A couple of months ago a friend of the blog sent me a princely gift: 450 rounds of bulk practice 115-grain 9mm and ten boxes of 124 grain. Yesterday I burned through (almost) the last of the 115-grain, and so…
…I used the sweet little 500-round ammo can they came in to start on the 124-grain stuff.
And while I was sitting at the table in Ian’s Cave doing that, I took the opportunity to check something that had been bugging me.
See, after a (lengthy) break-in period the Arex has become completely reliable with all types of ammo except one in one very specific circumstance: If I insert a 19-round magazine completely full of 115-grain practice ammo into the pistol with a round already in the chamber, something that (almost) only happens during practice sessions, there is a very high probability that the pistol will experience a hard jam after firing the first round. By hard jam I mean a cocked round that can only be cleared by dropping the mag, racking the slide, then completely reloading. The pistol doesn’t do this under any other circumstances. And it seems to me that what’s happening is that a round trying to enter the chamber while under full magazine spring pressure just decides it’s a little too long to make the trip. I’m not saying that’s what’s really happening, only that that’s what it looks like. The Arex has always fed 124-grain ammo – and all service ammo I’ve tried it with – just great. Can’t think of a single malfunction. And looking at the ammo it always seemed to me that 115-grain bullets of all brands* – and I deliberately tried a bunch, because early on this looked like it was going to be a bigger problem than it proved to be – stick out of the case just a little tiny bit more than 124-grain bullets do.
So anyway I’m sitting at the table, and it happens that on this same table is a micrometer digital caliper I never got around to taking back to my reloading bench. So…
115-grain FMJ
124-grain FMJ
The difference is consistent across several measured samples. I can think of no logical explanation for this. But it does seem to explain why the Arex isn’t happy with the lighter bullets. I now believe it simply wasn’t made for them.
Of course the lighter bullets are cheaper than the heavier ones, and I only use them in practice**, and while practicing there’s nothing wrong with an occasional malfunction drill. So I just ordered another 500 115-grain factory reloads from the same supplier. Because I’m not a naturally great pistol shooter, and anything that encourages me to shoot a lot is a good thing.
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* the single exception being Wolf, for reasons I won’t even speculate about.
**Okay a couple of days ago I did experience a hard jam while using the pistol as a noisemaker to drive cattle out of my yard, and that was very annoying but hardly life-threatening.
While I have some theories, I’m not a gunsmith, nor do I play one on TV, so I will be looking forward to the comments and learning which one is correct.
Uncle Joel, I’m not going to speculate on the effects of a desert climate on cognitive functions, or anything, but back East we call that a digital caliper.
We still love you, Joel.
You know that’s been low-key bugging me all day? I wrote micrometer, I re-read it an hour or two later and thought, “That’s not what that’s called.” And then I went off and washed dishes or something without giving it any more thought than that.
Well. My digital caliper is so superlatively fine and accurate that it rates as a micrometer. Prove me wrong.
This only happens when you insert a full 19-round magazine into the gun where there is already a round chambered . . . right?
Unless you desperately need that twentieth round, I believe I’d just not pre-load the chamber.
I’ve seen/heard more than one “pro” say that the “plus 1” loading procedure puts the magazine stack spring load high enough to cause the failure you describe.
Heavier projectile = less powder, therefore can be seated deeper?
There isn’t any reason at all, other than that’s how those companies chose to load those cartridges. Given that I haven’t ever loaded powder into a 9mm case anywhere near to capacity, as in affecting bullet seating depth, I think we can dismiss that as a factor.
Given that the max cartridge length for 9mm Luger is 1.169, I would say that your pistol really ought not to have any feed issues here, at least not related to overall length.
It looks like the ogive of the 124gr bullet is a slightly longer taper, so that could also be a factor. Higher spring pressure = greater pressure on the feed lips + a bit more friction to overcome? Perhaps a bit of polishing on the feed lips could help. Any little burrs or rough spots? Any roughness in the feed ramp?
It’d be nice if my ammo stash were a tad bit easier to get to, as I might then be able to measure some of mine, though I couldn’t say whether I happen to have any factory 115gr around here. I suppose I could put it on my to-do list.
If the factory crimp isn’t too tight, you might try using your press to shorten a couple cases. Yeah, officially, that isn’t recommended practice. 🙂 So I’m not recommending it, just sayin’ is all. Hypothetically.
If both weights are loaded by the same company, it may just be as simple as they used the same setting on the seating die, figuring that both bullets have similar round noses and both result in a loaded round within spec. Or it could be that Murphy is just in a bad mood, he does that.
Well, Joel, if you set it to mm, you ARE measuring micrometers–you’re just doing it by the thousand, so you’ve got it!
Yeah, and that’s why I carry it with 16 rounds in a 17-round magazine. And (so far) it has never jammed on me that way. The 19-rounder only gets used on the range with FMJ, I don’t usually carry a second mag.
Loading a 19rd mag with 18 is an easy enough solution. Especially since it lets you practice with the most widely available and affordable plinking ammo.