Kahr PM9: I'm suprised by my groove measurement @ .353

[Whizzer]

I rarely post here, but prefer to read and learn. (And that, I have done! This is a great forum!)

I am loathe to shoot a lot of J-words through this Kahr, or any piece which I can cast for. But at the same time, I am a little paranoid about the whole "kaboom" thing. I loaded a box of 124 Round Nose Lee's, 4.6 grains of Unique, 1.070" COL, Recluse Lubed (cooked 45-45-10) before sizing to .357 and lubed once again after sizing. Now, after slugging the barrel with a .380 "pure lead" round ball, I hate to take them to the range.

FOUR thousandths over size!!!??? Really?? I've read where some of you guys load your PM9's with .358's! Yikes!

Most of my loading for this piece has been focused on reliable cycling for the practice range. Having achieved that, now I'm focused on leading. That, and careful monitoring of swelled cases. They don't belly like a Glock at Major Loadings, but DO swell about 5 thousandths in the area of least support.

Can someone re-assure me that these ~.004 oversized pills are actually okay?

Thanks!
Stan

[bobthenailer]

I also shoot .357 dia boolets from my PM9 as well as Witness Elite Match and two 1911's in 38 Super with a Nowlin and a Kart barrel's. with no leading & excellent accuracy, and the barrels go from .355 to .355.5 dia I also orgionaly tried .356 dia and .357 dia shot tighter groups in my guns.
Remember that the PM has a Lothar match grade barrel with Polygon rifleling.
The norm for cast in semi autos is usually one to two thousands over bore dia,
How did you measure your slug ? a micrometer must be used ! not a veriner dial caliper.

[Whizzer]

I drove a lead .380 ball into the PM9's lightly oiled muzzle end until flattened--with a small plastic hammer. Then, I used a small wooden dowel to push the lead into the barrel about one inch, then out the muzzle end once again. I used a 0-1" micrometer that "zero's" okay, but I haven't had it calibrated, since it is not exactly a Brown & Sharpe from the sadly past heyday of the U.S. industrial age. I'd be embarrassed. It carries a placard: KD Tools (china). With an ever so slight kiss of the "clicker knob" I could sometimes imagine .354, or nearly so.

However, I repeated the adventure driving the slug all the way through the breech end with nearly identical results. And then I used my cheapo Harbor Freight digital caliper and found the measurements were in the same range, or maybe just a skosche under that---say a half-thousandths or so.

I'm not a REAL machinist and I don't play one on TV. But I'm reasonably confident that these grooves are measuring .353-354" and that is generous. At least with my method. I considered Cerrosafe (sp?), but I don't have any.

A .380 ball is awfully large to drive into my tiny tube, right? Should I "roll" it between a couple of steel plates to reduce it a little before driving it in? Am I making another mistake?

Thanks!

[OptimusPanda]

I would imagine that warm jacketed hollow point at .355" would produce higher pressure swaging down than a cast bullet .002" larger. Assuming the measurement of .353" is correct. Makes me wonder what a case from a fired factory Fmj looks like.

[Whizzer]

OptimusPanda, I'm not quite tracking your comment just yet. Can you clarify for my feeble mind?

I can certainly fire some JHP's from this pistol and measure the brass case. I'm not sure I have any equivalent weight JHP's at the moment. I could pull a factory 357 124 grain JHP bullet from a factory self defense round, size it to .355 and load it, I guess. (I might have a box 'o' bullets lying around, but I didn't see any in a brief glance around.)

What will this tell me? (I'm not a high timer at this game, sorry.)

Stan

[DougGuy]

Kahr barrels are made by Walther. Generally they are along match grade dimensions. If you can chamber the round, it's okay to fire it. Going by the throat in my CW45 which won't allow even a .452" boolit to plunk, I'm surprised you can chamber anything over .355"

[jonp]

Kahr barrels are made by Walther. Generally they are along match grade dimensions. If you can chamber the round, it's okay to fire it. Going by the throat in my CW45 which won't allow even a .452" boolit to plunk, I'm surprised you can chamber anything over .355"

Both of my CW45's are the same way. Very tight. Love both of them though and we hung up our MK/K9's and made them our daily carry.

