What can I do with an arm roast?
Even though this thread is old, it's the first thing that comes up when you search "arm roast" at the moment, so I thought I would comment with what I ended doing after googling arm roasts two days ago! I also had a totally grass fed 4 lb. arm roast and it turned out amazing. Most importantly, I cooked it very long and slow, about 5 hours at 300F.


Chop 1 carrot, 1 celery stalk, half an onion and a slice or two of bacon and saute them together in a large pot until lightly browned. Remove from pot.
Salt and pepper the arm roast and then brown it on both sides in that same pot. Remove.
Deglaze pan with red wine, I had the tail end of a bottle of super cheap stuff.
Then throw back in the veggies, the roast, a large can of tomatoes (I used San Marzano), and a few sprigs of fresh rosemary (I really recommend not skimping with dry on that part because it's the main flavor that gets infused). I also put marjoram in because I have that growing, but I don't think it's as important. The top of the roast will be sticking out of the tomato/wine concoction so I studded it with numerous garlic cloves so they would roast.
Put the pot in a 300 degree oven for as long as it takes for the meat to just be falling apart. It was like, 5 hours for me, and I turned the roast over about 2 hours in. Add more liquid if needed; I didn't. When it was done I took the roast out and pulled out the bone and picked off the fat and threw it back in--it was semi-shredded by then--and served it on egg noodles. 


It was the best roast I've ever made!