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Keyholing with a new barrel

25 creedmoor 1 in 7 twist. 26 inch. A round 30 shots , all keyholed. 133 berger , 117 sst,and 117 round nose bullets. All keyholing. Brass looks normal
But the crowd looks rough. I'm no machinist. And it's a McGowen barrel. Any suggestion?
 
The condition where I have observed keyholing were:

1. Bullet without enough length for the twist, i.e. twist to fast for the short bullet, e.g. 7" twist 223 Rem loaded with 50 grain bullets.

2. Damage crown (severe effort that you could see the damage with the naked eye).

But I am not a gunsmith nor am I an expert, just reporting what I have observed in other shooter's equipment over many years of shooting at various ranges.
 
Bore diameter should be .250" easy enough to check with the tail of a quality drill bit (a 6.5 barrel has a .257" bore) Measure twist rate, too.
 
Might be a velocity problem if it's an extremely light charge and barely clearing the barrel. Need velocity to stabilize so the bullet RPM is sufficient for the twist rate. Hence my questions in post #4.
 
Check the twist rate with a cleaning rod. Easy to get very close. Just make a lengthwise mark on a cleaning rod. You'll need a couple more marks, one where it starts down the bore with the long mark at top and another where it ends with one complete revolution of the rod while pushing it down the bore. Then mark and measure between the two marks. The distance is the rate of twist. Hope that's clear enough. 1 revolution in x amount of inches(between your marks) A bore guide helps.
 
Unless the twist ends up being slower than 1/12, there’s more going on than twist. The 117 round nose is perfectly fine in a 1/12.

Might even get by with a 1/14 at 3000 fps since it’s a flatbase. A quick look and McGowen offers a 1/14, so anything is possible.
 

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