Sizing and how it affects accuracy

[wv109323]

I cast some boolits with my new Mi-hec .360 -158 SWC mold. As cast they were .360 . I sized them through my Star .358 die. They had a little resistance going through the sizing die. I noticed that the sizing on some of the boolits caused a small flair of lead on the base of the bullet. Would this flair of lead have affects on accuracy like a bad bullet base?
Is not there an old wife's tale that boolits should not be sized down over .002? IIRC it was from the Lyman book. What are your experiences in this area?

[runfiverun]

that little flair is a bad boolit base. [especially if it's off to one side]

[popper]

Good reason to stick with a BB design. A 30 cal sized down 0.002" gives ~ 0.0003 cu" lead volume that must go someplace. It ends up on the base, that is just from bbl sizing. Do the same for the sizer and you get 0.0006 cu". Gives you a 0.010" 'tail' in the base. Part of the tail gets 'blown' off and CB is inaccurate. My theory is that although the BB is more difficult to get a good cast, it survives the muzzle better. Doesn't make a whole lot of diff. in pistol but will in rifle.

[Wayne Smith]

It doesn't really matter if the boolit is originally a bb or fb. If the base of the bullet is not flat when it leaves the muzzle of the gun you will have an inaccurate boolit. If the gas exits the muzzle of the gun as the boollit leaves more on one side than on the other it will steer the boolit in the opposite direction. We want the base of our boolits to be absolutely flat and the muzzle of our gun equally round and flat as the boolit leaves that muzzle.

[turbo1889]

It doesn't really matter if the boolit is originally a bb or fb. If the base of the bullet is not flat when it leaves the muzzle of the gun you will have an inaccurate boolit. If the gas exits the muzzle of the gun as the boollit leaves more on one side than on the other it will steer the boolit in the opposite direction. We want the base of our boolits to be absolutely flat and the muzzle of our gun equally round and flat as the boolit leaves that muzzle.

Yup, that's the theory. I have recovered bullets fired into snow drifts (specifically for recovery in as close as possible to muzzle exit condition) and this has lead me to believe there is a little more going on. Not sure what the other factors at play are but I'm pretty sure there are some others. For example a particular plain-base load in my SKS always leaves a tooth like divot notch out of the edge of the base in one particular spot in the rifling patter just to the edge of on of the rifling lands that with some finagling with a bore scope I figured out exactly matches up with the gas port on the top of the barrel that works the semi-auto action. Yet I was not able to get any difference in accuracy that I could tell when using the exact same boolit only with an aluminum pop can plain base gas check swagged over its base that did not show the same gas cutting tooth like divots on the boolit bases.

In another case firing a particular plain base boolit with a fairly hot load in my 30-06 at ranges in excess of 100-yards where I was firing on a target that allowed me to dig the boolits out of the soft clay bank backstop and the fliers that were outside of the pattern showed definite off-kilter bases where those in the main pattern did not. Started doing a better job of culling my bullets and ensuring the bases were not damaged during loading and I was able to eliminate the vast majority of the fliers I was getting.

Long story short, yes, the theory holds water and there is validity to it, but it is by no means the only or even the most important factor in a complex fluid situation.

[Wayne Smith]

Read Dr. Mann's The Bullet's Flight. Experiments done at the turn of the last century.

[Echo]

Tails are one reason that I size my boolits base-first. Maybe more hassle, getting the right nose punch, but doing it that way produces the best boolits.

[JWFilips]

I'm having accuracy issues with that same mould also....Starting to wonder.... since it started life as a GC mould.... Maybe the FB re-make equivalent is not as good.
I'm still waiting to hear from the rest of the guys that got this config!

[HARRYMPOPE]

Shoot them and tell us what happens.don't just listen to theory test and see what happens .its how we learn.I have shot some pretty poor looking 38 wc's in a custom pin gun and even bullets with horrible bases shot into the group 90% of the time.and the worst 6 I.could.find still shot 1.5" at 25 yards.

[dtknowles]

bevel bases, gas check designs without gas checks and boattail bullets. Anything that does not have a very small radius corner at the bullet base is inherently less accurate. This applies at least out to 200 yards based on benchrest records. Fins on the base of a bullet are bad. A bevel base pistol bullet that gets loaded without shaving lead is better than a square base bullet that get lead shaved when seated.

Tim

[Doc Highwall]

How about opening the sizing die .001".

[kevmc]

How about opening the sizing die .001".

Good thought....
but wonder what OP's throat dia. is.....???
If he opens the die to .359....if throats are .358, are we then throat sizing to .358 and back to deforming bases??
Perhaps not as sizing would be .001 and then another .001 rather than .002 all at once.....
Maybe one way would be working with the alloy/temp to get as-cast dia to .359 and size to .358.......
Thoughts???

[Leadmelter]

If can find a copy of "The Art of Casting Bullets" Wolfe Publishing. There is a chapter on bullet deformities where the author purposely drilled small holes in the cast bullets. His standard load would shoot perfectly but those with base and nose deformities became unstable and the groups opened up wildly.
Leadmelter
MI