Why different alloys for BP

[indian joe]

Don't know about your TDs but mine and all I've looked at has little, if any, "throat". Mostly the leade comes right up to the chamber mouth or very close to it. Any transition of the bullet from case/chamber to that leade is rather abrupt. What I do know is with both original TDs, my two H&R TDs and a couple replica Sharps, RB and '85s I shot is that if there is any antimony in the alloy then some leading [mostly long streaks of it] can be expected with BP loads.

With my 1873 45-70 loads with Lee 405 HB bullets or my M1884 with a Rapine 460500 bullet loads I've settled on the 16-1 alloy Frankford arsenal found best back then. For my 45-55 Carbine loads with the Lee 405 HB bullet I fall back to a softer 30-1 alloy. My BP lube is simply 6 parts beeswax to 5 parts virgin olive oil.

Larry - no leading problems at my place - but I am shooting new barrels
mix is about 50/50 soft lead and wheelweights with a tad of linotype - test is just scratch it with a 3B pencil
not much tin in that mix. - gets good expansion in soft dirt at 100yards

I like that LEE 405 HB but I modified it some
milled the nose flat for safety in my tube mag guns and lost the HB so I could use a wad under it still weighs 405gr
Also modded a second one by lengthening the base plug - lost one lube groove and driving band it drops at 335 grain
Its a nice profile and nice big lube grooves

[Gray Fox]

Larry:

How do you apply your lube? Do you pan lube, water melt, cool and make a lube cookie, or what? thanks, GF

[indian joe]

The composition of lead to tin alloy for the best accuracy depends on the bullet weight (mass), the expected velocity and whether a lubed bullet or a PP'd bullet. If shooting a lubed bullet at or over groove obturation is not an issue. The bullet will actually be less than groove diameter as it will ride over and be swaged down by the layer of lube in the barrel. However, if obturation is wanted the alloy softness needs to match the bullet weight (mass). A lighter weight bullet will need a softer alloy with a given velocity (acceleration).

As to velocity (acceleration) bullets 400 - 500+ gr of 40-1 or 30-1 do best down around 1000 fps+/-. If pushed to 1100 - 1200 fps then a 20-1 is most often best. With velocities of 1250 - 1500+ fps a 16-1 alloy was proven the best after extensive testing by Frankford Arsenal back in 1880 - 1882. That was with the 45-70 with the new 500 gr bullet. It was found the 405 gr bullet with the 70 gr powder charge did not adequately obturate [obturation was the thought of the day as they used .459 sized bullets in .460 - .464 groove diameter barrels]. However, with the mass of the 500 gr bullet [still sized at .459] over the same 70 gr powder charge the bullet did obturate. The 16-1 alloy then gave the best accuracy. The 405 gr 45-55 carbine bullet was of a softer alloy that did allow sufficient obturation with the 45-55 load. No, the dish [it is not a hollow base], does not and is not intended to act as a hollow base as with Mine' style ML bullets.

With all that said a 20-1 alloy is often recommended because it is useful over a broad spectrum of BPCs. It may, or may not, be the most accurate alloy in your rifle with your load. Only testing will determine the correct alloy.

Larry why the "hollow base" on that boolit ? Its puzzled me some -- Youre right its not gonna work like a minie - was that just to balance the projectile?

I modded that mold - milled the nose dead flat and bigger enough it would no longer protude into a primer pocket - then took the tit off the base plug sos it casts flat base - still comes out neat 405 grain (sometimes we get stuff right by accident)

It shoots fine anywhere within its useful range - might do a little better with a boolit like that blue one in Lead pot's post but you would need to be having a good day to see the difference .