Call of Duty 3

This achievement is a little misleading. There are only three assult rifles in the game that you can use: The Bar, Bren and MP44. I originally thought that an assult rifle was the same thing as machine gun and I couldn't figure out why I wasn't getting the achievement when using a MP40 (which are everywhere) and my trusty (but crappy) Thompson.

This is how I got the achievement: I did the Island level (level 2) on Easy. You start out with a BAR so right away you are looking good. Conserve ammo! I didn't find any MP44's on the level and obviously there are no Brens so if you run out of BAR ammo, you are hurting at the end part (getting up that hill with no bullets is pretty tough, even on Easy). I was able to really conserve ammo by meleeing every chance I got. Clearing the houses and barns? Melee! Gerry in the open? Melee! All in all it's a pretty easy achievement to get once you get the gist (or is it jist?) of it.

** As a few people have pointed out using granades will not affect getting this achievement so feel free to let pineapples and potatoe mashers fly **

On the second mission of the game you can use the BAR for this achievement. Be precious with your ammunition as it is not plentiful. You can also use an enemies MP44. If you have problems with this, try it on Easy difficulty. Some have been saying that you cannot use grenades or melee attacks if you want to get this one.

On the level the Island use your BAR the whole time. Save your ammo. Only use the BAR until you get to the houses. Then fire one bullet at each enemy and it will kill them on easy. Dont use grenades it will forfeit the achievement. But you may still melee.

An alternate and i feel easier way for this chevo is the level "corridor of death" (the last canadian mission)
you will start with the bren, as you start the level take the left route and kill the first 3 enemys (try it on easy) they will drop the MP44 swap your second weapon for this and you have 2 assault guns with plenty of ammo for both throughout this very short level. (most enemys drop ammo for both guns)
Also theres no need for grenades on this level for those unsure whether you can use them or not, so blast away!!
Hope this helps anyone struggling with other methods. :)

You start out with a Bren on mission 3, "Falaise Road". Well, you really start out with a half-track .50 caliber, but I have the achievement to prove this means nothing as far as the achievement goes. It is the only weapon you have so you won't have to worry about switching weapons on accident. You will most likely run out of ammo on the final part. You have to start a crane, blow up an entrance, and turn a valve to keep the Jerries at bay. I ran around like a lunatic on Veteran with no ammo in my gun and naught but a single smoke grenade.

Now don't get me wrong, I had to do this several time to come up with a good sequence on doing things. I am sure you have an "assault rifle" on some other levels. This level was fairly simple even on Veteran, and it popped without me even thinking I would get it, because of the .50 caliber at the beginning.