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Ammo Weight

12036 Views 42 Replies 10 Participants Last post by  stanc
I am having a discussion about the benefits/drawbacks of 6.8 SPC vs 5.56 and one thing that has come up is size and weight.

The physical size is not a concern to me, but I would like to know the difference in weights.

Does anyone know the overall weights of the average 6.8 round and the weight of an average 5.56 round? I would like it in grams if possible.

I want to calculate what the weight difference would be of a 200 round SAW mag in 6.8 vs 5.56.

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Remember 7000 grains to the pound and then you also have the aluminum 5.56 mags vs the steel mags for the 6.8
So -
7000 grains = 1 pound.
1 pound = 16oz.
1oz = 28 grams.

So (7000/16)/28 = 15.265.
1 gram = 15.265 grains

A 190 grain 5.56 round would be 12.16 grams.
A 268 grain 6.8 round would be 17.152 grams.

Does this seem right?
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A 62g 5.56 M855 round weighs 11 grams or .4 oz

A SSA 110g Pro Hunter 6.8 SPC weighs 16 grams or .6 oz on the same scale.


Thanks. It looks like we were writing at the same time.

Using your weight figures I come up with -
200 rounds 5.56 = 4.9 lbs
200 rounds 6.8 = 7.1 lbs

So roughly there is about a 2 lbs difference.

If you haven't considered it, the size difference may be more important than weight. For magazines of the same size, 5.56 has 30-rd capacity, 6.8 is 25-rd. For the SAW, a 200-rd container for 6.8 would be so large that I doubt the military would use it. A more likely capacity for a 6.8 SAW is 100 rounds.
probably fit 75 rounds into a nut sack, and 150 or so rounds into a 200 round drum......
I feel that the 150 or so round count would probably be more accurate. I do not agree with the assessment that a 200 round container of 6.8 ammo would be too big to consider. We used to carry 200 rounds of 7.62 for the M-60 so you are talking about a lot more weight and size.

Based on a size and weight increase, would you prefer the effectiveness and increased range of the 6.8 or stay with the 5.56 in the SAW platform?

While it is certainly important that everyone carries 5.56 and the SAW will accept AR mags, please do not factor them in for this discussion.

Thank you.
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I think if they are going to switch then we need to switch completly, I would rather have my SAW use the 6.8 then the 556...
That is my thought exactly but there seems to be little movement on this.

Right now the Marine Corps is looking to replace the SAW. One of the complaints I have read about is that the SAW is too big/heavy for CQB, even with the para versions.

All I have seen submitted so far is modified full auto AR's and to me that is unsat. It is a joke to give the squad's A-gunner a 30 round magazine fed weapon.

I think whatever they replace it with should be belt fed and they should go up to the 6.8 to increase effectiveness. I think once you get on thing chambered in 6.8 the move completely switch would not be far behind. With the shorter barrels that are being issued now there needs to be a change to keep the weapon effective.
I think the biggest reason they dont like the saw is that it is an open bolt weapon, it isnt cool if you are the first dude in a room and your get a click instead ofa bang, a MG is more prone to that kind of thing as compared to the M4....
You are absolutely correct, that is a big concern that I forgot about. Sorry.

The weapons that were submitted for replacement consideration shoot from a closed bolt in semi-auto and then switch to an open bolt for full auto. You would chamber the round in semi mode and then switch the selector switch to full auto I guess and then you would get that first round reliability of the closed bolt.

I cannot see why a re-tooled SAW couldn't be set to fire the first round closed bolt and the switch over also.
Back when I wore Army green, the container that attached to the M60 only held 100 rds. What on-gun container did you use that held 200 rds of 7.62 ammo???
I am thinking of the ones that were used on mounted weapons.

Does anyone know the weight of a 7.62 round?
Is that relevant to a 6.8 SAW?
Not really, my mind got stuck on the 200 round figure.
I would think they would maintain a minimum wall thickness so I think the barrel would be heavier.

While my post was mainly about ammo weights, it was to support my overall position that the next IAR should be upgraded to 6.8.
My position hasn't changed, the military should upgrade to 6.8 all across the board.

I knew going in that there was increased weight and cartridge sizing but thought that it was a worthwhile trade off.

It was interesting to see the numbers though.

The interesting thing is that the 150 rounds of 6.8 weighed exactly the same as 100 rounds of 7.62.
Actually I just looked again and the 100 rounds of 7.62 weighed the same as 200 rounds of 6.8.

