Testing, testing...

[warped]

That was the sound of money being flushed down the toilet.

In the end I think that was exactly the exercise, not doing anything but spending money was the important part.

[Tony Williams]

Okay, Gary Roberts posted the following on arfcom:

"As presented at a joint USG meeting this past March, the bullet diameters tested were described as: .224", .243", .257", .277", .308""

Converted from inch to metric measurement, those figures correspond to projectile diameters (not calibers!) of 5.7, 6.2, 6.5, 7.0 and 7.8mm, the sizes Tony said were tested.

Which means that it was .264" which was omitted from the test. The Army did about the same thing once before. When developing variations using the 7.62x51 case to create the "homologous" rounds, there was a .25-caliber version and a .27-caliber version, but no .26-caliber.

Yes, that is correct - my initial assumption that the usual military convention of quoting bore diameters applied was wrong. Neither the classic 6.5mm (.264 bullet diam) nor the 7mm (.284 bullet) were tested.

[warped]

If ever a new cartridge gets accepted for a NEW weapon, not just one for the existing platforms, I would bet even money it will look an awful lot like the 6.5x47Lapua.

If they only wanted to fit the AR/M series magazines it would be the Grendel

[JASmith]

If ever a new cartridge gets accepted for a NEW weapon, not just one for the existing platforms, I would bet even money it will look an awful lot like the 6.5x47Lapua...

Do you mean the .260 Remington, the 6.5 Creedmoor, or an even shorter version of the .260 Rem?

[warped]

http://www.midwayusa.com/viewproduct/?pr...g-_-462149



And I really like the .260 rem

But if it were a new weapon design the 6.5x47 Lapua uses the case capacity more efficiently.

Think of it as the Grendel on performance enhancing drugs

108grain Scenar # Muzzle Velocity: 2952 fps
# Muzzle Energy: 2090 ft. lbs.

139 Scenar # Muzzle Velocity: 2690 fps
# Muzzle Energy: 2231 ft. lbs.

These appear to be mild loadings

Notice there is not a case intrusion problem on these

IIRC it works from existing 7.62NATO mags, therefore it would work from a .260 Mag

I have a friend shooting one, he says the cases are abnormally tough and can take far higher pressures than what the factory ammo is loaded to.

He shoots it in his AI.

[JASmith]

That is a very good-looking cartridge!

From the functional point of view, you are very close to being on the mark.

On the political side: Referring to the recent discussions of the ARDEC test series and the inferred mental state of the folks who designed the test, it would look a little different and might be a caliber above or below.

[warped]

I would wager as well that this cartridges genesis came from looking at the Grendel


When I was looking at the loaded cartridge it appeared to be a larger cased Grendel

[JASmith]

"Great minds think alike!"

[Tony Williams]

The problem with these 6.5mm rounds which are basically necked-down 7.62x51 is that they save very little space or weight over 7.62mm, and generate too much recoil for good controllability in auto rifle fire. So IMO they don't really meet the criteria to replace either 5.56mm or 7.62mm.

[JASmith]

Tony,

You're spoiling our fun!

Your criteria are part of why Warped is probably right about a military cartridge fitting the AR-15 magazine well will likely be the Grendel. I would go as far as modifying the statement to one based on the Grendel...

A necked-down 6.8 SPC might have some adherents, but the brass is too long for decent 6.5 nose shapes. Maybe 6mm but I'm not so sure about the space there either. Going all the way down to 5.56 is about the best that case might do for getting decent nose shapes and velocity.

Cheers!
Joe

[stanc]

Tony,

Your criteria are part of why Warped is probably right about a military cartridge fitting the AR-15 magazine well will likely be the Grendel. I would go as far as modifying the statement to one based on the Grendel...

A necked-down 6.8 SPC might have some adherents...

Me! Me!

...but the brass is too long for decent 6.5 nose shapes.

As is, yes. However, if the neck is trimmed by ~1 mm, the resulting 6.5x42 would permit use of bullets with an ogive like that of the Norma 120gr FMJ.

