In section 3.1.3.a of the NRA Rifle Silhouette Rules, when discussing sights it clearly says that "no extended bases are permitted." I started out with my Marlin 336A using the Williams FP sight, but wanted to use a Redfield 75 on it like I do with my other rifles. I got a base for it and thought I was ready to go.
Unfortunately, it wasn't so simple. The hammer hits the Merritt adjustable aperture with the Redfield 75, where the Williams was just far enough forward that it missed it. It looks a bit like it's just barely pushing on the rubber in this picture, but it's pushing pretty hard on the metal through the rubber.
That left me choosing between using the Williams with the adjustable aperture or the Redfield with the standard, non-adjustable aperture. Since I shoot primarily in western WA and our lighting varies a lot over the course of a day, even in summer, I chose to just use the Williams sight until I had time to figure something else out with the Redfield. Today, I had an idea. What I reversed the sight base to move the adjustable aperture back behind the swing of the hammer? Would that work? Here's a picture of the base as it was mounted.

(Posting as reply since the forum limits to three images)

Here's a picture with the base reversed. Note that the screw in the sight body is going into the hole in the base right by the screws into the rifle, so cutting the base shorter wouldn't actually make any difference in where the sight sits once mounted.
Finally, here's a picture with the sight mounted.
The hammer swing does indeed miss the adjustable aperture, but I am wondering if the sight is too far back to be allowed under the "no extended mounts are permitted" rule. It's not as far back as the tang sight was that I tried briefly on this rifle (couldn't get accustomed to the tang sight being in the way of my thumb) and it's far from being one of those long mounts like used to be used on some styles of target rifle. Even so, I'm not really one to push rules. Since we've been sorting through rule clarifications here lately, I thought we might as well clarify this one, too. What do you think?

Same problem I had. I drilled and tapped a new hole in the sight moving the threaded attachment hole in the sight backwards in the sight rail about .35-.40. That moves the top part with the aperture of the sight forward and everything clears fine now.

Jason, I'm afraid that would not fly at the Nationals were they do check guns. When they loosened the rules a bit on some of the sights you could use, I heard terms like "if they are mounted on the rifle in area intended for traditional sights."

Your sight in my opinion is too far back from the intended mounting area. I have seen Williams top mount sights installed on long Weaver bases on top of Marlins extending back over the hammer like yours. They were not allowed by the match director.

You know they make those Merits with different length shanks. Maybe the shortest would work for you. Or you may have to cut away some of the rubber shield. I have had to do that on some guns where they contacted the hammer.

Al Foust

Merlin,

The sight is already mounted as far forward as it can be, or at least within 1/16" of it. The channel in the sight matches the curvature of the base.

Al,

Thanks for the reply. That matches my interpretation of the rule, too. I didn't think about different shank lengths on the Merit aperture. I'll measure this one and see what else is available.

You started out with a different base mount than I had. All you need to do is take an end mill (the size of the existing channel in the sight) and run the groove all the way back to just barely clear the elevation screw hole that runs down the sight....



and you will have all the clearance you need....



You will also have to drill and tap another hole in the sight or the mount itself to properly locate the sight. On this rifle I flipped end for end and then drilled and tapped the mount to fit the gun rather than relocate the screw in the sight to locate it (the sight) in the correct place in relation to the hammer..



And for those of you that are thinking how ugly my gun is...you should see me....

Thanks for the great pictures, Merlin. They make it very easy to understand. I don't have access to an end mill, but I'm heading to WA state smallbore match in a few hours and I'm sure there are multiple people there who do. Do you happen to know the size and thread pitch of the Redfield 75 screws that screw into the base? I have a drill press and a nice set of bits but might need to pick up a tap.

My 39a with a 75 and the small Merrit Hunter model disk had the same problem . Worse it barely touched the disk & only on Chickens. Took me a while to figure out why I got Fail to fire 10 % of the time on Chickens only.

Short term I chucked several fixed hole disk in my lathe and drilled them to sizes I often use. Longer term will raise my front sight a bit so I can zero Chickens with the Merrit and not touch the hammer.

You ought to try the smaller Merrit. It won't close as much as the target model but opens wider. Useful for low light days. Small hole is as small as I ever want. The round rubber shade is easily duplicated by thin leather fitted over the shaft like a washer. Cut it to to suit your gun avoiding the hammer .

Easier than machining and no rule problems.

Boats

I think it's 8-32

and the holes in the side of the rifle are 6-48

Im gonna protest this guy......lol

Thanks to Steve Wooster for helping me out with milling out the channel on the sight a bit further like Merlin pictured. I contoured the end a bit more and also contoured the base to fit the end of the channel, so I can slide it back plenty far to clear the bigger Merit disk that I like. As a bonus, I can use the hole already in the sight and just drill and tap another hole in the base between the two existing holes. Steve also found that the thread pitch was 40, so I'll need an 8-40 tap. I thought I had one but evidently I have two 8-32 taps (don't know why). Amazon should have an 8-40 tap to me on Tuesday by the time I get home from work. I've got the base in the press waiting for it.

Got the new hole drilled in the base and the sight mounted up just perfectly tonight. There's about 1/32" between the edge of the rubber shield on the Merit and the hammer when it's all the way forward.