Thursday, September 20, 2012

PMR-30 Keyholing Update

Thanks to the due diligence of fellow gunbrony and official Lurking Rhythmically fact-checker The Jack, I have determined the source for the key-holing that occurred during testing:

After extensive testing with various ammunition we have concluded that all remaining key-holing issues have been isolated to one particular brand and weight of ammunition. Unfortunately this seems to be the most common and available ammunition: CCI Maxi-Mag 40gr.
The 30gr and 50gr varieties of CCI shoot flawlessly, as do other brands of 30gr., 40gr., and 50gr. ammunition. For some reason, though, it seems that the 40gr. CCI Maxi-Mag in particular still has sporadic key-holing. At this point in time we have deemed it ammunition specific and recommend trying a different grain or brand of ammunition if your PMR-30 is still continuing to key-hole with an updated barrel.

On the one hand, this is great news.
  • They've fixed the chronic key-holing with a new barrel;
  • They sent me a proper barrel instead of an older version;
  • A 10% key-hole rate for one specific kind of ammo is quite acceptable. 
On the other hand, CCI Maxi-Mag 40gr was specifically recommended in the literature that came with the pistol. While I understand not wanting to change the manual for something like this, the fact that this card was included in the case bothers me:


Come on, guys. If you're going to include a "Oh by the way" card, you need to get your information right. 


15 comments:

Stephen Carville said...

Personally I would not consider a ten percent key-hole rate for one specific brand and weight of ammo to be acceptable. Especially if that ammunition is from a manufacturer as reputable as Speer/CCI. I never seen or heard of any 22 magnum that had a key-holing problem that didn't trace to a worn out, damaged or badly leaded barrel.

OTOH, historically the locked breech, blowback and delayed blowback designs all have a poor reputation for reliability with long cartridges.

McThag said...

What's odd about this situation is the lighter and heavier bullets are fine.

I would think that if it were a twist issue, the 50gr would be worse than the 40.

I wonder if it's related to velocity and the 40 is hitting the sour spot in the twist/bullet length/velocity formula.

.22 WMR was designed for rifles so some learning curve is kind of expected.

I wonder if there's some parallel to bullet selection for the 6.8 SPC.  .277 bullets were almost all for cartridges going into necked down .308 or .30-06 cases so were much longer than optimal for fit in an AR magwell.  Now the bullet makers are making bullets just for it.

If the PMR becomes popular I expect there to be tailored ammo for it and S&W to make an almost identical version that costs at least twice as much.

geodkyt said...

Interestingly enough, one of the things that soured me on .22WMR (vice .22LR) was keyholing and accuracy issues I've had with various pistols. . . and my "go to" round was always CCI Mavi-Mag 40gr, because of how well the other CCI loadings performed in .22LR.  (Forgive me, I was young and convinced the solution to any ballistic issue was MOAR POWER.  I pretty much wrote .22WMR out of my awareness as a pistol round 20 years ago or so. . . )

The idea of that loading hitting a ballistic "sour patch" sounds plausible.

geodkyt said...

Of course, if this was chambered for .22LR, I'd run out and buy it tomorrow, even if it meant Ramen for a month.  (Just as I would have with the Automag II, if it was available in .22LR.)

Erin Palette said...

I've mentioned to Kel-Tec that offering this in .22LR, or perhaps a conversion kit, would would sell like hotcakes. 

Erin Palette said...

When next I shoot, I'm going to try it with different grains and see if the keyholing goes away. I think it will. 

Target Brony said...

i've a LOT of the "suspect ammo", as a result of finding it 100% reliable, both in function and feeding.  sooo, pmr-30 gets "rebuilt" after an ooopsie with the original breach.  new barrel.  basically, whole new upper.  Gen 1 + Gen 3 (current is Gen 4 i think with the stippled lower).

i was MORE accurate with the original.  so, i'm annoyed.  something changed.  getting used to it.  need to try with a good red dot to see if it's the new sights or not... (or me). 

keyholing - i THINK that if you assume this gun is so light and has no recoil that if you aren't 100% solid with your grip (it's a big grip too), a kinda limp wristing occurs, and keyholding of a sort occurs.  if i'm dead solid, and smooth, nothing.  pretty rare to happen anyway with this build.

would like to try the Gen 4 build at some point. 

can't wait for the RMR-30...

oh, and got some rare (to me) Mosins :>  collect them all :)

Erin Palette said...

The keyholing could very well have occurred during the final five quick-shots. I probably didn't have the best grip on the gun during that time. 

McThag said...

A limp grip is not going to cause a keyhole!  A poor grip or bad trigger pulling is going to cause the impact point to move around, but it's not going to affect the stability of the bullet.

Old_NFO said...

That would assume they actually DO enough testing to find those little issues, but they depend on their CUSTOMERS to be their test bed...

Weerdbeard said...

 Keyholing happens when the base of the bullet attempts to get in front of the tip of the bullet in flight...and because of low resistance of air and the fact that it leaves the gun tip first, this leaves the bullet tumbling end-over end.

The only way that happens is if the bullet isn't properly stabilized by the rifling.   Limp grips only really effect which way the muzzle is pointing as the bullet exits.  I can't imagine enough force being done by the muzzle flipping to actually cause the bullet to tumble.

This CAN effect how the spent case is ejected because it is orders of magnitude slower.

Nope, this is all an issue with the rifling of the barrel...or an under-sized bullet (or over-sized bore).   Given that other .22 WMR rounds were printing well, and that Erin wasn't using suspect ammo,  the rifling twist rate is likely the culprit.

Tocotox said...

yeah, intellectually, i want to believe that...

however, actually seeing my (and other guns/brands) that sometimes keyhole for a given user, never keyhole for others, there's SOMETHING going on.  can't explain WHY though.

same for FTEs and FTFs in some users.  guy had a weak grip, and this "crap gun jammed all the time".  just not for me (or others).  in one case, the extractor was marginal, and a poor grip just exacerbated the issued.  better grip helped, but a new extractor really was the ticket.

we've also seen MANY pmr-30s that simply do not keyhole at all with the new barrels and the CCI stuff.  weird, eh?

there's some though that the escape gasses on the muzzle might cause a turbulent enough event to impart some wobble - if that's so, the new threaded barrel with flash hider might be useful (and it looks cool).  i want one.

McThag said...

Your grip most certainly has an affect on the action, you are letting the energy needed to cycle be put to other purposes, like flipping the whole pistol up.

If one example of a gun keyholes and another doesn't we call that poor quality control instead of poor design. Bad QC from Kel-Tec?  NO!

The issue seems consistent with wrong twist or a loose bore.  Shot out barrels will also keyhole because the base of the bullet cannot expand enough to engage what rifling is left.

On further reflection, a really loose bore and a REALLY loose grip might just zing the round to keyhole.  You'd really have to take the gun and put it in something like a Ransom rest and shoot a buncha rounds to see if it's really some shooters and not others or the gun.  I'll bet that it will keyhole from the rest if you fire enough shots.

geodkyt said...

It can also happen if the bullet gets smacked in the ass by an off-center puff of propellant gas, such as can happen with a really loose bore, a mangled crown, or (drum roll, please), a loading that is tailored for a significantly longer barrel, and thus has a LOT of propellant flashing after leaving the muzzle.  The bigger your muzzle flash, the more likely this is to occur (note -- the flash is a SYMPTOM of the same SOURCE of the problem; big fireballs alone don't necessarily do squat to the bullet, especially not with a good crown or muzzle device.)

geodkyt said...

Probably too cheap to test the pricier ammo for accuracy; only testing it for reliable cycling.

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