Military round comparisons

[stanc]

So I think that to claim that these features "may not be achievable in practice" really isn't justified...

You may be right. But, I'm still going to consider it only theoretical until somebody actually makes one.

[Trooper]

Unfortunately, there is negligible info available on terminal effects with ball ammo, whether conventional FMJ or more recent types like M855A1. Without adequate hard data, I don't see how anyone can claim 6.5 Grendel is "good enough" to replace 7.62 NATO, or if a more capable round (6.5 GPC, 7 UIAC, etc) is necessary.

Well the 6.5 Grendel is looking more and more to be the "6.5 GPC". The 7mm UIAC is also interesting. The limiting factor is using the M4 platform for now. It basically means only having to do a barrel change at the least, an upper change out at the worst (ie HK 417).

What is needed is for some data on how the various round perform. The 5.56x45 and the 7.62x51 would be the standards of comparison. How does the Grendel compare to the 7mm UIAC? Or to the 260 Rem and other 6.5mm rounds? Are their better rounds out there? At the moment it appears that the 6.5 Grendel is at the bottom of the range and the 7mm UIAC at the top. Does anyone have any good comparison data?

[LRRPF52]

How does the Grendel compare to the 7mm UIAC? Or to the 260 Rem and other 6.5mm rounds? Are their better rounds out there? At the moment it appears that the 6.5 Grendel is at the bottom of the range and the 7mm UIAC at the top. Does anyone have any good comparison data?

The 7mm UIAC requires a larger action, larger magazines, larger magazine pouches, and takes up more space on a vest than traditional intermediate cartridges like the 7.62x39 and 5.56 NATO. The original 7.92x33 Kurz takes up the least space for length of magzines, but the magazines had to be taller because of the case head diameter.

The .260 Rem is a necked-down .308 to 6.5mm, so it would occupy the same practical space as any current 7.62 NATO weapon, with reduced barrel life. It is not ever going to fit in an assault rifle frame, so it falls into the traditional battle rifle footprint, which we're trying to get away from, while retaining as much downrange performance that battle rifles have.

If a general purpose cartridge is what one seeks, there have to be trade-offs on both ends of the spectrum:

Weight/recoil penalties for heavier projectiles driven at faster speeds

Reduced External & Terminal ballistics performance for lighter projectiles fired from low-recoiling weapons

I can't think of a cartridge that hits a more optimum balance point between these than the Grendel, especially since it allows a carbine or rifle that is lighter than a 5.56 equivalent, with better wind drift at 600yds than a 16" 7.62 NATO carbine, with a higher magazine capacity, and 50% of the recoil.

During one of the last DMR Courses I was running, I was really wishing that I would have had my little 16" Grendel with me, as the 5.56 wouldn't knock down steel poppers at 200m and 300m unless you did a rapid pair accurately into the head, whereas the 7.62 NATO HK417 sent the poppers and their bases clanking head over heel, and was punishing on the steel plates...but recoil and mag capacity were issues.

[stanc]

Well the 6.5 Grendel is looking more and more to be the "6.5 GPC". The 7mm UIAC is also interesting. The limiting factor is using the M4 platform for now. It basically means only having to do a barrel change at the least, an upper change out at the worst...

Judging from the historical record, being able to easily modify the M4 probably does not offer any real advantage to 6.5 Grendel. The last time that the US military adopted a new cartridge for the express purpose of upgrading existing weapons was immediately after the Civil War. Since the introduction of smokeless powder in 1892, whenever a new cartridge was adopted, a new rifle was also developed and fielded.

What is needed is for some data on how the various round perform.

That's just what I've been saying for years.

The 5.56x45 and the 7.62x51 would be the standards of comparison. How does the Grendel compare to the 7mm UIAC?

IIRC, there are photos on the internet of gel tests with 6.5 Grendel/123gr HPBT and 7 UIAC/130-140gr HPBT. I don't know of any other relevant testing.

