What To Do If Your Polymer80 Slide Seems To Stick Open Randomly – Introducing Our Sanding Toolkit

I finished my Polymer80 PF940CL build and was pretty happy with the results. This is a really interesting Glock-compatible variant that is unique to Polymer80 that I really like. It’s a G19 lower designed to work with a G17 upper. This is why they call it the “compact long” (CL) model. Basically the handle doesn’t print as much under clothes plus you have the longer barrel and slide with the longer sight radius. It’s a win-win.

The Slide Sticking/Catching Open vs. Locking Open

Due to a function problem on the PF940CL, I realized that I needed to come back and update this post. If your slide gets caught open part way then this blog post is relevant – the recoil spring is getting caught.

On the other hand, if your slide is actually locking open and then slide lock lever is engaging the slide when it should not be, then you need to assess the lever specifically – click here for a new post I wrote about that.

Fixing the Slide Sticking Open

Back to the story, I built the PF940CL and it function tested just fine. It shot like a dream other than the slide sticking, or catching, open once in a while. I had a pretty good idea the recoil spring was catching on my purposefully so-so sanded area where I removed the barrel block from in the frame.

I bet you’re wondering – wait – what? He did it in purpose? Yes, I did. I’ve read about guys having this problem and wanted to recreate it for a blog post and also to allow me to demonstrate a new sanding tool kit I’ve assembled to make the work easier and faster.

That piece of plastic that forms the inside of the letter “U” is the barrel block and needs to be removed. You want to remove right up to the line and do so cleanly with no burs/ridges for the recoil spring to hang on.
I did this CL with just enough lip so you can see what needs to be removed. Note, I circled the bottom because of the lip but there were no scuff marks from the spring. The left side show the scuffing done by the recoil spring as it ran against the plastic and sometimes even caught.

To avoid this, just be real careful about not leaving an edge. Historically, I would mill out most of the plastic and file the rest down flat using a combination of wood dowels and popsicle sticks to provide a stiff backing for different grits of sand paper. It was tedious but it got the job done and it will work for you as well.

Here are my sanding supplies that normally stay in the repurposed Polymer80 box.

A better way…

Ever since my first Polymer80, I was wondering how I could reach in there with a hand tool and get ridge of the plastic in a more automated fashion but also still have enough control to not make a mess. For example, a die grinder with a burr would scream through the plastic and destroy everything in the blink of an eye,

Dremels / rotary tools give you a ton of sanding options but nothing that would allow you to reach straight back from the nose of the frame and be able to sand the “U” and its curved surfaces.

I kept digging around and hit on the idea of using a 4″ shank mounted in a slow turning hand drill and using sanding rolls. That worked great! I was able to source 80, 120, 180 and 240 grit rolls to allow me to start course and move finer and finer.

Here’s the shank and a sanding roll in my ancient Ryobi 18 volt drill.
Here, I am smoothing out the channel. The trick is to go slow and keep the tool moving – don’t sit in one spot. Work for a few seconds and check how things are shaping up. Bear in mind that a low grit can remove material pretty fast and a high-grit (finer) drum can clog up if you are removing a lot. Compressed air can blow the plastic out of the sandpaper and old toothbrush can help as well.
Here’s the end result. It took me longer to try and get the photos than to do the cleaning up of the barrel block area. There are know more ridges for the recoil spring to hang up on. I’m not sure what the two lines are that you see at the bottom but they are not a ridge.

So the sanding kit includes the You don’t need it to be so smooth that it looks like it was never sanded – that’s why the sanding kit only goes up to 240 grit.

Start with a lower grit and move up to the 240 grit. The 180 and 240 grit drums will clog up with plastic pretty quick so they are more for finish sanding than removing a lot of material. I use compressed air to blow the plastic out of the drums and you could do that or use a stiff brush to clear the drums as well.

Please let me stress to you that slower is better. If you are using a drill on high speed or chuck these into a die grinder, they will remove material super fast. In my honest opinion, too fast. I have my old Ryobi drill on it’s low first gear speed and just take my time by sanding a bit and checking over and over. I would urge you to do the same – you want to remove all material inside the “U” but no more.

I hope you folks will buy one to make building your Polymer80 pistols. Click here for the order page in our store.


Polymer80 and Glock Parts Vendors

When you want to customize your Polymer80 or Glock, or you need replacement parts, there are a number of solid vendors you can go to and I have dealt with all of the one’s listed below and can vouch for them:

Those are all reputable vendors and aren’t going to sell you inferior counterfeit products.


Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

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