ak454
.240 Incinerator
Posts: 17
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Keyholing
Sept 6, 2020 19:08:45 GMT -5
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Post by ak454 on Sept 6, 2020 19:08:45 GMT -5
Tried some Grizzly Cartridge 357 200gr hard cast ammo today. It was keyholing at 10yds. I assume the bullet is to long for the S&W twist rate. I'll get some 180gr ammo next if it ever becomes available.
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Post by bradshaw on Sept 6, 2020 20:39:19 GMT -5
Tried some Grizzly Cartridge 357 200gr hard cast ammo today. It was keyholing at 10yds. I assume the bullet is to long for the S&W twist rate. I'll get some 180gr ammo next if it ever becomes available. ***** ak454.... Lack of detail allows only sketchy response. TwistSmith & Wesson twist for .357 Mag is 1:18-3/4”. I haven’t heard of an exception. The N-frame Model 27 & M-28, K-frame M-19, along with stainless counterparts use 1:18-3/4”, as do L-frames and J-frames of my acquaintance. The M-27, notably with 8-3/8-inch barrel, enjoyed success in IHMSA silhouette, usually with 180 grain cast or jacketed bullets. A few shooters cast 200 grain bullets and to my knowledge didn’t have keyholing. My J-frame Model 640 Centennial with 2-1/8” barrel shoots well @ 100 yards with the Federal #357G 180 JHP. I’ve been meaning to try the cast, POWDER COAT Bradshaw-Martin 194 SWC Gas Check The Dan Wesson Arms Model 15 has 1-18-3/4” twist, and shoot very well in silhouette with 180 grain bullets, including the long Speer .358 Flat Point, made for rifles. I tried a pair of Hornady .358 rifle bullets in an 8-inch Colt python, the 200 Round Nose and 200 Spire Point. To fit the Python cylinder, I deep seat the RN and SP in .38 Special brass, and even trimmed .38 cases. Deep seating little room for 296/H110. Without being able to drive the bullets----to do so put the forcing cone a severe risk of cracking----I stopped the experiment for a “ram load.” The Python 1:14 twist had ne problem stabilizing the 200 Round Nose, but it looked like the 200 Spire Point was on the wire edge. Providing the revolver barrel has uniform bore & groove, a bullet which keyholes may be too long for the twist, or too loose for the groove diameter. I would be very reluctant to blame your keyholing on a lousy forcing cone. Bullet recoveryWith your bullet keyholing so close to the muzzle, penetration will be poor. Thus, by lining up 8 gallon plastic jugs----filled with water----you should be able to capture a fired bullet. Boards laid to either side of the line of jugs will help capture a bullet that escapes out the side of a jug. A close look at the recovered bulet will contain clues. If engraving of rifling is symmetrical front to back and all around, chances are the twist is as you surmise: too slow. If engraving on the bearing surface is deeper on one side than the other, chances are the bullet is skinny for the groove. David Bradshaw
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ak454
.240 Incinerator
Posts: 17
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Keyholing
Sept 6, 2020 23:20:20 GMT -5
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Post by ak454 on Sept 6, 2020 23:20:20 GMT -5
Thanks for all that info Mr Bradshaw. I was shooting a 686 plus with a 3" barrel. Thought this ammo would work for winter snowshoeing if a moose is on the trail. But not if it keyholes. I will try some 180 gr if I can find some or I will just carry a big bore revolver.
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Post by x101airborne on Sept 7, 2020 11:46:07 GMT -5
Is it possible the depth of the rifling in the barrel could be shallow and allowing the bullet to skid? I dont know, it is just something to check. A recovered slug should show some evidence.
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Post by 98redline on Sept 14, 2020 11:20:43 GMT -5
My understanding is that the ability of a bullet to stabilize is based on the actual spin rate of the bullet, not necessarily the twist of the barrel.
In other words a shorter barrel would need a faster twist in order to stabilize a bullet similarly as a longer barrel that has a significantly higher muzzle velocity.
I don't think the short 3" barrel of the 686 is doing you any favors here.
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Post by bradshaw on Sept 14, 2020 16:51:32 GMT -5
My understanding is that the ability of a bullet to stabilize is based on the actual spin rate of the bullet, not necessarily the twist of the barrel. In other words a shorter barrel would need a faster twist in order to stabilize a bullet similarly as a longer barrel that has a significantly higher muzzle velocity. I don't think the short 3" barrel of the 686 is doing you any favors here. ***** Twist sets up spin rate. A .357 bullet fired through a 2-1/2” twist and an 18-3/4” twist rotates the same amount per foot of travel. To spin the bullet faster it must be driven faster.... much faster. A small increase in spin equals a much larger increase in velocity. The higher the ballistic coefficient, the smaller the window for twist. David Bradshaw
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Keyholing
Oct 5, 2020 19:37:07 GMT -5
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Post by Alaskan454 on Oct 5, 2020 19:37:07 GMT -5
I have experienced keyholing with undersized bullets and suspect you might want to check your bullet, throat, and bore sizing.