[Trooper]

Then how does the 6.5 Grendel (not sure what the 6.5 GPC or how it is different than the Grendel) stacks up against the 260 Rem., the 7mm UIAC or any other contenders for the GPC.

Moreover how does the 6.5 Grendel compare to other rounds like the 6.5 BRM (eabco.com), the 6.5x55, the .308, 6.5x47 or the 6.5 Creedmore? If we are going to talk about producing a GPC then we need data.

[JASmith]

It is all trade offs -- flatter trajectory and heavy bullets get more recoil, heavier rifles, and fewer rounds per lb or kilogram.

Then one decides which receiver or to assume an entirely new variant or design -- and so on.

Of the cartridges than are arguably functional and reliable in the AR-15, the Grendel comes the closest to satisfying many of the desirable traits of a "General Purpose Cartridge" (GPC).

[Guardsman26]

Sorry to take so long to reply to previous posts.

LRRP52, according to live fire test results I have seen using 6.5 mm Grendel rounds fired from an AR15 platform, barrel length reductions DO have a significant effect on muzzle energy and retained energy at range. There is also a significant difference between direct gas impingement designs and AR15 clones with piston operated systems. This wouldn't be the first time that data calculated using a ballistics programme differed from real world testing. I think the best thing to do is to agree to disagree with your data.

Secondly, once a military spec ball round is developed, rather than an open tip match ammunition, you would also expect to see an performance degradation. Creating a finely tuned target round that performs well on a range is, as I am sure you will agree, a very different proposition from creating a military spec round designed to deliver consistent results across a variety of combat theatres, with varying operating temperatures, at all battle ranges, across all engagement types and against human targets with and without body armour.

So, while the 6.5 Grendel is pretty darn good, it isn't quite the match for 7.62 mm that it needs to be, once you refine it for military use. This is something that at least three military weapon manufacturers have been looking at over the last 12 months, plus the US Army Marksmanship Unit.

My contention is that any true modern GPC cartridge must be a match for 7.62 mm in terms of range and terminal effectiveness from 0 to 1,200 metres. Without meeting this requirement, we will be overmatched by an enemy using 7.62 mm x 54R as well as 7.62 mm NATO.

The current Grendel case is filled to capacity, so the only way to put more energy behind the projectile is to lengthen it. As soon as you do this, you need a longer action length than that of the AR15 platform. So the ideal platform will either add length to an existing AR15 design or to lighten an AR10 action. In either case, you end up with a weapon that weighs in between an AR15 and and AR10. Give me 12 months and I'll tell you which option works better. The extra weapon weight also offsets the increase in recoil versus 5.56 mm.

The 7 mm UIAC is a very interesting design, but it is so close to existing 7.62 mm NATO in size and weight, why would you bother changing? Too much cost for too little benefit. My view that a GPC cartridge is only viable if it delivers 7.62 mm performance in a lighter package.

Is it possible to create a lengthened 6.5 mm Grendel that delivers superb performance in a package that still weighs around 18 grams? I believe it is.

For a long time, people viewed the ideal military cartridge as having a performance in between 5.56 mm and 7.62 mm. That view is now wrong. The 6.25 mm British and 6 mm US SAW cartridges were very close to matching 7.62 mm in a lighter package. With improved propellants and bullet design, we can achieve the same goal, albeit with a slightly larger calibre to deliver the necessary projectile weight in a lead free bullet.

[Variable]

Sorry to take so long to reply to previous posts.

LRRP52, according to live fire test results I have seen using 6.5 mm Grendel rounds fired from an AR15 platform, barrel length reductions DO have a significant effect on muzzle energy and retained energy at range. There is also a significant difference between direct gas impingement designs and AR15 clones with piston operated systems. This wouldn't be the first time that data calculated using a ballistics programme differed from real world testing. I think the best thing to do is to agree to disagree with your data.

Can you share the results you are referring to? We try to stick to real numbers here as much as possible. We can't discuss things of which we know not. I'd be interested in seeing exactly what you are referring to.

