Machine Gun Kelly Posts Video Showing Full Upper Torso Blackout Tattoo

Machine Gun Kelly's giving us a peek into what it was like to get his entire torso blacked out in a near-full-body tattoo ... and it looks like it hurt like hell.

The singer posted footage that shows the behind-the-scenes process of him getting blasted from the waist up ... and as you can see, there's a lot of scarring, bleeding, and swelling as he takes us through 7 intense sessions over the course of 2 weeks.

From the armpits to the belly button and even around the nipple -- MGK tatted it all, which looks particularly excruciating -- with the needling journey hitting every nook and cranny.

In fact, MGK states the obvious ... describing the process as the "most painful s*** he's ever done in his life." And yet, he came out the other side ... and doesn't seem to regret it.

Kelly wasn't messing around when it came to recovery -- 'cause in between sessions ... he actually used a hyperbolic oxygen chamber to speed up the healing process.

As we told you ... the whole saga of covering his OG inkings kicked off back in mid-December. He said at the time he was undergoing the transformation for "spiritual purposes only" ... as his other tatts were too chaotic for him now.

His tattoo artist didn't hold back the praise, telling us he was the toughest client she's ever had. BTW, Megan Fox actually attended one of these sessions ... and she recounted it on her recent 'CHD' appearance ... giving her fiancé kudos for going through with it.