Piston vs. DI weight comparison

AR/M4 AR Technical Discussion
1

So, there has been quite a bit of speculation regarding the weight differences between DI guns and piston guns.

Some claim as many as 2 to 3 pounds difference (with the piston gun being heavier of course).

So I decided to grab the good old postal scale and do some non-scientific weight measurements to give a few general weights for folks to go off of.

Here are the two uppers weighed. A 14.5 inch govt. profile M4 style barrel, an AAC blackout pinned and welded, a KAC freefloat RAS, with the full BCG installed. Other then that it is as clean as I can get it as all other accessories are user dependent and obviously add more weight.

The other is an MR556 with the barrel profiled to .72 under the handguard, barrel cut to 14.5, and a Gemtech bi-lock pinned and welded. Once again, a full BCG, and slick.

Here is the MR556 upper with the handguard removed to show barrel profile:

Here is the DI upper on the scale:

And here is the MR upper:

The MR556 upper is 4 lbs, 14.6 oz. The DI upper, with a slightly smaller barrel profile and the M4 stepdown, is 4 lbs, 1.7 oz. A difference of 12.9 oz.

This means that a real HK416 with a govt. profile will be somewhat less then my MR556, and probably around a half a pound heavier then a similar DI gun, if that.

Also, keep in mind that the KAC FF RAS is a damn light rail system as well, which might be skewing the results a little bit.

What does this mean in the greater scheme of things? Not a damned thing as I don’t have a “real” 416 upper in my hands. But it’s a start.

2

It’s good to collect empirical data but this is an apples to oranges comparison as the barrel profile, handguard and gas system length are different and skew the results.

The difference in weight between the op-rod upper and the inline piston upper will be the difference in weight between the op-rod & gas tube, gas blocks and gas keys and should only be a few ounces.

When weighing uppers for comparison, they both should be otherwise identically equipped.

Still, I applaud you for actually weighing uppers to find out for yourself instead of just repeating what you read on the internet :thank_you2:

3

Mistwolf,

I think Grumpy’s intent was not an ounce for ounce scientific comparison, but a general view that piston uppers aren’t really that much heavier in the real world. Sure, ceterus perebus, a DI upper will be a few ounces lighter, but here you have two closely configured uppers that for all intents and purposes weigh the same.

I took it as a counter view to the oft repeated mantra that piston guns are unnecessarily heavy. Real world they’re not really that much heavier.

4

Good job Grumpy I do agree with Mist.

Also ounces=pounds.

If you have rifles with the same exact everythin and one being a piston it will always be heavier but only ounces heavier.

5

If you have rifles with the same exact everythin and one being a piston it will always be heavier but only ounces heavier.

So, the “piston is heavier” argument is pretty thin then?

“Ounces=Pounds”

Sure, but a few ounces on a gun is NOT going to be the straw that breaks the camels back.

6

Sure it’s not much but one thing to consider is not just the weight but the location of that weight.

With longer handguards accomodating the support hand further out these days we are having to push accessories (if we choose to use them) closer to the muzzle to give breathing room for that hand.

My own personal rifle has a 13.5 Noveske NSR with a DD fixed front sight, Surefire M600c with a Larue offset mount and SR07 tape switch, and a tango down stubby with rail panel attachment. All that stuff (except for the vert grip mount is FORWARD of my grip. None of this is being supported where they could be the most stable and stave off fatigue-between my arms.

Take a 10 pound weight and hold in directly centered in your hand. No problem-I am He-Man. Take that same weight and hold that puny 10 pounder on the edge with just your fingers where most of that weight is forward of your hand…fatigue comes much faster.

Back to the rifle…Now could I change some things around to make it lighter? Sure but I would have to change my support hand grip on the rifle and that I wont do.

Adding a piston would be more unneeded weight on the forward portion of my rifle and I’ve already got enough crap on it anyway. IMHO thats (the added weight from the piston)something I can live without. That and the other drawbacks to a piston gun. YMMV.

