M1 carbine has variable size magazines. The "hold open" on empty relies on the follower in the magazine. My rifle had no mags at purchase. Hunting around town, I found 5 rd and 10 rd mags. One with the "hold open" follower. If the bolt face has a fitment for a stripper clip, you can push them in from the top. My SKS has a bolt like that. The magazine is fixed. Most of the laws are written around the capacity of removable magazines that can be quickly exchanged.
OK, you guys - yes, they do make stripper clips and magazine adapters for M1 Carbine magazines. They are really magazine fillers and they make the same thing for M-16s.
But they can’t be used in the weapon directly like the Springfield ‘03, or the 1917 Enfield, or the M1941 Johnson or the SKS. All those weapons and the Mausers that feature came from, have a machined slot at the top of the receiver to enter and hold the stripper clip so the new ammunition can be directly added to the magazine in the weapon.
You guys are fudging the definition to win a debate...