Whitney Remington Rolling block

It could possibly be .38-55 Winchester.

38 long centerfire is exactly the same as the rim fire
not only is the bullet 375, but it takes a heeled bullet because the case crimps to the tail of the bullet like the 22rf

my cartridge books are at the office I will post the dimension tomorrow

according to my cartridge conversion book, 38 Long Centerfire cases can easily be made from either 357 mag or 38 Spl cases. trim to a case length of 1.03 inches and size in a 38 Spl die. a 38Spl case length is ever so slightly longer and is 1.155 and a 38Spl may fit the chamber without trimming if the chamber was cut with even a little extra room. The empty case will fit because the chamber is straight, with the bullet added you might be pushing the bullet into the rifling to close the breech. The difference is only a tenth of an inch.

As for bullets, you will need a heeled 375 bullet. The alternative is breech seating the bullet into the rifling and just loading a case full of powder behind it. (be careful to leave no gaps between the powder and bullet.)

Folks have tinkered for years about ways to reload the outside lubricated bullets. I suppose a small gizmo could be made to shave a lip around the base of the bullet. The old Ideal nutcracker tools for 38 long centerfire do come up on the big on-line auction perhaps once or twice a year. They have a mold incorporated in the tool. I needed one in 32 long centerfire and got one for $35.00. The alternative would be to have the chamber recut for a cartridge that is availible and takes a modern style inside lubed bullet, like the 38-55 Winchester. There are a few other 375 bullet cartridges that would fit the bill, but would require making cases from others, 38-50 Maynard, and 38-50 Remington.

Is it a first or second model Whitney? If it is the first model, the action is not strong enough for many modern cartridges even when loaded with black powder. Frankly, I wouldn't shoot a first model in 45-70 or 40-65. 38-55 with reduced loads would be max for the first model.

Just a word of caution relative to that Whitney. Buddy of mine has one....re-blld to .44. He'd been having problems with it...........stated the locking mechanism was not working correctly and that it'd opened on occasion and blown just fired cases out, narrowly missing his face.

Asked me to look at it for him........sure nuff, it was only partially locking....the internal mechanism was NOT catching.....got it going and ran about ten or so rounds thru it with no issues & then once again it began to unlock on firing. He finally gave up on it and stuck it in the attic.........and that was after a lot of parts chasing and tinkering.

Be aware that the Whitney action is NOT...repeat that in cap's NOT anywhere near the Remington design where the hammer actually locks the breech...the Whitney depends on an internal 'catch' for that and is nowhere near as safe as the Remington rolling block.

In my humble opinion the things are wallhangers at best and you run a substantial risk of serious injury playing with them.

Your call, but take this for what it's worth.

That must have been a first model
the second was much stronger although never as strong as the 1902 remington

Greetings
I have a Marlin-Ballard that is a 38 Long. Breach block has the dual rotating firing pin to be able to shoot center and rim fire.
My Marlin Ballard uses a .383 heeled bullet. About 150- 175 grain lead shoots well and makes for a fine under 50 yards ground hog rifle.
Brass can be made from 38-55 or 375 Win brass. Slide a whole case into the chamber. case mouth might need a little flare but will butt into the chamber shoulder. Measure how much to chop off. Leave the initial cut a shade long then finish it to perfection.
For load development I highly recommend 3F BP. I have been hard pressed to beat 3F for accuracy in many BP cartrige rifles. Once I have my accuracy baseline then you can start playing with powders. Unique, 2400 have shown good for my 38 Long.
For smokeless you will need to be aware that filling the throat diameter is a must. 3F will "bump up" a 40-1 bullet. Unique may but powders like 2400 will not.
There is alot of info out there. But there are the basics.
Mike in Peru

Missionary. I have a 38 Extra Long Wesson rifle and there is no way a 38-55 case will fit in the chamber, too big in diameter. Ironically, 38 Extra Long cartridges are exactly the same as the modern 357 Maximum cartridges, length and all.

A 38-55 case mouth is simply too large. The case rim of a 38-55 would be far far too big.

Greetings
Well all I know for sure then is what works in my Serial # 70xx Marlin Ballard.
Is there another 38 Long out there that I do not know about ? I would not be surprised.
Mike in Peru

Was your gun rechambered to a modification that was sometimes referred to a 38 long inside lubricated. Not commercially loaded to my knowledge, but also not an uncommon modification when 38 Longs became hard to find.

I was tempted to have my 38 Ex long rechambered to 38-55, which would require a substantially larger diameter chamber.