Tension Testing - It is official!!! According to Instron there is such a thing as tension testing

[seymour fish]

For a given case neck grip on a given bullet, I don't think it matters if your push the bullet out from the back with a pin through a hole in the case head or pull the bullet out with a bullet puller. The same force to move the bullet will be needed.

Mount a shell holder upside down above a hole in something clamped to bench top so it's past the edge. Slide a case in it then put a collet type bullet puller tight on the bullet. Affix a tin can to the bullet puller then slowly but incrementally load it with bullets. When the bullet gets pulled out of the case, weigh everything whose weight did that.

One could use a hand scale affixed to the bullet puller and get numbers good enough to make comparisons

Seems clear enough that GRIP is the bottom line. Mechanical press-fit and co-efficient of friction. Condition of the internal neck lubricity: bare metal, carbon, etc. breakaway force influencing pressure rate of rise, initial harmonic timing, etc

 

[seymour fish]

Seems clear enough that GRIP is the bottom line. Mechanical press-fit and co-efficient of friction. Condition of the internal neck lubricity: bare metal, carbon, etc. breakaway force influencing pressure rate of rise, initial harmonic timing, etc

As an aside, would not seating into the lands render this entire discussion moot ?

 

[Bart B.]

As an aside, would not seating into the lands render this entire discussion moot?

No. I commend you for mentioning it; not many think about it.

Yes, grip is the bottom line. Seating into the lands is the top line. Pressure curves from burning powder start at the bottom then go to the top for getting bullets all the way into the rifling, then resistance is more uniform. Pressure rises to peak then drops down to close to what it took to get the bullet fully into the borenehen it leaves the barrel.

It adds another friction issue needing force to overcome. How much depends on throat angle, bullet shape and jacket hardness and the bore cross section area. Bore cross section area in square inches is one of SAAMI barrel specs and is equal to groove diameter cross section area minus that of each lands cross section.

Smaller throat (leade) angles tend to yield more uniform pressure curves that typically makes for better accuracy.

 

[SheepDog]

Whether you start with the bullet engaged in, or off, the rifling before the bullet leaves the case it engages the rifling and the neck is expanding so the amount of friction between the bullet and the cartridge has been reduced or disappeared completely.

 

[Bart B.]

That's true.

Some barrels have enough freebore (cylindrical, same diameter, larger than bullets, from chamber mouth to start on the rifling) that bullets are out of the case before touching the throat. 300 Win Mag has zero freebore, 300 Wby Mag has .336" freebore.