Alloy hardness for BPCR vs. accuracy

  • 4.4K Views
  • Last Post 24 December 2009
jporter posted this 28 January 2009

Although I sympathize with 2 frogs on another post wanting to get away from cleaning

cases and messing with black powder I on the other hand love the black powder single shot competition.

I shoot a 40-65, 45-70, and 45-90 and I'm finding my group size does shrink with an 18 to 1 instead of 20 to 1 or 25 to 1

Believe me I know how many different variables there are in loads ! powder, compression, wad material, neck tension etc. but all that being said there is something to say about a harder alloy, but i'm finding it a fine line because I lose a little of the weight when tin is added etc. your thoughts would be appreciated.

Attached Files

Order By: Standard | Newest | Votes
JetMech posted this 28 January 2009

I shoot a 45-70 BPCR and it amazes me what minor variable changes produce a measureable difference on target. The difference in BHN between 18:1 and 20:1 in about 0.3 BHN. Most tools on the market probably can't even measure that difference.

The vast majority of CB shooters wouldn't even consider changing alloys that little to achieve better accuracy, but it would certainly be a place for further experimentation.

Attached Files

JeffinNZ posted this 28 January 2009

It's a good question.

My .38-303 shoots marginally better with 20-1 than with clip on wheel weight even though they have the some BHN.

Cheers from New Zealand

Attached Files

RicinYakima posted this 28 January 2009

Guys,

This is one of my “soap box” subjects: bullet hardness is a/the major factor in a bullet's accuracy potential.

There are a large number of lead based alloys that can have the same BHn, and if you add heat treating, many more. But that is only one factor; others such as malleability, specific gravity, plastic deformation and shear strength are all factors that effect accuracy.

I will get off the soap box now.

Ric

Attached Files

JimmyDee posted this 28 January 2009

"...bullet hardness ... is only one factor; ... malleability, specific gravity, plastic deformation and shear strength are all factors that effect accuracy."

See, this is why I hate coming here and reading posts.  Now I've got to figure out how to measure all this other stuff, too!  Then figure out how much difference each factor makes.  Or read about it.  (Just when I thought I had read everything there was on the internet!)

It's all too much -- there isn't enough time!!

Attached Files

RicinYakima posted this 28 January 2009

JimmyDee,

I'm really sorry. But, no matter what others think, cast bullet shooting is an art, not a science. One of the reasons I left jacketed bullet benchrest shooting, is that is that there were few variables, that it became “monkey see, monkey do". Cast bullets have enough challenges that it will keep me researching, thinking, experimenting and shooting at targets for the rest of my life.

Life is a journey, not a destination.

Ric

Attached Files

JetMech posted this 29 January 2009

Are there any references out there that would indicate how different alloy elements affect those factors, Ric?

I'm like you, as I suspect most CBA members are, itinerate casters, wandering down one road after another, looking for the “perfect” bullet for a particular gun, load and application.  An example would be a silhouette shooter who needs a bullet @2500fps that will transfer energy to the target rather than shatter. His (her) needs are different than the person punching paper. Both have the same velocity and accuracy requirements, but different terminal needs.

Attached Files

RicinYakima posted this 29 January 2009

No, there are not any consolidated works on the other factors besides hardness. And the ones on hardness may not be valid, unless you can determine what alloy was used. Measuring bullet properties for the home caster is always a problem. There has been a lot of work done from Dr. Mann's pioneering experiments through today, but digging it out, validating it and publishing it has not been done.

You are very perceptive with the comment on bullet performance. Since I like my holes in the paper to be close together, I don't care about terminal impact performance. For the last three years my match bullets have been linotype, just because they can be made with 1/2 the time and effort of my previous alloy, WW's +2% tin.  They don't shoot any better within my velocity range, 1400 to 1550 f/s, but when you are making 2000 a year, a major time savings.

"I'm like you, as I suspect most CBA members are, itinerant casters, wandering down one road after another, looking for the “perfect” bullet for a particular gun, load and application."

Bill, that is me to the “T". :D

Ric

Attached Files

Fred Sinclair posted this 29 January 2009

” But, no matter what others think, cast bullet shooting is an art, not a science. One of the reasons I left jacketed bullet benchrest shooting, is that is that there were few variables, that it became “monkey see, monkey do". Cast bullets have enough challenges that it will keep me researching, thinking, experimenting and shooting at targets for the rest of my life."

Damn, I wish I had said that.

 

Attached Files

Ed Harris posted this 30 January 2009

Fred Sinclair wrote: ” But, no matter what others think, cast bullet shooting is an art, not a science. One of the reasons I left jacketed bullet benchrest shooting, is that is that there were few variables, that it became “monkey see, monkey do". Cast bullets have enough challenges that it will keep me researching, thinking, experimenting and shooting at targets for the rest of my life."

Damn, I wish I had said that. 

