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.280 Enfield...Ahead of its time - stanc - 04-15-2012
JASmith Wrote:My own view is that when LRRPF52 convinces the powers that be to adopt the Grendel for the LMG role, it will be in a mode where the pressures go to more like those allowed for the PPC and the overall cartridge length is relaxed to accommodate the longest bullets (e. g. 130 - 144 gr copper-steel) with the bullet so that there is no protrusion into the powder volume beyond that needed to get about a caliber of contact between the bullet shank and the case neck.Since Paul wants to stick with 5.56 NATO for carbine and rifle, and use 6.5 Grendel only for (what I like to call) his Optimized Machine Gun (OMG
), there is no need for cartridge OAL to be constrained by M16 mag well dimensions.That does allow the projectiles to be loaded long for minimum impact on powder volume, and together with higher chamber pressure, would enable a significant increase in muzzle velocity.
However, even if the target muzzle velocities be achieved in LMG barrel lengths (14.5"-18") currently used, and assuming the link issue can be resolved, one very important question remains:
Are 130-144gr "green" (steel/copper and steel/steel) and conventional steel-core ball bullets actually feasible? Nobody has yet presented any evidence that such military projectiles are viable.
The heaviest example I know of is the 6.5 Swedish AP, at 113gr, well under the specified weight range for the OMG concept.
The 130gr TSX cited by Paul is a 100% copper bullet with a flat base. Weight loss incurred by using lower density steel, and going to a boat tail shape (to maximize long range performance), would reduce projectile weight to circa 115gr, at best.
If anyone can prove me wrong, please do so.
.280 Enfield...Ahead of its time - LRRPF52 - 04-15-2012
There is zero need for a 5.56 NATO rifle, since a 14.5" or 16" barrel will give you all the velocity you need.
For the MRMG (Multi-Role Machine-Gun) load, there is plenty of room to play with for weight in the high sectional density of 6.5mm projectiles without magwell restrictions. Here's an extreme example of a very long Japanese 6.5mm projectile:
![[Image: chapter1figure9.jpg]](http://history.amedd.army.mil/booksdocs/wwii/woundblstcs/chapter1figure9.jpg)
.280 Enfield...Ahead of its time - stanc - 04-16-2012
LRRPF52 Wrote:For the MRMG (Multi-Role Machine-Gun) load, there is plenty of room to play with for weight in the high sectional density of 6.5mm projectiles without magwell restrictions.What does that mean? Have you revised your MRMG (I still think Optimized Machine Gun makes a better acronym. :p
) concept to use bullets lighter than 120 grains?Quote:Here's an extreme example of a very long Japanese 6.5mm projectile::confused: It's not unusually long for caliber. L/D is ~5.0, about the same as for 6.5 Swede 140-144gr, lead-core, FMJ bullets.
Military 130-140gr "green" and steel-core ball projectiles would have L/D in the 5.6-6.2 range. That might raise issues with rifling twist, terminal performance at <200 meters, and torsion effects of the long-loaded bullets in machine gun links.
.280 Enfield...Ahead of its time - Tony Williams - 04-16-2012
stanc Wrote:Like the British, the Americans wanted to have a rifle of their own design. To this day, the US Army has disliked bullpup rifles, which ruled out adoption of the EM-2, and they clearly weren't ready to accept the AR-10.
I've been re-reading Dugelby's EM-2 Concept and Design and the only reason which the US gave for rejecting the EM-2 rifle was that it wasn't ambidextrous. Well, there are lots of different ways to achieve ambidextrous bullpups, so they could have designed their own.
The plain fact is that just as there was only one way to achieve the US Army's requirement for a 2,000 yard performance matching the .30'06 in a lightweight automatic weapon (i.e. by reducing the calibre), there was also only one way to achieve the requirement for a rifle with such long-range performance that was also compact enough to replace an SMG (i.e. a bullpup).
Any serious attempt to meet the US Army's requirements inevitably led to a reduced-calibre bullpup - nothing else stood a chance of ticking all the boxes. If they didn't want to drop below .30 cal and didn't want a bullpup, they should have come up with a different set of requirements.
