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View Full Version : Lube purging, ignition & other stuff



Blackwater
10-20-2005, 09:57 PM
Fellows, I've been over at Mountain Molds playing with the designs, trying to see if I could learn anything. Bass gave me some answers to some questions that I think have helped. Hope to see for sure before long.

I've also been doing some searches on this site trying to get a handle (or a finger or two at least) on just how to design a good bullet. Trial and error isn't my forte', but unfortunately, vascillation and uncertainty are.

I also remembered talking with Jump some time back about one of the bullets he'd been using, and his saying something about "lube purging." Couldn't remember what that meant, so I did a search, and some of you newcomers might want to check out the thread at:

http://castboolits.gunloads.com/showthread.php?t=1671&highlight=lube+purging

I kinda' want to design a some moulds for high speed in my Whelen and my .30's and .31's. Want them on the heavy side, so they'll be long. As I 'get it' right now, the key to pushing a bullet hard on the back end in order to get higher velocity, I'll need fairly high lube capacity. The long bullets will be at higher risk of 'slumping' if not cast very hard, so I'll need longer bearing surface, which I THINK (???) means I'll need to go with a bore rider to get the lands at least to support more of the bullet along its path out the muzzle. To use a bore rider, I'll have to be very careful to get the bore riding portion to FIT really well, expecially if I drive it fairly hard. The throat will of course have to fit very well to prevent blowby.

Does this sound about right, or do I have yet a bunch more to learn before I can feel comfortable ordering a mould?

felix
10-20-2005, 10:20 PM
Blackwater, you are on the correct path. But you might find a boolit design is already out there for your wishes. What is the twist of your 35? You might try to fit the David Mos version of the Lyman 280 grainer in your cases and see just where the hangups, if any, are. If there are no hangups with this boolit, then a bore rider will degrade performance. If you need boolits, just indicate so in this thread. If your twist is not 14 or better, then this boolit will be too long. But at least you will find out if you need a bore rider or not. ... felix

The Nyack Kid
10-21-2005, 12:17 AM
a really good read is Veral Smiths " Jacketed Performance With Cast Bullets" . it is Kind of pricy but worth it IMO . this handy little book will explane alot (plus it is nice to have a "hard copy " to study when in the ...aaah emwhen a laptop is not avalable . longer bearing surface is like, longer drive bands and lots of them .

Blackwater
10-21-2005, 12:35 AM
Thanks, Felix. Coming from you, that's pretty reassuring.

Does Mos have a website?

Blackwater
10-21-2005, 04:25 PM
OPne more question: Dan's program allows the front driving band to be tapered, as well as a different diameter from the main driving bands. Would tapering the front band from whatever dia. chosen, down to a bore-rider's bore dia. be of any benefit, such as allowing the bullet to "self center" just a smidge better as it enters a throat?

Contrarily, are throats generally concentric enough for this to be of help? I'm assuming that throats do NOT wear evenly and concentrically here, so am concerned that this feature MAY (?) create additional problems rather than solving them.

Looks at first glance like the tapered front driving band might be a help, at least in some cases, but after thinking about it, and how throats are generally shaped, I came up with that darned second concern, and confused myself .... again! :-?

I guess it's like everything else in the world - the more you learn, the more questions you have, right?

One more question:

Isn't it generally true that faster burning (pistol type) powders will give enough pressure to obturate the case (even if not the bullet all the time, depending on parameters of the load of course), and thus are better (if accuracy can be found at that level with that bullet, alloy & lube) for low velocity plinker type loads and lower recoil? The reason I ask this one is because I think I'm going to introduce my 6 yr. old grandson to centerfires this year. Thanks.