+- 6.5 Grendel Forum (https://65grendel.com)
+-- Forum: 6.5 GRENDEL DISCUSSION FORUMS (https://65grendel.com/forumdisplay.php?fid=3)
+--- Forum: 6.5 Grendel Military & Law Enforcement (https://65grendel.com/forumdisplay.php?fid=13)
+--- Thread: Optimized Caliber (/showthread.php?tid=691)
Optimized Caliber - bwaites - 12-06-2011
stanc Wrote:That's true for 6.8 only when limited by 5.56 mag length. Remove the mag length restriction, as Paul intends for his LMG, and 6.8 SPC becomes a viable option at least as good as - and possibly even better than - 6.5 Grendel.
Not really, because the Grendel has a significant advantage in SD when using same weight projectiles. That increases barrier penetration. Since powder capacity is essentially the same, using same weight bullets the Grendel will have higher BC's and improved SD's.
Optimized Caliber - BluntForceTrauma - 12-06-2011
It's a matter of balance. Bigger projectiles and more powder give more recoil, and we're back to where we started. Limitations must be understood and set . . . somewhere.
John
Optimized Caliber - stanc - 12-06-2011
bwaites Wrote:Not really, because the Grendel has a significant advantage in SD when using same weight projectiles. That increases barrier penetration. Since powder capacity is essentially the same, using same weight bullets the Grendel will have higher BC's and improved SD's.Yes, really.
SPC's smaller case diameter allows higher pressure for the same bolt thrust. Higher pressure = higher MV.
Without mag length limit, SPC can use heavier bullets to match Grendel's former BC advantage.
Heavier bullets at same or higher velocity = better penetration of barriers like concrete block.
With "green" (and steel-core) bullets, 6.5 may have a practical max weight of ~120gr, whereas for 6.8 it'd be ~130gr.
Then there is the question of reliable feeding of Grendel's short, fat case in a belt-fed machine gun. The SPC has a configuration much like that of cartridges that are proven to work.
Of course, the most critical aspect of a Grendel LMG is that it requires we ASS-U-ME viable disintegrating links can be designed. In contrast, no such assumption is necessary with the SPC case, which has dimensions compatible with the existing link design.
If testing (not just theory) were to prove 6.5mm bullets are truly better than 6.8mm projos, then IMO the prudent course of action would be to go with 6.5 SPC.
Optimized Caliber - stanc - 12-06-2011
HANKA Wrote:It's a matter of balance. Bigger projectiles and more powder give more recoil, and we're back to where we started. Limitations must be understood and set . . .I agree. Question is, what are those limits?
Optimized Caliber - bwaites - 12-06-2011
If you are designing a new chamber and rifle, then the bolt thrust issue is a moot point, you can run whatever pressure you designate as the ideal, and build the bolt assembly to match. The longer, skinnier 6.8 case requires a longer extraction movement, with the attendent larger recipricating issues, which creates at least as big a disadvantage as does the ability to make links work for the shorter, fatter case. We know that full auto is no issue with the Grendel because its been run that way in AR's by plenty of people with no complaints.
Heavier doesn't necessarily equal better penetration. At equal velocities, penetration also is affected by frontal area, so a bigger bullet that is heavier might have the same penetration as a lighter, but higher sectional density bullet. (Thats why elephant hunters shot 6.5's instead of bigger bullets, at least some of the time.)
And once again, using same weight bullets, the Grendel has a higher SD, and thus will penetrate better. With a lighter bullet with the same SD, it will also have less recoil, which is another factor in its favor.
Recent development has pretty conclusively shown that short powder columns are more efficient than long powder columns, as well.
BUT....we are arguing about this just to argue, because all of it is theoretical.
Where is JMB when you need him?
Optimized Caliber - BluntForceTrauma - 12-06-2011
stanc Wrote:Question is, what are those limits?
A starting point is to ask: Are we OK with small arms that would be bigger and heavier than the current M4/M16 series? Longer cartridge overall lengths start a growth spiral.
John
P.S. One niggling point I had meant to make: I believe M855A1 is not ONLY copper and steel, but includes a bismuth alloy core under the steel penetrator. (I THINK it's bismuth!)
Optimized Caliber - JASmith - 12-07-2011
HANKA Wrote:A starting point is to ask: Are we OK with small arms that would be bigger and heavier than the current M4/M16 series? Longer cartridge overall lengths start a growth spiral.We could start a poll, but I am reasonably sure that weight and bulk are anathema to the grunt, so he will be happy with the lightest one that works.
