What is my muzzle velocity

[Seeking_Coyotes]

Hi Shooters... Rarodin/Robin (one awesome dude!) offered to calculate my muzzle velocity based on drop data. I lost his email but hoping he comes back on here and sees my data for his calculation.

If anyone can explain how to do the math I 'd appreciate understanding how I can calculate my muzzle velocity. Here is the data:

Wind was variable at 5 mph on the 200 yard groups and pretty much nonexistent on the 300 yard groups. The five mph wind switched from a tailwind to a right to left wind. I would say it was about seventy degrees with no humiity I could feel. The .243 Win. was a Savage Model 10 with a 24 inch barrel and a 1:9.25 twist. The bullet is a 70 grain Sierra Match King bullet with a published ballistic coeffient listed on the web site as:

Stock Code: 1505 MatchKing 6mm .243 Caliber (.243) 70 gr. HPBT Match (100 bullets)

Ballistic Coefficients
.243 70 .169 .259 @ 2800 fps and above
.257 between 2800 and 2200 fps
.270 @ 2200 fps and below

Group 1: Drop from 100 to 200 = 3.301" Group Size = 1.027 (five shots)
Group 2: Drop from 100 to 200 = 3.726" Group Size = 1.977 (five shots)
Group 3: Drop from 100 to 200 = 3.237" Group Size = 1.666 (five shots)

Group 4: Drom from 100 to 300 = 10.719" Group Size = 1.457 (five shots) No wind
Group 5: Drop from 100 to 300 = 10.942" Group Size = 1.787 (five shots) No wind

 

[BigDMT]

Don't know the math, but I'd think your scope zero range would have to factor into that equation...

Then a guy could just play with a ballistics calculator until he came up with the elevation drop you witnessed. Simple enough.

But a chronograph would also be a very sound investment when curious about bullet velocities

 

[Seeking_Coyotes]

I sighted the gun in at 100 for this day at the range.

Borrowed a friends chronograph but I don't have confidence in the numbers it gives me. Don't have a second one to test it against.

 

[CatShooter]

What is the height of the center line of the scope, above the center line of the bore?

If it is ~1.75" over the bore (average), then your MV is 3220. That's not real fast for the 243 and a 70gr bullet. (Pull the trigger harder )

 

[BigDMT]

What is the height of the center line of the scope, above the center line of the bore?

If it is ~1.75" over the bore (average), then your MV is 3220. That's not real fast for the 243 and a 70gr bullet. (Pull the trigger harder )

lol! Yeah I thought that 200 yard drop sounded like a bit much if he had a 100 yard zero like I assumed. I push the 75gr Sierra HP bullets out of my 6mm Remington at about 3480 fps from a 24" barrel and I don't have any pressure signs. So the 243 should be able to do at least that.

 

[wyoming .260]

What is the height of the center line of the scope, above the center line of the bore?

(Pull the trigger harder )

lmao

 

[Seeking_Coyotes]

Yeah...I am trying to shoot it as slow as possible and luckily the good shooting load is just a tad below the starting load. My hornady manual says I should be at about 3000 velocity but my chronograph is giving me much higher readings (see below). Going to find the average tonight. Was hoping the bullet would be at only 3,000.

Here are the reading I got on the last ten shots last night.

3383
3384
3394
3398
3382
3393
3369
3345
3388
3359



Sounds like it must be somewhere around 3200 based on the drop? Any idea what number velocity I should give Burris to make the Turret?


These Sierra MKs sure do shoot.

 

[Pres100]

Before having a custom turret made, I wold definitely verify a good average velocity over a chronograph. What was it about your friend's chronograph that you didn't trust? At least find someone you can trust to chronograph the loads.
I would hate to have custom turrets made (that will be an approximation to begin with) based on a guestimation from the Internet . Absolutely no disrespect to those that have tried to help out.

Edit
I checked my Hornady manual and 3200+ fps is about where you should be with a 70 gr bullet out.of a .243. However, you won't find Sierra info in the Hornady book. I would lean toward trusting the chronograph.

 

[BigDMT]

Yeah...I am trying to shoot it as slow as possible and luckily the good shooting load is just a tad below the starting load. My hornady manual says I should be at about 3000 velocity but my chronograph is giving me much higher readings (see below). Going to find the average tonight. Was hoping the bullet would be at only 3,000.

Here are the reading I got on the last ten shots last night.

3383
3384
3394
3398
3382
3393
3369
3345
3388
3359



Sounds like it must be somewhere around 3200 based on the drop? Any idea what number velocity I should give Burris to make the Turret?


These Sierra MKs sure do shoot.

How close was the chronograph to the muzzle of your rifle?

 

[Seeking_Coyotes]

10-11 feet

 

[Seeking_Coyotes]

Lots of variables on my plate with this one. Think I will go with this as it hits the 300 yard drop perfectly.

Name: 243, Bullet weight: 70 gr, BC: 0.259, Muzzle velocity: 3275, Wind speed: 10, Wind angle: 90
Range (yds) Velocity (fps) Energy (ft-lbs) Path (in) Drift (in)
0 3275 1667 -1.5 0.0
50 3079 1474 -0.3 0.3
100 2892 1300 0.0 1.1
150 2713 1144 -0.7 2.4
200 2541 1004 -2.7 4.4
250 2376 877 -6.0 7.1
300 2216 764 -10.8 10.6
350 2063 661 -17.4 14.9
400 1916 571 -26.0 20.1
450 1776 490 -37.0 26.3
500 1643 420 -50.8 33.7
550 1520 359 -67.8 42.4
600 1405 307 -88.6 52.4
650 1302 264 -113.8 63.9
700 1212 228 -144.1 76.8
750 1137 201 -180.3 91.3
800 1076 180 -223.3 107.1
850 1027 164 -273.7 124.2
900 986 151 -332.6 142.5
950 951 140 -400.3 161.7
1000 920 132 -477.5 181.9

Will probably never get to see how accurate the turret turns out to be past 300 yards since that is the farthest range I can access here. That is the farthest I could imagine a shot at a deer in this state. Groundhogs maybe out to 500 but much past 350 is just to far for me.

 

[Pres100]

Now take that card and verify it before your custom turrets get ordered!

 

[Trapper243]

I measure exactly 10 feet and make sure the measurement stays the same on every shot. Make sure the bullets are traveling level over the chronograph and not at an angle. If you are prone, you need material of some type in front of the chronograph, or blowing dirt , dust etc... will mess things up. It is cheaper and easier, at least for starters, to just tape your own data to the turret. Just a thin strip of paper wrapped around the turret with your data and secured with clear packing tape. See how that works and then adjust. You will also need to check new loads from different lots of powder, primers, brass.... . Even if all the components are the same. You may find you need to adjust the powder charge to keep the velocity the constant. When setting up a turret, I find it helps to just zero everything up at 400, then back up and get closer to see how close I actually am and if it will work for the kind of hunting I do. What surprises me doing this, is how far the advertised BC on some bullets is off.