Secondly, once a military spec ball round is developed, rather than an open tip match ammunition, you would also expect to see an performance degradation. Creating a finely tuned target round that performs well on a range is, as I am sure you will agree, a very different proposition from creating a military spec round designed to deliver consistent results across a variety of combat theatres, with varying operating temperatures, at all battle ranges, across all engagement types and against human targets with and without body armour.

So, while the 6.5 Grendel is pretty darn good, it isn't quite the match for 7.62 mm that it needs to be, once you refine it for military use. This is something that at least three military weapon manufacturers have been looking at over the last 12 months, plus the US Army Marksmanship Unit.

My contention is that any true modern GPC cartridge must be a match for 7.62 mm in terms of range and terminal effectiveness from 0 to 1,200 metres. Without meeting this requirement, we will be overmatched by an enemy using 7.62 mm x 54R as well as 7.62 mm NATO.

The current Grendel case is filled to capacity, so the only way to put more energy behind the projectile is to lengthen it. As soon as you do this, you need a longer action length than that of the AR15 platform. So the ideal platform will either add length to an existing AR15 design or to lighten an AR10 action. In either case, you end up with a weapon that weighs in between an AR15 and and AR10. Give me 12 months and I'll tell you which option works better. The extra weapon weight also offsets the increase in recoil versus 5.56 mm.

The 7 mm UIAC is a very interesting design, but it is so close to existing 7.62 mm NATO in size and weight, why would you bother changing? Too much cost for too little benefit. My view that a GPC cartridge is only viable if it delivers 7.62 mm performance in a lighter package.

Is it possible to create a lengthened 6.5 mm Grendel that delivers superb performance in a package that still weighs around 18 grams? I believe it is.

For a long time, people viewed the ideal military cartridge as having a performance in between 5.56 mm and 7.62 mm. That view is now wrong. The 6.25 mm British and 6 mm US SAW cartridges were very close to matching 7.62 mm in a lighter package. With improved propellants and bullet design, we can achieve the same goal, albeit with a slightly larger calibre to deliver the necessary projectile weight in a lead free bullet.

"We" being whom? Just curious in the interest of disclosure. Are you a solo tinkerer, a manufacturer, a rep for a manufacturer, mad scientist, etc....?

As for your comments on velocities and barrel lengths--- We don't need calculators for real world velocities. We already have our own barrels of various lengths, and chronographs to boot. What lengths are you specifically questioning, and with what ammo?

I already have 10.5", 14.5", and 19.5" barrels myself. What ammo are you questioning data on? AA factory 123 Scenar loads? Wolf 120 MPT loads? Hornady 123 Amax loads?

If we seem itchy, it's because we've owned and been shooting these cartridges ourselves for years, and when someone new pops up and tells us we don't know jack, well.... Show me, please. I'm always open to correction if i'm factually wrong on something. Velocities are facts, not opinions. Perhaps I've misunderstood something somewhere?

Would you like velocity data for 10.5", 14.5", and 19.5" barrels? I can chrono mine if you happen to pick something I own ammo wise.

It could just be me, but I kind of get the impression you may be splitting hairs here intentionally-- with some possible ulterior point to prove? Do you perhaps have something to market, and are setting up your case for it before presenting it? I'm just being sure I understand your motives completely.

[stanc]

It could just be me, but I kind of get the impression you may be splitting hairs here intentionally-- with some possible ulterior point to prove? Do you perhaps have something to market, and are setting up your case for it before presenting it? I'm just being sure I understand your motives completely.

If I may butt in here, I'd like to opine that Guardsman has no ulterior motives. I've engaged in a number of discussions with him on the MG&A forum, and have no doubt that he has a sincere motivation to optimize the combat capability of infantry riflemen and machine gunners.

[JASmith]

Can you share the results you are referring to? We try to stick to real numbers here as much as possible. We can't discuss things of which we know not. I'd be interested in seeing exactly what you are referring to...I'm just being sure I understand your motives completely.

Right on!

Way too easy to impute ulterior motives when assertions are not backed up with facts and figures.

I will concede, however, that too many numbers can make the read tedious, but zero is too few.

