That's the force that's needed to push a bullet out of a case mouth.
It's caused by how tight the case neck grips the bullet along with the friction coefficient between casse neck and bullet that's caused by the force they're against each other, the area that force is applied and the lubricity of each.
Here's a simple yet very precise way to measure it.
1. Get a shell holder for the case used, heat it up so its softer then thread it with a tap for a 1/4-20 thread eye bolt a couple inches long you'll also need to get. Assemble them with the bolt going into the bottom of the shellholder stopping flush with the headspace flat in the shellholder. That's where the case head's gonna fit. Weigh it and add nuts and big washers to make this rig weigh 1/4 pound.
2. Use different amounts of bullets (nuts, bolts, nails etc.) to put in bags of them ranging from 1/2 to 16 pounds. First two will be a 1/2 and 1 pound ones, then double that number across several so you end up with those plus a 2, 4, 8 and 16 pound one. Their total combined weight's 31-3/4 pound. If you think some bullets may well have greater pull numbers, make another that weighs 16 or 32 pounds. Each bag needs a strong cord so several can tie onto the eye in that bolt.
3. Get a collet type bullet puller then affix it in the middle of a 1 x 4 board about 6 inches long through a hole in its middle to hold the bullet puller that normally screws into your press.
By now, you may well have figured out what the next two steps are; but I'll list 'em anyway.
4. Tie a bunch of bullet bags together for your first test weight, then tie them to the eye in that bolt with the shellholder screwed onto it.
5.. Seat a bullet in a sized but empty case as you would. Then put it in the bullet puller.
6. Slide the loaded case into the shell holder in that board, then slowly raise that boarded bullet puller until all bag strings are taught and their total weight's about ready to lift.
7. Raise the board holding the puller at a rate of 2 inches per second until the weight of the bullets pulls the one in the case out, or does not pull it out. Here's the conditional jump in this routine:
* if the bullet stays in the puller, lower the bags to the ground add more weight, then go back to step 4 then continue with 5, 6, .....
* If the bullet pulls, lower the bags to the ground then remove some weight, then go back to step 4 then continue with 5, 6, .... and so on.
This is called a "bracket and halving" process. (Learned about it spotting the fall of 5" naval gun projectiles making range spot corrections on surface targets.) Add amounts of bullet in one direction until the event changes, then cut the amount in half and go the other direction. Add or subtracting as needed. That's the bullet release force that case has on that bullet seated that way. The objective is to find two bag weight totals a pound or two apart where the heavy one pulls and the light one doesn't, a bullet in the case.
Sometimes there may be a 5 pound spread in what works and otherwise. That shows that bullet release force is another variable.
If case necks are so sized to have only a couple pounds of average bullet release force needed, a 20% spread across them will have a small variable of 6.4 ounces. If the spread's a couple dozen pounds, well, you can see that spread's near 5 pounds is gonna have a big influence on both peak pressure and muzzle velocity.
It's caused by how tight the case neck grips the bullet along with the friction coefficient between casse neck and bullet that's caused by the force they're against each other, the area that force is applied and the lubricity of each.
Here's a simple yet very precise way to measure it.
1. Get a shell holder for the case used, heat it up so its softer then thread it with a tap for a 1/4-20 thread eye bolt a couple inches long you'll also need to get. Assemble them with the bolt going into the bottom of the shellholder stopping flush with the headspace flat in the shellholder. That's where the case head's gonna fit. Weigh it and add nuts and big washers to make this rig weigh 1/4 pound.
2. Use different amounts of bullets (nuts, bolts, nails etc.) to put in bags of them ranging from 1/2 to 16 pounds. First two will be a 1/2 and 1 pound ones, then double that number across several so you end up with those plus a 2, 4, 8 and 16 pound one. Their total combined weight's 31-3/4 pound. If you think some bullets may well have greater pull numbers, make another that weighs 16 or 32 pounds. Each bag needs a strong cord so several can tie onto the eye in that bolt.
3. Get a collet type bullet puller then affix it in the middle of a 1 x 4 board about 6 inches long through a hole in its middle to hold the bullet puller that normally screws into your press.
By now, you may well have figured out what the next two steps are; but I'll list 'em anyway.
4. Tie a bunch of bullet bags together for your first test weight, then tie them to the eye in that bolt with the shellholder screwed onto it.
5.. Seat a bullet in a sized but empty case as you would. Then put it in the bullet puller.
6. Slide the loaded case into the shell holder in that board, then slowly raise that boarded bullet puller until all bag strings are taught and their total weight's about ready to lift.
7. Raise the board holding the puller at a rate of 2 inches per second until the weight of the bullets pulls the one in the case out, or does not pull it out. Here's the conditional jump in this routine:
* if the bullet stays in the puller, lower the bags to the ground add more weight, then go back to step 4 then continue with 5, 6, .....
* If the bullet pulls, lower the bags to the ground then remove some weight, then go back to step 4 then continue with 5, 6, .... and so on.
This is called a "bracket and halving" process. (Learned about it spotting the fall of 5" naval gun projectiles making range spot corrections on surface targets.) Add amounts of bullet in one direction until the event changes, then cut the amount in half and go the other direction. Add or subtracting as needed. That's the bullet release force that case has on that bullet seated that way. The objective is to find two bag weight totals a pound or two apart where the heavy one pulls and the light one doesn't, a bullet in the case.
Sometimes there may be a 5 pound spread in what works and otherwise. That shows that bullet release force is another variable.
If case necks are so sized to have only a couple pounds of average bullet release force needed, a 20% spread across them will have a small variable of 6.4 ounces. If the spread's a couple dozen pounds, well, you can see that spread's near 5 pounds is gonna have a big influence on both peak pressure and muzzle velocity.
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