John
P.S. One niggling point I had meant to make: I believe M855A1 is not ONLY copper and steel, but includes a bismuth alloy core under the steel penetrator. (I THINK it's bismuth!)
I've been closely following the 5.56 replacement debate for several years now, and know it has been going on for more than fifty years. The one constant is that those who have used the 5.56 in its design performance envelope swear by it. As long as the combat fits within that envelope, experienced combat veterans seem to be well-served by the cartridge. So, we get another indicator that folks would not be OK with bigger and heavier small arms.
The Grendel "toe in the door" results from the fact that, even in the jungles of Vietnam, there were times that terminal performance at longer ranges was shown to be less than desired. The back-fill in capability has been done with things like 7.62, Grenade launchers, mortar, artillery, and air assets.
LRRPF52 is suggesting that the grunt who uses a SAW or M240 to give team support for engagements beyond a couple of hundred meters could see a significant weight reduction while keeping pretty much the same terminal effects on targets as with the M240 by using a Grendel cartridge in a properly designed LMG.
-----
As for your question about M855A1, can we expand the question to include resulting ballistic coefficient? As I understand, a couple of different forms were looked at and reported on during the development. I think the early reporting was needed to garner support, but there seems to be less than detailed discussion about the final product, its design, and how well it performs.
Optimized Caliber - stanc - 12-07-2011
bwaites Wrote:If you are designing a new chamber and rifle, then the bolt thrust issue is a moot point, you can run whatever pressure you designate as the ideal, and build the bolt assembly to match.That's true, but less beefing up of the bolt and other components will be needed for a cartridge with less bolt thrust. That translates to increased durability and/or decreased weight.
Quote:The longer, skinnier 6.8 case requires a longer extraction movement, with the attendent larger recipricating issues, which creates at least as big a disadvantage as does the ability to make links work for the shorter, fatter case.Do you seriously think that a 4mm longer extraction poses anywhere near the difficulties as design and development of a new link???
Quote:We know that full auto is no issue with the Grendel because its been run that way in AR's by plenty of people...We know that 6.5 Grendel does full-auto fine in magazine-fed rifles. We do not know how it does in belt-fed machine guns.
Quote:Heavier doesn't necessarily equal better penetration. At equal velocities, penetration also is affected by frontal area, so a bigger bullet that is heavier might have the same penetration as a lighter, but higher sectional density bullet.The problem with that idea is, with the 5.56 mag length limit lifted (as in Paul's LMG concept), 6.8 SPC is not limited to bullets of the same weight. It could use bullets of the same SD, launched at equal or higher velocities.
And once again, using same weight bullets, the Grendel has a higher SD, and thus will penetrate better.
Optimized Caliber - stanc - 12-07-2011
HANKA Wrote:A starting point is to ask: Are we OK with small arms that would be bigger and heavier than the current M4/M16 series? Longer cartridge overall lengths start a growth spiral.Paul wants to keep the M4 chambered for 5.56 NATO, so there wouldn't be a weight spiral for carbines. What he proposes is a special, long-loaded, high-pressure 6.5 Grendel solely for an LMG (and maybe DMR).
Quote:One niggling point I had meant to make: I believe M855A1 is not ONLY copper and steel, but includes a bismuth alloy core under the steel penetrator. (I THINK it's bismuth!)The previous version (M855A1 LFS) did have a bismuth alloy slug behind the steel tip. However, that caused problems, so the current loading (M855A1 EPR) has a copper slug.
Below:
[Penetrator] [M855A1 LFS ------------------->] [M855A1 EPR ->
![[Image: BismuthvsCopper.jpg]](http://i129.photobucket.com/albums/p208/tpb2002/BismuthvsCopper.jpg)
Optimized Caliber - BluntForceTrauma - 12-07-2011
If you're OK with exceeding AR15 mag constraints, then all bets are off. Let the military define a set of requirements and design a cartridge to it.
The 6.5 Grendel's genius is the performance it gives from weapons currently sized for the 5.56 cartridge. One could, I suppose, make a pretty good case for the 65G as is, in terms of performance relative to size and recoil, even with a blank slate. And it's a case I'd be tempted to make if I had a fully developed 6.5 Grendel M855A1 analog.
