John
I'll bet there are a number of forum readers who can help you. It would however be helpful to know what type of rifle you want to build. Is it for fixed ammo silhouette, breech seated schuetzen, or what? Different applications might dictate different chamber configurations as does the brass you intend to use (StarLIne 2.080, 2.125 or WW brass?).

Schuetzendave Thanks!   Appreciate your posting that even though it's not a 38-55.   I have that in a Cody - as of yesterday!    Glad to have the drawing.   Checked my twist as soon as I took it out of the box and it's a 16:1.  Other than being sure about how this was chambered I reckon 'some' of what I'm doing in having a good look at the 38-55 variations was to be sure that is really what I wanted vs the 38-50.  Appreciate the drawing and the information you added.

My first CPA built in 1993 is a 18 twist .375 and always use 300 gr bullets fixed. Still using the same. 500 case  lot of WW brassIt's a standard set up and  won a lot of offhand matches. You read about fast twist today and no doubt fast is required if shooting longer heavier bullets I have a 40/65 for heavy  work no need to push a 38.

Shot it a for while breech seated with black powder using a different bullet, tapered . It performed very well, switching bullets was key.

My advice is pick the bullet needed to give adequate ballistics based on expected targets plus brass you can obtain, and set the barrel up to suit. I have no idea what reamer Paul Shuttleworth used, left that up to his experience . Based on on friends experience .379 bore is a mistake. I can't say for sure.

Boats

Thanks Frank! 

The PTG has .100 free bore in common with the 38-50HR.    Interesting!   Tackling the chamber before selecting bullets presents floating variables that complicate decision making.   Been there with the 40-65; glad that is behind me.   

Thanks again… btw, been meaning to send you a PM.  I sent one some time back after buying the TMT software.   I finally got my start & used it to design a couple bullets to send to Tom @ Accurate.   Just got two molds back yesterday.   Be testing them in the Marlin 1895 in 40-65 and the Pacific 40-63.   I can’t imagine how many hours you’ve spent or how proficient you must be by now.   I’m coming along!   Sure appreciated all your efforts there on your thread!!!

Boats,   
I counting on the same about the 40-65.    Having a 38-50RH in the wings is another reason why I’m not really targeting this one for anything beyond ‘general’ shooting.   Hoping to experiment with Breech seating soon.  Marlinman93 sent me the hook for a seater and a drawing of his tool so maybe this spring.      Interesting about the .379 experience.   My exposure to the 38-55 has been  with a Marlin 1893 and more recently with a Cody Ballard.   I’ve only got the one mold for the 1893 (probably a little light for the Cody) but the bullets from that fly very well in the Cody too.   Broke my own streak on a 300yd diamond with it and had very good performance at 650yds.    Should only get better with  a weight better matched to Cody twist.    On a related note I’ve looked at Dave Manson’s McPherson diagram – but thought that an effort to meet lever gun modifications based on his Starline article.

SSShooter,
Thanks for the thoughts here.    I went up and spent about an hour and half with Crossno before sending these two Ballards off to John Taylor.    I wish I would have touched bases with Steve Baldwin too.  Might have impacted my caliber decision.    I may give him a call just to get his thoughts.   Could be an option to ask John Taylor how much he’d knock off the reline price if he didn’t do the chamber on that reline “if” Steve would consider reaming and setting up the lock-up on that one currently slated for 38-55.    I’ll add research into the 38-40 and 35-40 to my list.   Complete ignorance there.      

Thanks All, appreciate the input and drawings.
John

Here is the thing about 375 vs 379. Original bores were 379 Winchester and Marlin lever actions.  Some of the Italian reproductions are too. Guys I know that have .379 bores have trouble with brass and chambers fitting. It's big, fine for black powder, but go with a bullet .002 over like most of us do for smokeless powder it's hard to get the brass to accommodate it, not impossible just not easy.

Modern builders, when I set my rifle up 20 plus years ago, were limited to .375 blanks, because of other calibers that were intended for .375 bore it's about all they could buy. As it turned out .377 cast bullets in a .375 bore is a happy combination, not too big for the brass and nice bullet fit. All my molds are custom but think it's easier to get a mold .377 than it is .381

Anyhow the Lever Silhouette Shooters I know always have trouble with brass and bullet fit in .379 bores. Most of the single shot rifles we use are .375 bore

Boats

Boats,  I went and had a look at the Boomer site.   Sure has some great testimonials.    I’ll add that one to my favorites.   And since Tom at Accurate does not cut round noses, I’ll be needing a mold once that is back at the ranch. 

For my 38-50 (Cody) I was fortunate enough to get some RMC brass along with the rifle as well as a Steve Brooks mold (thanks Vall).    I’m looking forward to shooting that one for sure.
The 38 caliber line up stands like this here.
*Marlin 1893 in 38-55.   .379 groove and 18 twist.    
*Cody Ballard 38-55.   .376 groove and 15 twist.
*Cody Ballard 38-50.   16 twist.    Just arrived yesterday so have not slugged it yet.  I’m expecting .375.   
*Marlin Ballard in 38-50 with bad bore – this one is my focus here.  Obviously my original plan was gonna be for a 38-55 chamber.  There are some interesting options being offered though.   As usual I start raking in enough options to make decisions more difficult

The issue you talked about with .379s is discussed here by M.L. McPherson on the Starline site.    (You need to Login or Register to view media files and links);
Read it some time back and recently obtained a copy of the reamer mentioned there.     He talks about a lot of people fouling up their accuracy by trying to open up the chambers in their lever guns.    Can’t attest to any of it but it was an interesting read for someone with an original Marlin with a tight chamber.

I'll add some personal experience to the M.L. McPherson article.  My Marlin 336 Cowboy in 38-55 has a .381" groove, which flummoxed me before I heard of the Starline brass. I ended up buying a outside neck turning attachment for my Forster case trimmer and thinning the necks on some W-W 38-55 brass.

Now that I've heard of, and tried the Starline brass, the problem is solved. I've got a 382-250B mold from Tom at Accurate that throws about .383-384" depending on alloy, and I size them to .382", load them in Starline brass, and my Cowboy 38-55 gobbles 'em up without a hiccup.

Starline brass is the solution to a .379" groove diameter 38-55.