Geek Life!

The whole 5.56 vs 7.62x 39 vs 6.8 vs 7.62x51thing gets a bit boring.

So let's compare in GURPS terms!

A 'd' in GURPS is a standard everyday 6-sided die.  Just like you find in Yahtzee.  'pi' is the kind of damage bullets do.

Ranges are expressed in yards.  Number before the slash is the distance where you get full damage rolled, number after the slash is the maximum range.  Between those values you get half damage.

An M16A2 does 5d pi with 800/3,500.  30 round mag.
An M4 does 4d+2 pi with 750/2,900.  30 round mag.
An AKM does 5d+1 pi with 500/3,100.  30 round mag.
A REC7 does 6d with 820/3,500. 30 round mag.
An FAL does 7d with 1,000/4,200. 20 round mag.

On average a 6-sider rolls 3.5 points per roll.  So, the M16A2 does an average of 17.5 points of damage.  The M4 16, the AK 18.5, REC7 21 and FAL 24.5.

But a magazine from an M16A2 throws, on average, 525 points of damage down range!  The M4 480, the AK 555, the REC7 630 and the FAL 490.

The mighty .308 just barely beats the mouse-killing M4!

There are no official stats for 6.5 Grendel; but a home-grown formula gives it 6d+2 pi for damage.  That's 23 per shot and 575 points down range from the common 25 round magazine.  My formula (developed by Douglas Cole for third edition GURPS) gives a range number of 870/4,400 (This assumes a 24" barrel; a 16" tube gives 6d-1 pi and 730/4,000).  My formula also gives a 16" 6.8 barrel ranges of 500/3,200 which don't match the official ranges at all.

Subsonic .300 Blackout comes to 3d pi 130/1,500.  10.5 points per shot and just 315 from a normal 30 round mag.  Supersonic give a better 5d+1 pi and 520/3,300; same damage as the AK!  Since this round is functionally identical toe .300 Whisper and .300/.221 we're going to lump them with it.

7.62x40 WT with their published numbers with the 125gr bullet and 16" barrel gives us 5d+2 pi with the same range as the supersonic Blackout (Range is basically a factor of bullet diameter v barrel length and a power factor kludge in the formula I have).  That's 19.5 points per shot and 585 for a mag.

.30 RAR sounds more promising with its 125gr loading getting 6d+2 pi and ranges of 790/4,200 with a 24" barrel.  An average of 23 points of damage per shot sounds impressive until you hit the normal AR mag will only hold ten of the, dropping us back to 230 points.

What does this have to do with the real world?  Not a damn thing!

To quantify this a bit better.  The average person has 10 hit points.  If you take 10 points of damage you have to start checking to see if you're knocked unconscious.  If you take 20 points of damage you have to start checking to see if you got killed and a total of 60 points is dead-right-there.  That's for hitting the "body".

Hits to the "vitals" do three times as much damage and a hit to the "brain" will do four times as much.  The average vitals hit from most of these is a death dealing blow.  Even a body hit works pretty well.

Remember, this is a GAME, not real world; but it's crunchier than a lot of its forbears.