Well, I'm not an expert, but it could well be that the ammo is getting weak, the recoil impulse being the reason I'm saying this. Ammo lasts a long time, as I'm sure you know, but a lot of how it lasts is based on storage conditions I'm told.
A side by side comparison with known good ammo seems in order.
Major danger, I think, is possibly getting a bullet stuck in the barrel if underpowered and firing another or several more after it without being aware of the non-exiting bullets.
I spoke to the former Speer tech a few years ago who told me they sectioned one barrel a customer sent in and found so many bullets in the barrel they eventually filled it and stopped the cylinder rotation on his revolver.
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