Why is there such a gap in AR15 suitable cartridges?


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R.W.Dale
December 6, 2008, 02:49 AM
Namely medium bore large case offerings. I'm a bit perplexed.....

At one end of the spectrum you have the small bored stuff and the quintessential mid powered assault rifle chamberings. 5.56,204,6.5g,6.8 and 7.62x39 to name a few

Then at the other extreme end of the caliber spectrum you have the large case head big bores. .450, .458socom and 50 Beowulf

HOWEVER

There's practically NOTHING in the middle in terms of large case head medium bore offerings 7mm to 35 caliber other than a few obscure WSSM wildcats. I want a cartridge that'll work in the ar15 platform that'll basically replicate 7x57 or 300sav ballistics. The 30RAR looks promising but I don't expect this cartridge to make it much beyond the initial press release. I hope some manufacturer steps up and introduce some new cartridge offerings in this range. The wildcats are OK but I really would prefer a chambering with factory data and production brass and dies avalible.

With the exploding popularity of the AR15 maybe hornady or remington will step up to the plate. I'm hoping that I won't have to wait long.

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TAB
December 6, 2008, 03:11 AM
Its the short OAL that will still feed thru the mag well that is the prob.

nicholst55
December 6, 2008, 03:12 AM
Your two main limitations with the AR-15 platform are:

1) magazine length; a cartridge must fit in the available magazine well, or the rifle becomes a single shot, straight-pull bolt action.

2) bolt face; a cartridge must fit in the existing bolt face, or within the diameter of what it can safely be opened up to and still maintain a useful bolt life span.

The 6.5 Grendel case is being wildcatted to .338 and .35, among others. I know the 6.8 SPC case is being opened up to 7mm and .30, so you might look at one of those. The problem with 7mm and .30 bullets is their length and the resulting powder capacity of the assembled cartridge. You've got to be able to obtain enough velocity to make the cartridge a viable proposition. All of this is limited by #1, above, and that's one reason why the many AR-10-type platforms are so popular - they can be chambered for many more useful cartridges, but at a significant weight disadvantage.

R.W.Dale
December 6, 2008, 03:16 AM
yes the case must be short and three years ago this would have been it for these projects, but we now have WSSM uppers so you can offset this issue by going with a fat case in one of the new large diameter single stack uppers. If anything the wssm's make more sense in the AR15 platform than they do in any other rifle. The 300wssm wildcat supposedly matches .308 ballistics in a package that'll feed from an ar15 lower


That's the point of this thread..

It can be done now

But why hasn't anyone ran with it yet?

gazpacho
December 6, 2008, 04:35 AM
Because not many people want to shoot a semi-automatic medium-bore high-power 7 lb rifle.

Buy an AR-10 or an M1A

C-grunt
December 6, 2008, 04:42 AM
My brother in law rented a 16 inch AR10, DPMS I think, when we went to the range a while back. It wasnt that bad handling. Not as good as a M4, but not to bad either.

RyanM
December 6, 2008, 05:21 AM
Other than overall length, there's bolt face thrust. The AR can only take so much, I believe about 5,000 pounds. The bigger the case head, the lower the maximum pressure (pressure * area = force, thus larger area requires lower pressure for the same force). Something equal to .223 case head diameter (.377") can be up to 62,336 PSI, tops (darn metric conversions, NATO specs are in Pascals. SAAMI max pressure for .223 is 55,000 PSI, in comparison). 7.62x39mm case head diameter (.443") allows for 45,000 PSI. Both work out to the same amount of bolt thrust.

The WSSM parent case has a head diameter of .555", similar to the .50 Beowulf at .535". However, if we do some simple math, the max pressure for a WSSM case is about 28,760 PSI. There is absolutely no way you're going to get .308 Winchester velocities with only 28,760 PSI (.308 max is 62,000 PSI). However, replicating the ballistics of the .45-70 (28,000 PSI max) is no problem whatsoever with modern propellants.

HorseSoldier
December 6, 2008, 05:37 AM
Isn't 7.62x39 sort of in the middle of the 7mm-35 cal range you're talking about?

moooose102
December 6, 2008, 08:24 AM
i think that part of it has to do with these being primarily warfare weapons, and the geneva convention crud, and for military use, they dont really use long action semi's. civillian rifles really do not NEED to be the "ar" platform, as there are capacity regulations for semi auto rifles, and many civilians do not want the "ar" look. i do want an "ar" style gun, but i dont think they are necesarily the best rifle type for sporting purposes. i like wood stocks, i like to looks and feel of wood. i would like more capacity than the standard 4 round removable magazines though. a nice double stack 8 round mag would be fine with me.

