A quick way to see if fixed ammo will work is fire a high pressure round and measure the inside diameter of the brass. That measurement will be the maximim diameter of bullet's base.

I don't know the particulars of your rifle, but I think of all classic/antiques as wildcats. I generally try not to worry that ammo has to fit different rifles, preferring to just designate some brass and keep notes of load quirks if needed. Somehow or another you'll get that bullet into the mouth of the case, it just may take adjusting the process. 

I'm not recommending to do it, but I do suspect an undersize bullet can shoot okay in a pinch. I'd think you're headed in a good direction because of slugging the bore, maybe add a chamber cast and some measuring. Best of luck with it.

Indeed...there will be no high pressure anything in this beauty, it's forged, but it's still a Ballard.

So far I've found one mold online that would likely work, but it's out of stock. .385 dia., 260 grains. Sounds like a great place to start  if I can find one.Buffalo Arms website.

Thanks for all the replies so far!

Paul

Your chamber cast should have told you the diameter of the front of the chamber behind the transition or leade. Subtract .001" or .002" from that diameter and you have the maximum diameter of the neck of a loaded round.

You could load an undersized (for the groove dia.) soft bullet that keeps the cartridge neck at the above determined diameter and shoot with black powder and hope for the bullet to slug up to fill the groove diameter.

Another possible solution is to have Tom at Accurate Bullet Molds make you a mold that has a heel of appropriate diameter to keep the neck at the above determined diameter and a driving band just in front of the case that fills the chamber throat, and forward driving bands that are bore diameter or just barely engraved by the lands so that you can chamber the loaded round with reasonable finger pressure.

I recently lucked into a Ballard #8 Union Hill that is in great shape internally, but quite rusty on the exterior. The neck area of the chamber is .344" in diameter, the throat and groove .331" in diameter, and bore diameter .321".   

I had Tom make me a tapered bullet mold that casts a base band of .331", and forward bands (from base band) of .329, .327, .325, .322 and .321 inch. I will breech seat this bullet with a stirrip-style breech seater.

I'm also considering having Tom make a heeled bullet mold so that I can shoot fixed ammunition in the Union Hill.

I've got the same issue on a couple guns and the easiest way around it is to simply breech seat. I resisted going this route myself for a very long time as I considered it too "fiddly" when in truth I knew zip about breech seating. My worries were unsupported, and silly. Once I was forced to begin breech seating by a large groove diameter, I soon realized it was easier than sitting at the bench making up cased ammo. And of course usually more accurate too.|
I wouldn't hesitate to breech seat for it, but if you still want to use fixed ammo I'd have Tom at Accurate make up a "heeled" bullet as mentioned previously. A heeled bullet design would allow it to seal, and still keep the neck size down where it would readily chamber without issues.
Accurate's molds can be changed however you prefer at no extra cost. Just go to his web site and pick a bullet weight and design there. Then reduce or enlarge whatever bands you want during the ordering process. Pretty easy, and very reasonably priced.

That's great info...I wondered about the Lyman mold, have heard bad things about the current Lee molds but everyone has an opinion I guess.
Chuckster was pretty sure I'd be able to shoot at distance if I found a mold that throws a well fitted bullet.I sure hope so, although my primary interest is 200 yard Schuetzen and as V all says above, breech seating is the way to go in that game.

The Hepburn I lost in the fire was also 38-55, that's next on my list to find once I recover from bringing this Ballard home.

Yes, get a mold from Accurate. You can order just what you need to your specs. I have a bunch of them. Just for the record, though, the latest Lees (with the caliber and weight marking on the top of the mold) are very nice molds.