What Happens on HV Rifle

[Bama]

Started looking at a number of cast bullet designs and have question on gas checks with PC or conventional lube. I understand gas checks protect the base of the bullet from the hot gases and give a more uniform base when leaving the crown. Comparing the neck to most drive section designs results in gas check being loaded past the neck and into shoulder or main case. The question is how much damage is done to bottom portion of bullet that is passed neck and before gas check? In one case first grease groove would be exposed to full pressure and temperature.

[runfiverun]

powder coat will protect it till it's gone from there.

[Bama]

If it fully protects it at the point of highest temperature and pressure, why should a gas check be needed. Also in conventional lube, I don't think the lube would stand it either.

[Smoke4320]

Bama I have absolutely no scientific proof just edjamacated guess .. we/they were using gas checks on lubes bullets to maintain accuracy before PC
and it seems we are doing the same .. The PC may not burn off BUT the soft lead will deform .. The gas check is much tougher to distort hence the increased accuracy

[405grain]

I'm not sure where I read this, (think it was Glen Fryxell, but not sure) but to show that the heat has absolutely no effect on the base of the bullet, they were gluing a disc of tissue paper to the bullet base and then firing them. The recovered bullets showed no scorching or burning of the paper. This is just like quickly passing your finger through the flame of a candle, and not getting burned. The reaction happens so fast that there's no time for the heat to transfer. The gas check protects the bullet base from pressure, there is not enough time for heat to transfer into the bullet. If a lube groove were sticking below the shoulder, the lube could become deformed by the pressure, but with powder coated bullets there should be no effect. It would be the same as seating a long jacketed bullet with the base projecting into the case.

[runfiverun]

'in the case' isn't the highest point of pressure nor heat.
if you look at a pressure trace you can see the bullet engraving the rifling very early in the pressure sequence.
usually you will see a slight pressure rise.
then a bump from the engraving.
then a slight fall off of pressure.
then a steady rise up to peak pressure and acceleration before a steep decline.

the little bump is where you will get your gas cutting, riveting, and lube blow out.

[Motor]

405grain is absolutely correct. The heat has no effect on the base of a the bullet. Probably the number 1 reason being exposer time.

The gas check serves one purpose and one purpose only and that is to act like a piston ring and prevent gas from going around the bullet. In fact if gas checks were simply rings that left the base looking like a 45 caliber full metal jacket they would still do their intended job perfectly.

A lot of guys are more worried about the gas check being stripped off when seated below the case neck or simply falling off inside of the casing. I don't know how likely either one is but I guess it could happen.

Motor

[Phantom30]

RP can you show the trace and annotate what is going on?

Here is a link to a reference which discuss the pressure wave stuff, hope this adds to the discussion

http://www.the-long-family.com/shock%20wave%20theory%20summary%20explanation.pdf