Grantham,
I am but a nimrod compared to many on this forum. We do all "share" what knowledge that we have. Toward this, thank you for pointing out the obvious!
I thought that perhap you were NOT refering to the barrel lug or as most call it, the recoil lug. The recoil lug protudes under the barrels to "hook" the barrels to the action and absorb recoil.
I forget the technical name of the point where the watertable and standing breach meet. I'm sure the British named it long ago... This 1879 Parker has a square breach intersection. There were some Parkers of this design that cracked.
This is the earliest existing LC Smith Syracuse made 10 gauge, made appoximately 1886. This gun is a Grade 2.
Please notice that the breach intersection has a radius.
The Syracuse LC 10 with later Fulton Chain Damascus and Fluid Steel barreled 10 Gauge Grade 2's.
Now that I closely observe the bottom of the recoil lugs on these Smiths I see that the Syracuse gun has square front edges. The later Fulton guns are radiused. The Chain Damascus gun from later Fulton production having a slight radius and the even later fluid steel barreled gun having more radius on the recoil lug. Hmmm... "Stress cracks concentrate at sharp discontenuities of geometric shapes."
In theory recoil might cause the recoil lug to "hammer" the action and crack it because of square fronted recoil lugs. There isn't a lot of metal in the action between recess for the recoil lug and the recess for the hinge pin! Now I can see why LC Smith's designs were changed over time! "Researcher" might know about this happening to early LC Smiths.
All that stated, I''d still load for 6000 psi and shoot that LC Smith!!! I won't hesitate to shoot this Syracuse Smith or early Parker.
PS: I have since had Bachelder restore the metal on the Syracuse LC Smith as he did on the Chain Damascus gun. I'll have to shoot some more "group" photos for your guys who appreciate pretty guns, regardless of maker. They are like blonds, brunettes, and readheads. I like all the pretty ones....
Mark