I have a small ring 6.5x55 with a Weaver one piece base. I was shooting out to 1000 yesterday for the first time, and discovered that I only had elevation for about 800. I found that the scope has plenty of adjustment (Buckmaster 4.5-14), but it is mostly down. I have 35 min. down and that only leaves 17 min up. If I do the math correctly, and I put .02 under the rear of the 5inch base, that will put me 14.4 inches lower at 100yds. Does that sound right, or am I looking at it wrong?
Rifle Scopes Math for scope base elevation
- Thread starter JeffP40
- Start date
Re: Math for scope base elevation
Shimming is almost always a makeshift arrange that is less than ideal. If you have a one piece base, take it to a gunsmith and have him mil it. Or just buy a 20 moa base if one is available for your rifle.
As for the math, it can be calculated using trigonometry. Not terribly complicated. 20 moa is 1/3 of a degree. Measure the distance between the middle of front and back mounting holes. Call this x. y, the height you need to solve for is y = x * tan (0.333 degrees). hope that helps.
If you are going to go to all the trouble of making a custom base, why not make a base that takes up ALL the down elevation you have and you will have all the up you could possibly use and, even more important, you will have a "poor man's zero stop".
Shimming is almost always a makeshift arrange that is less than ideal. If you have a one piece base, take it to a gunsmith and have him mil it. Or just buy a 20 moa base if one is available for your rifle.
As for the math, it can be calculated using trigonometry. Not terribly complicated. 20 moa is 1/3 of a degree. Measure the distance between the middle of front and back mounting holes. Call this x. y, the height you need to solve for is y = x * tan (0.333 degrees). hope that helps.
If you are going to go to all the trouble of making a custom base, why not make a base that takes up ALL the down elevation you have and you will have all the up you could possibly use and, even more important, you will have a "poor man's zero stop".
Re: Math for scope base elevation
14.4 inches at 100 yards is right for .020" and 5". Since it's a one piece base, shimming is an acceptable solution.
To reduce stress on the base, put a dab of epoxy (JB weld or something) under the rearmost part of the front bridge, and let that set with only the first and last screw lightly screwed in.
If you don't do something to reduce the stress caused by torquing down the base after shimming, the base will flex and force the rings out of alignment.
14.4 inches at 100 yards is right for .020" and 5". Since it's a one piece base, shimming is an acceptable solution.
To reduce stress on the base, put a dab of epoxy (JB weld or something) under the rearmost part of the front bridge, and let that set with only the first and last screw lightly screwed in.
If you don't do something to reduce the stress caused by torquing down the base after shimming, the base will flex and force the rings out of alignment.
Re: Math for scope base elevation
Re: Math for scope base elevation
Kombar,that's exactly what I was trying to do with my simple math. Every once in a while, I regret not knowing trig. I can't justify putting any money into this rig, it's kind of my bubba project. It's been driving me nuts with it's inconsistent grouping, but I decided yesterday that I just won't shoot paper any more. I was hitting all the steel with it, and that is fine with me. I have to use what limited funds I do have to feed my 6.5-06AI. I managed to hit two anti-freeze jugs at 1014 with it yesterday, so it is my go-to stick for sure. I'm going to try the shim and bed method with the swede, mostly so I am not bumping the limits of the adjustments. I will probably keep it to 5-600 is all.
Pat, that is quite a chart, I haven't seen it before. It give me something to work with.
Thanks for the replies, guys.
Kombar,that's exactly what I was trying to do with my simple math. Every once in a while, I regret not knowing trig. I can't justify putting any money into this rig, it's kind of my bubba project. It's been driving me nuts with it's inconsistent grouping, but I decided yesterday that I just won't shoot paper any more. I was hitting all the steel with it, and that is fine with me. I have to use what limited funds I do have to feed my 6.5-06AI. I managed to hit two anti-freeze jugs at 1014 with it yesterday, so it is my go-to stick for sure. I'm going to try the shim and bed method with the swede, mostly so I am not bumping the limits of the adjustments. I will probably keep it to 5-600 is all.
Pat, that is quite a chart, I haven't seen it before. It give me something to work with.
Thanks for the replies, guys.
Re: Math for scope base elevation
Small update. I diassembled the scope and base last night. As I was fiddling with the base on the action, I noticed when I located the rear hole under the base, the front of the base did not sit on the action properly. When I checked the screw holes, I could see they were not in alignment, the front two being at an angle in relation to the rear one. This was inducing torque to the base when I tightened the screws. My shimming project is actually going to correct this to a certain extent, because of the bedding I am putting under the front of the base. When I checked the windage on the scope itself this morning, I was left with twice as much adjustment to one side as the other, so this should get me back towards the middle when I am done. The bedding is curing right now, so I should have an idea what I have later today. The base was already on the action when I got it, so this probably turned out for the good in the end. Hopefully, I will get out this week to shoot it and find out for sure. Sometimes, Murphy is good to me!
Small update. I diassembled the scope and base last night. As I was fiddling with the base on the action, I noticed when I located the rear hole under the base, the front of the base did not sit on the action properly. When I checked the screw holes, I could see they were not in alignment, the front two being at an angle in relation to the rear one. This was inducing torque to the base when I tightened the screws. My shimming project is actually going to correct this to a certain extent, because of the bedding I am putting under the front of the base. When I checked the windage on the scope itself this morning, I was left with twice as much adjustment to one side as the other, so this should get me back towards the middle when I am done. The bedding is curing right now, so I should have an idea what I have later today. The base was already on the action when I got it, so this probably turned out for the good in the end. Hopefully, I will get out this week to shoot it and find out for sure. Sometimes, Murphy is good to me!
Re: Math for scope base elevation
I reassembled the optics late this afternoon. The windage didn't seem to change much, but the elevation looked to change almost two full turns (24min) with the eyeball bore sight. My shim was about .040 and with the bedding under the front it should be good to go. I am more than pleased so far. Time and shooting will tell.
I reassembled the optics late this afternoon. The windage didn't seem to change much, but the elevation looked to change almost two full turns (24min) with the eyeball bore sight. My shim was about .040 and with the bedding under the front it should be good to go. I am more than pleased so far. Time and shooting will tell.
Re: Math for scope base elevation
I love that more than pleased feeling after a project. I just finished my first bedding job this week and after I alter my new scope base for the larger screw size, I am hoping to have that feeling.
regards,
DT
I love that more than pleased feeling after a project. I just finished my first bedding job this week and after I alter my new scope base for the larger screw size, I am hoping to have that feeling.
regards,
DT
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