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Old 05-01-2016, 08:39 AM   #1
acrosome
 
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Default M855A1 ammo- AP?

Well, just as it says on the tin: Should M855A1 5.56mm ammunition be considered some sort of armor-piercing round in GURPS terms, i.e. AP or APHC?

It was clearly developed with increased penetration in mind, and seems to have succeeded in this goal. Further, the design- a copper jacket around a steel core- certainly sounds like APHC. But either of those (AP, APHC) in different ways reduces damage as well, whereas the M855A1 was designed to retains the 5.56mm round's tendency to fragment in a target and thus increase wounding.

Should it be it's own "special" thing? That seems like a poor solution.
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Old 05-01-2016, 09:01 AM   #2
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Default Re: M855A1 ammo- AP?

Gurps AP rules leave a lot to desire as there is not enough variability at the lower end of the range. The first step of basic penetration to (2) is just too big.

In third edition there were optional rules in modern firepower where there was a (1.25) modifier semi armor piercing rounds. I think that M855 was listed as such in there.

Also note that M855A1 definitely does not perform as well in penetrating as a full AP round like the M995.
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Old 05-01-2016, 09:14 AM   #3
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Default Re: M855A1 ammo- AP?

Frankly, reducing damage by 0.7 and dropping the size modifier by one (pi++ becomes pi+, etc.) is excessive for a human target. Really, what's the significant difference if the projectile passing through your body is steel or jacketed lead? (Ignoring fragmentation.) Most modern small arm AP is really a sort of APHC, anyway (see the M993 frex) so you should probably only get less damage if the bullet has to penetrate significant DR- for instance, if the AP modifier makes the difference between a penetration or not, shaving the soft outer layer off the smaller penetrator.

Last edited by acrosome; 05-01-2016 at 09:23 AM.
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Old 05-01-2016, 09:25 AM   #4
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Default Re: M855A1 ammo- AP?

By standard rules in fourth edition it is likely just ball. thus (1) penetration and *1 damage with no modifiers on base damage.

In third edition you could have used the semi armor piercing modifier (1.25) penetration and *1 damage with no modifiers on base damage optional rule if you wished and still be RAW.

Of course as GM you are free to do and use any rules you feel like.
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Old 05-01-2016, 11:39 AM   #5
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Default Re: M855A1 ammo- AP?

Quote:
Originally Posted by acrosome View Post
Frankly, reducing damage by 0.7 and dropping the size modifier by one (pi++ becomes pi+, etc.) is excessive for a human target.
It's excessive for no-living targets too. One you factor in IT:Unliving there's almost no level of DR for which AP is not inferior to regular ammo in dame to vehicles.

Gurps needs better rules about non-deforming bullets (among other things in the area).
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Old 05-01-2016, 12:13 PM   #6
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Default Re: M855A1 ammo- AP?

My impression is that the treatment of AP is what it is because they didn't want to use a fractional penetration factor. I can't see another reason for the base damage reduction, anyway...

So I'd suggest handling it as no reduction in damage but a (1.4) or (1.5) pen factor if you're willing to.
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Old 04-17-2019, 09:03 PM   #7
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Default Re: M855A1 ammo- AP?

As far as I can determine from those ballistics tests I can find online, the M855A1 (and the CBC 5.56x45mm SAT Improved Performance, which is a Brazilian-made equivalent) penetrate as AP in GURPS. That is, they penetrate steel far better than M193 or M855 rounds, even better than M80 ball in 7.62x51mm, but not as well as APHC rounds like the M995.

Unless the terminal ballistic tests in gelatin are unrepresentative of actual performance, however, the M855A1 does not suffer reduced wounding for being AP. It should perform similarly to M855 from 20" barrels from the 14.5" barrel of the M4, even possibly somewhat better.

Personally, I don't see any harm in assuming that Mk318 SOST, M855A1 and a number of advanced rounds being adopted in the 2010s simply represent a TL advantage over typical TL6 and TL7 FMJ and AP rounds. CAD and CNC technology, ever improving propellants and the use of more expensive materials than simple jacketed lead ball allows optimizing rounds for their intended role and improving penetration doesn't automatically reduce wounding.

The published performance of M855A rounds seems to justify Dmg 2d+7(2) pi+ from 14.5" M4 barrels, though at longer ranges, the pi+ would be reduced to pi (as carbines in ordinary 5.56x45mm ball become pi-).
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