Las sunday I shot my BSA 12/15 rebarreled to 32-20 and converted to CF at 200m, 1st try with PP bullets.
Those that have been following my experiments, know that the little rifle sports a 1:15" twist barrel, so allows the use of heavier bullets - in this case a 150gr PP bullet

The remington case was loaded with 17.4 grqins of 1 1/2 Swiss, with an overpowder card wad, the .301 bullet patched with 8 lbs paper seated on top in fireformed cases.
Primer was the federal small pistol, and the bullet was seated out in order to be hard into the lands when the breechblock is closed.
For a 1st try, the results were very encourqging, as illustrated by the target below - remember, prone, sling only, no support and aperture sights:
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The 1st shot from a clean barrel was a 7 at 5 o'clock, then 1 shot the other 4 - with a moderate-fresh fishtailing 6 o'clock wind.
I was pretty pleassed for a 1st try - for reference, the 10-ring is 2 MOA, the 9 4 MOA.
One thing that kinda surprised me was the BC of my bullet - looking at the elevation difference between 100 and 200, it would be about 0.45, which is quite bit better than I had assumed when designing the bullet.

Well, I can give you the drawing of the bullet ) essentially a PP duplicate of my GG bullet:
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And the rifle?   It's a bit of a hybrid - take-off .308 match barrel, chamber cut off and rechambered to 32-20.  Original sights used, period 2-point sling.
Typical fouling management too:  2 moist patches, followed by one dry.
The most important one is of course holding your tongue in the right place while pulling the trigger...
I t is a bit like a BP 'whisper' - small case, heavy subsonic bullet (MV at about 1070 fps) - which will reduce wind drift and increase BC considerably.   Maybe not ideal for long range, but it does seem to work for the shorter ranges.

Richard, don't forget this is not benched - and with a fresh fishtailing 6 o'clock wind.  Even then, it is about 3 MOA vertical which isn't too bad in my book.
And faster?  I might get 5-10 fps more, but that's it - FFG might be faster, but the case will hold less weight, which will tend to negate the burning rate effect.  I'm thinking more working on minimizing ES.

In order to get 17.3 grains of Swiss in that little case leaving enough room for the bullet, I both settle AND compress.   Upping the compression a lot might allow me to pack in an extra grain, but no more.  If I'm lucky, that might yield 20 fps at most - which I doubt.
Still, I'm still experimenting, so I'll try going up and down a bit, but there's not all that much room to start with...
The main objective will be a good ES together with the best possible accuracy.  It's the ES that will be most important for the longer ranges...

The intention is to use it as BPTR - so no duplexing.  And for breechseating (well, kinda) I have the Pope 308403, but as it is quite a bit heavier at 171 grains, it won't get the MV up appreciably... 20 grains might just get me to 1100 - 1110 fps with it if I'm lucky - but more would be just about impossible with BP and this bullet.

Chris,

What made a big difference for me was the use of thinner paper to patch the bullet - replacing my airmail paper with 8 lbs sketch paper gave a dramatical difference.  Unfortunately, also in patching - with the sketch paper I have to patch dry, otherwise I'm all too easily tearing the paper.
And the barrel has to be just about spotless, i.e. no lead:  That will also ruin accuracy with PP bullets.  Some people claim that shooting PP will clean the lead out of a barrel, but that's not my experience - more like stripping the patch and causing even more severe leading....
I wipe with 2 wet, 1 dry - for the moment.  maybe I should put the chrono up again to check velocities.

Gert