I'm wondering what would keep you from permanently removing the baffles in your "lead dust collector" eliminating possible issues in the future.
Concerning pellets, I had the same issue (pellet flipping out of the leade) when I shot some supposedly 4.52mm 8.4 grain exacts from my .177 Beeman R9. Loose and variable fitting pellets for sure. I also had two "dry fires" at a THAGC match shooting the supposedly 4.52mm JSB Exacts and I would have had a 3rd if I didn't notice that loose pellet flipping out of the leade when relatching the barrel.
A couple seasons ago I bought a .177 HW95 and I believe that HW has reduced the .177 bore size a bit with the later offerings because
some of the supposedly 4.52mm JSB Exacts actually "almost fit" the leade OK with the remaining pellets from the tin having a variable/loose fit. Matter of fact the boxed 7.9 grain Crosman Premiers that always fit "perfectly snug" in my R9 leade loaded "too tight for comfort" in my HW95 leade.
A while back I ordered 4 tins of 4.52mm Air Arms Domes and found that they actually fit the HW95 leade "nicely consistently snug"........
LOL...the AA domes were actually accurate from the HW95 when I tested them upstairs at 18 yards shot sitting on a bucket resting the gun on cross sticks. Matter of fact, the 4.52mm AA head sizes were so consistent that I ran the tins through my home made 4.50mm pellet sizer and to my surprise almost all of the AA pellet heads were sized a bit with my sizer...........
I did have one dented tin of AA Domes in the PA shipment and there were a few pellets with dented skirts in that tin........
Here are a couple test groups I shot at 18 yards with unsized and sized AA Domes........
Since these two groups were shot "bucket and sticks" I wouldn't claim that the tighter head sized group had anything to do with reducing the head .01mm. The pellets from my 4 tins of AA Domes (marked 4.52mm) actually measured 4.51mm with my digital caliper.
I haven't tested the AA domes sized to 4.50mm yet because it's been too cold, rainy or windy so far this spring.