I have been working on a new cartridge and thought I’d post here to get some feedback
Here is a link to a pdf of my 6.2mm OCC
Interesting please keep use informed of future developments please.
I have sent a prototype to Superior Shooting Systems Inc. , they are going to run figures and measurements. They said they would take it and the results to Shot Show this week and will let me know. We’ll see
There are terms and requirements that need to be explained or expanded on. “Case ergonomics” is a new term for me, which can mean anything from how easily they feed to how efficiently they direct burning/expanding propellants. “Poor capacity” should also be expanded on and qualified; I’m not sure I’d call 25 rounds “low capacity”. Additionally, unless you can demonstrate even theoretical numbers, I would be very hesitant to describe the 6.8 SPC as an example of “poor ballistics” without providing an example.
As for the actual design: how much luck have you had finding 6mm SAW cases in large enough quantity for adequate load testing? Have you found any bolts that would grab the case?
Onto the bullets. I’m curious why you stayed with bullets similar in weight to heavier 5.56mm rounds, especially given your complaint with the 6.8 SPC was that it was relegated to lighter bullets that moved quick but had less-optimal external ballistics. A 6mm 75 gr bullet isn’t really an improvement over, say, a 5.56mm 75 gr bullet. Sure, the slightly larger capacity can push it a little faster, but it’s also fatter and will be less efficient moving through the air. Bumping the shoulder up could help, as would giving it something closer to 30 degrees. Did you have any specific bullets in mind for this project?
I’m not sure I’d call your wildcat a 6.2mm anything. First, because it’s a 6mm. Second, because 6.2mm implies closer nominal nearness to the venerable 6.3mm (aka, the .257) than to the 6mm it actually is.
Good luck on your wildcat and please remember to post the numbers after SHOT!
-B
“Case ergonomics” = case design. 6.5 parent case was a benchrest cartridge = bolt-action.
“Poor capacity” = as compared to 30 rounds of 5.56
“poor ballistics” = 6.8 110-115gr BC compared to 6mm 85-87-90gr BC
Brass would need to be manufactured
Bolts are cheap and easily manufactured, possible to just mill out 5.56 bolt.
Compare 5.56 62gr w/ 6mm 75gr. Compare 5.56 75-77gr w/ 6mm 85-87-90gr.
6mm = 6.17 - 6.2 . .257" = 6.5mm
I am also curious to know the figures from a professional, as my numbers are that, mine and may be bias. Will see.
Thanks BAC
As BAC mentioned, using “6.2mm” flys in the face of convention. In this regard, nearly all previous attempts at this have had negative results. For example, the .244 Remington, 280 Remington, 220 Swift, and so on. Sometimes it’s best to stay with convention to avoid confusion, it’s my opinion this is one of those times.
Twenty-five round magazine capacity is not poor. The M16 had a 20 round mag as standard until the mid-80’s when the 30’s were fielded. Lots of folks would argue that a 25 round M16 mag would be plenty, others would like 40 rounds. For the current Tier One AR-15 cartridges, the 6.8S and the 6.5G, 25 rounds are simply standard.
Last, I’d strongly suggest you concentrate your efforts on bullets of not less than 95 grains and preferably 100 to 110 grains, you need that weight for penetration, sectional density, and a reasonable ballistic coefficient. I think it’s accurate to say you need a 30-35% performance increase over the 5.56NATO to be successful.
Please continue with your development, it looks very interesting.
Thanks for the explanations.
The one issue with “case ergonomics” as you describe them is that we don’t have an established record demonstrating 30-40 degree shoulders won’t feed well in semi-autos. I hear it, and understand what “they” say, but there isn’t data right now to justify it. On the other hand, I’ve seen both the .223 Rem AI and 6mm AR & AR Turbo do very well out of AR-15s. The Grendel doesn’t appear to have problems feeding, either.
Magazine capacity I suppose is subjective; my opinion happens to align with fastpat’s, in that I would not see 25 rounds as a “significantly reduced capacity” compared to 30 rounds.
Ballistics… fastpat hinted at it, but there’s more to ballistics than ballistic coefficient. I believe the general consensus even among bullet makers is that BC and speed are equally important at 500 yards, and the further past 500 yards the you go the more important BC becomes. All of this is external ballistics, though, which is just the bullet getting there. Sectional density is important due to its impact on barrier penetration. Bullet construction is similarly important; any replacement for the 5.56mm will have to be limited to JAG-approved bullet designs (this is why I asked what bullets you had in mind for the cartridge). I would like to compare those bullet weights you mentioned, but I don’t know what bullets specifically I’m comparing and what speeds I expect them to be moving at.
