No, the fit changes with pressure, where the pressure peaks in the barrel, how fast the pressure peaks and a whole lot of other variations. For that matter the shape of the bullet changes with pressure. At his lower pressures his bullet is fitting the barrel and there's a balance point met that gives him good groups. Raise the pressure and the bullet reacts differently and he's pushed it beyond what that particular bullet (and everything that goes with it) in that particular barrel wants. So he gets worse grouping. Dynamic (an object in motion) fit.If it's all about fit, how come Sevenfan can get fantastic groups at slower speeds but when he speeds them up, the groups turn into shotgun patters?
My understanding is that the fit was the same at both speeds!
The problem with thinking your way through it is that many of us, me included, either don't factor in things that happen or don't think things that happen even exist. That's where reading the musings of guys like you and Ian (and many others!) come in, 'cuz you thought this stuff out and bring new ideas to the table that the Larrys and Joe Brennans of the world never considered.when you add in hunting your talking another whole level of performance and a totally different set of expectations.
if your gonna go faster you need less meplat.
that's for on target results not aerodynamics.
anyway if your gonna think about bullet design you have to think about what happens to it when the pressure is applied to the base.
then your next thought is gonna be well i'll just use some lino-type.
yeah,,,, no.
that's the exact opposite thought you should have.
think.. your... way... through... what happens to the bullet.... remember pressure is applied from one direction only.
yeah,yeah yeah it goes in all directions, but the bullet only gets it applied from one.
If it's all about fit, how come Sevenfan can get fantastic groups at slower speeds but when he speeds them up, the groups turn into shotgun patters?
My understanding is that the fit was the same at both speeds!
Good analogy!!!Isn't fun trying to push a gummy worm down a rigid smaller hole?
Come on Ian, don't be shy! I sat here thinking, (scary, I know!), and came up with 3 or 4 possibilities of what you meant by that. Take pity on an old man with a head overflowing with a million other things and give us a hint!!!Because every system has limits. After the trigger is pulled, you no longer have what you started with. Add more powder, it changes even more and usually not for the better because the whole set-up isn't correct to deal with the changes that will happen.
You can do a lot of things wrong and still have decent results with wheelweight alloy, common production moulds, Lyman manual reloading techniques, and book loads up to about 1700 fps, but when you start to push things, you find out it stops working so well. Some people blame it on excessive RPM, some on pressure/alloy strength limits, and others on the unattainable perfection of the hand-cast bullet. Each of these is true to a degree, but only part of the bigger picture where a factor not often discussed or understood plays the biggest role in cast bullet accuracy.
That's all part of dynamic fit to my addled mind. Finding a balance point between what the specific firearms internal dimensions and style are and what the bullets specifics are and what the powder charges specifics are in that gun. I put the question you ask on the "100fps" down to exceeding the point of balance. I don't have the definitions of all the little pieces parts down yet. There's an awful lot happening awfully fast.What do you think happens to that gummy back end when the solid front end slams into a brick wall at 400-600fps and the pressure spikes from 5,000 to 30,000 almost instantly? Why isn't it so bad if you just back off 100 fps? Is it the RPM? Bad casting? Bullet alloy too weak? How about.....none of the above.