John
Optimized Caliber - stanc - 12-07-2011
HANKA Wrote:The 6.5 Grendel's genius is the performance it gives from weapons currently sized for the 5.56 cartridge. One could, I suppose, make a pretty good case for the 65G as is, in terms of performance relative to size and recoil, even with a blank slate. And it's a case I'd be tempted to make if I had a fully developed 6.5 Grendel M855A1 analog.Unfortunately, such a critter doesn't exist, and in any event, you most likely don't have any M855A1, either.
But, since performance should be relative as long as the same type bullets are used in each caliber, you ought to be able to make your case (if the premise is valid) via comparative testing with lead-core FMJ bullets in 5.56, 6.5 and 7.62 ammo. There's no need to wait for a 6.5 M855A1 analog.
Optimized Caliber - LRRPF52 - 12-07-2011
With the 6.8, you would want to neck it down to 6.5mm, but a 6.5 SPC or 6.8 SPC with longer projectiles for an LMG would make a COAL close to 7.62 NATO. What I like about the Grendel case is that I can still have a relatively short COAL compared to 7.62, and that means more optimum space utilization on the soldier's load. An ammo bag closer to what is used on the SAW would be wonderful, whereas the ammo cans used on the PKM are way too bulky, as would be a 7.62 ammo bag that attaches to the weapon...especially for the curve ball I have for ammo placement on one of the LMG designs I have.
The .277 projectiles require way more velocity to get them to do what a moderate velocity 6.5 will do...I learned that with the 140gr 6.5 Berger VLD for my .260 Rem versus the .277 140gr Berger VLD for my .270 Winchester: The .270 requires 250fps more muzzle velocity to match the .260 Rem at 1000yds, and the .260 still has it beat for wind deflection.
These factors are what make the Grendel case more appealing to me for an LMG. The one possible advantage I see with the 6.8 case is the shoulder angle might be more conducive to feeding, but the inverted feed ramp of a belt fed would be tapered to articulate with whatever cartridge it was chambered in.
Optimized Caliber - stanc - 12-07-2011
LRRPF52 Wrote:With the 6.8, you would want to neck it down to 6.5mm, but a 6.5 SPC or 6.8 SPC with longer projectiles for an LMG would make a COAL close to 7.62 NATO. What I like about the Grendel case is that I can still have a relatively short COAL compared to 7.62, and that means more optimum space utilization on the soldier's load.The difference in cartridge OAL would be only 0.16" for 6.5 SPC, and ~0.20" for 6.8 SPC. It's hard to imagine that such a tiny amount would be noticeable.
Even if it is, the other side of the coin is the increased bulk of the 6.5 Grendel case makes for a longer belt, or for fewer number of rounds in belts of the same length.
200 - 5.56 NATO
160 - 6.8/6.5 SPC
150 - 6.5 Grendel
Quote:The .277 projectiles require way more velocity to get them to do what a moderate velocity 6.5 will do...I learned that with the 140gr 6.5 Berger VLD for my .260 Rem versus the .277 140gr Berger VLD for my .270 Winchester: The .270 requires 250fps more muzzle velocity to match the .260 Rem at 1000yds, and the .260 still has it beat for wind deflection.That's the same thing Bill said, except in different words. Again, nothing says 6.8 SPC must use the same weight bullet as 6.5 Grendel. The 6.8 can use heavier bullets with BC and SD comparable to those for 6.5, thereby achieving similar trajectory, wind drift, and retained energy.
Quote:These factors are what make the Grendel case more appealing to me for an LMG. The one possible advantage I see with the 6.8 case is the shoulder angle might be more conducive to feeding, but the inverted feed ramp of a belt fed would be tapered to articulate with whatever cartridge it was chambered in.I don't view 6.5 Grendel's 30-degree shoulder as significant. After all, the 7.5 Swiss has a 28-degree shoulder, and it was used in belt-fed GPMGs for many years.
Far more critical is the issue everyone else wants to ignore: There is no empirical evidence to support the idea that viable disintegrating links can actually be developed for 6.5 Grendel. Those advocating a 6.5 Grendel LMG are assuming that proper links can be done. They may be wrong.
