Designing the 6mm Badger

[Glock Glockler]

If we were to have a 105 gr 6mm at 3000 fps using VLD bullets we'd have a Muzzle energy of 2096 Ft lbs and it would have 1246 ft lbs at 500 yrds while only dropping 31 inches with a 200 yard zero.

This, IMO, would make an outstanding general purpose round, and could still be controllable in the right package. Ok, so we have the ballistics, we have the gun (modified Sig 550 in a bullpup configuration), well, almost, but we don't have the cartridge yet. Anyone want to take a stab at what would be the best way of making the cartridge for it?

 

[MLC]

I'll bite

I don't think you will get that velocity with a 105 out of case that would chamber in the Sig 550.
That is the top end in velocity for the 6mm Rem Ackley improved(6x57) with a 26" barrel.
That velocity is no problem with the 240 Weatherby but that is an 06 sized cartridge.
I'd skip the 105 and look at a lighter weight 75-95g VLD bullet and the 6mm PPC.
That would be more doable.

 

[MarineTech]

I'd skip the 105 and look at a lighter weight 75-95g VLD bullet and the 6mm PPC.

Problem with the PPC style fat case (applies for the WSSM cartridges too) is that you're not going to get many of them in a magazine.

 

[Andrew Wyatt]

what about a lengthened 10mm case?

 

[Jim Watson]

Well, the 6mm PPC is on the Rusky head size, so I figure a given magazine will hold as many rounds as an AK box of the same length, with appropriate adjustments for less body taper.

But we seem to have been as far down the velocity track as necessary, maybe more. How about the .280 British? (The 1950s EM2 round, not the near magnum 1913 cartridge.) Or a 6.5 Jap or Italian? (Head diameter of a 10mm is pretty close to those.) Shortened and running at higher pressure with modern powders, but those ballistics; a 129 - 140 grain spitzer at 2500 fps or so. Or the rumored 6.8 mm... in a H&K?

First, though, we need to take some test pieces, perhaps AR-10s in .22-250, .243, .260, .270 Titus, and 7-08 and get them into field trials. While there are still some Afghans and Iraqis to shoot at to see if a new caliber would reach farther and hit harder in the real world.

But we are rearranging the deck chairs on the Titanic. We need to get the H&K G11 team out of retirement and work on caseless some more; and look at the telescoped and semi-telescoped cylindrical cases. Something new and better for our tax money, not just a 50 year old wildcat of some sort.

 

[Gabe]

Something 6mm with the 6.5x52 Carcano case might be doable. Headsize is between the .30 short Russian and .308. And the cartridge length would fit a .308 rifle.

 

[Zak Smith]

Are you guys aware of the 6.8x43mm (I think) that's in the works for some military units? Check over on AR15.com

When you increase bore size, you get more velocity for the same mass at the same pressure.

That being said, 105gr @ 3000fps would rock. Can you stretch it to 340 PF (power factor = MV in FPS * bullet mass in grains) so it'll make Major for IPSC/3Gun?

-z

 

[Andrew Wyatt]

6mm projectiles heavier than 60 or so grains perforate our armor plate, when loaded to .243 velocities. We wouldn't allow it at our match.

 

[Zak Smith]

Andrew, do .223 projectiles at over 3000fps penetrate/perforate your plates?

For comparison, here are some figures of sectional momentum (m*v / sectional area) for different loads:

.223 62gr @ 3100fps: 4,877,200 grain*fps per sqin (at muzzle)
.223 62gr @ 2262fps: 3,558,800 " (at 300 yards)

.223 55gr @ 3200fps: 4,466,100 " (at muzzle)
.223 55gr @ 2170fps: 3,028,600 " (at 300 yards)

.243 70gr @ 3400fps: 5,131,900 " (at muzzle)
.243 70gr @ 2472fps: 3,731,200 " (at 300 yards)

.243 100gr @ 2900fps: 6,468,700 " (at muzzle)
.243 100gr @ 2204fps: 4,752,400 " (at 300 yards, approximated on 95gr data)

.308 150gr @ 2700fps: 5,435,800 " (at muzzle)
.308 150gr @ 2064fps: 4,155,400 " (at 300 yards)

In other words, once you get past about 50-70 yards, the sectional momentum of the .243 is not significantly more than that of .308 or .223. Certainly it's comparable to .308 in terms of sectional density * momentum.