I have almost given up casting for them. I thought I had the leading under control after much help here but it came back with a vengeance. I may stick to plated and j-words with them.

[OptimusPanda]

I may have been a bit confusing. What I meant was (lets assume your groove diameter really is .353") when you fire any projectile itll be resized(well sorta) on firing from .355" or .357" to .353" (your measured groove diameter). Resizing a jacketed slug should take more force than a cast one. So my "I dont do this for a living but wished I did" estimation was that a +P jacketed 9mm loading should be harder on the gun than the cast bullets you loaded. Though I'd like to hear what others have to say about it.

[williamwaco]

I routinely fire cast bullets .003 over groove diameter.
In fact, that is my preferred diameter.

If your loaded rounds pass the plunk test, they are safe to fire.
That .004 over sized cast bullet looks like a pat of butter to the gas pushing it out the barrel.

That said, I do not think your groove diameter is .353.

I think you are confusing grove diameter with bore diameter. Take another look at that slug.

[Whizzer]

<snip>That said, I do not think your groove diameter is .353.
<snip>

You may certainly be right, but I assure you, I'm measuring Max Diameter of my slugged .380 round ball. Them's the grooves as I understand it.... NOT the lands. Am I right in my thinking? My micrometer is admittedly suspect, but I'm working on that. (I have an acquaintance who owns a machine shop.)

[williamwaco]

<snip>That said, I do not think your groove diameter is .353.
<snip>

You may certainly be right, but I assure you, I'm measuring Max Diameter of my slugged .380 round ball. Them's the grooves as I understand it.... NOT the lands. Am I right in my thinking? My micrometer is admittedly suspect, but I'm working on that. (I have an acquaintance who owns a machine shop.)

Yes you are thinking correctly.

BUT I am still suspicious.

I have never seen or even heard of a 9mm bbl that tight.

[Whizzer]

Williamwaco,

I was able to sneak an hour at the range tonight. The above loads in post #1 left some light leading after 40 rounds. 4.6 Unique, 125grain Lee Round Nose, air dropped wheel weights, one 45-45-10 recluse tumble, then size to .357, tumble lube again. 1.070 length. Functionality was 100%, but I'm still leading. Point of impact was WAAAAY low from the POI of factory loaded 115 grain FMJ White Box Winchesters. But I don't care an awful lot about POI for the intended purpose of this EDC pistol. I have other molds, but I don't happen to have a 115 round nose, to approximate the load of factory FMJ (except in lead).

And I don't blame your suspicions about the Kahr groove diameters. .353 just seems wrong, but all my rounds passed the "plunk" test, so I went ahead.

I have a Cabine Tree hardness tester. I'll run a test on some tomorrow. Maybe I'm a little too soft with this batch. (or too hard maybe.) What would be your target hardness for a PM9?

[williamwaco]

Williamwaco,

I was able to sneak an hour at the range tonight. The above loads in post #1 left some light leading after 40 rounds. 4.6 Unique, 125grain Lee Round Nose, air dropped wheel weights, one 45-45-10 recluse tumble, then size to .357, tumble lube again. 1.070 length. Functionality was 100%, but I'm still leading. Point of impact was WAAAAY low from the POI of factory loaded 115 grain FMJ White Box Winchesters. But I don't care an awful lot about POI for the intended purpose of this EDC pistol. I have other molds, but I don't happen to have a 115 round nose, to approximate the load of factory FMJ (except in lead).

And I don't blame your suspicions about the Kahr groove diameters. .353 just seems wrong, but all my rounds passed the "plunk" test, so I went ahead.

