New Army "Caliber Configuration Study"

[Variable]

I think your numbers are in line with calculations on Tony Williams' MG&A forum. FWIW, consensus there is that a lead-free, military ball projectile would likely weigh no more than 108-112 grains. (The steel-core FMJ bullet of Wolf's steel cased ammo is reportedly 110 grains, which seems to confirm that idea.)

??? Copper plated steel jacket with lead core? Right? Not lead free? Maybe I'm misunderstanding though?

[stanc]

??? Copper plated steel jacket with lead core? Right?

No. I don't remember in which thread, but it was reported that the bullet construction is like that of the 5.45x39 7N6.

[Tony Williams]

Let's see 39mm to 43mm is a 10% increase in capacity.

If you look carefully at the photo you'll see that there is a bigger difference in the case capacity than that, because the neck is shorter. The main body of the case is around 25-30% longer. The increase in propellant wouldn't be as great as that because of bullet intrusion, but it should still be significantly more than 10%.

[woohoo]

Let's see 39mm to 43mm is a 10% increase in capacity. Using LRRPF52's data using 123 AMAX and CFE223 in a 14.5" barrel, http://www.65grendel.com/forum/showt...6-quot-Grendel
31.1gr 2489 fps
31.4gr 2520 fps
31.7gr 2532 fps
32.0gr 2553 fps
32.3gr 2572 fps
32.6gr 2598 fps
32.9gr 2612 fps

Increasing 31.1 gr by 10% is 34.2gr and increasing 32.9gr by 10% is 36.2gr. Interpolating from the known data, 34.2gr would result in 2700fps and 2828fps. Now these calculations are elementary at best, but I think we could expect a MV in that range. If we were to see the military develop a canister powder I think we might see a MV in the 2800fps.

What say y'all am I completely off.

On a side note, I'd like to see how H4350 worked in that case.

NOTE: Interpolating outside the boundaries of known data will skew the results to some degree.

Apx 40gr H2O case capacity. Every 2mm increases the capacity 1.5gr when based on the Carcano case.
Carcano bass is in production, the brass Murray used is not. The powders that work best are the same ones used in the Grendel. 8208, CFE, N540. My 6.5x45 has a capacity of 42gr and will propel a 120 class bullet to apx 2800 from a 20" at near max pressure. The range of this 6.5x43 should be 2700-2750.
A case that long will feed from a Magpul 308 Pmag in any 308 AR10/SCAR/DPMS rifle.

[stanc]

The steel-core FMJ bullet of Wolf's steel cased ammo is reportedly 110 grains...

Oops. Make that 100 grains. http://www.65grendel.com/forum/showt...ll=1#post46898

[Variable]

Oops. Make that 100 grains. http://www.65grendel.com/forum/showt...ll=1#post46898

That's cool. I brain farted too. It's been so long that I had forgot it was supposed to be a 7N6 style projo. I was thinking about the regular wolf stuff.LOL

[Tony Williams]

My 6.5x45 has a capacity of 42gr and will propel a 120 class bullet to apx 2800 from a 20" at near max pressure. The range of this 6.5x43 should be 2700-2750.

That sounds about right and fits well within the parameters for a GPC (general-purpose cartridge for use in portable rifles and MGs).

Assuming your 120 grain is lead-cored, a lead-free bullet (and especially a tracer) would be longer and use up more case capacity, other things being equal, thereby presumably reducing the velocity slightly.

Incidentally, Mitch Shoffner's 6.5x40 (based on the 6.8x43 case) gets good results from the 126.5 grain Barnes LRX, which is solid copper with a plastic tip (not Geneva-friendly, but a useful indicator of performance potential).

A polymer case (which any new military rifle/MG cartridge will have to be designed for) will also have thicker walls, further reducing capacity, although that seems not to reduce performance significantly because of the greater thermal efficiency.

[LRRPF52]

Polymer cases have better thermal efficiency than brass?

I saw a very interesting statement recently from someone who is fairly well-known in the alternate caliber market (.458 SOCOM). Basically, the guys working on propellant technology are light years ahead of what is commonly available. The claim was made that the 5.7x28 case was lengthened and out-performed .223 Remington using these new propellants.

I haven't seen any verifying data, but it isn't outside the realm of probability. I have my own ideas of different propellant geometry for existing metallic cartridge designs, that would stage different burn rate mediums in the case for optimum pressure curve, without spiking pressure, while keeping it higher down bore.

