Sure, you could put gun oil in it but wouldn't you rather keep things spicy?
Yeah, it's a special place in our heads
Store your favorite battlefield taste enhancer or lubricant in your grip.
We needed this for one of our guns because it was finicky before we switched to froglube on it.
Thanks to Magpul for filling the need. Check it out:
"The MIAD/MOE Lube Bottle Core is an internal grip core that holds an included 1/2 oz. reusable lubrication bottle.
Comes standard with the MIAD GEN 1.1 Grip, the Lube Bottle Core also works with the MOE, MOE+®, MOE-K2®, MOE-K2+, and MOE AK, and MOE AK+ Grips."
(note: we are not associated with Magpul or Froglube and not sure if it is food grade or BPA free plastic.)