6.5 Creedmoor keyholing

[wombat13]

I was at the range recently and for the first time saw keyholing. A fellow shooter was firing the 143 gr Hornady ELD-X Precision Hunter ammo from a Thompson Center Compass rifle and every shot keyholed. In fact, the holes were perfect profiles of the bullet!

Anyone know how long that bullet is? The load obviously wasn't stable, but Berger's online stability calculator indicates the load should be stable as long as the bullet is under 1.6" long.

If anyone is interested, here is the online calculator and the parameters I used, all taken from Hornady or Thompson Center website:

http://www.bergerbullets.com/twist-rate-calculator/

BC: .621
Caliber: 6.5
Weight: 143 gr.
Length: 1.5" (guess, because Hornady website doesn't list the bullet length)
MV: 2,650 fps (Hornady ammo show 2,700 fps, but the TC barrel is 2" shorter than the test barrel)
Twist: 8"
Temp: 35F
Altitude: 400 ft.

 

[ATLDave]

Did he measure the actual twist rate? Nominal twist and actual twist are not always the same.

 

[joed]

Creedmoors seem to have a fast twist, my guess is either the barrel is shot out or the person is shooting very light loads.

 

[wombat13]

Did he measure the actual twist rate? Nominal twist and actual twist are not always the same.

He did not measure the twist. We are assuming it is 1:8 because that is what Thompson Center claims.

 

[wombat13]

Creedmoors seem to have a fast twist, my guess is either the barrel is shot out or the person is shooting very light loads.

It was a brand new rifle, so it shouldn't be shot out. He was firing factory Hornady ammo.

 

[ATLDave]

He did not measure the twist. We are assuming it is 1:8 because that is what Thompson Center claims.

I would measure it... at the very least, you eliminate that as an explanation.

 

[joed]

It was a brand new rifle, so it shouldn't be shot out. He was firing factory Hornady ammo.

Wow, that really sounds weird. I gave my best guess on causes.

 

[ridgerunner1965]

there is some kind of monkey business going on inside that barrel.

 

[wombat13]

Wish I knew the guy so I could find out if he solves the problem. I suggested he try a lighter bullet to see what happens.

 

[Llama Bob]

Either the twist or velocity is lower than you think or the air pressure is higher.

 

[Blue68f100]

What does the crown on the barrel look like? Damaged???

Have you determined how much free bore the chamber has? Most ELD's are not jump sensitive.
May want to do a casting of the chamber and see if it's actually within spec's. You may have a 260 Rem but you would notice that on the fired brass as it was reformed.

 

[wombat13]

Its not my rifle and I don't know the man who was shooting it. I'm interested in this issue because I've been wondering how reliable this Berger calculator is. I had poor accuracy in a .25-06 with all bullets 110 gr. and heavier. The Berger calculator indicates marginal stability for those loads.

Anyway, in this case the shooter just showed me the target, the rifle, and the box of ammo and asked if I knew what was happening. All I can say is that the rifle appeared brand new as he claimed and the barrel was marked 6.5 Creedmoor. The box of ammo was the 143 gr. Hornady ELD-X Precision Hunter. The target showed keyholing on every shot, not just poor accuracy.

It's interesting playing with the Berger stability calculator. The stability is most sensitive to barrel twist and bullet length. Small changes in either yield large changes in the calculated stability. Even large changes in velocity barely affect the calculated stability.

Does anyone know the bullet length of the 143 gr. ELD-X? Hornady doesn't publish that.

 

[ArchAngelCD]

Sometimes what looks like really isn't. I have personally seen paper targets with no backing support look !like the bullet is tumbling but in reality the paper is moving as it's hit giving that appearance. Granted, I see that mostly with handgun ammo but it's still a possibility.

 

[Varminterror]

Google JBM bullet length list. You’ll find it.

It’s 1.440”

 

[Llama Bob]

Be aware that the Berger calculator will be unduly pessimistic for tipped bullets and flat base bullets. For the ELD you probably need to take the better part of 0.1" off the length to get an accurate result.

 

[LoonWulf]

wrong dia barrel installed and chambered......no rifling....something like that....

Not likely, but it would be something id check.

 

[blue32]

The center of gravity on those bullets could be off. I've shot a lot of Hornady bullets in component form and have never had a problem but there's always a first time.

 

[jmr40]

The gun has issues, but it isn't barrel twist. The 143ELDX's have EARNED a solid reputation for excellent accuracy since being introduced. And I've never seen a factory production 6.5 CM that didn't have a 1:8 twist. The biggest difference between 260 and 6.5 CM is the barrel twist. The primary reason to choose 6.5 over 260 is to get an 8 twist barrel designed to shoot 140-147 gr bullets.