.280 Enfield...Ahead of its time - stanc - 04-16-2012
Tony Williams Wrote:I've been re-reading Dugelby's EM-2 Concept and Design and the only reason which the US gave for rejecting the EM-2 rifle was that it wasn't ambidextrous. Well, there are lots of different ways to achieve ambidextrous bullpups, so they could have designed their own.Well, if it was that easy, then the Brits should have designed the EM-2 to be ambidextrous.
Personally, I doubt that was the real reason for the US rejection. The US Army just doesn't seem to like the bullpup concept...for rifles, anyway. The M60 GPMG was a semi-bullpup.
Garand did develop a bullpup in the same time frame as the EM-2, but it didn't go anywhere, either.
![[Image: Garand_T31_bullpup_edit.jpg]](http://www.nps.gov/spar/historyculture/images/Garand_T31_bullpup_edit.jpg)
Quote:The plain fact is that just as there was only one way to achieve the US Army's requirement for a 2,000 yard performance matching the .30'06 in a lightweight automatic weapon (i.e. by reducing the calibre), there was also only one way to achieve the requirement for a rifle with such long-range performance that was also compact enough to replace an SMG (i.e. a bullpup).Hey, I agree with all that. I just disagree that the .280 British was the answer. It wasn't the best option then (as you noted, the .270 British w/high-BC bullet would've been much better), and there are better alternatives now.
Any serious attempt to meet the US Army's requirements inevitably led to a reduced-calibre bullpup - nothing else stood a chance of ticking all the boxes. If they didn't want to drop below .30 cal and didn't want a bullpup, they should have come up with a different set of requirements.
I also am not enamored of short, fat cartridges for machine guns, if only because it makes a belt of linked rounds longer than necessary.
.280 Enfield...Ahead of its time - Tony Williams - 04-17-2012
The British Army doesn't seem to be bothered about ambidexterity. After all, the .303 Lee Enfield and the Bren gun were both for northpaws only, and the southpaw version of the SA80 was rejected.
The reason why Garand's T31 was rejected is pretty obvious: it's surely one of the fugliest rifles ever proposed!
.280 Enfield...Ahead of its time - LRRPF52 - 04-17-2012
That Garand bullpup definitely is fugly. It makes Russian firearms look like pieces of art. As far as bullpups go, UK, New Zealand, and Aussie Special Operations units use Colt Commando variants as a rule for an individual carbine preference, even with the Grenadiers.
I still think the 7mm in a T65-based case would have been a better belt-fed weapon and DMR/sniper cartridge than the 7.62 NATO, alongside 5.56 carbines. Colt shot itself in the foot by not trouble-shooting the 605 Carbine with an appropriate length gas system, postponing the widespread adoption of an AR15 family carbine until 1997.
.280 Enfield...Ahead of its time - stanc - 04-17-2012
Tony Williams Wrote:The British Army doesn't seem to be bothered about ambidexterity.Yeah, that's pretty obvious. Like I said, I think ambidexterity was not the real reason the US turned down the EM-2.
Tony Williams Wrote:The reason why Garand's T31 was rejected is pretty obvious: it's surely one of the fugliest rifles ever proposed!
LRRPF52 Wrote:That Garand bullpup definitely is fugly.Jeez, you guys done hurt my feelings. I always rather liked the looks of Garand's T31. :p
LRRPF52 Wrote:I still think the 7mm in a T65-based case would have been a better belt-fed weapon and DMR/sniper cartridge than the 7.62 NATO...I agree. But, I still think the .270 British would've been even better than the .280 British. And either one would still have led to your cherished 5.56 NATO.
Likewise, I think 6.5 SPC (w/long, high-BC bullets) would be a better choice than 6.5 Grendel for your MRMG. I know it's heresy to say that here, but the extra 4mm of case length would eliminate some problems inherent to the short, fat Grendel case.
.280 Enfield...Ahead of its time - adamjp - 04-17-2012
stanc Wrote:Yeah, that's pretty obvious. Like I said, I think ambidexterity was not the real reason the US turned down the EM-2.I think you are onto something there. I've been toying with the SPC cartridge, but in different calibres. The 6mm SPC (pretty much aka the 6mm WOA) looks quite nice as a little hunting round.
Likewise, I think 6.5 SPC (w/long, high-BC bullets) would be a better choice than 6.5 Grendel for your MRMG. I know it's heresy to say that here, but the extra 4mm of case length would eliminate some problems inherent to the short, fat Grendel case.
