^ This is a better drum style. Not sure why more don't copy it.
simple, it's very time consuming and it's a bit of a PITA to modify. you're taking a double stack MP5 mag, cutting it down and and installing a spacer in it making it a single stack feed tower, then you have to precisely position it over the SUOMI drum opening, with no room for error and attach it to the drum, not to mention you have to adjust the spring tension so it feeds the rounds up the feed tower reliable.
and even if you think you got it right, you really don't know if you succeeded, you have to fully load it and shoot it. the first time I took mine out to check it after finish making it, it jammed.......I have to tweak the spacer ever so, so that it feed reliably and consistently
in other words, unlike a plastic mold injecting drum and it's components where you can " spit them out" 100s at a time and each one will be exactly the same as the next and each drum from the first to the last will work .....each of those modified SUOMI drums are "handmade" and have to be checked for feeding issues and tweaked, that's why those C&S WERKS drum are like 450-500 bucks!!
if you're interested, 5 months ago I started a thread about the drum I made complete with video
Made my own MP5 71 round drum...... | HKPRO Forums