Keyhole with 9mm Remington 147 Golden Saber

[okie john]

The title says it all. I was checking POIs at 25 yards today with a Gen3 Glock that had a Wilson Combat barrel installed and fitted by TigerSwan several years ago.

First, I fired five rounds of S&B 115-grain FMJ. They're the five hits that are in or near the black and left of the X (a 10, three nines, and an eight).



Then I fired one round of Remington 147-grain Golden Saber. That's the hit in the five ring at the extreme left edge of the paper. We all mash the trigger now and then, but I was pretty sure that this one wasn't me. Then I fired four more rounds of the 147 GS, and got the four hits that are in or near the black and right of the X (three nines and an eight). Then I went downrange and checked the backer. This is the hole that the first 147 GS left.



I wasn't shooting so my bullets would have hit the backer at an angle, so based on the facts that 1) the hole is oblong and 2) the POI is so far out of the main group, I'm calling it an honest-to-Pete keyhole. I'm VERY glad that it happened on the range and not on the street.

Has anyone else had this happen with this load?

Thanks,


Okie John

[Hambo]

That's my current carry load and no keyholes. It's time to shoot up the ammo I've been carrying and I'll let you know if anything weird happens. All my shooting with this ammo has been through a 92F.

[LSP552]

I've shot a lot of the GS 147s and found them accurate out of both SIGs and Glocks.

[farscott]

A factory Glock barrel twist rate is 1:9.84", but the Wilson barrel has a much slower rate of 1:16". I suspect the slower twist of the Wilson barrel is not properly stabilizing the 147-grain bullet. If you crank the numbers into a ballistic calculator, the minimum twist rate to stabilize a 147-grain bullet is 1:16.9". The Wilson barrel twist rate is too close to that for me to be comfortable as the real world has too many tolerance stack-up issues.

[Jim Watson]

Which seems strange since a 16" twist (Colt) and even an 18.75" twist (S&W) have been stabilizing 158 gr .38s at lower velocity for over a century.

[farscott]

I agree that it is strange. Wil Schuemann wrote this:

While the shape of a bullet, expecially the nose shape, can somewhat affect the minimum twist needed to stabilize the bullet, the most important single factor is the length to diameter ratio (the bullet's L/D). As the bullet becomes longer the force on the bullet nose has more "leverage" to tip the bullet. To counteract this increased leverage the rotational velocity of the bullet has to be increased to maintain stability, and the barrel therefore has to have a faster twist (smaller twist number) to produce the higher bullet rotational velocity.

and

When the bullet is trans-sonic the force on the bullet increases somewhat more than the squared velocity dependence predicts, which causes a bullet to be somewhat less stable when it passes through the speed of sound. If the bullet is transsonic and marginally unstable, increasing (or decreasing) the velocity of the bullet will allow the bullet to stabilize.

http://www.schuemann.com/Portals/0/D...ist%20Rate.pdf

[okie john]

I've wondered about twist rate.

Last summer, I tested a number of hand loads with cast bullets in this G17 and another G17 with a Wilson Combat barrel while I was getting ready for a deer hunt. (Deer where I hunt are really small and 30 yards is a long shot, so I figured the G17 would be OK.) I quickly found a load with the 124-grain XTP that outshot every factory load I've ever tried in this gun, so I switched to fiddling with cast bullets. Neither WC barrel shot 0.356" cast bullets well at any velocity from 800-1,100 fps. I switched to 125-grain cast bullets sized 0.358" and pushed to about 1,150 fps. Groups improved considerably in both guns, shooting almost as well as the XTP load, but went south again with 0.358" 140-grain bullets at 950-1,000 fps. One barrel would barely keep 10 rounds on the paper at 25 yards--making keyholes about half the time. The biggest surprise was that both pistols shot 125-grain cast bullets very well in the OEM barrels. One of them even shot better with the cast bullet in the OEM barrel than it did with the XTP load in the WC barrel.

So yeah, there's a certain mystery to it...


Okie John

[KevinB]

Which seems strange since a 16" twist (Colt) and even an 18.75" twist (S&W) have been stabilizing 158 gr .38s at lower velocity for over a century.

Solid Lead bullet. Shorter in length and requires less twist to be stable.

[TiroFijo]

Solid Lead bullet. Shorter in length and requires less twist to be stable.

Come'on, how much longer is the 147 gr GS compared to a .357" lead RN 158 gr? And compared to a 158 gr JHP? You can shoot upt to 200 gr RN lead bullets perfectly out of any 18.75" twist 38 spl S&W revolver, even with the lower velocity. I'm sure a 180+ gr RN lead bullet would be longer than a 147 gr JHP.
This is not due to barrel twist. Perhaps the GS bullets are just finicky for some reason in this barrel.

[KevinB]

Could be type of rifling as well - the jacket on the GS does not like your rifling.

I shoot a lot of GS - and have no issues in M&P's or my BHP.