Barrel Fitting

Contributions from bapegg

Barrel fitting tips and tricks.

Time for another write up folks. This time we will discuss barrel to slide fit, measurements to take, and how to hand fit a barrel.

It seems that the issue of the barrel lugs hitting the cross bar of the FLBR has popped up more frequently on the forum lately and we will discuss what to check and how to fix this and other barrel fitment issues.

We will start by looking at the slide first. Always test fit the barrel first. The main thing to check on the slide is if there is any excess Cerakote on the breech face. If your slide in not Cerakoted, then skip over this check.

Next we will look at how the barrel fits into the slide itself, you want the top of the barrel hood to sit within 0.003" to 0.006" to the top of the slide. This is critical for a few reasons. One is so that the locking lugs clear the FLBR and also if the barrel is sitting too low, it can cause feed issues.

Here are some other critical dimensions to check. And I did a separate thread with all of the dimensions and have updated it a few times. All dimensions are listed in the next subject below.

Now for the fix. This is also used when you buy a semi fit barrel. You want to file on the front ledge of the barrel only. This is critical. Filing on the back of the barrel/chamber area can effect head space issues leading to light primer strikes, failure to fire and worse case ruptured or split cases and case head separation.

Here is where you want to file. As noted in the photo: File the vertical surface (blue arrow) if the barrel is tight in the slide (after checking the breech face). File the horizontal surface (red arrow) to get the top of the barrel hood to sit flush with the top of the slide.

NOTE: You do NOT want the top of the barrel hood to sit above the top of the slide. You also want to keep both surfaces flat and parallel/square to the rest of the barrel. It is important that you use a file with safe sides (smooth sides that do not cut). I personally like to use a small jewelers/Swiss file for this. A bigger flat file will be harder to keep flat and have a tendency to roll the surface edges.

Here are a couple of photos of the Swiss file that I use for barrel fitting. Notice that one edge is smooth. I had to take the file to a good honing stone to put a safe edge on it. The smooth side is to ensure that you are only changing one surface at a time. Always keep the smooth edge towards the 90 degree surface.

Now if you are still having problems with the barrel locking lugs catching the FLBR then we need to look at other things such as are the rails too low or is the FLBR out of spec? We will leave those for another day.

I hope this helps everyone out and they find it valuable information.

Slide to barrel fit dimensions

Here are the critical dimensions for the slide to barrel fit. I measured 2 G19, 1 G17, 1 G34, 1 G26, and 1 G43 slide.

G19 P80 slide and barrel

A) 0.094"

B) 1.219"

C) 1.218"

D) 0.090"

G19 KM Tactical slide and barrel

A) o.o94"

B) 1.221"

C) 1.220"

D) 0.090"

G17 P80 slide and Rockey Brass barrel

A) 0.094"

B) 1.219"

C) 1.217"

D) 0.091"

G34 80P Goon slide and barrel

A) 0.096"

B) 1.220"

C) 1.219"

D) 0.092"

G26 Zaffiri slide and KM Tactical barrel

A) 0.091"

B) 1.220"

C) 1.219"

D) 0.091"

G43 OEM slide and barrel

A) 0.115"

B) 1.220"

C) 1.219"

D) 0.114"

Measurement E - top of barrel hood to bottom of feed ramp.

G19 barrels:

A) 0.816" - NineX19

B) 0.820 - Polymer 80

C) 0.821" KM Tactical

G17 Barrel:

A 0.809" Polymer 80

G34 Barrel:

A) 0.813" - 80P Builders

G23 Barrel:

A) 0.809" - OEM

G22 Barrel

A) 0.811" OEM

Measurement F - top of slide to top of barrel hood

I measured the majority of my builds along with a few OEM Glock pistols from the top of the slide to the top of the barrel hood using a depth micrometer.

Smallest - 0.003" difference.

Largest - 0.006" difference.

Average - 0.004" difference.

I updated this with measurement E since there seems to be a problem with barrels hitting the crossmember of the front locking block rail for some people.

Another update for measurement F for those that are having issues with the barrel hitting the FLBR and/or trying to hand fit the barrel to the slide.

Hopefully this will help everyone that might be having issues with the barrel to slide fit.

Marine Gun Builder

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