Home Forums Hunting & Shooting Handguns S&W 66 shooting low

Was at the range today and found my S&W 66 is shooting almost 6 inches low at 15 yards with the rear sight adjusted as far up as it will go. Any idea what would cause this?

I was shooting 7 grains of Unique and a 158 grain MBC powder coated bullet. I've used this load for years but with the regular lubed MBC bullets, and never had a problem. I did a thorough cleaning of the gun (which hadn't been done in a while) since last time I shot it. Those are the only new variables I can think of.

I just checked my powder scale. It's accurate.

Last time you shot it it was on target? Same bullet weight and load?

Yes.
I shot a cylinder of factory ammo too, and it was low too. Good groups, just low.
I dunno what's going on. That rear sight is essentially a leaf spring. Is it possible it flattened? Just wondering if someone knows something.

I had this sort of issue with a Model 17 S&W way back in the 1990s. I had broken the rear sight blade, called S&W, and they sent what they said was the right blade. I had a local gunsmith install it, and it either shot low no matter how high I set the rear sight or the other way. Can't recall. I explained it to S&W and they sent me what they guaranteed would be the right one, and I had the very same issue. I couldn't afford continually paying someone to install these, so I sold it at a low price. Before this, though, it was one of my favorite revolvers.

The elevation screw and its flanged nut are in hard contact with the frame. So, the rear sight can’t get lower by itself, regardless of spring tension. But, there must be something in the air, lately, ‘cause the same thing happened to me last Fall with my 66 I’ve had since the mid ‘80s. Likely gotta be some kinda change in the way I now grip it (maybe the fault of the COVID). So, I simply installed a taller rear sight blade:

Gave it two clicks up after this group.

I guess you could file down the front site but if this is a newer model with the red insert in the blade that might not work.

If its not a pinned front sight, please don't file it down.



Did you change the grips?

Shooting a bullet faster makes it go lower, but six inches at that range is pretty extreme. A heavier bullet loaded lighter will also make the POA go up. I would go back to the traditional bullet you've been using.

Midway, Numrich or Brownells sells the parts to put a taller rear blade and if I could't figure out that much variance between the grip, hold or load I would go that route, but for me its always been the oposite of what you're dealing with.

Is it a new gun or is it one that you’ve shot before? If you’ve shot it before, what ammo were you using and where did it hit?

.
What hold are you using ?

This one has me baffled. I've been shooting this revolver for decades with all sorts of loads including a lot of screaming light bullet H110 loads. It's always been accurate, exceptionally so with some loads. Never had a problem to get poi aligned with poa. It's a Snubby -1. Makes no sense.

Check that forcing cone closely.

Try different ammo. If it shoots the same, something happened to the sights. If not, it's the ammo. It's not a forcing cone or timing issue in my opinion, not with the precision (group) you shot. It's a POA/POI issue.

I’m curious how and why the forcing cone would affect a revolver printing low or high. So if I’m checking the forcing cone closely what am I looking for that would cause my shots to print low ?

Regards
Rick

Hot loads allways shoot low. Back off a grain see where it shoots then.

Only thing I can figure is the sights got buggered up somehow though they look fine. Or someone is playing a practical joke on me and messing with it.
Ordered a new sight assembly and a taller blade. I'll try the new assembly first with the factory blade.

I don't get the forcing cone question.
I've shot this revolver using everything from target .38s to full boom 125 h110 loads. Have never run out of adjustment or even needed very much.

Let's walk through this.
You cleaned the revolver. Need more details. Was there any buildup?
You changed the cast bullet used in your load. Did you compare the OD's of the powder coated to the wax lubed? Have you ever fired for groups the powder coated bullets before? Do you sort your bullets at all for size or weight?
Did you use a different lot of Unique in the recent load?
There can be changes to POI when fouling is removed or allowed to build up. And if a forcing cone is showing gas cutting or erosion...

There are just too many variables.

Are you doing anything different with respect to how the gun is being held, offhand or rested?

I have seen a dramatic change in poi when zeroing very accurate, scoped revolvers by resting them solidly, with a some downward force on sandbags, then shooting them with only forearms rested over a rail or whatever.

The business of fast, light bullets hitting lower from a handgun and slower, heavier bullets hitting higher ( as mentioned above) is a well-known dynamic in handgunning, a result of the fact that the gun starts recoiling before the bullet leaves the muzzle. Giving the gun more resistance to recoil against can have the same effect.

Just closing the loop on this in case someone finds it useful. After much trial and error, ordering and returning of parts, and test shooting, I found out the original rear sight leaf had flattened out and wasn't raising the sight blade as high as it should have. I tried to take a photo of the "new" leaf and old leaf side by side, but it didn't really show the difference. But in this picture with the new sight leaf installed, you can see the gap between the leaf and the topstrap:




The old sight leaf ran out of spring before getting that high.

I can now get poa and poi properly aligned. Didn't know the leaf spring could lose curve but there it is.

Are you sure you had sighted this with the same ammo prior?

Just wondering because in your example that 145 silver tip is both faster & lighter than typical 158 magnum loads, both of which tend to lower impact.

I found it easier (and less expensive) to simply swap out the standard rear sight blade for a taller one (as HawkI suggested), such as this blade (made for one version of the S&W Model 41 pistol sight, and obtained from Numrich):


No longer any need to adjust the rear sight leaf so high out of the frame, either, which is JNR (Just Not Right).

Its deeper notch makes for a better sight picture, too: