Requirements for Replacement of Currently Issued 5.56 M-855 and 7.62 M-80.

[stanc]

Something I've been wondering about: In setting requirements for a potential replacement of 7.62 NATO, is it better to require the same trajectory and wind drift as M80 Ball, or to call for superior performance?

Achieving a flatter trajectory and less wind drift seems doable, judging by ballistics charts for the 7mm UIAC. However, the military has a lot of $$$ invested in optical sights with BDC for M80, so a strong economic argument could be made for having an exact ballistics match.

[JASmith]

We need to keep separate the terms "requirements" as in threshold vs "requirements" as in objective.

We have previously converged on near-universal concurrence that a new cartridge must at least match the trajectory, including wind drift, of the 7.62X51 M80 round. This statement constitutes a threshold performance requirement. Busting this kills the initiative if it were in a source selection activity.

How much better we would like to see the cartridge perform establishes the "Objective Requirement" statement. The degree to which a submission meets the objective statement while meeting ALL of the threshold requirements helps establish the score for the submission. Even here wisdom suggests setting objectives that have a possibility of being met, if for no other reason, to maintain credibility in the source selection document.

Hence the answer is that the submission must equal or decrease the trajectory and wind drift compared to the M80 round from barrels of equal length.

The above sentence almost contains both the threshold and objective. Adding language that specifies "by how much" would complete the objective statement.

[stanc]

Joe, you typed five paragraphs, and not one of them addressed my question.

[JASmith]

Stan,

I was trying to be polite. I suggest you re-read the information.

Last I heard, we are exploring paths that reduce weight of loose and linked ammunition while maintaining the trajectory, wind drift, and barrier defeat capabilities in the 7.62X51 M80. Lethality might be allowed to slide a tad. This is different than demanding a "superior" trajectory.

Or perhaps I should answer with "Asking the question the way you did invites disaster by demanding the cartridge get so large as to be the same as the 7.62X51"

Unwise to demand "superior performance" in an area that is not the target of the exercise.

[stanc]

<sigh> Joe, you're still not answering my question. But, perhaps the fault is mine. I thought I was clear, but since you keep addressing other issues, maybe I wasn't.

[JASmith]

Stan,

Your post has two paragraphs. One is posed as a question -- I responded to it.

The other question is posed as a statement. I did not address the issue posed there partly because it wasn't a question and partly because the point made is a valid point. My apologies if it's the one you wanted commentary on.

Comments:

I don't like imposing trajectory matching as a requirement, but cannot say it would not be imposed on an acquisition.

As for trajectory matching to save money on sights, there are precedents for new loads (e. g. M855A1) mapping more or less into existing trajectory tables. I personally don't like the notion because I believe it to be a false economy compared to what one could get with appropriate ammunition. This is particularly true with optical (vice iron) sights.

There are also precedents for not matching the existing trajectories when new ammunition types (e. g. Mk 262). The difference is in the role the ammunition is to play.

Even so, the differences in trajectory between the M855A1 and the Mk 262 are small enough that a silhouette will still get hit most of the time with a standard center of mass hold all the way out to 300 meters. (I haven't run the trajectories, but it would be better if someone actually tries it with a rifle sighted in at 25 meters using the M855A1. Then shoot both rounds at 100, 200, and 300 meters using a center of mass hold. The bet I would make is that this has been done. I would wager a little less that my claim is valid!)

It is less difficult to dumb down a trajectory than it is to make an existing design do better.

My vote is for an "equal or better" trajectory for our discussions and let the sighting implications sort themselves out.

[stanc]

Stan, Your post has two paragraphs. One is posed as a question -- I responded to it.

The other question is posed as a statement. I did not address the issue posed there partly because it wasn't a question and partly because the point made is a valid point. My apologies if it's the one you wanted commentary on.

Joe, there was only one question. The second paragraph was just meant to elaborate on the first, in an attempt to make it perfectly clear what my concern was. Obviously I failed in that regard. Perhaps my writing skills are deteriorating from insufficient practice. After all, it has been over a year and a half since I wrote my last magazine article.

As for trajectory matching to save money on sights, there are precedents for new loads (e. g. M855A1) mapping more or less into existing trajectory tables. I personally don't like the notion because I believe it to be a false economy compared to what one could get with appropriate ammunition. This is particularly true with optical (vice iron) sights.

