Home Forums Hunting & Shooting Handguns Perfect keyholes

I have this S&W model 69 that I got the first year they came out. I would guess I have at least 2,000 rounds through the barrel, probably a lot more than that. But saw something new today. Since I ran out of Blue Dot a few months ago I’ve been working up loads with AA7. Don’t know if that has anything to do with it but today I shot some 225 grn Acme Hy-Tek coated bullets with 17.1 grns of AA7. That’s the highest load I’ve used so far with this bullet.

Accuracy was horrible and about every third bullet made a perfect key hole, see below for a couple of examples. I chronoed a few rounds to see if that would give me a clue. They averaged about 1290 fps plus or minus about 30 fps so that seemed in line.

Before I left the range I shot a couple of cylinders worth of 210 JHCs and they made a bunch of perfect little holes close together.

When I got home I ran a couple of patches with Hoppes down the bore and it looked pretty clean. I went ahead and took a brush to it but didn’t get much out at all.

I also checked the diameter of about a dozen unloaded bullets. They’re supposed to be 0.430” and they were pretty consistent, a little closer to 0.431.

Anyone have any thoughts for me?


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Well since they are PC/poly coated, at least the leading component wasn't an issue....

Only time I experienced handgun keyholes was using plated bullets with too much crimp.

Got any other proven cast bullets to try?

Is that the first time you’ve shot those bullets? If so, my first guess would be that the bullet diameter just doesn’t agree with the barrel.

Have you shot those bullets before at lower charge weights? It could be that the alloy can’t take that much pressure.

Maybe another thing you could do is shoot a couple into some sand or some water jugs so you can recover them and see if they're slipping the rifling.

I am not an expert. Read further at the risk that I am wasting your time.

It has been my experience that there are half a dozen causes or combination of causes that are the "best" place to start, with no guarantees you'll identify the issue. Almost all relate to things you can't change (bullet diameter, size/rifling combo, ogive, and defective manufacture). Bullet speed is another common culprit, but one that you can control.

From your post, my thoughts are:

-Since you're the original owner of the gun and it shoots other loads just fine, it isn't the gun (I know you know that, but it needs to be said).

-You didn't say whether you've shot this bullet before with success, and whether it was done at different speed(s). I will ASSUME that this was the first time you've shot the bullet, and that it was consistently inconsistent.

-My first guess is related to what navlav8r said--the bullet diameter combined with bullet shape is just a No-Go in your gun for science reasons beyond me. However, if I were determined to find a way for that bullet NOT to keyhole, I'd start with changing speeds. Begin with low-end loads, then drive it faster and faster, using a normal crimp the entire time, until I reached max velocity.

If that doesn't fix it, just ditch the bullet and use what works. Life's too short--unless you're bored and are one of those "love a good mystery" types, and this is fun for you. But then, you're likely on a path to discover a reason that you won't be able to change--you'll know WHY the bullet keyholes, but you'll still not be able to shoot it out of your gun.

I wish you all the best!

I’ve got some #503s ready to load. Probably be in town this week

I have shot these same .430 225 grn Acme bullets from this gun, with 16.5 grns AA7. Yesterday was the first time with 17.1 grns of that powder.

I didn’t want to give the impression that I’ve only shot coated bullets with it, I’ve also shot a lot of plain cast bullets as well. I did see just a little bit of residue (lead?) in the grooves near the muzzle. I wouldn’t have thought it would be enough to cause this, maybe so?

Tomorrow I’m going back to the range with this revolver, another .44, and a wide variety of ammo. Hopefully I can solve this little mystery.

I wonder if I just exceeded the max velocity for this bullet that caused it to start skipping the rifling? I’ve gone over 1400 fps with 200 grn cast bullets and no issues. But that was with other revolvers, not this one.

??

Frank……Those should penetrate nicely! memtb

Although not a handgun, this is an enviable group at 100 yards. Carbon build up in the throat can cause this…

Did those suckers buzz going down range?😁

I had the same result as Shrapnel with a 700 Sendoro 22-250, 50 gr Rem .224 HP at 3800 fps. Seems that having rifling in the first eight inches of the bore is necessary for proper stabilization.

