Why claymores do 1300dmg?

It was for me. I was at xenotech labs the other day and base was heavily surrounded. I went out through the teleport room and around a corner and placed claymores in front while kneeling behind them. Killed three enemies that way and suffered no damage.

I had the opposite experience. Camping a door and figured a claymore would help (since they only seem to kill half the time) and it exploded killing me as well.
Also right after I placed a claymore an enemy stepped near it taking us both out..
I even had it explode with unknown reason (enemy shooting it?) while I was standing behind it killing me as well.

Flak 4 will always save you from a single claymore. Effective health against explosions at each level of flak are about 1111, 1250, 1428, 1666, 2000 for a normal soldier and 1000, 1125, 1285, 1500, 1800 for infiltrators.

You can't place them "just anywhere". They're easier to see than claymores.

Claymores have been 360º for the last few updates, have they changed them back to directional??

All mines deal 1,000 damage. The Claymore myth is a lie.