One thing I have found on many LE's is that the barrel cannot headspace properly with a flat breech. When the barrel seats against the inner seat, the headspace is still excessive. If a longer bolt head was available,that would fix it but, failing that, I simply cut the tenon long so I could form an extension and establish the headspace when I cut the chamber. Of course, given the variation in rim thickness, a minimum chamber will still exhibit some head clearance on the brass.
My own No.4 is currently chambered for the 30/40 Krag. The case capacity is essentially the same as the 303 and the difference will favour one cartidge or the other dependent on the brand of the brass. When this rifle was still a 303, it was very accurate with most bullets and shot 30 caliber bullets very well; with some exceptions. In fact, the very best five shot group I fired with it was with 125 grain Sierra 308 bullets. This group measured right at .6" and although, I never duplicated it, I did fire many groups which were well under 1 moa. Other .308 bullets which shot very well included the 150 Speer, the 165 Speer, 200 Speer spitzer, the 150 Norma, and the 180 Norma. One bullet which absolutely would not shoot was the 180 Sierra Boattail. When I say it wouldn't shoot, I mean it really would not shoot. 100 yd groups were usually right around ten to twelve inches. The reason I shot so many 30 caliber bullets was that Dad had them on hand and the price was right. At the age of fifteen, my income was more limited than Iwould have liked and I had to stretch that reloading dollar. I did buy some CIL 180 CPE bullets which worked quite well for me and which I used the take my first big game animal (a doe antelope). Later, I got some 180 Sierra .311 bullets and these weremy preferred bullet for that rifle for as long as it was a 303.
As a 30/40, it has the advantage of being a 30 caliber with the abundance of bullets that provides. The barrel is a twelve twist MRC, stainless and it works well with everything from 125's to 220's.
I load the 30/40 a bit stiffer than I would for a Krag but not a lot. I have found that loads which duplicate a 300 Savage are great and give long case life while loads which approach 308 levels will reduce case life quite a bit. Workable maximums are like this:
125's... 2800fps
150's... 2700fps
165's... 2600fps
180's... 2500fps
220's... 2275fps.
For the most part, these loads give reasonable case life (a half dozen loads) and are adequate for any game I want to shoot. Reduce them a hundred feet and case life is easily triple and field performance is still fine.
When I was a kid, I always thought a 375/303 would be a great cartridge but I think a 35 would be better. The ability to use 357 pistol bullets for small game loads is a real plus, I think.
Steve, the cera-cote looks great; quite a bit better than the Tremclad I dobbed onto my stainless barrel. GD