[LRRPF52]

We've hashed this out before over the years. For any serious students of the discussion, I would suggest the following reading assignments:

http://www.65grendel.com/forum/showthrea...-Cartridge

http://www.65grendel.com/forum/showthrea...es-Article

http://www.65grendel.com/forum/showthrea...ammunition

http://www.65grendel.com/forum/showthrea...y-Soldiers

If you want a 6.5mm "GPC", you don't need any extra case capacity over the Grendel, unless you are trying to keep the pressure down at 50,000psi. If you're willing to develop a Grendel-specific industrial powder for a particular military load, using a larger bolt design, you can find a load that will exceed the 147gr 7.62 NATO trajectory and drift from equivalent barrel lengths. The 123gr AMAX, NCC, SMK, and Scenar will already do that, but they are BTHP target bullets, except for the AMAX, which is tipped.

The problem you run into with the 7.62-augmenting/Replacement requirement for sheer performance numbers is that you pull the GPC further away from a viable assault rifle cartridge, into the albatross battle rifle category, which should have never been created post-WWII. Augmenting, then replacing 7.62 NATO is the most logical course of action in my opinion, so therein lies the challenge.

Option 1: This is why I lean to the idea of a mix of 5.56 NATO carbines with a 6.5x38 DM/Sniper/LMG system, where a 123-130gr set of military projectiles are used. The DM's and Snipers would have a target load BTHP with cannelure, and the LMG would have a Boat-Tail FMJ, a new barrier-blind round, and a tracer.

Option 2: If you really needed a single caliber system, you have the option of making a separate assault rifle load with a very light bullet of 85-100gr going 2700-2850fps, and a 130gr LMG load, or

Option 3: Penalize the Riflemen/Assaulters/RTO's/Key Leaders/ Engineers/Scouts with an LMG-based load meant for 500-1200m performance, with one distributed in links, and the other on stripper clips, so that every swinging Richard is slinging a too-heavy-for application load, especially in built-up terrain in close quarters, through a dual logistics packaging & distributing system anyway.

You reduce the already dismal qualification standards that mostly urban youth conscripts produce with the current, virtually recoilless 5.56 NATO, while burdening the logistics system across the board in the only area where it is currently efficient (5.56 NATO).

Has it been done before? Yes, in several armies with the FN/FAL and MAG58 GPMG, or G3 and MG3, or M14 and M60, but none of those small arms mixes are viable when you look at combat duration from contact-to-contact, or contact-to-continue mission. One contact with 7.62 NATO, and you're basically done until you can get a resupply.

One aspect of this problem I will always bring up is from the Riflemen Skill Level I-through-General Officer logistician perspective. Having occupied and functioned as a:

Rifleman
Grenadier
PLT RTO
SAW Gunner
Fire Team Leader
Rifle Squad Leader

Scout Observer
Scout Sniper
Assistant Recon Team Leader

Assistant Machine Gunner
Ammo Bearer
Weapons Squad Leader

My experience is anecdotal, yet relevant and diverse to this discussion. I know what will happen when you put a heavier load into an assault rifle and then hand it to entry-level soldiers. I especially know what will happen when you try to add weight to everyone's fighting load, while reducing ammunition capacity.

That's why I think the biggest thing that needs fixing first is the LMG, making it lighter, and capable of providing an acceptable replacement for the current 7.62 NATO belt-fed machine guns, while adding an improved DMR/SASS chambered in an intermediate 6.5mm that is the same chambering as the LMG.

[Tony Williams]

Interesting that the New Zealand army has decided to replace their 5.56mm Minimis with the 7.62mm flavour: http://www.thefirearmblog.com/blog/2013/...chine-gun/

[Variable]

If I may butt in here, I'd like to opine that Guardsman has no ulterior motives. I've engaged in a number of discussions with him on the MG&A forum, and have no doubt that he has a sincere motivation to optimize the combat capability of infantry riflemen and machine gunners.

