Designing the 6mm Badger

[Grump]

Remember that part of the equation is materials use. Copper is a strategic metal, and the less we use of it per round the better.

The badger will stack as long at 7.62 NATO in magazines, which is a disadvantage in my eyes. However, the proposed OAL is just more than 7mm less than a .30-06 empty case.

I currently lean more towards the 6mm variant. Anyone for a 6.25mm? That's a groove diameter of .246 plus a little.

 

[Futo Inu]

Hey Badger, how can you ream a .243 win for your new round in your Rem 788, if the case length on a .243 is 2.035" and yours is 1.7"? Wouldn't you need to add steel to the chamber, not take away, requiring a blank barrel, or shorter 6mm round gun as a platform? Yes, yours is definitely a fatboy being based on .284Win (.500 instead of .470), but shorter. I don't get it. I wish you luck and keep us posted - it's very interesting.

 

[Glock Glockler]

Badger,

I was thinking of a bullpup design for the round, so we could easily manage a 20 inch barrel and it would still be compact enough for CQB and SpecOps uses. Just how much difference is there between your theoretical case and a .250 Savage case?

Futo,

Actually, it is named after our resident gun encyclopedia Badger Arms. I was thinking of the of the 6.5mm Glockler, which was recently stolen and renamed the 6.5mm Grendel. The 6mm would make a great general purpose round, but perhaps we could also have a 6.5-7mm big for longer range work. I thought a 45mm Czech case would do the job but apparently not, the goal being .243 ballistics with the heavier bullets but in a smaller package.

If anyone has a .243 and loads it with the appropriate rounds we could do some empirical testing to see how it performs on various media.

 

[Badger Arms]

Hey Badger, how can you ream a .243 win for your new round in your Rem 788, if the case length on a .243 is 2.035" and yours is 1.7"? Wouldn't you need to add steel to the chamber, not take away, requiring a blank barrel, or shorter 6mm round gun as a platform?

You forgot the other option. To be fair, so did I. I'll need to set the barrel back. I also need to make a single-shot adapter. That's easy enough to do when I have a brother with his very own CNC machine!!! The whole goal of reaming out the 788 (after setback of course) is to test the round and get a good idea of ballistics from a barrel just sligthly shorter than 18" it turns out. I'm frankly WAG'ing it with the size of the case. I have no idea if we'll be able to get to 3000 fps or not.

If we can't make 3k from the 18" barrel, we might have to go with a belted magnum case and turn the belt off and the rim down to .473", but that gets expensive and tedious. This yields a base diameter of .511" but because the belted magnum case is thicker, capacity doesn't jump as much as one might imagine. There are two other 'cheap' steps we can take. We can use either the Remington SA Ultra Mag case shortened. This gives us a .532" base diameter. I am not sure what the Winchester short magnum specs are, but I'd imagine the case is bigger so that would be yet another step up. A prototype round would have to have a .473" base so the bolt doesn't have to be altered, but a production round with a base diameter of .532" really needs a standard -- not rebated -- rim.

Okay, reality check here. What we are trying to do is build a cartridge that will function through a .223 length action. That limits us to a maximum overall length of about 2.200" and no more. I like round numbers and standardization so the idea of using the .284 and its rebated rim works just fine for me. We are trying to get a 105gr Very Low Drag (VLD) bullet to 3,000 fps at safe pressures from an 18" barrel. We want to be able to retrofit .223 rifles as well as build a purpose-built, standard capacity (25 rounds?) bullpup. I'd rather have no part in a bullpup design, although I really like the idea of a magazine that projects to the left of the gun, right above the trigger group!

We don't have to go through the entire thought process here either. Savage helped us some. They faced a similar delima with the design of the 250-3000 Savage cartridge. They thought -- and rightfully so -- that hitting the magic number of 3,000 fps with a 25 caliber projectile would be tremendous marketing coup. IIRC, the wanted to do this with a 100 grain bullet (another round number) but pressure concerns kept the bullet weight down to 87gr. What they did was scale the bullet to the gun, 3,000fps velocity limit, and to the case.

