Home Forums Reloading Big Game Rifles sight hight question, I need help!

Hey folks, its been a while since I have been on here, as I have mostly been shooting rimfires . Now that I am back to the CFs I am getting a rifle set up for long range shooting, and want to put a turret on the glass on top of it. What I need, is to know how I can measure the sight hight above bore on this thing. Its an Interarms MK X in 6.5-284. Leupold FN Mauser bases, Leupold medium height STD rings, Leupold VX III 6.5-20 x 40 AO without turrets, 1 inch tube. If someone has a method for measuring all of this, I am all ears! The turret will be a kenton Industries, and its not urgent as I dont have a load worked up or anything, so I dont have any data to send them as far as MV BC or true to fact field data.

Thanks
Nick

I just hold a small ruler against the forend and measure (estimate) the distance from the center of the barrel to the center of the scope tube. If there is any other way to do it, I am unaware. Good luck.

Yep. Hold up a ruler from bore centerline to scope centerline. That's plenty accurate for this. Small inaccuracies in this measurement mean absolutely nothing in practical terms, even at distances beyond where most of us hunt or shoot. You'll need to confirm your dope anyway and there are many more critical factors that can affect your results.

The above are WRONG.

Pull out your bolt and measure its diameter with calipers. Divide by 2

Measure your scope diameter with your calipers. Divide by 2

With the bolt in the action, measure from the bolt body to the scope tube and record.

Add "A" to "B" to "C" and this equals your sight height...

Small inaccuracies in this measurement mean absolutely nothing in practical terms, even at distances beyond where most of us hunt or shoot. You'll need to confirm your dope anyway and there are many more critical factors that can affect your results.


Nothing wrong about that.

From the creator of Ballistic AE

very clever rcamuglia I will do that, and write it down, and safeguard it. I have 3 MK Xs and this should be the same for the same model bases, same rings, and same dia tubes on all 3! I like it.

Total nonsense. Using my 16" barreled .308 and M118LR or similar as an example, there is no difference -zero difference- at 1000 yards if I start with a 2.2" sight height or a 2.5" sight height (known data & JBM). That's 0.3" error which is WAY more error than you'd ever get eyeballing this measurement with a ruler. Furthermore, you're going to have to go out and validate your numbers in the real world, especially with a new scope with unknown accuracy of adjustments. You can measure the height-over-bore to the 0.00000001" and it is irrelevant when your Leupold scope adjustment measures .235 MOA/click instead of .25 for example.

Point is, get a starting measurement that's eyeball close and go shoot to work through your new system. This HOB measurement is not critical enough that small error will matter.

Whether you give a [bleep] or not, that's the ACCURATE way to measure your sight height. If you want the most accurate output from a ballistic program, you have to input accurate numbers.

Same goes for everything else

Some throw their powder and some throw and trickle to the exact charge. Some anneal their brass and seat bullets with a competition seating die so OAL is the most consistent and accurate as it can be. Some measure distance to the lands with the bullet they're using and some have no clue how far off it is. Some weight sort brass, neck turn, and do full case prep to get the best results from their ammo; Match grade ammo and accuracy. Some use dippers and stuff bullets in and are happy with 2" groups.

A friend of mine calls one of the methods "BWDT"

Bailing Wire and Duct Tape Method

I guess variety is the spice of life.

I'm all for those things when there is a tangible benefit to doing them. In this case, there is not. Same as weighing brass in a hunting rifle (and even most match rifles). There is no real-world benefit. If going through those steps gives you more confidence, that's fine, but it shouldn't be sold to a new guy as gospel. Many times, that's what happens. If someone can show me how there is a meaningful real-world benefit I'll be all for it, btw.

Anything worth doing is worth doing right

Just wish they made a thingy to measure it, right rc?

As soon as they do, you'll own it!

Think HC might want to start using a wooden ruler to check PHE & CRE.

Uh, or is it CHE & PRE? LOL

Here is a real world test of sight height.

Does the height of the rings above the barrel affect trajectory? Sixty shots says, �Yes!� Arbitrarily I decided on a single ten shot group at 100, 200, and 300 yards with two scope heights. According to the computer, if you sight in a firearm at, say, two hundred yards with the low or the high sight, it hits dead on at two hundred yards. Novel concept. The fun information is at one hundred yards or three hundred yards. And beyond.

