What forces do GC's and jackets counter, anyhow?

[jabilli]

When we place a gas check on the base of a bullet, we are protecting it from immense heat and pressure...

Full jackets, why do they fill this purpose better?

[oneokie]

Guilding metal jackets have a higher shear strength than lead alloys. Thus they are able to be gripped by the lands better. Not much worry with them stripping the lands.

[runfiverun]

or have the nose set-back or slump to the side,isn't afected by gas cutting....

[beagle]

A GC protects the base and will "bump up" to bore diameter to fill the lands and grooves to prevent gas blowby. This blowby actually causes some leading and is present in every round fired....jacketed, GC'd and PB. On jacketed it shows up as copper fouling, in GC'd it's leading and in PB bullets it's leading. This happens in a very short time between ignition and bump up of the bullet...microseconds. But it's still there for a short period of time. The GC also "hardens" the base of the bullet and grips the rifling and gives better accuracy provided the bullet isn't driven too fast in which case, it starts skidding or strips the rifling./beagle

[jabilli]

Thanks, for the answers guys :-)

I feel a bit dumb for asking- What is stripping? (No not THAT kind. :-p ) I ran a quick google to look it up myself before asking here, to no immediate avail. How do you determine when a bullet is stripping the bore?

Beagle- So if I'm understanding you correctly, the chief difference between using a gas checked bullet and a full metal jacket is within the tiny amount of time where gas blows by the gas check before the check expands nice and tightly in the bore(The difference being that the copper jacket is deformed less by blowby) ...Right?

I suppose the thing I'm trying to find out is, why can't GC'ed bullets tolerate shooting velocities in which one may obtain with jacketed bullets?

[Smokin7mm]

Stripping is basicly as the bullet engraves the rifling and starts down the barrel there are stresses at the point where the lands meet the grooves and the softer lead material can shear which in worse case gives you an under size bullet that is just riding on top of the lands. The tighter the twist the more stress indused. Lead is deposited in the grooves causing severe leading.

Bret

[oneokie]

Stripping is when the shear strength of the lead alloy is less than what is required to grip the rifling and shears away from the mass of the boolit. The remaining boolit bounces/wobbles down the barrel. You will have poor accuracy and severe leading of the bore.

[beagle]

Couldn't have explained stripping any better myself. Stripping is when the torsional stresses imparted by the rifling due to velocity overcome the tensil strength of the alloy you're using for bullet metal and the bullet jumps the rifling.

The GC does seal better than lead and protects the base. Imagine a very small sharp corner of lead with a lot of heat and pressure on it. That's your bullet base. It will melt or errode even in the short time that combustion occurs and this will be blown by the bullet and end up as leading in front of the chamber. The GC eliminates most of this errosion and at the same time, adds more tensil strength to the base band of the bullet. Not as much as with a more heavily jacketed bullet but it helps some and that's one reason we use more moderate velocities with cast bullets./beagle

[curator]

Jacketed bullets are also much harder than just about any lead alloy (BHN 40-50). They won't slump or deform much from G-forces when fired. They will "self-center" in the bore even if they don't expand to fill the grooves. Most J-word bullets allow some gas-blowby in the grooves. I'm not sure this causes "copper fouling" which may really be from smearing due to rough bore or just friction. Smooth oversize bores rarely copper foul even at high pressure. Gas checks reduce pressure-melting (heat of fusion is higher with both copper and aluminum) of the cast boolit's base, and help the rifling to grip the boolit.