In another thread - http://thehunterslife.com/forums/showthread.php?t=17116 (see post #19) - I point out that I am abandoning for the foreseeable future all efforts at making a subsonic round for the AR-10, and constraining that use to the AR-15 platform. Also, I am focused on the 8mm caliber because I have an 'armload' of old milsurp 8mm barrels 'laying around'. Given that, I have decided on the 8x223 Remington.

Having made that decision, I asked Pacific Too & Gauge (PTG) if they had a drawing of an 8x223, and they responded "No", so they sent me an "editable" drawing of a .223. I modified that to what I thought were reasonable and appropriate dimensions and sent it back with the request that Dave Kiff - the proprietor - have look at my dimensions and make sure there wasn't anything 'funny' with respect to reamer fabrication or function.

Instead, I got back drawings of two "new" 8mm cartridges suitable for use in the AR-15. The first one is the "8mm Blackout". The name gives the origin away. It is simply the .300 Blackout necked up to 8mm. This cartridge would make getting/making brass easy, it'd still be a "Blackout". I don't want a "cool" (popular with all the 20-somethings), cartridge in a rifle I MAKE. Here's the drawing:


The second was the "8mm Commando". This IS a cartridge I could own. If you look at the title panel you will see "British Infentry" beneath the 8mm Commando name. Ignoring the misspelling, I don't know whether this is something the British Gov't is considering or just the pipe-dream of a wannabe. Here's the drawing:


All of that considered, I decided to just make my own 8x223 - sort of. I started out with the intent of making my own single-flute reamer. However, 1) I hate to have to make something if I have a 'suitable substitute' available, and 2) I haven't had much success with making my own reamers. The reasons why are not mysteries, but nonetheless, I didn't want to spend a lot of time in fabrication and have YET ANOTHER one not work.

As I was getting the drill rod indexed, I thought I might look through all of my reamers and see what I had in hand that might allow me to forgo making a reamer. AHA! I have a reamer for a .17 Predator. This is a cartridge that is a .223 Remington blown out to almost straight body, 40 degree shoulder, and necked down to .17. Other than going the wrong direction in neck size, this reamer would work. The neck wasn't an issue. That could be reamed separately. Making a reamer was no longer necessary. That simple substitution saved AT LEAST 6 hours of shop time. Probably more like 10 or 12. Now I could focus on the barrel.

I started with a '38 Turk take-off. First was desoldering the front and rear sights. Next, the breech was cut off at about the point where the 8x57 shoulder is, then cut the muzzle off 22 inches in front of that. (When I dropped an 8mm bullet down the muzzle, it dropped in 2", and the muzzle hadn't been reamed!) Next I trued the OD of the chamber area, cut the diameter of the stub that would be threaded into the barrel extension, and cut the 3/4-16 threads 0.625" along that shank. The barrel extension fit with the proper 0.500" of "headspace" between the barrel breech and the breech end of the barrel extension. Now to chambering.

The neck was a bit of an issue. With a bullet diameter of 0.323" and neck walls somewhere in the vicinity of 0.015", I needed a chamber neck diameter of about 0.353". 9mm is 0.354", and that would work fine, but I don't have a 9mm chucking reamer. Because I was necking UP, the neck walls would get a little thinner. In fact they went down to about 0.012". That meant I could get by with a chamber neck diameter of about 0.348". Unfortunately, there aren't any non-custom reamers with that diameter. The next Imperial size down from 9mm is 11/32nds (0.34375"). That, was gonna be a bit small. However, I was "on a mission" by now.

I decided to use the 11/32nds reamer to cut the chamber neck, and shave the neck walls down to a thickness that would give me at least 0.001" of expansion. (I have a Forster neck "lathe".) It was going to be a close shave (pun intended), but, like I said, I was on a mission to get this DONE.

The importance of the "order of operations" cannot be overstated. When one is "making do" with the tools "in hand", it's difficult to get the order of operations right the first time. Especially when one is as inexperienced as I am. While you can 'adjust' to getting the order of operations out of sync a little, it doesn't usually leave a satisfactory product. Especially to someone that prefers to do the best that they can.

The first 'pass' at all of this (6 hours of shop time) left a  chamber and barrel stub that I just wasn't happy with. The next day,  with the experience of the previous day in hand, I cut the stub off,  reindexed everything, and started over. Here is the proper 'order of operations':

1) Run 11/32nds reamer into barrel the proper distance for the chamber length to the mouth of the case. This cuts the neck, and reams most of the body of the chamber close to final dimension. That not only makes it easier on the actual chambering reamer, but helps keep it centered as well.
2) Cut chamber with chambering reamer - In this case, the .17 Predator - fine-tuning true headspace.
3) Profile stub for 3/4-16 threads getting both diameter and length of stub right. Length of threaded stub, as barrel extension indexes on stub shoulder, sets actual headspace.
4) Use 8mm "throating" reamer to cut throat and leade appropriate for 250-grain cast lead bullet seated to proper depth for fitting in AR-15 clip.

