Something I first read a loong time ago was that an imperfection in the base of a bullet is far worse for accuracy than a flaw in the nose; the base is the last place airflow interacts with the bullet, and something off there can have a huge effect. There's been lots of experiments, but I decided to try one of my own.
In comes the .45-70, which was fired yesterday. Specifically, the practice load using the 255-grain semi-wadcutters(intended for .45 Colt). I was going through some of the bullets cast to select those with clean, sharp bases for use, when this idea occurred. So I picked out some that had filled-out properly everywhere except the base, leaving little flaws like these:
What I've been doing is running the bullets through a .452" sizing die, then putting on the paper patch, sizing to .459" before loading. Marked each of the bad-base bullets with a 'F' for 'flawed' on the nose so they wouldn't get mixed up(Sharpies are very handy), and loaded five of these. All were loaded over 10.0 grains of Green Dot propellant, with a cardboard* wad pushed in to keep the powder near the base, and the bullet seated to an overall length of 2.54", then just enough crimp on the case mouth to get rid of the bell**.
Fifty yards, off a solid bench rest, five rounds with flawed bases:
Same distance, bullets with good bases:
So, although it's been proven before, we now have the Firehand Determination: a screwed-up bullet base will screw accuracy.
*Like the back piece of a notepad. I found that the dividers used in liquor boxes work very well. I'm not packing the powder tight, just making sure it's down near the base and flash hole. I've read of some powders in small charges giving some large variations in pressure when loaded in a big case like this, whereas keeping it together near the base cleans that up. You can tilt the cartridge up so as to make the powder fall to the bottom just before loading, or load and then tilt the gun muzzle up before aiming, or use a wad like this.
**When you're loading cast or plated bullets(and most all handgun cartridges even when using jacketed bullets), you use a die to expand or 'bell' the case mouth; that opens it up so you can seat the bullet without the edge of the case mouth shaving material off the side of the bullet.
Why size the bullets before patching? Reducing variables: all of them start out with the same diameter, plus if there's a slight imperfection at the edge of a base, this will usually clean that up.