WB
I feel you are very correct, up to the point
Wednesday, April 02, 2025, 10:43

The bullet fills the bore. At that point it’s sealed and pressure builds. Could those gasses ahead be the leakage prior to the bullet seating in the bore?

We know a gas check (?) helps greatly. Perhaps it does mainly prevent blow-by? The old BP guns did well with cork and card, felt wads under soft pure lead bullets.

I once did a scientific test to the best of my ability, noting accuracy enhanced with gas check bullets. At 25 yds. it was 1.5” vs 1.25” for 5-shots. Same shooter, gun, load, bullet, alloy, rest, conditions. One with check, one without.