Gunfunpow, you've got a very nice pair of original No.1 RBs. I also shot an original in .44/77 (stamped 44 CTG'E S under the barrel) with a twist of 1 in 26". I think part of the problem you have been having in determining the groove dia. stems from these early Remingtons having 5 groove rifling which makes measurement difficult without the use of a vee block. The fact that you can push a .446" bullet down the bore by hand pressure alone suggests to me that you need to use a wider bullet.
The barrel in my .44/77 slugged at .453". I used a older version of the Lyman 451114 mould that cast a .454" bullet weighing 420 gr with 20:1 alloy. Loaded in fire-formed Bertram .43 Spanish cases with 70 gr of Curtis & Harvey FFg this bullet grouped well (10 shots in 3" @ 100 yds). I also tried the RCBS 44-370FN with a softer alloy of 30:1 (cast dia. of .449). With a load of 72 gr GOEX FFg  this bullet gave similar results as the Lyman. However, the best performer turned out to be the Lyman 439186 (.43 Spanish bullet) cast with 30:1 & paper patched to a dia. of approx. .448" with 70 gr GOEX FFg. This combination shot really well. So it pays to experiment!
My advise to you is to invest in a quality outside micrometer, you'll never regret it, an essential tool when fooling around with these old single shots. Have fun!
Spud.

I have no trouble chambering larger grease groove bullets in my Rolling Block of the same caliber. I use .452" bullets for fixed ammo and they chamber fine.

If you are buying a caliper and v block to measure an odd number of grooves then save your money. A caliper is not that accurate to start with and introducing another piece of equipment is another opportunity for error. The proper tool is a vee anvil micrometer and they aren't cheap . A well equipped machine shop should have one and might be willing to measure it for you. A Vee anvil mic will only measure one number of flutes or grooves and at about $400 each you need to do a lot of measuring. If you only have one measurement to make I would even be willing to pay to get a measurement that I had confidence in . I'm not sure how you would do it with a vee block anyway. I have never seen such done as a professional machinist.

Longdistance1 wrote on Jul 16^th, 2018 at 12:54am:

That would work but does he have a set of pin gages? That is another stack of money. Another method would be to put the block on a surface plate and use a height gage to measure to the bottom, zero the gage, measure the top  and that would give you a number. Again, though it requires gaging that the OP likely does not have. Even simpler, now that I think about it, just measure from the plate to the top of the bullet. Of course the rifling has to be fast enough that the bullet does not try to sit across a groove. In any case a caliper and vee block alone won't be any help.

Thanks Marlinguy for that bullet idea. I have not purchased a bullet mould yet. I will once I settle on a bullet and load. I'm going to chamber cast and see what actual dimensions are, freebore, etc. I was told this could be 44-90 as well, so there's that. I'll use up the 50 bullets I have and go from there. Thanks for the help!

Well, heres my two cents FWIW.   Buying pin gauges and worrying about exact groove diameter is a waste of time unless you know the thickness of your brass at the neck and chamber size.  Marlinguy mentioned using a .450 something bullet but his brass would likely be pretty thin necked.  In mine which measures about .453 I think I couldn't chamber rounds using the RCBS bullet and reformed .348 brass from Baco.  It wasn't until I got thin necked brass (.009) from RMC that I was able to.  Then Jamison came forth with there excellent brass  and solved my problems with the Roller and Shiloh in same caliber.

Now, down to brass tacks.  You have an original RB with a state of the art Paper Patch Chamber and shallow rifling...it was made to shoot PPB even in a fouled barrel!  That means the bullet was supposed to be smaller than groove and only slightly less than bore diameter when wrapped in the appropriate linen paper.  Your rifle is essentially a 45 caliber rifle  in modern parlance but back in the day Remington used the British system of using bore diameter (Colt cap and ball pistols too).  If you'll read the old catalogs it clearly states that bores are 44/100!!!  I use a .434 diameter PPB out of an KAL mold and wrap to .442.  Believe me when I say not to worry cause it bumps up nicely when kicked in the butt by 85 or even 75 grs of Fg.  That is how the system is supposed to work!

Thank you all for your thoughts and suggestions. Especially yellow house for his insights into paper patching. What he says makes absolute sense as that was the original design brief for the barrel at that time. This is an early roller, according to Mr. Womack at Rolling Block Parts, we had a great time discussing this rifle back when I ordered new screws, etc. for it. So I just need to know a few more specifics on the type of paper to buy and I'll learn how to paper patch, much to my chagrin.

I don't do much paper patch bullet shooting, but a friend recommended onion skin paper for my uses. He helped me make a template to cut the correct length patch so it would make two wraps and come back together perfectly.