Help! Velocity and target interpretation ... Chrony? Reloads? Heat?

[Tikka223]

Perhaps some folks can use their wisdom to help me sort through a problem.

I was shooting today with a T3 CTR in .308 shooting Federal GMM and some reloads:

Lapua brass, full length sized with a Redding die
CCI BR2 primers
Hornady 178gr ELDX
OAL of 2.85”
44.0gr Varget

Shooting over a Shooting Chrony to get some velocity data for my Kestrel.

Kestrel weather data was as follows:

30’C, 35% humidity, 14.5’C dew point, 999mb, 782m density altitude. It was hot!

Federal ammo velocities were as follows:

2894
2572
2842
2851
Err1
2858
2889
2871
2860
2880

178gr ELD-X was as follows:

2647
2644
2672
2658
2692
2679
2712
2594
2574
2588
2694
2672
2731
2584
2826
3236
2598
2600
2620
2615

What’s with the crazy extreme spread????? Can I trust my Chrony? Is there a problem with my handloads? Was the heat throwing things off?

For handloads, I individually weigh each charge on an RCBS 10-10 balance beam. I am quite careful about consistent charge weight. I do find neck tension to be a bit inconsistent with my Lapua brass but they have all been full length sized.

I noticed that the velocity numbers started spiking when the barrel was getting hot but a quick good search suggested a hot barrel may lower velocity. I was also trying to keep my ammo shaded.

Any idea what’s going on here?

Here is my target with the Federal and Hornady groups. It was a bit windy and I wasn’t trying to be super accurate, I was more focused on gettin velocity data. This gun can pass the 10 shot at 300m MOA challenge with the exact same load but clearly I wasn’t doing my part today.





As you can see from the data set, the numbers have terrible consistency, even if I remove velocities above 2700fps.





Any ideas about what is going on here?

 

[Cameron SS]

Did you have a lot of intermittent cloud cover?

 

[Tikka223]

Some but it was mostly sun.

 

[Tikka223]

I did get Err1 quite frequently but it still showed a velocity. No idea why that was happening either because I was shooting across the Chrony consistently.

 

[mikeelliot]

I would think something to do with the chrony here... i would hope anyway. I would think 600fps difference you would see noticeable variance in POI and pressure/ bolt lift signs

You would have to hammer your bolt open on a 3200 fps 178gr load...you can't get enough varget in the case for 3200 fps

 

[just having some fun]

How many feet from muzzle to chrony ?

I try to do 15 feet min

At 10 ft i have had High readings from muzzle blast

 

[Janeau]

44 grains of Varget behind a 178 is over max based on the Sierra manual. Max is 43.8 with a 175 SMK.
Were did you get that load from ? Did you work it out from lower ?
Like others have pointed out, I would not trust that Crony data.
For how long have you been reloading ? Once fired brass or new ? Bushing sizing die or standard ? What is you neck tension ?
How do you measure your powder ? Any inconsistency in your reloading equipment or method will show big time in data.

 

[yodave]

crony might be reading a shadow, you might need cardboard pulled over the screens to shade the unit, how fresh was the battery in the crony??

 

[Airgunnr]

Why dont you borrow someone's chrony and compare the numbers to your own? That way you can eliminate the most likely cause of your wild numbers. Just a thought.

 

[Lukrative]

Highly recommend Magnetospeed chronograph, would eliminate a ton of variables.
The 'sporter' version can be had for less than $300.

 

[Tikka223]

I would think something to do with the chrony here... i would hope anyway. I would think 600fps difference you would see noticeable variance in POI and pressure/ bolt lift signs

You would have to hammer your bolt open on a 3200 fps 178gr load...you can't get enough varget in the case for 3200 fps

My thoughts exactly. There was no noticeable difference in recoil, bolt lift or primers for any of those shots. I inspected the fired case for the the 3200fps shot and it was normal.

 

[Tikka223]

How many feet from muzzle to chrony ?

I try to do 15 feet min

At 10 ft i have had High readings from muzzle blast

The Chrony was exactly 10’ from the muzzle. The muzzle does have a Heathen brake on it so maybe there is some sort of effect. The instructions say 10 feet. I suppose the velocity drop over the extra 5’ (if placed at 15’) would be insignificant.

 

[Tikka223]

44 grains of Varget behind a 178 is over max based on the Sierra manual. Max is 43.8 with a 175 SMK.
Were did you get that load from ? Did you work it out from lower ?
Like others have pointed out, I would not trust that Crony data.
For how long have you been reloading ? Once fired brass or new ? Bushing sizing die or standard ? What is you neck tension ?
How do you measure your powder ? Any inconsistency in your reloading equipment or method will show big time in data.

I worked up to this load. If I remember correctly I started at 42gr and went up .5gr at a time until I noticed pressure signs at 44.4gr. As I mentioned, this load has been accurate in the past.

I know the target isn’t impressive but there was quite a bit of mirage and I wasn’t shooting for group size.

 

[Tikka223]

crony might be reading a shadow, you might need cardboard pulled over the screens to shade the unit, how fresh was the battery in the crony??

I had the plastic sun shade installed because of the sun. The battery could be getting old. I can try swapping that out. The sun was quite high in the ski, I was shooting at 2pm, so there is a chance it was shining into the sensors.

 

[Tikka223]

Why dont you borrow someone's chrony and compare the numbers to your own? That way you can eliminate the most likely cause of your wild numbers. Just a thought.

Yeah I’d like to. Would be especially nice to compare to a Labradar or magnetospeed.

 

[Tikka223]

Highly recommend Magnetospeed chronograph, would eliminate a ton of variables.
The 'sporter' version can be had for less than $300.

I wouldn’t mind trying one but from the videos I’ve seen, they seem a bit finicky when it comes to the installation. Labradars are quite a bit more expensive but I think I’d lean more towards one of them.

 

[Janeau]

The max velocity for the .308 with a 175 is listed at a MAX 2700. There is no way you can push that 178 to 3200. And the majority of your data show around 2650-80.

Time for a new Chrono..

 

[Cameron SS]

The max velocity for the .308 with a 175 is listed at a MAX 2700. There is no way you can push that 178 to 3200. And the majority of your data show around 2650-80.

Time for a new Chrono..

Not sure if its the chrony itself but there is definitely some interference.

I can get 3200 FPS with a 175 gr bullet, but I am doing it with a custom 300 WSM and a 30" barrel.

 

[Tikka223]

For reference, the rifle shot this group on May 14 with the same brass, bullet, and load:



It was even windier that day.

 

[Potashminer]

Curious - first post was shooting a 308; last post has picture says it is a 223??