Odd question and I am having some issues getting it worked out.

Ares HVAR , states that it cannot have barrel or underbarrel mounted accesories... and Gas Vent system is a barrel mounted accesory...but (and this is using Hero Lab btw) I can put an internal Gas Vent system on it, but it doesnt give the option for the external, whereas other automatics I looked at give the option for either. Is this just a glitch in Hero Labs or what?

I dont have all the specs with me, but basically one of my players has an Ares HVAR with 9 points of recoil comp, and I want to see how and if its kosher.

Thanks Dumpshockers!

It's not a glitch, it's just a very very strictly literalist reading of the RAW. Yes, barrel accessories are forbidden to HV weapons. But barrel-based modifications ...? The rules don't say. Ergo, what is not expressly forbidden ........ must be permitted.

By the by, when checking that RComp rating? Don't forget to read the section Restrictions to Recoil Compensation, on page 148 of Arsenal.

There is at least one weapon in Arsenal that states "This weapon cannot be further modified." The HVAR does not. Nor does the sidebar for high velocity modification say that the weapon with it cannot be further modified.

As for reasons for why the prohibition exists...

First, looking at the sidebar for High Velocity it indicates that the barrel and cartridges are designed to reduce heat. This is the reason why barrel mounted accessories (like gas vent) are not permitted. Stock accessories are not designed to handle that sort of velocity. The reason why barrel modifications are allowed is because the modification is made to the weapon and thus the barrel modification is tailored to handle the additional heat.

Thanks to both of you! See, this is my issue, I can take stuff apart, and I can put it back together so that it works....i cant tell you squat about the how and why most of it works, so these help alot!

Additionally, an internal gas vent is using up slots which might be needed for other recoil compensation. An external one doesn't, which is why I use the barrel slot whenever I can.

I agree with that. Leave as many gun slots as possible, I say. But it sounds like the question in general has been answered: as a barrel accessory gas vent would be forbidden on the HVAR. (though _Pax._'s take on that was a wonderful point on wording errors, I tend to agree)

Keep in mind, this may not even be a hard-rail interpretation of the rules in the Lab software. You would have to completely rework a separate category for something like a barrel mod vs a barrel accessory, and it's a fine point that would hardly be high priority on a project. A real-life gas vent system is simply a barrel modification, making it neither internal nor external.

No, you would just have to add a pre-requisite to Gas Vents (etc) that said, in essence: "does not have the High Velocity modification".