Maybe 6mm but I'm not so sure about the space there either.

Oh, yeah. A 6x42 on the SPC case? Me likem mucho grande!

[bwaites]

Me! Me!

As is, yes. However, if the neck is trimmed by ~1 mm, the resulting 6.5x42 would permit use of bullets with an ogive like that of the Norma 120gr FMJ.

Oh, yeah. A 6x42 on the SPC case? Me likem mucho grande!

Naw, useless. Couldn't get the velocities you want from a 120 bullet. The 6.8 barely manages with short bullets. No way with anything with a decent BC.

A 6MM 105 or similar might work, but 6mm is barely better than 5.56, and I can't imagine the .mils considering such a minimal change.

Actually, scratch that, it wouldn't work. You would lose too much powder room even with the 6mm light bullets, at least the ones with decent BC's. It's been tried, and its why Robert Whitley is using the Grendel case in his 6mm AR and 6mm AR Turbo.

[LRRPF52]

http://www.midwayusa.com/viewproduct/?pr...g-_-462149



And I really like the .260 rem

But if it were a new weapon design the 6.5x47 Lapua uses the case capacity more efficiently.

Think of it as the Grendel on performance enhancing drugs

108grain Scenar # Muzzle Velocity: 2952 fps
# Muzzle Energy: 2090 ft. lbs.

139 Scenar # Muzzle Velocity: 2690 fps
# Muzzle Energy: 2231 ft. lbs.

These appear to be mild loadings

Notice there is not a case intrusion problem on these

IIRC it works from existing 7.62NATO mags, therefore it would work from a .260 Mag

I have a friend shooting one, he says the cases are abnormally tough and can take far higher pressures than what the factory ammo is loaded to.

He shoots it in his AI.

A few guys I know have 6.5x47 Lapua's in AI's and other custom actions. My partner for FinnSniper last year used one, and made continual 1st-round hits at 900m on E-type silhouettes pushing 140gr Berger VLD's at well over 2900 fps. It's an awesome sniper round, and would be great for the M110.

I think barrel life would be an issue in an assault rifle and definitely an issue in an LMG. The small rifle primer with a .473" diameter case head could prove problematic in extreme cold weather as well. If the metallurgy is there with some of the treatments gaining popularity, it would be interesting to see barrel life increase with it, but we're talking about pressures way in excess of the 7.62 NATO.

It is a great caliber, but I think a bit much in case size for an assault rifle. An assault rifle still needs to be able to fit the basic profile of a shoulder-fired weapon that has the firepower of an SMG. That case diameter will not allow feasible 30rd mags, and remember that trends in mag capacity are increasing well above 30rds, not decreasing. Examples are the new Russian coffin mag for the AK100 series and An-94, as well as the Surefire and Magpul high-capacity mags.

The Grendel and 7.62 short are where I would draw the line on case diameter for a practical assault rifle. The MP44 presented problems with causing a larger profile for the shooter while in the prone, as does the AKM and variants, while the AR15 does not, even with a 30rd mag, which also serves as a great monopod.

[stanc]

Naw, useless. Couldn't get the velocities you want from a 120 bullet. The 6.8 barely manages with short bullets. No way with anything with a decent BC.

I didn't say to use the 120gr Norma, just that a bullet with its ogive shape would (barely) fit in a 42mm case. The bullet would have to be lighter than 120gr, and BC would certainly be less than the more streamlined bullets suited to 6.5 Grendel, but to replace 5.56 only it might be worth testing.

A 6MM 105 or similar might work, but 6mm is barely better than 5.56, and I can't imagine the .mils considering such a minimal change.

Probably they wouldn't. Then again, 6mm was one of the bullets in the recent ARDEC tests.

Actually, scratch that, it wouldn't work. You would lose too much powder room even with the 6mm light bullets, at least the ones with decent BC's.

I don't see why it wouldn't work. The 90gr E-Tip and 95gr SMK have decent BCs, and look like they'd cut powder capacity less than a 123gr Scenar in the 6.5 Grendel case.

