just another 300 cartridge

[pug]

I was curious if there was any interest in another 308/223 based cartridge for the AR-15 or any other .223 platform. Not really for subsonic use because of increased case capacity but suited ideally for (supersonic) 125 to 150 gr bullets yet all the heavys can be used as well. Calculated power shows higher than 7.69x39 for same bullet weight but that can be off somewhat. This isn't a money maker because I don't make barrels for sale. I am just wondering what everyone thought.

[Spook]

Pug , I've actually formed up a few 30 TCU's...I was thinking the old 147grain steel core milsurp for an AR -pistol or SBR ,what shoulder angle were you looking at? There's a load a Reloadersnest for 150's at just over 2100 FPS!:uzi2: :smile:
The 7mm TCU was always pretty accurate even at distance out of TC's.

[pug]

Spook you are talking about a whole lot more case capacity than I am. The guy at the shop shoots TCU and the cases are a little long for what I had in mind. I was looking more at a 30 degree shoulder and case capacity just shy of 25 grains. In order for the cartridge to run fairly smooth at full auto rates the cartridges must stack correctly in the magazine and that is why I think I would go with a shorter case. As far as velocity I am not going to guess although the computer that doesn't always know what it is talking about says over 2200 fps for a safe load out of a 16" barrel. It also says pressures can go up to a max of 70,000 psi so I don't think there is a problem of not enough pressure. I got the cartridges made up and most of the specs filled out but I may still lengthen the neck.

You know I looked at over 75 different 308 cartridges and still didn't see the 30 TCU which I knew about. I was also surprised to see the 30-223 had less case capacity than the 300/221.

Not sure this was the right place to post this subject so forgive me if I made a booboo.

[pug]

Spook here is a picture of the cartridge with a 150gr FMJBT seated to 2.200" compared to a 300/221 on the left. I was initially testing mags with magpul followers and everything stacks fine but green GIs cause a little more drag.

[Spook]

Pug, I cant see a pic?

[320pf]

Pug,

I would like to see the picture. Somehow the picture did not come throught with your post.

320pf

[pug]

I will see what I can do but it may be beyond my skills. There is a thumbnail pic of the two cartridges side by side in the post but perhaps it is local on just my machine.

Removed the attachment and uploaded it again. Let me know if it still isn't there. The reamer should be here in a few weeks so I should know a little more about the performance.

[320pf]

Pug,

Cool!! It looks like you can rechamber an existing 300-221 fireball barrel for the new round... Am I correct?

If it works I would defiantly like one :)

So what are the actual dimensions? It looks like the case is about 1.5". It looks like there might not be enough shoulder to get reliable headspacing. However, I assume that you blow out the case and increase the shoulder. An honest 2150-2250 fps velocity with a 150 gr bullet would be just the ticket for major rifle!!!! Very interesting!!!!

320pf

[kurtz]

How do the dimensions compare to the HK 7.62x37mm, see pic

http://www.quarterbore.net/forums/photopost/showphoto.php/photo/335/cat/535

[pug]

kurtz I am very glad you showed me that. Even though I didn't see that particular one in any of the databases I couldn't understand why know one had come up with it because it seemed logical. After entering the dimensions for that size cartridge I found very little performance increase over the 300/221 using ballistics software so I changed the dimensions and bumped up the case capacity until I saw a reasonable increase. Then I tried to form up the case and it seemed to work out so off everything goes to have the reamer made. We shall see and I know for a fact these things don't always work out as we expect them to. There are details missing both in picture and data but I hope everyone understands I would like to see how it works out first.

320pf yes as far as rechambering but I am going with a smaller neck diameter than 300 fireball initially. There will most likely be a small step in the neck diameter right above the shoulder if a 300 fireball chamber is recut to the new dimensions. With the neck I specified I do not seem to experience the big first round drop in velocity and a lot of the loads have standard deviations under 10.

[kurtz]

Pug, I sent you a PM....

