Let me rephrase the question....

[ezypikns]

I believe that shooting cast lead bullets at too high velocities will increase leading in barrels. Is that a true statement? If so, I want a fairly mild load for 9mm cast lead bullets.
In my Speer reloading manual, I can find load data for a 9mm 125 gr LRN bullet using a minimum of 4.1 grains of Unique powder (911 fps).
I happen to have a quantity of 115 gr LRN bullets, and a quantity of Unique powder.
Since the weight of a 115 gr bullet is 8% (or so) less than a 125 gr bullet, can I cut the minmum load of Unique by say 10% to find a good starting place for a load of Unique under a 9mm 115 LRN bullet? Say, 3.6 or 3.7 of Unique?
Logical?

 

[PotatoJudge]

Doesn't the powder charge usually go up as bullet weight goes down? I'd just go with 4.1 grains of unique, though the minimum load is around 5.5 grains.
Are your bullets hard cast?

 

[trickyasafox]

lighter bullets usually take more powder. that being said, it is safe to use load data intended for a heavier bullet on the next lightest one. IE 125gr Lead data will be safe for 115 gr lead loads.

 

[Sunray]

"...a true statement..." Yep. 3.5 grains of Bullseye is the accuracy load for a 121 grain cast bullet in my old Lyman book. I've used it with truncated cone cast bullets with decent results out of my Inglis BHP. 3.5 to 4.5 is the range of charges. 4.4 to 6.0 for Unique, but I've never used Unique.

 

[ezypikns]

The bullets are..

Meister. Hard cast.

2% tin, 6% antimony and 92% lead

So actually, if the maximum load for a 125 gr LRN bullet is 4.5 grs of Unique, then that would probably be a good starting place (minimum) for a 115 gr LRN?

or as trickyasafox says:

IE 125gr Lead data will be safe for 115 gr lead loads.

 

[BruceB]

The best way to avoid leading is to use the fattest bullets which still allow your rounds to chamber freely. In general, this applies to almost any rifle or handgun using cast bullets. Bore and groove diameters are largely irrelevant, if you can chamber rounds with larger-than-"normal" bullets in your gun.

Most of my 9mm shooting now uses (my own) cast bullets sized at .359". Yep, .359, and you won't see that in any manuals. I also don't get much in the way of leading!

I have even used 160-grain 358156 semi-wadcuters with surprising success in my 9mm pistols. At a muzzle velocity of just under 1000 fps, they move the 9mm into a new area. Although the bullet doesn't look like it has a feed-friendly profile, it works fine in a Ruger P95 and in a Browning Hi-Power of lamented memory.

 

[mc223]

Carefull with cast bullets in barrels with parabolic twist. They can cause a catasrophic instantaineous disassembly of a firearm due to leading.
And no he didnt say what gun he is using. Just Info for the public.

 

[JDGray]

Lighter bullets can use more powder, less pressure, but dont need more powder. Nothing wrong with light target loads with light bullets, as long as the slide cycles.

 

[EddieCoyle]

I believe that shooting cast lead bullets at too high velocities will increase leading in barrels. Is that a true statement?

That's a true statement, but you'll be hard-pressed to make those velocities in most handguns, and it would be very difficult to achieve in a 9mm - downright impossible if you choose a hard enough alloy.

You are more likely to see leading as a result of a charge that is too light.

If a charge is too light, the bullet will not compress enough to seal in the barrel. This will allow hot gases to escape around the bullet, melting the sides and depositing the lead in the barrel.

BruceB's post above alludes to this. He uses larger bullets that will "seal" at lower pressures.

 

[Walkalong]

If your alloy is too hard for the velocity it will lead just the same as if your alloy is too soft for the velocity only for difference reasons. PM if you have any questions about alloy etc. I can at least tell you what to look for to give an idea of what is giving you leading and how to cure it.

 

[ezypikns]

Parabolic Twist?

Is that the same thing as polygonal rifling?

Apparently Parabolic Twist refers to rifling in which the twist becomes more pronounced as the projectile nears the end of the barrel. Are modern semi auto pistols commonly rifled in this way?

Polygonal rifling (I believe) refers to the actual shape of the rifling itself, and I've heard that shooting cast lead bullets is NOT a good idea in these pistols (mostly Glocks?)

 

[LHB1]

My experience as a reloader/shooter of cast bullets (42 years) in pistols is that you can get leading from multiple causes:
1. Too small diameter bullet = leading right in front of chamber because the bullet does not fill/seal the bore and lets hot gases flow by. Fix: use bullets of .001-.002 larger diameter.
2. Too light a load = leading right in front of chamber because the bullet does not fill/seal the bore and lets hot gases flow by. Fix: use higher pressure load to expand bullet to fill barrel bore.
3. Soft/swaged lead bullets: streaks of lead in barrel. Fix: Do NOT use soft or swaged lead bullets.
4. Inadequate lube/insufficient lube/too high velocity: streaks of leading from muzzle back depending on severity. Fix: reduce load or change lube. I use NRA ALOX lube (50% ALOX and 50% pure beeswax). Might also change bullet type/brand altho most modern pistol bullets are pretty good designs.
5. Too hard a bullet = same as #2. I have never encountered this problem. I mostly use straight wheelweight alloy for my bullets. Fix: use bullet with a little more tin in it to soften the alloy slightly.
6. Rough barrel = luckily I haven't run across one of these. Don't know if lapping would help. Might have to replace barrel.

I shoot bullets cast from H&G molds to 1400+ fps (measured by Oehler chronograph) thru four S&W M629 Classic pistols with no leading for 50+ shots. Shoot H&G #68 cast bullets thru four different 1911's with no leading for up to 100+ shots. YMMV

Good shooting and be safe.
LB

 

[mc223]

Thanks ezypikns, That is what I meant. 4:30 in the A.M. Brain was off.