Load Development Process for BP PP Bullets?

[1885_Highwall]

So what is the best way to develop a bore riding PP bullet with black powder?

The procedures must be special? With normal load development, the max OAL will be limited to where the bullet hits the lands. However, with a bore riding PP bullet, the max OAL will be limited to the minimum amount it can be inserted into a case without falling out when loaded? Say 1/8th or 1/10th of an inch? Do you start with incrementally seating the bullet deeper, each with zero compression, until you find an OAL your rifle likes? Then start incrementally increasing powder/compression to find a node? You would certainly be limited by how much powder/compression you could increase by if the best OAL is a bullet barely seated in the case. I am assuming you probably want as much bullet sitting out in the lands as possible?

Or do other variables have a much greater affect on precision?

[country gent]

The bore riding PP bullet actually has no oal since it sits in the bore.
I normally start with the bullet seat .150-.180 into the case.
I start with no compression no airspace on the charge of BP.
a .030 napa rubber fiber wad and 2 typing paper wads.
Then as I work up I increase the powder charge 1 grn at a time this also increases compression of the charge.
I chronograph these as fired in 10 shot groups watch not only velocity and group size but standard deviation and extreme spread. As the charge goes up velocities increase some, standard deviation and extreme spread goes down. As you work up fouling will also go down and become more manageable.

I have loads that are single digit ES But most times I also have to uniform primer pockets, deburr flash holes. Sometimes a primer wad may be needed.
Once I get close with the inital then its test with different primers.
My PP loads are almost all very light neck tension also. hand seated onto the powder wad stack which is compressed to depth with a compression die.

Another thing is to recover some of the patches they can tell you a lot. Ideally the patches come off at the muzzle the outer layer will be confetti the inner wrap will show rifling marks with the under fold intact. It shouldnt look much different no burns or heavy color changes.

My fold under is such that a small circle of lead shows in the center, this makes for a flatter base

[Don McDowell]

If you’ve got a good grease groove load,use the same weight and nose profile patched bullet. Add 2 grains of powder and a thin felt wad over the wad you use.
Equally important or maybe in the load development is bore wiping regimen

[MichaelR]

Something to keep in mind. The longer, heavier, or softer the bullet or larger the powder charge, or faster powder, the more the bullet will be upset. Shorter, lighter, harder bullets or smaller charge or slower powder, the less the bullet will upset. Sometimes a felt cushion wad under the bullet can help with excessive bullet upset.

[Lead pot]

Felt or cork has a major effect on the bullet base because of the cushion effect it has from what I have seen with recovered test bullets checking this out.

[1885_Highwall]

Thanks all! Certainly a lot to think about, consider, and test. But this should get me going. A few weeks ago I tried sizing down some of my GG bullets and patching to bore. Results were encouraging enough to order a proper slick sided mould. So we’ll see how it goes. Planning to start with 1:16 and SC 55w. I already prefer the patching process over pan lubing. Hoping to find a decent load without too much agony.

[Lead pot]

Cutting the patches can be time consuming. That can be worked out so it's not bad. The way I do it I can cut about 600 in an hour or less if I stay with it.
Patching has it's benefits over lube grooved projectiles.

[1885_Highwall]

So far I’ve been cutting them with a Cricut. Probably not the fastest method but was very easy to fine tune the length and width. Has been great so far. I’m not really a high volume shooter

[MichaelR]

If your bore is .450”, the SC 55W works well with a .446 bullet. If the mold drops a .444” bullet, the thepapermill.com 9# onion skin works well.