Keyhole issue

[bluetopper]

All these opinions about throat size and load adjustments do nothing about the underlying main problem and that is the factory twist rate of 1:18.75 is not fast enough to stabilize well, a hollow base wadcutter bullet.

 

[fredj338]

All these opinions about throat size and load adjustments do nothing about the underlying main problem and that is the factory twist rate of 1:18.75 is not fast enough to stabilize well, a hollow base wadcutter bullet.

Then likely every round would keyhole, not just a few. If the shooter is loading random cyl with 5rds for his group, then there will be a random keyhole if one cyl throat is smaller, even 0.001" smaller. Why the old timers used to test shoot groups from one cyl then repeat for all 6 & mark any offending cyl. The only way to get it right is make them all uniform in dia, ideally the same as the the bore + 0.001".

 

[elpac3]

It seems we have focused on the load as being the culprit
in the keyhole issue - which it could be. But - - - -have we considered shooter technique?

Many years back while shooting BE, one of the military shooters did a demonstration on keyholing by using heel pressure on the grip at the time of trigger let off. Could make the bullet keyhole right or left and call the direction of the keyhole depending on heel pressure.

Just a thought

 

[fredj338]

It seems we have focused on the load as being the culprit
in the keyhole issue - which it could be. But - - - -have we considered shooter technique?

Many years back while shooting BE, one of the military shooters did a demonstration on keyholing by using heel pressure on the grip at the time of trigger let off. Could make the bullet keyhole right or left and call the direction of the keyhole depending on heel pressure.

Just a thought

Sorry, calling BS on that. Your grip doesn't affect the rotation of the bullet. IT does affect POI, but not bullet stability.

 

[bluetopper]

Point is, you wouldn't have a keyholing issue at all if the hbwc's were shot out of a 10 to a 14 twist barrel, regardless of load or if a chamber was a thousandth off. The factory twist rate of 1:18.75 is right at the cusp of the long hbwc bullet losing its stability. The barrel was designed for 158gr bullet.

 

[BigMuddy]

Point is, you wouldn't have a keyholing issue at all if the hbwc's were shot out of a 10 to a 14 twist barrel, regardless of load or if a chamber was a thousandth off. The factory twist rate of 1:18.75 is right as the cusp of a long hbwc bullet losing its stability. The barrel was designed for 158gr bullet.

Did the twist rate change in the 686 at some point? The reason I ask is I had a 6" gun back when they were first available and it would literally cut the X ring out of a B27 at 20 yards, and all would land in the 10 ring at 50 if I didn't yank on the trigger. This was with HBWC's supplied by the department I was shooting with. Not doubting the twist rate issue as I'm still and always learning.

I recently worked with a M-15 that was keyholing at times and it turned out to be a pretty good amount of thread choke. It was with 140gr. RNFP's. Lapped out the thread choke and all is well now.

Dan

 

[ameridaddy]

I have slugged the barrel but I do not have a three point micrometer to check diameter at this time.

I have one for a five groove barrel. If you'd like to mail me a few slugs for measurement, PM me.
Do you have access to a chronograph? That might be some good info as well.

 

[ameridaddy]

....

....thread choke. It was with 140gr. RNFP's. Lapped out the thread choke and all is well now.
Dan

I have a Mod 25 that has thread choke. How did you lap it out? I'd love to know, because pistol smiths are scarce around here.
I don't want to hijack the thread, so PM me if that's a concern.

 

[Electric3002]

I know you said the paper is flat, but make sure it is tight against cardboard backer.

I purchase one target at the range and then tape my Dirty Bird targets onto that. They are flat. I am anal about my shooting and I even make sure my targets are straight and level and centered on the target used as a backer.

 

[Electric3002]

Verify your bullet size versus your bore size. Have you slugged the barrel? I would also up your powder charge to3.0 to insure your HBWC is obturating properly.

Measured today at work.
Cylinder throat size:
.3576
.3576
.3576
.3576
.3574
.3576

Slug looked odd on the three point mic so I looked at it using an optical comparator with Quadra-chek 3000 system. I seen how the rifling is not straight cut and is not polygonal. I digitized slug and the measurement was .3548 using largest size of "lobes".

 

[fredj338]

Your throats are close enough. So I would check dia of say 12 bullets. Are you using the infamous LFCD to crimp? Is all your brass the same manuf? Bullets do not randomly keyhole w/o a reason.

 

[Electric3002]

That's a very light load to begin with so depending on what type of powder thrower you are using what you may be seeing is the throwers inconsistency with dropping the charge. I run 2.9gr of green dot under a 148 hbwc for an M52. And while I don't see it in the targets, if there is a metering issue I notice right away based on how she cycles.

