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I have similar snap caps and they cycle just fine in my RDB-C. Granted that I have already ran about 200 rounds of XM193 in my rifle at the range without any issue.

One way to determine what could have caused the damage is by slowly let go of the bolt when doing manual cycling. You should not feel any resistance with the bolt movement until the very end of its travel where it locks in to the barrel extension. When I carry out this action too slow, sometimes the bolt will fail to lock properly. Good thing is on RDB when the charging handle is unfolded and is locked into the operating rod, it can also act as forward assist.
I'm going to keep cycling my remaining 6 snap caps and see if they also end up damaged. maybe I need to polish the feed ramps like others have mentioned.
 

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I'm going to keep cycling my remaining 6 snap caps and see if they also end up damaged. maybe I need to polish the feed ramps like others have mentioned.
One caveat to bear in mind is if you let the charging handle out slowly it will prevent the extractor from seating on a round most of the time. So have your brass rod from your cleaning kit handy to tap the snap cap out from the barrel end.

Also try decocking (as in dry firing) then taking the 'grip' assembly of the RDB off entirely as if field stripping + taking out the last pin at the rear entirely, putting the mag in, and see how everything's fitting together since a lot of the action happens down there and it's by far the most mechanically complex portion of the firearm. You can manually pull back the hammer and work the mechanism through it's process to make sure there's no obvious binding.
 

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Mine seems to be potentially a problem with the magazine latch sorting a bit too low. Opening the lower, I can see that if the magazine is torqued downwards, the top of the bullet will strike the feed ramp at the tip (also damaging it which will affect accuracy). But if it is just 1-2 mm higher, it will instead slide forward avoiding blunting the tip and chamber without anything more than sliding against who notches along the edge of the bullet. In all my failures, there was significant blunting of the tip, so it's likely that a heavier magazine makes the problem worse than a smaller lighter magazine. There is about 2mm of play in my magazine latch so possiblity adding a shim underneath might help improve reliability.

Magazine lifted up
53959

Magazine sagging
53960
 

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Opening the lower, I can see that if the magazine is torqued downwards, the top of the bullet will strike the feed ramp at the tip (also damaging it which will affect accuracy). But if it is just 1-2 mm higher, it will instead slide forward avoiding blunting the tip and chamber without anything more than sliding against who notches along the edge of the bullet.
interesting, I had it disassembled recently and I think the same thing may be happening with mine. I didn’t try to move the magazine around though. These feeding issues were with one of those flip magazines, not the stock pmag.

looking at the damage to the snap caps, the “bullet” is definitely getting banged up on the feed ramp.

I’ll take another look and see if it’s actually just the magazine.
 

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interesting, I had it disassembled recently and I think the same thing may be happening with mine. I didn’t try to move the magazine around though. These feeding issues were with one of those flip magazines, not the stock pmag.

looking at the damage to the snap caps, the “bullet” is definitely getting banged up on the feed ramp.

I’ll take another look and see if it’s actually just the magazine.
There's a lot of forward and back slack even after I shimmed the magazine latch last night. That's enough to give it a couple degrees of rotation forward and back which actually gives a pretty big variation on whether the bullet strikes the feed ramp. I'm guessing this is to accommodate a wide variety of stanag magazines as it's pretty loose for pmags. I wonder if I can find a leaf spring that can fit in the lower rear of the magazine well to pivot the the magazine up (it might not drop free with this change though, but i'm ok with that). Otherwise, there's always reshaping the feed ramps to create a larger slot so the tips don't blunt. It must do a real number on BTHP rounds.
 
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