-Jax

7

Stupid phone.

8

Wrong

I have a KAC 14.5 with 1-8x, laser, sling, etc that now equals than my 416 naked*.

A “few ounces” might not be noticeable to one transporting from your safe, or on a flat range. It will be noticed in operational athleticism, sprint distance or longer. In the unlikely event your in the mountains, the arena 99.9% of forces have ceded to the opposition, every ounce is noticeable.

*416’s have a much heavier barrel than .70, a more substantial lower with heavier buffer & spring necessitated by the piston upper. 14.5" HK416 weighs 8.24lb per HK website.

9

From what I understand, the newer 416s are coming with a govt. profile barrel, meaning that the weight differences will be even less then the numbers I posted.

10

See, that is what it is. Decisions. I wouldn’t run the Surefire light, but something lighter on it. And I wouldn’t have the light on the gun all the time. That more than compensates for the extra weight of the parts for the piston. And I get the other positive effects of the piston.

Weight & manouverability of the rifle is so dependent on the barrel length and profile, that other factors become quite small in comparison. Piston has really no effect.

Why H&K then has also heavier buffer etc. and weighs more in general? That is what I see as a move towards reliability: they use heavier masses and more gas to make the gun work also when dirty. They use heavier, more durable parts in some places to give them durability. They could have made the gun lighter, no doubt, but they chose not to for a reason.

11

Damn, had a whole reply typed up, but got a bad gateway error when I hit the submit button.

Here is a short version.

My reply to sinless was a bit sarcastic. I will concede that the HK416 will be heavier than similar DI counterparts. However, my personal opinion is that the extra weight is not a problem. I have not worked at high altitudes, so have not felt the effects of that particular terrain.

Here is a pic of my gun the way I set it up for Afghanistan, “sort of” similar to Dano’s setup:


It was equipped with:

S&B Short Dot - 570 grams
LaRue LT104 mount - 201 grams
Harris Bipod - 400 grams
LaRue FUG - 137 grams

This totals 1,308 kgs or 2,88lbs. Total weight of my gun was 5,108kgs or 11,26 punds.

Some comparison numbers:

Hk416 16.5" with steel mag: 8,4lbs/3,8kgs
HK416 14.5" with steel mag: 8,24lbs/3,73kgs
KAC SR-16 14.5" with steel mag: 7,17lbs/3,25kgs

The KAC is 1,23lbs lighter than the 16.5" gun and 1,07lbs lighter than the 14.5" gun.

This is noticeable, of course, but not the main culprit in regards to excessive weight for soldiers’ total combat load, IMO. If people can hump Minimi’s, Mk46’s or Mk48’s, they can hump the HK416.

Again, it is heavier when compared to similar DI systems, so if that is a concern then a DI will be lighter.

I also whipped out my calipers, and barrel dimensions on our guns are as follows:

Under handguard: 19mm/0.74"
After gas block: 15mm/0.59"

12

Ounces do equal pounds. Considering I go hiking with my rifle after a few hours of it you come to appreciate saving ounces.

13

Considering the loads soldiers carry the difference in weight is in the range of half a percent.

Also considering the fact that my service rifle weighs 4.3kg’s loaded with iron sights only I find it a bit amusing to hear that a rifle weighing less than 4kg’s is too heavy for service. :slight_smile: I have no problems at all with my rifle and if you ask me, doing arms drills becomes heavy when you do them with heavy AT weapons or machineguns with hundreds of rounds of ammunition.

14

I have not seen anyone say they cannot manage the weight. Even if you can handle it I can almost guarantee every would appreciate a lighter weapon or pack as well. When you are hiking all day with little rest you come to appreciate every ounce you save.

15

Ounces do equal pounds. Considering I go hiking with my rifle after a few hours of it you come to appreciate saving ounces.

