What causes leading????

[abunaitoo]

Ok, I'm opening a big can of worms with this question. But I'm kind of confused.
Same rifle, slugged to .427. Same batch of lead, WW water dropped. Same lube, Lar45 Carnuba. Same load, 13gr Unique. Different bullets.
Lee 430-310 GC, 427di. Lee 429-240 PB, 427di.
Aside from the weight, and one is gas checked. Both shoot about the same.
GC one no leading. PB has some leading.
I'm thinking the gas check has a lot to do with no leading.
So the leading is caused by no gas check?????
What would stop leading with the plain base bullet????
Softer or harder lead.
Different lube.
Slower or faster powder.
Larger or smaller diameter bullet.
Filler or paper check.
I've never had much luck with plain base bullets.

[Maven]

"Same rifle, slugged to .427. Same batch of lead, WW water dropped. Same lube, Lar45 Carnuba. Same load, 13gr Unique. Different bullets. Lee 430-310 GC, 427dia. Lee 429-240 PB, 427dia."

As you know leading may be caused by many intertwined things. E.g., smoothness of bore; BHN of alloy; powder charge; burning rate of powder; velocity & pressure generated by powder charge, which interacts with BHN; bullet bearing surface; amount of lube the CB holds; quality of lube; diameter of bore; diameter the CB is sized to; etc.

In your example, I don't think bullet design, lube or powder speed or alloy are the problem. However, if your bore is .427" (assuming no typo here), shouldn't you be sizing to .429" or .430"? Or, to put it another way, are one or both of your molds dropping undersized CB's? If so the plain-based one will almost certainly -> a leaded bore. I'd try beagling the 429-240PB until it drops a larger CB (.429" or .430"), or possibly returning the mold to Lee if that doesn't produce an immediate improvement. Btw, I've been using a Lee 429-240TL mold which drops a .429" CB in my Ruger SBH and don't get much leading with 8grs. of Unique (1,000fps) even though the cyl. throats & bore are .430".

[missionary5155]

Good evening
As the load is 13 gr Unique I assume this is a 44 Mag ??
I AM limited on reloading manuals here.... BUT I have looked and even with a 240 J Thang the MAX load is 12.7 grains... Are you sure this is a safe load with 310 grain boolit?? But you are DEFINATLY getting into the LIMIT of Unique... why not swap for a slower powder.
That .427... is this the chamber area ? This is THE most important area to find out what is the real size of boolit to feed it.
If your chamber is .427 I would be sizing my Boolits at least .428+. What are your as cast Diameters ? To small a PB boolit will not Hold Back the pressures... especially WWWD as it just is not gonna seal off the chamber.
So me if all I had was Unique (like here) I would back down to 8 grains and work up. I also would Cut my mix to 50/50 WW + Pure lead. I would NOT size to .427 but to .428+ . If you want to stick with WWWD then you still need a fatter boolit... .428+
An example... my 1892 44-40 here has a .432 chamber area... I shoot .433++ boolits.
I am sure others will add commo.. so be ready.
Shoot safe ! You can damage a rifle....
God Bless you. Mike

[OLPDon]

As with alot things in life SIZE MATTERS,,,, that being said I agree with Maven. Plain base are more prone to leading the GC not only keep the gas cutting of Boolit but also scrapes lead as it moves down the barrel. I would say first get the Boolit up to size by beagleing the mold (do a search on Beagleing Mould) that should fix the leading. If not follow the rest of what was stated above.
Don

[Bret4207]

Don beat me to it, you may be getting leading with both your boolits but the GC is scraping it away. Sounds like you need a fatter boolit to start with.

[Shiloh]

Boolit size is probably #1

OLPDon and Maven nailed it.

Bore condition, lube, velocity, alloy hardness, quality of boolits, will all contribute to leading issues.

Shiloh

[Alex Hamilton]

Ok, I'm opening a big can of worms with this question. But I'm kind of confused.
Same rifle, slugged to .427. Same batch of lead, WW water dropped. Same lube, Lar45 Carnuba. Same load, 13gr Unique. Different bullets.
Lee 430-310 GC, 427di. Lee 429-240 PB, 427di.
Aside from the weight, and one is gas checked. Both shoot about the same.
GC one no leading. PB has some leading.
I'm thinking the gas check has a lot to do with no leading.
So the leading is caused by no gas check?????
What would stop leading with the plain base bullet????
Softer or harder lead.
Different lube.
Slower or faster powder.
Larger or smaller diameter bullet.
Filler or paper check.
I've never had much luck with plain base bullets.

The principal cause of leading is gas cutting. High pressure gas blows past the bullet, rips small particles of lead off the bullet sides and deposits them further up the bore where they are "ironed" over by the passing bullet. Leading builds up relatively quickly in first 1 or 2 inches of the bore and accuracy goes out of the window. If you are experiencing this, then your bullets are probably too small. They should be .001" over groove size or, in revolvers, interference fit in the cylinder exit holes.

Even if the bullets are good fit, the huge torque imparted by the rifling can cause wear of alloy against the leading edges of the lands, which in turn opens up small gaps at the trailing edges and thus enables high pressure gas to blow by and cause gas cutting. Reducing powder charge minimizes this type of leading and to some degree using harder alloy also helps.

Once the bullets are good fit and fired within the capability of the alloy, it makes no difference what kind of bullet base you use. I am regularly firing bullets of gas check design without the gas checks up to 1400ft/sec without any leading.

Gas check not only obturates the bore and does not allow blow by by high pressure gas and, being made of hard material, it resists the "torque wear" and thus effectively prevents gas cutting.

It is also possible to eliminate gas cutting by using soft gas checks - see [url]www.caversham16.freeserve.co.uk for details, but these work safely only in straight walled brass. I would not use them in bottle necked cases, because they can easily fall onto the powder instead of staying in the neck.

Leading that appears near the muzzle is caused by either insufficient lubricant or lubricant breaking down, but this condition is very rare these days as the lubricants are very good.

[abunaitoo]

I should have said what I was shooting.
Swiss Vetterli.
The bore looks shiny. Don't feel any rough spots when cleaning.
Slugged the bore and it measured .427.
With the 430-310, if I seat it out far enough to cycle in the mag, it has a hard time chambering. If I resize to .427, it fits fine.
The 429-240 fits fine as cast.
I'm going to try to lube then Alox dip to see if it helps.

[Marlin Junky]

Too much friction resulting from various conditions is the cause of leading. One example of a condition would be a gas leak breaking down the lube film. Another example would be too much pressure obturating the base of a rifle bullet into the barrel walls with enough force to break down the lube film.

MJ