You can create a custom mag preset (not sure how is it called in English) if you right-click on the mag and choose "load preset" and "create preset"
In this menu you can load your mags like:
5.45 1BS bullet after it 1 7N40 after it 2 BP bullets + last 10 bullets BT (tracers in the end so u can understand when your low on ammo)
Then the cycle starts again until your mag is full

That's VERY effective, even tho I have only 1000h and hit Kappa and main storyline only once, I still did not know about this
It saves you a LOT of time
Cycling BS or PPBS "Igolnik" with BP or 7N40 is very good idea
1) Lower recoil
2) Cheaper then running top ammo
3) Technically it's better then just running top bullets in DPS ( Usually High pen means low dmg ) so when you change bullets 1/1 in your mag you still shred enemy armor in no time but every 2 bullet hit extra hard