Another member and I have briefly discussed by PM the idea of an 8mm on the AR15 platform. We started by talking about the 7.92x33 Kurtz. Since it's a factory load, then that avoids the wildcat. However it's such an obscure cartridge that it's practically a wildcat and requires a special custom reamer and all the tools for handloading to really get the best out of it if used in the AR.

It occured to me that maybe taking the 458 SOCOM brass and necking it down to 8mm would result in something really special - low pressure to suit the platform, yet real ballistics. I don't have software to compute the possibilities, say with 150gr and 170 gr bullets. It would be interesting to run the numbers.

Two of the significant reasons I think this will work is bolt face and magazines. The AR15 bolt with the proper face already exists, and I'm thinking that the std 223 mags are used to feed the 458 SOCOM, which would also work for the 8mm SOCOM. I like wildcats that are as simple as possible, with minimum alterations to the platform for feeding, etc. as possible, and readily available brass requiring only neck work with no other case forming necessary.

KB

I think you would have pressure issues with so large a case necking to 8mm
My suggestion is getting the 30 RAR platform and neck up to 8mm and you should get it to work with existing mags. Or start with the 450 bushmaster and neck it to 8mm with more flexibility.

So far the 30 RAR brass is a scarce item, and it has a unique case head size.

I didn' think about the 450 bushmaster. Necked down, it would headspace on the shoulder.

What is the size of the case head of the 450 bushmaster?

Edited: OK, I looked it up, and it seems that the 450 Bushmaster case is a blown out and shortened 284 case, with the rebated rim.

KB

I show the Bushmaster as .473 and the socom as .471

Interesting idea.

Use the 8mm rem mag reamer to the depth of about 1.6" and use either RAR, bushmaster or 284 brass.
Would be a great round.
I thought about this for a 35 cal but would work just as good with an 8mm.
The case capacity, bullet diameter and not too much bottle neck design should be good for a semi auto AR 15 keeping pressures at say 45k PSI IMHO. Another option is one similar to the 35 Gremlin and just neck up 6.5 Grendel brass. The 35 Gremlin gets 180s @ 2,350 fps. The 8-284 short should get you all that and more.

8mm Kabluewy. I'm flattered.

M.C.
I believe the max pressure should be significantly under 50,000 psi to be suitable for the AR15, or whatever works. That's beyond my knowledge, but it's very relevant.

Thanks for the numbers and the drawing. Given the case capacity and the correct safe max pressure, can the ballistic software available predict the velocity? I'm predicting something very acceptable, and perhaps surprising. It's something one wouldn't build in advance of some reasonable expectation of the result. I crudely estimate 2400 fps ++ with a 150 gr bullet, and 2300 ++ with a 170 gr bullet, maybe a lot more. The reasons I say that is because as I remember I can get about 2100 fps out of a 150gr bullet from the 7.62x39, and this 8mm Kabob has a lot more powder capacity, assuming it can be run at the same pressure levels.

Remember, it has to work well (perfect) in the AR15, with existing bolts, and existing magazines. No special mods at all, or the deal is not viable.

Also, I can think of no other rifle platform in which this cartridge is applicable, other than the AR15. It's a specific cartridge for a specific platform.

Boomie,
If I did a project like this, it would be with a custom reamer, and specific drawings of the cartridge in advance, with reloading dies made to size perfectly for the chamber.

KB

I would use the Bushmaster brass because it is optimized for larger capacity.
Purchase a 450 Bushmaster and use the same mags. Do a barrel swap and shoot the 450 Bushmaster.
Think about what bullets you would use and the neck tension area. Need to calculate magazine length, bullet protrusion and case length. Maybe a long neck from 1.2" to 1.6". 15 thou body taper and 20 degree shoulders for easy feeding and extraction.

quote:

Originally posted by Kabluewy:
8mm Kabluewy. I'm flattered.

M.C.
I believe the max pressure should be significantly under 50,000 psi to be suitable for the AR15, or whatever works. That's beyond my knowledge, but it's very relevant.

Thanks for the numbers and the drawing. Given the case capacity and the correct safe max pressure, can the ballistic software available predict the velocity? I'm predicting something very acceptable, and perhaps surprising. It's something one wouldn't build in advance of some reasonable expectation of the result. I crudely estimate 2400 fps ++ with a 150 gr bullet, and 2300 ++ with a 170 gr bullet, maybe a lot more.