Optimized Caliber - Variable - 12-07-2011
stanc Wrote:Do you seriously think that a 4mm longer extraction poses anywhere near the difficulties as design and development of a new link???Again for the umpteenth time... LOL You have a problem with seeing a Grendel link. OK, I just accept that as your own personal quirk. I've shot plenty of belt feds, I instructed on belt feds, I own a belt fed, I've shoveled tons of links, and fixed belt feds when they broke. I take a Grendel round and look at a disintegrating 5.56 link... I see zero issues with modding it to work with the Grendel. It's only making different stamps for the manufacturing process. A non-issue to me really, but you disagree. I agree to disagree with you until the cows come home. If anything, the only thing I can see which would actualy boost your argument (IMO) would be if you shifted your attack to the difficulty of getting someone to actually MAKE Grendel links. There you'd have something to chew on IMO. LOL!!!:p
We know that 6.5 Grendel does full-auto fine in magazine-fed rifles. We do not know how it does in belt-fed machine guns.
Optimized Caliber - stanc - 12-07-2011
Variable Wrote:Again for the umpteenth time... LOLOh, come on. I'm sure it's been more than umpteen times.
Quote:You have a problem with seeing a Grendel link. I take a Grendel round and look at a disintegrating 5.56 link... I see zero issues with modding it to work with the Grendel. It's only making different stamps for the manufacturing process. A non-issue to me really, but you disagree.That's because to modify the design for the Grendel case would require reducing width of the link loops considerably. They are already pretty darn narrow along most of the loop, and even more so at the junctions between loops. Reduce the junctions any further and the link will become extremely thin and weak at those points. For that reason, I can't help being skeptical.
Optimized Caliber - JASmith - 12-07-2011
Variable Wrote:Again for the umpteenth time... LOL You have a problem with seeing a Grendel link. OK, I just accept that as your own personal quirk...I agree to disagree with you until the cows come home. If anything, the only thing I can see which would actualy boost your argument (IMO) would be if you shifted your attack to the difficulty of getting someone to actually MAKE Grendel links. There you'd have something to chew on IMO. LOL!!!:pDitto!
Optimized Caliber - BluntForceTrauma - 12-07-2011
stanc Wrote:Far more critical is the issue everyone else wants to ignore: There is no empirical evidence to support the idea that viable disintegrating links can actually be developed for 6.5 Grendel.
Stan, Stan, Stan. . . . Speaking for myself, I deliberately ignore this line of discussion because, to me, it's patently ridiculous and completely unworthy of comment. I have no idea why, in this day of space shuttles, high-definition TV, cell phones, and computers, that stamping a piece of sheet steel in a slightly different shape seems so daunting.
It's utterly . . . it, wow . . . it leaves me speechless.
John
Optimized Caliber - Variable - 12-07-2011
stanc Wrote:Oh, come on. I'm sure it's been more than umpteen times.Sure you reduce the width, and then you stamp them out of very slightly thicker sheet material. It's all to get the right tension while having enough strength. There really isn't anything unique about it. If anything, the lack of case taper makes it even simpler in a push through design.
That's because to modify the design for the Grendel case would require reducing width of the link loops considerably. They are already pretty darn narrow along most of the loop, and even more so at the junctions between loops. Reduce the junctions any further and the link will become extremely thin and weak at those points. For that reason, I can't help being skeptical.
Optimized Caliber - stanc - 12-07-2011
Chris, you make it sound so simple. "Just reduce the width, and stamp them out of thicker sheet material." Well, the M27 link loops are so narrow that it makes me wonder if they actually can be reduced enough for proper operation with a cartridge that is substantially fatter and heavier. Width of the loops has to be cut back quite a bit for the Grendel case shoulder to extend enough ahead of the link so as to contact the cartridge stop.
![[Image: M27_links.gif]](http://www.inetres.com/gp/military/infantry/rifle/5.56mm/M27_links.gif)
![[Image: Ammunition_Belt_5.56_mm.jpg?format=jpg]](http://wapedia.mobi/thumb/d920507/en/fixed/470/313/Ammunition_Belt_5.56_mm.jpg?format=jpg)
John, stamping a piece of sheet steel in a slightly different shape is hardly a daunting task. The problem is reducing the dimensions to the extent necessary, while retaining the requisite strength and flexibility.
You guys are going on faith, a belief that it can be done.
I prefer to have proof, or at least convincing evidence.
Optimized Caliber - stanc - 12-07-2011
![[Image: 2-28.jpg]](http://i381.photobucket.com/albums/oo255/FEDE_EL_SOMALI/2-28.jpg)