Bad chambers?

[LonesomePigeon]

I have a 2017 production Uberti Flattop Target in .44-40 with a 7 1/2" barrel from which I am getting very poor accuracy. With factory smokeless cowboy loads I'm getting like 6 - 8" groups at 15 yards from a rest. I've also tried a few different loads using 2F and 3F black powder with pure lead "Mav Dutchman" bullets, the best groups were still only about 4" at 15 yards from a rest. 

I slugged the bore and chambers. I am not 100% sure of my measurements but here's what I got:
Lands .421"
Grooves .427"

I numbered the chambers 1 thru 6:
1) .4275"
2) .431"
3) .4315"
4) .4305"
5) .4305"
6) .431"
Did I get a bad cylinder or what? I also just noticed that in the bore the lands are smooth but there are fine lines in the grooves, which I think are "chatter" from the tooling.

[Abilene]

If you aren't positive about your measurements, bear in mind that Uberti specs all their .44 barrels at .429 groove, .4215 bore.  What sized bullet?  Have you tried more than one type or size bullet?  And is cylinder #1 any worse accuracy than the others?

[pony express]

Try shooting a group with only one chamber. If it's still as large, then that would seem to eliminate chamber variations.

[LonesomePigeon]

I've tried factory cowboy loads from Hornady and Magtech, not sure what size bullets they use. I've also tried pure lead cast bullets from a Big Lube Mav Dutchman mould, which drop at .431" as cast. I also tried pure lead Mav's sized to .429".


I plan to get a .427" sizer and also order some 1:20 tin/lead from Rotometals.


Pony, that's a good idea. In the past I have set up 6 bullseyes and shoot each chamber at the corresponding bullseye. I will try that with this gun.