Grendel ballistics overstated?

[JASmith]

Thanks!

[JASmith]

...I'd love to see a subsonic 6.5mm Grendel
factory load. Wonder what the heaviest/longest bullet the 1-7.75 inch twist would stabilize?
Perhaps we need to get a custom 205 grain .264 mold and try some cast bullets
at subsonic velocities........

You have probably looked over the thread on subsonic loads, so you know a 160 gr. bullet can be made to work. While I think a 205 gr bullet, even cast, might be a bit long for magazine-length seating in the Grendel, the heavier bullet will improve reliability of operation while staying subsonic.

Have you looked at Corbin's subsonic bullet swages http://www.corbins.com/subsonic.htm -- This may be an easier and more direct path and we might also be able to vary the length and weight a bit without purchasing a second or third mold.

[LRRPF52]

We should I suppose at this junction start a new thread to examine the 130 and 140 Berger VLD projectiles in hand loads, compare recipes and examine accuracy from differing barrels and ranges. This would avoid confusing the OP request and subsequent answers.

Bill,

I'm planning on messing with the 130gr VLD's when I get back, but using a 10rd PRI magazine, since I can load to 2.300" COAL, and the VLD's don't engage the lands unless you really push them out. The 130gr VLD at 2500fps is no joke for distance, and I bet you could work up a mixed powder that would reach that speed.

[BluntForceTrauma]

NOT a 24 inch barrel........NOT misinformation but what factory ammo clocked from my 20 inch gun
on a hot Kansas day on my range.

Ah! Very good. I stand corrected. I had no idea the guy who quoted the figures mentioned here originally had quoted YOUR data.

John

[rasp65]

Thank you for those results. 6.5 Grendel is totally lousy in SBR applications I note.

Instrumented velocity is typically taken at 10 feet, I doubt that 12 ft would have much influence. Temp, humidity and air pressure are useful records to keep.

Those 100 Hornady projectiles look good I need to look at those. My existence is cursed by the proliferation of projectiles in 6.5 caliber. Now new powders and loading data could become a full time career. I need a minion!

I await your call to service for the good of the Grendel nation.

[IN33DAMM0]

[stanc]

What is clearly illustrated by both David Fortier and also LRRPF52 is that the cartridge has the capability to meet the requirements outlined by the OP within the current space envelope and loading.

My consideration would be to push the requirements to a shorter more compact weapon, hence a shorter barrel. I would be interested to see how a balance could be struck between an 18" barrel and a stronger mechanism running slightly elevated pressures.

I (and others here) would be very interested in seeing that, too. Do you have any plans in that vein?

I concur with the need for a short barrel, because that's the clear choice of armies which do not use bullpup rifles. However, the range of barrel lengths currently used is 14-16 inches, so while I myself like 18 inches for this, I'm skeptical it would have much appeal to the military.

[Tony Williams]

I think that the ballistics needed for long-range (1000m) fire (c. 123 grains / 2,620 fps) only need to be achieved in DMRs and LMGs, for which a 20 inch barrel is appropriate. If an army doesn't want a bullpup then a shorter-barrelled carbine would have a shorter effective range - but still vastly superior in both range and effectiveness to the 5.56mm.

Having said that, it would obviously be desirable for the loading to lose as little velocity as practicable from a shorter barrel.

The main ballistic problem for the Grendel as I see it will be in achieving the long-range ballistics when using military (presumably cannelured), lead-free bullets rather than lead-cored target types.

[stanc]

I think that the ballistics needed for long-range (1000m) fire (c. 123 grains / 2,620 fps) only need to be achieved in DMRs and LMGs, for which a 20 inch barrel is appropriate.

The trouble is, while some such as yourself consider 20 inches to be an "appropriate" length for DMRs and LMGs, it appears that these weapons are joining the trend to shorter barrels, too.

The UK L129A1 has a 16-inch barrel, and the proposed carbine version of the US M110 will likely copy that. Then there is the Mk17 SCAR, which also has a 16-inch tube as standard.

On the M249 LMG, the 14-inch barrel is in widespread use, and the Mk46 has a 16-inch barrel.

Considering these facts, IMO it's a substantial mistake to plan for 20-inch ballistics.

Having said that, it would obviously be desirable for the loading to lose as little velocity as practicable from a shorter barrel.

I think it would be much wiser to optimize velocity for the shorter barrel lengths likely to be used.

The main ballistic problem for the Grendel as I see it will be in achieving the long-range ballistics when using military (presumably cannelured), lead-free bullets rather than lead-cored target types.

On that we agree.

[Tony Williams]

The trouble is, while some such as yourself consider 20 inches to be an "appropriate" length for DMRs and LMGs, it appears that these weapons are joining the trend to shorter barrels, too.

The UK L129A1 has a 16-inch barrel, and the proposed carbine version of the US M110 will likely copy that. Then there is the Mk17 SCAR, which also has a 16-inch tube as standard.

The MK17 is not a DMR, it's a heavy assault rifle. The DMR version of the SCAR is the MK20, recently adopted by SOCOM - with a 20 inch barrel. The M110 carbine will probably be for special purposes where compactness is at a premium and some loss of performance is acceptable. I have not seen any suggestion that it will replace the M110. The decision on the L129A1's barrel length is regarded by many as rather bizarre given the official role of the gun. Having said that, it seems to be commonly being used as a heavy assault rifle, largely to make up for the weakness of the 5.56mm guns.