[demonslayer]

please keep us updated. i think that i would be interested. thanks, brian

[pug]

Update is things are moving a lot slower than I like. Got the reamer and got the blank. Mounted it between centers and took a couple of roughing cuts and the drive went out on the lathe. Just got it fixed last weekend so now all I need is some time.

[320pf]

Update is things are moving a lot slower than I like. Got the reamer and got the blank. Mounted it between centers and took a couple of roughing cuts and the drive went out on the lathe. Just got it fixed last weekend so now all I need is some time.

Pug,

Thanks for the update. Boy wouldn't we all like more time. I would like to invent a time machine.... just think of the possibilities. :grin:

320pf

[pug]

Finally got to try out the 308R2 cartridge yesterday. A 16" AR barrel is the longest I can do at the moment but it turned out a respectable 2090 fps with a Hornady 150 FMJ and 18.5gr of powder. Pressure signs are good and still have some room in the case so will be moving up slowly. Would really like to make major power with the 16" and 150s but it is going to be close.

[320pf]

hey pug,

It sounds pretty good. What powder are you using to push the Hornady 150 gr. FMJ?

320pf

[pug]

Hey 320pf. Lil' Gun right now. May switch to the slightly slower 296 later on. The 296 should give a slightly higher charge but will keep working with the lil gun until I get pressure signs or run out of space. Ran a few quick test rounds today looking for pressure signs only and appears I am ok still at 19gr and still more room but temps were a little cooler. Didn't take the chrono with me but now wish I had.

[320pf]

pug,

In my 16-inch barrel, I was able to push a 155 g at 2086 fps (a PF of 339) with 18.5 gr Lil'Gun, but this load would blow primers. This batch of reloads prodcuced 2117 fps from the 20-inch barrel without blowing primers. I could only fit another 1/2 gr on powder into this batch because on the bullet seating depth.

The next batch of reloads, I seated the bullet out as far as possible. With this configuration, 18.5 gr of Lil'Gun gave me 2023 for the 155 gr Palma bullets in a 20-inch barrel. I could get 20 gr of Lil'Gun to push the 155 gr Sierra Palma BT to 2150 fps. in same barrel. I have not tried this loading in the 16-in. barrel.

I think that if I seated the bullet out as far as possible I might get 18.5 g of Lil'Gun to run in the 16-inch barrel but I would probably lose a bit of velocity.

So I am willing to bet that with the larger volume case you should be able to get ~20 gr of Ll'Gun to run without getting too high pressures.

..... Didn't take the chrono with me but now wish I had.
I have done this too... and had the same regret :)

Good luck and keep us posted

320pf

[pug]

320pf,

I hear you and have run them up to the point of blowing primers but the AR bolt doesn't seem to take that constant pounding very well. I don't want to follow the route of the first 6.8s and claim velocities that turn out to be unrealistic. Also because the case is longer I don't have a great deal of room to change seating depth that much. Increase overall length too much with a standard mag and the cartridges will have to roll inward to allow the mag to seat. I never liked having to beat the mag on the bottom to get it to lock with the bolt closed. A drum would cure this problem of course and I may have to get one before I try the ol' cinder block wall test. Hehe.

[pug]

320pf,

You were right on the money. Made it to 20gr of lil gun and the pressure was still good. Slightly compressed load and velocity change per powder increase had dropped off but still made it to 2172 fps. Changed powders and am currently at 2267 fps with the Hornady 150s so guess I will go on and get some gauges and dies made as it looks like a keeper. Will try to get a 20" made and as soon as I have any more info I will start a new thread somewhere where it is more on topic.

[320pf]

320pf,

....Changed powders and am currently at 2267 fps with the Hornady 150s so guess I will go on and get some gauges and dies made as it looks like a keeper.

pug,

You are always such a tease. Which powder did you get 2267 fps with? If I had to guess... I would guess W296 or AA1680.

If you are getting 2200 to 2300 with 150 gr bullets I bet you will get about 2400 to 2500 fps with 125 gr bullets and 2500 to 2600 with 110 gr bullets.

This is great news

320pf