I posted this on AssaultWeb during the ARFC outage and got a few interesting responses.  With ARFC back on line, I thought I would ask the dedicated Black Rifle community for it's thoughts.  The AW post is here: www.assaultweb.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=004898

We're working on a new wildcat for the AR-15 type rifles. Granted it would require different magazines (that are readily available right now in 10 round variety) and a modified lower, but bear with me.

With all the talk of the 223 Rem just not quite doing the job with short barrels (M4) or not quite reaching far enough where terrain allows/dictates (Afghanistan), we are building a new round.

NOTE:  We are not trying to offer this as a competitor to the 6.8, but more as another option intended perhaps more for the competition shooter or the enthusiast.  As you can read in the AW post, the 6.8 is hard to beat so we're not even trying.

Right now, the final decision is whether to go 223 or 6mm (243). The 223 variety would allow simple conversion of existing 223 uppers - just chase out the chamber with the new reamer and replace the bolt. The 6mm would open up a whole new arena of ballistics.

So here are the numbers we're looking at. These are all based on 55,000 psi (the SAAMI max for the 223 Rem) and a 24" barrel.

In 223 caliber
Speer 55 gr (M193) - 3,600 fps (223 Rem FL = 3250)
Speer 62 gr (M855) - 3,400 fps (223 Rem FL = 3100)
Sierra 77 gr SMK - 3,200 fps (223 Rem = ~2800 fps)

In 6mm caliber
Sierra 90 gr - 3,000-3,175 fps 243 Win =~3000 fps)
Sierra 107 gr - 2,800 - 2,970 fps **
(** these do NOT fit the mag, but have to be loaded through the ejection port. The 3rd Gen of this lower would allow that round to seat in the mag ...) (243 Win =~ 3100 fps)

My question to you:
1 - Should be bother with this, or just work on something else, with the 223 AI, Mk262 and 6.8x43 offering "good enough"
2 - If we should go ahead, do we go with the 223 or the 6 mm version?
3 - Should we try a different caliber or approach all together?

Thanks for your time and answers.

I see folks are voting, but surprised that nobody has posted any comments.  And right now the 6 mm version is the clear favorite.

Now I just need to find a buyer for this match grade 223 barrel I have ....

Olympic is about to start producing AR uppers that will fit on standard lowers with no modification for the 243 WSSM.  Winchesters website has all the ballistics on this and the 223 WSSM which Olympic has in production as we speak (write).  Check Olympics website for more info. [url]www.olyarms.com[/url]

My first AR-10 was in .243.  Fine shooting rifle.


5sub

Rather than going with a longer case, go with something fatter.  Similar concept to the short magnums that are all the rage.  This way you would only need to replace a barrel and bolt and possibly modify a mag follower.  Certainly would be easier from an engineering standpoint since most of the component work is already done.  If your worried about more/higher pressures, look to some of the beefed up uppers already in production. I like 6 and 6.5 mm rounds.  Ballistics are great.  Keep us informed.

I voted why bother...

I feel that the biggest detriment to the 223 is wind drift. As far as its capabilities, I have found through years of hunting that the 223 is far superior to the 243 in the damage caused by the bullet.....(using factory ammo) easy guys...

Now if speed is what you want certainly you can look towards the 223 WSSM.....but why.....Couldnt a mag be developed for the 22-250 ......your talking super sonic out of a 24 inch barrel with very similiar bullet performance and ballistics grain for grain.....
This is just my thought......The 22-250 is by far the best 22 caliber as far as long range shooting/hunting that Ive found......Let me know what you think

Replies to some of your questions:

243 WSSM loaded with some of the heavier bullets will likely exceed the 2.255" max length of the AR-15 magazine. It will cause extremely deep seating of the bullets and eliminate some of the advantage the case would offer.

223 WSSM suffers from throat erosion far beyond that of the 220 Swift or 22-250 AI.  Rumor has it that even Winchester is looking to phase it out ....

Operating pressure of the WSSM cases is 60+ K psi, whereas our wildcat is 55+ at the spec listed (it can go to 63K)

The wildcat case is both FATTER and LONGER than the 223 Rem, and the performance in 223 caliber is right smack in the middle of 22-250 performance according to my Speer manual.  

We tried going even fatter than the case we decided upon but without the new bolt like the Oly, bolt thrust will shear the lugs.  The beauty (in our opinion) is that the upper is all STOCK parts in this case.  The lower is commercially available, and the magazines are too (albeit that they require modification but we would supply them in final form).  Brass is also off the shelf requiring some trimming.

Looking at the 458 SOCOM project, we tried to eliminate some of the pitfalls of that saga, such as custom bolts, extractors, extensions, brass.

Hope these answers help?

123whisper - I here ya, but it's a disease, this wildcatting .... ;o)

Edited to correct some mistakes on dimensions of the 243 WSSM and the 22-250.

It isn't that I don't find it interesting.  I would be much more interested in something of about 6.5-7 mm in a scaled up AR15 rather than make-do's based on the current 223/5.56 AR platform.  Then again, it might turn into something that is if not this, then that.  This being a AR15 firing 75-77 grain OTM and that being an AR10 firing some sort of plastic nosed hollowpoint.  But with the reports of the 6.8mm being so "spectacular" and all terminally and probably very good as far as accuracy, I personally doubt it.

But that is not really feasible.  To make new receivers and all.

Ah, I got ya.  This is actually something between the AR-15 and AR-10, but with a lot of the AR-15 components to keep cost down for you and me.  And we looked at calibers up to .308 and found that we could not improve significantly/sufficiently over those currently offered (ie we could not get 100 fps more than the 26 Grendel gets and that would not warrant the expense involved.  For the 270 caliber, we are eagerly awaiting our 277 WSSM dies ... gonna rebarrel an Oly, I guess ... and we are working out the kinks in our 308 Sabre which duplicates the 300 Savage from the existing AR-15)

Gives us a little to work out the kinks, we might have just the ticket for you

Marty