80-grain 223 in HK93 ?

Is it a real deal HK93 or a clone? If I remember correctly the originals have really slow twist (1/12) barrels and wouldn't work well with heavy bullets at all. From a safety/reliability standpoint you shouldn't have any problems but they will probably keyhole and accuracy will be lousy. For best results stick with 55 grain bullets unless you know it's a rifle with a faster twist.

Not sure what the twist is on Vector clones but I seem to remember the C93s being 1:7.

It's worth trying with heavy bullets but I would probably see if there is something in the 60's that would work.

Overall length shouldn't be a problem at all... I'm hardly an expert in cartridges but apart from really special loadings the overall length should be the same. The only round I have seen that was "too long" was Palma Match .308, it was some special made stuff from Winchester and I don't think it would even be safe to shoot in non Palma gun.

What Taliv said. I've never seen or heard of anyone loading 80 gr rounds that would fit in or feed from a magazine.

AFAIK the 77grain is the heaviest 223 you can load mag length ... from the 80's I've shot they prefer a 1/7 but I have got acceptable results in a 1/8 at 100yds

Speer makes a 70gr soft point,and Sierra has a 65gr soft point boat tail.Both bullets are better suited for hunting than the match bullets.
I shoot several 75gr and 80gr bullets out of my AR's and bolt actions,but most are loaded past mag length,and have to be shot as a single shot rifle.