Ballistics by the inch

EMP4 can’t handle the pressure.

Earlier this month I took my EMP4 out to the range, and ran into problems documented in this post. My conclusion:

Since I haven’t had any problems with my standard-pressure reloads, I’m assuming that it’s the over-pressure which is causing this problem. Both the Underwood and the BB ammo are *really* hot. But I wanted to check everything out again before shooting the gun any more. If everything looks good, then I’ll start with standard pressure loads and then slowly step up to hotter loads. I expect that will resolve the issue, and I don’t mind carrying SD ammo which is a little less powerful — shot placement is more important than power.

With one thing and another, it’s been a busy month, and I didn’t have a chance to get back out until this morning to test my conclusion. But first I did a thorough cleaning of the gun, pulled the firing pin and examined it closely. One possible problem could have been the firing pin having sharp shoulders, which could have led to it punching too hard into the primer metal. But upon close examination the firing pin looked perfectly normal and very much like every other firing pin I’ve ever seen.

In preparation for going out to the range today, I picked up some additional good self-defense ammo and grabbed a box of standard factory target ammo:

Starting on the top left (all 9mm Luger ammo, of course):

I started with the Remington, and ran a couple of mags through the gun, examining it closely between reloads. No problems.

Then I switched over and shot each type of ammo, a full mag (9 rounds), again checking the gun between reloads. It ran absolutely flawlessly with each and every kind. I checked some of the spent cases of each type, and all of them showed a perfectly normal primer strike.

Then I loaded up a mag of the Underwood 124gr +P+ I had shot previously. The first couple of rounds were OK, though I checked the spent cases and saw that the primers were completely flattened — the firing pin strike was still visible, but it was no longer an indentation. That’s a sign of too much pressure in reloads, and something you always check when you’re working up a powerful load. The next shot was similar, but there was a missing disk of metal on the primer, which was stuck on the firing pin of my gun. I popped it off, shot the next round. Same thing happened.

I unloaded the gun and the magazine, put the rest of the Underwood ammo aside. Then I loaded it with the Buffalo Bore 124gr +P+ SD ammo. Basically, the exact same thing happened, though I think I made it through three rounds before the first punched-through primer. Again, I unloaded the gun and the magazine, and set the rest of the Buffalo Bore ammo aside. Again, I checked the gun thoroughly to make sure everything looked right. It did.

Then I went back and tried each of the lower-pressure ammos again. Each again ran flawlessly.

I could do more testing, but I’m convinced: the problem is that the +P+ ammo is just too damned hot for the EMP4. Now, my other 9mm guns do shoot it fine (even the little Boberg, which is really picky about ammo), so I guess I could say that the EMP4 is somehow flawed in design or construction. And if you want to hold that against the EMP4, then go right ahead.

But I’m happy enough with the gun otherwise, and there are plenty of types of good self-defense ammo available which are just a little less powerful. Works for me.

 

Jim Downey

 

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August 30, 2018 - Posted by | 9mm Luger (9x19), Boberg Arms | , , , , , , , , , , , , , , , , , , , ,

2 Comments »

  1. Part of it may boil down to the rifling leade and throat. It might be worth chamber casting the EMP barrel as well as some others for comparison.

    Comment by dewatters | August 31, 2018 | Reply

  2. You might want to try a square bottom firing pin stop to delay slide unlocking a bit. It gives the mainspring better leverage on the slide than the radius type. It will make it a bit more difficult to rack the slide.

    I’m not sure if that will solve the problem but it can’t hurt. I’m not sure if premature slide unlocking could cause pierced primers. My gut says unlikely but changing that part is an easy and not terribly expensive experiment (about $15 for an EGW).

    By the way, the common large radius was a M1911-A1 change to make the gun easier to cock, the initial M1911 had a smaller radius and some people run the square bottom square or with just a light chamfer.

    Comment by Dan | November 4, 2018 | Reply


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