I believe brass can be manufactured, but it would require a pretty big order since it’s a custom case head. I promise you that if it was cheap I’d be sitting on a pile 6mm SAW brass for projects. 
Milling out a 5.56 bolt is probably not a wise idea. I am curious how much a bolt costs and how easily manufactured it is, though…
Concerning names, remember that the 6.5mm has always historically meant .264 (or .260, as with the .260 Remington). I don’t know how commonly the .257 is called “6.3mm”, but I know it has been in the past even if it’s only historically. Again I agree with fastpat that it might be best to be conventional here so readers and potential buyers know what they’re getting. If a bullet sounds custom, that means they’ll be an unknown rather than a well-established known.
(Likes wildcatting, but like I needed another expensive hobby… :o)
-B
I would agree with BAC and fastpat with name its uses 6mm bullets I wouldn’t call anything but the 6mm OCC. The great appeal is being able to use standard magazines GI and P-mags. The projected velocity of 3000 FPS you didn’t say what barrel length. It would be Ideal to be able to achieve that goal in a short barrel 16’’ and still retain good velocity in shorter barrels say down to 10.5’’ .
25rd capacity for you, me and many others would be fine, but the military does not see it that way, they want high mag capacity, they want firepower and they do look at the weight per round count.
I did look into the 95,100 to 105gr 6mm projectiles, they would ‘diminish
velocity and degrade the cartridge performance’. I researched thoroughly. 75gr through 90gr (in this case) will produce good velocity & good energy & good BC. I did not design this cartridge to be a benchrest cartridge. If we had the luxury of a new platform design then my choice would have been .257 cal or .264 cal but we don’t, I have tried to design this 6.2mm round to be the optimum round within the restrictions of the current platform.
Thank you for your critique Fastpat, they are very welcomed
BAC,
As for the bullets, there are no current produced bullets for what my ‘ideal’ bullets would be, as far as I know. They would have to be developed.
These would be my ‘ideal’ projectiles
CR = 75gr FMJBT
MR = 87- 90gr OTM
I used my figures from Hornady 75gr. V-Max & Hornady 87gr V-Max
Did black hills beat you to it??? http://www.thefirearmblog.com/blog/2010/01/21/6x45mm-makes-a-comeback/
Looked on BH web site but didn’t find any info.
Any body have any info on this is Black Hills really going to make this?
No. That article mistakenly states 6mm SAW, but the cartridge in question is the 6x45, aka, 6mm-.223.
-B
I saw the comments but was not sure if it was the 6x45.
On second look at the case it does look like a .223 and not the 6mm saw case.
The article also describes how only a barrel change would be needed, which also precludes the 6mm SAW (which has a larger case head than the .223 Rem and is far too long to fit into the AR-15 magazine). I like the AR-15, but the magazine length certainly limits our options. Mentally, I still keep coming back to the Global/KEC research on blended propellants…
-B
Googled it is the PDF doc the only info on this powder?
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA433982&Location=U2&doc=GetTRDoc.pdf
It would seem the logical step in the evolution would be better powders and case design that allow higher operating pressures. 30-06 to 308 for example.
That’s it. It’s a shame that the study’s dated 2005 and it doesn’t look like a thing has been done with it since.
-B
BAC was correct. who ever stated this at thefirearmsblog must not know much about ammunitions.
As far as my 6.2mm OCC, the last I heard was SSS has sent the prototype to SSA.
Was notified by SSS/David Tubb that the 90gr projectiles are the weight to go with because of their SD.
Both Sierra & Lapua have a 90gr FMJ
Also both the Berger MTBT & the Lapua Scenar 90gr have BC +.400 and SD +.200
(L-R) Sierra 70grMK,85grHPBT,90grFMJ,Hornady 87grHPBT,Berger 90grMTBT,6.2mmOCC w/ Sierra90grFMJ
Is ssa going to make the brass?
It’s one of the reasons why SSS sent it to them. Whether they are going to produce the brass or not I haven’t heard, I haven’t talked to them(SSS) in a couple weeks, figured they dont need me harassing them, I’m sure they know what their doing.