On the M249 LMG, the 14-inch barrel is in widespread use, and the Mk46 has a 16-inch barrel.

These are 5.56mm weapons intended for close combat. It is interesting that the USMC has rejected that concept in favour of the M27 IAR, also optimised for close range. The long-range 7.62mm MK48 LMG has a 20 inch barrel (well, 19.75 inches if you insist).

Considering these facts, IMO it's a substantial mistake to plan for 20-inch ballistics.

The logical approach to small arms designed around an intermediate calibre general-purpose cartridge, given the stated need by PEO soldier for a rifle to engage the enemy at "8 to 800 metres", is to use a bullpup rifle with a 20 inch barrel. Thereby combining in one gun the compactness needed for urban fighting with the long barrel needed to optimise the ballistics for long range. Then back that up with an LMG also with a 20 inch barrel.

Those armies who won't use bullpups will instead need to use a mix of rifles and carbines, depending on the circumstances, but they'll lose some tactical flexibility as a result.

[stanc]

The MK17 is not a DMR, it's a heavy assault rifle. The DMR version of the SCAR is the MK20, recently adopted by SOCOM - with a 20 inch barrel.

The Mk20 is not a DMR, it's a sniper support rifle. Different purpose than a DMR.

SEAL teams have been using the Mk17 as a DMR, with 16-inch and 13-inch (!) barrels.

The M110 carbine will probably be for special purposes where compactness is at a premium and some loss of performance is acceptable. I have not seen any suggestion that it will replace the M110.

I never said it would replace the M110. What I've read indicates a desire for a compact DMR, like the L129A1.

The decision on the L129A1's barrel length is regarded by many as rather bizarre given the official role of the gun.

But quite logical for a general purpose rifle.

The logical approach to small arms designed around an intermediate calibre general-purpose cartridge, given the stated need by PEO soldier for a rifle to engage the enemy at "8 to 800 metres", is to use a bullpup rifle with a 20 inch barrel. Thereby combining in one gun the compactness needed for urban fighting with the long barrel needed to optimise the ballistics for long range.

The major flaw in that "logical approach" is the unwillingness of most Western armies to adopt a bullpup rifle. If you try to sell them on a GPC that requires a 20-inch barrel to achieve the necessary performance, but they won't use a barrel longer than 16 inches, it seems to me you're setting yourself up for a fail.

Develop the GPC for 14-16 inches, then any army that opts for a bullpup will get a plus in performance. But, designing for the bullpup means all those armies that stick with conventional carbines won't have the performance needed for the GPC concept to work. Why would they want to switch?

[JASmith]

I don't yet know what an ideal rifle for dismounted infantry would look like beyond the generalities common to all of these discussions.

What I do know, however, is that we need remember that the training and tactics special forces like the SEALS enjoy are well beyond that of infantry recruited for one enlistment period and gone after that. Further, it is cleat that the special forces are allowed to try new things tailored to their immediate needs. Put these observations together, and we can easily conclude that their weapons may not prove to be useful either in the special forces in other environments or in general purpose line units.

Some of the weapons they use may morph into items suitable for line units, most will not.

[P-P]

not 2620, but it's only 18 fps off - that is just statistical error.

[LRRPF52]

There is no need for a 20" barrel and a cartridge like the Grendel, if you're trying to achieve substantial velocity. 16" is plenty, and the bullpup code has yet to be cracked anyway. There is not one current bullpup design that gets anywhere near addressing all the challenges presented by a bullpup action for a magazine-fed rifle.

That is also a good point about SOCOM and SOF units with regard to weapons selection. The SEALs and other units have actually used COTS to purchase certain weapons outside of the standard military procurment system. The Stoner 63 system, Sig P226, Colt Model 727 Carbine (often referred to as an M16A2 carbine), and SCARs are examples of that.

A bolt and locking mechanism designed around the Grendel, combined with a specific mixed powder for the load would yield significant increases in velocity.

[SHORT-N-SASSY]

The small case of the Grendel demands careful consideration when examining the internal ballistics. High case fill with many powders will amplify the effects of temperature so powders must be matched both for volume and temperature effects. . . .

My consideration would be to push the requirements to a shorter more compact weapon, hence a shorter barrel. I would be interested to see how a balance could be struck between an 18" barrel and a stronger mechanism running slightly elevated pressures.
I would also like to see how the balance of powder, burn rate, barrel and bullet weight may change with the above scenario.

Back to the future:

http://www.youtube.com/watch?v=EpIDj...ature=youtu.be;

http://bullpupforum.com/index.php?to...56846#msg56846 --- srfnken, K&M Arms, "That's a bunch of pressure to be the first [to offer a 6.5mm Grendel-chambered Bullpup]. . . . I have been thinking about what size bolt to use for my 6.5 [Grendel] and I think you will be pleasantly surprised and excited, when I show the prototype and start my production."

With a beefy triangular 3-lug Bolt and matching Barrel Extension, 3 1/2-pound trigger, left- and right-side ejection versions, I think Ken's on track to make it happen. I can't wait!