Keyholing with a new barrel

[Jerald]

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?

 

[rwj]

Post picture(s) of the crown…

 

[K22]

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.

 

[DShortt]

What powder and charge weight and what range distance?

 

[swd]

Bore scope it and see if the throat is rough and check the crown. I would also check the actual twist rate.

 

[Dave Way]

Second on checking the twist rate.

Dave.

 

[Tommie]

First try some shorter/lighter bullets. Like 100 grain. If those keyhole then you have a barrel quality issue. Otherwise it sounds like incorrect rifling twist.

 

[gme]

had that happen here once, a 6mm blank stamped as 8 twist (from a big name barrel maker) keyholed right from the start, turned out it was a 13

 

[tommeboy]

twist or bore size. Crown will not make it keyhole unless it is deeply damaged into the bore. An oversized bore will make the bullet act like the twist it too slow as it can not grab the bullet enough.

 

[cb186]

twist or bore size. Crown will not make it keyhole unless it is deeply damaged into the bore. An oversized bore will make the bullet act like the twist it too slow as it can not grab the bullet enough.

Maybe its a 6.5 barrel.

 

[fisherman987]

Twist is too fast, 8 would be better

 

[ChrisNZ]

An overly quick twist will -prevent- keyholing, not cause it.

 

[Fast14riot]

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.

 

[fkimble@charter.net]

McGowen blank, chamber cut by a gunsmith or a McGowen cut chamber? Call the seller get your money back.

Frank

 

[243winxb]

All keyholing

Oversize barrel groove diameter?

 

[Fuj]

An overly quick twist will -prevent- keyholing, not cause it.

This is correct. The only thing a faster twist for a shorter bullet will
cause, is a blow up when speed is chased. Possibility that the barrel
was lapped and the last inch or so was not cut off before crowning.
Also crown not cut square.

 

[urbanrifleman]

Mis marked barrel.

I did that once.

None of those other things will make a bullet hit the target sideways. It's the wrong twist.

 

[DShortt]

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.

 

[gunsandgunsmithing]

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.

 

[dellet]

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.