DIY Hopper Extension for GMG

One of the big drawbacks to the pellet smoker is the limited capacity. My GMG Jim Bowie model holds about 15lbs worth of pellets in the hopper, and lasts about 5 hours. So for longer smokes, things like brisket, pork shoulder, etc, you would need to keep an eye on it through the night and refill the pellets once or twice. Because the last thing you want while smoking a $60 piece of meat is to run out of fuel.

So I got to thinking… If I were to make an extension for my hopper, I just might be able to increase the pellet capacity of my smoker. I got searching, and it looks like Louisiana Grills offers something like this for their grills. Ive also seen pictures where people have used empty pop cartons. But I wanted a less redneck solution than that.

One of the perks of my job is that Im afforded access to expensive tools and leftover building materials. In this case, a Van Mark Mark II 4-foot sheet metal brake and some black aluminum trim coil.

First thing I did was measure out the interior of the standard hopper to figure the dimensions. This drawing was for my first version of the extension, which i made a mistake on so I had to start over. But I also decided that I might as well make it bigger to try and get as much added capacity as possible.

Next I cut my first piece of coil stock to make a half box for the section up against the side of the smoker.

Measurements were made, the piece cut to size, and edges were trimmed so that I could hem them. The edges need to be notched so that you dont crack the aluminum by hemming the same piece “twice”.

After a lot of tedious snipping and measuring several times, I ended up with this sheet, 4 sides hemmed. Hemming the sheet has a couple of benefits. It makes the edges a lot smoother, and also adds rigidity to the panel. Aluminum is very soft, so without hemming it would be extremely flimsy.

The next thing I did was add 2 90° bends to complete the half box.

Piece 1 complete.

Now to piece 2. This is the piece that completes the box on the outside.

All bent and you can see the fit is spot on.

Piece 1 and 2 complete. Piece 3 will rest on the angled portion of the inside of the hopper. This isnt a totally necessary piece, but I think that it will help add stability when the extension is filled with pellets.

I still need to add a small angled bend to piece 3, but i need to add it once I see how everything fits in the smoker. But the weather is way too nasty to be screwing around with the smoker today. Later this week I will fit all of the pieces and rivet them together.

The standard hopper volume is about 470 cubic inches.

As you see below, the added volume is about 9.5″x9.825″x13.375″. Additional volume of nearly 1,250 cubic inches!

Which means that Ive increased the volume of the hopper by ~2.66 times, for a whopping total volume of about 1,720 cubic inches!!

With the extension, I figure that On a regular day, I should be able to get around 17 hours of smoke time before having to re-fill.

Fitted all of the pieces and riveted together. Fits perfect!

I drilled some vent holes in the angled piece to match the fan vent in the standard hopper.

It fits perfect and Im really happy with how it turned out. This weekend maybe ill test it out with a few racks of ribs or something.

I definitely cant wait to make a brisket this summer.

Update: 4/16/18

Added a baffle to help reduce the amount of weight from pellets pressing down directly onto the auger. Added some 1×1 aluminum legs to help hold the weight and prevent to much stress in the grill.

Then I filled the unit with pellets. It now holds 45.x lbs worth of pellets! Increased from the 17lbs of the factory hopper.

Aaaaand best of all, my math from above was spot on. Exactly a 2.66x increase. Hooray for math!

Now, im going to let the grill sit as-is for about 36 hours until I test this badboy out on saturday. More updates to come.

3 thoughts on “DIY Hopper Extension for GMG

  1. So, how did this turn out? Any plans to make a couple to sell? I would love to expand the capacity of my GMG hopper but all the ones I can find are quite expensive.


    1. It works great. But you definitely need the legs if youre gonna load it up. With regard to making more, my design works great with the hopper fan, etc. Unfortunately its just too time consuming for me to make them to sell. The materials themselves dont cost much, but the cuts and bends need to be pretty precise.


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