Well I was one of the first people to purchase a Magpul STR when they first came out and I immediately fell in love with it. It is a great stock and I found the cheekweld very comfortable. The only issue that I had with the stock was that the friction lock did nothing to "lock up" and make the stock rock solid on the extension like the CTRs do. So last week I figured that I would fix it myself and lucky for you I took some pictures along the way. I am pleased with the fix and now the stock only slightly wiggles due to the size of the slightly oversized hole at the extension.

Tools needed:
Drill
1/8" drill bit
Flathead screwdriver
Needle nose pliers (preferably locking)
Hammer
1/8" punch
Rivet tool
1/8' dia. 1/4" grip

In order to get to the roll pin that the friction lock pivots on the storage tubes need to be removed.

Directions:

Step 1: Remove the buttpad and rubber storage tube caps. This reveals the factory rivets that will need to be removed to take the storage tubes off.


Step 2: Using the drill equipped with the 1/8" bit, remove the head of the rivet. Then use your flat head screwdriver and gently pry the storage tube away from the rivet. With this rivet removed you can then slide the storage tube off by pushing on the flat area at the front of the tube towards the rear of the stock. Do this on both sides.


Step 3: With the storage tubes out of the way, use your screwdriver and pliers to remove the remaining part of the factory rivet so we can re-rivot it at the end.



Step 4: Using a hammer and 1/8" punch, remove the roll pin retaining the friction lock.


Step 5: Remove the black pin that is retaining the metal clip in the friction lock. I just pushed the metal clip towards the direction of the pin and it just slid out.


With the metal clip removed you can see that the metal clip is supposed to provide the additional clamping action on the plastic tabs on the stock to provide the friction on the extension to lock it.


Step 6: Take your pliers or use a bench vise and push the ears of the metal clip in slightly. This will give us the additional friction we want. Don't go too crazy and incredible hulk and destroy the metal clip, a little adjustment is all that is needed here.


Step 7: Now we can put it all back together the same way we took it apart. Now it may be necessary to place the stock on the extension and reinstall the friction lock while installed depending on how much you bent the ears in.


Step 8: Reinstall the storage tubes and buttpad. Rivet the storage tubes using 1/8" diameter, 1/4" grip rivets.



Step 9: Pat yourself on the back and enjoy your STR and it's newly added friction lock feature.

I did this on a CTR a few yrs ago.  Just didn't have any storage tubes to mess with and it works great.

Good to know, might have to do mine

I hope that someone finds this helpful.