How to modify a SOPMOD stock to work with an A5 receiver extension!

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#1 How to modify a SOPMOD stock to work with an A5 receiver extension!

Postby Jack » Tue Apr 04, 2017 8:36 pm

As everyone is already aware, the SOPMOD stock doesn't quite work with an A5 length receiver extension. It works to an extent, but you can't quite get it to fully collapse. All in all, the stock choices for the A5 extension are pretty limited if you want full range, so it's nice to have a standard stock like the SOPMOD that can be modified to fit. The SOPMOD is by far my favorite stock on the market, and there's really nothing like it that's made for the A5 extensions. All the current A5 stocks I'm aware of have an angled buttpad, like the Magpul variety, which I hate with a passion.

(Note that I used a B5 systems enhanced SOPMOD stock and a Bravo Company Manufacturing A5 length receiver extension.)

1. Cut out the back of the stock so that the receiver extension can slide up all the way in there. This stock is actually an OD one that has been dyed black, so you can clearly see where material has been removed. Cut off the attachments from the buttpad so that it's smooth. Drill some matching holes in the back of the stock and the buttpad so that later the resin will form a mechanical lock when you glue the buttpad back on.

2. You can see that the receiver extension now clears and can slide all the way to the rear, locking in the fully collapsed position.

3. Tape everything up. Put a piece of tape over the drainage hole in the back of the receiver extension so that playdough doesn't get down into it.

4. Put a thin layer of playdough over the butt end of the receiver extension to form a dam between it and the resin. This will keep the resin from running down into the stock, thereby gluing it to the extension. If this happens you're up a creek, so make sure the playdough forms a tight seal.

5. Butter up the butt of the stock with resin, being careful not to disturb the playdough underneath. It's a very thin layer of playdough, so don't press too hard. Make sure and get it down into the holes you drilled though. I'm using acraglas here because it's what I had on hand, but lots of different stuff would probably work. JB Weld comes to mind, and maybe even two part epoxy, like Gorilla Glue.

6. Butter up the buttpad, again making sure to get the resin down into the little holes to form a mechanical lock.

That's pretty much it. You then just put the two together and press down. Be sure and scrape off the excess resin or you'll have a mess on your hands. Some of it will definitely squish out the sides when you press the two together, so just scrape it off. Then run a q-tip soaked in brake cleaner around the edges to clean it up and get rid of the excess resin.

At this point, I removed the stock from the receiver extension just in case any resin had made it past the playdough. That's the beauty of the acraglas is that it held it's shape so the stock could be left to dry.

It worked like a charm! Now the stock looks the exact same on the outside, but it will now fully collapse and lock into place like it was made for the A5 extension.

Here are some photos of the finished product:


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