Kind of a clunky, imprecise title but I was struggling for a way to title this with just a few words.

Do you have a bright line regarding when or what to modify when working on a project rifle?  Obviously one wouldn’t (usually) consider modifying a rifle that was 95-100% original and correct.  Nor would one consider a patently unsafe modification such as converting a Favorite to something like .444 Marlin.

I’m more curious about situations such as numbers matching but rotten bore.  Do you reline back to original?  Reline/rebore to a caliber that was factory original for that rifle?  Or is it fair game for any caliber suitable for the action regardless of factory originality?

Some decisions I find to be easy, like cleaning off active rust without disturbing the underlying finish/patina.  Or unbuggering screws and refinishing them as they were originally and to match the other screws and the amount of wear (if any) common use would have created.

Beyond that, like Vall, I have to think, sometimes long and hard, about the guns overall condition, rarity, and such provenance as can be proved.  And quite often I end up following one of my dad's (many) rules: "When in doubt, don't."

Bill Lawrence

In the case of a Ballard in .38 Long with a shootable barrel, it would be easy enough to flip the firing pin from rimfire to centerfire, trim .38 Special cases down, buy a heeled-bullet mould and go shooting.

That’s what I did with my Ballard in .32 Long, only in that case, I was able to scrounge up .32 Long Colt shells, moulds and reloading dies.  The rifle was in usable, but by no means pristine collectible shape, and it was much more interesting, and much less work, to shoot it in its original condition.

I found another Ballard in .38 Long, with bore and chamber hideously rusted, brown and pitted outside, the buttstock repaired in antiquity but by then with finish oxidized nearly black.  I had no qualms about converting this to centerfire, restocking and getting it relined to .32-20.  I even drilled and tapped the barrel and put a scope on it; one of the outside-adjustment types that look “period.”  Never lost any sleep about “originality” on that one; it shoots nicely with blackpowder loads.

A third Ballard was originally in .22 Long, was shot-out and sent to Stevens to be rebored and rechambered to .25 Stevens, and then was shot-out again.  I relined it back to .22 caliber and chambered it to .22 LR.  I tightened the linkage with new screws and pins but otherwise have left it alone.  The gun is a uniform brown patina with no pits, as is the original stock, and it says “Rebored and Rerifled by J. Stevens Arms Co” on the barrel.  A fun and interesting shooter.

If the .25 barrel had still been good, I’d have done some soul-searching about the reline, and might not have had the heart to do so.  But I was spared that crisis of the soul.  Another was a Stevens 44-1/2 barrel in .25-20 SS, in perfect shape inside except for bad pitting ahead of the chamber, probably from corrosive/erosive primers.  I did everything I could to get that to shoot, but nothing worked; not lapping, oversized bullets, nothing.  I sent it to Redman for a .25 caliber liner and chambered it to the original caliber.  But not without pains in my heart.

It shoots nicely now, so the pains have pretty much been forgotten.  The only way to have saved the original barrel (and I am usually at pains to save original Stevens barrels, as they were very well done and set many records) would have been to rechamber to a longer shell, like the .25-35, and that would have been an even worse compromise in originality.

They are out of stock already.  They are a good company to be on their mailing list as they send out in stock notices regularly. 

The issue with a Ballard in .38 Long if using the original barrel is groove diameter. They are not a .357" or anything close, so you can use .38 Special brass, but as Bob mentioned you'll need to cast and load with a heeled bullet to fit the much larger groove diameter. Usually run around .375" groove.

Might be easier to modify an existing mold to open up the diameter just above the heeled portion to the larger diameter you need? I've done this on occasion and just enough to seal the base band and got great accuracy.
Might also consider breech seating a larger non heeled bullet first to test and see if that makes groups tighten up before going through the work of modifying a mold. Could just build up a push seater from an old case for testing too.

Wonder if an ideal or lee mold for the .36 caliber percussion revolvers might be a good candidate for this cartridge?

If this is the typical Marlin Ballard #2 in .38 Long with octagon barrel I've never seen one that couldn't be large enough to accept a liner in .357"? Should be plenty of meat to allow it to be bored and lined.