Thanks, Macon Due:
Big help, especially about the bridle screws restricting tumbler movement. I have seen that in others.
Your feeding issue can be from many factors. I had a lot of difficulty at first and found the spring under the cartridge feed guide (finger-like flipper on top of receiver) was weak. Replacement with a stronger one helped.
If the parts are ok, a Spencer should feed ctg's within a range of overall lengths. Bullet nose shape and hardness matter for cycling smoothness. I use hard alloy. Cycling chews noses, loosens bullets in case mouths and can change the ctg's OAL. Because of this ctg damage, after a couple cycles each, I have to file away the raised gouge edges and try to recrimp the cases. PLEASE, use only dummy ctg's to test cycle. When fumbling and jacking the lever back and forth, I have had dummy ctg's firmly lodge against the tip of the cartridge feed guide! If a primer had been in that ....
The rhythm of moving the lever matters. Try to minimize the hesitation at the bottom of the lowering arc and quickly lift it with a firm continuous motion to force the following round rearward a bit. Being used to operating Winchester's, I could not achieve the cadence and hesitated as the upward motion of the lever reached the spot of pushing the next round slightly rearward. Another person easily cycled my test rounds! Try feeding with only one round in mag tube. If that works, then the second round's resistance under mag tube spring pressure is a factor.
There are lots of posts about the magazine tube spring being another factor and how to diagnose its issues. One thing, please; never stretch a coil spring. That usually damages it. A spacer can be used to make it a bit stronger.
I found Cody Conagher at Cowboy Gunshop, Berkeley Springs, WV. Please tell us what he finds. Thanks. Smiles.
El Supremo/Kevin Tinny