You'll find these when HW goes a tad too deep with the recess, so they can kick the seal forward a few thousandths. What makes you think you have leakage at the breech seal?
Lack of crosshatching in a spot MAY have implications, as I've encountered some HW sliding chambers that were as much as .007" out of round! It's rare, but some others ran .004" out of round too. These low areas (affectionately referred to as "gully's" at El Rancho Pneumatico) can allow some lubes to get by the piston seal and cause occasional dieseling and inconsistent shot to shot velocities.
HW's factory seals are pretty decent if they aren't scored or sliced up during installation. No aftermarket seal I know of is a direct fit and allows the boss end of the piston to be visible. The piston can be modified however to take some Diana/Apex style seals, but you'll need a lathe and specially ground cutter to do that mod. Jim Maccari and Venom sell some no modification required seals, but their general design is similar to HW's.. just higher end material. RB
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