Thanks! Now you're providing feedback I was wanting to get.

But, I'm not sure that I'd agree with it being a false economy. Have you seen the prices for military optical sights? List price on the 6x48 ACOG the Brits use on their L129A1 rifle is nearly as much as for the rifle! The M145 Machine Gun Optic is less expensive, but it still ain't something that a fiscally responsible agency would want to discard.

There are also precedents for not matching the existing trajectories when new ammunition types (e. g. Mk 262). The difference is in the role the ammunition is to play.

Yeah, but Mk262 is a special purpose, limited issue load. I think we should be primarily concerned with general purpose, ball ammo.

Even so, the differences in trajectory between the M855A1 and the Mk 262 are small enough that a silhouette will still get hit most of the time with a standard center of mass hold all the way out to 300 meters. (I haven't run the trajectories, but it would be better if someone actually tries it with a rifle sighted in at 25 meters using the M855A1. Then shoot both rounds at 100, 200, and 300 meters using a center of mass hold. The bet I would make is that this has been done. I would wager a little less that my claim is valid!)

No bet here. At 100-300 meters there is negligible difference in trajectories, even between 5.56 M855 and 7.62 M80. It's at 500-900 meters where the difference in trajectories between bullet types becomes very noticeable.

It is less difficult to dumb down a trajectory than it is to make an existing design do better.

Of course.

My vote is for an "equal or better" trajectory for our discussions and let the sighting implications sort themselves out.

That may be a little short sighted. (Pun intended.)

However, I was thinking less about applicability to the discussion, and more to incorporation into a new magazine article I've been contemplating.

[JASmith]

...At 100-300 meters there is negligible difference in trajectories, even between 5.56 M855 and 7.62 M80. It's at 500-900 meters where the difference in trajectories between bullet types becomes very noticeable...

I guess myopia is in season

I'm pretty sure that adjustable optics are used for the 500-900 meter and beyond environment. This would imply a simple change of hard-copy or electronic range tables.

The picture will be different, of course, when a new cartridge enters service, but we can reasonably forecast that electronic-adjustable sights are not too far around the corner. At that point, absent truly stupid implementation, changing ammunition would require a simple change in drop and drift tables.

No, we don't need to debate the nuances of implementation just now...

So, my vote remains "equal or better" trajectory for our discussions and let the sighting implications sort themselves out.

If the DARPA and other intelligent sight initiatives bear fruit, we'll have a whole different picture, but the one thing that will remain is uncertainty in actual range, and wind variability. These will continue to favor the flatter, better wind-bucking load.

****

I'm hoping that these and other debates are helping sharpen recall and writing skills for all of us!!

My wife and others complain that I'm too verbose -- perhaps because there's so much to say!!

[Tony Williams]

Since the sole purpose of replacing the 7.62mm is to reduce its weight (its performance is fine), and the more the performance exceeds that of the M80 the heavier the cartridge will be, my view is that the new round should match, as closely as possible, the trajectory and wind-drift of the M80 at long range. The round should be the lightest which can achieve that.

[JASmith]

Tony,

It would appear that a 100 gr 6.5 bullet with a muzzle velocity of 2750 ft/sec from a 20" barrel would do just that.

There are already commercial offerings 100 gr 6.5 velocities with BC's ranging upwards of 0.444, so duplicating the trajectory and wind drift of the M80 in a military-grade 100 gr 6.5 bullet should be tractable.

BTW the Grendel can launch a 100 gr pill at these velocities!

Cheers!
Joe

[Tony Williams]

That's encouraging, Joe, as it makes a copper/steel bullet of that weight look feasible in terms of both weight and performance.

[JASmith]

Tony,

The other part of the news is so-so, but not particularly discouraging if one takes the M855A1 as an example.

The sectional density of the 100 gr 6.5 is about mid-way between the 62 gr 5.56 and the 147 gr .308. This would suggest, based on the M855A1 example, that paths to getting the barrier defeat capability up to near equivalence with the M80 should be doable.

While "stretching" the M855A1 and enlarging to 6.5 is one path, there are others that may get to similar or equivalent barrier defeat. Some of them may be more in line with the bullet design constraints placed on UK and European military services.

BTW a 110 gr 6.5 bullet has a sectional density that is within about 0.2% of that of the 150 gr .308 bullet. Adding 10% to the bullet weight and keeping the nominal 2750 ft/sec muzzle velocity, however, means increasing powder capacity by a similar amount, weight goes up, etc.

Cheers!
Joe
Joe

[LRRPF52]

I just returned from a 2-day course I ran, and had an opportunity to shoot one of the guy's HK416's with a 10" barrel. It feels nothing like an AR in recoil-more like a semi-auto 12 ga. It literally feels like the upper and lower are trying to twist apart or something-very strange and uncomfortable compared to a DI AR. I shot it suppressed and unsuppressed, and it is the same. I actually am wondering if even an AK handles more smoothly now, but didn't grab one of the guy's AK's to do a side-by-side.

I wonder who will start making a Direct Impingement drop-in system for the HK416, since it has a higher op-rod hole in the upper...

On another note, we encountered several situations where pretty dense vegetation was partially-obstructing most of the targets on the patrol lanes (by design). We were wondering how these obstacles in the path of 5.56 might affect shot placement, so I had one of the guys get down and purposely shoot through tall grass and weeds that were between him and the target. POA-POI was on, with no signs of key-holing that we could detect on targets from 24m out to about 60m. Everyone had 10-16" barrels on the AR's, wit most being 11.5" or 14.5". I didn't notice any key-holes throughout the two days of high-volume shooting on any of the targets, and every target in the patrol lanes had vegetation partially-obstructing it.

[JASmith]

...On another note, we encountered several situations where pretty dense vegetation was partially-obstructing most of the targets on the patrol lanes (by design). We were wondering how these obstacles in the path of 5.56 might affect shot placement, so I had one of the guys get down and purposely shoot through tall grass and weeds that were between him and the target. POA-POI was on, with no signs of key-holing that we could detect on targets from 24m out to about 60m. Everyone had 10-16" barrels on the AR's, wit most being 11.5" or 14.5". I didn't notice any key-holes throughout the two days of high-volume shooting on any of the targets, and every target in the patrol lanes had vegetation partially-obstructing it.

And here we hunters have "don't shoot through vegetation" drummed into us from our first hunter safety course onward.

The little secret is that the bullet gets through most of the time. A lot will depend on the relative size/thickness of the vegetation in causing deflections and bullet upset. Your environment places a high value of getting hits somewhere on the target. Multiple shots are frequently taken, so the few that actually pick up some green on the way through and the still smaller number that actually get disrupted aren't important. When shooting only one shot at a valuable game animal, however, the need to minimize the chance of deflection increases.

Also, "brush shooting" leads to accidents where a human might be the unintended target but the shooter doesn't recognize his presence, let alone ID as a person.

Bottom line: You demonstrated an important point in combat shooting! The environment you describe and tested reflects one of the many differences between responsible hunting and the imperatives faced by infantry.

*************************

PS MK82 Daisy Cutters do a lot better getting the grass and brush out of the way than do M855A1 or Mk262! (I guess we don't use much of those these days...)

[stanc]

I just got returned from a 2-day course I ran, and...we encountered several situations where pretty dense vegetation was partially-obstructing most of the targets on the patrol lanes (by design). We were wondering how these obstacles in the path of 5.56 might affect shot placement, so I had one of the guys get down and purposely shoot through tall grass and weeds that were between him and the target. POA-POI was on, with no signs of key-holing that we could detect on targets from 24m out to about 60m. Everyone had 10-16" barrels on the AR's, wit most being 11.5" or 14.5". I didn't notice any key-holes throughout the two days of high-volume shooting on any of the targets, and every target in the patrol lanes had vegetation partially-obstructing it.

I'd say it depends upon the vegetation. Grass and weeds may not offer sufficient resistance to cause bullet deflection.

Years ago I ran a test to check on the reported claims that bigger bullets fared better in brush busting. I stuck a 3/4" dowel into the ground, with a target several feet behind it. I fired three shots each of FMJ ammo in .45 ACP, 9x19, 7.62x51, and 5.56x45. To my surprise, .45 deflected more than 9mm, and 7.62 more than 5.56, with all rounds showing severe keyholing.

The only trouble with said testing is that all of the .45, 9mm and 7.62mm bullets grazed the side of the dowel, whereas all of the 5.56mm bullets punched through the dowel. I tried several more shots with 5.56, but was unable to achieve any grazing hits, which IMO renders the 5.56 portion somewhat inconclusive.