At what velocity does leading start - query

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  • Last Post 06 September 2015
bigbore52 posted this 03 September 2015

Over the years I have always pondered why some barrels lead up more than others with cast pills so thought I'd post this theoretical query and try to pick the extremely knowledgeable brains on this forum...naturally that excludes me....:shock:

Here's the problem....Given the various hardness of different cast lead pills that people make, is there a general rule as to what velocities are approached before noticeable leading occurs?......

Before going on, I know there are heaps of variables to consider and this may not lead to a specific answer - but it strikes me that if you can consistently cast to a set hardness say 15BHN, does that mean the velocity also has a sweet point before leading becomes a factor based only on that BHN?

In asking the question, naturally would be necessary to make a few assumptions to keep it simple such as same powder and load, pressure levels same, no gas checks, same hardness, same case, same pill shape and size is cast along with same gun being used etc - in fact nothing other than the hardness of the cast is changed in this exercise -  yes, I know it's impossible to do that...but this is hypothetical.....much like me shooting MOA bulls all day  - so is there a sweet point in velocity based on the BHN and can that be (easily) calculated or applied to different brews?

Just wondering if anyone here has come across an answer or a reasonable suggestion?...be gentle now....I wasn't too good at quantum theory .>

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fa38 posted this 03 September 2015

Probably bore condition and bullet fit more than velocity

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TRKakaCatWhisperer posted this 03 September 2015

I'll take a guess at the nature of the process. I would think it would be at the point where the alloy bullet stops sliding and starts gauling. This implies that strength of the alloy, lubricity of BOTH the lube and the alloy, smoothness of the bore, and amount of oversize the bullet is to the ID of the bore will ALL be influences.

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onondaga posted this 03 September 2015

http://castbulletassoc.org/view_user.php?id=9193>bigbore52

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Ken Campbell Iowa posted this 03 September 2015

a related question :: do gas checks allow higher velocity/pressure ... because

they stop the leading ( gasket effect ) ... or

because they scrape up the leading that occurs at the higher velocity thus it seems there was no leading in the first place ??


in 60 years of shooting cast bullets .. the only significant leading i encountered was overspeeding/pressuring commercial swaged bullets in pistols ... all other ” leading ” wiped out with a few bore patches .

in rimfire, i superpolished one match grade barrel interior .. no matter how shiny it got, it still didn't lead ( g ) .

ken

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onondaga posted this 03 September 2015

http://castbulletassoc.org/view_user.php?id=9193>bigbore52

 

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onondaga posted this 03 September 2015

http://castbulletassoc.org/view_user.php?id=40>Ken Campbell Iowa

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gpidaho posted this 03 September 2015

Not being a self-proclaimed expert, take this advice with the thought in mind that it might be worth just what you paid for it. I've had very good luck measuring the ID of fired cases and sizing the bullets to leave .002 clearance in the chamber neck. (cast bullets) This and I seat the uncrimped bullets so that closing the action finishes seating them the last few thousandths. The only rifle I've found to be problematic using this method is my old Polish Mosin, It's bore is too large for it's neck and it requires neck turning to get a proper fit. Also Gary's bore polishing technique works very well for me. Gp

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runfiverun posted this 04 September 2015

they are called gas checks,,, think about it. leading and velocity are NOT inter related. pressure does not cause leading. Richard lee is full of baloney.

you'll figure them all out as you get more into casting and shooting rifles at higher and higher velocity's.

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bigbore52 posted this 04 September 2015

Gee, thought posting what I thought to be a simple question would lead to a discussion on what the question entailed, not a shortcoming of my abilities, whether I am a beginner or not nor how serious I am in asking what I thought was a fairly relevant question.....I must stand corrected then

Long before the 5 decades ago when I first started shooting, casting and reloading, I learnt that no question is irrelevant, more so the answers given....perhaps it's time then to train my brain and move on as life is much too short to dink around......thanks for the replies.....

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joeb33050 posted this 04 September 2015

RiflesI don't know, and I don't know how or if velocity and leading are related.I have found that leading occurs when bullet diameter is too small. I test by putting a bullet in the throat to where it stops, then look through the barrel. If there's light showing, coming through the grooves, leading is likely. Making the bullet bigger frequently stops leading. I have shot soft = ~ wheelweights bullets fast, without leading. Fast enough so that rings of lead are left in the chamber. The shape of small o rings. I think the bullet expands, moves forward, and the chamber step where the ball seat/throat/leade starts shears off the ring. Rings happen first without gas checks, then with gas checks as powder charge increases. I suspect that bullets of about any hardness, large enough, won't lead a rifle barrel at any practical = reasonable accuracy velocity. I've proven to my satisfaction that the alleged relationship between accuracy and pressure and bullet hardness, see Davis, Harris and Lee,  as imaginary at best. Revolvers If the bullet is large enough, and the chamber, cylinder and barrel dimensions-barrel at where it screws into the frame especially-are such that the bullet never gets squoze then goes into a larger diameter place; there's no leading.If the bullet has to go from a .xx7” diameter place to a .xx9” diameter place, for example, it is likely to lead.Norm Johnson proved long ago that UNLUBRICATED big bullets in correctly-dimensioned revolvers won't lead after long strings of shots. Autoloading Pistols I know nothing joe b.   

