Ian
Notorious member
Damn, where have I been?
I'm one of the weirdos who will adjust alloy before powder, primer, or jump. I'm pretty set in my ways about neck tension and what brand of primers I use. Jump is more of a function thing, much of the time the rifle requires it and I'm stuck with either a little, or a little more, not none, so I ignore Barlow bullets and use a shape that wiggles into the middle of the hole a little easier and give them some room to do their thing.
I'm also one of the weirdos that does stuff like pop some squib loads with different seating depths and measures the bullet travel, then repeats the test with 3/4 case of corn meal. You can learn a lot doing that. I have no way to measure pressure directly but can tell you that a bullet with more "run" at the throat will definitely go farther into the barrel with the same applied force. A jammed bullet sometimes won't hardly move at all, more than likely the primer pressure in an empty case just escapes around the case mouth and back around the chamber since a primer won't obturate the brass at all. A load of powder or inert filler behind the bullet reduces volume (air spring) drastically as well as probably helps become a granular stop-leak. Extra O2 in the powder space doesn't help the powder burn (there's a close to stochiometric oxidizer ratio built into the powder chemistry already), but it DOES allow the powder to be fluffed up and suspended in the space, exposing more to the primer heat faster than a full load of powder....however this diminishes at a certain point based on too much space and too few "targets" for the primer particles to hit, so we get poor ignition at very low load densities. We fix that in a variety of ways, most of which involve taking up space with filler if we insist on using a powder that creates a very low loading density.
Breech seating with smokeless powder introduces a couple of variables that we aren't used to dealing with. One is the starting resistance and the other is case obturation. I would use only well-annealed, never resized cases because sealing the chamber up consistently without a bullet to cork it up is difficult. If you aren't swabbing between shots, slight bore condition changes or even temperature changes between shots can have a pretty big effect on the resistance the bullet puts up to the powder each time before it gets moving. An engraved, MOVING bullet isn't much of an obstruction, but an engraved, STATIONARY bullet is a tremendous obstruction. Just run simple F=Ma where "a" is extremely high and F goes through the roof, we're talking milliseconds here. I've also experimented with the raw force needed to engrave a bullet vs. moving one which is already engraved and the results are pretty inconclusive to our cause because it doesn't account for inertia, IOW not a good test.
I would advocate trying a much faster powder because it will spike pressure and obturate the case, then slam the bullet with a high pressure wave so quickly that the effects of gas leaks and varying bullet sticktion (here's where Lamar and I start making up descriptive verbs, get used to it) are greatly reduced. Kick a ball and it just goes straight. Push it with a feather and any slight surface change or slope makes it roll willy-nilly. Another thing you could do is add some lofted Dacron to hold the 2400 powder in place, so long as there is minimal gap between the front of the Dacron and the back of the bullet, otherwise you're replacing a barrel. That would allow the powder to build more pressure before the bullet sees it and would also improve ignition in that "square" case better, as Lamar pointed out. You have to get that bullet moving consistently from shot to shot so it exits the muzzle at the same point in the whip, otherwise you get vertical stringing just from the harmonics and it will leave you scratching your head as to why a load with low ES/SD shoots like crap when you know the powder is lighting well and one with high ES/SD shoots better but happens to be timed better with the harmonics of the rifle system even though you think it wouldn't be with such variations in velocity.
I'm one of the weirdos who will adjust alloy before powder, primer, or jump. I'm pretty set in my ways about neck tension and what brand of primers I use. Jump is more of a function thing, much of the time the rifle requires it and I'm stuck with either a little, or a little more, not none, so I ignore Barlow bullets and use a shape that wiggles into the middle of the hole a little easier and give them some room to do their thing.
I'm also one of the weirdos that does stuff like pop some squib loads with different seating depths and measures the bullet travel, then repeats the test with 3/4 case of corn meal. You can learn a lot doing that. I have no way to measure pressure directly but can tell you that a bullet with more "run" at the throat will definitely go farther into the barrel with the same applied force. A jammed bullet sometimes won't hardly move at all, more than likely the primer pressure in an empty case just escapes around the case mouth and back around the chamber since a primer won't obturate the brass at all. A load of powder or inert filler behind the bullet reduces volume (air spring) drastically as well as probably helps become a granular stop-leak. Extra O2 in the powder space doesn't help the powder burn (there's a close to stochiometric oxidizer ratio built into the powder chemistry already), but it DOES allow the powder to be fluffed up and suspended in the space, exposing more to the primer heat faster than a full load of powder....however this diminishes at a certain point based on too much space and too few "targets" for the primer particles to hit, so we get poor ignition at very low load densities. We fix that in a variety of ways, most of which involve taking up space with filler if we insist on using a powder that creates a very low loading density.
Breech seating with smokeless powder introduces a couple of variables that we aren't used to dealing with. One is the starting resistance and the other is case obturation. I would use only well-annealed, never resized cases because sealing the chamber up consistently without a bullet to cork it up is difficult. If you aren't swabbing between shots, slight bore condition changes or even temperature changes between shots can have a pretty big effect on the resistance the bullet puts up to the powder each time before it gets moving. An engraved, MOVING bullet isn't much of an obstruction, but an engraved, STATIONARY bullet is a tremendous obstruction. Just run simple F=Ma where "a" is extremely high and F goes through the roof, we're talking milliseconds here. I've also experimented with the raw force needed to engrave a bullet vs. moving one which is already engraved and the results are pretty inconclusive to our cause because it doesn't account for inertia, IOW not a good test.
I would advocate trying a much faster powder because it will spike pressure and obturate the case, then slam the bullet with a high pressure wave so quickly that the effects of gas leaks and varying bullet sticktion (here's where Lamar and I start making up descriptive verbs, get used to it) are greatly reduced. Kick a ball and it just goes straight. Push it with a feather and any slight surface change or slope makes it roll willy-nilly. Another thing you could do is add some lofted Dacron to hold the 2400 powder in place, so long as there is minimal gap between the front of the Dacron and the back of the bullet, otherwise you're replacing a barrel. That would allow the powder to build more pressure before the bullet sees it and would also improve ignition in that "square" case better, as Lamar pointed out. You have to get that bullet moving consistently from shot to shot so it exits the muzzle at the same point in the whip, otherwise you get vertical stringing just from the harmonics and it will leave you scratching your head as to why a load with low ES/SD shoots like crap when you know the powder is lighting well and one with high ES/SD shoots better but happens to be timed better with the harmonics of the rifle system even though you think it wouldn't be with such variations in velocity.
