Range Report Is my MV off, or am I not converting mils right?

[ZLBubba]

Went shooting yesterday and quickly found that I had underestimated my muzzle velocity for my round. I'm shooting a 155gr Scenar behind 45.7gr of RL15 out of a Badger M2008 build and a Broughton 18" barrel. My scope is a PH 3-15 with double turn turrets.

This is a buddy's load that works well in his gun, and shoots pretty accurately in mine as well. Usually in the .2s or .3s at 100 yards if I do my part. I haven't chrono'ed it, but my buddy did and got around 2750fps. That's what I used for JBM and yet the numbers were way off when I tried to use the table JBM gave me yesterday.

At 2750fps and using a 100 yard zero, I should have had the following results:

300 yards: -13.6in or 3.8mils
500 yards: -55.8in or 15.5mils
600 yards: -90.6in or 25.2mils

Either my muzzle velocity is off or my conversion to mils is off, or both. Here's the results I had on the range yesterday:

300 yards: 0.5mils
500 yards: 2.3mils
600 yards: 3.4mils

I'm stumped as to what I'm doing wrong, but I'm sure it's an obvious mistake I'm making. It was completely baffling to be drilling hole after hole in the target at 600 with only 3.4mils dialed in, but that's exactly what was happening.

So is it my mil calculations that are off, my muzzle velocity that is too slow, or does it having something to do with my scope turrets?

 

[herr.baer]

Re: Is my MV off, or am I not converting mils right?

You are off because you converted inches to mil and not MOA to Mil. Using your given info into JBM calculator here are the readings.

300 yards: 1.3mils 4.5MOA 4.7in/100y 14.1inches
500 yards: 3.1mils 10.7MOA 11.2in/100y 56.1inches
600 yards: 4.2mils 14.4MOA 15.1in/100y 90.4inches

Looks like your velocity if off as well.

 

[Top Cat]

Re: Is my MV off, or am I not converting mils right?

In order for your range data to be correct in mils, your velocity would have to be greater than 3000fps. I doubt that is the case, so you may be mis-reading your scope turrets as well.

If there was one piece of accurate data available there might be a chance of figuring this puzzle out.

TC

 

[dareposte]

Re: Is my MV off, or am I not converting mils right?

Try using this calculator: http://dop3.com/index_csmrad.php

It does all the conversions for you.

You also need to make sure your 100-yd zero is exactly on at exactly 100 yards. Not 95 yards, not 105 yards, and not an inch high or low. If you haven't measured your scope height over bore, that needs to be accurate too if you want to get good computer dope so measure it within 0.1"

Your conversions look like they're way off to me. According to the "computer" data you gave, I'm getting a calculated correction of 4.2 mils @600 yds using a 155gr scenar.

Post your altitude and temperature and I'll give you a better estimate.

 

[dareposte]

Re: Is my MV off, or am I not converting mils right?

Your profile says Potomac, MD. Altitude 100m / 330ft.

Weather yesterday was a high of 93F, with Barometric pressure of 29.69 inHg.

Using those conditions and 2800ft/s mv, I compute 3.87 mils for 600 yds.

 

[ZLBubba]

Re: Is my MV off, or am I not converting mils right?

Yeah, that's about right for the conditions yesterday. I must admit that though I was shooting at exactly 100 yards for the zero, the rounds weren't precisely dead center. I'll have to remember that.

Thanks for the hlep, dareposte, I'll be using that calculator in the future.

 

[dareposte]

Re: Is my MV off, or am I not converting mils right?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ZLBubba</div><div class="ubbcode-body">Yeah, that's about right for the conditions yesterday. I must admit that though I was shooting at exactly 100 yards for the zero, the rounds weren't precisely dead center. I'll have to remember that.

Thanks for the hlep, dareposte, I'll be using that calculator in the future. </div></div>

Yeah if you're off center then it can mess up the dope. If you were shooting an inch high at 100 yds (~.3mrads) that (along with the weather) would explain the error at 600yds.