[Scott60]

Here are a few angles of my latest creation - the 5.56x24.
It is derived from the .22 TCM.
The .22 TCM was originally meant to fit in the 1911 size action with an OAL length of 1.270". Armscor got happy when they introduced the "9R" version with a proprietary, stub-nose bullet that they have never seen fit to offer for sale. The result is those who load for the .22 TCM9R in States like California where buying factory ammo can be a problem, find no ready bullet choices. The end result are bullets that must be seated too deeply for the nose ogive - even stubby 35 grain V-max bullets.

The right answer is found in a "new" cartridge case design shortened to place the case neck correctly for normal seating of the Armscor 40 grain HP. The cases are the same length to the shoulder, with the 5.56x24 case being 0.935" long and the TCM case being 1.025". Considering the bullets take up most of the shoulder region, there is little volume loss due to the different shoulder.

This round is designed to feed and function through a 9mm size magazine and chambers correctly in a standard .22 TCM chamber. On firing the case neck and shoulder will move forward and form to the TCM chamber in much the same way any other "improved" design does. Traditional "improved" chambers allow a factory case to "blow forward" to form to the shoulder. The 5.56x24 reverses this by having the forward portion of the shoulder "blow forward". The case "head spaces" perfectly in the chamber.

One possible "improvement" other than a cartridge truly made for a 9mm action is the 40 degree shoulder and forward movement of the case will likely enhance breech face thrust with a slow-burning powder. This could benefit those who want to use a simple drop-in barrel and not have to lighten their Glock slide for cycling.

Range tests will be forthcoming.

It will either blow up - not likely
The brass will fail - equally not likely
The brass will be extruded an undesirable amount - this is somewhat expected, but as with the 5.7x28 which also experiences a great deal of shoulder-neck movement, yet resizes and functions just fine, I suspect the 5.56x24 will as well, though brass life might be reduced a few times, this would not be so undesirable consider brass can be formed from .223 cases.
Accuracy MIGHT be less than desired, but since the bullet starts out in exactly the same relationship to the barrel throat as with the TCM, accuracy potential should be about the same.

 

[TheDreadnought]

Well, it’s cool looking. I’ll give you that.

 

[BOOSTED12A]

Interesting. No offense, but why?

 

[Mr Meeseeks]

Very interested in how your tests turn out. If accuracy turns out to be acceptable and I can figure out how to form the brass from 223, It might make buying the drop-in barrel worth it.

 

[Mr Meeseeks]

Interesting. No offense, but why?

Armscor got happy when they introduced the "9R" version with a proprietary, stub-nose bullet that they have never seen fit to offer for sale. The result is those who load for the .22 TCM9R in States like California where buying factory ammo can be a problem, find no ready bullet choices. The end result are bullets that must be seated too deeply for the nose ogive - even stubby 35 grain V-max bullets.

The right answer is found in a "new" cartridge case design shortened to place the case neck correctly for normal seating of the Armscor 40 grain HP.

To make the 22 TCM 9R a viable cartridge for reloaders. Bullet options. I think the TCM round is a neat concept, and would love to be able to really experiment with it in a Glock.

https://www.lonewolfdist.com/Detail.aspx?PROD=922519

 

[VoodooMountain]

What velocities are you expecting?

 

[Scott60]

I'll be honest, as with any ad-hoc cartridge development it's always a crap-shoot, because what seems perfectly reasonable when thinking it up, turns out to be a nightmare.

Loading for the .22TCM9R has "been" that nightmare for me because the case neck is too long, and way too far forward to hold any standard bullet. If the Armscor design were available and I didn't have to invest all the additional time to measure, weight, and shorten bullets, I would not likely have thought of this approach.

But as I sat there dejected at the prospect of finding ways to seat 35-46 grain bullets in a way that the necks had proper tension, and knowing that any approach meant sawing the bullets off, or trimming noses, the idea started to gel that if the neck could be set back, once all the development work is done, the end product will be nor more difficult to load for than standard .22 TCM. IF the idea works, one can still shoot factory TCM ammo for those who can get it without paying a premium on top of a fortune.

The genesis of the idea is a modified take on the "old" Ackley Improved case designs, only instead of have a chamber cut with a longer shoulder and "blowing out" factory load shoulders to fire-form brass, it works in reverse. A custom brass case head spaces perfectly and "blow forward" on firing to form to the original TCM chamber. I remember a certain brand of .30-30 ammo that had a very "undersized" body, shoulder, and neck, since it head spaces on the rim, yet when fired, blew-out and formed perfectly to the chamber and with no failure.

I won't bore everyone with the details of how the cases are formed and cut, but IF it works as planned I expect .22 TCM level velocity - or close enough.

To answer the "why" question that inevitably gets asked...well, why not. A more practical reason is because I REALLY like the performance of the 5.7x28 with handloads running at high as 2,300 fps from the FiveseveN pistol, and the Glock 19 can deliver similar velocity and power from a much smaller, more compact pistol, AND even if Armscor never made another component for the ammo, hand loaders can form their own from a near endless supply of cheap brass!

