Tapp, work on those smoothing groups. That's the first step in helping you surface the model.
NOOO! This is a horrible tutorial, and is not to be used! Not only did the guy making it not know what he was doing, he's also got some inverted normals on his example model.
The proper way to do smoothing in blender is to use the edge split modifier. Set it on your model, turn off "from edge angle" and then select the edges you want sharp and hit ctrl+e and select mark sharp. You'll notice that the edge is now sharp.
Before you export you'll want to apply the modifier. This will chop your model up based on what you've marked sharp. Export and you're good. You can save before you apply the modifier, or if you've already applied it, but want to make changes to your model, you can select your entire model in edit mode, and hit "W" and select "Remove doubles". Then just re set the edge split modifier and you can edit your model again.
I'm guessing i wasn't the 1st one... but the gas trap, upper hand-guard, front band, and the flash hider resemble my M1D and the magazine and its release resemble it's brother the m14's. I dunno, all i know is it looks good and it represents what you were going for well
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Thanks! I've really got to pick myself up a Garand one of these days.