Its a S&W, it has thread choke. Doesn't affect jacketed but lead bullets it does.

Same here, I had problems with keyholing out of 3 different 9mm pistols with some cast lead 124 grain and after backing off the crimp I had no problems.

Conventional wisdom on key holing is usually (1) bad crown usually cut uneven by somebody who didn’t use a pilot, ( 2 ) barrel crush in way of the barrel shank and frame threads. This is often found on K frames sometimes with a fractured frame same location, (3) undersized chambers throats on revolvers. Happens occasionally but Ruger released a couple runs of Blackhawks with this problem years ago around late 80’s early 90’s not sure. They recalled them and fixed them.

Find a gunsmith with a range rod setup with tight pin gauges. Run the gauge through the barrel cocked action SA. run pin all the way through the barrel and cylinder. If the pin hangs up gets tight at the barrel shank/ frame area this is probably contributing especially with jacketed bullets.. If the gauge hangs up or tight at front of cylinder then it’s chamber throats. Should find copper smear or lead deposits in forcing cone and top strap. You’ll have to have the cylinder honed out or reamed. Honing is smoother. Otherwise check the muzzle crown closely with a glass. Hard to see sometimes but a good smith can recut it easily.

BTW the range rod should go through all six chambers without nicking the cylinder. If it does hit the cylinder you have a timing problem. Any this the I can do without hands on. I’m assuming bullets are sized right and bore is fine.

Good luck
Rick

I figured it out today. First I proved it wasn’t leading. I fired five rounds from the model 69 that now had a squeaky clean bore and had two keyholes. Then I tried a cylinder’s worth of the same load from an old 629 that I’m pretty sure has never thrown a keyhole in its life. And it had one. So it had to be the ammo.

Again, the box I had been shooting was loaded with 225 grn Acme coated flat points and 17.1 grns AA7. I had a box previously loaded with those same bullets with 16.5 grns AA7. I fired them from both revolvers and got nothing but perfect little holes with good accuracy.

I had chronographed both loads. The older load averaged about 1250 fps, the newer one about 1290. I wouldn’t have thought that 40 fps would make that much difference. But I guess it’s the difference in the rifling of two different revolvers catching the bullets and not.

I’ve shot a bunch of cast bullets in my life and never really run into this. It doesn’t bother me much. Acme bullets are cheap and I buy them for target loads. I am tempted to test some higher priced 225 grainers - I have some from Montana Bullets Works - and see what happens.

Maybe it more a question of PSI than FPS. I wonder If the 16.5 grain load fired in one or the other of your two handguns exceeds the velocity of the 17.1 grain load in the other. I think that would tell you that it's a question of pressure rather than velocity.

I can’t say that for sure, I chronoed both loads in the model 69 and in that gun, the higher powder load had a velocity of 40 fps more.

Do you think that something else besides higher velocity causing the bullets to skip the rifling could be what’s happening here?

.

I think I don't know, but would like to. I'm pretty sure it's either pressure or velocity, but I am prepared to be completely wrong.

I agree it’s the pressure. Semantics, but the higher velocity is a product of the higher pressure and it’s the pressure messing with the bullet.

For instance, shoot the lower charged round which doesn’t exhibit a problem in a rifle and you’ll see several hundred feet per second more than the problem load but no problem.

Maybe

I respectfully suggest this is complete BS. 40 fps spread in velocity isn’t going to create an unstable bullet that will key hole. The pressure difference in a 40 fps is minor if at all. A chronograph can account for 40 fps if there are problems. If it’s the bullets let’s see a recovered one that key holed.

You need to (1) slug the barrel to determne measurement of the bore or lande to lande, (2) mic your bullets to see they are correct dia for your barrel. These two steps are essential for good bullet performance and accuracy. High pressure/velocity does not create key holing unless the base of your bullets are damaged resulting in uneven gas and pressure on the bullet’s base as it exits the muzzle. Same condition occurs with a poorly cut or nicked muzzle crown. The gas pressure is uneven as it leaves the barrel pushing the bullet off its axis. On lead bullets and some gilded or coated bullets a nicked or damaged base allows hot gas to run up past the base and melt a portion of the bullet also resulting in a lopsided bullet.