Me too! 

As to the question on alloys, I'll throw out an opinion, which you can consider or discard.  For the same hardness level, the richer tin content alloys stay liquid longer and a large sprue can continue to feed the casting as it solidifies using an alloy such as 1:18 vs. a low tin  Pb/Sb/Sn alloy, which sets up quickly.  This reduces the effect of solidification shrinkage and the presence of small shrinkage cavities or voids in the casting.   Minimal weight variation and selection of bullets in the center of the bell curve isn't the whole thing either.  Casting technique, the rate of pour, whether you drop pour straight in or use a dipper and roll the blocks over all affect how the bullet solifies, and the placement of voids when they occur.

Anytime you cast a bullet in which the ratio of length to diameter is more than 2:1, especially in larger calibers, it is difficult NOT to get at least small voids.  Dennis Marshall convinced me of this after mounting and sectioning in epoxy some of John Ardito's match bullets which I gave him.  The voids were tiny, and were all uniformly located along the axis of the bullet, but they were still there.

What we are practicing, Gentlemen, is ALCHEMY! 

We are trying to turn lead into gold!

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

Attached Files

JetMech posted this 30 January 2009

Ed Harris wrote: Anytime you cast a bullet in which the ratio of length to diameter is more than 2:1, especially in larger calibers, it is difficult NOT to get at least small voids.  Dennis Marshall convinced me of this after mounting and sectioning in epoxy some of John Ardito's match bullets which I gave him.  The voids were tiny, and were all uniformly located along the axis of the bullet, but they were still there. I wonder if those were air bubbles entraped during the pouring, or were a gassing by-product of the alloy cooling? The later might be indicated by the voids being located in the middle of the bullet, that being the last part to solidify. Or is it achieved by a certain pouring technique, such as starting with the mold sideways and rotating 90 degrees during the pour? Alchemy is right, Ed, with a little of Jeff's Voodoo thrown in for good measure!

 

Attached Files

Dale53 posted this 05 February 2009

I shot BPCR Silhouette for fifteen years. That is, at least eight matches a year for 15 years.

I finally settled on 30/1 lead/tin using pure metals. My most successful changes were bullet fit. I eventually ended up with a nose pour four cavity mould from NEI (when Walt Melander was at the helm). My standards for my most used rifle (40/65 Browning BPCR) were +or- .6 grs (bullet weight) using a 422 gr bullet. I could make that even with the four cavity mould. When the phase of the moon was right, I could keep ten shots in a minute of angle using a 20 power scope for testing (off the bench). It was difficult to do it but that was a shooter problem not a rifle problem.

I have shot 6-8” groups at 500 yards (off a bench with a 20 pwer scope when testing) in front of witnesses but again, difficult to do in prevailing conditions.

My favorite powder was Swiss 1½ using a LDPE .060” wad and compressing .035"-.075” depending on powder lot. I firmly believe that the LDPE wad seriously reduced flyers.

Dale53

Attached Files

codarnall posted this 05 February 2009

As a matter of course I would drop castings in to water. The reason being they'd be cool to the touch, less damage will also occur, dings etc. I have have read and understand that like carbon steels they will be hardened. I then read that in the case of castings they loose their hardness over time. This to me seems like BS. Does anyone have measurement that would support the charactistics of the hardness over time? -Charlie

Attached Files

JetMech posted this 05 February 2009

Charlie,

Lead alloys do not react like steel. Water quenched alloys containing arsenic harden initially, but do loose there hardness over time. There's several posts on this forum with folk's actual measurements. The Lyman Cast Bullet Handbook states that it occurs after 2 years, but I believe it's dependant on the amount of arsenic and tin in the alloy. Some people have measured a marked decrease in hardness after 1 year.

 

Attached Files

Dicko posted this 24 December 2009

Dollar Bill wrote: I'm like you, as I suspect most CBA members are, itinerate casters, wandering down one road after another, looking for the “perfect” bullet for a particular gun, load and application.  An example would be a silhouette shooter who needs a bullet @2500fps that will transfer energy to the target rather than shatter. His (her) needs are different than the person punching paper. Both have the same velocity and accuracy requirements, but different terminal needs.

That summarises it perfectly, Bill.   I don't think there's any serious question that for chasing tight groups at whatever MV, harder is better within reason, bearing in mind that linotype bullets are a fraction of the hardness of jacketed.   For that you need linotype hardness.   I use 12% antimony which is not quite as hard as lino but saves the cost of tin.

But hunting needs enough MV to do the job and you sure can't use linotype because it is too brittle and fragments causing surface wounds.   You need a softer and more ductile alloy.   How you get both that and the required MV is another matter.   But the point remains that hardness can't be discussed in islolation and depends on use.

 

 

Attached Files

Categories
Search
Popular Tags
This Weeks High Earners
Hot Topics
Close