What we want to do is scale the case to the bullet, OAL limit, Barrel length, and Velocity limit. That means just finding the right sized case to do the job. We need to base it on another case because WE AIN'T WINCHESTER HERE.

How to do it: We can finalize the case above (with a little refinement to the drawing) and submit it to Redding and Clymer for dies and a reamer. If I can go out on a limb, I'm going to coin this round the 6mmBX-1 for Badger Experimental-1. I suggest we use the Berger 105gr VLD bullets initially. If it takes off, we can use a 71gr bullet for a screaming varmint load. Next, we need a reloader to form the cases. I'd be happy to pimp out my 788 for the purposes of testing the cartridge, but for accuracy testing, we need a tighter twist like 1-10" or 1-8" of which I prefer the 1-10" so the owner can shoot lighter bullets if desired. To modify my rifle, I'd foot the bill for the gunsmith services. I've got a good gunsmith here in town who could set the barrel back and do the reaming and throat job. For the accuracy rifle, we need a 6mm 1-10" twist barrel blank and an action to build on. We can use the same reamer or perhaps redesign the cartridge if the inital tests fail to meet our requirements.

Market: The market, if we want to market the gun, will initially be AR-15 upper conversion units. New bolt with AR-10 extractor, ejector, etc. from Armalite. New barrel and barrel extension. We're in business. It's just a matter of finding the right diameter hole for proper function. I'm not a gunsmith. We can use the wider magazines designed for the 7.62x39 cartridge to get better feeding and more capacity. We're in business. That's an AR-15 with the power of an AR-10 and all that's required is an upper change. Now THAT'S exciting!

http://www.redding-reloading.com/pages/customadedies.html
http://www.bergerbullets.com/catalog.htm

 

[Badger Arms]

Just how much difference is there between your theoretical case and a .250 Savage case?

I looked into that as well. There are two cases that came up in my research. The first is the 6mm International which is simply a necked-down and shortened 250 Savage (this is the Donaldson Version). This is as close to what we want as I could find in my limited research. The case is the correct length, but we're about 2-300fps to slow with that case. The reason is that the Savage case tapers from .468" at the base down to .413" in less than 1.5" This degree of taper really slashes case capacity and makes standard-capacity magazines curve way too much (look at the AK-47 mag). I thought about blowing out the taper in this case some and that is still an option, but I seriously doubt that we'd get the required velocity especially from a short barrel and reasonable chamber pressure.

One more thing. The 1962 issue of Gun Digest had a short article about the 6mm International. The author reports 3000fps with 100gr bullets but fails to list the barrel length, which I suspect was in the area of 24". He also suggests 1-12" twist at that velocity, but the VLD Bullets are longer and need more rotational velocity. So why go with a different cartridge? Because I KNOW that the shorter barrels are going to be used. With a longer barrel we could really claim some tremendous velocities, but I think it's best to stick with the honest, no-crap velocities from a real cartridge in a useable barrel length mounted on a real gun. I always hate when cartridge makers exaggerate.

The other round I looked at is the 6mm/284 which is a simple necked-down 284 case. This is a screaming number and borders on overbore capacity. It's too long, too powerful, and too fast for our purposes. It does, however have the base diameter we need, so my thought process was to use the case, but shorten it.

 

[Futo Inu]

Badger, what is the exact length of the 105gr bullet you're using for drawing board purposes? And in that case you posted here, how much of said bullet length is within the case, and how much outside the case, with the OAL you show? And, I'd imagine that you may ultimately have to compromise on your velocity goals to say 2800, or use an 85 gr bullet, because there's still not THAT much taper in that case, and with high pressure loads, you're probably going to have some extraction problems. I think compromising the vel goal is better than going with the shorter bullet - of course, what's to stop you from offering both? - the 85 grainer for marketing purposes, to reach the magical 3k barrier, and those who want to can reload 105s. Oh yes, I think there would be a market for it. Wouldn't you also have to design a mag follower to make it work?

 

[Badger Arms]

Well, I certainly don't want to lower the weight of the bullet, or we'd just use the 6mm International and reinvent the wheel. I did think about this and I do not know. Earlier I said:

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!!!

