How do i figure out the moa on my lyman 48

My scout rifle is a Rem 700 ADL 3006 with a factory polymer stock and with what appears to be a very early lyman 48 with the flip up reticle, 125 slide and a Thompkins globe front sight. Barrel cut to 19" with fresh muzzle crown. I have set it up with a Bushnell Banner 1.75-4x32 scope #611436 and QD rings. Boolet is a Lee for 303 Brit sized to 311. At 50 yds 3 shots will be 3/8" to 1/2". 21 gr 2400 load in FC brass.

Eyes are still good enough to use the irons as primary.

The sight is tight and holds zero but I suspect it is not a correct matchup. Does not matter if not correct as I am happy.

Question is how do I figure out what approximate MOA each mark on the slide is? Am interested in 300 yd shots. According to JBM Ballistics, with a 1850 fps velocity, and 100 yd zero, 25 yds is -0.2 MOA, 150 is -2.7 MOA, 200 is -5.9MOA and 300 is 14 MOA. plan to round up to next even # for the elevation clicks.

Pls accept apologies for long winded question. :o)

seabreeze

At 100 yards shoot a group of sufficient sample to know it is correct and determine the center of the group A vertical line through the horizontal center and a horizontal line through the vertical center is close enough. Move the sight up 20 clicks and left or right 20 clicks. Shoot another group and locate the center of that group. Measure the horizontal and vertical distance from the center of the first group to the center of the second group. Divide each distance by the 20 clicks. The answer is the adjustment value for each click. The elevation click value may be different from the windage click value.

Easiest way is to shoot at 100 yds and zero it there. then at 200 yds keep track of the number of "clicks" to zero, Divide the number of clicks by 2 and that will tell you how many clicks to the minute. With standard set up I believe the lymans were 4 clicks to the minute nut this changes with sight radious also. A 24" barrel on your receiver should be 4 clicks to the minute. with your shorter 19" barrel it may be 3 clicks to the minute.

Lyman include a chart in the box with each sight,....they probably have it on their website.....all you need to know is the distance between the sights on you gun.Then read from the chart what the adjustments will be.........even without a chart,its a simple exercise in geometry...but you will need to be able to measure the graduations on the sight with a vernier ,or like.

I do a simple short range test
I use 1" graph paper and take a few shots at a aiming point then see how much it moves.
I switch my Lyman sight between a few rifles.
My 513t runs about 7-9 clicks from 25-50 yards. I think my eyes have a larger impact on MOA than sight radius.:bigsmyl2:

well,

Easiest way is the Tall Target Test. Straightforward and used by long range shooters.

Get a piece of cardboard more than 40" long and at least a foot wide. Use a fat sharpie and draw a crosshair for an aim point. give yourself a good 40 inches of "up" on the target once you set it up. I usually draw 5-8 parallel lines so I don't have to move the target and can shoot a bunch of tall target tests.

Set up your target. I usually use the 100 yard line but 50 is fine too. The key is to use a carpenter's level to make sure the vertical lines are perpendicular to earth. The horizontal line at the bottom is just to give you an aim point, and doesn;t even need to be perpendicular, though we make it close as best we can.

You sight in perfect at your distance then shoot the tall target. start at zero, shoot the target, then move the sights by a predetermined amount (2 clicks, 3 clicks, 5 clicks, we use 5 MOA for scopes) and shoot the same POA again. Adjust, shoot. Adjust, shoot. After we've gone up 30-35 MOA of adjustment (shot the target 6 times), adjust back to zero and shoot the target one last time.

This test tells us if our sight (scope) has any cant to it, and lets us measure hole-to-hole spacing to know how many inches of adjustment we actually get per MOA of adjustment on the scope, to measure the tolerance. Typically, we care less if 1 MOA = 1 MOA on target as much as we care that every 5 MOA adjustment is an equal spacing of adjustment downrange.

In your case, you will absolutely calibrate your actual drops to adjustments on your sight.

Here's a better Idea.

Depending on which model 48 you have(A,B or C) the Elevation Clicks are either 1/4 or 1/2 MOA at 100 yards.

My M2 Springfield (made in 1935) has a Model 48A which is 1/2 MOA per click or 2 clicks between the numbers on the knob, and my Springfield 03A3 has a 48C which is 1/4 MOA per click or 4 clicks between numbers on the knob.

One revolution of the knob is 5 MOA or one hash mark on the Vertical Slide. 5 revolutions is 25 MOA. or 25" at 100 yards 50" at 200 yards and 75" at 300 yards.

This is based on Sight Radius of 28" or a barrel length of 24" which is standard for most rifles using these sights.

There will be a minor difference in the actual movement of your groups per click (a few thousandths) with the shorter sight radius however you will never be able to see it. Same will be true with a longer sight radius. This is not something to worry about until you are past 1000 yards then it might make a small difference in your POI but since you won't be able to hold well enough to see the difference this won't matter either. IE: you will be close enough.

