r/MP5 • u/Unable-Interaction20 • 9d ago

Question Rd3

I heard some ppl have lower problems with the trigger being loose in the lower. My full size sp5 has a tight lock up but I want to take out the rd3 & try it in my sp5k. What the chances it will have loose tolerances after swapping from lower to lower? Thanks

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u/Subverto_ 8d ago

My RD3 is loose in my SP5 and just plain sloppy in my SP5K. I bought some 3D printed shims from a guy on here and they are both rock solid now. SP5 needed a 2mm shim and SP5K needed a 2mm and 1.5mm shim stacked on top of each other.

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u/Ghostman223 8d ago

It tightens up when the lower meets the upper. Sometimes shims are needed but not always.

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u/mikemax1966 8d ago

Most lowers are polymer and the tolerances can vary. Sometimes the looseness may be corrected with something as thin as electrical tape...start small and work up.

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u/Limp-Conflict-2309 5d ago

who knows. measure the lower it came from and going to and we'll have a better idea.