IMHO the 277 bore and the reasons put forward for it's choice make sense - for SF types. Since they represent a tiny proportion of the Army perhaps a wider viwe should be taken and that means a 6.5mm bore is more logical.
TO be honest it is all academic, the way to do this properly is to decide the effect you want to deliver, and then design the bullet to do that, and a cartridge to propel it. Things like the Grendel and the SPC are still tied to the available parent cases - a company with resonable resources could start with a greenfield design. I think this is what is suggested in the Optimised Calibre discussion (I've been away and have not had the chance to read it yet).
.280 Enfield...Ahead of its time - LRRPF52 - 04-18-2012
Quote:QUOTE=adamjp;29232]I think you are onto something there. I've been toying with the SPC cartridge, but in different calibres. The 6mm SPC (pretty much aka the 6mm WOA) looks quite nice as a little hunting round.[/QUOTE]
IMHO the 277 bore and the reasons put forward for it's choice make sense - for SF types. Since they represent a tiny proportion of the Army perhaps a wider viwe should be taken and that means a 6.5mm bore is more logical.
TO be honest it is all academic, the way to do this properly is to decide the effect you want to deliver, and then design the bullet to do that, and a cartridge to propel it. Things like the Grendel and the SPC are still tied to the available parent cases - a company with resonable resources could start with a greenfield design. I think this is what is suggested in the Optimised Calibre discussion (I've been away and have not had the chance to read it yet).
There never was, nor is there widespread support for a carbine caliber other than 5.56 in the SF community. The 6.8 SPC was literally a project pushed by less than a handful of guys, with the blessing of a more senior officer to experiment. It was never an official SF program in any shape or form, despite what many have claimed or believe.
It is interesting to note that the officer who did bless off on that experiment is now the USASOC Commander, Lt. General John Mullholland Jr.
There was a ton of internal and external resistance to the proposed adoption of the 6.8 SPC from within SF, as well as the US Special Operations Community as a whole, with far fewer advocates than opponents. Especially within JSOC, and seasoned shooters within SF, 5.56 NATO has a high level of respect and it is the go-to cartridge for indivudual service carbines. There are a minority of proponents of this or that cartidge, but 5.56 is superb at what it does, especially with those who have been using it for so long to accomplish the mission without complaint.
.277 pills are definitely not optimum across the board, but do provide a lot of impact energy transfer with more blunt ogives. The trade-off is retained energy at distance.
My position is that trying to fix something that ain't broke is a waste of time, resources, and leaves the areas that truly need fixing unattended to, and that is the status of our GPMG's, and LMG's, being of limiting size, weight, and effectiveness when contrasted against the maneuverability of riflemen or dismounted personnel carrying M4 carbines.
The pigs need to be replaced, not the M4.
.280 Enfield...Ahead of its time - stanc - 04-18-2012
adamjp Wrote:TO be honest it is all academic, the way to do this properly is to decide the effect you want to deliver, and then design the bullet to do that, and a cartridge to propel it. Things like the Grendel and the SPC are still tied to the available parent cases...I agree. That's the way I would do it.
I suggested using the SPC case because Paul seems set on 6.5mm as the caliber for his proposed MRMG, and a 6.5 SPC could use the M27 link design with little or no alteration other than an increase in loop diameter. Design of links for 6.5 Grendel will necessarily be more involved.
Also, the SPC's smaller case diameter allows packing a belt of ammo in a marginally smaller volume. (See attached pic.)
.280 Enfield...Ahead of its time - LRRPF52 - 04-18-2012
A 43mm case + long ogive projectile will have a depth volume longer than a 39mm case though. No matter what projectile diameter is selected, trying to invent a new case from scratch will probably invoke at least 2 existing parent cases that have already existed for 50-70 years. The 7mm UIC uses 6.5 Carcano case head dimensions, the 6.5 Grendel has a family tree with the great grandfather being the 7.62x39, and the 6.8 SPC has the .30 Remington as its parent-a cartridge introduced more than 100 years ago in 1906.
We know that 6.5mm projectiles are the optimum, most efficient bullet for retained energy and penetration at distance from short-action cartridges and rifle/MG platforms. Those are traits that serve a GPMG and DMR well, but not a carbine meant for closer range work.
