Pressure or Temp zones destabilize bullet or something else

[Vivacious Stallion]

So the other day I was out shooting in the afternoon (Central Texas) and all my reloads were seemingly performing well. I had initially shot some 5 shot groups at 100m to get the zero reset after changing scopes. Then I shot on a mini IPSC steel at 300 and 400 to finish. I was observing <2" groups on my 400m steel. I also had my girlfriend shoot at 400 and she had similar results to mine. As I was wrapping up I decided to shoot some groups at 300m on paper to measure drop. At this time the sun had gone down and temperature was starting to drop. It had been 69 degrees during the middle of the day but I could feel the temp dropping pretty quickly with the sun going down. As I went out to retrieve my target at 300 which was down hill towards a low area I walked through at least 6 different bands of noticeably hot and the cold air flows. They felt like 15 or more degrees in difference between one another. After I got to my target I saw that I had keyholing on the first group and then destabilized marks on the second group. I will place pictures below for reference.

My question for readers: Is there a a plausible explanation for this occurrence? Can these temperature bands have influenced the stability of the projectile? Obviously I am going to go and reshoot the ammo this week on paper at 300 & 400m to insure the loads are performing correctly, but I have not noticed them to be performing strangely before this. I am not an extremely experienced reloader, however, I do not quite know what's going on here.

The rifle:
Tikka Tac A1 24" barrel
~2900 rounds on it
1:8 twist
Silencerco Hybrid on DA keymo-not removed during shooting

The load:
Hornady once fired brass
CCI #34 primer
Hornady 147gr ELDM
42.8gr Staball 6.5 powder
COAL-2.800"

The right keyhole group was shot first, and the left second. Point of aim were the top small targets above each respective group.

 

[Txshooter3]

I don't see any "keyholing".

 

[6.5SH]

So given low light are you sure you had a clear path to the target? Looking at the other groups I'd say you clipped some brush.

 

[Steel head]

My first suspect?
That Hornandy 147!

I quit using them because they were doing wonky stuff.

 

[Vivacious Stallion]

I don't see any "keyholing".

???

 

[Vivacious Stallion]

So given low light are you sure you had a clear path to the target? Looking at the other groups I'd say you clipped some brush.

I am almost certain. But I suppose that I could have made a mistake. The 300m meter target was shot in the same lane as the 100. This is of course a possibility though. Can brush/grass delfect it that much?

 

[BCX]

I’m surprised people are still shooting the Hornady 147. We had similar results w keyholing and gray puffs of smoke at longer ranges. Get yourself some Berger or Sierra bullets, problem solved

 

[mtang45]

I don't see any "keyholing".

Look below the last target in the cardboard

 

[Vivacious Stallion]

My first suspect?
That Hornandy 147!

I quit using them because they were doing wonky stuff.

What issues did you have? I've heard that they don't take PRC speeds well but I'm not generally that on 6.5 creedmoor.

 

[BCX]

Plenty of guys posted bullet issues at 6.5 CM speeds. This has been going on since 2019

 

[Steel head]

I was having blow ups, hokey holes and mystery fliers.
All at 260 speeds.
Had excellent results with them ran out of lot lot and new lots started misbehaving.

 

[Steel head]

Plenty of guys posted bullet issues at 6.5 CM speeds. This has been going on since 2019

Yep
That was when i started having issues.

 

[Vivacious Stallion]

Plenty of guys posted bullet issues at 6.5 CM speeds. This has been going on since 2019

Interesting. Has there been any consensus as to why? I had previously loaded the 140 eldms and never saw any issues. But I am only now seriously getting into reloading for rifle.

edited for grammer

 

[BCX]

Hornady guess I wasn’t bat shit crazy when I called to discuss your bullets having issues

 

[Vivacious Stallion]

I was having blow ups, hokey holes and mystery fliers.
All at 260 speeds.
Had excellent results with them ran out of lot lot and new lots started misbehaving.

Strange, I'll be interested to shoot the remaining ones I have loaded further out on a larger backing board. They seemed promising when I started out and they definitely impact the steel more that the 140s I was shooting previously.

 

[BCX]

Interesting. Has there been any consensus as to why? I had previously loaded the 140 eldms and never saw any issues. But I am only now seriously getting into reloading for rifle.

edited for grammer

Give Hornady a call! They will happily tell you, it’s the first they have heard of these issues

 

[Vivacious Stallion]

Give Hornady a call! They will happily tell you, it’s the first they have heard of these issues

Lol, maybe I will if I have time this week. I'll probably just standardize on Sierra MKs, I already use them for my LMT anyways.