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The keyholing is the puzzle. A 12" twist isn't fast, but I would still expect it to handle the V-max OK. A 14" twist, like on a Triple-deuce, will see them opening up as compared to shorter bullets, I know from experience, but keyholing is pretty extreme.

I would want to check to be sure no copper ring is deposited in the bore. Those can squeeze a bullet down to the point it goes slightly eccentrically down the bore. It can also narrow one to the point it strips in the rifling and doesn't spin up properly. Both can cause keyholing.

Since the velocity is fairly high, it is necessary to watch out for core stripping. This is where the bullet is spun up so quickly the lead core slips inside the jacket. Such bullets are underspun at the muzzle as well as unbalanced, and can keyhole as a result. Bonded bullets and solid bullets generally won't do it and can provide some basis for a comparison to see if core stripping is the problem.

The OP might consider getting one of the Teslong borescopes. They are inexpensive and, while the one I have is not as sharp as my Hawkeye, it is more than good enough for over 95% of borescope inspections and the convenience of being able to save both stills and movies is a big boon when you want to share what you find with others. With 0.048" of throat advancement, the OP might discover the fire-cracked surface of the throat has chipped off on one side only and is unbalancing bullets. One can also look for a fouling ring with it. Useful tools.
 

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Always good advice.... but that generally doesn't make bullets go through the targets with oblong holes, as the OP reported ;)
Loose scopes/scope mounts won't account for oblong holes, but such things may still be a contributing factor to overall accuracy degradation. I cannot count the times I've experienced, observed, or heard of rapidly degrading accuracy in a rifle that consisted of MULTIPLE causes, each apparently trivial on its own. And I don't think I've EVER heard of a rifle losing its precision to just one factor, especially when it happens quickly.
 

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Yeah but it's hard to shoot bugholes, when the bullets aren't flying down range point-forward ;)
 

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Oblong bullet holes are usually caused by a wrinkle in the target or it not being straight up and down.
Assuming the crown is good, the scope and mounts are good, bedding is good and the ammo hasn't changed....look at the throat with a borescope. If it looks like this one, it might throw a flyer outside an inch every now and then, but still minute of rockchuck at 300yards. I'm betting your barrel is ok.
The one pictured thought it was a Swift (its 22-250 AI) and the owner shot at what he could see when he saw it. I've seen it smoking, but it's not (quite) 'shot out'.

the last picture is a barrel ruined with a cleaning rod. Brand new Kimber of Oregon. M82 Hornet
 

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The Hog Whisperer (Administrator)
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This thread reminds me of a problem I had with my .444 Marlin and the slow-twist (allegedly 1-38") micro-groove barrel. I got some 335 grain bullets from Marshall, which he said shot fine out of his Marlin with the same type of barrel. Try as I might, 6" - 8" groups were about all it could do. Finally, after staring at the target long enough, it dawned on me that not all of the holes were round!

I took a handful of those bullets and faced off about 0.050" from the nose, gently holding them in a 6-jaw scroll chuck. That got the weight down about ten grains, and just short enough that they shot a LOT better. The gun still has an issue throwing the first shot WAY high of a cold barrel, and I've about given up on that. Anyway.... my only conclusion was that my "1-38" twist barrel, wasn't quite the same rate of twist as Marshall's. I believe Marlin button-rifled those barrels, and twist rates are NOT absolute when doing that. If I ever get a bore-scope, I will try to figure out what the twist rate on that gun actually is.

An interesting test to the OP might be to file anywhere from 0.050" to 0.100" off the nose of some bullets and reshoot. Defects on the nose of the bullet aren't nearly the problem that defects on the base are, so just try to file them all reasonably close to the same. If that shrinks groups down from minute-of-pie-plate to something more reasonable, then stability is the issue.
 

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Sorry I got distracted a bit ago, and didn't get to finish my thought.

You never said what powders you've used to that point, or how you cleaned it; so this may seem a bit like fishing, but hang on a moment and we'll see.

Many powders, especially those that fall into the "extreme" lineup; have coatings. Those coatings, especially in small bored, tend to rapidly accumulate a row of fouling known as "Hard Carbon". Many cleaners don't adequately address it with normal cleaning. Old time Hoppes in particular, seems quite inadequate at addressing it. If any of this fits your usage patterns, then you may need to truly and aggressively clean your barrel. Get some aggressive or modern cleaners, and scrub the heck out of the barrel. Then switch to JB Bore paste, and REALLY go to town on it. If it is a hard carbon issue, you'll see tiny black bits show up in the paste. Then you'll really have your answer.

Cheers
Using carb cleaner with one end plugged barrel filed let soak for a good while then scrub with a good brass bristle brush wet with carb cleaner repeat as necessary.