The AR500 plate we use up here will only be marked (a 1-2mm dent) by M855/SS109, and probably .30-06 AP. A 70gr .243 hitting at 2800fps (175 yards) with a sectional momentum of 4,226,200 grain*fps/sqin doesn't leave a mark.

regards
-z

 

[Badger Arms]

The 250 Savage necked down fits the bill nicely. Might have to blow the taper out a bit to get to 3000 fps with a 6mm bullet. Problem is, your gun is a bit too small to handle the load without some significant modification. This is neraly a 308 power round.

 

[Daniel Watters]

In order to shoehorn such a cartridge into a 5.56x45mm sized action, you would need to use a very fat cartridge case. The closest thing that fits the bill would be the .243 WSSM. However, this would turn a standard 5.56mm 30rd mag into something around an 8rd mag for the .243 WSSM.

 

[Grump]

I'm afraid that the loaded cartridge length will need to grow by at least 3mm and perhaps 5mm to get the desired compromise in performance.

Ever notice how the Ruskie 5.45x39 leaves so much of the bullet hanging out there past the neck like an original 6.5 Swede? Even with a VLD bullet, blowing the case itself forward by even 3mm should be doable and also let you pack some more powder in around what becomes a deeper-seated bullet of the *same* OAL. Stretch the OAL along with it and you get a bit more powder in.

Since we're all the way down to 6mm instead of going 6.5, wouldn't the 85-90 grain bullets give us some impressive muzzle AND downrange performance?

 

[Newton]

Or we could just work on improving the accuracy of standard 7.62x39mm cartridges, combine that with the Yugoslavian bullet design and end up with .308 terminal ballistics as was found during gelatin testing of Yugo 7.62x39.

Those Germans were pretty sharp.

 

[Andrew Wyatt]

Andrew, do .223 projectiles at over 3000fps penetrate/perforate your plates?

Nope, but any .243 or .270 does. i'm willing to bet any 6.5 would, too.

these plates last thousands and thousands of rounds with heavy bullet .308 ammo, and any .223 besides ss109 (which pocks them some)

 

[uglygun]

Why not ditch the 6mm and go 6.5mm?


Just a little additional diameter and it's likely you can get into the 100grn weight class with the 6.5mm where as the 6mm would leave you with a longer bullet for the same given weight.



If designing for a firearm typically meant for 5.56x45mm and having to take into consideration loading to magazine length within the constraints of magazines meant for 5.56x45mm, the 6.5mm PPC is said to be a better choice than the 6mm PPC when loading to mag length.



I realise that the following is written by somebody who has an AR15 built/chambered for match shooting, but I think much of it could apply to using an AR15/M16 in a battlefield situation with the same cartridge.

http://www.competitionshooting.com/pages/708565/index.htm

Then there's the .26 "Grendel" by Alexander Arms which is from what I can tell just their proprietary name for the 6.5mm PPC. Magazines in 10 round offerings for civilians and I believe 25 round mags for law enforcement are said to be in devleopment, specifically meant for the PPC taper that shares it's lineage with the 220Russian and 7.62/5.45x39mm cartridges. That's all been our main problem in the AR15/M16 community, finding GOOD mags to use with the 7.62x39mm cartridges due to the way the things want to stack and needing much more curvature to the magazine body compared to that of a GI 30 rounder meant for 5.56x45mm.



I'm a big fan of the 6mm and 6.5mm PPCs, I think they'd make the ultimate intermediate cartridge. Good long range performance yet not as cruel to barrels as something like a 243Winchester would be.

 

[uglygun]

Andrew wyatt, where'd you get your plates?


