Miss Matched Mounts

[Bellycrawler]

One of my rifles kept shooting well off center at random times & I couldn't understand why. I'm downsizing my rifle & bigger scope collection so doing a lot of scope to rifle swop around to choose what to keep, often I've needed to swop between low to medium mounts for lens size, I use low mounts mostly where I can. Also shopping between 1" to 30mm scope tubes. Every mount swop I put the mounts together with the screws on opposite sides to check they are central. The rifle in question Checked out on the last mount swop. Frustrated at the last session shooting miles to the left with adjustment maxed out I was putting a known good scope on, I double checked the mounts, 13mm dovetail 30mm tbe low mounts, the only set I have with that spec, the only other 13mm mounts I have are 1" low & 30mm reach forwards. All my mounts were bought new. The mounts lined up perfect. Turning round the one mount I tried again, miles out ! Turns out this set is one 13mm one 11mm & effectively twisted the scope to the right meaning my barrel was pointing to the left, no wonder it was miles out, no wonder it took me so long to find out what was wrong.

[TonyL]

As you say, if you bought them new and they're the only ones you've ever had in that specification, they must have been supplied like that as of new.. Demonstrates the value of working through things methodically, though; well diagnosed.

[Bellycrawler]

As you say, if you bought them new and they're the only ones you've ever had in that specification, they must have been supplied like that as of new.. Demonstrates the value of working through things methodically, though; well diagnosed.

When it was off it was miles off. Nothing made sense. I narrowed it down to eye / face on the stock position with certain scope / mounts combinations. The only reason I checked with screws the same side was thinking maybe one mount or clamp wasn't seated correctly. Gobsmacked to find a 11mm / 13mm combination. Every day is a school day even when you think you know it all.

[angrybear]

I'd have thought that 2mm difference would be obvious when you check they match before fitting

[Segata]

You'd say that but I didn't notice I was loading a .177 pellet into a .22 on one occasion so anythings possible.

[Bellycrawler]

I'd have thought that 2mm difference would be obvious when you check they match before fitting

I check for alignment with screws on the opposite sides , they aligned verry good, that's how you check for central location. In theory with screws the same side they are perfect. Let's just say when they aligned the opposite way it never occurred to me before to check again with screws on the same side there should be no need. Thankfully 11mm +13mm as a miss marched set is a rarity. I have no other sets anywhere near the same specs so definately not a mistake on my side.

[Segata]

Have you got or are you able to sort the right size mounts out?
Ash helped me sort the problem with my Falcon so bar maybe keeping a set for the SMK I'm buying I'm going to give away the spares I was given so happy to help if needed.

[flyingfish]

I'd have thought that 2mm difference would be obvious when you check they match before fitting

Not always
As I recall from my rimfire days 1 size is measured across the top of the dovetail and the other across the narrow point of the groove
I like the Sportsmatch way of doing it
There 13mm mounts have different size screws in the bases and joint
The 11mm all screws ate the same size

[Bellycrawler]

Not always
As I recall from my rimfire days 1 size is measured across the top of the dovetail and the other across the narrow point of the groove
I like the Sportsmatch way of doing it
There 13mm mounts have different size screws in the bases and joint
The 11mm all screws ate the same size

Definately an odd one then, my reach forwards 23mm have different screws as you say but this miss matched pair have the same size for all screws top / bottom 11mm/13mm.

[Bellycrawler]

Have you got or are you able to sort the right size mounts out?
Ash helped me sort the problem with my Falcon so bar maybe keeping a set for the SMK I'm buying I'm going to give away the spares I was given so happy to help if needed.

Thanks for the offer but not needed. I've used my reach forwards set , a bit higher than I like but they will do. The wonky set I'm marking up to avoid future problem & keeping for spare screws / caps / clamps.

[Segata]

No Worries