To be honest, I find the sights on the 610 to be pretty miserable for indoor ranges. I don't think I'll ever shoot it as well as I wish to until I mount a red dot on it. Off the bench today in single action the best I could manage today at 60 feet was a 2.4 inch group, which was pretty poor in comparison to the sub 1 inch group I shot with my red dot equipped 617.
I really don't think the rough machining in the chambers will have any effect on accuracy. Mine has machining marks left by the boring operation for the chambers that are quite visible and leave a very slight imprint on the brass. However, the bores where the bullet transits to the barrel is perfectly smooth without any hint of machining. Obviously, a first class job of reaming to size with a reamer in good condition and properly lubricated. Those marks in the chambers won't effect accuracy, at most it'll cause issues with sticking brass, which I have not had any problem with. I also checked the transit bores with precision gage pins when I first got my 610 and all 6 were dead on at 0.400 inch in diameter. So they were dead on for size in addition to haveing a first class finish. In fact the finish is so good I suspect that they may have been honed to final size after being reamed.
If your shooting a lot of 40 caliber ammunition in your 610, I would urge you to patch your barrel and see if your accumulating lead in the area just past the forcing cone. If so, you'll also probably find some chambers that won't permit you to seat a 10mm case in.
I've had to put in about 30 hours of hand stoning the headspace ledge in the chambers of my 610 in order to get it to stop shaving jacketing from fired rounds. Until I got that resolved, leading just past the forcing cone was a big problem. IMO, S&W should NOT have designed this gun to headspace the 10mm round, they should have made it a moon clip only model like it was when it was first released.
BTW, I do NOT recomend that anyone except an experienced Tool and Die Maker attempt duplicating my solution. It's fussy and tedious work and it's essential that the resulting cone shape be even for the full perimeter or accuracy could be effected.
Since your hand loading, I would suggest that you dump all your 40 caliber brass or dedicate them to another gun and only use 10mm cases in your 610. You'll probably have to use a pick to clean out your chambers to the 10mm cases will seat fully but one you do it will solve any leading issues. BTW, you'll also have to spend several hours getting your barrel cleaned out. The first time I shot my 610 with 40 caliber I had 8 to 10 hours of patching the barrel with Lead Away cleaning patches in order to get it cleaned out.
As for the sight issues, the solution is dependent on where your shooting. If your mainly shooting at indoor ranges, get a red dot or reflex sight. I have enough experience at indoor ranges to know that they are the best solution for the poor lighting typical at indoor ranges. If your shooting outdoors, S&W offers a fibre optic front sight that will work quite well. They also offer a gold bead Patridge that will work well outdoors and might just be usable at an indoor range. You'll still find it difficult to pick up the rear sight but at least you'll have the gold bead for reference.
Unfortunately, S&W doesn't yet offer a red ramp interchangeable front sight, so you can't mount the Meprolight Tritium sights developed for the red ramp setup. Of all the sights I've used indoors, the Meprolight sights on my Sig Sauers are the only dot type sights I have found to be visible at most indoor ranges. Meprolight uses a reflective surround on their tritium sights and it's very good at picking up lighting at the visibility threshold for tritium. For a low profile sight system, Meps are optimum because they'll work in almost any lighting you might encounter.
Finally, if you doing any rapid fire drills, the muzzle weight of the 610 can be an issue. I never figured out why I could consistently shoot my tapered barrel 67 better than my 620 in rapid fire until I got my 6 1/2 inch 610. The difference in muzzle mass made the problem very obvious. What I found was that the muzzle mass caused me to swing past my intended point of aim due to the inertia of that long heavy barrel. Turns out taht those who designed the original M&P knew what they were doint when they made them with a light tapered barrel with just a small lug for the latch and a welded on front sight. Now, every single gun has a full length sight rail that adds mass to the barrel and most now have a full underlug that adds even more mass. While weve gain in barrel stiffness, wever lost the nimble handling that the lighter barrel produce. IMO, for rapid fire drills the optimum barrel length today is 3 inches in spite of the short sight radius it results in.
To sum it all up, you probably need to engage in a bit of "tuning". To be honest, I don't think it's the gun, it's just that out of the box it's a bit compromized, especially in terms of the sights. If you want to do rapid fire work, such as bowling pins, start with a 4 inch model and plan on doing exercises to build wrist strength. If you want to shoot bullseye, look into improving the sights for that purpose. One plus for the 610 is that S&W made it very easy to tune the sights. That interchangeable front sight is a very slick setup. They have also provided the mounting holes for a rail, so mounting optics or reflex sights is a simple matter of coming up with the scratch for it.
BTW, now that I've shot with a red dot sight, I have to tell you that they are the best sight I have ever used on a handgun. Not only are they quick to pick up, they also act to magnify any movement during the trigger pull and this makes it much simpler to improve the trigger stroke. The only issue with this type of sight is that they do require more thought when using a holdover or holdunder to compensate for distance. Someday I may have to step up to one of the high end sights that features a graduated reticle. However, at 500 bucks plus, it's going to be a while before I do. BTW, up to 25 yards a 4 MOA dot is just fine for precision work, if you want to shoot from 50 to 100 yards I would suggest looking into a 2 MOA dot. I'll also note that I consider the scope type red dot and the reflex, or holographic, sights pretty much interchangable. One advantage to the reflex sights is that some, such as the Burris Fastfire, are very compact and light weight. So, if you want to go in this direction, choose what you think will work best for you, from a functional standpoint they are nearly equal. Personally, my plan for the 610 is a Fastfire because I think in the rearmost position I'll be able to modify a standard holster to allow it to be holster carried.