After your gun is zeroed at 100 yards in both windage and elevation with your most used load or Factory Load of choice, You will Zero out the Slide Pointer by moving it to 0 and the Knob to 0 by loosening the set screw, and finally move the Elevation Slide Stop screw to contact the top of the slide. This will become your "Mechanical Zero" If you change your base load,,, it changes everything and you get to start over!

The load chosen for Mechanical Zero should also be the fastest load that you will shoot with that gun, thus all subsequent loads will be slower and require Positive Elevation Changes which can be done easily without upsetting the Mechanical Zero.

By loosening the slide release you can move the slide up or down to your desired elevation offset plus or minus clicks for whatever new load you use. Then simply press the clamp button in and drop the slide back to 0 and re-zero the knob and you are right back to Mechanical Zero where you started. This is the beauty of these sights and they had all this figured out before 1920.

Mechanical Zero should be done with some readily available Factory Ammo so you have a baseline load you can always revert to, with a known ZERO.

Sinclair sells a small book that you can use to write down all your elevation and windage offsets for any other loads you may choose to shoot. AS long as those loads don't change you can go back to the offsets at will and be assured that your gun will be sighted in accurately for each load combination.


What you are getting with these sights is Predictable POI Movements of your groups and Repeatability .

Here's pics of the sight on my M2. You can clearly see the 5MOA hash marks on the slide, and the 1 hash mark in between the numbers on the Elevation Knob.

Randy

Randy nice post. Thanks!!!!!!!!

Seems that knowing the threads per inch on the elevation screw and the sight radius should be sufficient to figure out what's going on at range.

If your rifle is not a 28" sight radius (per W.R.Buchanan's post), then a longer sight radius will reduce the PoI increments and a shorter sight radius will make the PoI adjustments coarser. It should be proportional. Half the sight radius will double the adjustment's PoI shift, Twice the sight length should halve the PoI shift, etc.

Mc Fred: that is probably true, however the actual shift in POI will be so minimal it would be of little consequence because you are not going to change the sight radius by 50%. In his case it is maybe 10%.

On my Enfield #4 Mk1 the sight radius is 31". I have a Redfield Olympic mounted on that gun which is just a nicer version of the Lyman Sight. This sight allows me to make accurate and repeatable movements to the POI, and I installed it so I could establish a more permanent and repeatable Mechanical Zero.

With the stock sights you have to move the front sight to make the major adjustments until it gets to Mechanical Zero which is built into the rear sight. The rear sight is only adjustable for elevation, so with the rear sight set on it's lowest point (200 yards,) you change front sights and move them around until the Mechanical Zero comes in. After which the POI will answer the markings on the sight based on the standard .303 British Military load's velocity very accurately out to 1300 yards. This is based on a known Velocity and Ballistic Coefficient (IE: Trajectory)of the "Ball Load" which is standardized. All Military Rifles are set up this way.

There is a Front Sight Pusher (now available from BPM!) that moves the Front Sight in its dovetail. A movement of @.008 equals 1 MOA. There are nine different Front Sight Blades which vary in height .015 per step, or 2 MOA. This is almost set in stone and my Tool uses a 1/4-28 thread on the adjustment screws which is .041 per revolution. The bolts have a hex head which generates @.007 movement per Flat on the head.

Since the relationship between the Sight Radius is proportional to the difference in the movement when the radius is changed we see that 1/8th of the sight radius is @4". Which would generate a difference of .001 on the sight, which would generate a movement of 1/8th " on the POI. Neither of which you can see or compensate for.

My point is nobody can hold that close with iron sights, and even if they could the inherent accuracy of the guns in question would prevent you from knowing if it was you, the sight, the ammo, or the gun itself, or the wind, or Demons from Hell working against you!

Too many variables for an exact result.

In other words once it is close enough,,, it is close enough.

Randy

Yes, The proportion I referenced was to mean that once zeroed, .5 MOA 'clicks' could be calibrated by using the actual sight radius versus the 28" standard e.g. a 23.75" actual vs a 28" baseline would be a ~18% more or ~.6 MOA instead of .5 MOA. A simple ratio.

You're right, though, that PoI might not be greatly affected until the range is beyond the practical limit of the human eye. It just depends on how anal you want to be. :) I spent too much time QA-ing prototype aerospace machine parts to 4 decimal points and am prone to getting bogged down in the minutiae.

That's why if the OP actually tests on a target he will know for sure the "value" of each click of elevation and windage.

Quote:

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Originally Posted by Larry Gibson

That's why if the OP actually tests on a target he will know for sure the "value" of each click of elevation and windage.

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+1 test at 100Yds and do the math. Straightforward and simple.