Rodney,
Thanks for posting the pictures of the Spencer rifle submitted for the Army trials of 1872.
I was impressed by the differences between the patent drawings and the action frame shape, used by Spencer, in his submitted rifle. His submitted rifle looks more like a Ballard than a Spencer.
He also used a sliding extractor and I sure would love to see the details of how Spencer's extractor worked.
Mqabbi
Attached is a photo of a full sized Spencer single shot rifle. The breechblock drops down enough that the larger cartridges are easily chambered.
Otto

Chipmaker, I doff my hat. That is a beaut. VERY WELL DONE. It is amazing how both of us, a couple of thousand miles apart have done away with that unsightly lump at the bottom of the action in the Spencer    I have resized and superimposed your action picture in my CAD and found that your dimensions from the centre of the barrel bore to the top of the action is much bigger than mine. Hence my apprehension at 45-90 or 100. You have shown me a way out, but as my late wife would say, it would be cute to have a big brother and little sister combo, so I will stick to 45-70. 

Once again well done. Did you document your build and post it anywhere?

The Stabler Cut-Off Device is the part between the trigger and the block.
It is turned sideways or backwards  for either use as a single shot or as a repeater.

Yes it actually stops the block from dropping low enough for the bullets to be inserted above the block from the repeater tube.

I was just alerted to this thread and thought I would post. Here is a picture of my Romano Spencer SS in 50-90. I spoke with Larry Romano at length about this rifle and he told me he built it from the patent drawings. The story goes that Spencer sold the rights to his repeater to Winchester who made him sign a noncompete that prevented him from building another repeater. He built the single shot and submitted samples to the Ordinance Board for testing during the trials of 1873. I read that the Spencer did very well but it appears the fix was in and the award went to the Springfield. I understand that there are two rifles remaining from the trials located in a museum in Washington DC but I have not been able to locate them. Larry Romano is an excellent gun maker and a fine craftsman. His work it top notch and my rifle shoots exceptionally well. He is off the internet because some claim jumper bought his domain name and he is trying to get it back. I believe it is some fallout from the covid pandemic that caused it. Anyway, sorry for rambling. Here is the photo. Thanks, ratseye

Mqabbi Here is the information on the other two guns in the photo with the Spencer.

mqabbi
No. I didn't document my build or publish it.
Ratseye and those trying to find an original Spencer single shot rifle
The curators of the NRA, Smithsonian and Cody museums told me that they searched their collections and could find no examples of the Spencer SS.
Otto