It's a pretty old movie (25 years +) in which 2 groups of hunters in full Hi-Viz jackets accidentally fire on each other. The whole movie is from one groups point of view. If I remember rightly our group has a member slightly wounded in the exchange of fire.
Our group return home angry and hell bent on revenge. As they are members of the USA army reservists and have access to automatic guns, ammo grenades, heavy equipment and camo gear, they set about getting prepared to return to the forest in what we can only imagine will be a wipe out of the other hunters. After all the preparation and build up we follow them as they deploy back into the forest to hunt their foe. Our group are no slouches in manoeuvres and it would seem the other group doesn't have a chance.
SPOILER ALERT
In the final moments our team approach a river with a heavily snow covered bank opposite. Our group slowly get into position to take out the opposition when they (the opposition) suddenly spring out of fox holes, better armed and better prepared and simply obliterate our team. The viewer is had never thought that the other mob could also be preparing to the level of our team and that is what makes this movie quite worth watching.

Sounds like Shoot (http://www.imdb.com/title/tt0075212/)

Certainly does sound like "Shoot" though I don't remember Earnest Borgnine being in it!
Thanks for that as I have been trying to figure it out for years. 36 to be precise.