The Ultimate Combat Round

[Glock Glockler]

GunTech,

If we maintained the same ratios you have with your round but used a 6mm bullet instead what kind of velocities would we be looking at?

Thanks

 

[Grendelizer]

In the mean time, I am going to order a barrel and pursue the 6.5x45 with 144 FMJBT since that's what I have to work with, but I'll look at other bullets too and report back.

Tod, if you're looking for 6.5mm FMJs, I believe Norma has a 120, although it's BC is fatter than it should be, sort of like a 120 SMK.

John

 

[Nolo]

Nolo, I'm inclined to a lighter bullets as well, but there isn't a Hague compliant one in the weight range. Besides, having multiple loads defeats the point of a single universal cartridge. If you are going to have multiple loading, you might as well have multiple cartrdges

I agree with you that is leaves a bad taste in one's mouth, but after studying the problem, I really don't think we can get around it. Not if we want an actual military to adopt the cartridge. As it remains, we need at least three (tracer, match, ball), and MGs would be really happy with an AP round. You could make the AP and tracer round one and the same, but you'd be compromising the abilities of both. There would be some benefit to having them all in the same platform. Commonality of parts for weapons, commonality of machinery for producing ammunition, etc.

If we maintained the same ratios you have with your round but used a 6mm bullet instead what kind of velocities would we be looking at?

Are you talking about necking or scaling the 6.5mm GT? It results in a much different cartridge depending on which.

I'm just trying to spur and channel to greater heights the genius that is Nolo.

I really hope you're kidding...

 

[Glock Glockler]

Nolo, scaling the case is what I mean, so the same relationship would exist between that and the bullet.

 

[GunTech]

There's two ways to approach a 6mm form the 6.5x45 - just neck it down, or neck it down and shorten the case. If you can live with a 90gn bullet, you can shorten the case to 43mm and get an overall length of 2.260 - max length for the 223 and compatible with the M16.

I can only run the number through quickload, and I'll stick with the 52,000 PSI limit. Barrel is 20 inches.

First, 6x45

For the 105gn Lapua scenar, velocity is around 2700 fps
For the 90gn Sierra FMJBT, velocity of 2900 fps

Next 6.5x43, OAL 2.260 (M16 compatible)

for 90gn Sierra FMJBT, velocity 2850

Finally, for comparison, 243 win

for 90gn Sierra FMJBT, velocity 2990

The 90 SGK FMJBT has a BC of about 0.380, similar to the M80 ball.

 

[GunTech]

Glock Glockler

You might be interested in the 6mm/6.8 SPC, if you want to scale the whole cartridge.

It's interesting that theoretically, the 6x43 in a AR compatible COAL is within 140 fps of the 243 with the 90gn FMJBT. But the shorter OAL means you are limited to 90gn or under.

 

[GunTech]

Nolo

I am thinking in terms of interchangeable cartridges, which is exactly the selling point. You could have AP, tracer, ball and match, as long as all will function in all weapon systems.

 

[SDDL-UP]

GunTech,

I like what you're doing, but think you're overplaying the importance of using "Hague compliant" bullets. If something new was adopted they would be making compliant bullets by the hundreds of millions, to tool up and make something new would not be a big deal.

I also think you should stick with 6.5 or 7mm, anything smaller is giving up too much to the 7.62x51 as far as bullet diameter IMO. Quite a lot of development went into the 6.8SPC and I really don't think anything smaller than 6.5mm would be seriously considered as the "one cartridge" solution.

 

[mr.trooper]

1,800 ft-lbs from an 16" barrel?

You DO know that neither the 5.56 NATO or 7.62x39 meet that?

556= 1,200 from 20"
7.62 = 1,400 from 20"

 

[GunTech]

Hague compliant or not, the 144gn Lapua FMJBT outclasses just about everything else out there. BC of 0.636 ?!

I happened to stumble onto this accidentally because I was only looking at FMJ bullets with military applications in mind. But the more I look at it, the better it look for universal applications. I've done a bit of shooting with 6.5 142gn SMK from my 6.5 Grendel, and recoil is certainly manageable. The 6.5x45 would be more, but about half that of the M14.

Grendelizer, thanks for the tip on the Norma 120s. I am going to order some. Looks like a BC of 0.428

 

[GunTech]

Norma 120 FMJ - BC 0.428 ~2600 fps from a 20 inch barrel (calculated). Estimated recoil is 9J, equal to the 7.62 AK.

Compared to M80 ball, the 6.5 120 FMJ drops 42 MOA at 1000 yards versus 40. The M80 has superior energy at all ranges, although by 100 yards the difference is very slight. Energy advantage over M855 is 50% at the muzzle, and by 1000 yards 6.5 gains a 600% energy advantage.

