Lets start over: how do you design a GPC?

[stanc]

Sadly, there is no Supreme Court of JAGS where the precedent is established law. Kinda makes it hard to be a soldier these days I reckon. But, yhea I get the reasoning...we had a deal with those countries and these lot were not part of it. Though to be completely Boy Scout about it, I really don't see the greater humanity of being shot with a FMJ versus a polymer tip or SOST. If I were picking, and hopefully I never will be, I would pick varmint grenade to the dome for sure, but I am sure there is a very good reason nobody asked me. : )

Heh, heh. Yeah, a case could certainly be made that a varmint grenade or other high-lethality, hunting bullet is more humane than FMJ for killing. But, the other side of the coin is that many, if not most, bullet wounds are non-fatal. In those cases, the varmint grenade is far more likely to inflict amputating, very destructive, "inhumane" injuries than (non-fragmenting) FMJ.

To reverse your example, would you rather take a hit to the abdomen or thigh with a varmint grenade, or a slow-yawing, non-fragmenting, 7.62x39 M43 round?

[KentuckyBuddha]

I think your point is better at the extremities, but if the shot were going to kill me...hitting the aorta or iliac arteries (or even the femoral triangle) it probably isn't going to matter much as both options are going to have a devastating cavitation pattern and put you down and out fast (at least in geological terms). If you have a lateral injury to the abdomen that is non-lethal either way you are probably going to have peritonitis and either some poor cutters are going to get carpal tunnel with all that bowel resection or....well there really is no way to come out good on that deal...getting gut-shot with rifles is nasty, nasty business.

Maybe if you get hit in the tricep or something where you have a terrible ripping and exploding wound with the varmit grenade versus a clean and cauterized through and through with the fmj round you have a clear choice. : )

:Shudder: I am sorry I brought this up all of a sudden. lol But, it reminds me of a video I found educational even after having studied this stuff for a while.
Cliffs, pistols mostly wound, rifles at a much much higher rate.

skip to a min in to skip intro, and it is 30 min.... but as I said informative but some of it is very graphic...so be warned

http://www.youtube.com/watch?v=tku8YI68-JA

[Tony Williams]

Nammo Lapua has developed a second-generation 5.56mm "green" round using a steel-cored FMJ bullet (matching all Hague/Geneva interpretations) which they claim matches M855 ballistics, yaws rapidly and reliably on impact, and penetrates better.

[SHORT-N-SASSY]

The latter is no problemo. We have a JAG who has demonstrated he will approve virtually any bullet design the military wants to use. Examples:

- Sierra MatchKing hollow point bullet (7.62 M118LR, 5.56 Mk262)
- Barnes TSX expanding hunting bullet (5.56 "Optimized")
- ATK SOST expanding, fragmenting hollow point bullet (5.56 Mk318, 7.62 Mk319)

Thanks for the clarification. Upon a review of the Sierra MatchKing HPBT projectiles used in the 7.62 M118LR and 5.56 Mk262, it appears that the nearly closed tips of those approved designs are identical to the tips of the 6.5mm Sierra MatchKing 123-grain HPBT, the 6.5mm Nosler Custom Competition 123-grain HPBT and the 6.5mm Lapua Scenar 123-grain HPBT.

[stanc]

If you have a lateral injury to the abdomen that is non-lethal either way you are probably going to have peritonitis and either some poor cutters are going to get carpal tunnel with all that bowel resection or....well there really is no way to come out good on that deal...getting gut-shot with rifles is nasty, nasty business.

Maybe if you get hit in the tricep or something where you have a terrible ripping and exploding wound with the varmit grenade versus a clean and cauterized through and through with the fmj round you have a clear choice. : )

Okay, go with that example, then. I know which I'd prefer.

The reason I said abdomen is because of the experience of an old acquaintance, a Marine veteran of Vietnam who was gut shot with 7.62x39 rounds during a firefight. I don't know how much internal surgery he went through, but he survived with only three little pucker scars as a visible reminder.

:Shudder: I am sorry I brought this up all of a sudden.

Yeah. Maybe we should get back to topic. The military will use whatever bullet type they deem appropriate.

[Trooper]

Nammo Lapua has developed a second-generation 5.56mm "green" round using a steel-cored FMJ bullet (matching all Hague/Geneva interpretations) which they claim matches M855 ballistics, yaws rapidly and reliably on impact, and penetrates better.

Tony is there any chance that we are going to see a GPC? Or are we stuck with two calibers that do the mission but with lots of logistical headaches?

How do we develop a GPC, test it, in such a way that the Sergeant Majors at Ft Benning have to notice?

[woohoo]

Tony is there any chance that we are going to see a GPC? Or are we stuck with two calibers that do the mission but with lots of logistical headaches?

How do we develop a GPC, test it, in such a way that the Sergeant Majors at Ft Benning have to notice?