I have a Cabine Tree hardness tester. I'll run a test on some tomorrow. Maybe I'm a little too soft with this batch. (or too hard maybe.) What would be your target hardness for a PM9?

Hardness only matters if you are too hard AND to small at the same time.
I cast my 9mms at 10 to 12 BNH because it is so easy to make.
Range scrap is already about that range.
Wheel weights are usually around 12. Add a little tin ( not more than 1% ) and they make really good bullets.
I do not water drop OR heat treat. I have no quarrel with those who do, I just never have and have never had any problems that "they" say hardening will help.

The only leading I have had with the 9mm was caused by "hard cast" commercial bullets lubed with some kind of hard blue lube. They were the worst I have ever fired. Some one on this board told me that hard lubes do not work well with loads below maximum. I increased the load to the maximum Mr Lyman allows and the leading went away.

I use LLA or Xlox straight out of the bottle. I do not find that it improves the performance but it makes tumbling easier and reduces the mess. I size .357 for 9mm and .358 for .38/.357.
I size every bullet then tumble. I do not lube before sizing. The only problem with that is they are slightly harder to push through the Lee die. If I have a batch that is just too hard, I touch my index finger lightly to my case sizing lube and then lightly touch every fifth or sixth bullet with that finger before sizing.

45/45/10 is an excellent lube. I do not believe the lube is your problem.

Some times ( not always, so don't jump on this comment. ) you can raise the POI by reducing the velocity.
I am not saying it will work in this case but load up 5 rounds with half a grain less powder next time you go out and try them.
( Obviously they have to feed and function. so don't load a bunch of them and wind up shooting them single shot to reclaim the brass.)

When developing a load for any semi auto handgun, I start with the starting load, reduce it by two to three tenths grain and locate the power level at which the slide will not function. Then I increase it one tenth at a time until it feeds and functions perfectly, then I stop. Your initial post does not indicate a need for a specific power level so this scheme might work for you too.

[Whizzer]

OK. I tested some of these boolits and found them to be aged, water dropped wheel weights. I'd forgotten I had them. I tested them repeatedly at about 22-23 BNH...IF I do it right. If you are familiar with the Cabine Tree tester, that is about .094" deflection of the dial indicator. Pretty consistent and repeatable. I do have pencils too, and my pencil testing is right about in the same hardness.

[Whizzer]

William Waco, I actually posted my last reply before I saw yours. If my pills are too hard, yet sized okay, and lubed alright...then you are saying lead fouling ought not happen? Is that about it?

I also took a SP101 in 357 Mag to the range yesterday. 6.1 grains of unique under the very same Boolits I use in my Kahr PM9, except sized to 358 before crimping. Its hard to measure the grooves on it, since it has 5 grooves instead of 6. But it leaded also, and was harder to clean it out. 6.1of Unique is a plinking, target type load that may even be worse at obturating those hard cast pills of mine.

Hey, I really appreciate all this help!

[DougGuy]

I dunno how well your crunchenticker will like it, but I have the best luck with 50/50+2% ww/lead/tin in my Rugers, lubed with Felix lube I get zero to a tiny smidgen bit of leading, a lube star at the muzzle, and a "black" bore with lube left in it. If I swipe the bore I get a patch full of lube and powder residue but no lead.

[williamwaco]

William Waco, I actually posted my last reply before I saw yours. If my pills are too hard, yet sized okay, and lubed alright...then you are saying lead fouling ought not happen? Is that about it?

I also took a SP101 in 357 Mag to the range yesterday. 6.1 grains of unique under the very same Boolits I use in my Kahr PM9, except sized to 358 before crimping. Its hard to measure the grooves on it, since it has 5 grooves instead of 6. But it leaded also, and was harder to clean it out. 6.1of Unique is a plinking, target type load that may even be worse at obturating those hard cast pills of mine.

Hey, I really appreciate all this help!

Ordinarily I would say if they are .004 Over sized, they should not lead.