I have already started to investigate starting with a custom chamber blank and turning down a dedicated 5.56x24 liner for a Glock barrel, but IF this works as I think, and one can use this cartridge plus factory TCM ammo, well, that's even better!

I decided to give the cartridge a completely new name because for all intents and purposes it is a different cartridge that just happens to fit into a TCM chamber - kind of like a .300 Whisper vs. .300 Blackout.

 

[Scott60]

Oh, I also think the front section of the case will act as a more efficient "piston" to drive the case back since the shoulder is flatter, and less of the expanding gases will be "wasted" creating a high-pressure concentration in the space between deep-seated bullet shank and long, tapered neck. This design might explain why a lot of users report stuck cases and hard extraction. I think the 5.56x24 will work better.

 

[Taterhead]

VERY interesting project. Hopefully you'll keep us posted as you progress.

 

[Mr Meeseeks]

I won't bore everyone with the details of how the cases are formed and cut

Pretty please? This is the opposite of boring. At least If the experiment works I’d like to get a basic rundown of how to make the brass. If it proves workable, I might have to buy this mold:
http://arsenalmolds.com/products?product_id=97

 

[Borg Warner]

I'll be honest, as with any ad-hoc cartridge development it's always a crap-shoot, because what seems perfectly reasonable when thinking it up, turns out to be a nightmare.

Loading for the .22TCM9R has "been" that nightmare for me because the case neck is too long, and way too far forward to hold any standard bullet. If the Armscor design were available and I didn't have to invest all the additional time to measure, weight, and shorten bullets, I would not likely have thought of this approach.

But as I sat there dejected at the prospect of finding ways to seat 35-46 grain bullets in a way that the necks had proper tension, and knowing that any approach meant sawing the bullets off, or trimming noses, the idea started to gel that if the neck could be set back, once all the development work is done, the end product will be nor more difficult to load for than standard .22 TCM. IF the idea works, one can still shoot factory TCM ammo for those who can get it without paying a premium on top of a fortune.

The genesis of the idea is a modified take on the "old" Ackley Improved case designs, only instead of have a chamber cut with a longer shoulder and "blowing out" factory load shoulders to fire-form brass, it works in reverse. A custom brass case head spaces perfectly and "blow forward" on firing to form to the original TCM chamber. I remember a certain brand of .30-30 ammo that had a very "undersized" body, shoulder, and neck, since it head spaces on the rim, yet when fired, blew-out and formed perfectly to the chamber and with no failure.

I won't bore everyone with the details of how the cases are formed and cut, but IF it works as planned I expect .22 TCM level velocity - or close enough.

To answer the "why" question that inevitably gets asked...well, why not. A more practical reason is because I REALLY like the performance of the 5.7x28 with handloads running at high as 2,300 fps from the FiveseveN pistol, and the Glock 19 can deliver similar velocity and power from a much smaller, more compact pistol, AND even if Armscor never made another component for the ammo, hand loaders can form their own from a near endless supply of cheap brass!

I have already started to investigate starting with a custom chamber blank and turning down a dedicated 5.56x24 liner for a Glock barrel, but IF this works as I think, and one can use this cartridge plus factory TCM ammo, well, that's even better!

I decided to give the cartridge a completely new name because for all intents and purposes it is a different cartridge that just happens to fit into a TCM chamber - kind of like a .300 Whisper vs. .300 Blackout.

The original 22 TCM has greater case volume and therefore greater velocity potential that the 5.7 x28. if your 5.56x24 can at least equal the 5.7 x 28 from the same length barrels and do it with more effective projectiles than what are used in the 22TCM9R I think you will have accomplished something worthwhile.

 

[Scott60]

Managed to get out and do some testing today.
The 5.56 x 24 was loaded with 9.5 grain of Enforcer under the Armscor 40 grain JHP.
The rounds fed smoothly from magazine to chamber and headspace was perfect.

Even with a full-weight G19 slide and a below maximum powder charge the cartridge cycled the slide, albeit a bit weakly, but this is easily corrected.
Discovered the OAL of 1.169" was just a tad too long for the G19 OEM magazine. OAL of 1.165 will probably be ideal with this bullet nose profile.

Velocity averaged 1,678 fps from a 4" barrel. Temperature around 58 degrees which is pretty good considering these small-capacity bottleneck cartridges, fired from short barrels tend to really loose velocity at lower temperatures.

Recoil was close to non-existent.

 

[Scott60]

A few more photos showing the comparison between the 5.56x24 and .22TCM.

 

[Mr Meeseeks]

So did you have custom dies made to form this brass? I’m following with interest!