If you claim high pressure then what do your primers look like ? Hard extraction ?
With too low of pressure/velocity this can result in unstable bullets that sometime key hole. But I’ve cleared barrels in my shop where the primer ignited but the reloader forgot the powder and the bullet still traveled up the barrel enough to engrave the bullet. Your velocities don’t fit that scenario. So from what you’re telling us I think you need to do more homework cause you haven’t found the answer yet unless there is more to the story

Good luck
Rick

No one said a thing about the cartridge being loaded to over pressure. What is being suggested is that possibly the bullet base is not tolerating the pressure it's being subjected to. So, maybe not complete BS, huh?

I didn’t see any flattened primers nor were the spent cartridges hard to eject.

??

Please re-read my post and let me know where I said “ over pressure “ so like you said “ nobody said a thing about the cartridge being loaded to over pressure “ . The OP is shooting loads around 1200 fps so these are not limp loads so pressure is up there. So again never said he was pushing beyond the pressue limits of the gun but I don’t know based on hands off info. Also understand every gun handles pressure differently and why reloading manuals tell you to work up your loads gradually. Either way there is some information missing as bullets don’t key hole unless something is really wrong.

Rick

You implied that we were speculating an over pressure load.

Assuming the op’s observations are not coincidental, the 40 fps lower load did not tumble while the higher load did.

So, ya, maybe not bs…

I had this very thing happen with my CA Bulldog and some 185 gr. wadcutters I had cast. This may not apply to your situation, but what I ultimately discovered was the barrel of this revolver has very shallow rifling and a soft bullet sized at groove diameter simply wouldn't engage it enough to stabilize the bullet. I cast a harder bullet, left everything else the same and my problems went away.

Have you measured /determined the following from your model 69 (?)

Groove (not bore) diameter from complete "soft slug push through" of barrel (starting at muzzle)?

Do you notice any increased resistance when pushing through the frame/barrel section? If so, you may have some degree of frame choke/restriction ("thread choke"). If so, this would size down your bullet as it enters the first ~1/2" of the barrel, causing degraded accuracy/lessened bullet engagement with rifling. If shooting naked cast bullets, you could experience gas blowing and leading. By shooting coated bullets, the lead might be coated enough to not be exposed to the hot gases, and give a "false negative" for leading.

If thread / frame choke is present, you may want to either fire lap the barrel / frame area or get it "Taylor throated" (essentially rifling is reamed out to a diameter that matches the maximum groove diameter), removing the detrimental thread choke
https://www.bullseyeforum.net/t5517-revolvers-barrels-forcing-cones

The medium-frame model 69, combined with a large bore barrel ("44" caliber) makes the threaded section of the barrel thinner, and more susceptible to frame / thread choke. The groove diameter of the frame area may be marginally restricted (thread choke), that provides acceptable accuracy with some loads, but may not work for all loads (ie. varying bullet hardness/softness, velocity/pressure issues)

Measure each cylinder throat's diameter?
Compare to each other. They should be all the same, and, ideally equal to, or maybe 0.001+" larger than maximum groove diameter. If not, the tight (and variable) cylinder throat sizes down the bullet creating groove fit issues (like thread choke, or can be in addition to thread choke issues).

Ideally, you want all the cylinder throat measurements equal to each other, and the largest measurement of the bullet's travel path in a revolver (again, at !east equal to maximum groove diameter). Then, the first part of the barrel (frame area, should be at least equal to maximum groove diameter (not tighter than the cylinder throats).

Fire lapping creates a desirable tapered choke throughout the barrel, from cylinder throat, to frame area, to muzzle (larger at the throats, tapering SLIGHTLY to the muzzle. This provides optimal gas sealing (minimum gas blow by) and maximum bullet /rifling engagement for bullet stability (eliminate key holing).

Here is an excellent article about fire lapping and thread choke ( by Ross Seyfried):
https://gunsamerica.com/digest/ross-seyfried-lipseys-ruger-flattop-44-special-bisley-revolvers/

You need cylinder throat and barrel groove measurements (muzzle and thread / frame area) from your model 69 not just bullet diameter to fully diagnose. (IMO). Good luck.

