You might want to watch your BM 10 rounder.
Mine worked fine after being stored loaded for a few days.
Then I left it in my range bag (unloaded).
After a few weeks, back to the range, grab the mag, and have to really work hard to get no. 10 in the mag.
Then it jams the rifle!
The springs will "set" again after the mag is left unloaded.
The only answer that I see, if we want to use these mags;
1. Use a drill on the plastic nipples, take the mag apart, clip the spring, so it will actually hold 10 rounds. Then use a bolt and nut to reassemble it. (Nice!)
2. Use it as a 9 round mag, which apparently it is.