smokeless powder in a trapdoor

[Triggersmith]

 I am putting a 38-56 barrel on an 1873 Springfield receiver and am wondering if anyone is using low pressure smokeless cartridges in a trapdoor?  I have been told by a competent gunsmith you can safely shoot smokeless in a trapdoor using lighter loads.  Any comments
Triggersmith

[St. George]

I've always shot factory smokeless in my Trapdoors - with no problems at all.

So long as the load equals or is less than the factory specification - you shouldn't have problems in a piece in good condition.

Vaya,

Scouts Out!

[Triggersmith]

I appreciate that information.
Triggersmith

[GUAMBEAR]

Can't get black or pyro where I live so I use 32 grains of 3031 smokeless powder. Get the round down range and it's a heck of a lot easier to clean the rife/cabine after you've had your fun.

[Cyrille]

No, it ain't!

[Ranch 13]

You can use smokeless in a trapdoor, using trapdoor data available from various component resources.
However with that said I've yet to run into a trapdoor that will shoot as well with smokeless as black.
Those that say cleaning smokeless is easier that cleaning black , haven't shot black, or they'ld know better.
There's no excuse to not being able to get black, with places such as Grafs, Track of the wolf, Maine Powder house, coonies, Powder Inc, and others that will ship black to your door.

[Cyrille]

^
What he said! Hear,  hear!

[Trailrider]

Howdy, Pard,
Yes, it is possible to use LIGHT smokeless loads in an original Trapdoor Springfield...PROVIDED it is checked out by a gunsmith who knows Trapdoors!  There are a number of loads listed for the .45-70 by Lyman, in their 48th Edition Handbook.  The main problem with using smokeless in most .45-70 Trapdoors is that the original barrels often run as much as .462" and the 3-groove rifling makes measuring the actual diameter difficult.  For the .45-70 with oversized barrels, the main solution is to use a soft bullet and the black powder tends to make the bullet slug up to fill the barrel.  With smokeless powder, you don't generally get that effect.

Now, you say you have rebarreled the rifle to .38-56 WCF, so presumably you have an even number of lands and grooves, and can determine the bullet size to use. 

The biggest difficulty I see with your .38-56, is determining the proper smokeless loads to use.  You CANNOT use .45-70 data, and I have never loaded for that cartridge, so I don't have data to provide.  One possible way to start out is to weigh a case empty, but WITH a FIRED primer in place.  See if you can expand the case neck enough so you can easily slip a bullet in and out with your fingers.  Fill the case with water, slip a bullet in as far as the normal seating depth; excess water will slop out around the bullet.  Wipe the outside of the case off so you don't rust your powder scale pan.  Remove the bullet, and weigh the case WITH the remaining water inside. Subtract the weight of the empty case from the same case with water in it.  This will give you the water capacity of the case. Repeat with at least 4 more cases.  Do the same thing with a .45-70 case and a .45 caliber bullet which is the same weight as those used in published .45-70 data.  Add the water capacities and divide by the number of cases used for each type cartridge.  Divide the .38-56 water capacity by the .45-70 water capacity.  This SHOULD be a number LESS THAN 1.  The smaller water capacity of the .38-56 case means you have to REDUCE the .45-70 powder charge.  But...we need to go further!

The next thing  you will need to do is calculate the Relative Sectional Density of the bullets for each cartridge.  The RSD is determined by dividing the bullet weight (in grains) by 7000 times the SQUARE of the bullet diameter.  For a 260 gr. .380" bullet, the RSD is .257.  A 405 gr .458" bullet has an RSD of .275.  Since the 260 gr. .38 bullet is "lighter" than the equivalent .45 cal., the powder charge can be INCREASED slightly, so divide the .45 cal. RSD by the .38 cal. RSD.  In this instance .275/.257 = 1.073.

Multiply the 1.073 by the ratio of the case capacities.  Let's say (it ISN'T...you'll have to determine the water capacities) the ratio of the water capacities is .95.  Multiply that number by the ratio of the RSD's, and we get 1.0195.  Multiply the recommended charge weight by that figure and you will get FAIRLY CLOSE to a starting point.

I know this sounds complicated, but it is the best guide you have.  Oh, yes...DEFINITELY HAVE A CHRONOGRAPH AVAILABLE to check the velocities.

[I can assume or accept NO RESPONSIBILITES FOR THE USE OF THE ABOVE INFORMATION.  It is presented ONLY for the academic interest of readers!]

Ride careful, Pard!

[French Jack]

The loading I used on several occasions was a 249 gr. cast bullet, 30-1 lead/tin, cast from Lyman mould # 375248 seated over a lubed wonderwad over 17 -18 gr. of IMR SR4759.  You can leave out the wonderwad if you like.  Primer is CCI 200.
Wad is placed in mouth of case after powder put in, and allowed to seat by the bullet.  This leaves no air space between bullet and wad that can lead to chamber ringing.
That said, be advised that this load may or may not be safe in your firearm.  Caveat Emptor.