Remember, it has to work well (perfect) in the AR15, with existing bolts, and existing magazines. No special mods at all, or the deal is not viable.

Also, I can think of no other rifle platform in which this cartridge is applicable, other than the AR15. It's a specific cartridge for a specific platform.

Boomie,
If I did a project like this, it would be with a custom reamer, and specific drawings of the cartridge in advance, with reloading dies made to size perfectly for the chamber.

KB

Kabluewy,

Sorry that’s just the pressure of the parent cartridge I used (284 Win). I was mainly trying to show you the case volume. But I have a feeling, knowing how hard an AR slams the shoulders are all wrong.

boom stick,

What do you think the idea shoulder angle would be on a cartridge that thick in an AR platform? 50 degrees or a little less? The drawing about is just a transformed 284 but I can modify it.

Maybe a long neck from 1.2" to 1.6". 15 thou body taper and 20 degree shoulders for easy feeding and extraction.

quote:

Originally posted by boom stick:
Think about what bullets you would use and the neck tension area. Need to calculate magazine length, bullet protrusion and case length. Maybe a long neck from 1.4" to 1.6". 15 thou body taper and 20 degree shoulders for easy feeding and extraction.

Yes, you are onto it. I think the OAL is 2.26, so to get the case right, we back up from the OAL. That might require some trimming, but the least the better. Either way, the 450 brass is long enough, as is or trimmed. It will depend on the seating depth of the bullet, and how much neck is needed.

These are relatively easy problems to resolve with a wildcat like this. It could be a lot more complicated.

The only deal breaker is performance. The question is whether it's worth doing. Of course the only major cost, over SAAMI cartridges, is the reamer and dies. In the big scheme of things, it ain't that much.

I have a question: what other cartridge (well) suitable for the AR15 shoots a 150gr bullet at 2400 to 2500 fps? That's assuming that this 8mm kabob will do that.

KB

Knocks a little out of the case volume.

Here are some pictures of 8mm bullets that I consider appropriate. Notice how short they are:

150gr Hornady:


170gr Hornady:


150 gr Speer:


170gr Speer:


150gr Sierra:


To get it right, I think the neck should be no longer than need be to seat the 150gr bullets to the base of the neck. That's plenty of tension. If longer bullets are used, then just seat them below the juncture of the neck with the shoulder. The case length will depend on how the OAL turns out, with the 150 gr seated as described. If too long, then trim the brass back till the OAL is correct.

The neck will be a lot shorter than the picture shows, if the bullets are seated as described. I'm considering the 150gr bullet as the ideal weight for this setup, with full power loads, but certainly heavier bullets can be used, even 220gr subsonic.

KB

quote:

I have a question: what other cartridge (well) suitable for the AR15 shoots a 150gr bullet at 2400 to 2500 fps? That's assuming that this 8mm kabob will do that.

I wonder why you limit yourself to the AR-15? If you want a big caliber move to the AR-10 platform.

Kabluewy, Boom Stick:

An 8mm based on 284 brass, cut-down 8 Rem Mag?

I've done it. Read about it here:

http://www.thehunterslife.com/...owthread.php?t=15105

quote:

Originally posted by MickinColo:
I wonder why you limit yourself to the AR-15? If you want a big caliber move to the AR-10 platform.

The way I see it, as with all wildcats, there is no point in doing it just for the sake of experiment. It's only worth doing if it fills a niche. So, IMO there is no point of it on the AR10 platform, for one example there's the 338 Federal, which will out perform this 8mm wildcat any way you look at it. There is no problem finding cartridges that perform well on the larger platform.

So, the AR15, being a smaller and lighter package, and very popular, is the right home for a cartridge like this. I suppose it sorta competes with the 30 AR. Yet I'm thinking it will perform on or close to that level, with less pressure, and less bolt thrust, with the standard case head size.

Besides, when all is considered, if designed for optimal performance within the constraints necessary to use in the standard AR15 receivers, that sorta keeps the parameters in check. There are just too many variables, if other platforms are deemed suitable, and IMO no niche not already covered by the 8x57, for example.

KB

quote:

Originally posted by Kabluewy:

quote:

Originally posted by MickinColo:
I wonder why you limit yourself to the AR-15? If you want a big caliber move to the AR-10 platform.