I can tell you they may notice it, look at it, and test it themselves but that doesn't mean it will go anywhere. The cartridge and platform would have to be far ahead of the current system. It must be a big company that can develop a complete system that blows everything else out of the water.
Just goofing off 5 years ago we dropped $40k into testing several different chamber and rifling designs to increase performance. It takes a lot of money to develop, test and PROVE a complete new system.
The problem I see is the military doesn't know what they want. Someone will have to prove their system and then sell the idea to the military that it IS the system they need.
Everyone at the top is going to want what THEY think they need and they will cast a shadow of doubt on every product that they as individuals don't want.
If company "A" does come up with an idea that the mil can actually agree on. The govt will snatch the design and hand it to company "C" to produce.
Sorry for the negative view but it seems that is the way our government works these days. If it was run like a business it would be a totally different game.

[stanc]

The problem I see is the military doesn't know what they want. Someone will have to prove their system and then sell the idea to the military that it IS the system they need.
Everyone at the top is going to want what THEY think they need and they will cast a shadow of doubt on every product that they as individuals don't want.

That pretty well sums it up. The fact is, there have been a multitude of new cartridges developed over the years, many within the military itself. Only rarely does a new round get adopted. (Logically, they can't all be adopted, or the system would be in chaos.)

IMO, to get a GPC into service will require the active support of one or more high level entities, such as 5.56x45 and the AR15 received from the Commanding General of CONARC and others, in the late 1950s and early 1960s. Without such backing, the GPC will go nowhere.

[Guardsman26]

Reading this discussion convinces me that Bill Alexander and the team at Lapua did a truly excellent job with the 6.5 mm Grendel. To package that amount of performance in a cartridge the same length as a 5.56 mm M855 is truly impressive. The point that is well made here is what happens when you mass produce Grendel rounds, need to use an FMJ projectile or fire the round from a weapon with an excessively short barrel: you get a certain amount of performance degradation.

Then there is the need for a tracer, which eats away at case capacity.

Then there is a possible future need for a polymer cartridge, which also erodes case capacity by about 10%.

For all these reasons, giving the Grendel a longer case is the perfect start point for a GPC contender IMO. You don't need a wider case, like the 7.62 mm one, simply a slightly longer version of the existing Grendel 11.3 mm head diameter.

As soon as you extend the Grendel case length, however, you will need a weapon with a longer action length. You need an AR12.5. Once you accept that requirement, then you are on the road to a perfect GPC. The net result is a weapon that is about 1 lb / 500 g heavier than a 5.56 mm equivalent.

But, here comes the good news. When it comes to building a SAW variant, you can actually start with a 5.56 Minimi M249 rather than the 7.62 mm M240. So with the SAW, you can create a much lighter machine gun, but with much greater firepower.

[LRRPF52]

Reading this discussion convinces me that Bill Alexander and the team at Lapua did a truly excellent job with the 6.5 mm Grendel. To package that amount of performance in a cartridge the same length as a 5.56 mm M855 is truly impressive. The point that is well made here is what happens when you mass produce Grendel rounds, need to use an FMJ projectile or fire the round from a weapon with an excessively short barrel: you get a certain amount of performance degradation.

Then there is the need for a tracer, which eats away at case capacity.

Then there is a possible future need for a polymer cartridge, which also erodes case capacity by about 10%.

For all these reasons, giving the Grendel a longer case is the perfect start point for a GPC contender IMO. You don't need a wider case, like the 7.62 mm one, simply a slightly longer version of the existing Grendel 11.3 mm head diameter.

As soon as you extend the Grendel case length, however, you will need a weapon with a longer action length. You need an AR12.5. Once you accept that requirement, then you are on the road to a perfect GPC. The net result is a weapon that is about 1 lb / 500 g heavier than a 5.56 mm equivalent.

But, here comes the good news. When it comes to building a SAW variant, you can actually start with a 5.56 Minimi M249 rather than the 7.62 mm M240. So with the SAW, you can create a much lighter machine gun, but with much greater firepower.

I've looked at the cross-section of the 6.5mm Swede Tracer, and the existing sectional density and bullet profile of 130gr class 6.5mm pills would facilitate the tracer element without impacting case capacity like tracers do to 5.56 and 7.62 NATO. I don't think there's a need to affect case capacity at all really with an LMG using a 2.400" COAL.

A wider case is also a no-go because you just departed from the intermediate cartridge concept and weight parameters, falling into self-loading battle rifle territory-a system that shouldn't have progressed past WWII in my opinion.

If you were with me when I put 4 rounds on-target at 1200yds from my 16" Grendel as fast as I could index the reticle and pull the trigger, I think the words "performance degradation" would evaporate from your perspective on this cartridge in its existing form. That type of performance is currently exploitable by Machine Gunners and Snipers/DM's. A system built around a military projectile with a BC in the low-to-mid .5's G1 is easy to do. I think a 130gr would be the ticket, run at 2500-2600fps. An LMG will have a bolt/chamber/breech built around the cartridge. I still see no reason to increase the case length & weapon weight, especially for a DMC/SASS.

