Lines of Effort
Effort Thumbhole is an AR compatible thumbhole stock made from bricks or other easily manipulated materials. Bell & Carlson no longer make their AR thumbhole stock, which was also fitted to the Remington R-15 series. The Anderson Manufacturing rifles exported to New Zealand now use this cute number which I've been unable to locate. The thumbhole stock will not only reinforce the lower receiver behind the rear lug pin, it will also locate the buffer tube without threading it into the plastic receiver (we hope).
Here's a video of Version 5A being tested on a Remington 870 12 ga shotgun on 12 May 2014, with 30 rounds of 2&3/4" 00 buck. Many thanks to Elk Castle for accomodating us (and letting us rip off 30 rounds for free) and Omar, for graciously filming using my potato. Ammo purchased from WalMart, thanks to SWIRE.
Here's what we've arrived at so far - Version 5. Version 5 is clearly NOT a thumbhole. This is proof of concept, and is ready for testing. Ladies and Gentlemen, it is time to start building.
Our first test of Effort Thumbhole. 20 rounds, you can see the top endcaps pop off, as they were not glued down. A small crack developed below the glued area, which I pushed down afterwards.
Our second test of Effort Thumbhole. 29 rounds, you can see the top endcaps pop off again. You do not see in the video the stock completely come apart. Large amounts of messy epoxy is indicated.
Our third test of Effort Thumbhole, following application of $15 (3 tubes) of Loctite Plastic Epoxy. The first 10 round Thermold magazine is of American Eagle .223" FMJ. The second 30 round Cammenga magazine starts with 20 rounds of PMC .223" FMJ, followed by 10 rounds of American Eagle. You can see at the beginning of the video our unglued top endcaps pop off, while at the end the entire bottom portion that was not epoxied falls off. We're going to have to start ordering expoxy in bulk, apparently. You'll note the entired glued portion up top did stick solidly to the buffer tube.
Due to the parts on hand, we built from the bottom up; as such, this design MUST be glued.
Here's the Version 5 MLCad file. It will open as a text file in your browser, so you'll need to save it, & open MLCad to read it. See the Links page for MLCad.