The way I see it, as with all wildcats, there is no point in doing it just for the sake of experiment. It's only worth doing if it fills a niche. So, IMO there is no point of it on the AR10 platform, for one example there's the 338 Federal, which will out perform this 8mm wildcat any way you look at it. There is no problem finding cartridges that perform well on the larger platform.

So, the AR15, being a smaller and lighter package, and very popular, is the right home for a cartridge like this. I suppose it sorta competes with the 30 AR. Yet I'm thinking it will perform on or close to that level, with less pressure, and less bolt thrust, with the standard case head size.

KB

From my point of view,,, I see nothing in it. Interesting but not exciting.

quote:

Originally posted by MickinColo:
From my point of view,,, I see nothing in it. Interesting but not exciting.

I can understand that. I'm not being rude either, but agreeing with you, or at least trying to.

I suppose it depends on what a guy is satisfied with in the AR15. If that's a 223 --period--, then I surely see your point. Apparantly there is a search for more out of the AR15, hence the 458s, 500s, 450s, 30 AR, perhaps some of the SS mags, etc.

I'm just doing a mental excercise delving to that thought arena, considering what would actually work, and what wouldn't.

After all, a cartridge in a short and light semi auto carbine, giving 2400-2500 fps with a 150gr bullet, and perhaps 2300-2400 with a 170gr bullet, without straining the platform, would capture my interest farely well.

If the obvious solution is to go to the AR 10 types of rifles, in 308, then so be it. I've seen a lot of other wildcat threads here that IMO are a lot more "wild" than this one.

KB

And I don’t mind making drawings of those ideas. Hell, have nothing better to do before I have to go to bed and get up in the morning and go to work.

And one heck of a good drawing it is. Thanks.

It's sort of my evening entertainment too, while sipping on a relaxing beverage.

KB

Well have the neck go from 1.2" to 1.525" to fit those bullets to a maximum oal of 2.3"

quote:

Originally posted by Nelsdou:
Kabluewy, Boom Stick:

An 8mm based on 284 brass, cut-down 8 Rem Mag?

I've done it. Read about it here:

Can you show a drawing and furnish ballistics info.
KB, if my 7.62x41 can get 2300 fps w/ a 150 grain bullet than this cartridge should exceed 2400 fps. with the same weight bullet.That is if the neck length is no longer than .320". roger

Well, the 8mm is still in the queue of both QD and QL so let me make a few adjustments. Boom Stick’s new neck length (.325) and Bartsche’s 150-grain bullet and see what QL thinks of it.

2516 fps predicted/computed by the software. That's great.

I'm glad my prediction wasn't far off. Frankly, I am impressed with all of you guy's analysis of this. Obviously you study this stuff and have the software. I just have to do some educated guessing, which is fun, but not good enough for something like this if it is actually taken further, to a shooting barrel.

As said all along, obviously the 8mm wildcat cartridge can't compete with the 308 or the 338 Federal, but also obviously those cartridges can't be used in the AR15.

KB

All those numbers look good.
I think the bushmaster case may give more volume though. 160s @ 2,500 in the low 40s PSI seems a potent 250 yard combo in an AR 15. It would be similar performance to the 30 RAR but a 8mm version.

Think the taper is good, case length good for nominal 8mm bullets, maybe slightly shallower shoulders say 18 to 20 degrees but looks like as good as that's going to get. Any more case capacity and you will run into other problems.

Low 40s psi seems especially appealing, if it's really possible, and still get this level of performance.

Just to think about some comparisons, the 6.5 Grendel produces about it's best at 1700 ft lbs with a 123 gr bullet at 2500 fps. The 30-30 as I recall gets around 1800 ft lbs with a 150gr. This 8mm AR at 2082 ft lbs is worthy, IMO.

It's only money. PTG for the reamer, Redding for the dies, ???? for the barrel. In about three or four months, plug and play, yippi-ky-aye.

KB

quote:

Originally posted by Kabluewy:
The 30-30 as I recall gets around 1800 ft lbs with a 150gr. This 8mm AR at 2082 ft lbs is worthy, IMO.KB

The 30-30 gets 2450 fps.( 1981 ft# ) when properly loaded at 40,000 psi.
It's still no slouch. roger

Roger,
I did the numbers again on the 30-30. I went to Hodgdon's load data site, picked the top loads and velocity for the 150gr and 170gr bullets. Then I went to Hornady's ballistic calculator. The numbers are:

150gr at 2390 fps = 1902 ME
170gr at 2138 fps = 1725 ME

Sure you can load them hotter, but I'm using published data, which is the best I've got. I've generally always considered the 30-30 about the prefect standard of a deer or hog cartridge, to measure others by. As said a few years ago, the 30-30 had killed more deer than all others combined (in the U.S.). I'm relatively sure that's not true anymore, but it's still a "deer" cartridge.

