Making 500g Lee work in Marlin GG

[Driller640]

This is what I want to do, shorten Hornady 45-70 Brass until 500g Lee boolit seated at the crimp grove will function through the action. Can I use existing load data for Marlin 45-70? I will use IMR3031 and Win LR primers.

[NickSS]

I wouldn't use 45-70 load data as you will be decreasing the volume of the case and pressures will go up. You would probably be OK with trapdoor loads but not marlin loads. Actually you probably could not get some of the top loads in the case without crushing the powder.

[rob45]

Whatever you decide to do, remember that you are now firing a short case in a long chamber. This is no different than 22 shorts in a 22LR, 38SPL in a 357 Magnum, etc.
Be sure to check for powder fouling in the end of the chamber any time you shoot the short brass.

[dubber123]

How about picking a powder that will be compressed at the velocity you need, and just seat the boolit deeper? I loaded some Lyman 462560's, (550+ grains) in full length brass, and seated them to function (quite slickly), in my 1895.

[rob45]

This is what I want to do, shorten Hornady 45-70 Brass until 500g Lee boolit seated at the crimp grove will function through the action. Can I use existing load data for Marlin 45-70? I will use IMR3031 and Win LR primers.

General rule: If you can find data for that type of bullet at the COAL you're wanting or less, you should be fine. The place you will run into problems is when you have more of the bullet in the case than what they did during testing. The same concept applies with a heavier bullet; e.g., if you cannot find data for a 500grn at 2.55", but are able to find data for a 530grn at 2.55", then you're probably fine to substitute the lighter bullet since less of it is in the case.

SAAMI specs for the 45-70 call for a COAL of 2.550". The carrier assembly in your particular gun may allow you to go longer than that, and that is preferable, as the further the bullet is out of the case, the lower your pressure will generally be. One of my Marlins allows me to go only to 2.58", while another allows me to go to 2.63". I like to make dummy cartridges for each gun to let me know what the maximum COAL is for each gun, then load accordingly. Or you could play it simple and just load to 2.55".

The largest problem you will encounter is lack of load data for the heavier bullets in the lever actions. For pressures applicable to leveractions, most of the powder companies and bullet manufacturers will specify bullet weights in the range of 300-450 grains. Sure, you will see the heavier (and hence longer) bullets listed at safe pressure levels for your Marlin, but upon closer inspection you will notice that the OAL which provided that (safe) pressure is no longer 2.55", but it is now something like 2.85" or even longer. In other words, that load was designed to function with a single-shot to take advantage of the longer length. If you take that same load and shorten the COAL to work in your gun, everything changes.

As mentioned by NickSS, seating the bullet shorter than what the data specifies will usually raise pressure. I'm not talking about the length of your brass; I'm talking about more of the bullet taking up space inside the case.

So where to start?

The first place to look is published data, but as mentioned above, you need to make sure that the data presented was not based upon a longer COAL. Currently, the powder manufacturer that has done the most pressure testing with bullets in the range of 500 grains- seated to SAAMI specs and delivering pressures commensurate with leveractions- is Accurate powders. I'm not throwing an advertisement in here; just stating where you'll probably get the most information for that weight of bullet seated to a length applicable to leveractions. But suppose you cannot find published data for your particular powder/bullet/COAL combination? A call to the powder manufacturer may help, but don't count on it; they are as hesitant to give out info as any of us are simply due to the fact that nobody is supervising your reloading except you. But sometimes you get lucky and get to talk to one of the ballisticians who can give good starting recommendations for your combination.

Next would be internal ballistics software (Quickload, etc.); these are also a shady area, as some report reliable approximations, while others say they're an accident waiting to happen. The best results with load software seem to be when you have as much (and precise) input as possible before computing the final result.

And, as always, you have the recommendations of others who have already "been there, done that." If you can find someone who loads the Lee bullet in their Marlin (to a COAL that still allows it to function), you're halfway there. Now you only have to worry if the pressure level is actually where you want it. And if the velocity they're getting is what satisfies you. And if they have experience with the powder you want to use. And...:veryconfu

Good Luck.:smile:

[Marlin Hunter]

I don't know if it matters, but the SAAMI pressure for the 45-70 is far lower than the Marlin can take. That does not mean you can use C-4 as a propellant.