Voila' - an 8x223-chambered barrel for an AR-15. The proof is in the pudding as they say. It was time to test-fire. First I had to make some cases.

Because the shoulder on this case was more like snake hips than 'shoulder', the primary task was necking up to .323 from .224. I used the following dies:

1) .243 Win,
2) Hornady "universal" .25 caliber neck-sizing die,
3) 6.5x55, (.264)
4) .270 Win (.277)
5) 7x57, (.284)
6) .308 Win
7) 7.92x33 (.323)

I annealed only before starting. Unfortunately, when the case being resized doesn't fit in the body of the resizing die at least fairly close, the neck can get pushed to one side. This happens because the necks are not PERFECTLY symmetrical in thickness. When getting 'pushed around', the thinner, weaker side gives more and the neck ends up lop-sided. Not TOO big of a deal for testing because case would be fire-formed anyway, but unacceptable in 'production mode'.

After necking up, I used the Forster neck "lathe" to thin the neck walls so that the case just fit in the chamber with 'finger pressure'.

After the first case for necked up and the neck walls thinned, I used the "Blue Dot and Cream of Wheat" (http://thehunterslife.com/forums/showthread.php?t=14377), method of fire-forming. The first two attempts were fruitless. Not enough "oomph" to blow the case into the shape of the chamber. I decided that a bullet was needed to provide the necessary resistance so the case would be properly formed. For the third attempt I used a 125-grain Hornady. Worked like it was 'supposed to'.

Finally, I wanted to try the 250-grain bullet with the 1050 f/s MV charge calculated by QuickLOAD. QL wasn't designed to work with a system such as this, but I was hoping it would get close enough, then I could tweak charges using chronograph results to get the desired 1050 f/s MV. However, my greatest concern was for feeding from the clip. The issue of MV was irrelevant if I couldn't get the thing to feed from a clip.

(I'm going to digress a moment here and discuss terminology. There is of course a lot of 'heat' over the proper use of the term "magazine" vs "clip". I don't give a 'tinker's damm' about terminology AS LONG AS there isn't confusion about MEANING. I learned that there was a difference between "clip" and "magazine", and the difference was that a "clip" was the thing that fit IN a "magazine", and the "magazine" was the FIXED part of the firearm. Now I'm not going to get into a spitting match over this. As usual, I DON'T CARE what term is used as long as
there is clear understanding of what is meant. I think that separating "clip" and "magazine" into to "portable" and "fixed" makes sense, and that is how I intend to use the terms.)

I resized the neck so that it would hold a bullet, primed the case, charged it with about 6 grains of Blue Dot, seated the 250-grain bullet, put it in the clip, put the clip in the magazine, released the bolt, and the cartridge seated perfectly. :D

When I fired it, it was louder than I thought it 'should' be for a 1050 f/s MV load. However, I don't have much experience with "heavy" bullets and 1050 f/s MVs. I do have some experience with the 8mm Max - and that was not loud.

Here's a picture of the case after firing with the 250-grain bullet:


Chrono results tomorrow.

Paul

Ah... Now that's better.

I was thinking about why the fireforming wasn't working, and it occurred to me that I was necking up and THEN fireforming. I should have started with an unmodified .223 Rem case. So I did. Here's the result.


MUCH better outcome and WAY easier than going through all of the "necking up" steps.

:D

Of course it will need to have the neck walls thinned.

Paul

Snake hips is an exaggeration! I thought the .44-40 and .32 -20 cases had very little shoulder!
I have always understood that a clip either went into a magazine, ala Garand, or charged a magazine as so many military rifles use.
No big deal.

So... One always faces extra challenges when one wishes to 'plow my own furrow'. Such is certainly the case here. I'll skip most of them. One of significance is that once the necks are thinned to 0.009", they don't "resize" to a diameter that holds the 250- grain cast bullet. That's not exactly correct. What happens is that when the bullet WITH GAS CHECK is seated, the GAS CHECK enlarges the neck back to a diameter that won't hold onto the bullet in front of the gas check. Since the gas check drops below the neck/shoulder junction, the bullet drops into the case. I made a "work around".

The charge calculated by QL to produce a MV of 1050 f/s was 6.9 grains of BlueDot. Since I thought that might be a little 'fast', I decided to load three cartridges to 4.0, 5.0, and 6.0 grains, and see what the chrony told me.

It missed the first (4-grain) shot because I didn't have it set sensitive enough for a solid lead bullet. It got the second (5.0 grain) shot, but that shot blew off a shield I had for the chrony, so that was the only shot I got tested. So far. That shot clocked at 797 f/s.

