45-70 popping open

[Hunternz]

Took my 45-70 to the range on Saturday, every shot it popped open, it has always popped open but not every shot in the past, this is a 45-70 barrel fitted to a my .243 superlight frame, the 45-70 barrel was fitted by the gunsmith who works for the H&R importer in New Zealand,, lock up is the same as my .243 barrel which dosn't open but I can see daylight between barrel and action, looks even from top down to where action meets the barrel when closed. With calipers it measured  shorter between the pivot on the underlug to the latch shelf, so I folded some foil a couple of times and fitted to the pivot on the underlug, the action won't lock up at all, any ideas/fixs? before I send my rifle to the said gunsmith.
Regards Howard.

[quickdtoo]

Check latch engagement, could be too little, that can be fixed with a little honing of the latch shelf, see barrel fitting in the FAQs.

Without the forend on, is the barrel loose in the frame? There shouldn't be any visible gap between the standing breech and the barrel face. The barrel may still need to be fitted a little more, the gap may be slightly more at the top and is hitting the standing breech at the bottom.

Tim