6.8mm Stats

[Blaskowicz]

First post in this forum.
I'm coming back to GURPS after a couple of years and, after searching through High Tech 4E, I could not find stats for any weapon using this cartridge. Am I missing something (got the book, not the PDF, so I can't do an electronic search) or is it just not there?
If not, is there any other book I can try?
I'm especially interested in stats for the Bushmaster ACR chambered for 6.8mm.

Thanks!

[Fred Brackin]

Originally Posted by Blaskowicz

I'm especially interested in stats for the Bushmaster ACR chambered for 6.8mm.

I don't think it's in HT. In fact I've never heard of it so I certainly didn't read about it in HT.

[Anthony]

In any case, the 6.8mm is basically an intermediate caliber between 5.56mm and 7.62mm. It's usually done as an upgraded 5.56mm, so I'd just take a 5.56mm weapon, reduce ammo capacity by 1/3, increase recoil to 3, and bump by about +1d (1/2d and max will change slightly but probably not enough to be interesting; acc shouldn't change within the limited resolution of GURPS).

[Icelander]

Originally Posted by Anthony

In any case, the 6.8mm is basically an intermediate caliber between 5.56mm and 7.62mm. It's usually done as an upgraded 5.56mm, so I'd just take a 5.56mm weapon, reduce ammo capacity by 1/3, increase recoil to 3, and bump damage to 6d (1/2d and max will change slightly; acc shouldn't change within the limited resolution of GURPS).

If you increase Rcl to 3, you've made this a 7.62mm weapon, only worse. I doubt that will be the route taken in official supplements.

[Anthony]

Originally Posted by Icelander

If you increase Rcl to 3, you've made this a 7.62mm weapon, only worse.

No, because you haven't increased the weight of the weapon. Recoil is a function of bullet weight, bullet velocity, and weapon weight. 6.8mm increases bullet weight, reduces bullet velocity (but by considerably less than weight is increased), and doesn't much affect weapon weight; therefore it increases recoil. You could also generate stats by taking a 7.62 weapon, reducing damage by 1d, increasing ammo capacity, and reducing recoil to 2, but then you're dealing with an 11 lb weapon instead of a 7 lb weapon. I chose to describe it as based on a 5.56mm because the people hawking the concept of 6.8mm (and 6.5mm, and 6mm) generally have a theory of converting existing assault rifles to the new caliber by replacing the chamber and barrel, rather than purchasing entire new weapon, and therefore the base frame would be a 5.56mm assault rifle (with a modest increase in weight due to a larger barrel).

[Icelander]

Originally Posted by Anthony

No, because you haven't increased the weight of the weapon. Recoil is a function of bullet weight, bullet velocity, and weapon weight. 6.8mm increases bullet weight, reduces bullet velocity (but by considerably less than weight is increased), and doesn't much affect weapon weight; therefore it increases recoil. You could also generate stats by taking a 7.62 weapon, reducing damage by 1d, increasing ammo capacity, and reducing recoil to 2, but then you're dealing with an 11 lb weapon instead of a 7 lb weapon.

Recoil and Rcl aren't the same thing.

Rcl 2 is a minimum stat for any weapon that has a recoil at all. It does not follow that anything that recoils more than any given 5.56mm weapon must necessarily have a higher than Rcl 2.

Using that logic, an M4 would have to have a higher Rcl number than an M16, as it is a lighter weapon firing the same round.

A 6.8mm weapon would have higher than Rcl 2 if it was significantly more difficult to control on full-auto than the lightest 5.56mm weapons with Rcl 2.

I've not fired one, so I can't judge. But nothing I've heard or read suggests that this is the case.

In any case, the design goal is a weapon that can be used in the same tactical role as a 5.56mm weapon, but which has more punch. If the stats come out Rcl 3, that goal was not met and this round is a white elephant. As I said, I did not get the sense from HANS that he feels this to be the case.

[Icelander]

If it's anywhere, it will be in GURPS Tactical Shooting first. I've got high hopes for it being there, in fact, but that depends on how well HANS did on space concerns with his final draft.

Failing that, we'd have to wait for HANS to cough up a GURPS Modern Firepower book for 4e.

If all you want is something to muddle through with, though, you're not likely to go far off base by simply taking weight, RoF and other real world data from manufacturer's literature and average the Dmg and Range from 5.56mm and 7.62mm. 6d sounds about right for the damage and the range will end up somewhere between these two rounds.

[DouglasCole]

Originally Posted by Icelander

If it's anywhere, it will be in GURPS Tactical Shooting first. I've got high hopes for it being there, in fact, but that depends on how well HANS did on space concerns with his final draft.

I asked for it in the playtest offline, and he'd already put one in. :-)

6d is the right number. I get that for a 115gr projectile at 2650fps, given known pressure and assuming a 16.5" barrel. True 1/2D range is about 550yds, max about 4100yds, given my spreadsheet.

[Icelander]

Originally Posted by DouglasCole

6d is the right number. I get that for a 115gr projectile at 2650fps, given known pressure and assuming a 16.5" barrel. True 1/2D range is about 550yds, max about 4100yds, given my spreadsheet.

But in your spreadsheet, 5.56mm (and 7.62mm, for that matter) has a significantly lower 1/2D range than in GURPS rules, right?

So using 550 yds would make the round inconsistent with other GURPS rounds.

[DouglasCole]

Originally Posted by Icelander

But in your spreadsheet, 5.56mm (and 7.62mm, for that matter) has a significantly lower 1/2D range than in GURPS rules, right?

So using 550 yds would make the round inconsistent with other GURPS rounds.

True. Split the difference between 5.56 and 7.62.