Jumping lead?

[flyingstick]

I'm just curious as to just exactly how a barrel leads. It seems if you sized a Gas check to a bullet say .002 over groove diameter that the check would scrape all of the lead out and you would just have splatter on the muzzle but none in the rifling. Does the gas check actually jump over the stuck lead? or does the lead in ever so small melted amounts slip under the gas check ? It seems unless there was an awful lot of lead the next checked bullet would scrape it out. New Casting minds would like to know.
Don

[MT Gianni]

To begin to partially answer a deep question, start knowing that no bores are perfectly smooth, no holes are really round and each tube varies from diameter as you go through it. It might be measured in .001 or .0001 or heaven help us .01. Lead is elastic enough to fill and shrink through these imperfections but leaves some behind in them, copper is less elastic and cannot react as fast leaving lead in rough spots. Lube helps to minimize this. I will let the really smart people take over from here. Gianni

[flyingstick]

I would have never thought about the variations inside the barrel. So if I understand this right, Once the check is formed to the groove if it then comes to a place where the groove is not that thick the lead or gas can and will get by eventually causing a buildup?

[montana_charlie]

I have no experience with gas checks (never even seen one) but...

Isn't the leading edge on the cup shoved up against a lead driving band when it's put on a bullet?
With that edge covered, how can you expect it to 'scrape' anything?

The part (of the gas check) which does touch the barrel is the flat side. I would expect this 'flat' to smear lead over a greater length of barrel...but not scrape it out.

I also don't believe the theories about copper bullets scraping lead out of barrels unless said bullet was a pure cylinder with a sharp leading edge, and the 'nose' had a cup to act as a 'collecting bowl' to hold lead shavings as the bullet exited the barrel.
CM

[sundog]

CM, I have [alot] more than several GC moulds. Only one or two have the GC jammed right up against the back of the bottom driving band. Seems like two and both SAECOs, #301 and #432. All others leave enough space that they carry lube between the GC and the rear band.

I think Don's is on track, but I'm not sure about a GC being able to squeegee out lead deposits. We all know the GC helps prevent leading in the first place. Since we do not have a way to effectively catch the boolit as it leaves the muzzle without altering it too much, it's difficult to determine.

I've always subscribed to the idea that to some extent the GC can (not does - can) help carry stuff out of the barrel, especially if it is well fitted. Actually I kinda thought that long before I heard it form anyone else. That might include helping to keep clean both the windward and lee sides of the lands. Can I prove it? Nope. Just a theory. I don't think a GC is strong enough to scrape out leading. It seems more likely that the boolit would get deformed and poor accuracy would result. I've seen THAT more than once.

[Freightman]

Over size boolits and good lube an you will not have leading. I have a new 45/70 H&R and I shot a 300 g PB boolit a 405 HB boolit and a 450 GC boolit all with the same charge of powder 1600FPS +- and had no leading from any of them. I did clean the bore between each five shots with RemOil with teflon, I don't know if that helps but it cann't hurt.
O the only one I sized was the 450gc to install the GC.458 the other two were as dropped 405 HB .460 and the 300 PB .461.