If you toss out FMJ, the 123 Lapua scenar looks far more promising with a BC of 0.547. If you can get an FMJ that's close, sat 0.500 that 123 weight range look very interesting indeed. At 600 yards, the 6.5 and M80 ball are very close in energy, but 6.5 is flatter across the whole course.

The again, if we go back to the 6.5 144gn FMJBT, it passes the M80 ball in energy at 300 yards.

The only liability I can see for the 144 FMJBT is recoil. The question is will the 144gn at 2500 fps be too much in an assault rifle application.

BTW, I am excluding the fact that the 6.5x45 is too long for 5.56 based weapons, and 7.62x51 based weapons are unnecessarily large.

This is an all purpose, compromise cartridge designed to do everything. It actually performs better that M80 ball at ranges over 300 yards (on paper), and better than 5.56 in all conditions.

 

[GunTech]

SDDL-UP.

I agree with the idea of a heavier, larger bullet for a universal round. A side benefit to 6.5 over 7.62 is that with similar bullets weights, the smaller bullet has a much higher sectional density, which is a big factor in penetration. One of the big complaints about 5.56 is it reduced penetration in built up areas. 6.5 should equal or exceed 7.62 in these situations.

 

[GunTech]

56= 1,200 from 20"
7.62 = 1,400 from 20"

M80 ball = 2502 from a 22 inch barrel
6.5x45 (144 FMJBT) = 1998 from a 20 inch barrel

 

[Nolo]

You could have AP, tracer, ball and match, as long as all will function in all weapon systems.

They would. The only reason I said "extend the neck" on the sniper load is because in that particular load I saw the need to crank up the speed and pressure, thus it would be operating at maybe 65KPSI whereas the standard infantry rifle would be operating at 55KPSI. You wouldn't want to shoot the sniper/DMR load through the infantry rifle. So you extend the DMR load's neck by a millimeter and now it won't chamber in the MBR but it will chamber in the snipers and DMRs, just like the .357 Magnum in .38 Specials.
But you may not need all that pressure after all, I don't know.

 

[GunTech]

As I posted, the 144 F MJBT at 2500 fps performs better than the M118LR special ball. At 100 yards it has 2 MOA less drop and more energy. That's at only 52,000 psi.

 

[Nolo]

Okay. So then there's no need to increase pressure. I thought you said it outperformed M80 Ball, which is a "duh".
I'd definitely like to see the 144 in action. I think it'd make a great counter-sniper cartridge in a light rifle and skilled hands.

 

[icebones]

oh hell, here we go again.

if it hasent been posted yet, someone will say something about using .458 lott or some other big game round. always do.

what we need is a middle ground.
in handguns we have 9mm, .40, and .45.

in rifles we have 5.56mm, 7.62mm. what we need now is the ideal middle round. 6.8x43mm, 6.5 grendel, or something else.

 

[Nolo]

in rifles we have 5.56mm, 7.62mm. what we need now is the ideal middle round. 6.8x43mm, 6.5 grendel, or something else.

I would recommend reading at least part of the thread. I think you'll find we have a pretty good grasp on what we're doing. Well, at least GunTech does...

 

[Glock Glockler]

GunTech,

What kind of penetration would we be looking at in various media with different 6.5GT loads?

 

[gvnwst]

not to go off track, but about bullets, dont we allready use "open tip match" bullets? These are hague compliant? i bielive they are SMKs Sorry if i am wrong...

 

[HorseSoldier]

Nope, you're correct. OTM is deemed legal by JAG for combat use.

 

[gvnwst]

then why are they saying that hpbt bullets can't be used for the DMR load?

 

[Nolo]

That's a really good question...

 

[GunTech]

GunTech,

What kind of penetration would we be looking at in various media with different 6.5GT loads?

That will require testing. I have some 120 and 144 gn 6.5 FMJ on the way. It is reported that 6.5 Grendel with the 144 FMJBT will out penetrate 7.62x51 with M80 ball at all ranges, but I cannot personally confirm this. See 6.5grendel.com

Right now it is has been way too hot for ballistic gelatin, since the range is 40 minutes away and it has been in the mid 90s. But other suggestions for penetration tests are welcome once the FMJs arrive.

I have a ton of milspec M80 ball for comparison testing, and even M855 if anyone care to compare that round.

 

[GunTech]

RE: Hague compliant rounds.

Aside from worrying about Hague compliance, FMJ is typically the military round of choice because it has to do everything well - or at least not poorly. You need not only lethality but penetration. The open tip match bullets are notoriously bad against barriers that are frequently encountered in military operations. At short range, match bullets often disintegrate. What if you need to shoot through a car door, for example? Not an uncommon scenario in urbanized terrain.