Has anyone ever loaded up some air cooled and water dropped wheel weights from the same casting session and observed a different point of impact? I think I will try this if no one has already completed this assignment.

Matt,

The harder bullet may produce slightly higher pressures (all else equal) and leave the muzzle at a higher velocity. I'd be interested in the results of such an experiment.

44

Matt and 44, Generally speaking, the harder the bullet, the lower the pressure. A harder bullet has less drag as it travels thru the barrel. The softer the slug, the more drag involved, hence higher pressure. Point of impact depends on type of firearm used. In a rifle, higher velocity usually raises POI. In a handgun, the opposite is true. Slower speeds raise POI, due to longer barrel time and muzzle rise due to recoil. Something to chew and ponder on. Good question. The more you learn, the more curious one becomes when talking about handloading, shooting, or casting. Jeff

cast-n-blast,

Sorry, I don't buy that at all. Slug a bbl with a Lino slug and a Pb slug having the same diameter and configuration and tell me which one is harder to manually get through the bbl. Coefficient of friction of a particular surface enters little into this equation. What we're concerned with here is greater resitance to deformation exhibited by the harder bullet which will increase pressure, all else equal.

44

44, greater minds than my own would have to disagree with you. Check out Veral Smith's "Jacketed performance with cast bullets" or our own Marshall Stantons "Tech. Guide". These books plus my own personal experiences back this up. As to coefficient of friction having nothing to due with it, it has every thing to do with it ! Think of an automobile sliding on ice, or hot tar. What will the vehicle slide the most on. Hopefully you'll say ice. Ice has a much lower coefficient of friction than tar, much like a hard cast bullet to a soft bullet. The lower the coefficient of friction, the less drag, hence more velocity, given the same variables.

cast-n-blast,

My exact words were, "Coefficient of friction of a particular surface enters little into this equation". I didn't say "nothing", I said LITTLE. Provide me with concrete evidence that a hard bullet traveling down a bbl produces lower pressure than a soft one (all else equal) and I'll listen. Please spare us the slipping on ice analogies, though. Were not talking just about traction between two surfaces, were talking about INCREASING THE SURFACE AREA OF AN OBJECT BY FORCING IT THROUGH A SPRIAL GROOVED TUBE. Did you hear me that time? ;-)

44

44, check out the post on Age Softening. In it, I tell of a good load that I have been extremely sucessfull with in terms of accuracy and velocity.2700 fps with a 210 gr. projectile in my .35 whelen. Shot like gangbusters for 1 1/2 yrs. Then accuracy fell off, and I started getting flattened, and then pierced primers. Obvious signs of excessive pressure. All loads were loaded at the same time, with same componets. The only difference could be lead softening of the projectile. This was verified by later testing my home cast bullets with a LBT hardness tester. Bullets went from21-22 BHN to 14-16 BHN. That's about as real as I can get. Jeff

Jeff,

That's an interesting situation indeed and one worth further examination. Actually, I was pretty sure you'd cite an example like this when you referenced Smith's book. The loss of accuracy is very well due to the bullets' softening over time since the base area of a 14-16 BHN bullet can't withstand the amount of pressure that one made of an 21-22 BHN alloy can. In this case however, the distortion of the bullet's base is what's causing the increase in pressure not the relative hardness (or softness) of the bullet... yes, it is all related! In this case, force vectors were pushing out the edges of the bullets' bases against the barrel walls, causing more drag, or friction, at the base and therefore more pressure. It's kinda like this... if one were to peen a distortion on the end of a shaft before extruding it trough a tube, it would require more work than a harder shaft of the same dimensions without the distortion. So, yes I agree that a softer bullet can produce more pressure UNDER CERTAIN CONDITIONS than a harder one, but we should be careful not to generalize. After all, your loads were running 2700fps and probably over 40K CUP... what I would call the bleeding edge of cast bullet performance. Can I assume that this particular load was made of all the same components from all the same lots and the barrel was in the same condition and ambient temperatures were always the same over the course of your 1 1/2 years of working with this load? Perhaps your lube is suspect as well?

44

44,

The softer bullets are forced against the barrel with more pressure than the harder bullets.

energy lost due to friction = coefficient of friction * surface area * pressure.

The softer bullet deforms farther up the shank of the bullet, increasing the area where the bullet has high friction with the bore (after the initial engraving of the rifling, that is). Then you have the base of the bullet going plastic sooner and being forced against the rifling harder (pressure) for a longer period of time (till the pressure drops below the level needed for plastic deformation).

The harder bullet ends up having less area against the rifling (once it's been engraved, that is), and for a shorter period of time (because the base of the hard bullet isn't undergoing plastic deformation starting as soon or for as long of a duration).

Make sense?

Mike,

Yes, "The softer bullets are forced against the barrel with more pressure than the harder bullets" is essentially what I said except I was referring to bullet bases, or about the first 1/4 of the bullet's shank. The pressures you are describing sound astronomical... what pressure levels are you referring to? I don't work with these "magnum" type loads and I normally don't use alloys softer than Lyman #2.

Thanks for the input,

44

Lead deforms pretty easily. I think the rule of thumb is something like 1440 times the BNH number is where you start getting deformation.

Note, if the bullet is soft enough, and the pressure high enough, it is deformed (obturated) farther up the shank..... so it's not necessarily just the bullet base or lower driving band.

I just wanted to say thanks to those who contributed here. I usually work with relatively mild pressures and learned something from this exchange.

44

44, I too have learned something new , in this post, and that is what this site is all about. After conversing with Marshall, it was learned that in fact, with low pressure loads, hard cast bullets will raise pressures. However, with high pressure loads, the opposite is true. The harder the bullet, the lower the pressure. Where this point of role reversal takes place is unknown. Interesting stuff. Good casting to all. Jeff :D

Jeff,

Logically, this point of reversal (as you put it) would be when obturation begins.

I remember a conversation I had with Veral Smith many many moons ago and he claimed the most accurate loads he'd ever seen were those that did not produce any obturation. So, if that's true (as I am inclined to believe it is) the most accurate loads for your blockbuster Whelen should be those launching very hard bullets.

44