I was watching some gameplay (feaR) and he would crouch shot with the DMR when the enemy was far away but did not see him...that situation seems like the most effective one
Nothing is effective when your ponked though...
theres a little trick i now with the DMR if you shoot the gun three times standing up the bullets go everywhere but if you shoot the DMR while crouching all of your shot are way more accurate.Please try it it works
http://www.haloforever.com/xbox/reach-weapons.phpThis is the haloforever.com halo reach weapons page. On it is some useful information about the weapons, including a note about the grenade launcher that says:"- when you hold the trigger after firing you can control when to detonate the round"I haven't tested this yet, but if its on the site I'm sure it works.