The SAW round had .300" more portrusion than our cartridge will have and it used basically the same bullet. Remember that the 6mm International hit the 3k mark with a smaller case and longer barrel. I'm not overly sure what the OAL was and maybe they seated the bullet pretty far out. Yes, with the bullet seated deep, you'll definitely lose case capacity but making the case fatter is going to compensate for that. If you understand, we can still redesign the 6mmBX-1 if we don't hit the 3k mark and utilize the Remington or Winchester Short Magnum cases instead of the 284 case. I'm optomistic that we will get a little over 3k fps with 105gr bullets and an 18" barrel.

This picture shows (top to bottom) the Russian 5.45x39, 7.62x51, 5.56x45, and 6mm SAW rounds. What I want to note is how far the VLD bullet sticks out from the case compared to the SS109 round next to it. Also compare this to the other two rounds. I don't think it's a stretch to seat the bullet .300" deeper and call it good. If handloaders want that extra capacity, they can use a gun with a longer action.

 

[BigG]

we are rearranging the deck chairs on the Titanic

Couldn't agree more, Jim bud. What we DON'T NEED is another cartridge. What we DO NEED is a new bullet launching technology.

 

[Badger Arms]

Couldn't agree more, Jim bud. What we DON'T NEED is another cartridge.

On what grounds do you make this assertion? The 300 Whisper, 17 rimfire magnum, and the 40 S&W were unnecessary? Please offer us something practical in the caseless department. Only the likes of GE and H&K have tried and FAILED with no less backing than the US and German Governments. If you want new bullet launching technology, it needs to be sanctioned by the US Government or it isn't going anywhere. Caseless doesn't work, won't work, and isn't going to happen. Present me with the crow, and I'll eat it... I'm waiting... Sure, you can make a caseless rifle, but it won't perform.

It seems you are predicting the demise of the metalic cartridge industry? How and on what basis do you make this assertion? Metalic cartridges are basically unchanged since the late 1800's. They are unchanged because they work. They work because the design is sound, economical, and easy to work with. I can send the specs to Clymer and Redding and, for triple figures, have everything I need to make a new cartridge. Governments have spent hundreds of millions on caseless ammo and, hmmm, where's the beef?

Let me respectfully ask your opinion on which direction you think we should go in cartridge and weapon design. Submit your own thread and then link us old-timers over there so we can be enlightened.

 

[BigG]

Badger, excuse me while I get all choked up!

See if you can snag a copy of cartridges of the world or some old PO Ackley/Elmer Keith stuff and you will see that everything you can invent has existed since, oh, 1930. Governments will prolly never invent anything. Once a gomt gets involved in something the objectives get fuzzy and all sorts of stuff not related to the project begins to drive it. The guy who perfects caseless or the next wave will be a little guy, probably cantankerous, in his garage or basement, like Henry Ford, Thomas Edison, John Browning, or YOU BadgerArms!

 

[Badger Arms]

I don't believe that anybody said anything about inventing here, we're innovating like everybody has done since the 8mm Mauser. We can argue semantincs all day, but please get to work yourself on the next step. It's been, what 115 years? Caseless ammo relies on utilizing either the bullet or the powder itself as a cartridge. Making somthing that is supposed to burn cleanly and reliably also act as the structural and environmental protection envelope is impractical in the short term and possibly impossible in the long term.

So start another thread and design the perfect bullet launching platform, at least in theory.

 

[uglygun]

Hating to go back to the PPC yet again, but one could summize by looking at the picture that a PPC case in 6.5mm would probably fit in very nicely between the 5.45x39mm and the 6mm International.


I know, you'd like to go with a VLD in 6mm for aerodynamic reasons, but simply moving up a tad in diameter can really help to make the load length restriction to share commonality with 5.56x45mm. That or seating just as long and gaining case capacity. Here is where you could get away with marketing a round that feeds/fires from all guns by seating it deep and retaining the ability to feed from a magazine but yet offer handloaders something fairly substantial, such as they would quickly find out that seating the bullet out a bit further yields improved case capacity for more powder.


But other mods could be made, case could probably stand to be lengthened a tad and maybe blow out the case taper a little bit to gain a tad bit of additional capacity.


