IMR Data Center Loads Too Hot for 45-70 Trapdoor?

[Speedo66]

I've got a bunch of Trailboss powder, so I went to the IMR Reloading Data Center for loads for the 45-70 Trapdoor Springfield. The original trapdoor I have is in good condition.

Interested in loads with a cast 405g bulllet. They have a page just for Trapdoors.

They show a load with 12g Trailboss, 24,500 CUP, and max of 13g Trailboss, 26,500 CUP.

Neither the Lee 2nd Edition nor the Lyman 49th Edition show loads near those pressures for a Trapdoor.

I'd like to use the Trailboss, but I don't wish to go home wearing Trapdoor parts.

Wanted to know what the feeling is here.

OK loads or too hot?

 

[freakshow10mm]

Use the data they provide and work up.

The 45/70 is a strange creature for powder companies and their data. They set power levels at different places. Some put trapdoor presures at 21,000 CUP, while others run 28,000 CUP. Hodgdon, IMR, Winchester use 28,000 CUP as their MAP pressure in trapdoor rifles.

 

[Jim Watson]

I consider Trail Boss to be a pistol powder and would not use it in a Trapdoor. It is false economy to push the limits just because that is what you have on hand.

Accurate Arms stops at 18,000 psi for the Trapdoor, which is strange because they go to 22,000 for the .50-70. I guess they figure there are few 1870 Trapdoors left and that the .50-70s being shot are stronger guns. Lyman only goes to 17,000 CUP but you can beat black powder velocities with 3031 or Re7 at that pressure.

 

[ten bears]

Trapdoor Load

Speedo,

Try 29.5 gr of Hodgdon 4198, CCI 250 primer and a 405 gr SWC. Stuff half a cotton ball on top of the powder and shoot away. A friend turned me on to this load and I now shoot it in all my trapdoors. It falls in at around 15400 CUPs, about half of the 25000 max for a trapdoor. The cotton ball holds the powder back against the rear of the case for a full burn. This data, minus the cotton ball, is printed in Hodgdon's 5th Edition Cowboy Action Data. Recoil is very mild and they are accurate. My boys can shoot this load all day! Now I just pretty much reload for them. Take Care!

Ten Bears

 

[ArchAngelCD]

The Hodgdon Load Data Site covers Hodgdon, IMR and Winchester powders. They have separate load data for the 45-70 Trapdoor Rifles, 45-70 Lever Action Rifles and 45-70 Government in Modern rifles.

 

[Speedo66]

OK, now I'm confused. I checked out loads for the 45-70 Trapdoor with IMR 4198 on both Hogdon's site and in Lyman 49.

Here are the loads:

Hodgdon- 405g cast bullet 30g IMR4198 vel. 1370fps CUP 17,000

Lyman49-405g cast bullet 31.5g IMR4198 vel. 1312fps CUP 12,400


Based on this data, increasing the charge from 30g to 31.5g of powder DECREASES the velocity and pressure?

What am I missing here?

 

[Jim Watson]

Different barrel, different bullet, different lot number of powder, different calibration on the crushers. Get a couple of those with variances in the same direction and you see stuff like that. Makes it hard to compare data across sources, you just have to do the best you can.

Me?
I don't have a .45-70 and my .38-55 and .40-65 get black, so I cannot give specific recipes for nitro.

 

[ArchAngelCD]

Speedo66,
In addition to what Jim mentioned is there a difference in the seating depth or COAL between the two sources? Even if the COAL is the same a different bullet with different profile could seat deeper than the other increasing the pressure even though less powder was used. (I'm too lazy to go into the basement and check Lyman 49)

Hodgdon lists a COL of 2.540", what did Lyman use?