I went back to QL and looked at the MV that a 5.0 grain charge was predicted to produce - 829 f/s. So... that's fairly close. Within 30 f/s out of 800. That's within 4%. All things considered, I think that's pretty good. Of course, that's a sample size of ONE!

Here's the workaround on the seating depth. Because the charges were below 50% of the case capacity, AND because I was using a "pistol" powder, I decided to put some filler in. Just enough to keep the powder against  the primer. When the issue of neck grab came up, I simply increased the filler (toilet paper) sufficiently that the bullet dropped into the case to a point that gave the proper OAL. I am quite confident that this doesn't effect internal ballistics much because BlueDot is VERY fast, and everything happens too quickly to cause any 'funny stuff'.

Anyway, it's a start. Oh yeah. The 4-grain charge wasn't TOO loud, but the 5-grain charge was definitely louder than I expected. Hearing protection would be appropriate for the 4-grain charge.

More when I have more.

Paul

Just a quick question,...
Do you plan to develop this cartridge to include Light(er) For Caliber bullets as well?
Or is this strictly for subsonic, HFC bullets?

I've learned the wisdom of "never say never", but my primary intent is HFC subsonic only. I'll shoot the ANVBs (and chrono them) out of it to see what there is to see, but the .223 Rem is tough to improve on in the AR-15.

Why do you ask?

Paul

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.

When I tried this, I cut the shoulder off, leaving pretty much a straight walled case, and had plenty of "neck" wall thickness (more than enough actually, but crimps would have been strong), and with the room offered in an AR mag, that left plenty of room for bullet, in terms of COAL.
In retrospect, mine may have been too short, but it still would have had no problem holding 5-7 grains of BlueDot, and you can skip the fireforming.

Just a thought.

Once the case is that short however, LFC (125gr) slugs become a bit of a challenge, without a spacer in the AR's mag.

And now you know,...
Why I asked!  :D

I think it's a very viable deal... :)

I can see this going somewhere in an AR-15, but like you said, I see no fit in the AR 10 platform. Just too sloppy to work with.

I bet you cuss the guy that got you into AR's, don't you?...Come on... At least every once in awhile. :D

That would be a great hog round.

I gotta say, RBB, I am deeply indebted to you for 'forcing' me to consider a "black" semi-auto rifle. I wouldn't have given them a second thought had I not respected your opinion. I'd probably be bored to tears by now with the 'variations on a theme' with old milsurp Mausers. I remain quite amazed at the versatility of the AR platform.

It would be a great hog round! I may get down Texas way this year to snipe some pigs. This rifle will make the trip if I do. With the .223 barrel too!

Jamie.270 - I do recall that now that you mention it.

Knocking a caliber off of the case length would indeed improve some of the characteristics for subsonic HFC application. I also looked at the M1 Carbine case. In the end, one just needs a "power pill" behind whatever bullet they intend to use. The power pill needs to feed well, but other than that, "looks" are immaterial. The NAME... now that's an entirely different story...

Paul

Paul,

I think I was probably worse than you with my opinion of "black guns"...

I'm surprised I even tried one out at all.

What it all boils down to is accuracy and reliability. That's when I got hooked.

You know you could probably go "commercial wildcat" with that cartridge..

RBB - Possibly, but the better cartridge is the .338x.223 and SSK has the .338 Whisper in two configurations for the AR-15. The ONLY reason I'm not making that one is because I have a bunch of 8mm barrels laying around, and no .338 barrels laying around.

I like the 8mm caliber, but with a coldly objective eye, the .338 is just that much better than the 8mm. The one aspect that the 8mm has going for it that is missing in the .338 are some truly light-for-caliber bullets. At least the 8mm has the 125s and 150s. I don't think anyone is even making the 165 for the .338 any more. At supersonic speeds and from a barrel at least 22" long, the 8mm 125 is a "good" deer bullet (1000 ft-lbs of energy) out to 200 or so from the AR-15. That would appeal to those that want to use a heavy (250-grain) bullet for sub-100 yd subsonic applications and still be able to shoot deer out to 200 without changing barrels.

Jamie.270 - I did some number crunching last night considering your above comments. First, let me clear up what may be a little confusion I created about "thin necks". The reason the necks are TOO thin is that I didn't ream the chamber neck to proper diameter because I didn't have the proper reamer. Yet. It should be here Monday or Tuesday. When I enlarge the neck of the chamber, the unmodified neck of the 8x223 shouldn't have any "grab" problems. On to shortening the .223 case...

Let me give you an idea how 'complicated' this gets. I quite literally LOVE "crunching numbers". To a fault sometimes. It is very rarely that I get 'overwhelmed' by permutations. Last night I was getting overwhelmed with permutations. Here's the gist of it:

There are 'competing' forces at work here. (The "no free lunch syndrome".) While it is true that the short case still has plenty of room for sufficient powder to launch an HFC - 250-grain 8mm bullet in this case - at the just-subsonic muzzle velocity of 1050 f/s, as you decrease the combustion chamber size, you increase the pressure to produce the same MV.

