Perplexed to find keyholing


October 1, 2011, 09:09 PM
Most of my reloads have beent towards my cz75b 9mm. I have reloaded mostly lead bullets that i but from MBC.

My favorite so far is the 125 gr cone from MBC. I have shot a couple hundred loaded with 3.7 gr of HP38 with an oal 1.09 with good results. I wanted to increase the loads some, so I loaded 4.0 grains and just finished some test rounds. I noticed some keyholing in my test rounds. Without fail the 3.7 gr rounds were fine and the 4.0 was keyholing. I compared the 2 rounds over and over and redults were the same without fail. I dont understand what could cause this.

Any ideas?

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October 1, 2011, 10:25 PM
Truthfully, I'm not familiar with that bullet; but conical nose bullets at 125 gr have to be loaded mighty short in my 75B or they'll hit the leade/lands. (Berry's 124 HP is conical nose and most use around 1.01" in CZ's). I know it's not necessarily the same with MBC's.

3.5 should be a pretty light load. Have you chrono'd them? IF they are are touching the lands when fed, the pressure increase might be more significant with 4.0grs.

Have you done some "drop-in-the-chamber tests" to see if they contact the cone or rifling? Is there any sign of leading?

Just a consideration.

October 1, 2011, 10:46 PM
Yes, I did a drop test and it did fine. I dont have a cronograph yet, but it is in my next purchase. I have not inspected the gun yet. I have fired less than 100 rounds since cleaning it last week. I think that keyholing usually results from problems with the barrel, which is why I dont understand shooting the 3.7 rounds flawlessly after keyholing the 4.0 rounds.

I dont even have 3000 rounds experience since I started reloading. I think I am just learning enough to ask good questions and know very few of the answers. reloading is like a continous mystery novel. Some new element of the mystery is continually being revealed.

October 1, 2011, 11:08 PM
Have you slugged your barrel to determine the groove diameter?

Many factory barrels are oversized and may not allow the lead bullet to grip the rifling enough to rotate so it can stabilize during flight out of the barrel - and cause keyholing.

The lead bullet may lose grip with the rifling if driven too fast as grip with the rifling will be stripped and the bullet essentially goes down the barrel straight without much rotation.

October 1, 2011, 11:10 PM
Lets verify the problem before seeking a solution. What are you shooting at? Targets printed on copy paper without proper backing can tear out and appear to be keyholing even when the bullet is not.

October 1, 2011, 11:16 PM
if the "keyhole" rounds are just as accurate as the others, don't worry about it.


October 1, 2011, 11:18 PM
bds. that makes sense.

I was shooting at paper on a brand new backboard at our gun club. When I noticed it keholing on the paper, I shot the pristine backboard just to make sure of what I was seeing.

Jim Watson
October 1, 2011, 11:20 PM
If 3.7 grains of powder does not give keyholes and does function the action, load 3.7 grains and not 4.0.

I have seen keyholed and just plain wild shooting in a lot of 9mms with lightweight cast bullets. I don't know the reason but I know it happens.

October 1, 2011, 11:23 PM
These are john16443's pictures of keyholed targets at 7 yards, very different from paper tearing from inadequate backsupport (shows clear side profiles and elongation of the bullet holes).

Master Blaster
October 1, 2011, 11:35 PM
When you drive the bullet faster, the groove depth and also the twist rate comes into play, some 9mms have a faster twist rate.

The worst leading and Keyholing with 9mm lead bullets I ever saw was in my Beretta 92 Inox compact. It hated lead bullets and the first time I shot it with hard cast lead bullets (Same load I had used with no problem in my Glock 26) they started keyholing by shot 5. Perfect sideways profile of the bullet at the 50 foot target, I removed the barrell and there were shreads of lead hanging from the rifling, like strips of lead foil.

Scarry, I immediately stopped shooting until the gun was clean. I blame this on the faster twist rate stripping the lead and casuing it to fly straight down the barrel without turning disengaged from the rifling.

After that I shot only jacketed bullets in that gun until I sold it.

Did you find lead in the barrel when you cleaned it?

