Is ignorance bliss?

[Digital Dan]

Puzzled about something that perhaps someone can explain. I see reference to bullet sizing in measure that is .002" to sometimes .003" over groove. I don't dispute the success, but haven't found the need to do so and I wonder what goes on that makes that necessary. I'm shooting cast in a .38 Special, multiple 1/4, 7mm, .30 bores and a few other odds and ends. On occasion I shoot several 1/4 bores sized to groove w/o gas checks and otherwise size to .001" over groove. I find good to excellent accuracy across the board and have never had a bullet I've cast cause leading.

What am I missing here?

[Tatume]

Sizing bullets to 0.001" over groove diameter (rifles) or throat diameter (revolvers) is considered by most to be the minimum bullet diameter that is likely to be accurate and leading free. Any less allows the possibility of high-pressure gas escaping past the bullet and "cutting" the bullet in the process. This is also the maximum required. However, using larger diameters does not hurt anything, and offers the flexibility of being able to use one bullet diameter for multiple guns, having different groove or throat diameters.

[fredj338]

With a gc, correct size is not as important IME. Naked lead, 0.001" over bore di is minimum. It works for most of my handguns. The only rifle that gets lead is my 45-70, bigger is better their too.

[rintinglen]

Digital, if I had luck like yours I'd invest heavily in lottery tickets. Alloy, rifling twist, thread constriction, poor loading techniques, bad boolit design, hardness: all can have an impact on bore leading, but the practice of going large by a thousandth or two has been common for many years, and many people have reported it helped or cured their leading problems, improved accuracy and made life better for them. That said, I have not had occasion to go more than .002 over groove save in the 30-30, where a .311 boolit often gives better accuracy than a .310 or .309 one does. YMMV

[Digital Dan]

I fairly well understand the other issues you speak of, it was just a question about sizing in regards to groove dimension for smokeless loads. Took the simple path, had success and was wondering why others were finding need to go to larger dims. .258, .285, .309 etc has worked well for me.

On another note, I do not tend to load for high velocity, capping things in the sub 2000 fps realm for all of the above, and have found no need for any alloy with hardness above BHN 12, usually more in the 10 range.

[HangFireW8]

Puzzled about something that perhaps someone can explain. I see reference to bullet sizing in measure that is .002" to sometimes .003" over groove. I don't dispute the success, but haven't found the need to do so and I wonder what goes on that makes that necessary. I'm shooting cast in a .38 Special, multiple 1/4, 7mm, .30 bores and a few other odds and ends. On occasion I shoot several 1/4 bores sized to groove w/o gas checks and otherwise size to .001" over groove. I find good to excellent accuracy across the board and have never had a bullet I've cast cause leading.

What am I missing here?

Nothing. Phil Sharpe noted this in the 1930's, that .003" over was unnecessary but oft-given advice. (He also recommended measuring and sizing to fit). This was re-re-discovered in the 60's and you can find it in the NRA Cast Bullet Handbook, sadly out of print.

With soft enough boolits and enough pressure, sometimes even slightly underbore boolits do just fine. Hard boolits even slightly undersized can lead-up a bore. However I shot a bunch of .3085" Lyman's in a .310" bore with zero leading. I was driving them hard, though. I will say this... I didn't find accuracy until I found a .310"+ mold.

At some point someone will chime-in that fitting the throat is more important than fitting the bore. Usually sizing to bore sizes to throat, but some throats are cut larger than bores. We have names for chambers cut like this, but none I can use on a family forum.

[Digital Dan]

Thank you, makes sense.

[DrCaveman]

In the revolvers, it seems that a 'throat fit' can help align the boolit prior to entry into the bore, where it will invariably be sized to groove (assuming equal or smaller than throat). And any revolver worth its salt has throats equal to or larger than groove diam.

So you see how this can lead shooters to prefer boolits .002, .003, or even (gasp) .004 over groove diameter for best accuracy in that gun

Just as hangfire predicted

My statements are based on limited personal experience, and largely the testimony of others, so take from it what you may

[HangFireW8]

Yeah, I forgot to mention revolvers. The are in a category of their own for sizing.

[Wayne Smith]

At some point someone will chime-in that fitting the throat is more important than fitting the bore. Usually sizing to bore sizes to throat, but some throats are cut larger than bores. We have names for chambers cut like this, but none I can use on a family forum.

Sure there is a name ... 1895 Steyr!

[gwpercle]

Is Ignorance Bliss?
Sometimes....when you got daughter's , there are a lot of things Daddy just doesn't want or need to know about...Ergo, ignorance is bliss. Or as I put it.....what I don't know can't upset me.
Gary