[cory]

But, here comes the good news. When it comes to building a SAW variant, you can actually start with a 5.56 Minimi M249 rather than the 7.62 mm M240. So with the SAW, you can create a much lighter machine gun, but with much greater firepower.

Coming from someone who carried the SAW (no longer than I had too), starting at the SAW design is the last thing we need to do. To put it in the proper light, when breaching a room you NEVER lead with SAW gunner unless you had a death wish.

Anyways, I don't want to get this thread off topic.

We're assuming the necessary length of a tracer round is a constraint for using the Grendel. That assumption comes from another assumption that if we wanted to use a 130gr FMJ round as the primary round we need a 130gr tracer round, but what if we used approximately a 123gr Tracer round that would be shorter than the 130gr FMJ. Could the BC and charge of the Tracer round not be adjusted to match the trajectory of the 130gr FMJ or at least to the tolerance of the current 556 tracer round to the M855A1?

[LRRPF52]

Maybe Tony Williams could do some scaling on this pic for a Grendel-appropriate tracer. Tracers are appropriate for a beaten zone of a machine gun, so the fact that there will be shot dispersion is intentional.

One would have to identify and clarify the maximum dispersion parameters to go forward with a serious discussion about a Grendel tracer. The 123gr idea to match the form factor of a 130gr FMJ or Green projectile makes a lot of sense to me.

I also agree that the SAW/FN Minimi design is not a good starting point for a serious LMG, since its operating system is basically an inverted AK, which is why SAWs have such a problem with longevity-the action beats itself apart, and the SAW weighs as much or more than a PKM, which is insane.

You need to start with a constant-recoil receiver design, with a good feed tray cover (which the SAW actually has from the MAG58 scaled-down), and go from there with a 12lb max empty weight goal, 11lb preferred. I actually like the barrel change mechanism from the SAW more than most other machine guns. It's very fast, very simple, and very user-friendly.

[JASmith]

...Could the BC and charge of the Tracer round not be adjusted to match the trajectory of the 130gr FMJ or at least to the tolerance of the current 556 tracer round to the M855A1?

Frankly, this looks like an idea worth pursuing. I will admit that it hadn't occurred to me.

Implementing might be a challenge, but probably doable if we don't ask for the best possible BC for the FMJ and are willing to allow a bit more manufacturing cost for the tracer to keep its BC higher. That trick, combined with carefully crafted specs for harmonizing the tracks, might lead to an interesting tracer & ball combo for the Grendel.

I am not convinced that one must go with a 130 gr 6.5 caliber projectile to have a credible replacement for the 7.62 M80 round. Take a look at the Norma 120 gr FMJ. That bullet with a BC of .428 should have comparable barrier defeat capability to the M80 at all ranges when launched at a muzzle velocity of 2600 - 2650 ft/sec. This assumes the M80 has a barrel length of 20 inches. Furthermore, we get an idea of how well that bullet can transform into a steel-core version by looking at the Barnes TSX (BC .381), the Barnes TTSX (BC .412) and the Hornady 120 gr GMX (BC .450). Any of those shapes should have enough velocity at long range to have barrier defeat potential consistent with that of the M80.

Further, the variation in BC tells us that we could indeed harmonize the FMJ and tracer even if the tracer weighs somewhat less to accommodate the trace element.

Wounding potential is another question, but I can flatly state that kinetic energy is inappropriate and misleading metric for wounding potential.

[stanc]

[One would have to identify and clarify the maximum dispersion parameters to go forward with a serious discussion about a Grendel tracer. The 123gr idea to match the form factor of a 130gr FMJ or Green projectile makes a lot of sense to me.

I'm curious as to how a 130gr "green" Ball round is feasible. The steel core 6.5x55 AP bullet weighs only 112gr.

The lead core 6.5x55 Tracer projectile is 120gr. Substitute copper for core material, and it'll have to be significantly longer in order to weigh 123gr.

[cory]

I was only using those using those weights to make my point. I do think a heavier bullet like a 130gr makes since in an LMG and possibly DMs too.

Let's say we use a 123gr ball round we can go with a 110-115gr tracer, if we go with a 115gr ball round, we go with 95-100gr tracer. I think you get my point.

I do think the LMG and rifles should have different weighted rounds developed to compliment the platform. That being said the LMG round will need to function in a rifle and vice versa.

If possible develop a round that compliments both the LMG and DMs, therefore the DMs can acquire their needed ammo by grabbing a LMG drum and delinking rounds.

Even if the LMG and rifle uses an identical round, a LMG requires link ammo in drums requiring a dedicated logistics chain. What I'm getting at is I don't believe only ONE round will benefit logistics.