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RicinYakima posted this 04 September 2015

BIGBORE52, Some guys are pretty passionate about this subject. My experience is much like Joe b. There is no direct relationship between velocity sand barrel leading, it has many variables.

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TRKakaCatWhisperer posted this 04 September 2015

bigbore52 wrote: Gee, thought posting what I thought to be a simple question would lead to a discussion on what the question entailed, not a shortcoming of my abilities, whether I am a beginner or not nor how serious I am in asking what I thought was a fairly relevant question.....  ... ......thanks for the replies.....

It is a very good question.  Welcome to the real world of “my opinion is right and if you were only reasonable you'd agree with me".

The filter I use is to look for “this works for me ...” and I ignore “so-and-so is wrong".

Keep the qustions coming!

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bigbore52 posted this 05 September 2015

Thanks for all the replies and such - and to placate TRK, the Chief of Smoke :) continuing the question - in my experience I have never seen a direct correlation between the two in shooting disciplines that I could competently state one way or t'other but thought as with most metals, albeit the softer ones; then it should have some effect - let me clarify that.

When I make lead babbitts - then I have to calculate the hardness of the mixture to guarantee a particular life of the bearing as required. The mixtures are often identical to those I cast for shooting and both essentially being friction suffering applications, shooting and bearings then I thought perhaps a babbitt would be similar in many ways to what happens in a barrel given it's the same composition

The motor babbitt is made stipulated to a particular rated load, usually rpm (speed or even sfm) and to meet that spec with minimal wear, you make the babbitt harder....but not so hard at it causes heat from friction.

Now a lot of shooters including myself, cast at 20:1 with my BHN at 14.5 - some swear by 30:1 or 10:1 plus antimony and we all claim that it works well for us with no noticeable leading....this is why I purposely left out the variables in my original question....

Without going into metallurgical details, I know for instance that a babbitt I make 20:1 in a particular machine running at 2400 rpm will last minimum 48 months and longer before replacing...the same machine with a babbitt of 30:1 won't last a month and if I make the babbitt harder with the addition of say antimony, then within a week or so, it will cease up from over heating....melt and short the wiring..quite expensive to fix..so I know that machine prefers 20:1.....

That's the conundrum I face trying to relate that to barrel leading. In bearings there is essentially no variable other than friction caused by the starting, stopping or load placed on them much as with a projectile (aside from the initial heat and explosive forces etc) as down the barrel, friction plays a bigger role until it exits ...you could say it's a short term friction and lots of different forces apply on a pill unlike a motor which is based solely on the speed it moves and the resistance between the babbitt and the drums - so if the machine babbitt can be directly calculated to the rpm, why not a cast bullet?

It's an interesting thought (to me at least) and just asked if someone had an answer as to whether it had been done or not.......thanks again for your comments and good shooting

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TRKakaCatWhisperer posted this 05 September 2015

FASCINATING. Not too many folks still mess with babbitt. My LIMITED understanding of it includes two major types? Do not some types contain a significant percentage of copper? Tin has a high lubricity, but tin (itself) doesn't conduct heat and transfer it well.

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RicinYakima posted this 05 September 2015

The difference I believe is that the Babbitt bearing has a constantly renewing oil film?

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bigbore52 posted this 06 September 2015

Yes, babbitts are are black art indeed nowadays and I know little of them other than those I have made seem to get the job sorted.

Have never bought a commercial mixture and believe you are correct TRK - most contain other metals for various properties but I've just used what I had at hand. That was how I was taught/shown by my elders long gone now....frugality has a lot to do with it no doubt :P - what intrigued me being the same mix as cast bullets and fellow shooters having huge leading issues, while others none - far too many variables and not enough grey matter for me to nut this one out so will put it down to one of those unknown unknowns :) ......anyway, it's another of those things meant to confuse the believers such as how they manage to include more headaches in a bottle of blend than a single malt whiskey...... :coffee:coffee

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RicinYakima posted this 06 September 2015

Single malt Whisky only has one evil sprit, blended whiskey has many evil sprits, a fall from purity.

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Ed Harris posted this 06 September 2015

My ancestors would disagree with the idea that single malt would contain an “evil” spirit. But I suppose that is a fundamental difference between Calvinist Presbyterians, Methodists and Southern Baptists.

Blends were invented by the bloody English!

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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billglaze posted this 06 September 2015

Ric, about the single/double malt whiskies: I don't drink any more.  Of course, I don't drink any less. Bill

In theory, there's no difference between theory and practice. In practice, there is. My fate is not entirely in Gods hands, if I have a weapon in mine.

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onondaga posted this 06 September 2015

I make it a point to have 1.5 oz of 10 High Bourbon once a day. Usually it is in a cup of black coffee but sometimes I drown an ice cube.

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