Subsonic 8mm AR-15 Cartridge

[drinksgin (deceased)]

Oh me!
That sounds like a government bureau!

[22hornet]

Well, as you may remember, I fooled around a bit with this case/bullet combo.
I even phoned you about it IIRC.
 
(Here goes,...)
If I were you, I would shorten the case. By at least the neck, and maybe even the shoulder.
The reason(s) being, are:
You don't need the room (for powder),
More meat/thickness in the finished "neck",
Less seating depth required for the HFC bullet.
 

Going with this Paul, would a 8mm .222 be a sound idea? The longer neck would give better support to the 8mm projectile.
 
Myra Sports here at Broken Hill, (now past into histroy) made a series of cartridges on the .222 case. .227, .243, .257 and .308. An 8mm version would certainly "work".

[gitano]

Actually, 22hornet, that's the case that SSK Industries chose for their Whisper series. It would indeed be a good choice. The only down-side I can see is the relative availability of brass. At my last range session, I picked up 400+ pieces of .223 Rem brass. 400+ cases for free is tough to overlook.

That said, should the .223-based cartridge become problematic, the .222 would be high on the list of alternatives.

Paul

[22hornet]

Actually, 22hornet, that's the case that SSK Industries chose for their Whisper series.  
Paul

I thought the Whisper series were based upon the .221 Fireball not the .222 Remington?

[gitano]

You're right. I get that wrong all the time.

Paul

[j0e_bl0ggs (deceased)]

The furball itself is a derivative of the 222.

[gitano]

The neck reamer came in the mail yesterday. Took a week to get the reamer in hand and after setup, took all of 30 seconds, maybe, to ream new neck. Then I made a resizing die. Worked just like I knew what I was doing. At that point, I had pretty high hopes. However, there was more 'learning' in my future.

There are three problems:
1) Heaspace,
2) Neck tension, and
3) Feeding.

Feeding and neck tension are 'fixable'. Headspace is a bit more of a challenge.

The fundamental issue with headspace is auto feeding from the clip. There is essentially nothing to headspace on. The shoulder is practically non-existent and headspacing on the mouth of the cartridge is "out" because of the thinness of the brass at the mouth. What that means, is that as the cartridge is forced into the chamber by the bolt, there is nothing to stop its forward movement so that the head can be forced into the boltface. Kidding aside, a "magnum belt" would be perfect for this application. I am giving that real consideration. Drinksgin knows exactly how to accomplish this belt.

There is considerable irony in this. First, I am the most vociferous detractor of the issue of "headspace" that I know of. As many will recall, I am usually quite ready to romp on the 'boogey man' of headspace. However in my defense, I am romping on the DANGER boogey man, not the "precision" boogey man. Second, I don't think much of "magnum" belts either. But again in my defense, my lack of 'respect' for "magnums" (and their belts) is that the term "magnum" is far more significant as a marketing PLOY than it is an informative descriptor of a cartridge. By the way, and for the information of those that might not know, ALL belted magnums headspace on the belt. The reality is that the belt was always for headspacing, NOT to "magnumize" the case.

The neck tension issue is relatively easily resolved. Because of the thinness of the brass at the case's mouth - now about 0.010 to 0.011 inches - the grip on a relatively slippery cast lead bullet it a little weak. Grip is easily increased by reducing the diameter of the neck in the resizing die.

The existing neck grip would be fine if it weren't for the feeding issue. I was speaking with Jamie.270 about this cartridge and mentioned that so far I had only fed one cartridge at a time from the clip, and I KNEW that feeding from the clip with more than one cartridge in it would most certainly be different. It was. It is, because feeding from one side of the clip is different from the feeding from the other side. The issue is that the broad nose on the bullet is hitting the leading edge of the barrel extension. Here are a couple of pictures:


and


As you can see, there are two "feed ramps" in the leading edge of the barrel extension. Because there is no scale, you may not be able to see that those ramps are sized appropriately for the tip of a "pointy" bullet. The cast bullets I am using are not "pointy" by any stretch. So what happens is that the bullet noses are not only too large (meplat too big), but they are also not perfectly aligned with the ramp due to the larger neck on the cartridge. The clip makes has "bumps and wrinkles and bulges" that position the cartridge for feeding. One of those 'bumps' works on the neck and shoulder to push the point of the bullet toward the center. Having no neck, this cartridge doesn't get pushed toward the center. Coupled with the larger meplat, the nose of the bullet hits the feed ramp.

That in itself would be sufficient to warrant "adjustment" to the feed ramp(s). However, add a weak neck grip, and what you get is the bullet being shoved into the case and the neck getting rammed into the edge of the barrel extension. That in turn wrinkles the edge of the mouth.

Now, before Jamie.270 suggests that I shorten the .223 case down to where there's more "meat" to facilitate greater neck tension, let me say that that is the FIRST thing I did. Unfortunately, cutting the case off at the top of the shoulder does not  provide any more "meat" - wall thickness. It's still between 0.010 and 0.011 inches in thickness. I don't want to go much farther down the case.

And in fact, it isn't necessary. The entire issue is resolved by grinding the feed ramps out to larger diameter, or even making just one 'large' feed ramp. I was anticipating having to do this anyway. I have seen both done. The single, large ramp was for large diameter cartridges that "single-stack" in the clip. Widening but keeping two ramps was for somewhat larger bullets. I'll start with widening the two ramps "outboard" as that's where the 8mm bullets are catching.

This of course will mitigate the neck tension issue as well, even though I intend to increase neck tension by reducing the ID of the neck of the resizing die.