Regardless, I still like the idea. It'd be sort of a magnum version of the 1970s 6mm SAW round. Imagine if the M14 and M60 had been chambered for 6x42 (or better yet, 6x43, without the 2.25" length restriction), there would never have been a need for the M16 and M249!

http://www.youtube.com/watch?v=N06ySsT2EKU
http://www.youtube.com/watch?v=48pFvx4hlbo

[LRRPF52]

Regardless, I still like the idea. It'd be sort of a magnum version of the 1970s 6mm SAW round. Imagine if the M14 and M60 had been chambered for 6x42 (or better yet, 6x43, without the 2.25" length restriction), there would never have been a need for the M16 and M249!

Other than the fact that the M14 and M60 have some of the worst reliability issues and most maintenance-intensive schedules of all the small arms I have ever used. Both those systems are a PITA to operate reliably, maintain with armorer support, and keep spare parts on-hand for. In short, they suck big time.

Now the SAW cartridge I do like, at least the concept of it, but it does push the weapon size envelope for an assault rifle. The Chinese have basically adopted that cartridge with the 5.8x42 in their QBZ95, LMG, and DMR. I've heard they're not happy with its downrange performance at distance though, but who really knows...

[stanc]

Now the SAW cartridge I do like, at least the concept of it, but it does push the weapon size envelope for an assault rifle.

Yes, a little. But, nowhere near as much as Murray's 7mm UIAC. Although from a technical standpoint the 7x46 offers a slight advantage over 7.62x51, I think he's going down the wrong track.

The Chinese have basically adopted that cartridge with the 5.8x42 in their QBZ95, LMG, and DMR. I've heard they're not happy with its downrange performance at distance though, but who really knows...

They made the mistake of not going quite big enough. 6mm is the minimum necessary for long range, 6.35mm might've been the best, considering the trade-offs for minimum cartridge size and weight, and acceptable ballistics.

[JASmith]

...They made the mistake of not going quite big enough. 6mm is the minimum necessary for long range, 6.35mm might've been the best, considering the trade-offs for minimum cartridge size and weight, and acceptable ballistics.

You're probably closer to the mark than most.

At the risk of re-plowing some ground, my thinking is that the 7.62X51 NATO will almost certainly continue to be the "light caliber" for vehicle-mounted weapons. I think it may be possible to go with a unified caliber for dismounted units, but sense that the emerging plastic-cased ammunition Tony has observed will keep the 7.62 in the heavier dismounted units as well.

This opens the door a crack for the intermediate caliber by decreasing the high-end requirement. It would truly be interesting to see what one could get from a family of Grendel-based cartridges in 5.56, 6, 6.35, and 6.5 mm. We should also examine a similar family based on the 6.8 SPC.

LR1955 and others have argued that probability of hit out to 400-600 meters is of critical importance and that any new system needs to shine in at least one area.

Given the fundamental need to get a hit, it seems odd that we've spent a lot of time discussing on-target effects, ammunition weight, and recoil but almost none on trajectory and wind-drift. These areas are ones where higher-velocity and moderately well-shaped bullets might result in a significant improvement.

[stanc]

...my thinking is that the 7.62X51 NATO will almost certainly continue to be the "light caliber" for vehicle-mounted weapons.

Concur. The only complaint about 7.62x51 that I know of is the weight, and for vehicle-mounted weapons that is not a significant issue.

I think it may be possible to go with a unified caliber for dismounted units...

Sure, it's possible. In WWII and the Korean War, the infantry rifle, automatic rifle, and machine gun used the same caliber. The drawback to a unified caliber is that it results in ammunition and weapon that are heavier and bigger than needed by the rifleman.

It would truly be interesting to see what one could get from a family of Grendel-based cartridges in 5.56, 6, 6.35, and 6.5 mm. We should also examine a similar family based on the 6.8 SPC.