SSN Vet
December 6, 2008, 11:18 AM
RyanM,

That was quite a response and makes a LOT of sense.

Has anybody out there ever seen an AR configured in .45-70?

R.W.Dale
December 6, 2008, 11:19 AM
Other than overall length, there's bolt face thrust. The AR can only take so much, I believe about 5,000 pounds. The bigger the case head, the lower the maximum pressure (pressure * area = force, thus larger area requires lower pressure for the same force). Something equal to .223 case head diameter (.377") can be up to 62,336 PSI, tops (darn metric conversions, NATO specs are in Pascals. SAAMI max pressure for .223 is 55,000 PSI, in comparison). 7.62x39mm case head diameter (.443") allows for 45,000 PSI. Both work out to the same amount of bolt thrust.

The WSSM parent case has a head diameter of .555", similar to the .50 Beowulf at .535". However, if we do some simple math, the max pressure for a WSSM case is about 28,760 PSI. There is absolutely no way you're going to get .308 Winchester velocities with only 28,760 PSI (.308 max is 62,000 PSI). However, replicating the ballistics of the .45-70 (28,000 PSI max) is no problem whatsoever with modern propellants.



You guy's seem to fail to grasp that there's now ar15 uppers that will handle 65K psi on a .555" case head

http://www.dtechsuperstore.com/guns1/gund.jpg

http://www.dtechsuperstore.com/WSSM%20page.htm

Ben Shepherd
December 6, 2008, 12:47 PM
Case capacity is another biggie. An AR has a straight mag well. This does not lend itself to cartridge designs that have the heavily tapered boddies needed for large powder capacity with a short length case. Unless you don't mind living with low round capacity magazines.

HorseSoldier
December 6, 2008, 01:32 PM
Has anybody out there ever seen an AR configured in .45-70?

I think the rimmed cartridge is a show stopper, or at least more trouble than manufacturers have bothered to sort out. 50 Beowulf, 499 Leitner-Wise (dead cartridge?), and 458 SOCOM all deliver 45-70ish ballistics, though. I'm not sure how Bushmaster's version of the big-bore AR cartridge compares (more mild loading if I'm not mistaken?).

wkoonce
December 6, 2008, 02:01 PM
I just starter a new thread about the Remington Predator RT-15. It is based on the AR-15 platform but has calibers in the size you are looking for. I wouldn't have started the new thread if I knew this one existed.
I am trying to find out any info or reviews for this gun. Anyone?

benEzra
December 6, 2008, 02:25 PM
i like wood stocks, i like to looks and feel of wood. i would like more capacity than the standard 4 round removable magazines though. a nice double stack 8 round mag would be fine with me.

Sounds like you want an M1 Garand. 8 round magazine, .30-06, straight wooden stock.

RyanM
December 6, 2008, 03:04 PM
You guy's seem to fail to grasp that there's now ar15 uppers that will handle 65K psi on a .555" case head

It sounds more like an AR-15/AR-10 hybrid upper that's specifically made for WSSMs. That's fine, if you don't mind being dependent on one single company, which could go out of business at any moment, to supply all your spare upper and BCG parts. For something that just requires a barrel, bolt, and magazine swap, though, you're limited to about 29,000 PSI and 2.240" OAL.

Build a new upper from scratch, and you can have an AR-15 that will fire .50 BMG. It's been done a bunch. But that ain't a bolt and barrel swap, either.

gvnwst
December 6, 2008, 06:39 PM
Krochus

Seems like what you are talking about is Noo's 30PPC cartridge...You may remember that from the 30RAR thread. If only the 30RAR had better ballistics........

jpwilly
December 6, 2008, 07:09 PM
I think 6.8 SPC is well rounded enough for the standard AR-15 rifle. As for me I just went and got a DPMS LR-308 AP4...problem solved!

browningguy
December 6, 2008, 07:51 PM
I think the short answer is that no one wants them. If there was a market for medium bore AR's someone would try to make them.

To be honest case capacity, bullet length and feeding issues do limit you with the platform. I have .223, 6x45 and .50 Beowulf AR's, and if I wanted something else it would be a 6.5 Grendel. I can't imaging getting reasonable performance (2600-2800 fps) out of a .338 or .375 load with 200 or 275 gr. bullets, if you want a short range thumper get the .450 or the .50. But you are not going to get .338 winny performance out of an AR-15 platform, just not designed for it.

gvnwst
December 6, 2008, 07:57 PM
he never said magnum, just 300 savage/7x57 type ballistics. Only a necked up 6.5g or WSSM case can do that....

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