Beagle, my Father was stationed in Panama during WW2. He carried one of the so called Bushmaster 03 rifles. I have a picture of him setting on a Jeep hood with one on his lap, you really can't tell but he told me that's what it was. The first time I heard about it was in the mid 60's, we were in a gun shop, he picked up am 03 and explained what was done.
The rifle was cut back to about 18 in., the fore stock shortened and sight replaced. He said it shot well but was sighted for a shorter range, I think he said they shot at 100 yds. Said the thing was loud. The command wanted a carbine but none were available so the 03 was altered. They were not experimental but made for a purpose and eventually dumped in the ocean. There were about 4500 or so made. His platoon's rifles were replaced with Thompson Subs as they became available.
Just a little of his history if you don't mind. He was from NC but was sent to Panama with the 150th WV National guard. The original Bushmasters were the 158th Regimental Combat Team , they were shipping out to the South Pacific. They had a Jungle Platoon that patrolled the canal looking for enemy observers watching the canal. When they asked for volunteers to replace the platoon he joined them. They scouted the canal, trained in camo, jungle warfare and tested new equipment. He was in Panama from early 42 till 44 and was sent to Camp Blanding Fla. to instruct trainees in jungle warfare.
Sorry about the off topic but it got me to thing about my Dad, he passed at age 93 in 2013.
Dave