I've been thinking...

[RoyRogers]

Not to worry - my head did not fall off from the process, at least just yet [smilie=1:

Actually, just watching the loading process at the bullet crimp stage has me wondering what keeps a bullet crimp from scraping off the lube and popping the gas check off a cast boolit as it leaves the case mouth upon firing? I suspect the discharge blows the case wall, crimp included, out and away from the exiting projectile but since my fired cases still have some evidence of having been crimped I wondered if perhaps a crimp removes lube, etc and can lead to leading?

Thanks for all sage comments from the learned masters :-)

[bootsnthejeep]

Must be something in the wind Roy, its odd, I was just pondering that the other day myself. Especially with the heavy roll crimp I throw at my 44s and 45s cause Elmer sez so. =)

[Bret4207]

The theory? Powder gas expansion forces the ductile brass case against the chamber walls, the pressure build until the boolit starts to move, the combination of the boolit and gases push the crimp out. Does it scrape lube away? I would say it depends on a zillion variables but in most cases yes, a limited amount, until the crimp is pushed out to the nominal boolit diameter. at that point I imagine the boolit and gases carry the lube away from the crimp area.

Thing is, the pressure is still building in many cases long after this has happened and when the boolit hits the forcing cone and enters the barrel (smaller than the case,chamber and throat) all that lube still on the boolit comes into play. Most designs carry lots of lube and the amount scraped away by the crimp is tiny compared to the remainder. I would be more concerned if my brass is too hard and the crimp is distorting the boolit when it's moving the crimp rather than worrying about a tiny amount of lube that may be removed. Annealing can take care of that.

Just my thoughts and worth just what you paid for them.

[44man]

Not to worry - my head did not fall off from the process, at least just yet [smilie=1:

Actually, just watching the loading process at the bullet crimp stage has me wondering what keeps a bullet crimp from scraping off the lube and popping the gas check off a cast boolit as it leaves the case mouth upon firing? I suspect the discharge blows the case wall, crimp included, out and away from the exiting projectile but since my fired cases still have some evidence of having been crimped I wondered if perhaps a crimp removes lube, etc and can lead to leading?

Thanks for all sage comments from the learned masters :-)
The boolit opens the crimp with the first drive band, gas pressure can not act on the brass when a boolit is in the way.
If the boolit is too soft the crimp can indeed not open all the way and can make the boolit smaller before getting into the barrel. TL boolits can have a large portion of the lube scraped off.
It always amazes me when a fellow will slug the bore, buy or lap the size die, search for the best lube and use good dies for neck tension. Then he uses soft lead, sizes the boolit when seating and crimps the devil out of the brass, all of which ruins the boolit and causes leading. He will post about problems and the first 50 answers will be to make the boolit softer so it "obturates."
My suggestion is always make the boolit hard enough to withstand seating and fully iron out the crimp. At that point it will also withstand the transition through the forcing cone and into the rifling.
The gas check will not be scraped off, pressure holds it against the base but it could be sized and loosened, they are softer then the crimp and soft lead under them has little resistance. This is why a soft gas checked boolit can cause as much leading as a soft PB.
I did not even mention the boolit skidding the rifling before grabbing it.

[peter nap]

The boolit opens the crimp with the first drive band, gas pressure can not act on the brass when a boolit is in the way.
If the boolit is too soft the crimp can indeed not open all the way and can make the boolit smaller before getting into the barrel. TL boolits can have a large portion of the lube scraped off.
It always amazes me when a fellow will slug the bore, buy or lap the size die, search for the best lube and use good dies for neck tension. Then he uses soft lead, sizes the boolit when seating and crimps the devil out of the brass, all of which ruins the boolit and causes leading. He will post about problems and the first 50 answers will be to make the boolit softer so it "obturates."
My suggestion is always make the boolit hard enough to withstand seating and fully iron out the crimp. At that point it will also withstand the transition through the forcing cone and into the rifling.
The gas check will not be scraped off, pressure holds it against the base but it could be sized and loosened, they are softer then the crimp and soft lead under them has little resistance. This is why a soft gas checked boolit can cause as much leading as a soft PB.
I did not even mention the boolit skidding the rifling before grabbing it.

Ok I have it.
If the boolit is too hard, gas cutting and leading
If the boolit is too soft, lube scraping and leading

I had a fellow that worked for me once and he was always late for work.
When I asked why...he said he had a medical condition. He has to take his medication to wake up, but had to wake up to take his medicine.:killingpc

[462]

If the boolit is too hard, gas cutting and leading
If the boolit is too soft, lube scraping and leading

Yep, Papa Bear too hard, Mama Bear too soft. Our quest is to find the "just right" Baby Bear boolit.

[theperfessor]

I think 44man is right on the money. The answer is to control the bullet hardness, neck tension and only crimp as much as necessary.

If you're shooting soft wadcutters from a .38 you only need enough neck tension to keep the bullet from jumping forward from recoil. Most shooters use little or no crimp, since these types of loads don't usually recoil much.

If you're shooting hard-kicking magnums then you need a harder bullet, more neck tension, and a heavier crimp, especially with some "magnum" type powders (296 for example).

The answer lies in finding the right combination of alloys, neck tension, and crimp.

[runfiverun]

neck tension and crimp are enemys to a soft boolit there is a balance that needs to be reached.
enough crimp [just enough] to keep a boolit in place for the load being used but not enough to interfere with it being moved forward without distortion.
and neck tension tight enough to hold the boolit in place while the powder raises pressure high enough to burn efficiently without squeezing the boolit to a smaller diameter.
part of using a soft enough boolit is to get it large enough to account for any squeezing taking place here.
balance,measuring,testing.

[Bret4207]

5R5 took the wind from my sails! Find the balance point for your alloy. Hard or soft alloy makes no diff, you still have to find the balance point. And lets remember to add "may, might, sometimes and often times you'll find" type qualifiers to all of this. Every time someones lays down a "rule" someone else comes along and breaks it!

[RoyRogers]

Thanks for all your thoughts - keeps my little brain from going into overload when others add thier wisdom to my lack of knowledge. :confused:

I actually learned more than I had hoped for from the responses.

Happy Trails - RR

[Gunlaker]

Thanks for all your thoughts - keeps my little brain from going into overload when others add thier wisdom to my lack of knowledge. :confused:

I actually learned more than I had hoped for from the responses.

Happy Trails - RR

If you do the math, in a caliber like .45/70, at cast bullet velocities, you'll have between 4000lb to 5000lb force on the bullet base, decreasing as the bullet moves down the bore. I imagine that would make the crimp negligible.

Chris.

[AZ-Stew]

Imagine having a fixture that holds the cartridge case so it won't move. If you pull the boolit from the front to remove it from the cartridge, case tension against the perimeter of the gas check may be greater than the tension holding the check onto the boolit. In this case, the check will remain in the case as you pull the boolit out from the front.

Fortunately, this isn't what happens when a round is fired. Imagine the same fixture holding the cartridge, this time with a large hole drilled through the case head. Slip a steel rod through the hole and up against the base of the boolit. Now smack the other end of the rod with a hammer. The boolit and check will be driven out of the case, and no crimp will scrape it off since the pressure forcing the boolit and check out of the case comes from behind the boolit. When firing a round, the gas pressure from the burning powder continues to press against the boolit base through the bore until the boolit leaves the muzzle. The check CAN'T come off because there is thousands of pounds of gas pressure behind the boolit holding the check firmly against the boolit base.

Regards,

Stew