 

[Scott60]

I grafted a bullet tip to show how the Armscor 40 grain JHP seats in the TCM case. Most of the bullet shank is below the neck and protruding well into the case shoulder area. When pressure builds, this causes a concentration of pressure between bullet and shoulder which could explain why many have reported stuck cases - myself included.
The "flatter" shoulder angle of the "556" works similar to the way the 5.7 shoulder does. First there is less bullet shank protruding into the shoulder region because there is less of it, and the shoulder angle is less acute so the pressure tends to push forward. Because the chamber is more tapered, the case expanding forward to fire-form to the TCM chamber provides added push to the slide. In essence, the case is acting like a small piston just as the 5.7 case does as extraction begins and residual case pressure continues to "iron" the shoulder forward - it doesn't "stretch" the shoulder in the classic sense.
Previously I was loading the Armscor bullet to proper depth and slicing off about 3 grains worth of the tip to bring it into OAL constraint, but this resulted in a wide "meplat" that if cut to 1.165" was still too long due to how the cartridges cant in the magazine - both Glock and CZ mags. This resulted in having to slice off even more bullet weight, or go through a labor-intensive process of spinning the loaded rounds to form a bit of taper - talk about WAY too much effort!
By forming the case specifically for the 9mm action, no such after-loading antics are required, AND I'm not stuck sitting here waiting for Armscor to bless me with their proprietary bullet, or "make do" with the 35 grain Vmax with noses filed flush and still seated so deep into the case necks the nose ogive looks like the photo below.

 

[Scott60]

So did you have custom dies made to form this brass? I’m following with interest!

Not yet... I made my own "conglomeration" of dies to prove out the concept, because that's a lot cheaper than having a custom sizing die made.
So far I've had to mod several sizer dies, the bullet seating die, the trim die, and even made my own case trimmer (Lee style) from a 5.7 spindle.
I can report however that once all figured out and the tools perfected, loading the "556" is no more labor intensive than the standard .22 TCM.
The finished product works fine in a short barrel Glock 19 which is significant because prior to developing my own case design none of my loads was able to cycle the G19 OEM weight slide, nor the CZ75B standard weight slide. I attribute some of this to known and reported issues with new TCM brass that seems to be a bit soft and easily stretches the necks and sticks cases, as well as trying to get by with powders that burn to fast for this cartridge. With my starting load in this case design the G19 slide did cycle - though weakly and not sufficiently to lock the slide back, nor to reliably pick up the next round, however the cartridge does FEED perfectly. My next test will be a slightly heavier powder charge and I will also see if this round will cycle the CZ75.

One thing I have discovered is that the TCM and "556" both lose a lot of velocity when the barrel drops from 4.6-5" down to 4". But there are more powders to be tried once I'm satisfied with the case making process.

 

[Scott60]

One more thing. In the photos you can clearly see the "556" bullet is situated further back from the rifling than the TCM bullet, however, this is only when comparing the TCM "proper". When loaded in the .22 TCM9R the bullet would sit in almost exactly the same location as the 5.56x24 bullet relative to the barrel throat and rifling. So the bullet is making no greater "jump" to the rifling with the 5.56 than with the -9R spec.
While I haven't yet done specific accuracy testing, while testing basic performance and case changes, the bullets were hitting where the sights were pointed, though paper testing is needed.

 

[pgg00]

This is very interesting. I'm curious to see how it works out

 

[Deltic]

My experience with my own wildcat on a tight budget tells me don't do it unless you have the money, time and patience to make version two to correct any problems with version one. My mistakes making a round for AR-15's included making the neck too short and the shoulder angle too steep in order to maximize powder capacity.

 

[Scott60]

More testing of the 5.56x24
Ambient temperature around 55 degrees.

40 gr. Armscor bullet over 9.9 gr. Enforcer = 1,760 fps from 4.02" barrel
This is looking better - all rounds fed and ejected with empties averaging about 4 feet.
One issue is barrel length. These small capacity bottleneck .22s tend to do much better from 4.6"-5.0" barrels.

Speer 46 gr. over 9.1 gr. Enforcer = 1,612 fps from 4.02" barrel
This round chambered and ejected very well - no malfunctions at all with spent cases ejecting about 3-5 feet.

Nosler 35 gr. Varmageddon over Enforcer 10.1 gr.
For some reason the Lab Radar would not pick up this bullet! This has happened before but I thought it was the unit, but there must be something about the base of this bullet that makes doppler waves "slide around" it.

Primers from 9.9 gr. Enforcer/ 40 gr. Armscor

Primers from 9.1 gr. Enforcer / 46 gr. Speer

Primers from Enforcer 10.1 gr. / Nosler 35 gr. Varmageddon

The Winchester small pistol magnum primers seem to have rather soft cups easily deformed during seating. The primers on all these loads are quite flattened, yet the loads are mild and all other aspects of the fired cases indicated modest pressure.
Will probably swap over to CCI 550 primers.

View: https://www.youtube.com/watch?v=0s4sHXBH7BQ