Considering I carry a shit load of other mission essential equipment in addition to body armor and basic combat load, 1 pound +/- on the gun makes no difference.

Try humping a 33lbs M2 Carl Gustav or a 25lbs MG3 and 250 rounds of ammo (another 17lbs), in addition to your basic combat load, then an 8 pound rifle really is childs play in comparison.

Do this for weeks, with little sleep and crappy field rations (in terms of nutrition), and come back to me.

I’m sorry sinlessorrow, but to compare your “couple of hours” of hiking with what we as soldiers do is just plain ignorant.

16

Wouldn’t it be nice to have a lighter load? What I am saying is ever lunce you can save is a good thing, I have never met anyone who disagrees with this. When you are having to carry 75+lbs of gear saving 1 pound or so helps.

I was not comparing myself to you so don’t take things so personally, I was just using an example. I know you feel since I never served I should have no opinion but I live in America and I have an opinion.

17

Arctic1

Nice looking blaster there - I see you are rolling with the short dot as well; since I was heavily involved with both product developments that warms my heart !!!

Hit me on PM because I would love to ask you some questions about the Norwegian 416’s

Be safe

LAV

18

Man, I thought my hunting pack was heavy so I ditched it. But you guys in service don’t have that option.

You might need some of that kit, at night I go back home or to a cabin…

Sinless, I get where you’re coming from. Ounces equal pounds. But with what these guys are required to carry, another pound isn’t going to be that noticeable. Heavy is trying to manhandle an M2 on a tripod cause “the berm isn’t high enough”.

Arctic, Jippo, I can’t imagine what it would be like to have to pick up and move during excercises. And we are not even going to get into ammo cans…

What were we talking about?

19

Sorry but some of this is just dislike of the piston methinks. What I mean is that only in the HK 416 debate world is this 6 oz extra on a rifle so crucial and detrimental to success both stateside and in current AORs. The M4 with SOCOM profile barrel easily adds as much weight as the HK’s piston system. Yet I never seem to recall debates on how detrimental this extra weight is or maybe I just missed those posts. Sure the SOCOM profiled M4 is heavier but its still “light enough” to be handy and useable.

I think people get too hung up on these exact ounce measurement. The 416 used too be unnecessarily heavy mainly due to its barrel profile. Now that they’ve lightened the barrel profile its in the “light enough” range comparable to weights on all other modern assault rifles.

20

I know you feel since I never served I should have no opinion but I live in America and I have an opinion.

This really has no relevance to the debate, but this is not what I have told you via PM. You can have an opinion, but you don’t neccessarily have the experience in order to view things with the right perspective or within the correct context. Continue this via PM, if you want to discuss it further.

I was not comparing myself to you so don’t take things so personally, I was just using an example.

You brought up the “hiking” comment, so I was again trying to put it into perspective for you, within the context of Dano’s post, a military setting. That is the post my reply was aimed at.

Wouldn’t it be nice to have a lighter load? What I am saying is ever lunce you can save is a good thing, I have never met anyone who disagrees with this. When you are having to carry 75+lbs of gear saving 1 pound or so helps.

I’m sorry Mods/Staff, that this is going off topic, but I want to comment on some things with regards to the section I quoted above.

Like I said, 1 pound more or less on the gun does not matter. Is it 1 pound extra for the total combat load? Sure. However, there are MANY areas where saving weight could reduce the overall combat load significantly, more specifically reducing weight of the following items:

-sleeping bags
-comm systems
-batteries for comms
-body armor
-rucks
-thermals
-optics (not gun optics)
-fuel for cookers

and so forth.

The difference between 75 and 74 pounds (your example) is insignificant. By developing and improving the types of gear I outlined above, those 75 pounds could be reduced to maybe 55-60 pounds. That is significant.

And again, I agree that the HK416 is heavier compared to similar DI systems. I disagree that the extra weight, approximately 1 pound, is a back breaker.