80 gn Berger vs 80gn SMK major velocity differences

[JimSC]

Same weight bullet, same powder and charges, same rifle, and similar temps. 500 FPS difference ? I am going to rerun the Berger test next week. Both bullets have great SD's and 3 shot groupings down to the .2's at 300 but the velocity differences floored me. Anyone ever have a similar experience?

apologies for the formatting on the pdf's my office skills are lacking, hopefully most will be able to decipher

 

[MGYSGT]

Perhaps one has more of a bearing surface and slows it down. ??????????

 

[dcali]

Something is wrong. That's not right. Is it possible you misread the chronograph?

 

[JimSC]

Perhaps one has more of a bearing surface and slows it down. ??????????

That was my first thought also, never experienced anything this dramatic but then I am relatively new to this. Never paid much attention to chrono data except to get velocity for computing drop or checking PF for the wife's pistol ammo till recently

Something is wrong. That's not right. Is it possible you misread the chronograph?

that's why I will be re re checking, but I don't think so. I have the chrono data still, the Bergers were shot a couple of months back. I loaded up some SMK's did a depth to lands test and liked the results so well I never did a chrono on them. I noticed I had to crank in a lot more elevation at 600 This explains why. I decided to chrono them yesterday and my jaw dropped

The difference in the elevation on the 23.1 - 23.7 and 23.7 - 24.5 SMK test targets jumped dramatically also. First time I ever left the range both pleased and befuddled with my shooting. I will do a 10 shot test of both at the same charge next week side by side on the same day shooting round robin

 

[243winxb]

Make , model of chronograph. How far from muzzle?

 

[JimSC]

Make , model of chronograph. How far from muzzle?

Pro Chrono , always 12 feet measured with a cord I keep attached to the chrono

edit - looking about 1/2 way down page 1 on the Bergers there is a group of 4 shots then 5 shots and as best my memory recalls I tested a few Sierras that I had found on the back shelf and tested alongside the Bergers which inspired me to order 500 of the SMK's. I remember thinking my chrono must have messed up and thinking it is time I bought a Labradar. Looking at yesterdays data seems the chrono is working

edit 2 - Seating on the Bergers is .075 off lands, SMK's are kissing. I wonder if that could make that much difference?

 

[243winxb]

Use diffusers on sunny days.

Velocity errors with certain types of shiny ammunition. Try coloring the bullet tip with a black permanent marker to correct this type of problem.

Set at 15 feet.

 

[Laurie]

I mostly shoot on the UK's Diggle Ranges in the north of England which are situated in a deep upland valley and whose light levels can be quite limited especially in winter when the sun doesn't reach some of the ranges at all. With northern England's weather, varying degrees of cloud cover are normal as are constantly changing light conditions as clouds move quickly overhead.

I learned years ago that with the possible exception of the Oehler professional models, optical chronographs are a waste of time, ammunition and barrel life in these conditions. I have watched successive shots drop by up to 50 fps each as thicker cloud moves overhead until the chronograph eventually stopped reading at all.

Beg, borrow or steal a Magnetospeed or Labradar. I can positively assure you that there will then NOT be a 500 fps difference between these two bullets.

 

[expiper]

Pro Chrono , always 12 feet measured with a cord I keep attached to the chrono

edit - looking about 1/2 way down page 1 on the Bergers there is a group of 4 shots then 5 shots and as best my memory recalls I tested a few Sierras that I had found on the back shelf and tested alongside the Bergers which inspired me to order 500 of the SMK's. I remember thinking my chrono must have messed up and thinking it is time I bought a Labradar. Looking at yesterdays data seems the chrono is working

edit 2 - Seating on the Bergers is .075 off lands, SMK's are kissing. I wonder if that could make that much difference?

Hi Jim,,,,a budy of mine has a pro chrono and we sat it down right between the sky screens of my Ohler and it read within 5 fps of what my million dollar$$$ chrono said,,,,dont doubt your equipment,,,,but as you know and everyone implies lighting is a variable with any of the units that use available light,,I have a labradar now and dont know how I ever lived without it,,set up is quick and EZ and the unit is very portable and can be used at the firing line without and danger or bother to yourself or other shooters,,,back to the issue here,,,just because a bullet is the same weight as another bullet does not mean the vel will be the same with same load or rifle ,,,bullets vary in size (dia may be as much as .0015 bigger or smaller by brand or even lots,,,) and jacket thickness and hardness plus core material may vary with or without antimony or lead density pluse the obvious bearing surface from different style of bullet construction,,,,and you said some were jamed and some jumped ,,,I have found this to cause 50-100 fps in most cases,,,,the main thing is how do the targets look ??...if your vel is acceptable shoot em and spend time thinking about the wind,,,Roger
PS,,,to check vel aginst chrono. I shoot at 100 yds and 300 yds with no scope change and see if the ammount of drop coincides with the drop tables for that vel with a bullet of that BC....

