You should go to the following web site and look at the loads for a lead bullet and 7625. Your load of 5.8 is right at the midpoint so (5.5 to 6.0) your pressure should be fine to function. I personally have no experience with 7625 so I don’t want to make too many comments but I did look up the burn rate and it’s on the slow side compared to Unique and W231 which are my favorites (231 being first).
That would also explain why you’re getting a lot of unburned powder in the barrel.
I couldn’t find any hardness ratios on the Sutten's Choice 230gr but since they are cast they will easily handle 1000 FPS with minimal leading. I have pushed hard cast 20+ BHN bullets up to 1700 FPS in a 44 mag rifle with no problems. So even the max pressure that is listed by Hodgdon will only get you 892 FPS.
The only bullet you will have problems with is swaged.
Your 1.27 seems to be a little long for COL. I don’t know if you got that from the manufacture or not but most of my books and several web sites list 1.200. Since the Sutten is a very rounded nose bullet (found it on MidwayUSA) and not very long I think you might shorten your COL a little.
Since your using a slower powder how is your crimp? One of the best additions to my reloading bench for accuracy for all Semi autos was a taper crimp die. This allows you to get a firm crimp and still feed reliably. With the slower powders this can help you get more consistent burns and less residue.
As far as humidity differences. As long as you keep your can sealed and don’t let it set out open very long there shouldn’t be much difference. Here in Indiana we get anywhere from 100% to 20% and I haven’t seen any changes in my reloads.
Glad to see from other suggestions your accuracy has improved greatly. You’re learning the one true fun aspect of reloading. Load development and test.
Powder burn rate: http://www.reloadbench.com/burn.html