Kenn,

Interesting info you have posted.  A couple of questions?   

Did the #1 1/2's you've seen have a narrow lower tang shaped like a #1 sporter?  And a related question, have you seen what you have considered a #1 with flat sides, not rebated at the receiver ring, but octagon top? 
 
I have owned rifles that I considered #1 1/2's that were linear extractor, flat side, and I think had long sporter lower tangs.  What I remember for sure about the tang is that it had a through bolt, not two, so couldn't be used with a set trigger.  That agrees with what you posted.

A few years ago, I bought #1 1/2's occasionally.   They were much cheaper to buy than #1's, you could get them for less than the sporter parts were worth and use them for conversions of military rifles.  I have owned at least two rifles that I considered #1 1/2's that had linear extractors, flat sides and octagon top.  I thought at the time that they had the same length lower tang as a #1, but that might be faulty memory.  I know the breech block would interchange with a #1, because I tried that.  Both were .32 rimfire.  I eventually got leery of the thin sides and sold one of them.  I can't remember what happened to the other action shell, but I think I used the parts to make a sporter rifle out of a forager military shotgun.  I switched the lower tang and stock onto the shotgun action, and made a rifle out of it that looked like an original sporter, except the receiver top contour step was slightly different becasue the walls don't come up as high and I machined to that.  What I distinctly remember was that they had linear extractors and through bolt on the tang, as the parts interchanged with the shotgun.

A lot of things have happened to these over the years, by the owners.  I remember selling you an action shell once that someone had thinned to #1 1/2 dimensions from a military.  Someone gets hold of that in the future, and a new model is discovered!

dave

I've seen two very early #1 Sporters that wre not octagon top, but had all the normal sporting rifle features, and were unmessed with guns. Prior to seeing these two I had always assumed all #1 Sporters to be octagon top with rebated stepped receivers.

Let me first start by saying that I am no Remington rolling block expert.  I have two, love them, but that sure doesn't make me an expert, lol.  With that said, this is out of the book "The Rifle in America" by Philip Sharpe.  "Remington No. 1 1/2 sporting rifle was introduced in 1871.  Essentially, this was a motified version of the No. 1 and had but a short life on the market.  It was made in a number of calibers including the .22 short and Long rimfire, .25/10 Stevens rimfire, .25/20 Stevens singleshot, .32 short and long rimfire, .32 extra long rimfire, .32 long centerfire, .32/20 WCF, .38 long rimfire, .38/40 Win. rimfire and .44/40 Win. Centerfire.
It also had an octagon barrel with an oiled-walnut stock, case-hardened frame and butt plate, and the trypical sporting front and rear sights.  Extra sights of any of the standard makes were available through Remington and could be fitted to this model at the factory.  Barrels were  24, 26, 28 and 30 inches long and weights ran from 7 pds in the .22 to about 7 1/2 pds, regardless of caliber."  Not sure I added anything to the fire here, but thought it interesting.

I had a senior moment, I used the word "mortised" and I meant to say rebated. Sorry for the mistake. Interesting that I re-checked the Marcot Rolling Block book and he mentions that there is a small number of #1 Sporting Rifles without the rebate on the octagon topped receivers. That might cause some confusion in identifying some rifles.

The width of the receiver would tell you if it was a 1 or 1 1/2, the 1 1/2 being narrower (the exact measurements are mentioned in an earlier posting in this thread).