate enemy fire.
(2) Try not to stay up any longer than 3 to 5 seconds so that the enemy does not have time to track you with automatic fire.
h. Plant both feet just before hitting the ground.
i Fall.
(1) Sliding your right hand down to the heel of the butt of your weapon.
(2) Breaking your fall with the butt of your weapon. j.Assume a firing position.
(1) Roll on your side.
(2) Place the butt of your weapon in the hollow of your shoulder.
(3) Roll or crawl to a covered or concealed firing position.
k. Cover your buddy’s movement with forward by fire.”
If you go down this article you will find a portrayal of it. Notice the hand position change from D to E.
https://www.uakron.edu/armyrotc/MS1/9.pdfEven the M16 wasn’t ideal at this. With the M14 there was no need to slide your hand down to the butt. The M16 is weaker at where the stock joins to the receiver and the solution was to slide your hand from its normal grip at the trigger down to the butt so that the point of pressure is shifted to the butt where the hand is. Never found a way to use a bullpup to help break the fall. It always slammed down on the magazine, twisted the rifle and let you awkwardly collapse to the ground. Then on the ground the location of the magazine to the rear didn’t allow you to really hug the ground and still get a good firing position. The magazine became a teetering point lifting the shoulder and increasing your profile as a target. Magazine change on the ground was awkward and required using the non firing hand to move back to release magazine which meant the rifle became unsupported. Couldn’t get a real visual on the magazine and magazine well which usually lead to a little fumbling. Same with clearing stoppages.
Also can’t use it to buttstroke. Some complain that the shortness means it is not good for bayonet fighting, but I dismiss that as unimportant.