The headspace issue is a bigger problem. I really don't know of any way to solve it without adding a "belt". It doesn't need to be much, just enough to positively stop the cartridge's progression into the chamber so the bolt can grab the rim and hold the primer against the face. Adding a belt will most certainly be a real PAIN, but it's doable. The alternative is to go to a different cartridge. Either the x33 case (7.92 Kurz) or the x39 case of the 7.62x39.

I don't like changing to those cases. Both require different bolts to accommodate the larger heads. That in turn means that if I want to go from supersonic mode to subsonic mode, not only do I have to change the barrel, I also have to change the bolt carriage group (BCG). Changing the BCG is actually easier than changing the barrel, but it's still MORE to do and MORE to carry, and therefore more to LOSE while you're in "the woods".

A belted "magnum" .223 case. Hmm.... Probably could be manipulated into a real seller on that note alone. Imaging how cool it would be to have a BELTED MAGNUM on your AR-15.

Paul

[gitano]

I forgot to show you the "final" - at least at this stage of the development - look of the cartridge. Here are some pics:


And


Not great pictures because they were taken with my phone, but I wanted to get pics before I shot them.

What I want to point out is the differences in the points. You have to look closely, but the one on the left in the upper picture, and the one on the right in the lower, is "pointier". That's because I ran it into the point-forming swaging die. Doing so not only 'points' it a little bit, but also removes the gas-check heel. At these velocities, I not too worried about leading. I'll cross that bridge if I start seeing evidence of leading. I'm not averse to using GCs, in fact, I like them, but with the thinness of the necks, GCs present new 'issues'. The unswaged tip does not have a GC attached.

Not too much to report on the shooting. I changed to Unique powder and a QL-estimaed MV of 950 f/s. Actual MVs were 966 and 988. I didn't put the actual measured case capacities into QL so estimates could be off because of that.

Paul

[drinksgin (deceased)]

I still gag at "Magnum", the only "Magnum" I know of is a 1.5 L bottle of wine!
I admit, Weatherby has some that might come close to holding a "Magnum", but not quite.
Surely you would not use my old trick of shrinking a section of case on a larger case.
That was an expedient I used on getting some .303 Savage cases from .30-30 cases.
I no longer do that, of course, as the .220 Swift case makes fine cases for it with a bit of trimming and resizing.
This exercise is a perfect example of Murphy's Law, if it could ,it has!

[gitano]

That's precisely to what I refer, Don. Donnelly does the same thing in his book.

I'm looking for better solutions. One should keep in mind that I'm in a "hurry". I wanted this thing to be "ready" before the end of the month. If I have to start all over with another parent case, well... I'll be STARTING ALL OVER.

I went looking for a ".308" bolt for an AR-15. A preliminary look was fruitless. Plenty of 7.62x39 bolts, of which I already have two. Of course, the cartridge I WANT to use is the 7.92 Kurz, which of course has the .308 (0.473" nominal) head and rim. The 7.62x39 head/rim is nominally 0.411". The Beowulf's (.50 cal on AR-15) rim is nominally 0.440".

I would modify a 7.62x39 bolt, but these bolt faces are hardened, so I would have to: 1) anneal, 2)  machine, and then 3) re-harden. Heckuva lot easier to write than do.

At the moment, I am looking at using a .222 Rem Mag/.204 Ruger case and cutting it off in HOPES that there would be enough 'meat' on THAT case to headspace (stop the forward motion), of the case sufficiently to allow the extractor to grab the case's rim. Thereby ensuring ignition and extraction.

I'll keep you posted.

Paul

[Jamie.270]

I know you need it fast, and I know that you're lovin' the price of the .223 cases you picked up at the range,...
But, you may need to pick up a box/bag of .223 cylindrical (unfinished, no shoulder/neck formed) brass.
Buffalo Arms has some:
http://www.buffaloarms.com/Buffalo_Arms_Reloading_Brass_it-156918.aspx?PROD=156918

You might give them a call and find out what the neck thickness is.

[gitano]

First, THANKS!

Second, j0e_bl0ggs and I were just talking about this! I told him I had never seen "basic" cartridges in calibers smaller than .375. Wrong again!

Third, Did you see the prices! A buck a piece! For something they have to do LESS manufacturing on! I may have to 'bite the bullet and get some anyway.

Thanks again,
Paul

[gitano]

Just got off the phone with Buffalo Arms and asked them to mic the wall. Only 0.011". :(If it had been 12 thousandths I might have considered it. Wish it were at least 13.

This project is on hold for the next three days. I have some preparation for winter I HAVE to do around the house, I HAVE to get the AR-10 chamber cut with the RENTED .284 Win reamer, and I HAVE to go fishing with Jim again before the water gets hard.

Paul

[Jamie.270]

Yeah, I noticed the price,...  
They have to pay that guy to walk all the way out to the line, and grab them off the conveyor to the shoulder-forming machine, and then he has to count them, and then,...

It's redonkulous I know.
But sometimes, ya just gotta do what ya just,................

Sorry, that was a bust.

[drinksgin (deceased)]

A suggestion, .357 max. cases have a .379 base and are 41mm long, only 4 mm shorter than .223 brass, they are straight to start with and are easy to work with, a quick pass in the lathe to remove the rim and reshape the extractor groove and you may have a workable case with a thicker mouth.
You already have a quickload workup on 1200 fps loads you did for me with my 8x41R project and if you do not have a die one is easy to make.
Something to think about.
I believe the cases are in stock and I KNOW they are not $1 each!

Oh, if they are out of stock, I shall send a few along for you to play with.

It appears every dealer is out of stock, so I shall get a few to you by mail.