The 200 rounds of 5.56 @ 11 grams per round comes in at 4.91 pounds.
200 rounds of 6.8 @ 16 grams per round comes in at 7.14 pounds.
150 rounds of 6.8 is 5.35 pounds.
100 rounds of 7.62 @ 32 grams per round is 7.14 pounds.

They are issuing shorter and shorter barreled rifles which means equals a loss in velocity. The loss of velocity means a shorter effective range where the projectile will reliably fragment. Without fragmentation you are just shooting a .22.

Also the 5.56 has barrier, armor, and windshield penetration problems. The 6.8 does not have the same issues.

Here is something worth reading
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Look again. You were right the first time. The actual ratio is approx 200 5.56 / 150 6.8 / 100 7.62

It appears you transposed your 7.62 numbers. Weight of 7.62 M80 is approx 23 grams, not 32.
You are correct. I transposed the wrong cell in Excel. It is 24.96 grams which I rounded to 25.

The correct weight for 100 rounds of 7.62 is 5.58 pounds.

I'm still not sure how to quantify the difference in capability between 5.56 and 6.8 in order to show that the latter is enough better to justify a switch, though. I'm open to suggestions on that.
Combat has changed and the 5.56 round isn't cutting it anymore.

The enemy has changed by using body armor. Troops are coming up against barriers and windshields in urban combat.

The majority of combat in one arena is CQB so the military has adjusted by giving troops shorter rifles 14.5" barrels for regular troops and 7.5" to 10" barrels for SOF. So now you have a rifle that is great to maneuver around but has lost effective due to the loss of muzzle velocity.

Combat in our other arena is long distance where you need a round that will allow you to reach out an touch. I am sorry but shooting at paper targets from the 500 yard line isn't the same as hitting and killing a human target in cold weather type clothing at the same distance.

You now have suicide bombers hopped up on drugs that need to be stopped with one shot. A round is needed that will have stopping power and good fragmentation out of SBR in CQB, allow a shooter to kill at a distance, and penetrate body armor/barriers/windshields. Does this sound like 5.56 to anyone?

Once the switch to 6.8 SOF and infantry are issued one lower with two different upper receivers, one SBR and one carbine or rifle length so that it can be more tailored to the mission.

With the majority of other things changing in reflection of the current state of combat doesn't it makes sense to update to a round that will get the job done too?
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The 5.56 has proved to be inadequate in certain arenas of combat, and in my opinion, needs to be replaced. The 2 rounds most mentioned as a replacement are the 6.8 and 6.5G. The problem is that each camp says theirs is better. We need a round that is a hands down winner.
Seeing how the 6.8 was developed by soldiers on the ground, has JAG approval, and is currently being used by SOF troops my money is on the 6.8.

While the 6.5 has better velocity numbers and a flatter trajectory than the 6.8 it has problems with windshields and I have also heard of feeding problems.

The best thing I read on this subject was a post that compared the 6.5 vs 6.8 to Betamax vs VHS.
If that "paper target" remark is a slam against 6.5 Grendel, it is an illogical statement. Both 6.5 Grendel and 6.8 SPC have sufficient terminal velocity at 500 yards to easily penetrate the heaviest winter clothing and kill the wearer.
No, it is a slam against 5.56. You are trained to shoot it from the 500 yard line and it is 100% effective on the paper targets but that doesn't mean that it is effective against a live target.

One of the biggest things the 6.8 has going for it is its compatibility with the current gear which translates to lower cost outlay.
For example, take the "shooting through AK mag" test. The 6.8 wound channel is significantly larger than that of M855, having perhaps twice the volume. But, if I've understood correctly, the damage from the M855 projectile in such a center chest hit is almost certainly unsurvivable and would probably drop the enemy as quickly as the 6.8 round. You can't kill an enemy twice as much. Dead is dead.
The results from that test show the 5.56 round to be effective. If you are referencing the gel tests shown here -


the distance was only 3m. At what distance does the 5.56 fail to penetrate and at what distance the 6.8 round fail to penetrate?

I know I had seen some gel tests of rounds being fired through windshields to show the penetration and fragmentation but I could not find them. When shooting at a target behind a windshield or another barrier the 6.8 excels where the 5.56 is found lacking.

In some situations the 5.56 is more than adequate and in others it is lacking. When you start throwing in variables like distance, barrel length, barriers, etc the 6.8 has a much higher percentage of success and I for one would like the deck stacked in our favor.
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