Over the years so many different rams have been made and most of them all (excpet for a few) were basically the same. Of the rams I have used my favorite goes like this and in order. Nexus or Besales, and free flow or mpp. Most all the rest work about the same with the excpetion for a few crappy rams (I won't go there).
NEXUS vs 44 MAG vs EVO Rams
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-original was 44 mag by belsales,
-then the nexus eclipse ram was made by belsales with a different milling design for nexus.
-then belsales seems to be using the nexus milling design now except carving evo instead of nexus..
FREEFLOW vs MPP vs G-Force Technologies vs TX-tuning
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-all seem to be made by the same company. the MPP rams by moodypaintball had extra drilling for extensive flow. I can't say for the others.