Okay, my apologies to Guardsman then. I just felt compelled to ask because of the nature and style of his posts. I wanted to be sure. I've seen it many times in the past where a new poster pops up telling me how the current product is inferior, and then just happens to have the cure for the ailment I never knew I had.LOL Not that there would necessarily be anything wrong with having a potentially new offering, just that I like to know if there is a "hidden" motive at play. Not the case with him, so I'm slightly better informed now.

I still want some numbers though.

[LRRPF52]

Interesting that the New Zealand army has decided to replace their 5.56mm Minimis with the 7.62mm flavour: http://www.thefirearmblog.com/blog/2013/...chine-gun/

The Mk48 is an approach to the weight/length problem with the M240 (MAG58), however, it is nowhere near as durable according to those who have used it. It suffers from the same problem the AK has, which is beating itself apart. The FN Minimi and variants use an inverted AK piston/operating rod/bolt carrier & bolt if you ever get a chance to compare the two, and the SAW receiver is too short for even the 5.56 NATO, let alone 7.62 NATO. We already had plenty of issues with the M249's long-term durability.

The Naval Special Warfare community has been using the Mk48's for around 10 years now. When they break them, their budget allows for rapid replacement with no questions asked, and they are a very small organization. Trying to field the Mk48 en masse would be a maintenance nightmare. Another huge complaint with it is soldiers having AD's with it, since it is difficult to lock the bolt to the rear with the longer rearward movement required, in the same receiver size as the 5.56 SAW.

Any successful LMG in the recoil-management, accuracy, and long-term durability departments will use a constant-recoil system, not a "beat myself to pieces mitigated with a buffer" system.

[Trooper]

The way that I have seen rounds compared is looking at what would give similar BCs. Thus a 6.5mm with 140 gr. at 2500 fps is the bench mark (BC of .540). To do the same at 7mm would require a 162 gr bullet which would require more powder (longer case maybe) to just give 2500 fps. With a .308 it would require a bullet at 192 gr. The larger the bullet then the greater the felt recoil. A high BC (over .500) gives more velocity down range (the bullet retains velocity longer).

Thus my question. If we are looking for a GPC, using the 6.5mm family (6.5 Grendel, 6.5 BRM, the 6.5x55) as a baseline, what would a 7mm look like doing the same things (high BC, 2500-3000 fps)? One thing would be that it would have a heavier bullet (~160 gr.). Would the case be longer? What performance would it have down range?

[JASmith]

Trooper,

You are going in a good direction!

One of my long standing practices is to go to both sides of where intuition suggest the sweet spot might be. We all agree that 6.5mm is pretty good, and we know that 5.56 is too small.

What would 6mm and .25 caliber bullets for that same BC look like?

PS. There are many who reject the 6mm as being too small and a similar number rejecting the "quarter bore" as not having the right kinds of bullets, but let's see how the numbers play out. It could prove interesting...

[LRRPF52]

You don't need a 140gr 6.5mm to have a .500 G1 BC. You should also be aware that G1 BC's are meant for flat-based bullets, not boat tails, and 5.56 and 7.62 have been using FMJ Boat Tails for a long, long time. The weight-to-BC ratio for a 7mm makes it too heavy, generating too much recoil, and too much cartridge space/bulk for a viable system that will be lightweight enough for riflemen.

There is some interesting work on a 7mm Grendel for hunting, but it is optimum with 120gr bullets. Those are much lower than a 6.5mm 123gr .510 BC projectile. If you're relying on just BC and trajectory comparisons, the 16" Grendel currently beats a 16" 7.62 NATO L129A1 or SCAR-17 for wind drift when pushing the 147gr M80, assuming a 2450fps speed for the Grendel, and a 2620fps speed for the 16" 7.62 carbine (7.62 NATO M80 varies in 16" guns from 2550-2620fps).

