May 13, 2015
By Brad Miller, Ph.D.
Aftermarket barrels are quite the rage for some guns. A new barrel can transform your pistol into an entirely new gun by changing calibers, adding a compensator and so on. While I'm certainly not opposed to any excuse to buy another gun, the option to change barrels in an existing platform speaks to versatility as well as economy.
I recently bought a .960 Rowland barrel kit for my Glock 19C 9mm pistol. The "C" model Glocks have a ported barrel and corresponding slots in the slide. The .960 offers a substantial increase in muzzle energy over the standard 9mm Luger. The kit included a stainless steel barrel and a screw-on compensator.
In most instances, barrels are a drop-in fit. They require no fitting and will literally drop in place, and you're ready to shoot. That was almost the case with this barrel — the barrel fit easily in the slide.
I installed the new barrel, reinstalled the upper assembly on the frame, racked it and . . . "jam city." The slide had locked-up during its forward travel. Hmm, what's up? I pulled back on the slide slowly. The rear of the barrel dropped down, and then the slide went forward as it should. I racked it a few more times. It didn't jam every time, just now and then. It was hanging on something. But what?
Every time it stopped, all I had to do to clear it was to slowly pull the slide back and let the rear of the barrel drop. The slide only jammed when the barrel was up tight against the slide. The slide did not stop at the same place every time, which did not help diagnose the problem.
It wasn't getting stuck because the barrel was the wrong size. It had sufficient space on both sides, so that wasn't the problem. When I applied pressure to push the barrel up against the slide and slid the barrel along it as if it was returning to battery, it dragged a bit. To double-check this, I did the same thing with the Glock factory barrel. It didn't drag, so there was something about the new barrel that wasn't compatible with the Glock slide.
I noticed some slight machine marks on the top corner bevels of the new barrel's outer chamber and suspected that might be causing the drag. I then checked for rough areas in the corresponding inside corners of the slide but could not detect anything. It was smooth there.
Looking in the Wrong Place
At one point, I pushed the barrel hard against the slide as I slid the barrel back to lockup. It jammed good this time. But where? I turned the slide over and looked in the port cutout and saw the problem.
The problem was not the new barrel, it was the Glock. It was the unique feature of C model Glocks: the ports in the slide. The edge of the port cutout was so sharp that it was cutting into the top sides of the barrel. That is one hard slide!
Well, I suppose the barrel was partly to blame since this wasn't happening with the factory Glock barrel. The bevel on the square edges of the chamber on this barrel are smaller than they are on the Glock barrel, so the top surface was a little wider on the Rowland barrel. This is important because there is a slight curvature in the slide's internal surface near the corner, which would only help a sharp edge scrape along the corner of the barrel if its top surface was wide enough. These two small features combined to make ideal conditions for this very unusual mismatch.
This was easy enough to fix, and I addressed both the barrel and the slide. I increased the bevel on the top sides of the barrel so they were similar to the native Glock barrel.
The main offenders were the slide ports. Fixing them was, arguably, the only necessary fix, since that would prevent scraping on any barrel. I broke the edge on the slide ports with a round file and smoothed it out with 320 grit sandpaper. It didn't require much metal to be removed, just enough to round the inside edge of the port so it wasn't scraping on the barrel.
The finished work shows that the edge of the port cutout no longer threatens to scrape the barrel. That was all it took to fix the problem. Now it runs like a greased Glock!
The slide ports in the Glock C models pose a unique design, and folks who are buying additional barrels for these guns will now know to watch for this. A quick inspection of how the new barrel interacts with the slide ports could save them some confusion and aggravation. If they mismatch like mine did, it's easy to fix.