6mm/204 Who had done one?

[Pawnee Bill]

6-204 = 6x47 (222 Mag) What is old is new again.

 

[swd]

6-204 = 6x47 (222 Mag) What is old is new again.

The shoulder on the 204 is about .070" higher than the 222 Mag along with a 30 deg shoulder. Sort of like saying the Dasher is still a 6BR..

 

[1lnbrdg]

This is very interesting. I'm shooting a 6X45 now with a long throat and the 95gr Sierra's. Getting just short of .308 Palma 155gr performance. Supposed to be slightly supersonic to 1K if I'm not shooting into a head-wind. Haven't tried it yet though, need a 20MOA base. Just a bit over 2800 FPS now with IMR-8208 without any pressure issues. 6X204 should push a bit past that.

I couldn't get enough Varget or H-4895 into the cases to get velocities up and either didn't burn very clean due to low pressure.

Edited to add these are for single-loading, not magazine loading.

 

[John from MN]

This is very interesting. I'm shooting a 6X45 now with a long throat and the 95gr Sierra's. Getting just short of .308 Palma 155gr performance. Supposed to be slightly supersonic to 1K if I'm not shooting into a head-wind. Haven't tried it yet though, need a 20MOA base. Just a bit over 2800 FPS now with IMR-8208 without any pressure issues. 6X204 should push a bit past that.

I couldn't get enough Varget or H-4895 into the cases to get velocities up and either didn't burn very clean due to low pressure.

Edited to add these are for single-loading, not magazine loading.

How long is your barrel? I'm gathering info trying to decide between an 8t 6x45 AND 6X45 AI.

 

[1lnbrdg]

I'm running a 26" barrel.

After really thinking about the .223 flavor and you have to buy the reamer, go with the 6X45AI. Cost wont be any different to have a reamer made when it's a custom reamer. You're going to pay for a custom reamer to have one that will long-throat the chamber. Still be able to use the cheaper and very common .223 case with as much powder capacity as you can get out of it.

I'm going to have to check where to find dies, probably custom for either 6X45AI or 6X204.

 

[JSH]

After a lot of chasing on this subject, I gave up and am just going to go with 6TCU. I don't think there is enough gain with the 204 for doing the extra work.
That and I have played with the 6TCU in years past. Thought I kept my dies, but seems they are gone. Strange as I seldom sell them even if I sell said gun in that caliber.
Jeff

 

[AWS]

I've built a 6mm-204 about 12 years ago, I had built a 22-204 and a 25-204 so as long as I had all the cases sitting there and a 22-204 reamer, What the Heck. I ordered a Sav Barrel pre chambered in 6x47 Rem and reamed it out to 6mm-204 with a 6mm pilot on my 22-204 as the neck and throat were already in the correct place with the 6x47 chamber. Seeing as I had converted a 204 FL Bushing die to size and form 22-2044's I just changed out the bushing and added a 6mm tapered expander ball and one pass through the FL sizing die I had 6mm-204 brass ready to load and shoot, no fire forming, easy peasy.

I've been using it to test 6mm Lead Free bullets for coyote hunting, if I remember right 55gr NBT's were doing right at 3700fps, the lead free version about 100 fps less. For a lead bullet 58gr V-max have been like the Hammer of Thor and yet fur friendly on coyotes, 62gr Varmint Grenades left huge exits, 55gr NBT LF's worked much better in the fur department.

Think of the 6mm-204 as a 6x47 Improved.

 

[AckleymanII]

Thanks AWS!!!

 

[TAJ45]

So AManII, you still have this rattling around your fertile mind?

 

[Pawnee Bill]

I had a 6x47 Kimber. Same thing.
It was a 14 twist so I was limited tp perhaps no more than 70 gr bullet weight, so you'll probably want a faster twist barrel.

I had a 6x47 Rem (222 Mag necked up to 6mm). Nice little gun. Was finicky on loads.

 

[Oso]

Is there enough difference in a 6x45AI and the 6TCU to argue over?
Jeff

I recently built a 6x45AI with a custom reamer because it isn't a standard round and neither are the dies. I recreated the wheel after a long drawn out study on case length after necking up and AI'ing the chamber. If I were to do it again I would just go with the 6TCU, which is a standardized cartridge with reamers and dies available.