The 7.62 NATO at such low speeds for the bullet will not fragment at CQB (bad), and has the following drop/drift at 4400ft ASL (thinner air like A-Stan)...
Drop at 600yds: 4.6 Mils
Drift at 600yds: 1.4 Mils (10mph full value wind)

At 2550fps mv, it is:
600yds: 4.9 Mils
Drift: 1.5 Mils

The 16" 6.5 Grendel with current civilian factory 123gr at 2450fps:
Drop at 600yds: 4.9 Mils
Drift at 600yds: 1.2 Mils

The Grendel does that with 50% less recoil, much less ammo weight, less ammo footprint on the soldier's load-meaning more capacity to space. The energy difference at 600yds is 847ft-lbs for the 2550fps M80, and 763ft-lbs for the 2450fps 123gr 6.5mm.

Build a bolt based off of the .30 RAR, and you can push the pressure up to generate 2650fps in the 16" Grendel easily, as I have factory 123gr Lapua Scenar loads that have clocked over 2580fps in my 16" gun for some reason. Being moly-coated was one, and the temps on the range might have been another. You see the diminishing returns when you crank up to 2650fps:

600yds Drop: 4.0 Mils
600yds Drift: 1.1 Mils
Energy: 912ft-lbs (that's quite a difference actually)

[stanc]

If you're relying on just BC and trajectory comparisons, the 16" Grendel currently beats a 16" 7.62 NATO L129A1 or SCAR-17 for wind drift when pushing the 147gr M80, assuming a 2450fps speed for the Grendel, and a 2620fps speed for the 16" 7.62 carbine (7.62 NATO M80 varies in 16" guns from 2550-2620fps).

The 7.62 NATO at such low speeds for the bullet will not fragment at CQB (bad), and has the following drop/drift at 4400ft ASL (thinner air like A-Stan)...
Drop at 600yds: 4.6 Mils
Drift at 600yds: 1.4 Mils (10mph full value wind)

At 2550fps mv, it is:
600yds: 4.9 Mils
Drift: 1.5 Mils

The 16" 6.5 Grendel with current civilian factory 123gr at 2450fps:
Drop at 600yds: 4.9 Mils
Drift at 600yds: 1.2 Mils

The Grendel does that with 50% less recoil, much less ammo weight, less ammo footprint on the soldier's load-meaning more capacity to space. The energy difference at 600yds is 847ft-lbs for the 2550fps M80, and 763ft-lbs for the 2450fps 123gr 6.5mm.

Trouble is, you're comparing 7.62 FMJ Ball to 6.5 HPBT Match. Hardly a fair comparison.

Try the calculation again, with 6.5 FMJ 120gr, 0.420 BC.

[cory]

Trouble is, you're comparing 7.62 FMJ Ball to 6.5 HPBT Match. Hardly a fair comparison.

Try the calculation again, with 6.5 FMJ 120gr, 0.420 BC.

For that matter why does it have to in the 123 gr family. I agree the 123 gr seems to be the sweet spot for the Grendel in HPBT Match family, but I don't think we need a round that large for a GPR.

The issues are the 5.56's relatively poor lethal effects and the 7.62 excess mass. The 5.56 is effective with a 62 gr bullet at or above 2600 fps. Why do we need to double that mass to get what the desired results?

I'd love to see the Geneva convention thrown out and our Marines and Soldiers only be regulated by the Constitution and the UCMJ, allowing a HPBT GPR, but I don't see that happening anytime soon.

My engineering hypothesis is that we're going to find the best answer in a 6.5 Grendel FMJBT closer to 110 grs.

I'd love to see a FMJBT in the 105 - 115 gr range developed and optimized for the Grendel.

[stanc]

For that matter why does it have to in the 123 gr family. I agree the 123 gr seems to be the sweet spot for the Grendel in HPBT Match family, but I don't think we need a round that large for a GPR.

More importantly, the requirement for lead free construction makes it unlikely that a general issue ball projectile would be that heavy.

My engineering hypothesis is that we're going to find the best answer in a 6.5 Grendel FMJBT closer to 110 grs.

I'd love to see a FMJBT in the 105 - 115 gr range developed and optimized for the Grendel.

Even that may be heavier than is practical. The FMJBT bullet developed for Wolf's steel case ammo is only 100 grains.