It wouldn't neccesarily be new though and the exact round above is likely to exist shortly once Alexander Arms gears up for their .26 Grendel.

But then that would make for some cases to play with atleast.



Could 3000 fps be a little too much velocity to shoot for? 243Winchester specs show it kind of having a hard go at making 3k fps while shooting a 100grn bullet. Seems to me that 243Winchester is way over bore and especially in a semiauto it would lead to rapid throat errosion. Seems that was part of the downfall of the 6mm round being developed for the SAW as well, it was even hotter than the 243Winchester from what I'm starting to gather and would likely be even more harsh.

Kinda the reason I'm a fan of the PPC again, just enough performance increase yet a minimized amount of additional wear and tear on the firearm.



Adressing where somebody mentioned using an AR10 bolt in an AR15.... Not without drastically different changes to the upper assembly, barrel extension, bolt carrier you won't.

BIG differences in the two assemblies there. Olympic Arms has made huge changes to their upper assemblies that they are gearing up to produce for the WSSM line of cartridges, once those get out maybe there would be some freedom to start playing around with cartridges with case heads similar or slightly larger than that of a 308Winchester. As it stands now, the AR15 bolt is reaching it's limits when opened up to that of a 7.62x39mm head for the PPC.


Tony Rumore at Tromix would be a good one to talk to about some wierd wild cats for the AR15, his 458Socom and the various oddities like chambering for the 50AE could shed some light on how to get large diameter cases to feed reliably for the AR15 and what kind of magazines or modifications are desireable.

Just happen to have a comparision of the AR15 bolt to an AR10 bolt on my website,
http://home.bak.rr.com/varmintcong/misc/ar10ar15bolts.jpg

 

[Zorro]

So, What you REALLY want is a 6MM PPC Magnum!

Just use a 7.62X45 MM Case.

 

[Badger Arms]

Uglygun: Good points, but let me comment on some of them.

But other mods could be made, case could probably stand to be lengthened a tad and maybe blow out the case taper a little bit to gain a tad bit of additional capacity.

My case is as long as possible to feed in a .223 action. Blowing out taper is a nice idea and works great on the bench but not so much in the field. Many extraction problems involving the .308 and .223 involve their lack of taper.

243Winchester specs show it kind of having a hard go at making 3k fps while shooting a 100grn bullet. Seems to me that 243Winchester is way over bore and especially in a semiauto it would lead to rapid throat errosion.

I don't think it's overbore at all. It's nearing the limit of what might be considered practical. We essentially want a shorter version of the 243 with slightly more case capacity to make up for the lack of barrel length.

Seems that was part of the downfall of the 6mm round being developed for the SAW as well, it was even hotter than the 243Winchester from what I'm starting to gather and would likely be even more harsh.

Not at all. Look at the picture above. The 6mm SAW was an anemic round designed for controllable full-auto fire. It shot the same 105gr bullet at about 2500 fps, well below what we're going to operate at.

Adressing where somebody mentioned using an AR10 bolt in an AR15.... Not without drastically different changes to the upper assembly, barrel extension, bolt carrier you won't.

Well, I agree with you about using the AR-10 bolt, but I said that we needed a NEW bolt but could still use the AR-10 extractor and ejector parts but I'd have to pull the AR-10 bolt out and double-check. I might be wrong about that one. I also realize that the barrel extention would need to be new. I really hadn't given that much though.

 

[Grump]

What happens to the 6mm SAW if you blow the shoulder out another 3mm and deep-seat the bullet to match the M855 5.56mm OAL?

What if you also neck the SAW down to 5.56mm? could we then beat the 80-gr long-loaded performance of the AR15 match shooters?

Seems like a lot of the disadvantages of the mousegun get much smaller when you're launching bullets 69 grains and heavier. Get more case capacity and that bullet diameter might do everything we want the 6mm to do...

 

[uglygun]

Seems the proposed 6mm SAW round was a bit more mild than I originally thought, I've seen some other specs mentioned where it was ahead of the 243Winchester in performance but the specs may have been wrong.


