There are different follower configurations, but you generally run into problems related to those at one end of the ammo column or the other; the first rounds or the last rounds. The OP didn't make any distinction about where the rounds were in the magazine, so I'm not sure it's applicable here. If it is, the test is to load maybe 5 rounds in the magazine at a time and see if the first three always function.
I'd be looking at the cartridge dimensions, then at all the firearm related factors already mentioned.
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