Why a hollow base on 45/70

[BSkerj]

Just started casting and loading for my 45/70. I have casted for handguns in the past. I purchased a Lee single cavity HB mould, 405 grns. to try. It shoots great over the top of 45 grns of IMR 3031 but I was curious as to why the hollow base..Thanks in advance !

[Hardcast416taylor]

I was always told that a hollow base bullet is meant to better contain the powder gases and to flare out to better fill a larger bore weapon bore size. Your load is the same that I seem to like in my 45/70 rolling block.Robert

[Larry Gibson]

The hollow base on the M1873 45-70 bullet, of which the Le 405HB bullet replicates, is not there to expand or flare out ala minie style to seal the bore. If you note the skirts are very, very thick on the Lee bullet as when compared to a true minie style bullet that does flare out to seal the bore on firing. The HB on the M1873 bullet is there to is there to regulate the weight of the bullet while maintaining the same overal dimensions with different alloys. The M1873 bullet was dependent on obturation or "bumping up" to seal the slightly larger bore in the M1873 Springfield TDs. It was found the 400 gr bullet did not have sufficient mass to obturate completely and that led to the 500 gr M1881/2 bullet. It also had a dishout cavity in the base to regulate weight while maintaing the same overall dimensions. It had the mass at .459/.460 to obturate and seal the .460 - .465+ bores.

I have recovered numerous Lee 405 HBs that were cast of 1-20 & 1-16 tin/lead alloy (that's what the arsenals used) that were fired over service loads of 70 gr BP and equivelent smokeless loads and the bases showed no sign of expans because of the HB. Even the bases of softer alloyed bullets do not expand at carbine velocity. Several of the Lee moulds I have used drop bullets cast of 1-20 at .461 to .465. The best accuracy comes from using them "as cast" or at least sizing to not less than groove depth. Softer alloys in the Lee 405 HB will do alright if sized .459 but they will most often give better accuracy if used as cast.

I know Spence Wolf says to size .459 but remember that Spence was replicating the Service loads. I discussed this with him many years ago and he knew that properly sized to groove bullets shot better. That was not how the arsenals did it so he did not use it in his very fine book (anyone who loads for the TD should have his book). He was, as stated, replicating US Service 45-70 and 45-55 loads. He replicated those very well indeed and if you follow his instructions you will have ammuntion that shoots every bit as well in your TD as did that of 137 years ago which wasn't bad at all.

Larry Gibson

[rhead]

It increases the length of the bullet and the bearing surface without increasing the weight. It has the profile of a 405 grain bullet bit weighs around 380 385. It may also improve balance but I do not know that for a fact.

[BSkerj]

Thanks everyone for the informative posts, especially yours Larry.....once again the wealth of info on here is never ending !

[MtGun44]

In my experience, the HB will shoot accurately in my oversized bore Trapdoor and solid
boolits will not.

I attribute this fact to the minie ball type of base expansion. No way to prove it, but
several different solids cast of various soft and softer alloys were wildly inaccurate.
This boolit saved my Trapdoor, it is now accurate.

Bill

[Notes]

I recently acquired an 1884 Trapdoor in very good condition. I have been told the Lee 45-70 405 HB bullet is consistent and very accurate loaded with BP in the Trapdoor. Short of casting them myself, is there anywhere I can purchase this bullet, and is it available pre-lubed?

[44man]

The hollow base on the M1873 45-70 bullet, of which the Le 405HB bullet replicates, is not there to expand or flare out ala minie style to seal the bore. If you note the skirts are very, very thick on the Lee bullet as when compared to a true minie style bullet that does flare out to seal the bore on firing. The HB on the M1873 bullet is there to is there to regulate the weight of the bullet while maintaining the same overal dimensions with different alloys. The M1873 bullet was dependent on obturation or "bumping up" to seal the slightly larger bore in the M1873 Springfield TDs. It was found the 400 gr bullet did not have sufficient mass to obturate completely and that led to the 500 gr M1881/2 bullet. It also had a dishout cavity in the base to regulate weight while maintaing the same overall dimensions. It had the mass at .459/.460 to obturate and seal the .460 - .465+ bores.

I have recovered numerous Lee 405 HBs that were cast of 1-20 & 1-16 tin/lead alloy (that's what the arsenals used) that were fired over service loads of 70 gr BP and equivelent smokeless loads and the bases showed no sign of expans because of the HB. Even the bases of softer alloyed bullets do not expand at carbine velocity. Several of the Lee moulds I have used drop bullets cast of 1-20 at .461 to .465. The best accuracy comes from using them "as cast" or at least sizing to not less than groove depth. Softer alloys in the Lee 405 HB will do alright if sized .459 but they will most often give better accuracy if used as cast.

I know Spence Wolf says to size .459 but remember that Spence was replicating the Service loads. I discussed this with him many years ago and he knew that properly sized to groove bullets shot better. That was not how the arsenals did it so he did not use it in his very fine book (anyone who loads for the TD should have his book). He was, as stated, replicating US Service 45-70 and 45-55 loads. He replicated those very well indeed and if you follow his instructions you will have ammuntion that shoots every bit as well in your TD as did that of 137 years ago which wasn't bad at all.

Larry Gibson
Can't say it better.

[beagle]

Had a friend with an old trapdoor. The thing had about a .463" bore on it and I finally beagled him some bullets and he got fair accuracy out of it. The hollow base had it been around in those days would probably have helped as it expands to fill the bore./beagle

[StrawHat]

The hollow base on the M1873 45-70 bullet, of which the Le 405HB bullet replicates, is not there to expand or flare out ala minie style to seal the bore. If you note the skirts are very, very thick on the Lee bullet as when compared to a true minie style bullet that does flare out to seal the bore on firing. The HB on the M1873 bullet is there to is there to regulate the weight of the bullet while maintaining the same overal dimensions with different alloys. The M1873 bullet was dependent on obturation or "bumping up" to seal the slightly larger bore in the M1873 Springfield TDs. It was found the 400 gr bullet did not have sufficient mass to obturate completely and that led to the 500 gr M1881/2 bullet. It also had a dishout cavity in the base to regulate weight while maintaing the same overall dimensions. It had the mass at .459/.460 to obturate and seal the .460 - .465+ bores.

I have recovered numerous Lee 405 HBs that were cast of 1-20 & 1-16 tin/lead alloy (that's what the arsenals used) that were fired over service loads of 70 gr BP and equivelent smokeless loads and the bases showed no sign of expans because of the HB. Even the bases of softer alloyed bullets do not expand at carbine velocity. Several of the Lee moulds I have used drop bullets cast of 1-20 at .461 to .465. The best accuracy comes from using them "as cast" or at least sizing to not less than groove depth. Softer alloys in the Lee 405 HB will do alright if sized .459 but they will most often give better accuracy if used as cast.

I know Spence Wolf says to size .459 but remember that Spence was replicating the Service loads. I discussed this with him many years ago and he knew that properly sized to groove bullets shot better. That was not how the arsenals did it so he did not use it in his very fine book (anyone who loads for the TD should have his book). He was, as stated, replicating US Service 45-70 and 45-55 loads. He replicated those very well indeed and if you follow his instructions you will have ammuntion that shoots every bit as well in your TD as did that of 137 years ago which wasn't bad at all.

Larry Gibson




Can't say it better.

I'm not sure I could have said it that well.

Kevin