[SiliconeSword]

I recommend a CYMA Platinum SR25/AR-10/AR308 in whatever length and handguard style you like, and run it as an AEG until it breaks.

When it breaks, go for
Polarstar Fusion Engine, Polarstar F2, Mancraft something or other
Grizzly 5.98 barrel
SS-nub (tutorial in bio)
Possibly REVO kit
And a suppressor of sorts

My DMR is just a CYMA Platinum M4 with the Polarstar F2, but I recently got the Polarstar Universal Gas Stock/UGS and I made some mini air tanks, so I'm now tankless with the shots of a 13/3000, but without needing a stupid optics riser.
The whole thing is 5 pounds 10.2 ounces as you see it, completely ready to smoke some SSG10 owners.

 

[SiliconeSword]

Ya, I milled the forward assist off, but I couldn't bring myself to paint the shitty looking metal so I got a new upper as part of a payment.
Looks way cooler and doesn't add much weight, but at some point I'll build a way cooler MTW when I get around to it.

 

[SiliconeSword]

Maybe bother Wolverine until they make a .308 MTW, or hope for a Falcor Defense Petra that you can slap an engine in.

 

[SiliconeSword]

I think he mentioned something about a full power rifle cartridge, but using a VSS would be a bad choice due to how the inner barrel and outer barrel are as they are super unstable

 

[SiliconeSword]

Yeah, I suppose you're right, but the 39 has far less range than 5.56, so that wouldn't actually be realistic.
Imo if it's a rifle caliber at whatever power it could be a sniper or DMR, as people are using 112gr bullets with insane chamber pressure and they're stretching .223/5.56 out beyond 1000 yards and hitting body targets.
Not that that's common, but modern ish tech is making the caliber thing a bit weird.

Still, a Falkor Petra in .300 WSM or another crazy awesome DMR beyond .308 would be seriously awesome if it were brought to airsoft.

 

[SiliconeSword]

I'd say anything you'd snipe with, .308 and up

 

[SiliconeSword]

Well as far as the 30 cal debate goes, you can chamber an AR in .7.62X39, 300 blackout, .458 socom, .50 Beowulf, and a pile of other caliber above 5.56.
As far as 7.62X39 goes, that's definitely not a DMR caliber, it's an assault caliber, so you sadly wouldn't be able to run an AK style gun.

If your field allows an AK as DMR, I'd go for an AK platform or one of the bullpup ones that are around, as it would be a great DMR if it were HPA.