Breech seat your Mirochester 1885 and you won't need to buy one ! That'll tighten up your groups to boot .

You can get them from CH4D too. Most of the time fast delivery

Boats

Breech seating while popular perhaps necessary in Schuetzen is a special situation not practical or even allowed in many matches.  It's gets it's "bullet pull" from the bullet engaging the leade.

Cowboy with a lever action another special requirement, bullet has to stay in place in a tubular magazine on recoil most do it with Crimp.  Black powder cartridge rifle lot of guys use slip fit no bullet pull at all.  They get proper ignition from bullet weight, black is easy to ignite and the bulk of powder behind the bullet keeps it in place. One at a time no need to stand up to recoil.

What I think you need is information on less than case filling smokeless loads in the 38/55.  Bullet pull is important and you need some. How much and what size is hard to say, it depends, give you some general principles.

Too little pull with 4759 or 4227 you will see unburned powder in the bore more likely with 4759. Too much pull will deform your bullets, easier to do softer the bullet is.  Crimp can make up for neck pull if your bullet has a crimping grove in the right place for O/L length

My 38/55 shooting fixed in a CPA Single shot, been using a 300 gr bullet cast out of 1/25, not real hard, .002 over bore size. Neck size the cases then open up with the expander plug to about .001 less than bullet diameter. Then put a mild crimp on the case into the bullets designed crimping grove. Loaded this way it's a 1 1/2 moa load adequate for offhand matches or your Cowboy distance events. Load a large lot at one time the bullet stays in place, can count on the loads to perform in matches.

Am changing bullets this winter new mold for fixed loading and what worked before may not work with the new bullet. Going to use minimum neck pull, light crimp, 1/25 or perhaps 1/20 lead/tin mix 4227 powder as a starting point.   Suggest you do the same.

Boats

I have several .375 win's.  I expand to two diameters - one holding the bullet with .001 or so tension and for 1/10" at the top .001 or so slip fit for that bullet.  That allows me to slip the bullet without shearing anything into the case, seat to the depth I want and then just LIGHTLY 'crimp' the case to remove any "belling" (also a part of the expander).

Don't know if it's optimal or not for accuracy, it is convenient.

I don't believe in no tension for less than full smokeless. Did not believe in crimp either but went to it for a better burn with 4759. Switched to 4227 and kept the crimp.   It's true single shot does not have to 
Be loaded like a lever gun.  Only thing is I load 6 60 round MTM boxes at a time.  3 or 4 months later don't want to pull ctg number 335 out of the box and find the bullet slipped from all the carrying around. Little tension or crimp makes a secure load.

Boats

Thanks for all the replies - lots to think about.  I do have the molds for the Saeco #571, the Hoch .377 310 grain, and an NIB Lyman 375166 - haven't stepped up to pouring my own yet but do have a Waage pot, ladle, and thermometer.

I have been using 3031, but may rethink that on what I read here.  My last practice rounds, I seated just to where the nose of the bullet engaged the lands and did crimp with a Lee FCD (one lube groove exposed).  

I had some fair success with the factory supplied Marble's tang sight, but was using holdover - just not tall enough.  I bought a Montana Vintage Arms sight and really like it - just haven't had a chance to shoot with it much yet.  

I'll keep searching/reading here for tips and ideas as I figure out the best way to load and shoot this rifle.

Thanks again,

OVW

Hi boats and all -

The journey continues ...

Step one - just acquired (probably the last) keg of 4759 here (from a feed store!).
Step two - Buffalo Arms custom expander
Step three - ... ?  (load and shoot some)
Step four - learn how to pour my own boolits

I love "hanging out" with enablers on these forums who encourage me to get more equipment and shoot more! 

Thanks for the help.

OVW