October 1, 2011, 11:47 PM
bds. How did you get picture of my target? At least that is exactly what mine looked like. I think I have had explaine to me this portion of the mystery.

Well the wife just walked in laughing at me because I got out of bed to come see if there was any more input. She shoots all the bullets I can load for her but does not understand all that it takes to makes these home made bullets fly straight.

October 1, 2011, 11:48 PM
I have been shooting a lot of MBC 9mm 125 gr RN out of my G22 and short barreled G27 with Lone Wolf 40-9 conversion barrels.

I have range tested 3.8-4.3 gr of W231/HP-38 at 1.108"-1.125" OAL without keyholing.

This is Hodgdon's load data (
125 gr Lead CN W231 Diameter .356" OAL 1.125" Start 3.9 gr (1009 fps) 25,700 CUP - Max 4.4 gr (1086 fps) 31,200 CUP

BTW, LW barrel's groove diameter is .355".

chris in va
October 2, 2011, 12:02 AM
My 75BD keyholed badly with anything sized 356, no matter the shape or weight. A guy on the castboolits site recommended the Lee 358-125-RF for my CZ and it has worked beautifully after thousands cast. As the CZ has a very short leade, the bullet profile requires it to be seated rather short for it to chamber properly.

3.8gr Universal
1.01oal (no, that's not a misprint)

These drop at 361 and I have to size them back to 358. (

Also, I was told 9mm in general have very shallow rifling, really just meant for jacketed rounds. When you try and force a soft lead boolit through barely-there rifling, it tends to smear down the barrel rather than grab. To correct the issue you have to slightly oversize the diameter for a better barrel fit, hence the 358 size.

After all the initial testing I did with 356 bullets, one thing I haven't tried is air cooling instead of the usual water dropping I do (harder BHN). Curious to see if a softer boolit will affect anything.

October 2, 2011, 09:30 AM
I have not had any problem keyholing before this out of the cz. Though I have had o make some oal adjustments to the 125 rn from mbc.

I am going to start casting this winter. I have everything set and ready to go at it. The only mold I have thus far is a 125 gr lee mold that I bought off of a guy that was showing me the ropes. I am not sure what actual mold it is though, I will have to do some investigating

October 2, 2011, 10:42 AM
cleanview, make sure you slug your barrel first and size your cast bullets .001" over the groove diameter of the barrel.

Looks like that's what's causing the keyholing problem mostly, oversized factory barrels and undersized lead bullets that are driven too fast.

October 2, 2011, 10:54 AM
I have been watching videos on slugging the barrel. Ill have to get a few things with my next order (there is no end of ordering). I dont cast yet but will slug and cast to the proper size.


October 2, 2011, 07:00 PM
Keyhole or tumbling is caused by unstable projectile. It generally is a combination of twist(spin), bullet length and SPEED. Bullet size, groove depth, barrel fouloing are normal culprits, but as you are shooting a flat nose fairly slow OK, then speeding it up, not ok, i would suggest speeding up more if possible. If the low load is subsonic, second is transonic, you get tumbling. You may be shooting on the edge of SS flight. Problem is more common with short flat CB.

October 2, 2011, 09:22 PM
I had the same problem. I was told that it was caused by overdriving the bullet. Or pushing the bullet past the lands and grooves without turning. I had a Taurus 92 with a 10 twist barrel. I ordered a match grade barrel with a 16 twist barrel and have had no more problems. Also I ahve a friend with a taurus 1911 also with a 10 twist barrel and he has helped his with shooting a copper jacketed bullet at the bottom of each magazine. That cleans out the leading.

October 2, 2011, 10:20 PM
OK bds, that's at least 2 people with 2 different guns that have/are experiencing keyholing with the 9mm MBC 125gr cones. Thanks for posting my pics, it appears that they also show what the OP is experiencing. Chances are that bullet diameter may be cleanview's issue, just as it may be my issue. We'll know more in a couple days...

October 2, 2011, 10:32 PM
john16443, I hope so. :D

Over the years I have lurked on THR, there has not been too many problems the combined knowledge base of THR membership could not resolve.