Jim O
 

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This thread reminds me of a problem I had with my .444 Marlin and the slow-twist (allegedly 1-38") micro-groove barrel. I got some 335 grain bullets from Marshall, which he said shot fine out of his Marlin with the same type of barrel. Try as I might, 6" - 8" groups were about all it could do. Finally, after staring at the target long enough, it dawned on me that not all of the holes were round!

I took a handful of those bullets and faced off about 0.050" from the nose, gently holding them in a 6-jaw scroll chuck. That got the weight down about ten grains, and just short enough that they shot a LOT better. The gun still has an issue throwing the first shot WAY high of a cold barrel, and I've about given up on that. Anyway.... my only conclusion was that my "1-38" twist barrel, wasn't quite the same rate of twist as Marshall's. I believe Marlin button-rifled those barrels, and twist rates are NOT absolute when doing that. If I ever get a bore-scope, I will try to figure out what the twist rate on that gun actually is.

An interesting test to the OP might be to file anywhere from 0.050" to 0.100" off the nose of some bullets and reshoot. Defects on the nose of the bullet aren't nearly the problem that defects on the base are, so just try to file them all reasonably close to the same. If that shrinks groups down from minute-of-pie-plate to something more reasonable, then stability is the issue.
This is a problem the big bore BP guys have also with faster twist barrels. There is a huge discussion over on the Shiloh forum about this maybe step over there and check it out. The conscientious is faster twist and MV longer lighter bullet for good BC. Nose shape is important too.

Jim O
 

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That should produce fliers, but not keyholing. Some else is afoot here.
 

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The keyholing is the puzzle. A 12" twist isn't fast, but I would still expect it to handle the V-max OK. A 14" twist, like on a Triple-deuce, will see them opening up as compared to shorter bullets, I know from experience, but keyholing is pretty extreme.

I would want to check to be sure no copper ring is deposited in the bore. Those can squeeze a bullet down to the point it goes slightly eccentrically down the bore. It can also narrow one to the point it strips in the rifling and doesn't spin up properly. Both can cause keyholing.

Since the velocity is fairly high, it is necessary to watch out for core stripping. This is where the bullet is spun up so quickly the lead core slips inside the jacket. Such bullets are underspun at the muzzle as well as unbalanced, and can keyhole as a result. Bonded bullets and solid bullets generally won't do it and can provide some basis for a comparison to see if core stripping is the problem.

The OP might consider getting one of the Teslong borescopes. They are inexpensive and, while the one I have is not as sharp as my Hawkeye, it is more than good enough for over 95% of borescope inspections and the convenience of being able to save both stills and movies is a big boon when you want to share what you find with others. With 0.048" of throat advancement, the OP might discover the fire-cracked surface of the throat has chipped off on one side only and is unbalancing bullets. One can also look for a fouling ring with it. Useful tools.
Have you changed bullet weight? I have a 244 Remington with a 1:12 twist anything over 90 grains starts to keyhole on me. Loves 70 grain.
 

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Have you changed bullet weight? I have a 244 Remington with a 1:12 twist anything over 90 grains starts to keyhole on me. Loves 70 grain.
That is pretty much why Remington reintroduced the cartridge as the 6mm Remington. It was the same physical cartridge, but the rifles used a 1:9 twist in the barrels. Winchester pretty much ate Remington's lunch because of this as the 243 Win. with a 1:10 twist would stabilize bullets over 90 grains. I think Remington would have ended up with a bigger share of the .243 caliber market had they not made this fatal mistake. I have a 6mm Rem. and really like the cartridge, but I primarily shoot 75 gr. hollow points for varmint hunting.
 

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I inherited a 40x in 244 Remington. I load 70 grain for target shooting. It came from the factory with a target using 73 grain C. Hollidge bullets ( custom no longer exist) It is fun to shoot and very accurate. Although my Ruger in 6mm does give it a run for the money at less the fanfare. The Ruger likes 90 grain.
 

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If you read post #1, the tumbling bullet is a 52-grain Berger. It is long for its weight, at about 0.72", but while the longer 52-grain Hornady V-max (0.8") would be on the edge of stability with a 12" twist, the Berger should be OK with that. Something's up.

The only other thing it occurs to me would be to check for muzzle funneling. Take a pure lead slug and tap it just a quarter of an inch into the muzzle, withdraw it and measure across the lands with a micrometer to see if it is possible it has widened much beyond 0.224" across the lands there. If it has, cut an inch off and recrown.
 
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My 244 will actually shoot the Speer 105 gr. RN okay, but not lights out. The old style 95 Nosler Partition shoots okay too. 80 gr. Barnes are wonderful...it shoots great out of my Ruger 6mm too. I'm out of those old partitions...I gave away a bunch when I thought I was done with reloading/shooting. The 100 gr. in the 244 was always no-bueno.
 
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