Chronograph Procedure — Help?

[Brydawg512]

Hello,

I am trying to trace down a potential issue experienced today with my Magnetospeed Sporter chronograph.

As background - new custom rifle. It's a 300 WM with 26" barrel. I had the builder develop a load using 215 Berger Hybrids.

The builder chrono'ed 3 shots, with a High of 2945 FPS and Low of 2937.
So, I chrono'ed today, after shooting approximately 14 rounds, gun was warm and I didn't allow for cooling time, as I probably should have.

Here were my results from my 5 chrono'ed shots:
1: 2861
2: 2857
3: 2846
4: 2871
5: 2826

My questions:
1) Would a heated up gun cause this drastic different in MV, ES and SD?

2) Should I re-chrono with a cold rifle?

3) Is it possibly the chronograph?

I am not a highly skilled shooter by any means, but my 5 shot group at 100 yards was 3/4", if that add any value to the discussion.

Thank you.

 

[Koda_]

1) probably will contribute
2) yes
3) no.

IMO you should have at least 10 rounds chronoed to measure ES/SD. Did you chrono at the same range your gunsmith did?

 

[Brydawg512]

1) probably will contribute
2) yes
3) no.

IMO you should have at least 10 rounds chronoed to measure ES/SD. Did you chrono at the same range your gunsmith did?

Thank you. Yes, after some additional reading online, it sounds like 10 is the proper round count so will definitely need to redo.

I did not chrono at the same range as my gunsmith.

I do understand as well that the roughly 800' elevation distance between our chrono could play a role?

My main concern is with the ES/SD values being as large as they are.

 

[Koda_]

I did not chrono at the same range as my gunsmith.

A difference in altitude and weather might cause the 89fps difference in velocity. The difference in Chronographs might be +/-25fps maybe. I dont know if I would stress over 89fps

 

[Brydawg512]

A difference in altitude and weather might cause the 89fps difference in velocity. The difference in Chronographs might be +/-25fps maybe. I dont know if I would stress over 89fps

Fair enough point you bring up.

Now as for the ES and SD numbers, is this likely a heating issue with the barrel or leaving the round in the chamber for 10-15 seconds before shooting?

I did notice my MV trended downward, with the exception of my 4th shot

 

[Koda_]

Fair enough point you bring up.

Now as for the ES and SD numbers, is this likely a heating issue with the barrel or leaving the round in the chamber for 10-15 seconds before shooting?

I did notice my MV trended downward, with the exception of my 4th shot

That i dont know, not certain there would be any way to validate that. I wouldnt compare your 5rd ES to your smiths 3rds.... (your first 3 rds were only 15fps ES. ).
I would start over, shoot 10rds cold bbl and go from there. If your ES is higher than 30fps it might be worth finding out why. Sub moa groups arent bad though, you might just call it good...

 

[Brydawg512]

That i dont know, not certain there would be any way to validate that. I wouldnt compare your 5rd ES to your smiths 3rds.... (your first 3 rds were only 15fps ES. ).
I would start over, shoot 10rds cold bbl and go from there. If your ES is higher than 30fps it might be worth finding out why. Sub moa groups arent bad though, you might just call it good...

Copy that.

Final question..

When I go to re-chrono, should I wait enough time between each individual shot to allow for the barrel to cool?

Thank you for all of your insight.

 

[Tommo64]

Copy that.

Final question..

When I go to re-chrono, should I wait enough time between each individual shot to allow for the barrel to cool?

Thank you for all of your insight.

I would definitely do that. If you want reliable data, you need to eliminate as many variables as possible, including your barrel temperature, which is bound to affect your velocities.

 

[Bang4theBuck]

Also be sure that the temperature of your ammo is closely managed for consistency. Here are things that can affect temperature of ammo which can affect velocity, depending on powder:
1. As mentioned above, loading a round in the chamber and leaving it in there for more than the amount of time it takes to get in target and pull the trigger.
2. Loading from a magazine when the rifle is hot. Ammo hests up by convection/proximity to heat from barrel. I always single feed when doing load development. I recommend you do this.
3. Letting ammo sit in the sun. Keep it in the shade or covered.
4. Differences in powders and powder lots within the same powder type. You never said what powder the cartridges were loaded with that would be good to know.

Good news is you are already in the 'pretty darn good range' for velocity with a 215, ES, and accuracy. Practice with technique and some of the other things above, including reloading fireformed brass might really get your into the sweet spot without much more effort.

Keep us posted.

 

[PApa Black]

1) probably will contribute
2) yes
3) no.

IMO you should have at least 10 rounds chronoed to measure ES/SD. Did you chrono at the same range your gunsmith did?

I agree with Koda!!

 

[PApa Black]

Hello,

I am trying to trace down a potential issue experienced today with my Magnetospeed Sporter chronograph.

As background - new custom rifle. It's a 300 WM with 26" barrel. I had the builder develop a load using 215 Berger Hybrids.

The builder chrono'ed 3 shots, with a High of 2945 FPS and Low of 2937.
So, I chrono'ed today, after shooting approximately 14 rounds, gun was warm and I didn't allow for cooling time, as I probably should have.

Here were my results from my 5 chrono'ed shots:
1: 2861
2: 2857
3: 2846
4: 2871
5: 2826

My questions:
1) Would a heated up gun cause this drastic different in MV, ES and SD?

2) Should I re-chrono with a cold rifle?

3) Is it possibly the chronograph?

I am not a highly skilled shooter by any means, but my 5 shot group at 100 yards was 3/4", if that add any value to the discussion.

Thank you.

After developing a load and chrono-ing it; I then shoot a 500 yds and 700 yard drop to verify the FPS.

 

[Tiny Tim]

Agree with all the above. Let you barrel cool between shots.

Only time I rapid Fire is three shots to check poi shift for the sake of knowing if the rifle will string.

Also, I generally take my chronograph with every time I shoot. I record the data and over time I have much better statistical data and can trend barrel degradation. I'm no where near where I want to be, but getting better, thanks to the many helpful members here.

 

[Rick Richard]

Appears to me that you may need a different load recipe if you want to get down into the single digit numbers. Now begins the tedious process and expense of chasing accuracy.

 

[cajun]

So did you reload the ones you shot or did the builder?