Since they lead in both handguns and are not undersized in either, we need to get serious here.

Take one of your fired cases for each caliber.

Load each carefully following your exact procedures. BUT! no primer or powder.

Before loading, carefully mike and record the diameter of each bullet.
Mark a line across the base with a marker pen so you can measure the exact same diameter again later.
Load each case and crimp normally.

After they are finished, check them to be sure the pass the plunk test.
Then, carefully pull the bullets. Use a bullet puller if you have one.
If you don't you can use side cutter pliers by putting the loaded cartridge in your shell holder and running it up into your loading press ( minus dies ) grabbing the nose of the bullet and pulling the ram back down.

Now remeasure the diameter of those bullets. I suspect you will find they have been sized smaller during the seating process.

Let me know.

[Whizzer]

Williamwaco, I will do that. But I can't get to my stuff until after Church tomorrow afternoon.

But what to do, IF.... it turns out I'm covertly "resizing" during the seating or crimping phase, is something I can't fathom.

I "think" I'm creating handsome crimps in the revolver rounds, at least. I can "see" some neck tension in BOTH cartridges working against the resizing I just did, by observing the reflection of my brass, freshly tumbled in wet stainless steel pins. (I LOVE that cleaning method compared to vibratory.)

I have no cannelures. Just a single grease groove. This might play a role in resizing the 357's. I treat them like I load my plated Berry's Bullets.

I do have a puller...an inertia type plastic hammer. If they resize so easily my press is "sizing" them out of spec, the act of pulling them would seem to exaggerate the problem.

I doubt this is the problem. My "Inner Farmboy" is crying foul. Oh but I can't tell you how many times I've been wrong! Lotsa physics involved in 30,000+ PSI and HOTT gasses, mind-blowing acceleration vs friction coefficients that my inner farmboy never knew about. It's a rough world in there. Stuff happens in them barrels, I just know it.

I'll report back tomorrow.

Thanks!
Stan

[williamwaco]

Williamwaco, I will do that. But I can't get to my stuff until after Church tomorrow afternoon.

But what to do, IF.... it turns out I'm covertly "resizing" during the seating or crimping phase, is something I can't fathom.

I "think" I'm creating handsome crimps in the revolver rounds, at least. I can "see" some neck tension in BOTH cartridges working against the resizing I just did, by observing the reflection of my brass, freshly tumbled in wet stainless steel pins. (I LOVE that cleaning method compared to vibratory.)

I have no cannelures. Just a single grease groove. This might play a role in resizing the 357's. I treat them like I load my plated Berry's Bullets.

I do have a puller...an inertia type plastic hammer. If they resize so easily my press is "sizing" them out of spec, the act of pulling them would seem to exaggerate the problem.

I doubt this is the problem. My "Inner Farmboy" is crying foul. Oh but I can't tell you how many times I've been wrong! Lotsa physics involved in 30,000+ PSI and HOTT gasses, mind-blowing acceleration vs friction coefficients that my inner farmboy never knew about. It's a rough world in there. Stuff happens in them barrels, I just know it.

I'll report back tomorrow.

Thanks!
Stan

That is why you must pull the bullet instead of recovering a fired one.

[Quiettime]

Doesn't the PM9 have polygonal rifling?

[Whizzer]

Doesn't the PM9 have polygonal rifling?

Yup. Sure does.

[Whizzer]

So here is what I found after pulling a boolit.

I might note, that I managed to lose my 1 (one!) and only 9mm shell holder during a die set changeover, so I can't even do the test of a 9x19 boolit. After looking everywhere I can think to look, I decided to test the .357 cartridges which also cause leading in my SP101. (See post 15 above)

I sized the very same batch of Lee 125 grain round nose (Lee 356-125-2R) to .3575 and loaded it in an empty, freshly wet-tumbled and dried .357 magnum case. They measure .3595-.360 as dropped. This particular mold has no canelure. I seated the boolit and roll crimped as usual for revolver loads.

