nose slump on postal bullet question

[barnabus]

im rather new to sharps shooting and recently bought 20lbs of 20:1 from a reputable source.The RCBS 535 grain Postal Bullets poured and filled out great at .459 After pouring i waited about an hour and then proceeded to lube them with blue soft from Verals.I measured the overall length of the bullet and they all measured 1.418

Once i ran the bullet in my RCBS .460 lube die i measured the overall bullet length again and it measured 1.408-1.410 That is .010 shorter.

My question: Is this nose slump and what affect does or will it have on accuracy?

Im shooting a Pedersoli 1874 sharps with smokeless powder

[Chill Wills]

No. That is not what we call nose slump. That shortening you measured may be what happens after the bullet cools and starts to cure in your alloy.

Just FYI- nose slump in BPCR is when a long slender high Bc bullet nose is chambered to fire and is unsupported by the lands and grooves enough to retain its shape when fired in a black powder load. In some detail, when the big red light comes on behind the 20:1 bullet and the rear of the bullet starts to move forward before the nose, the bullet shortens and it is said the nose slumps. One or even two bad things happen, the bullet nose shortens and widens lowering its Bc and in doing so may also slump to one side a little or a lot and exit the muzzle all out of balance. As you can picture, this is not at all good for accuracy.

[john.k]

A lot of alloys recrystalize in the hours after casting....volume may change a little or a lot....depends on the alloy.....If you use a lubrasizer,the force applied will also shorten the nose somewhat,depending an alloy hardness.i have had slump on firing with Lyman 314299 bullets,and can just imagine what can happen with the needle nose lee 45 bullet.

[curator]

Lead/tin alloys do not reach full hardness for several hours (days?) after casting. You ran these through your lubesizer and they were shortened only .008", you did good. Are you sure your nose punch is not somewhat responsible? With really soft bullets, particularly long ones, I prefer to size them before they harden up using a push through sizer. When I run them through my lubesizer, they are not getting sized down, only lubed. Lubesizers are rarely perfectly concentric sizing base first, and they tend to crush (shorten) soft bullets if they provide much resistance. Pre-sizing with a push through die eliminates this possibility and produces a concentrically sized bullet with out any nose deformation. It also tends to square up the bullet base.

[barnabus]

QUOTE: Are you sure your nose punch is not somewhat responsible?
In what way? Im using the nose punch that RCBS recommends for this bullet. I don't have or use a push thru sizer as Ive never had a problem with this until now on any of my other cast bullets when sizing. I also have only used range lead or wheel weights for casting in the past. This RCBS mold cast at .459 no matter what alloy I seem to use so basically Im shooting as cast and just lubing. I will eventually have a custom mold made and have it machined so it drops at about .462 and then size down to .460-461 or so. I ran my pot at 750 and was wondering if a lower temp will give me a bigger bullet.