After working with M4As for almost a year now. We concluded that the Maxxpros benefit from stabilizing the hopup to the outer barrel. This allows for a more consistent positioning in a receiver. Maxxpros have tight tolerance, as a result there isn't much wiggle room if its off-axis to the gearbox. Things like air nozzle rubbing on an edge of the hopup is common in many builds.
We at UA developed an in-house solution that some of you may have dealt with using a Maxxpro, including poor feeding, or pinching buckings and thus causing jams!
The bottom feed chute spacer allows for some guns to have a tighter fit with magazines that are considered 'wobbly' in the magwell. If you have feeding problems with Maxxpros and tend to have to "hold" your magazine up or use some sort of velcro in your magwell to help you feed. This would be the solution to that issue.
At the time of writing, VFCs benefit from the whole set. Krytacs do not need the bottom spacer and may be "too tight"
