Keyholing?? what causes this problem and how to fix it???? - Pistolsmith
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Old 03-07-2015, 11:19 PM   #1
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Angry Keyholing?? what causes this problem and how to fix it????

Hi
I was at the range today shooting IPSC with my Tanfoglio HC custom 38 super. I found that a lot of the rounds on the paper cardboard targets looked they are key holed. I use 9mm 125 grain SWC with 7.6 grains of ADI AP100 powder and the speed is averaged at 1320 fps (over the chronograph).
Why does this happen? The barrel is compensated and when checked for leading was pretty clean and only needed 4 strokes with the brass cleaning rod.
One of the other shooters suggested that a bullet lube would help as the projectiles he said I have just recently bought does/can leave leading in the barrel.
Being a 38 super pistol should I use a 38 projectile instead as I was told that the 9 mm is used by most shooters???
How can I check which is better? Does the size of or diameter of the bullet make that difference? I think we are only talking about 4 thou difference between the 9mm and the 38 cal.
When I load with Winchester 231 4.5 grains behind a 125 grain projectile it goes fine with 1040 fps for minor power factor and I have not seen any tumbling with this load.
I have been thinking a different powder may be better to use and a 130 grain conical projectile with the AP100 powder.
Any ideas would be much appreciated.

Marke
 
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Old 03-08-2015, 07:50 PM   #2
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Have you slugged your barrel?

Have you measured the diameter of your bullets?

Are there any imperfections in the barrel, e.g. bad crown?
 
Old 03-09-2015, 01:09 AM   #3
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I have been told that the crimp for 38 super is straight walled type and I have done that.

Slugging the barrel with my 9mm 125 grain SWC before slugging, the measurement is 0.357 and after the measurement is at its widest 0.355 and at its smallest is 0.347.

After slugging the barrel with a 38 158 grain SWC the size before was 0.358 and after it is 0.355 at its widest point, smallest is 0.347 allowing for the inside shape of the barrel.

I presume that this tells me that the 9mm bullets are on the small size by only 1 thousand of an inch? By using the 38 cal bullets I hopefully would have a more accurate bullet and no tumbling? I have loaded some of the 125 grain SWC projectiles with bullet lube on them to see if that makes any difference. I will have to wait until next weekend to do so, I will post the results then.
Any other ideas would be much appreciated.
Looking down the barrel has shown no problems what so ever.
 
 
Old 03-09-2015, 02:45 PM   #4
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So your groove diameter is .355 inch and your bore diameter is .347" which are proper. Did you notice any tight or loose spots as you pushed your slug through?

Again how is the crown?

There are debates regarding lead bullet diameter. Personally I subscribe to either groove diameter or slightly less. In your case that would be .355 or .354, but .356 should not make much difference.

You stated someone told you to lube your bullets. Even swaged bullets at low velocity need some lube. Were you not using lube?
 
Old 03-09-2015, 06:21 PM   #5
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Hi Dave

The crown is good as the barrel has a screw on compensator on it for the high power factor loads. I will be trying out these same loads without the compensated barrel and just use the other standard barrel, as I have two barrels for the same pistol. If I still have key holing I would think it means that the projectiles are being pushed straight through. I may need jacketed projectiles to use for the major power factor loads. I might say that when I use loads in the minor power factor I have no key holing what so ever.
As for the lube I have not used any as the polymer coating on the projectiles I thought would do the job, that is the black or gold or blue coloured projectiles.
I will be trying out the lubed one next weekend.

Mark
 
Old 03-13-2015, 05:46 PM   #6
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looks like its the compensator

I tried out the major loads with the standard barrel and no keyholing what so ever. I tried out different loads (minor with the standard barrel) and no problems. I went back to the compensated barrel and the same thing happened with the major loads. So now I am going to try out polishing the inside the compensator and go from there??? This was told to me by another shooter, I will try out different loads again. I have some 38 cal 130 grain SWC and will try them out with the compensator and major loads again.
The lubed SWC made no difference, they still key holed.
The AOL rounds (1.260 thou) were no good either as they keyholed as well.
I will keep trying.
 
Old 03-13-2015, 06:36 PM   #7
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No keyholing with the standard barrel yet the compensated barrel does cause keyholing with the same loads? Bullets have to be striking the inside of the comp somehow. Is the exit hole properly sized and truly round?
 
Old 03-16-2015, 12:52 AM   #8
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The compensator exit appears to be OK and just for good measure I got some Hope's 9 to clean out the deposits if any and see what happens with that.
I think I will get some 9mm 135 grain conical projectiles and try them out with the same powder but at a lower amount. I'll also look at getting some different powder too. Al though I was at my gun shop today buying the Hope's 9 and told the guy who has the most experience with 38 super, IPSC etc and he informed me that he uses ADI AP70 with a 150 grained SWC and has no trouble. I looked it up and found the load for the AP70 powder and it clearly states 4.3 at 960fps to start and maximum load of 5.0 at 1111fps. Considering that the power factor of 160 equals 1067fps which is worth a look at maybe??? I am still looking at buying some jacketed projectiles to try out with the major loads. I might even look at getting the 9mm 150 grain conicals or SWC, I don't know which is best? Any ideas??? I have heard that the Hawksbury bullets are not the best. so I will try to find some other brands. I will keep plugging on.
 
Old 03-25-2015, 11:01 PM   #9
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Keyholing is most commonly caused by certain barrel defects. Sometimes by pressure excessive for a given bullet - usually cast or swaged.

If there truly is nothing wrong with barrel and comp, then it can only be your loads somehow.

Thanks for the update.
 
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