Magpul Bottom Metal

I run RH Custom Guns in Fredericksburg, Texas (RHCustom Guns. com) and recently had a client of mine wanting a more affordable box magazine system for his daughter’s pet .243 rifle. He said, "I’d like to find something that uses Magpul mags so I can get extras that are less expensive than the traditional metaltype box mag." He was definitely on to something. Now, I know that the parts from Magpul aren’t actually made of metal.

However, we gunsmiths typically refer to a trigger guard, floorplate, and magazine well as "bottom metal" so I will use that term throughout. Also, it sounds better than "bottom polymer." After a little research, I discovered that Magpul has recently released anew polymer trigger guard that has the ability to accept the company’s AICS-pattern P-Mag. This is a polymer magazine designed to fit in any Be sure to center the screws through the holes in the stock. Here you can see the tabs that need to be sanded off.

Accuracy International type shortaction magazine well. To top it off, the Magpul bottom metal was less than a third of the price of traditional metal detachable mag systems and it came with a five round magazine! Not knowing if it would fit, I contacted Magpul directly to ask what they thought. It could be made to fit, they told me, but they did not recommend it. My client immediately wrote their recommendation off as lawyer-speak and said he’d be glad to be a guinea pig for the project.

If it didn’t work, we could always install different bottom metal. I ordered the parts and inspected the rifle to see if I thought it would fit. After some inspection, I determined that it could be done and the profile really wasn’t that much different from others. With my client’s approval, I proceeded with the work. First, I have to say that Magpul probably doesn’t recommend this type of install because it is not for the unskilled.

It took approximately three hours of work both on the mill and on my bench to fit it. On the Magpul part, there are two tabs on the bottom metal in about the middle of the magazine well. Sand those off to the surface of the rest of the part. These are used to key into Magpul’s Hunter stock and are not necessary on a BDL stock. After going through the requisite safety checks, disassemble the rifle.

While not exactly necessary, I’ve found that removing the trigger and bolt stop assemblies helps to keep those parts from getting too dirty from sanding dust. It will save some later headaches. The most difficult part is ensuring that the bottom metal is going in level to the action of the rifle. The curved and angled surfaces on both the bottom metal and the stock make this a bit of a challenge. I’ve found that using Forster’s inletting guide screws (Brownells # 319-415-700) greatly aids in this.

After the rifle is disassembled, install the inletting screws and place the stock on the rifle. The screws should stick out below the bottom

of the stock and you can slide the bottom metal over them. Be sure the part is aligned correctly to the action (not the stock) and trace around the part of the bottom metal that touches the stock. This is the first section you need to work on. Place the stock in the mill and mill out as much as you can while still leaving your lines. After this, use files to slowly remove material up to your lines until the bottom metal starts to go in to the stock.

Note, it is easy to think you need Looks and works great! to file past your lines because the piece will not go any further in to the stock. It is more likely that you either are cocking the bottom metal as you try to seat it or that you are not filing straight down. Be sure to work as straight as you can. I recommend using inletting black (Brownells # 457-001-050), which is a black paste painted on to the part you are inletting.

When the part is pressed into the stock, it will leave a black mark wherever it touches, showing where to remove material. Trust the black mark. If there isn’t a black mark, it isn’t touching there. Once you get the bottom metal let in far enough that its outer edges are touching the surface of the stock, trace all the way around the outline of the piece. Using the mill or files, remove material up to your line. You did remember to file straight, right?

Now it’s just a matter of testing the bottom metal, removing material, re-applying inletting black, and repeating until it’s right. The Magpul bottom metal is fully inlet when the front and rear areas where the screws go through are touching the original inlet surface on the stock. In other words, the entire bottom metal will not be flush with the bottom of the stock. Do not go any deeper or the magazine will not fit. After you are satisfied with the fit of the bottom metal, test for function using dummies.

On the rifle I did, the box magazine had to have a bit of material sanded off of the top of the feed lips to seat correctly. This did not affect feeding at all and may or may not be necessary on other rifles. The only complaint I have about this system—and it’s minor—is that the magazines do not fall out when the release is tripped. I assume this is a function of the material the parts are made out of. At least you won’t be losing mags in the dirt. All in all, I found this a very rewarding project.

I am now able to offer my clients an affordable upgrade at less than half the cost of some of the more common bottom metals. My client went away very happy and I look forward to informing Magpul about how well it works. Good gunsmithing! AG