Felt wads and grease cookies

[JonnyV]

So the grease cookie has three jobs, 1 protect the base of the bullet, 2 keep hot gas at bay, 3 deposit lube in the bore to soften fouling...

Does it have any other jobs? I'm guessing some will use it to take up space and thereby use less powder, but any others past that? I must be missing something....

[martinibelgian]

Depending on the author, some state it acts as a scrubber to remove fouling, others say it will put a coat of lube in the bore to prevent the fouling from sticking to the bore.
Whatever, provided the cookie is thick enough, it allows shooting pp blowtubing only. Accurately.