Since we aren't approaching the pressure max for the AR-15, that would seem to be a non-issue. However, increased MAX pressure means increased MUZZLE pressure. Increased muzzle pressure means LOUDER. The PRIMARY purpose of subsonic is "quiet", whether suppressed or unsuppressed.

There is a MOUNTAIN of voodoo associated with suppression, but the simple truth is that sound suppression is governed COMPLETELY by the "Ideal Gas Law" - PV = NRT - where P is the absolute pressure of the gas, V is the volume of the gas, n is the amount of gas (measured in moles), T is the temperature of the gas and R is the ideal, or universal, gas constant. Since the combustion gasses are fundamentally the same KIND of "gas" in any firing, we can ignore "n", and since "R" is by definition a constant, we can ignore it too. That leaves PV = T. In English; the pressure times the volume is proportional to the temperature.

For suppression, we know two of the three variables - pressure and volume. We have the MUZZLE pressure and we know the volume of the suppressor. The temperature isn't relevant except in a relative way - goes up, goes down. Here's an example:

We start with a container with a volume of "1000" and in it is a gas under a pressure of "100" (units aren't important). If we double the size of the container to "2000", the pressure DECREASES to "50" and the temperature remains the same. If we keep the volume constant, and decrease the pressure, the temperature goes down. This is why canisters of gas under pressure get cold when the "air" is rapidly let out of them. Finally, if we keep the volume the same and lower the temperature, the pressure goes down. So...

If we know the muzzle pressure, and we know the "combustion chamber volume" (case capacity plus volume of the barrel), we can calculate the size (volume) of a suppressor that will decrease the pressure by the amount we want - say 10-fold.

The "bang" heard when a firearm is fired is PRIMARILY, but not solely, due to the HIGH PRESSURE combustion gasses SLAMMING into the air in front of the muzzle. Sound "suppression" is nothing more than reducing the "SLAM" of those combustion gasses into the air in front of the muzzle. If we reduce the PRESSURE of those combustion gasses before the bullet exits the muzzle, we reduce the "bang". How much reduce it determines how much the bang is reduced. Now, back to the 8x223.

If I make the case shorter, AND I keep the barrel the same length (maintain the combustion chamber volume), I have to INCREASE the muzzle pressure. If I increase the muzzle pressure, I increase the "bang".

Of course I could increase the barrel length (combustion chamber volume), but therein lies the path of "trade-offs" and where I got overwhelmed with permutations. One can reduce pressure by decreasing muzzle VELOCITY. One can reduce pressure by decreasing BULLET WEIGHT. So, one can decrease muzzle PRESSURE by:

1) Increasing case capacity (combustion chamber volume),
2) Increasing barrel length (combustion chamber volume),
3) Decreasing muzzle velocity (muzzle pressure),
4) Decreasing bullet weight (max pressure for given velocity).

If you have a suppressor (maybe someday I'll get the paperwork back), you can deal with increased muzzle pressure by increasing suppressor volume - make it larger diameter or longer. Without a suppressor - as I currently am - I have to watch the muzzle pressure if I want "quiet".

I think, in fact I am quite certain, that there is a "sweet spot" with regard to muzzle pressure, bullet weight, case capacity, and suppressor volume. Coming up with the equation to find that sweet spot gave me a headache last night. (And this morning too.) For the time being, I am going to stick with the "long" (45mm) .223 Rem case length.

The proper neck reamer should be here Monday or Tuesday. Frankly, reaming the neck out another 5 thou or so is probably going to make the "shoulder" all but disappear IN THE FIRED CASE.

Paul

Ok, logical extension, the .50 BM case, necked down to .22, 40gr bullet, 1050 fps and 48" barrel, solves everything, or close to it.

;<)

Sure.

Paul

I was thinking I remembered this incorrectly:

QuoteAt supersonic speeds and  from a barrel at least 22" long, the 8mm 125 is a "good" deer bullet  (1000 ft-lbs of energy) out to 200 or so from the AR-15.

It only carries 1000 ft-lbs to 110 yds. But... it does carry 845 ft-lbs out to 200.

Paul

Uhhh, if you are using an inert filler in the case, haven't you reduced the case volume by an amount similar to reducing its length?

And if there is a ratio that corresponds to case volume, combustion chamber volume and suppressor volume,...
Any decrease in case/combustion chamber volume could be compensated for, with a miniscule increase in suppressor length, given the disparity in their diameters.

Just tossing it out there.


Now, as for the name.
I'm thinkin' somethin' catchy,...
Like "the bio's no-bang!"
Or mebbe, the "ANEPR."