Otherwise, as sated above, the charge might not be enough to get the velocity to a point of stability out of that barrel. Depending who you ask 148 stabilize in a very fast twist rate such as 1:10, 1:12, 1:14. Youre working with a gun if I recall correctly as 1:18.75

I use an RCBS uniflow. I have done gage R&R on it and it will repeat nicely within about half a tenth of grain. I have tested by weighing each charge on a beam scale and also throwing ten charges in pan and weighing sum of all charges and all is well. I measured strings of ten and many singles, not just one and done.

 

[Electric3002]

What kind of expander are you using??? I like to use the lyman m-die when I load any hb bullet for several different calibers. Traditional expander dies are made for short .357" jacketed bullets. The m-die has a llloooonnngggger body to expand the case where it counts, at the base of the bullet. It also has a step in it that makes a shelf in the top of the case mouth that aids in starting the bullet straight. A picture of a lyman m-die.


Picture of a m-die next to a factory expander. If you look at the factory expander you can see where the brass has left a ring where it stops being expanded. Huge difference in the depth that it goes into the case compared to the m-die. That is what protects the base of the soft lead bullets.


If the bullets are seated crooked or being swaged down at the base too much. Bullet skidding will occur which in turn affects accuracy & stability. When I see #'s like 3% or 4% of my loads tumble, things like this come to mind. If incorrectly loaded the bullet will tumble as soon as it leaves the reloading press and long before it ever is in the revolver.

HBWC's are a long bullet and care should be taken when seating them in a properly expanded case. A picture of the 3 main wc/hbwc bullets I use/shoot in the 38spl's & 357's.
left: h&g #50 148gr button nosed wc
center: flat nosed 148gr hbwc from a custom mold
bottom: lyman 358395 148gr button nosed hbwc


Just something to think about

I also use Lyman M die

 

[BigMuddy]

I have a Mod 25 that has thread choke. How did you lap it out? I'd love to know, because pistol smiths are scarce around here.
I don't want to hijack the thread, so PM me if that's a concern.

PM sent

Dan

 

[Electric3002]

My past with keyholing causes me to suggest pin gauging the cylinder bores, and adjusting the bullet size to at, or just above that measurement. Also-does it keyhole with 357 ammo?

No keyholes with .357 ammo. Only the Precision Delta 148 HBWC keyhole and that was only about four out of 120 rounds. Hornady 148 HBWC do not keyhole. Just trying to find a solution as I purchased 1000 Precision Delta's and I am going to shoot em'.

 

[dave201]

All these opinions about throat size and load adjustments do nothing about the underlying main problem and that is the factory twist rate of 1:18.75 is not fast enough to stabilize well, a hollow base wadcutter bullet.

Bingo Give the man 2 cigars
Without a chrony and Greenhill
A man becomes lost very quickly

Barrel Twist Calculator

Me thinks you are low on the powder end of the equation
I fire my loads in the shop thru a chrony as I add or subtract powder
I don't need to fiddle with targets till I get the basics right
Least with Greenhill
Your will know if the combo is worthy of even loading or a waste of your time

 

[elpac3]

Sorry, calling BS on that. Your grip doesn't affect the rotation of the bullet. IT does affect POI, but not bullet stability.

OK - call it what you may, wouldn't have believed it if I hadn't seen it.

 

[fredj338]

OK - call it what you may, wouldn't have believed it if I hadn't seen it.

I don't know what you claim to have seen or if you understand the term "keyhole", but think about how that is even possible? It's not a Hollywood movie where you can bend the bullet flight path by flicking your wrist. As long as the crown of the barrel is in good shape, the rifling supports the bullets weight for the intended vel & the bullet fits right, it is not going to keyhole, no matter how you shoot it. Diff POI, certainly, but you can not make the bullet turn in flight & keyhole. I've shot handguns from just about every conceivable shooting position, including holding a gun upside down. I have never seen such a thing.

 

[elpac3]

I don't know what you claim to have seen or if you understand the term "keyhole", but think about how that is even possible? It's not a Hollywood movie where you can bend the bullet flight path by flicking your wrist. As long as the crown of the barrel is in good shape, the rifling supports the bullets weight for the intended vel & the bullet fits right, it is not going to keyhole, no matter how you shoot it. Diff POI, certainly, but you can not make the bullet turn in flight & keyhole. I've shot handguns from just about every conceivable shooting position, including holding a gun upside down. I have never seen such a thing.

This was always my understanding of a keyhole

 

[fredj338]

This was always my understanding of a keyhole

Fortunately, I have never exp such a thing.