Help needed feeding rounds through my original 56-50 SRC 1865

[TNSharps55]

Newbie Spencer owner here trying to solve a pesky feeding problem.  I've tried load lengths from 1.60" (max that my chamber will take and still close) down to 1.45" and have had little luck in reliable feeding.  I have found that longer rounds help in my Spencer.  I'm using a Lyman 518145 in Starline brass which extract great.  I've read that a rounder nose bullet helps so any input on alternate bullet sources is most appreciated.  My bore slugs .518" so if anyone knows of a good mold that will throw a .520 slug or one that can be sized to .519" or .520", please let me know.  I put some rounds in my lathe and rounded off the nose which did help, but I'm worried about round nosed bullets resting against primers in the magazine.  Most hangs leave a dig in the nose of the bullet behind the one I'm trying to chamber.  Should I round off the sharp leading edge on the upper breech block a bit and if so, by how much?  Have not tried molding from linotype yet, but have read that it helps as well.  My upper block, new magazine spring and magazine follower came from S&S.  One thing I've noticed is that there is about an .010" gap between the upper and lower breech blocks when I bring the lever up to chamber a round.  Sometimes pulling on the lever to bring the two block halves together as the lever is closed helps as well. The upper block fully bottoms with no gap in between when the lever is pulled open and the upper block post does not bind in any way.  I've checked the slot in the centerfire upper block post and it mikes the same as my rimfire original.  The spring between the blocks appears to be sufficiiently strong.  My cartridge follower spring is strong as well.  I've polished the new upper block and the action opens very smoothly and without tight spots.  Any ideas?

[Herbert]

My best bet on this problem for a original is that the cartridge guide spring is week or broken,BACO makes a very good .520 mould for the Spencer,OAL of 1.6 to 1.65 works best in my original Spencers

[TNSharps55]

Thanks for the mold info.  I've checked out my cartridge guide spring and it is plenty strong.  I'm stumped!