Why keyholing?

[PinnedAndRecessed]

I just took delivery of a pre 27 S&W with a 3.5 inch barrel. I worked up some loads with 6.0 grains Unique and a 125 grain Ranier plated bullet. But some of the rounds were keyholing. What causes that?

 

[KriegHund]

Destabilization of the bullet.

Using the wrong weight or length bullet in the wrong barrel twist causes that.

 

[PinnedAndRecessed]

Using the wrong weight or length bullet in the wrong barrel twist causes that.

So maybe I should try a 158 grain bullet? But, what do you mean by bullet length? Overall length?

 

[Mal H]

You're not getting enough spin to stabilize the bullet due to low speed and a slow twist rate in the barrel. Changing the bullet is a solution, but not a necessary one. 6.0 grains of Unique is a light load for a 125 gr plated bullet. I would increase the powder by 1.0 to 1.5 grains and see what happens with the keyholing.

What KriegHund is saying about the length (of the bullet itself, not the OAL) is that the length is a factor in the ballistic coefficient and therefore in the stability of the bullet in flight. Usually the longer the better, but not always. More often than not, you have no choice in the length anyway.

 

[dakotasin]

the fix to keyholing is velocity.
more velocity, and the keyholing will stop. this applies to all guns that i know of.

sometimes it is impossible to get enough velocity to stop the keyholing, in which case the solution is to drop to a lighter bullet.

bullet length, among other things, is dictated by the weight. the same design bullet that is heavier will be longer.

switching to a 158 grain bullet will probably make your problem worse.

 

[saltydog452]

Foot in mouth...

Not trying to modify any of the previous posts, but I THINK what everyone is trying to get across is the ammount of bearing surface, hardness,velocity, etc.,not exactly the length of the projectile.

I dunno. I haven't been wrong today so far. Only been up an hour though..

salty.

 

[boo586]

Max charge for a 125 grain JSP is 9.6 grains of Unique (according to the Alliant website) so I would say your load is way too light.

Max load for a 158 grain Lead SWC is 6.9 grains of Unique. 6 grains of Unique is a pretty common load for 158 grain bullets in the 357 magnum if I remember correctly.

Another thing that I know is pretty common is overcrimping of plated bullets and damaging the plating. This will also cause instabiliy in the bullet and keyholing.

Check your crimp and up your powder charge a little and see what shakes out.

Boo586

 

[KriegHund]

Err, when mentioned length it was in reference more to rifles.

IF the bullet is to long sometimes doesnt it destabalize in flight? But blunter pistol bullets wouldnt sem to make a huge difference...

 

[dakotasin]

yes, if the twist rate is too slow, or the velocity too low.

 

[Sharps Shooter]

Hey guys, not to hijack this thread, but is it the same reason why those Aguila .22 "SniperSubSonic" 60 grain bullets keyhole when I shoot them out of my Kimber rifle? Are they just too slow to stabilize with the rate of twist my Kimber has? Thanks.

 

[Mal H]

Yep. Not much you can do about that though.

 

[rockstar.esq]

Sharps shooter, try those Aguila's in a handgun! You'll love the result.

 

[Sharps Shooter]

Thanks guys. I WILL give them a try in a handgun.

 

[Rabid Rabbit]

Another possible source of the problem is lead or copper fouling in the barrel, most likely lead. If the previous recomendations on changing bullet weight, velocity and hardness don't work give your barrel a good cleaning with the fouling removers.

 

[BluesBear]

Several thoughts

What kind of targets are you using?

My local range has some really nice reverse silhouette targets that I like because it's easier to see the black sights on the white target. But they are printed on thin paper and meant to be used on a cardboard backing.

Except for full wadcutter bullets, everything shot from a .357 looks like a keyhole in them because the paper is tearing. For some reason .44s and .45 punch nicer holes in them.


Also try crimping your bullets a little tighter for a little more velocity. A slow moving 125gr bullet can keyhole easier because of it's shorter length.

Have you checked your forcing cone? If there's any imperfections it will be exaggerated with shorter bullets.
Same with cylinder throats.
Anything that could cause the bullet to be entering the barrel slightly crooked will play havoc with your accuracy and could encourage keyholing.