I used a Savage .223 with the 26" blued barrel for the test. A trigger job by Bud Hopson brought the pull down to about two pounds. Th scope was 8X - 32X Burris target scope. The loads consisted of a 65 grain JLK bullet (.397 sea level ballistic coefficient corrected to .411 for 1100 feet at the Grants Pass range according to the computer), a neck sized, trimmed to length Remington case with a deburred and squared flash hole holding a CCI BR-4 primer. The powder charge was 27 � grains of VarGet. The cases had a weight tolerance of .2 grains and have been fired four times. The average velocity for the first thirty was 3,221 feet per second with a standard deviation of twenty-one. (Who knows what standard deviation is, anyway? It shows up on the screen, so we read it. I think it's kinda like a group. If it's big, we don�t mention it.)

The HIGH rings: scope 2.2" above the bore.

The temperature started at forty-two degrees and went up to forty-eight degrees during the four hour session. All shooting was done on 32X. The targets were five eights inch squares.

The Burris settled on the left two hundred yard target to start. The first five shots appeared to make a group that looked more like a one hundred yard group in the square. I admired the group awhile through the scope. Even considered putting up another target. Being more lazy than vain, I continued shooting until the ten shot group was completed. Three of the next five went inside the original five, but a couple made holes on either side of it. The two hundred yard group had a vertical dispersion of only one half inch. Horizontally it opened up to one and eleven sixteenth inches.

Next I went to the one hundred yard target; leaving the setting for 200 yards. Shot number seven opened the one hundred yard oval shaped group to five eighths inch. Measuring from the center of the target up to the center of the group showed .63 inches on the caliper. The program said it would be .86 inches....not too bad.

At three hundred yards, the ten shot group consisted of a round group measuring a nice one and eleven sixteenth inches. The three hundred yard group was 5.5 inches low with the 200 yard zero. Barnes said it would be down 5.58 inches.

The LOW rings: scope 1.68" above the bore.

The rifle was cleaned and resighted at two hundred yards. A flier made a 2 inch ten shot group out of an enjoyable 1 3/16 inch nine shot group at two hundred yards. Now to the verification groups.

At three hundred yards the first eight shots were looking good for a factory rifle: 1� inches. Number nine and ten were on either side opening it up to 2 5/16 inches. It was 5.94 inches low. The 1.68 inch sight height centered 7/16 inch lower than the 2.2 inches sight height.

Moving onto the one hundred yard group: It was great! All ten shots went into a group of less than a half inch, which could be covered with a penny! The group was one inch above the line of sight. The program said it would be 1.12 inches high. There is only 1/8 inch discrepancy between the shooting and the program. There was about 3/8 inch between the impact points of the high and low rings at one hundred yards. The high rings hit lower...or was that the low rings hit higher?

In the book GAME LOADS AND PRACTICAL BALLISTICS FOR THE AMERICAN HUNTER, Bob Hagel suggests that we sight our varmint rifles in to hit one inch high at one hundred yards. I did that exercise in the computer. The high rings required an impact point of two hundred nine yards. The low rings needed a sighting of one hundred ninety-three yards. Shots from the HIGH rings would impact .29 inch HIGH at two hundred yards. For the LOW rings, the computer had the bullets hitting .24 inch LOW at two hundred yards. That's more than � inch . At three hundred yards, it�s more of the same. The high rings are punching holes 5.15 inches low and the low rings are down 6.20 inches. That's more than one inch higher for the same rifle shooting the same bullet at the same velocity under the same conditions.

Perhaps the outer limits for the .223 could be extended. Another computer generated range estimate: Three hundred fifty yards. The high rings impact 9.83 inches low, while the low rings come in at 11.14 inches down with the 200 yard sighting. For the lower sight to approximately match the higher sight over a three-hundred yard course of fire, one needs almost one hundred feet per second additional velocity....according to BARNES.

In conclusion, what can we conclude? The high rings shoot closer to the line of sight both before and beyond the range for which they are sighted. That means an apparent flatter trajectory without higher velocity.

Nice report ringman!

IMO, getting the scope nice and low on the rifle pays wayyy more dividends than 7/16" @ 300 'apparent drop'

I'm all for careful measurement and consistency. But variation does not add linearly. So it is pointless to work on small sources of variation while large sources are still at work.

Consider that with many powders and with common center fire hunting rifles, 3 degrees F in chamber temperature is equivalent to .1 grain of powder, and 30 F is equivalent to a full grain.

If you're not controlling barrel temperature to within a few degrees, and don't know the distance to your target within a few yards, it doesn't make much sense to spend a lot of time getting scope to bore difference to better than a quarter of an inch.

If you really want to do it carefully, measure the OD of your scope at the muzzle end. Then measure the OD of the barrel at the same point. Finally, measure from the top of the scope to the bottom of the barrel. The height of your scope above bore is that last measurement, minus half the scope OD, minus half the barrel OD.

Knowing that, I just slap a McDonald's Happy Meal ruler on it.