By use of flexible multi-body dynamics theory and ADAMS software,taking machine gun as study target,taking machine gun body and automat as rigid bodies,and taking mount and barrel which effect on muzzle dynamic response was larger as flexible bodies,simulating calculation and study of burst fire were performed.

On the base of physics structure, the finite element model for flexible parts of a machine gun is established and the free modal analysis is accomplished by Nastran software.

Dynamic characteristics of machine gun are main factor affecting its firing accuracy along with the decreasing of its mass.

The law of motion of the firearm bolt in underwater assault rifle was determined by a combination of experiment method and calculation method.

The production situation,including selection of pass schedule,characteristic of pass design,trial rolling process as well as whole process,of having applying the technique of producing 270mm seamless tube blank on 550 medium section mill is introduced and summarized in the paper.

The pass design of large gauge 20/12 5 unequal angle steel on medium section mill were introduced The butterfly pass and final pass design were mainly introduced The production show that the yield and percent of pass respectively reaches 90 62% and 99 57%,and the product quality meet the demand of standar