It looked perfect and after pulling it with my inertia puller, there was no measurable difference....except it had created a modest cannelure. As I said in an earlier post, these boolits are about 22, maybe 23 BNH.

So no, I'm not resizing the .357's in my seating/crimping routine.

And I measured the throats of that SP101 at about 358. As I stated above, I can't get a groove diameter measurement I'm really comfortable writing down here, but I'd guess .356 inches. 5 grooves=hard to mic. I can squirrel around the slug and get a reading of .356 (sortof) so a little over that number might be more accurate.

William Waco, I may well be squeezing the 9mm's down a little, based on how easy I'm producing a neat canelure with the factory crimp die on my .357 turret. But I won't know til tomorrow, when I can run down to the gun shop for a (grrrrr!) new 9MM shellholder.

[Whizzer]

Ok. I got back to the shop with a replacement 9mm shell holder and seated a boolit, then pulled it to measure. No unintended measurable re-sizing is being done with my 9mm die set either. I can however, see the faint imprint of the case mouth against the side of the boolit. So I assume it is a matter of degrees. If I were able to measure to a miniscule amount of deformation, my answer would be a little different.

So I must assume, boolits being TOO hard is still a possibility, as is poor lubrication a possible cause of my lead fouling. "Too small" of a boolit from unintentional resizing during the seating or crimping process is eliminated in my mind.

[williamwaco]

The only thing left to try is softer alloy.

In my experience that is not likely to help unless the bullets are too small and that doesn't appear to be the case.

Additional comment: The only thing that is constant here ( in the two guns ) is the alloy and the lube.

[Whizzer]

The only thing left to try is softer alloy.

In my experience that is not likely to help unless the bullets are too small and that doesn't appear to be the case.

Additional comment: The only thing that is constant here ( in the two guns ) is the alloy and the lube.

Agreed. And I'm going to try that.

I've been thinking my Cabine Tree Hardness Tester might be a "lemon" since I've been trying to determine my alloy's suitability. And I've been pretty busy at work the last few days. But Linotype Ingots and air cooled Wheel Weight Ingots should test differently, and they're not.

Something's not right here. The is a guy in Wichita (that might be available to help me) who is very experienced. He has the Lee Hardness Tester, and we might be able to determine the origin of the problem.

Thanks!
Stan

I'll follow up here as I learn anything new.

[williamwaco]

Agreed. And I'm going to try that.

I've been thinking my Cabine Tree Hardness Tester might be a "lemon" since I've been trying to determine my alloy's suitability. And I've been pretty busy at work the last few days. But Linotype Ingots and air cooled Wheel Weight Ingots should test differently, and they're not.

Something's not right here. The is a guy in Wichita (that might be available to help me) who is very experienced. He has the Lee Hardness Tester, and we might be able to determine the origin of the problem.

Thanks!
Stan

I'll follow up here as I learn anything new.


I don't know about your tester. It is highly rated but I have never used one.

I can tell you this.

New lino will test 21-22BNH period. I have never seen a rating different from this. Used Lino will test 18 to 22.

Air cooled wheel weights should test around 11-13.

That said "Alloy Suitability" is a red herring.

In your handguns you should get satisfactory results with some load with any alloy from around 8 BNH to around 30 BNH. I never use hard alloys because they are very expensive and in my testing they do not produce better accuracy. I use air cooled wheel weights and or range scrap for all my loads from .38 wad cutters at 700 fps to 44 Mag at 1300 fps, to .30-30 AT 2100 fps.

I agree that you can get very good results with lino. I just don't need it to get good results.

Leading is ( almost ) always caused by fit or lube. ( Occasionally by defective chamber or bore.)

PS:
One last reminder:

The very most accurate factory handgun ammo you can buy, ammo that produces zero leading in almost any handgun - .22lr and factory wad cutters are all made out of almost pure lead usually around BNH 6.