I friend of mine asked me a question that I don't have an answer. The question -when loading cast bullets for pistol does the burn rate of the powder have an effect on leading while keeping the velocity within reason (not pushing it for the max possible velocity)?

My personal experience in terms of leading is when I used swaged lead bullets or pushed cast to max velocity.

So what are your thoughts on how burn rate may effect leading.

I never thought burn rate of a powder had any effect on barrel leading.

Proper bullet fit is the biggest factor in leading. Then pressure vs bullet hardness comes into the formula. Nitroglycerin content can play a roll making the powder burn hotter possibly melting the bullet but not burn rate from everything I've seen.

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SWCA #3437

Proper bullet fit in the throat is a controlling factor in keeping down lead but in a marginal case powder burn rate can be used to control leading.I shoot a lot of 32 H&R magnum rounds in a modified Ruger single action.If I load bullets that are 12 brinell hardness,sized .313 in a .313 throat and I shoot faster powders( Bullseye,231,Unique etc) I will get some leading.In fact in some cases I have actually seen increased leading in the fastest powders that decreases gradually as a slower range of powders are loaded in my revolver.When I use the slowest powders this cartridge can use efficiently I get no leading at all.The powder range I am talking about here begins at Bullseye and stops at Winchester 296.
If I load .314 bullets I get no leading at all.
The problem with evaluating this is there are so many variables to consider.

To get back to your question; I have found that sometimes a faster burning powder will help reduce leading, but almost all leading can be done away with by proper bullet to gun fit. In my revolvers if a bullet is the same diameter as the cylinder throats, most, if not all leading does not happen, regardless of load (within reason).

I read about the formula for determining bullet hardness by chamber pressure, but the formula didn't work for me (according to the formula one of my loads needed a bullet of 25 BHN!)...

If you swipe your hand very quickly into an open flame,you won't burn the skin;the exposition time into the flame being too short.
Same for the lead;the hot gasses apply pressure onto the base of the bullet only for a few thousandths of a second.
What will cause leading is if your bullet doesn't fit the throat and barrel of your gun,gasses will blow by the bullet and the gasses being propelled at many thousands poundsX sq.in.will erode the bullet causing leading.
Since high temp is not applied long enough to melt lead,burning rate should not be considered as a cause for leading.

There may be something to the powder burn rate and its relationship to bore leading, but this is mostly armchair theory material. Best thing to do if you're going to shoot cast bullets is to educate yourself on cast bullet use. A Lyman manual may not be perfect on every point, but it's a good place to learn the basics.

Using bullets cast of appropriate alloy for the pressure / velocity that "fit" the gun will alleviate a lot of problems. I would certainly try at least three powders initially and a lot of experimentation and group shooting if you're serious.

Burn rate, not so much imo. As noted bullet fit is king, but burn temp, it can with certain bullet lubes. Many complain about leading with TG & certain lubes. My theory is the lube gets burned off on ignition, thus the oft times huge plume of smoke with TG & some lead bullets.

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Some powders burn hotter than others and can contribute to leading. Coated, plated and gas checked bullets all seem to resist leading effectively.

I used plain lead lube-in-groove bullets and never had a leading problem. Knowing what each type of bullet is capable of and not exceeding that goes a long way.

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This has been my experience (& frustration) with cast lead bullets in various calibers.

Load a bullet to ~1000fps with Unique & then load the same to ~1000fps using 2400 & generally leading is reduced. Other variables can obliously come into play giving different results.

I'll add that I recall it applied more to leading at or just after the forcing cone. I liken it to taking off in your car in 2nd gear vs 1st gear initially. The bullets hits the FC a tad slower.

It's something worth playing with if you have a bunch of bullets you want to use up but hate scrubbing lead out of the bore.

.

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The bullets alloy has far more to do with "leading" than the burn rate of the powder.

Commercial bullet casters have ruined the term "cast bullets" & how their cast bullets will be used.

To understand leading it's best to understand the mechanics of a cast/lead bullet along with how bullet lubes work and the difference between lubes.

Something to keep in mind:
Anything under pressure goes to the least point of resistance. The harder/faster the pressure is applied, the quicker any flaws/least point of resistance becomes.

If you are new to cast bullets look at this, it will answer a lot of questions...Cast bullet reference on lead alloy's, min / max pressure, lube, shrinkage,

In my experience, the single most important factor in shooting cast bullets is bullet to gun fit...