I'd be hard pressed to think your bullet weight or length alone is the problem at 200 gr. I've shot tens of thousands of slow, long bullets through different revolvers with varying dimensions. Several that "shouldn't" shoot well still ring steel out to 150 yards. Those with poor dimensions have shot sideways at 5 yards.
Generally I've seen this with bullets sized. 001" or more under groove diameter, or throats sized small enough the bullet swages down that small. Worst offender was .451-.452" into a .454" throat and .453" groove. Point blank they shot sideways.
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Post by ss30378 on Oct 8, 2020 11:13:08 GMT -5
I've had the same keyhole issues with undersized bullets not getting a good bite on the rifling. Twist and velocity may be an issue, I've run into that when pushing longer for caliber bullets, especially in rifle rounds with heavy match bullets.
At 1000fps muzzle velocity with your twist the bullet starts off at 38400rpm At 1200fps muzzle velocity with your twist the bullet starts off at 46080rpm
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Post by boolitdesigner on Oct 8, 2020 13:22:08 GMT -5
Twist sets up spin rate. A .357 bullet fired through a 2-1/2” twist and an 18-3/4” twist rotates the same amount per foot of travel. To spin the bullet faster it must be driven faster.... much faster. A small increase in spin equals a much larger increase in velocity. The higher the ballistic coefficient, the smaller the window for twist. David Bradshaw The above in bold must be the new physics they teach on computers in what they call school now. The following is off the Berger bullets site: Twist rate refers to the rate of spin in the rifle barrel, and is represented in inches per turn. Notice the inches per turn part.........................
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Post by bradshaw on Oct 8, 2020 16:49:17 GMT -5
Twist sets up spin rate. A .357 bullet fired through a 2-1/2” twist and an 18-3/4” twist rotates the same amount per foot of travel. To spin the bullet faster it must be driven faster.... much faster. A small increase in spin equals a much larger increase in velocity. The higher the ballistic coefficient, the smaller the window for twist. David Bradshaw The above in bold must be the new physics they teach on computers in what they call school now. The following is off the Berger bullets site: Twist rate refers to the rate of spin in the rifle barrel, and is represented in inches per turn. Notice the inches per turn part......................... ***** Permit me to clarify: meant to say: Rotation of a .357 bullet fired through 1:18-3/4” twist is the same regardless barrel length. Higher velocity raises rpm----but not degrees of rotation per foot of travel. RPM is increased by 1) raising velocity, or 2) tightening twist. Velocity is a very inefficient substitute for twist. David Bradshaw
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Post by boolitdesigner on Oct 8, 2020 18:02:04 GMT -5
Good clarification.... it reads correctly now.......... Thanks
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Post by bradshaw on Oct 9, 2020 15:25:27 GMT -5
Would like to learn what makes projectiles so accurate out of smoothbore tank guns. Projectile must be self-stabilizing. Elimination of rifling aids search to increase velocity. Roy Weatherby worked in this area. Also, I believe Weatherby put slow twists in some of his rifle to increase velocity. Dick Casull told me “for my .454, 1:24” is the most a accurate.” I didn’t challenge Dick, but consider his statement cushioned by the greater tolerance of revolver pumpkin balls for variations in twist. What Dick Casull didn’t say, is that by slowing the twist of is .454 Casull he stood to gain velocity. These numbers have significance when you try to break the 2,000 fps barrier with a big bore revolver.
We heavily considered 1:14 for the Ruger .357 Maximum. Certainly, prospects for stabilizing a pointed heavy .357/.358 bullet. For a new .357 Maximum I favor 1:14. That said, the cast powder coat Bradshaw-Martin 194 SWC GC holds remarkable stability from the 1:16 Ruger in testing thus far, shooting under 5-inches @ 200 yards with iron sights. And tracking pretty damn straight thereafter through snow @ 300+ yards, having punched through 1/2” plywood @ 200. Barriers detract from subsequent accuracy, yet a bullet really ON AXIS may continue to track straight. While a bullet arriving on target with any yaw at all deteriorates fast from the barrier on out.
Quite a few PPC .38 Specials were fitted with 6-inch, 1:10 twist pullman axle barrels. A full wadcutter given just enough gas to get out the barrel----stand behind the gun on the SUN SIDE of the bullet and watch it zip downrange----may want some extra spin. We shot prototype Maximum SRM-2 with 1:10 (along with 9 other twists) and I could not reign in the accuracy with 180’s, nor even Remington experimental 158 JHP.
The old Colt Python ran 1:14 and the exceedingly accurate Freedom Arms Model 353 .357 Mag runs 1:14. Again, bullets with a low ballistic coefficient are more twist-tolerant.
A bullet which yaws sheds both stability and velocity. I saw yaw & key holing with factory .45 Colt fired in the Taurus Judge .410/.45 Colt. Didn’t measure grove diameter; sure are shallow, probably to aid shot pattern. David Bradshaw
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