Board Thread:Questions and Answers/@comment-113.172.11.250-20141224134416/@comment-25730832-20141224144904

My best bet for you is probably doing Expedition 20. Other expedition do have DevMat chance of drop but Exp 20 is higher since it's in 1st slot. It's 2 hours per run and you need a sub for it and if you don't bother getting great success then it only requires 1 SS and 1 CL at minimum. Chance is not 100% so sometimes you won't get it.

The other way is sortie 2-4, which is pretty much the only map that gives DevMat right now. You'll need to hand your butt to RNG-god for this.

Other than that it's probably the daily that gives you most chance...if you want to you can try and aim for failing in developing equipment so you can get back your DevMat (do those than have higher chance of failing).

I don't know if 25 per day is possible or not...never bother counting.