These plates out at 5 doggie's? I got somethin mean and nasty I'd love to try against those plates

Heck, it's putting holes through 1 1/4 inch steel plate and it ain't a 50BMG..... But I'd rather just get some of this plate for myself rather than go shooting up somebody else's plates, my 10x10x 1 1/4 inch plate is pretty chewed up now after doing my experiments on it, it ain't mild steel either but it ain't hardened armor quality plate. Would like to see if my loads could atleast chew through 1/2 inch plate like you describe though. Totally for educational purposes ofcourse.

 

[Andrew Wyatt]

we use armorguard, but the stuff MGM targets sells is just as durable.

 

[Futo Inu]

6 or 6.5

Actually, uglygun, 6mm BCs optimize at around 100 grains (in lead spitzer boattail bullets - might be heavier with a steel core), and 6.5s at 140/142 gr, so if'n you need a lighter (100 gr) bullet to get the vels for what you're trying to do, trajectory-wise, then 6mm makes more sense for very long ranges. But, having said that, I agree that 6.5 *IS* the better all-purpose round (esp. for the fabled all-purpose ideal military round), in a 140 gr config - in a case somewhere in size between the 6.5 PPC and .260 Rem, closer to the .260 Rem - you should get vels of 2400-2600 or so from a standard barrel in this theoretical round (you get 2700 with 140 from a .260 Rem), and have more penetrative power and energy at range than the 6mm bullet, with not much more bullet drop, and certainly much less drop than a 150-168 gr .308 bullet. Gabe, I think you're right - that case sound like an interesting compromise. Oh yeah mightn't the 6mm might be more accurate than the 6.5s as I understand that 6mm makes for an inherently accurate cartridge? The 6mm Rem BR is a slightly fatter and longer case than the PPC (same width as a .308), giving more vel (around 3000 with an 80 gr bullet), and Glocker mentioned "controllable" - this should be a controllable round to shoot in full-auto, *if* that's what you meant Glocker. You'd have to have a case the size of .243 or bigger to get 3000 with 105 and that's too much powder for what I understand is the parameter of your question.

PS. The 6mm Rem BR might be a good starting point for your inquiry, but I think the OAL will be out of spec for that cartridge with 105-115 bullets - but voila, just make your own "wildcat" with a moderately longer OAL (and possibly a slightly longer case length) - but same basic cartridge. In fact, this 6mm Badger - is it named after Badger Arms of THR fame? ??

The 6x47mm is a .222 Rem necked up to 6mm. It shows vels around 2800 with 87 grain bullets. It's a narrower case head (.378, even smaller than a 7.62x39) than the BR so you could fit a LOT more in a mag, but slightly less vels than a 6mm BR.

I guess it just keeps coming down to trade-offs, and how you rank the relative importance of your goals for the cartridge: Performance at 300 yards? 500? 600? Controllable full-auto? Mag capacity? Etc...I'm fair to partly dangerous when I spout off, now that I have Speer and Hornady and Lyman manuals, and "The Handloader's Manual of Cartridge Conversions" - lol - the latter makes my head spin.

 

[Glock Glockler]

Badger,

The gun might have to be modified on order to get the desired ballistic performance, but there isn't a tremendous difference between a Sig 550 and a Sig 542. BTW, I'd also like the package in a bullpup configuration with all the pesky bullpup associayed problems solved, if you don't mind

I think that 6mm is the way to go because we'd need a fair bit heavier 6.5mm to get the same BC, and then what are the chances that we'll be able to push that heavier bullet downrange as fast. This 105gr has a BC of .529 and the 115gr has a BC of .597. I don't know how mucj potential there would be to launch the 115gr downrange at speed, but these rounds upen up a lot of possibilities, one can only imagine what would be possible with tungsten rounds.

Newton,

You can fiddle with the 7.62 all you want, but at the end of the day it's only going to be a 7.63 x 39. It will not be able to touch the flat shootering charachteristics and energy rention ability of the 6mm Badger.

 

[uglygun]

I know what you're saying about the 100grn 6mm being more aerodynamic than a 100grn 6.5mm....



A 260Rem is essentially a 243Win necked up to 6.5mm, I still feel that's too much case capacity as you'd have a weapon recoiling between that of a 243Win and a 7.62Nato. Not gonna be as controllable as something between that of a 5.56x45mm and a 7.62x39mm which is where a 6.5mm PPC would likely fall.


