My makeshift .45/70 has been a lot of fun so far,but after attempting to bag some venison with it,and failing miserably I decided it was time to get serious and mount a scope on it....so I have done so.... rough bore sight was abismal failure,so got serious yesterday and went and shot AT paper.... I wont say shot paper as holes were sprayed around the show like a mad womans poohs...and that was at 25 yards!!!!
combination of things going on I believe and I will get to bottom of it,different cast projectiles are main suspect...Im hopeing it just doesnt like them as the other cast ones were grouping better with open sights....
strange part of whole 12 shot exercise was again I had a misfire,recocked hammer and still wouldnt go off.....so this morning I pulled projectile with vicegrips and the press(wasnt game to go whacking it in inersha puller with primer dented,scraped out the well caked powder (which burnt fine) removed primer in press,took it out to the woodblock,sat it on piece of metal and tapped it with back of axe...my ears are still ringing 20 minutes later!!!!
so guess culprit is the shotgun action isnt hitting fast enough for about 1 in 30 loads......will have a read up and see what is reputed to be softest primer cup and see if can get them...I stopped using winchester LRM as had a few misfires in this gun...and have used either federal or CCI since as they have silver /nickle coating not brass,thinking it might help...but apparently not.

From my experience, I’ve found that Federal primers are the softest…albeit in the small pistol variety. I will assume that this has carried across to their other primers. The other thing to consider is the hammer spring in the action…it is not uncommon for them to loose tension and need replacing, along with the firing pin.

yes Im aware the hammer spring isnt ideal....the one the same I grew up with was the same,I remember vividly a 180lb boar turning towards me and having a misfire....2nd time it fired,it was my first big pig without adults around,just me and a school mate. we dragged it out to paddock and got it onto truck then waited for Dad to return to get it home...the flies nearly beat us..nearly but not quite,some quick knife work and into the freezer took care of the mechanical rice.....
what makes this weird is it didnt fire after 2nd strike...the primer was surely well dented... will make sure to use the federals next time thanks.

After bit of time and lots of learning I believe my mistake is to be loading black powder into a case and not using it soon enough.they are corroding again when cleaned and reloaded with black...... Must go shoot them off.

and after shooting clean the cases asap with hot water and oxy-clean washing-powder