A lot of hands touched that round before it was ever linked, added to stripper clips, or inserted in an military ammo box. In the manufacturing of ammunition, no one handles the stuff as though it was glass. Ammunition gets rough handling, and once it is packed into ammunition crates, those crates are dropped, piled on top of each other. Shippers are rather indifferent, everything is just "cargo" to them. That is one reason ammunition is shipped in spam cans inside heavy wooden crates.
Your ammunition was made at the height of the Vietnam war and the emphasis during war time is to ship the stuff. Defects that would cause alarm or rejection in peacetime were glossed over, ignored, rationalized, because everyone in the military industrial complex wants to get that stuff over there. Everyone is complicit in this, they all know non conforming equipment is more likely to fail in the field, but since so much is consumed in a war, they are right in assuming that equipment failures due to shoddy hardware will be lost in the noise. Vietnam, in fact all battlefields, are filled with dud shells, bombs, etc. You might have seen a few.
As for the dent, as long as the round chambers, it is not an interference fit going in, nothing bad is going to happen assuming the powder is good. I have shot brass cases with far larger dents. It is not intuitive, because a brass case seems to be very strong, but at 50,000 CUP, but that case is simply an expanding gas seal. Under the pressures of combustion that dent will flatten out to the chamber shape.
What I will say, your biggest risk is old gunpowder. That round is almost 50 years old, a reasonable shelf life for double based gunpowder is 20 years, single based 45 years. Wartime powder was rushed out the door with no expectation of being in storage longer than a couple of years, so you can expect in the environment of the times, it may not be of the highest manufacturing quality. I would recommend you pull the bullet, dump the powder, and inspect the bottom of the bullet and interior of the case. If you see green corrosion, toss the powder and case. As gunpowder ages, it outgasses nitric acid gas. It also does not burn evenly and that causes pressure spikes. There are lots of accounts of blown up guns with old ammunition.
Examples of corrosion caused by old gunpowder.
