Fillers and Buffers for Big Cast bullet cases

[Sharps]

Howdy Sir, your name keeps coming up as I collect info on using a buffer or filler for my cast bullet loads. If I can request some info from you it would be of great help. I have a C. Sharps 45/120 3.25 inch case. I have a custom made 553 grain cast bullet mold with gas check 30/1 alloy. I hold operating pressures to 28000 PSI max the same as a 45/70. Here is the problem. My load of IMR 4350 gives me 1520 fps and extreme accuracy, as long as I remember to point the barrel up before each shot. If I forget everything goes out the window. I have found that several people are using a new product called PSB sold by Precision Reloading. I know that any filler must have NO air space between the powder and cast pill and PSB must be compressed a little. As far as working up loads I can find no info as to how much to reduce a know safe load when filling the air space with filler. I need to fill .750 inches of case. The only info states that the weight of the filler has to be added to the weight of the bullet for calculations. I can understand that BUT, would not the filler reduce the case capacity and in effect make the case smaller to the powder charge ? Chamber PSI would go way up ? I have tried every available canister powder to include the 50 BMG stuff in an effort to get 100 percent load density at 1500 fps.  Any info you can provide for the safe loading of filler is greatly needed

Thanks

[Veral]

My answer is of coarse not just for you but everyone interested in fillered loads.

Pressures do go up some with fillers compared to loads with a lot of air space, but it isn't drastic nor by any means dangerous when working with mild loads. - On the other hand, if the load were approaching maximum safe pressure, and lots of air space were fillered withoug reducing the powder charge.  extreem pressure is certain.

The filler you spedify is my favorite.  I've also used sawdust with very good results, but it should be from hardwoods only, and screened so big chunks don't hinder loading.  Pitchy woods like pine and fir smear a bit or rosin on the bore under the extreme pressures, which is an excellent soldering flux, and not wanted.

Always compress when using fillers, so the filler stays on top and powder on the primer.  Lite compression is all that is necessary.  For your 3/4 inch air space, maybe one eighth inch is plenty, but much severe compression won't hurt.  I find loading easiest when the case is filled full of filler, and have never had too much compression if air space was at least 1/4 inch below the seated bullet.  Very long bullets, seated deep in straightwall cases will probably require that you measure the filler in or it may not be possible to seat the bullet deep enough.

[Sharps]

Though I have been honing my skills at handloading jacketed bullets for 28 years the art of cast bullet loading is new to me by two and a half years and so are the Sharps we have. Thank you Mr. Smith for providing the information requested. My buffer order should arrive this Friday. I look forward to getting the Sharps rounds in fine working order with the help you provided.