The bullet diameter looks to be correct and I doubt the coating is an issue.

I suspect the bullet base is beveled to make it fall out of the mold easier but the beveled base can funnel gasses around the bullet when loaded to higher pressure.

If you can recover a fired bullet and inspect for gas cutting that would eliminate one possible issue.

Let us know what you find!

Edit, Have you got any flat base bullets to test for comparison?

I’m thinking of making a bullet trap and catching one of of them. I usually use a cardboard box filled with soaked magazines. I really want to know and I am curious. But I’m lazy too.

Thanks everyone for all the good comments.

measure your barrel from both ends. I am telling you it is thread choke. You will not have a problem with jacketed bullets as they hold onto the bullet better than cast does. You don't have any leading as the pc is protecting the lead from blow by gasses. If you shoot revolvers enough you will run into this. And S&W seem to be common with this than all others.

Fit is king.

Deformation and imbalance start at the case mouth, then throat, then forcing cone. Yaw doesn't fix itself in the barrel. Lead deforms and spring-back is minimal.
As others have mentioned; make sure your throats and bullet match and every point thereafter must be tapering with the muzzle being the tightest point. You could have thread choke, one or two tight throats or not all of the bullets the same size. Find where the issue is.

"Hot gases" that can magically melt lead but leave poly alone do not exist. Jackets, coatings, waxes, checks and fillers reduce friction at the bullet base where pressure (and friction) is greatest. Some work as a lubricant, others like checks reduce base deformation and friction at that stress point. Friction and pressure causes leading. NOT gases that won't melt poly filler, poly coating, grease, wax, any bullet base or any number of items that will burn up on a unmelted lead pot at 500 degrees....

None will correct imbalance.

Where did you get your load data?

17.1gr of AA7 is too hot for a 225gr according to my Western Powder load data. AA7 is too fast.


17'ish grains of AA9 would be a good load.

From my Lyman Pistol and Revolver Handbook, 3rd Ed. It shows 15.5 grns AA7 for starting load and 19.1 grns for max. But that’s for a 225 grn JHP bullet, they don’t show data for a 225 grn cast bullet. That’s why I was going up gradually. For me, I’ve settled on 16.5 as max although I never expected keyholing to be the first sign of overpressure.

Interestingly, the velocity I chronographed was higher than what the handbook shows for the max load of 19.1 grns. That’s another reason I think 16.5 grns is enough.

I saw an article many moons ago that showed some samples of lead bullets that were fired at higher velocities/pressures than they were designed to be used.

One photo I remember showed a semi wadcutter that, after it was fired, looked like a round nose flat point because the lead was too soft for that pressure causing the bullets to slump and shoot erratically.

Acme shows a BHN of 16 on that bullet.
I can’t remember if it was Elmer or Veral who came up with the constant of 1422 for cast bullets, but that’d come up with optimal obturation/engraving just shy of 23,000CUP. I’d venture you’re WELL above that at 1,290fps out of a stubby .44.

While I’m sure some will disagree, his lighter load is shooting fine.

Anything I’m shooting that’s approaching 30,000CUP out of a revolver is heat treated wheel weight. I’ve yet to have a bullet hit sideways.

I believe Veral Smith shot hard tempered bullets with gas checks at those 1400 fps loads. I’d have to look in his book to confirm this but he was big on tempering his bullets to achieve greater hardness and he liked gas checks.

Rick

LDMAY375 had the same thing happen with his 480 Ruger and 410 grain hard cast bullets

He said the load keyholed with two different revolvers. It's an ammunition problem.

This may be a stupid question but I'll ask it anyway...
Is there any chance the bullet base was shaved as the bullet was seated in the case? Insufficient flaring of the case mouth, or a build-up of bullet lube in the seater die allowing the bullet to tilt just a bit could let this happen. If I'm not paying close attention, sometimes I don't get the bullet straight on top of the case, or it won't stay straight as I remove my fingers from the bullet. I then have to rely on the seater die to straighten the bullet as it is seated. It's almost never an issue with jacketed bullets, especially with boat-tails but I can see how it could cause a problem with lead bullets.

Sometimes the little things can drive you nuts. Been there; done that.