Simple explanation: The M41A pulse rifle usually fires 10mm explosive-tip caseless light armor piercing rounds... however the company 'dog handlers' weren't there to kill anything, they were there to retrieve a specimen... better to have the weapon loaded with ammunition that would give 'an incentive' rather than leave a xeno in a spicy pool of hissing blood burning through the floor... both 85 and Morse's leg showed no evidence of being hit by explosive tip rounds :-)