Leupold CDS M1 Dial

[JRS3]

I received a custom CDS M1 dial for a Mark IV 6.5-20x50 mm this past week and got a chance to shoot it today. It worked close but was off at 475 yards today. That is far as I could test it today but will shoot it again soon for additional testing.I was amazed that Leupold was able to give me a range from 100-1,200 plus yards on one dial! Anyway, back to my point.

After checking zero at 100 yards, my rifle was spot on at 100, which the dial was made for. The next shots were at a measured 475 yard steel target. I turned the dial to what I thought was 475 and shot twice over the 10 inch plate, while holding center . After dialing back to 450, the shot hit at the top of the plate, which was 5 inches higher than I aimed. Is this difference normal? It has me doubting how accurate it will be once I stretch it to further distances.

I mentioned what I thought was the 475 mark. The increments on the dial are in 50 yard segments. For 475, i turned halfway between 450 & 500. I am not trying to sound ignorant but is it that simple or do you have to error on the side and adjust closer to the higher mark when in between increment marks? Thanks in advance, John.

 

[bruce_ventura]

How did you order the CDS dial? Did you select a factory load, provide measured muzzle velocity and ballistic coefficient, or something else?

 

[JRS3]

Hand load, multiple velocity chrono averages, BC, temp., altitude,etc. The only difference i can think of is the temp. I ordered it for 60F but it was probably 90F tonight when I shot.

 

[bruce_ventura]

What caliber, bullet and MV?

I ran a quick calculation using .270 Win ballistics. If I include a 30 deg temp and an 0.5 in Hg pressure difference, I get about 0.9" rise in bullet POI at 475 yds. I don't think that's the problem.

I would calculate the bullet drop for the parameters you gave Leupold and then count clicks to 475 yds on your dial. Do they agree?

I see a call to Leupold in your future.

 

[JRS3]

.308 (300 WSM), 165 SGK, 3,110 FPS, 100 yard zero, 2" above bore.

 

[bruce_ventura]

I don't see that bullet in my database. What BC and pressure or altitude did you give Leupold?

I can come closer to your miss at 475 yds if I confuse meters with yards somewhere. For example if the CDS dial is calibrated in meters, but the target was actually 475 yds away. Or the targets you used to measure bullet drop for the BC calculation were at distances of meters, but you thought the range values were in units of yds. Any chance of something like that?

That might be a temporary fix for you. Assume the CDS dial is calibrated in meters. Then how far off are the impacts?

 

[JRS3]

.404 for the BC and 2,000 feet elevation since they said it had a +/- 2,000 feet tolerance.

The dial states yards.

My plan is to shoot it on paper and check it but I am still puzzled how it is off. The only confusing issue could be that the gap widens between increments as the yardage increases. It is not obvious where exactly 475 is on the dial but why did it shoot five inches high when I had it set at 450? By thy way, my gun was set on a heavy bag and tripod, with no wind.

My shot at 100 was dead on, through the X, so it should have been on. I will recheck it but this rifle and load is very consistent so I am confused how it could the setup was off. I don't feel as though it was the monkey (me) behind the trigger!

 

[bruce_ventura]

10" at 475 yds is equivalent to almost 2" at 100 yds. That would be a big aiming error for any experienced rifleman. Seems unlikely.

That said I never draw any conclusions from a single shot. I always fire a 3-5 shot group to check zero.

 

[JRS3]

Update after a long range session. I finally trust the custom dial but it took awhile and a few college tries to get it right.

The dial has a setup for 100 yard zero but this seems to leave too much margin for error, to simply sight in at 100 then bang away accurately at farther distances. I am convinced there is a minor tolerance for error at 100 that does not get exposed until shot at longer distances. Someone with more LR experience can probably explain in better detail but it seemed apparent to me. With that said, I sighted my rifle in at 300 yards with the 300 mark and set it. After doing this, I shot it at distances from 100-500 and it worked rather well. The 100 yard zero is approximately 3/4" high but I can live with that. It fell right in line after that to 500.