breech seating bore diameter pp

[Kurt]

Bruce.

I will give you some of what I have found breach seating bullets.

I have done quite a bit breach seating shooting on paper and snow to see what is happening to the breach seated bullets.
Breach seating does enhance the accuracy and I might start using it for the Creedmoor matches where I feel that there is enough time to load this way.
To cut down all of the typing I have trouble doing I will cut it short.
My best results breach seating is using a tool that will allow you to seat a PP bullet that is at least .003 over bore diameter. A palm seater is not the best for this because it takes a lot of pressure to get that diameter in the bore. What I found was that if I seat this diameter it fills the grooves and helps seal the bore to hold the gases back and prevents gas cuts because I just use a .012" card over the powder and I use a cup based bullet with a twisted tail tucked into the cup flush. This protects the bullet base from powder gradual damage. The tight bullet also holds a consistent lack of vertical by keeping all the gas behind the bullet.
I think that is what started the cup (not hollow base) bullet when they twisted the paper under the base and tucked it into the cup to keep flush mating with the over the powder wad.
I do not use lube when I breach seat but I have to wipe between shots.
I have not found any seeable difference seating the bullet deep past the lead or just in front of the case mouth.
I would take caution seating the bullet to deep with a compressed load of powder and even a thin paper wad in front of the powder to hold it in. If you look at the compressed powder in the photo you will see that the front of the compressed powder gets packed very tight starting at about .200" and .300" that hard compressed powder will act like a wad pushing a blast of air against the bullet base and this compressed air is what does the damage. How much of a gap does it take? I don't know because I do not want to find this out with my rifles.

Let us know your progress breach seating.