 

[JimSC]

This weekend I am loading 15 of each and will shoot them within minutes, the old pro chrono is long in the tooth and I am just waiting on a excellent deal to pop on a Labradar. If the SMK's are shooting slow it is still all good. This is going to be my go to rifle and load for 300 yards. Just about every charge gave me 3 shot groups less than .5 MOA and I have a beautiful flat node between 23.3 and 23.7. Here is a test target from the seating depth test at 23.5

 

[chkunz]

The problem with chronographs is that we have no way to calibrate them. Instrumentation that you can not calibrate is always a source of doubt (uncertainty).

Knowing this, I try to mitigate this problem by shooting a "baseline load" before and after my test load. My baseline load is one that I have a lot of experience with and agrees well with published data. This way I have a significant history for comparison and this history becomes larger with each use.

 

[Texas10]

Are both bullets seated down into the case exactly the same? Or is one taking up much more case volume than the other?

 

[Laurie]

Knowing this, I try to mitigate this problem by shooting a "baseline load" before and after my test load. My baseline load is one that I have a lot of experience with and agrees well with published data. This way I have a significant history for comparison and this history becomes larger with each use.

I used to fire a 22LR BSA Martini International over the chronograph with a good make of standard velocity match ammunition before risking the centrefire stuff. If the chronograph reported 1,050 fps (or 1,090 or whatever its MV was) with the 22LR I was good to go!

 

[JimSC]

Are both bullets seated down into the case exactly the same? Or is one taking up much more case volume than the other?

excellent point, the Berger is seated .075 off lands the SMK is dead on the lands so if everything else is equal there is almost a tenth of a inch less case volume with the Berger. I think you may have solved it

I have a fair amount of faith in the chrono, it's several years old but I can still take the data off it and run out to 800 yards with that data and be within a couple of inches on the vertical which was all I ever used for until recently after adopting Erik Cortina's load development method

great tip Laurie

 

[chkunz]

excellent point, the Berger is seated .075 off lands the SMK is dead on the lands. I think you may have solved it

I have a fair amount of faith in the chrono, it's several years old but I can still take the data off it and run out to 800 yards with that data and be within a couple of inches on the vertical

No doubt that may give you some velocity difference but 500 fps is a lot of difference, I do not think this is the whole story.

 

[Twitchy]

What powder? There is no way that those chrono numbers are accurate.

 

[shoot4fun]

Same weight bullet, same powder and charges, same rifle, and similar temps. 500 FPS difference ? I am going to rerun the Berger test next week. Both bullets have great SD's and 3 shot groupings down to the .2's at 300 but the velocity differences floored me. Anyone ever have a similar experience?

apologies for the formatting on the pdf's my office skills are lacking, hopefully most will be able to decipher

Assuming from the pdf that your powder is Varget.
I have always gotten a slight more velocity with the Berger 80 VLD over SMK.
I've seen a lot of things that were stranger than fiction but this would be way to the top of the list. No one has asked yet but did you test the Bergers with the same lot of powder, primers and brass as the SMKs?

 

[Ccrider]

Which is more accurate?

 

[JimSC]

I've seen a lot of things that were stranger than fiction but this would be way to the top of the list. No one has asked yet but did you test the Bergers with the same lot of powder, primers and brass as the SMKs?

Positive on the Lapua Brass, Federal 205 primer, a maybe on the same lot of powder. Yesterdays came from a eight pound jug of Varget I bought last winter, problem is I don't remember when I finished the last jug. It may have been before or after I tested the Bergers . Even if it wasn't I am skeptical that a lot change could make that much difference. But who knows maybe it could, at the moment I am leaning toward the seating depth theory and that can be tested.

The plan for this weeks range session is load up 10 rounds with the Berger load which shot best at .075 off, then ten with the Sierra .075 off. Ten more of the Berger on the lands and ten of the Sierra on the lands. All cases will come from the same prep lot, all rounds loaded with 23.5 gns Varget which is the charge originally used as originally tested at during the seating depth test. Charges will thrown and trickled as close to exact weight as I can manage on a camera modded Lyman M5 balance

I will start with a clean bore and at 300 yards will shoot 2 foulers then do a five minute cooldown . Shoot 10 test rounds followed then a ten minute barrel cooldown. Repeat for the other three test groups

The scope setting when I left the range was set about 2.5 inches low to the aimpoint for the 23.5 charge with the SMK. Using the velocities I have I figure the Berger @ 2750 should hit about eight or so inches or 3.6 MOA higher assuming what velocities I have are accurate. This will shot over the chrono of course but if I do my part the target will tell the story and could reinstate faith in the chrono

 

[JimSC]

Update

Looks like it was a simple chronograph issue. Now I will be waiting for a good deal on the Labradar and the first time I catch it with at least 10% off I will purchase

yesterday I shot 4 sets of 5 rounds each all using 23.5 gns Varget and all 4 came out pretty much where they should have been. Groups and SD's were mediocre but this was the last shooting done after a 3 hour range session so the wind/mirage and fatigue were setting in and taking their toll.

I finished up with a 15 shot group of the SMK's seated at 1.958 and ended up with a 1 MOA group including 2 I missed a wind shift with, I was using a target cam and paid more attention to the wind flags after I noticed 2 off to the left and managed to finish up with a acceptable group