Need Math help sorting MOA on a RIA TM22 rifle

[motorcycle_dan]

I know there is some math geek out there just waiting for a reasonable problem like this to solve.  Bought a Rock Island Armory TM22 (under $100) Rear sight is adjustable for windage and front sight adjustable for elevation.  I remember FORS,  My plan is to possibly use this as a loaner once I determine it will shoot 4 MOA or better.  I wanted to know how much movement of the set screw will move point of impact.
The front/rear sights are about 14" apart
The rear sight moves 0.084" with 5 revolutions of the 1.5mm hex screw
The front sight moves 0.078" with 2 revolutions of the 2mm hex screw (yeah that engineer needs flogged)

What I'm looking for is the amount of set screw movement to change 1 MOA
Clockwise movement of rear sight moves blade left (point of impact left)
Clockwise movement of front sight moves blade up (point of impact down)

Get out your calculators S=O/H   C=A/H   T=O/A  (Soak-a-toe-ah) or the military version not fit for mixed company about a not very observant sally.  The useless things that the mind remembers. Like resistor color codes which I'm quite sure I never used past school.
Thanks in advance for the math help.
Dan /¦\

[SteelThunder]

OK, it's been 30 years since I used trig, but here goes.  Someone that uses it on a daily basis may find an error in my logic.

The tangent of a right angle (measured in degrees) is the opposite side (a) divided by the adjacent side (b).  So tan (theta)=a/b.  In this case a is the side to side or up and down of the sights, and b is the distance between the sights.  The angle (theta) is 1/60th of a degree, or an MOA.

So,
tan 1/60 = a/14
2.908x10^-4 = a/14
a = 0.0041"...in other words, deflection of the sights by 0.0041" is inclded in an angle of 1 MOA

For windage -
5 rev = 0.084"
1 rev = 0.0168"
To move 0.0041", you need to rotate the hex screw .0041/.0168 ~0.244 revolutions...1 MOA for every ~ quarter turn or 4 MOA per turn

For elevation -
Using the same logic
2 rev = 0.078"
1 rev = 0.039"
1 MOA for every .0041/.039 ~0.11 turns  or 10 MOA per turn

Hopefully that's right...someone else check my math



 

[motorcycle_dan]

Thank you, I went at it using ratio and ended up with same results.  Trig beat me.  I can remember it could be done but couldn't get an answer I felt comfortable with.

Windage 1/5 rev = 1 MOA
Elevation 1/11 rev = 1 MOA (clock face easier to remember)

So again Thank you, and stand down.

[OldDominionIron]

Math checks out.

[ScubaSteve]

For those of us that could have never figured this out I would use my tried and true method.    Shoot a group, from a rest if you must. Then make an adjustment, say 10 clicks or turns or whatever it has, but make 10 of them as it keeps the math simple. Shoot another group and see how far the group moved in inches. Convert that to MOA.  No matter how far it moved divide by 10 and that is how much movement one click is.

My guess Steels method is right on (he is way smarter than me) but for us math challenged folks that could have never figured that out, shooting, adjusting and measuring works.

 

[SteelThunder]

My guess Steels method is right on (he is way smarter than me) but for us math challenged folks that could have never figured that out, shooting, adjusting and measuring works.

Yup, and that's the way to verify if your sight adjustments are REALLY true.  I always do this on day 2 of a KD..."let's box the sights to see if your scope tracks to what the adjustment SAY they are"

And for being smart...nah, I've been in product management/marketing for the last 30 years, so all that smart left me a long time ago   

[Rangerat67]

Some people like math!

Years ago, I created a spreadsheet to show the impact of poor sight alignment for pistols. I later added a tab for rifles. Don't ask me why, but I created a tab just for motorcycle_dan. I considered setting this up for windage and elevation and have it tell you the direction to adjust but I need to turn in and get a good nights sleep for Michigan's IBC which starts tomorrow morning. Maybe some other day I'll make a general sight adjustment spreadsheet!

Rangerat67

[Charles McKinley]

Dan please do a review of the rifle and your thoughts on it when you can.

Thank you,
Chuck