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karlrudin
05-14-2016, 09:51 PM
Through some fundamental reading on lead and its alloys I understand that there is a pressure area where lead alloys compresses to fill in the bore. Obturation. I also believe the equation for this is Brinell x 1440=the pressure at which to obturate. What I can't understand is that I've been seeing load data, including my own, that doesn't come close to the pressure curve compared to the formula. For my instance, I shoot 7-08Rem, using Lyman 160gr bullets of wheel weight, water dropped approximately 15Brinell. My load is 20.0gr of IMR 4198 and Fed 210 primers. According to Lyman manual, the starting load is 23gr which produce 19500lbs of pressure.

My main question is how are people including myself, coming up with any accuracy if our pressure curves are so much lower than the obturation. I've seen a trend that the top spots on cast bullet shooting is being done with straight Linotype, but there pressures are to low for obturation. Or is this just another mystery to the "silver stream". Just asking, and any input will be nice. Don't really want to fall into a trend or money of buying Linotype if there isn't much to back it up. I'm happy using wheel weights :-)

HangFireW8
05-14-2016, 10:57 PM
If the boolit is wide enough that it already fills the grooves, relying on plasticity for obturation isn't necessary. If your alloy is even moderately suitable for the velocity you're shooting, the only real strength/deformation issue is if the nose of the boolit slumps to one side.

When I started casting, Lee's promotion of the deformation formula was a hot topic, and I carefully loaded around that idea. Then I found out I had switched up some alloy, and some of my best loads broke all the rules. Many others noted the same.

My WW + 2% Tin/Pewter + a little lead shot, water dropped, is harder than linotype and a heck of a lot cheaper. I have been able to meet my accuracy and velocity goals with it. So, I ignore the formula for now. If anyone can show a truly good use for it, I'm all ears.

runfiverun
05-14-2016, 11:16 PM
because the number is a crush number not a flowing moving number.
in other words fitment and flow is important that number is meaningless.

karlrudin
05-15-2016, 05:34 PM
I would like to thank you guys for your great responses. It looks like a got bullet fit working good, my bullets are cast .001-.003 over the bore diameter. I don't get the hydraulic effect from my lube since I'm still using Lee Alox. It's been working good for me as far as no leading etc. Thank you for bearing with me since I'm definitely a newbie at casting since I only started in Jan of 2014. Been loading and shooting since childhood though. Looks like I need a lot more time with a mold in my hand to expect things to get better. I do consider myself thankful though to be shooting with you cast bullet folks. Definitely a whole new world.

nemesisenforcer
05-15-2016, 08:38 PM
It's all Greek to me.

runfiverun
05-16-2016, 12:21 AM
it starts to make sense after you spend enough time reading about it, and trying stuff.
the trying new stuff is the fun part and if you do it with the intent to learn something you'll have a lot more fun.
just learning alloy's or lubes takes some patience and study throw in a little swaging and the alloy flow thing starts to make a lot more sense.
then start looking at how powder reacts to engraving pressure of a boolit/bullet and you start to see how powder/pressure timing works.
try speeding your cast boolits up near jacketed velocity's and really pay attention to what your seeing then try learning about mechanical and static fitment to help put that together with the alloy flow [swaging] and the powder timing...
it just keeps going on and on....

w30wcf
05-16-2016, 09:34 AM
It does take more than just fitting a .001-.003" oversized bullet to a barrel. Obturation is still needed to keep the bullet pressure outward to prevent gas from escaping past. That is the reason that an oversized Lino bullet will produce leading at lower pressure whereas softer alloys won't.

w30wcf

runfiverun
05-16-2016, 11:25 AM
right.
and at some point you get to where the pressure drops off in the barrel [I call it the relax point]
this is when your lube and your boolit is at a highly vulnerable point.
quite often you see a lube smear just after it and then some antimonial or lead streaks.
many confuse this and say their boolit run out of lube [nooope] their lube failed to make it past the 'relax point' in a soft enough state to keep on flowing and doing it's job.

Blackwater
05-16-2016, 11:29 AM
You've gotten very good advice above. It's all about balancing all the factors out, and keeping them all within bounds. Let one get out of bounds, and that one thing can upset the whole performance. It's not ALL about bullet dia. or fit, or alloy hardness, or lube, or powder & pressure, but about keeping them all within due bounds. And it's a pretty forgiving proposition, really. That's why run5's comments are so spot on, as usual. The more you try in casting and reloading, the more interesting it really gets.

And it's in the learning that we really get to be better casters, reloaders and shooters. And we were once a "Nation of Marksmen." Not so much today, and with the world in the condition it's in now, that might not be optimum for us. Shoot straight and shoot smart. Ya' never know when it might come in really handy.