It would be interesting to play with these in the .221 Fireball case with a 6.5mm.

[Tony Williams]

Polymer cases have better thermal efficiency than brass?

Yes - in a brass-cased cartridge a small but significant percentage of the energy developed by the propellant is used to heat up the brass case and, through that, the chamber walls. Polymer is an excellent insulator (it is reportedly possible to stick your finger in the chamber of an MG after a long burst of fire without getting burnt) so this particular element of energy loss does not occur.

I saw a very interesting statement recently from someone who is fairly well-known in the alternate caliber market (.458 SOCOM). Basically, the guys working on propellant technology are light years ahead of what is commonly available. The claim was made that the 5.7x28 case was lengthened and out-performed .223 Remington using these new propellants.

That would be fascinating and a real game-changer, but I'll reserve judgment for now. Similar claims have been made in the past, the most recent a few years ago with a propellant based on rocket fuel. Apparently it sent the chamber pressures through the roof...

Having said that, my own (non-technical, and probably unrealistic) thought on gun propellant is that the form (if not chemistry) of a typical rocket motor might have advantages: that is, a solid fuel block with a central axial channel which ignites first and then burns outwards until it reaches the case walls. If feasible, this would mean that as the propellant burned outwards so the area exposed for burning would progressively increase, generating more gas and keeping the pressure curve much flatter. It would also minimise the heat transfer to the case and chamber because the burn would not reach the case walls until right at the end. The burning rate could be adjusted by the varying the shape of the axial channel (in rocket motors, the cross-section of the channel is often star-shaped to maximise the initial surface area to provide a boost phase). I suspect that a new shape of cartridge case might be needed for this to work well, though.

[Trooper]

6.5x43 GPC prototype, second from left, below.



Article: http://www.thinkdefence.co.uk/2013/1...ange-calibres/

"...the US discovered that various potential enemies have been quietly enhancing their own small arms capabilities and are on the verge of achieving overmatch.

There has been no specific information on what the evolved threat is, but it appears that the Chinese and Russians are about to field improved ranges of weapons and ammunition."

Maybe there really is a 6.5 Grendelski???

What have the Chinese and Russian been migrating towards? I think that the Chinese have a 5.8mm in a bullpup.

[cory]

...Having said that, my own (non-technical, and probably unrealistic) thought on gun propellant is that the form (if not chemistry) of a typical rocket motor might have advantages: that is, a solid fuel block with a central axial channel which ignites first and then burns outwards until it reaches the case walls. If feasible, this would mean that as the propellant burned outwards so the area exposed for burning would progressively increase, generating more gas and keeping the pressure curve much flatter. It would also minimise the heat transfer to the case and chamber because the burn would not reach the case walls until right at the end. The burning rate could be adjusted by the varying the shape of the axial channel (in rocket motors, the cross-section of the channel is often star-shaped to maximise the initial surface area to provide a boost phase). I suspect that a new shape of cartridge case might be needed for this to work well, though.

Solid rocket propellant to launch a tiny projectile, interesting thought. You could be on to something.

[SHORT-N-SASSY]

6.5x43 GPC prototype, second from left, below.



Article: http://www.thinkdefence.co.uk/2013/1...ange-calibres/

"...the US discovered that various potential enemies have been quietly enhancing their own small arms capabilities and are on the verge of achieving overmatch.

There has been no specific information on what the evolved threat is, but it appears that the Chinese and Russians are about to field improved ranges of weapons and ammunition."

Maybe there really is a 6.5 Grendelski???

What are the respective exterior case dimensions and case capacities of the 6.5x43mm GPC prototype and 6.5x45mm wildcat cartridges, along with their comparitive muzzle velocities, from a 16" barrel?

[stanc]

What have the Chinese and Russian been migrating towards? I think that the Chinese have a 5.8mm in a bullpup.

Yes, but the Chinese 5.8x42mm cartridge is nearly two decades old, so it hardly qualifies as a new threat.

[stanc]

What are the respective exterior case dimensions and case capacities of the 6.5x43mm GPC prototype and 6.5x45mm wildcat cartridges, along with their comparitive muzzle velocities, from a 16" barrel?

AFAIK, case dimensions and capacity for the 6.5x43 GPC are not yet available. I have not heard of a 6.5x45, so can't help you there, either.

[Trooper]

Will the 6.5x43 Grendel GPC work in the magazine well of the M4 platform? And how does it compare to both the 6.5x39 and 6.5x45?