Keyholing problem pre-existed long before Missouri Bullet Company, Darda Cast Bullets, Penn Bullets and many other cast bullet manufacturers. It's caused by a combined set of reloading variables that make the bullet less stable in flight because it did not get enough rotation in the barrel to cause the bullet to wobble in the air. So when the bullet hits the target, the hole is elongated or sideways.

My curiosity is identifying those variables and as many posted on keyholing threads before us, it is not necessarily bullet related but bullet-to-barrel fit and powder charge related.

As to other reloading component issues, there are plenty of reloaders who have used Lee dies for decades without experiencing keyholing problem (including me), so that reloading variable should be ruled out.

October 2, 2011, 11:37 PM
I watched a guy shoot 1/2 box of factory subsonic 22 and keyhole every one. The old 22 twist was too slow for the LONG bullet and SLOW speed. I shoot .40 180 TC MBC and 9mm 115 RB MBC with no keyholing in XD and Glock. Put in more powder!

October 2, 2011, 11:43 PM
I think that keyholing usually results from problems with the barrel, which is why I dont understand shooting the 3.7 rounds flawlessly after keyholing the 4.0 rounds.

AND sizing, oal and "leading" due to pressure and speed.

David Sinko
October 3, 2011, 09:43 AM
I have a S&W Model 940 9mm revolver with 2" barrel that keyholes with the 122 gr. truncated cone hard cast bullet and about 4.3 grs. of 231. This load also keyholes badly out of two 9mm carbines that my brother has. On the other hand, a hard cast 125 gr. LRN with the exact same powder charge shoots perfectly and produces nice rounds holes out to at least 100 yards in my 940. Both bullets are sized .356" so I can only imagine that the shape of the bullet is the reason for the instability. If I had any more of the TC bullets left I'd try them with a lighter powder charge to see what happens.

Dave Sinko

October 4, 2011, 08:02 AM
I am not sure how this thread got to where it is, but just to be clear I did not think (nor do I) that the bullet is the problem.

I appreciate the comments. the responses to questions on the forumn are simply amazing.

October 4, 2011, 02:15 PM
Ooops, sorry cleanview. My response post was to john16443 on similar keyholing issue and not directed to you.

October 5, 2011, 07:35 AM
bds I did no mean it like that. I get a kick out of many threads. The answer is given and then little by little a little deviation come in, sometimes down right arguments. I realize that is a result of people that are passionate about the subject and have been active in it for a long time. I think it is only natural when so several comments are given.

October 5, 2011, 10:47 AM
I get a kick out of many threads. The answer is given and then little by little a little deviation come in
Yeah, internet forums sometimes do that. :D

Maybe they can come up with "thread hijack" app?

October 5, 2011, 06:24 PM
I had a similar problem with my CZ85, but the Cones shot OK. The SWC, however, was going in sideways, perfect profile dados cut into my paper taped onto cardboard. Accuracy, needless to say, was all over the place. Two sideways bullets actually knocked big chunks out of my target frame :( I had moderate leading the whole length of the barrel. I was running 5.4-5.8gr AA#5 and my bullet was seated sub-1.07" OAL.

It's not a gun issue. I run the 115 Parabellum and the 125 Softball all day long and get excellent results with my CZ. I also don't think it was a powder issue. I usually run 5.4gr AA#5 with no problems.

I have Universal and Win231 that I also want to try - but this time, I'm not going to load 100 to try. :banghead:


October 6, 2011, 02:01 PM
You are shooting a TC (flat nose) bullet near the speed of sound. Funny things (instability) occur when going either way across the SS. That is why they make pointy bullets. .40 TC shoots about 900 fps. Your 3.7 is probably in the same range. Your 4. is probably ~1050. 4.3 may put you above SS and stop keyholing. You probably need a better lube than the MBC, like tumble lube with a lite coat of alox?

October 6, 2011, 02:52 PM
Are you post-sizing with a Lee Factory Crimp?
Are you over crimping?
Are you re-using lead bullets that you have previously pulled?

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