I bet a 100grn bullet from a 6.5mm PPC could be pushed faster than 2600fps. Certainly enough for some decent long range performance. The increased diameter of a 6.5mm 100grn pill could possibly make for a more effecient round than if the same cartridge were pushing a 6mm 100grn pill.


For general infantry use a 90-100grn bullet would probably do quite well, then there'd be room for special purpose rounds like a 120grn round for use in something close to the SPR program M16s or even lightening the bullet for a high velocity AP application(6.5mm PPC round with 60grn AP bullet probably going around 3100+fps). Heck, the 90 or 100grn bullets could even be given a more Russian bullet design where it shares a hollow core between tip and lead core much like the 5.45x39mm FMJ bullets use, make a VLD 90-100grn bullet(get a gander at those Lapua Scenars some time).

At any rate, even if it wasn't perfectly optimized a 6.5mm 90-100grn bullet would be a big improvement compared to the measily .224 55-62grn bullets used in the 5.56x45mm currently(BC in the .26 range isn't it?).


It's just too bad that the 6mm PPC or 6.5mm PPC weren't around back when the AR15 was just getting kicked off. Supposedly a 6mm was played around with for the SAW supposedly but decided against it, probably for ammo commonality with the M16s and other Nato weapons.

 

[JShirley]

The reasons for a cartridge with reasonably compact dimensions are more than just mag capacity; logistics, ultimately, is much more important than the elusive target performance (on live targets, that is: steel is more measureable).

One of the primary reasons for going to a slightly heavier, larger caliber round, should be to ease logistics problems, by replacing two rounds- 5.56x45mm and 7.62x51mm- with one round that has the long-range performance of one, but is much closer to the size of the other.

John

 

[Badger Arms]

Okay, I like the 6mm ~100gr VLD projectile concept. 3000 fps is a good number to shoot for, but from what barrel length? If you try to get that velocity from an 18" barrel, for instance, you know it would be shortened to 16" and shorter if used by LE and Military. This would mean a slightly larger case capacity.

If you're designing a cartridge, you must ensure that there is taper. Taper needs to be slightly more than the .223. That taper should be enough to allow reliable feed and extraction. The case neck should be short enough for reliable extraction and JUST long enough to hold the bullet. This also serves to increase case capacity. Base diameter should be around .500". Why? Because .473" won't give you enough velocity in a cartridge short enough to fit in a .223 length action. I feel that a shoulder of between 25 and 30 degrees is optimum and splits the difference between case capacity and reliability.

We can prototype this round by trimming the .284 Winchester to 1.7" OAL, with a 1.5" length to the neck, a 2.2" OAL. Here's a conceptual picture I just drew. Everything's to scale.

 

[AJ Dual]

How does this compare to the dimentions of the 6mm SAW prototype round?

 

[Badger Arms]

6mm SAW: Neck dia-.273" Shoulder dia-.382" Base dia-.410" Case length-1.780" OA length-2.580" The difference in case capacity is roughly comparable to the difference between the .308 Winchester and the 300 Win Mag.

Therefore the 6mm SAW was longer, skinnier, and shot about 2500 fps with a 105gr bullet. In my drawing, I only meant to display the layout of the case. It occurs to me that the bullet could have stuck out from the case a bit more, but it might be fine like it is with the base telescoping far into the case. My limitatioin was that I don't have any dimensions for the bullet itself. The 6mm SAW had .800" of bullet hanging out the from the end of the neck!!! Anybody want to foot the bill for case forming dies and a reamer? A .243 caliber Remington 788 I've got sitting around would make an excellent (albiet single shot) platform. Even has the 18" Barrel already installed. All I have to do is ream out the chamber and go to town. Base diameter is the same.

 

[JShirley]

What are estimated costs? I reckon I might be able to dredge up a few dollars for a pet project as important as this.

John

Oh- I suppose 19" bl for standard, 16" for SpecOps and such, and 24" for SDM. Ballistics goal 3,000 fps for 100 grn bullet from 19" bl.