I'm trying to compare apples and apples, rather than what can be done by pushing the limits of a particular cartridge. Also for consideration, I'm sure that PSI isn't the only factor in a suitable cartridge for the AR15. For example, I don't know how important bolt thrust is, or how to measure it. Frankly, I don't see how bolt thrust can be a problem with this cartridge.

Anyway, PSI alone may not be the whole story. The 223 generates a lot of pressure, and as I recall the Grendel runs about 50,000 psi. This is a delima to resolve by someone smarter than I am on this subject. I can tell such things as will it feed, and most of the details of how to handload for it, but the limits of the AR15 receiver is beyond my skill, but it's a critical piece of info.

If that pressure level turns out OK with this 8mm, all things considered, then that's gonna produce good results ballistically. Even lower pressure would still produce good ballistics. Say 150gr bullet at 2400fps, out of a 7 lb, 16"-18" semi-auto carbine. Imagine that. This generation's 30-30 equivilent, tactical deer rifle.

This cartridge should favor the relatively fast rifle powders, which is the perfect combo for carbine barrels.

KB

I can see this case being good for 338 and 35 calibers too.

quote:

Originally posted by boom stick:
I can see this case being good for 338 and 35 calibers too.

That really opens up the possibilities. I agree. There are a long list of factors that make this work. I may list them later, but for now, considering the .323 and .338 and .358 bullets, they all have something in common. There is a good selection of light for caliber rifle type bullets in all three. The main thing, IMO, is that the bullets available are inexpensive, and not limited to just a couple, but the selection is good, with prospects of staying that way. Also, the bullets I'm talking about are designed to open up nicely at the velocities obtainable with this cartridge, and IMO they are just right, not too hard - not too soft. I think this case would duplicate the 35 Rem ballistics handily.

The only down side that I see with this is that you can't go to Bubba's Hardware store in Smallsville and buy factory ammo. And you can't use range pick-up brass. Bummer.

I thought I had sworn off wildcats, with the last one I had built. Truthfully though, I have spent the amount of money it would take to make this one happen on lesser wildcat cartridges. I say lesser, because IMO, they filled a smaller niche, and particularly since they filled a niche that I'm not as interested in now as I was back then.

Right now, if I had to give a report on this, to my best estimate, I believe it would work very well indeed. However, with the tools I have, it would definately be an experiment, but a well calculated one. For one thing, by the time (actually before) the reamer was done, I would have an accurate drawing, the specs of which having been reviewed by those I considerd experts. The reamer wouldn't cost much more if any than a standard reamer. Actually, I would have the reamer maker colaborate with the reloading die maker to get the exact correct dies to match the chamber. It's not a big problem, since I've done that before. These dies may cost more than normal custom dies because this to my knowledge hasn't been done before. They have to make the tools to cut the dies, thus the second set of dies are much less expensive. Also most likely some form die or dies may be needed, and a neck reamer. The load development would be a bit tricky, but certainly not a huge problem. IMO, it would be less tricky if for a bolt action rifle, but of course the point of all this is for the AR 15.

I suppose a guy could set up a short action bolt rifle for load development. After all, it does have a standard bolt face. Hummmmm - I think I have such an action, looking for a job. After all, what are push feeds for? I may not even have to change the follower to get it to feed right, but even if I did have to go with a short magnum follower, it's no big deal. Push feed actions are forgiving that way.

KB

My 8mm wildcat based on a cutdown 8mm Rem Mag die and 284 case head. I don't have a QL drawing but here is the reamer:



It is a bit longer than what is discussed above due to the way the 284 diameter brass matches up with the Rem Mag, but the goal was to use cut down, not custom dies. No intention of using it in anything other than a bolt action rifle.

I've put two loads over the Chrony. 24" barrel. Estimated pressure from QL is 52 ksi.

