Factory Box Ammo Velocity Spread Examples From Yesterday.

[mxgsfmdpx]

Got a couple rifles onto the chronograph yesterday. My Sako .260 with a 20.5" barrel 1:8' twist, and my Tikka .22-250 with a 22.5" barrel 1:14" twist. These were shots at 50 degrees Fahrenheit and at 200 feet of elevation.

I shot 10 rounds through each rifle, rotating in 5 shot sets so the barrels didn't get very hot. I let the barrels cool back down to "cold barrel" before the 2nd sets. I used factory ammo from the same boxes for each shot.

Hornady Superformance .260 129 Grain SST (Maximum Spread: 56 FPS) (Average Velocity: 2,723 FPS).

Shot 1: 2,704
Shot 2: 2710
Shot 3: 2721
Shot 4: 2731
Shot 5: 2749
Break
Shot 6: 2693
Shot 7: 2732
Shot 8: 2743
Shot 9: 2737
Shot 10: 2710

Hornady Superformance .22-250 50 Grain V-MAX (Maximum Spread: 69 FPS) (Average Velocity: 3,912 FPS).

Shot 1: 3898
Shot 2: 3944
Shot 3: 3910
Shot 4: 3921
Shot 5: 3910
Break
Shot 6: 3875
Shot 7: 3933
Shot 8: 3910
Shot 9: 3921
Shot 10: 3898

 

[Justin Crossley]

Great info.

Which chronograph were you using?

 

[mxgsfmdpx]

Great info.

Which chronograph were you using?

Competition Electronics ProChrono DLX.

 

[archp625]

That's pretty normal for factory ammo. That's why a lot of guys get into reloading to help lower that ES way down below 10.

A normal person may never realize it shooting 200-300 yards. The furthur out is where you are going to see your differences and possibly wound or miss an animal.

 

[mxgsfmdpx]

That's pretty normal for factory ammo. That's why a lot of guys get into reloading to help lower that ES way down below 10.

A normal person may never realize it shooting 200-300 yards. The furthur out is where you are going to see your differences and possibly wound or miss an animal.

Correct. This is why I posted it here in the reloading forum. Always good to have recent real world data.

 

[archp625]

Correct. This is why I posted it here in the reloading forum. Always good to have recent real world data.

Absolutely. I wasn't questioning your intelligence. I've seen you post quite a bit and your always on point or give good advice. Keep rocking on.

 

[TxxAgg]

Good real world info

 

[mxgsfmdpx]

Absolutely. I wasn't questioning your intelligence. I've seen you post quite a bit and your always on point or give good advice. Keep rocking on.

Thanks. I question my own intelligence every day

 

[mxgsfmdpx]

After chronoing and before some coyote hunting (I LOVE daylight savings) I did some quick scope/ballistics verification work... I had previously dialed my .260 in at 100 yards and verified out to 200 yards with a 7/8" 6 shot group. The Sako is a damn shooter like always! I also have verified the tracking reliability of my Meopta MeoPro scope. I need to make a thread on how I do this using a total station.

After confirming the velocities I took the same factory ammo I tested with, and popped 3 shots off at 500 yards. I set my velocity into 2 different ballistics apps and compared (strelok and berger). Both came up with the same answer. So what velocity did I use?

I was torn between using the mean and a number somewhere between the mean and mode using a bell curve I made (confidence interval formula) I decided on using the modified formula approach, meaning a greater chance of more of my shots being spank on. Using the mean would be slightly better at mitigating the larger discrepancies, but those don't occur as often and those are shots that are going to be "off" anyway. I'd rather stick to something closer to the mode while still factoring in the mean... Landing me at using 2,728 (2727.613) for the app calculations. Ideally I'd have more data than 10 shots but that's all I felt like shooting through the chrono for each cartridge.

How did the shots at 500 go?

I was pleasantly surprised with the 3 shot group. 5 MPH of head wind, 52 degrees, 200 feet of elevation... I set up for the first shot, dialed for 11 MOA on the dot, got comfortable in the grass and let one fly. DING! I heard the gong ring but couldn't see my shot anywhere on target. Got the spotting scope out and realized I couldn't see it because it was in the bullseye on the right hand side of the 2" bright orange dot and my scope only goes to 14x zoom. Cool!

I set up for the 2nd shot, got comfortable and ringed another off the gong. This shot was also in the bullseye, really really close to the first shot (ended up measuring) 5/8" center to center from the first shot. I guess I better go for one more.

The 3rd shot, I was "trying too hard"... I wanted a 3rd bullseye really badly and I "overfocused". If I had relaxed and not worried like the first two shots it probably would have been better. Always learning! The 3rd shot rang the gong and this time I could easily see the hit. It ended up being 1.3" left of the bullseye and .5" lower than the first two shots.

So with factory ammo, and working hard to try and get a velocity I could work with in the field, I was able to put 3 shots into a 2.25" group center to center on the longest diagonal at 500 yards.

 

[Clarence]

Thank you for the info, and solid shooting man.

 

[MattB]

It is interesting that the first shot in each string was the slowest in each case. I wonder if you shot each shot on a cold barrel if the results would have differed? Meaning, does the heating of the barrel cause velocity to increase?

 

[mxgsfmdpx]

It is interesting that the first shot in each string was the slowest in each case. I wonder if you shot each shot on a cold barrel if the results would have differed? Meaning, does the heating of the barrel cause velocity to increase?

The short answer is yes... But it's much more complicated than a simple answer and you have to consider several variables The two most obvious factors in my specific test case are the relatively small data set and the large maximum velocity spread of the factory ammo. There are many other things to consider as well, some of them are touched on in this document https://www.shootingsoftware.com/ftp/Pressure Factors.pdf

There is a regression plot on page 8 that would seem to support your hypothesis as a general "rule". Although the "barrel temp" isn't the only factor. There are also data sets that show the exact opposite with certain rifles, cartridges and different powders used.