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optic mounting pattern question


DRichardson

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I'm getting ready to order a mount for my new to me open gun. The mount that I am looking to get is the Cheely horizontal mount. I know the mounting pattern on my frame is the older Dawson pattern at .330 center to center , not the more common .375 pattern and Matt said he could do the pattern no problem. When I was getting some other mesurements I noticed there is quite a angle to the hole pattern on my frame. The front hole is roughly .330 to the bottom of the frame and the rear hole is roughly .400 to the bottom of the frame. Will .070 worth of rake in the mount pose a issue with zeroing the C-more or should I forward the measurements to Matt and let him drill the mount with the rake taken into account so the c-more will sit flat?

Also is there any benifit to the set back mount over the standard? Wouldn't the standard mount give more percived dot movement due to the lense being further from the pivot point (the grip, wrist area) under recoil, or am I just way overthinking this?

Here are some pictures to help visualise what the problem may be. Thanks for the help

post-40901-0-17208400-1369495815_thumb.j

post-40901-0-43590200-1369495877_thumb.j

Edited by DRichardson
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When I was getting some other mesurements I noticed there is quite a angle to the hole pattern on my frame. The front hole is roughly .330 to the bottom of the frame and the rear hole is roughly .400 to the bottom of the frame. Will .070 worth of rake in the mount pose a issue with zeroing the C-more or should I forward the measurements to Matt and let him drill the mount with the rake taken into account so the c-more will sit flat?

There is supposed to be an angle in the mounting, Matt should be able to set it up to the correct angle (I do not recall the correct angle, I seem to remember something around .015 per hole on my mount which has less holes). I would let Matt know how yours is set up and he should let you know if that is correct or if he needs to do an offset.

Also is there any benifit to the set back mount over the standard? Wouldn't the standard mount give more percived dot movement due to the lense being further from the pivot point (the grip, wrist area) under recoil, or am I just way overthinking this?

Overthinking, with the correct load for the compensator there should not be a noticeable difference.

Edited by GuildSF4
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Well not looking like its going to work out with the cheely mount. Can anyone give me the measurement of your mount pattern on your frame. Most of the pictures I see it looks like the holes are drilled in the frame about in the center ( between the rail, bottom of slide, and the bottom of the frame. I think my front hole is pretty much where a standard mounts would be, and the back is higher than normal. If that is the case then most any mount that would normally clear a round top slide should be able to work.

Edited by DRichardson
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The mount has to be angled down toward the front of the gun somewhere in the 1 to 1.5 degree range. One degree is about .017 per inch. The angle can either be in the mounting screw hole pattern as yours is or on the top of the mount where the scope goes. If the mount does not have this angle your scope will not have enough down elevation adjustment to get sighted in.

The reason for this is because the barrel is only parallel to the frame when the slide is open. When the slide is closed the barrel is locked up into the lugs and going downhill at 1 to 1.5 degrees, depending on how the barrel is fitted, which link is used, etc. The scope needs to start out fairly parallel with the barrel in order to be able to sight in. One degree doesn't sound like much, but at 25 yards (900 inches) it is about 15.7 inches. One and a half degrees is about 23.5 inches.

Edited by Toolguy
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Yeah I just chated with Matt and I'd does look like it is going to work. My rough measurements were pretty off, and with the mount removed I got some better measurements. The pictures make the angle look worse than it is and with the mount removed the rake is only about .025. There is some huge optical illusions going on there. Matt has been great working with me through this, I hope the mount turns out great as well.

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Matt is great to work with. I got my custom drilled horizontal mount and slide racker today in the mail. Holes lined up perfect. He was fast too, I ordered during lunch on wed. And got a shipping confirmation before I left work, and that included a custom drilled mount pattern not just a off the shelf part.

Edited by DRichardson
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