150 Hornady
2.650 OAL
51.2g aa2520
3001 fps

185 Rem
2.716 OAL
47.2g aa2520
2624 fps

So far the brass is holding up well to multiple loads and I get by with only a partial resize to set neck tension.

quote:

Originally posted by Kabluewy:
Roger,
I did the numbers again on the 30-30. I went to Hodgdon's load data site, picked the top loads and velocity for the 150gr and 170gr bullets. Then I went to Hornady's ballistic calculator. The numbers are:

150gr at 2390 fps = 1902 ME
170gr at 2138 fps = 1725 ME

Sure you can load them hotter, but I'm using published data, which is the best I've got. I've generally always considered the 30-30 about the prefect standard of a deer or hog cartridge, to measure others by. . KB

KB, this data was published in Modern Reloading second addition by Richard Lee. ***150 grain bullet 36 grains Reloader 15. 2450 fps., 40,600 psi. This book is a composite of many other reloading manuals. It may not be the greatest but it ain't all bad.
The7.62 X 41 was designed to duplicate the 30-30 and it does but at elivated pressures. Your potential cartridge will do it at 40,000 psi., because of the larger case volume.Personally it's going to be a barrel saver and a worthwhile project.
Other than the .303 Brit. I think the 30-30 has killed more game than any other cartridge. Really hard to get stats ,however. roger

The 323 Kabluewy has a ring to it

Roger,

Any input from you is always welcome, and encouraging. I'm not sure, it's intuition at this point, but I think the psi in the low 40's is a good thing, and perhaps a big deal, when considering the AR 15 and this fat cartridge.

I checked my push feed Win 70 short action, and I'm pretty sure it will feed the rebated rim case with the .500 body just fine, and of course the OAL works in the magazine too. It will make a good test platform, and will be fun to shoot also.

Another thing I thought about, meanwhile, is that I'm pretty sure that a reamer maker can make a chamber reamer with a replacable pilot to accomodate all three calibers, .323, .338. and .358, which does not cut the neck. Together with the chamber reamer, three additional neck reamers will be necessary. You see my point, I'm sure. I have the tools to switch barrels on the M70 action. Switching uppers on the AR 15 is no big deal. However, the reamer set will probably be the least expensive part of this. It's the dies that will cost a bunch.

This thing could grow completely out of bounds. Suddendly, not only am I talking about another wildcat, but I'm talking about a three barrel/upper project on two different actions. Geeez. You guys are a very bad influence.

I think perhaps I should check my commitment reservoir, and see if it has enough oil.

KB

quote:

Originally posted by boom stick:
The 323 Kabluewy has a ring to it

Thanks for the input Boomie.

Question: This wildcat brass can be formed from 450 Bushmaster as well as 6.5x284 and 284W brass, right?

KB

I think the bushmaster brass should be measured for case capacity, case head and rim diameter compared to 284 brass. If using 284 specs than use any 284 variants. The bushmaster would be easy to convert and probably cheaper brass.

quote:

I think the bushmaster brass should be measured for case capacity, case head and rim diameter compared to 284 brass. If using 284 specs than use any 284 variants.

I have both CIP and SAMMI drawings for the 284 Winchester.

The only drawing I have for the Bushmaster that can be used in QL is in CIP format. When I tried to use the Bushmaster for this post the metrics would blow up for some reason. Here is how they compare in QD.

Interesting. Under case wall thickness, I think there is a typo under "Inner Radius at Web" for one or the other. They are probably close to the same.

Note the "Maximum Force on Head" at 6191# for the 450 and 9745# for the 284. Apparantly that's a function of pressure, rather than the size of the slug.

The big difference is in the MAP, and other pressure specs.

I think it's practically the same brass in the critical parts, as far as measurments are concerned. Since they run at greatly different MAPs, I wonder if there is a difference in the metal toughness or hardness in the way it's made?

Somewhere I got the idea that the 30 AR had a different rim diameter than the 450 or the 284, but not so according to this article:

http://bulletin.accurateshoote...ington-ar-cartridge/

Also see:
http://shootingwithhobie.blogs...30-remington-ar.html



I found where I got the idea of a different rim diameter: http://en.wikipedia.org/wiki/.30_Remington_AR

http://www.americanrifleman.or...ing-30-remington-ar/

I have been wondering if there is a lurking reason why Rem went with a different rim size, and if so what was the reason. It looks like Remington has stolen our idea, with a few small changes.

KB

Everything I have shows the 30Rem AR as having a .492 rim.