I can see potential problems with cartridges that have less of a taper to the case side walls but there's just something about how a 5.56x45mm stacks in a magazine compared to the way a 5.45x39mm stacks in a magazine. I'm a fan of things that are not drastically curved, one of the smaller more minor reasons why I like the M16 as well as other 5.56x45mm guns is because 30 round mags(even 40s) are noticably more straight compared to AK47 and AK74 mags.

Also the reason why I like my AR10 and other 7.62x51Nato rifles, straight 20round mags and no curvature.


Then if you had a larger than 7.62x39mm cartridge but with similar taper, I can only imagine that you'd wind up with a mag that is even longer with more curvature to it.



Maybe to cure extraction problems a more HK 91/93 fluted chamber sort of design could be implemented to account for straighter tapered cases? Or am I gonna get nothing but for even suggesting that?


Man, speaking of, getting ahold of one of the few Knights SR47s(all of the failings of the SR47 aside, where it failed due to low quality ammo which is far beyond our case) would be a sweet deal though, has the receiver changes needed for a longer bolt and clearances for fitting regular AK47 mags. That would be a great platform for doing some basic experimentation with while playing around with atleast the PPC line of 7.62x39mm based cartridges. Just move over to a more G36/AR18 style gas system to stop the *&%'s where it eats habits of the standard AR15/M16. Then, maybe if some other opportunities came up allowing for the bolt to be changed or opened up to a larger case head, maybe the AK47 magazines could still be implemented if the case used still required a magazine with a fair amount of curvature to match taper.

I can't believe I'm gonna say this, but the Toady Special Weapons AR47 lower receivers could be an opportunity to play around with standard AK47 magazines and the AR15.

 

[Badger Arms]

Maybe to cure extraction problems a more HK 91/93 fluted chamber sort of design could be implemented to account for straighter tapered cases? Or am I gonna get nothing but for even suggesting that?

I personally love fluted chambers. The FAMAS is another gun with a fluted chamber. They had problems with extraction with brass cases and standard chambers, so they fluted the chambers and use steel cases. Problems gone. The disadvantages of a fluted chamber far outweigh the advantages, IMO. The main disadvantage is a manufacturing one. Another is increased fouling. The French and Germans were both FORCED to deal with minimum taper from US rounds that were designed to work in nice, clean guns. Handloaders hate fluted chambers. My primary concern focuses on the fact that you can solve the problem by designing the cartridge right in the first place. Straight magazines are great, and I'm a fan of them also. Since you have to have SOME curve though, you might as well get enough taper to get the gun to work reliably.

 

[Futo Inu]

Badger, tangential question: If fluted chambers and steel cases instead of brass helps with extraction, then what's the other side of the coin on steel cases? What's the disadvantage of using steel instead of brass? More expensive to make? Non-malleable so cannot reload?

 

[Badger Arms]

You know, Brass works better in non-fluted chambers. Fluted chambers are a fix for design compromises. Both the G3 and the FAMAS have delayed blowback systems. The G3 utilizes rollers and the FAMAS utilizes a clever and simple lever. This means that primary extraction is accomplised while considerable pressure still exists in the chamber. In fact, there is a drop in the pressure curve where the extraction caused by chamber pressure is overcome by the inertia extraction of the bolt carrier group as the bullet exits the muzzle and pressure drops. This violent transition occurs while the case walls are still firmly against the chamber. Fluting keeps the extractor from extracting just the rear half of the cartridge!!!

Steel is just as expensive to MAKE as brass because it's harder on the tooling and requires additional steps to corrosion-proof it. Since brass is more expensive to buy, I'd say that Steel is a bit cheaper in the long run. That's why devil Wolf ammo uses it. Steel is bad for firearms because it performs differently. It doesn't spring back as far and the materials used to make it corrosion-proof can gum-up an action. Brass is also more forgiving and less likely to damage your gun.

If it were me, I'd use Steel exclusively and just design the gun to be tougher. Greater surface hardness, chrome or TiN coating on the bolt carrier group and chamber. Yes, even fluted chambers. Throughout the life of a gun, it will consume enough ammo where the added expense in manufacturing the gun the right way will pay off in the cheaper ammo costs.