Practically speaking the powder volume of a 6x45AI / 6TCU is the same as a 6mm-204. Really easy to fire form cases from .223 brass... unlimited supply of quality brass available from any number of manufacturers. If you already have a 223AI then use it to fire form... the shot case neck is now about right diameter for 6mm (no separate step for necking up).

 

[Oso]

Any thoughts on going to a larger bolt size and running the new 6GT? From what I have read its velocity is greater than 6x45AI or 6PPC, and at the same time the case design is based on proven benchrest case design so it uses less powder than 6x47, 6mm Creedmoor, etc. Also, it overcomes the shortfall of the smaller benchrest rounds with both greater velocity and the ability to feed reliably from a full size detachable magazine. Finally, loading for it is supposedly very easy, without being finicky like the 6x47/6.5x47.

If this all proves out then maybe this is got a future at my house.

 

[JSH]

Had to re read.
The GT is a short CM so how can we compare. Guess I am confused.

Oh got my 6TCU rifle built. Used an XP action, McMillan stock, Jewel trigger. Shoots like a dream. Extraction issues, nothing an AR style won’t fix, another winter project.
Jeff

 

[Dead Eye]

If you can find a copy of Rifle’s Varment Rifles and Cartridges the 2014 edition. There is an article about the 6-204RR. The RR stands for Ron Reiner the Hodgkin ballistician. The article was written by Brian Pearce. They have loads listed that they shot out of a 15” pistol and a 18 1/2” barreled rifle. They show rifle velocities for the rifle as 55gr over 3,500 fps, 70gr at nearly 3,200 fps and 80gr at over 3,000 fps. Brass is a simple neck up and dies are a .204 bushing die with the throat behind the bushing opened up a little like AWS said. I plan on building one in an XP-100.

Dave

 

[Oso]

Had to re read.
The GT is a short CM so how can we compare. Guess I am confused.

Oh got my 6TCU rifle built. Used an XP action, McMillan stock, Jewel trigger. Shoots like a dream. Extraction issues, nothing an AR style won’t fix, another winter project.
Jeff

I think the 6TCU was a good call. I went with the 6x45AI in part as a pet project and also lack of understanding that I was basically building a 6TCU... but just more expensive from cost of custom dies and reamer... at this point it is now a family heirloom! For me part of the appeal of the 6TCU / 6x45AI is safety... no one is going to mix up my 6x45AI with a .223. I have seen a novice detonate an AR15 by loading a 300BO into it. So I approached my build with a slightly different perspective

 

[Rdlningcltchdmpr]

I was just looking around at info on this the other night.
I have a bunch of 6mm bullets from 55-75 grains that need to be put to use.

I was looking to see how much gain in velocity there is between a 6TCU and the 6-204. I have shot 6-223 and 6TCU a lot, both are looked over a lot.
Jeff

24 nozler seems like a winner ? 223 bolt face.

 

[JSH]

24 nozler seems like a winner ? 223 bolt face.

I gave it some hard thought at one point.
I am really waiting on someone to play with a 20 Nosler.
There is some what of a reference to the 24 Nosler, but it is refered to as the 6-6.8. Have heard nothing but good.

I had played with the 6TCU enough, felt as comfortable as my old shoes.
I do have an action laying around though,lol.

 

[Rdlningcltchdmpr]

The 20 nozler opened to 24 would be excellent. That darned nozler is not putting any out though. ? Maybe soon i hope.

 

[JSH]

I had also looked at the 6-204. After having played with the 6x45 in a carbine length barrel and numerous 6TCU pistols, just couldn’t talk myself into it.
Those speeds, surprised me, I have the magazine article.

Built my 6TCU with a barrel from Ragged Hole, top notch guys. I went with an 8 twist. More than I needed, thoughts were with the extra RPM more splat factor with varmint bullets more intended for 243 type cartridge. Zero freebore, plan is for 55-70 grain.
As prior experience with the 6TCU, fire forming loads will shoot as well as formed cases.
As folks other than me mention on a regular basis, the 6-223/6x45/6TCU performs over its size for some reason.
Jeff

 

[AckleymanII]

I have a 22/204 in the works, got the 6/204 in my sights. Motivation is to get these small cases to feed in a Rem 700, and the 223 AI does not like to feed in a remington. I don't know how to alter feed rails to get the 223 AI or 6/223 AI to feed.