If, as I think likely, 7.62x51 remains in use for the MMG/GPMG, then the need is only for a cartridge to replace 5.56x45. IMO, that argues for a cartridge of minimum weight and bulk. The diameter of the Grendel case is less desirable than that of the SPC case, which is less desirable than than that of the 6mm SAW case, which is less desirable than that of the 5.45x39 case. Of course, cartridge size and weight must be balanced against the need for sufficiently improved terminal and exterior ballistics.

LR1955 and others have argued that probability of hit out to 400-600 meters is of critical importance and that any new system needs to shine in at least one area.

Given the fundamental need to get a hit, it seems odd that we've spent a lot of time discussing on-target effects, ammunition weight, and recoil but almost none on trajectory and wind-drift. These areas are ones where higher-velocity and moderately well-shaped bullets might result in a significant improvement.

They might. The few ballistics tables I still have from 2-4 years ago show a clear advantage in trajectory and drift for 6.5 Grendel over 6.8 SPC and 5.56 NATO. However, the 6.8 velocities I used were for SAAMI loads, not the newer Spec II ammo.

The introduction of Wilson Combat's 110gr @ 2700 fps (6.8 SPC) load may put that cartridge in a different light. SSA's 85gr TSX @ 3000 fps might also be interesting. I have a feeling that 6.5 Grendel trajectory and wind drift may not be significantly different than these 6.8 SPC loads out to 400-600 meters.

[Tony Williams]

I agree that even if we get a new long-range intermediate round, heavy 7.62mm MGs will remain in service in a support role for a while, and in vehicle mountings for much longer.

However, I don't agree that the task is to replace the 5.56mm rather than the 7.62mm. My perception of the UK view is that the weight of 7.62mm belted MG ammo is a bigger issue for dismounted troops than any lack of performance of the 5.56mm. So a round which can match the hit probability and target effectiveness of the 7.62mm at 1,000m while saving a lot of weight will look very attractive. By definition, this will be a smaller-calibre round with a lighter recoil, so could also do a good job in replacing 5.56mm, thereby bringing other benefits with it.

IMO, 6.5mm Grendel is currently the closest to the ideal performance of any current cartridge. When using 123 grain Lapua it is significantly better than 7.62mm M80 in both wind drift and trajectory at 1,000m - a service ball bullet wouldn't be as good, but should be in the same ballpark.

[stanc]

I don't agree that the task is to replace the 5.56mm rather than the 7.62mm. My perception of the UK view is that the weight of 7.62mm belted MG ammo is a bigger issue for dismounted troops than any lack of performance of the 5.56mm.

Hmm. That's just the reverse of what I got from your "bite the bullet" article and presentations.

IMO, 6.5mm Grendel is currently the closest to the ideal performance of any current cartridge.

That's what I used to think, too. However, with the switch from SAAMI to the Spec II chamber, 6.8 SPC is looking much better than it did. Muzzle velocity with bullets of the same weight and type, 6.8 SPC outdoes 6.5 Grendel by 200-300 fps. Since a new carbine/rifle/LMG need not have the M16 mag well dimensions, neither does cartridge OAL have to be 2.25 inches of the 5.56 round. Let cartridge length be 2.40 inches, and 6.8 SPC can use very streamlined bullets. Combined with the higher velocity, and now 6.8 SPC might not only equal 6.5 Grendel at long range, it might even beat it.

When using 123 grain Lapua it is significantly better than 7.62mm M80 in both wind drift and trajectory at 1,000m - a service ball bullet wouldn't be as good, but should be in the same ballpark.

I'm skeptical of that. The only real data we have to go on is for the 120gr Norma FMJ, which has a 0.428 BC. That's far below the 0.54 BC of the 123gr Scenar. I just don't see the BC of a 120gr FMJ getting above 0.44-0.45, and 110gr is said to be the "sweet spot" for this cartridge -- what's the likely BC for an FMJ of that weight? With a BC in the 0.42-0.45 range, to match 7.62 M80 trajectory and drift, it'd be necessary to have MV in the neighborhood of 2700 fps, and that just ain't gonna happen.