Unofficial Fallout 4 Patch

Sorry, I probably should have set the platform to "all", but I can't verify any other platform. I imagine this issue isn't PC exclusive though, that's just the platform I'm familiar with.

Actually, it's not just the ported barrels - the light barrels are the same as well. There are six barrel modifications for the combat rifle, but only two meshes used, without even material swaps (checked in FO4Edit):
Weapons\CombatShotgun\CombatRifleBarrel.nif for the long barrels
Weapons\CombatShotgun\CombatRifleBarrelShort.nif for the short barrels

There are two extra combat rifle barrel meshes in the archives that don't seem to be used at the moment, which were probably intended for the light barrels:
Weapons\CombatShotgun\CombatRifleBarrelFluted.nif
Weapons\CombatShotgun\CombatRifleBarrelFlutedShort.nif

The only readily-apparent difference (at least to me) between the hunting rifle's ported barrel and standard barrel is the holes near the tip, though NifSkope says the ported barrel uses almost twice as many triangles (358 vs 181), and changing the textures used for the combat rifle's barrel mesh looks like it would work, at least for the long barrel (the short barrel doesn't include the part that would look different), so a material swap that changes Materials\Weapons\HuntingRifle\HuntingRifle.BGSM to Materials\Weapons\HuntingRifle\HuntingRiflePortedBarrel.BGSM might suffice.

Huh, you're right. I had no idea that there was no short ported barrel for the hunting rifle. I also hadn't considered that the fluted barrels were probably meant for the light barrels as per the hunting rifle. I'm used to the fluted barrels being separate options as per the Cut Weapon Mod Restoration .esp, though I suppose the mod author didn't make that connection either. The only way I can see the inconsistency being sorted out is by removing the short ported barrel option from the combat rifle (or making a brand new mesh for it) and replacing the light barrel meshes with the unused fluted ones. Those options might be considered out of the scope of an unofficial patch though. It's weird as hell and inconsistent, but I guess we'll just have to live with it.

Fixing the ported barrels (by removing the short ported barrel or making new meshes) would probably be out of scope, but I'm not so sure changing the light barrels to use the fluted barrel meshes would be.

In the meantime, I found a mod "Combat Rifle Mod Restoration" for the ported barrels.