For cases, we are seeing that .421"-.445" case heads are being zeroed-in on in an attempt to reduce load volume and weight from the 7.62 NATO and its .473" case head. There isn't a real need to develop a new case when you already have one that is capable of 62,000 psi, has a .445" head, and is only 39mm long, leaving the ability to load long-ogive projectiles that are ideal for distance work. We're about maxed out on compactness and performance at the intersection of the Grendel for a metallic ammunition cartridge to be used in a smaller action.
.280 Enfield...Ahead of its time - stanc - 04-18-2012
LRRPF52 Wrote:A 43mm case + long ogive projectile will have a depth volume longer than a 39mm case though.Yes. A whopping 0.16" longer. Seems to me that's more than offset by the SPC's height and width volumes, which are each 0.22" less than for the Grendel case.
But, that's not terribly important. Of far greater impact is the simplification in design of metallic links, which you completely ignored. :confused:
.280 Enfield...Ahead of its time - adamjp - 04-18-2012
stanc Wrote:Yes. A whopping 0.16" longer. Seems to me that's more than offset by the SPC's height and width volumes, which are each 0.22" less than for the Grendel case.The improved feeding characteristics of the longer, more tapered case are a major plus too.
But, that's not terribly important. Of far greater impact is the simplification in design of metallic links, which you completely ignored. :confused:
I completely agree that the 6.5mm bore appears to be the top approach at this time, but I don't agree that the 5.56 is the last word in cartridge or caliber for personal weapons or section weapons.
.280 Enfield...Ahead of its time - Tony Williams - 04-18-2012
adamjp Wrote:TO be honest it is all academic, the way to do this properly is to decide the effect you want to deliver, and then design the bullet to do that, and a cartridge to propel it. Things like the Grendel and the SPC are still tied to the available parent cases - a company with resonable resources could start with a greenfield design. I think this is what is suggested in the Optimised Calibre discussion (I've been away and have not had the chance to read it yet).
Yes, of course that is the way to do it. But it isn't the choice of parent cases which is the constraint on cartridge design, it's the maximum permissible overall length for the round to fit within an AR-15 action. That limitation is what is causing both the 6.5mm Grendel and 6.8mm SPC to be less than optimal.
.280 Enfield...Ahead of its time - Tony Williams - 04-18-2012
Just a reminder - some photoshopping I did a couple of years ago of alternative general-purpose rounds, from my web presentation: http://www.quarry.nildram.co.uk/The%20Next%20Generation.htm
![[Image: Image110.jpg]](http://www.quarry.nildram.co.uk/Image110.jpg)
.280 Enfield...Ahead of its time - stanc - 04-18-2012
Tony Williams Wrote:...it isn't the choice of parent cases which is the constraint on cartridge design, it's the maximum permissible overall length for the round to fit within an AR-15 action.Why should that be a limiting factor?
Paul's MRMG concept requires a cartridge solely for the infantry machine gun, not carbines or rifles.
And in the event the military should want a universal cartridge, they could develop new rifles with longer mag wells.
.280 Enfield...Ahead of its time - adamjp - 04-18-2012
stanc Wrote:Why should that be a limiting factor?
Paul's MRMG concept requires a cartridge solely for the infantry machine gun, not carbines or rifles.
And in the event the military should want a universal cartridge, they could develop new rifles with longer mag wells.
Agreed. Why is the AR15 a limiting factor? There are plenty of other rifles on the market, many of them have features that are improvements over the AR design.
.280 Enfield...Ahead of its time - Variable - 04-18-2012
Tony Williams Wrote:Just a reminder - some photoshopping I did a couple of years ago of alternative general-purpose rounds, from my web presentation: http://www.quarry.nildram.co.uk/The%20Next%20Generation.htmI think the 6.5x45 looks pretty interesting.
.280 Enfield...Ahead of its time - JASmith - 04-18-2012
Variable Wrote:I think the 6.5x45 looks pretty interesting.This gives us at least three cartridges that should be looked at more closely for the LMG/MMG role:
- The 6.5 Grendel with extended COAL
- A 6.5 based on the SPC but with an extended COAL
- The 6.5x45