Anyone build a 300 Whisper / 300 Fireball / 300-221 AR upper?

[320pf]

There has been a interesting little thread going on at ar15

http://www.ar15.com/forums/topic.html?b=3&...21&t=382761

its a wildcat cartridge called 7.62x40, uses 308 bullets in reformed 223 cases.

http://www.ar15.com/forums/topic.html?b=3&...21&t=382761

Anyways here is some data

Average Performance Data

16” Barrel

110 Hornady V-MAX =2,575 fps

110 Sierra Varmint = 2,550 fps

125 Speer TNT = 2,450 fps

125 Nosler BTBT = 2,450 fps

123 Lapua FMJ = 2,475

20” Barrel

110 Hornady V-MAX =2,700 fps

110 Sierra Varmint = 2,675 fps

125 Speer TNT = 2,600 fps

125 Nosler BTBT = 2,575 fps

123 Lapua FMJ = 2,625 fps

Interesting. I won't suppress well though

I just got an upper from the guy that came up with this cartridge. I have been talking with him for several months now and he is a pretty sharp wildcater and knows his stuff. I was able to push 147 grain Win. FMJBT to about 2200 fps. It looks like the pressures were OK. If you are looking for a cartridge that uses standard mags, and bolt/carrier this round has some very interesting potential. It looks like a 20-inch barrel will push a 125 grain bullet to major power factor (2560 fps).

If you want to shoot mainly sub-sonic load, however, the 300 Whisper aka 300-221 fireball is the way to go. Here is a good article on the virtues of long range shooting with high Ballistic Coefficient sub-sonic loads:

http://www.lasc.us/RangingShotLongWhisper.htm

320pf

Edited September 14, 2008 by 320pf

[fastshooter03]

The 220 grain rounds will get sorta tilted in the mag due to the bullet curve hitting the indentation of the mag. I don't know if you can get full capacity using those bullets. They seem to feed OK though.

If you pick any good match barrel with 1x8 twist or faster you should be OK. Getting it to cycle with powders like H110 and N110 or faster in subsonic loads can be an issue without changing the spring and/or buffer weight. You will most likely need a RP spring and lighter buffer.

I would definitely get some sort of reliable gas adjustment in case you want to turn it off.

I used 221 fireball cases but you can trim 223 cases and turn or ream the necks. I will also turn the necks on the 221 if I need accurate loads.

I used an ordinary catalog chamber reamer that has a shorter throat so I can't load to mag length with the 220s without throating it.

AT the time I was using Lilja barrels but today I would go with a Broughten 5C.

I haven't heard of any body shots on deer with the 220s but my friend shot one in the neck with great results.

Nick

[cas]

I haven't heard of any body shots on deer with the 220s but my friend shot one in the neck with great results.

My brother-n-law dropped a large doe with his Contender pistol (125gr Nos BT) and she dropped on the spot. She fussed a bit and he was concerned she may get up, so he put a finisher in her. I had given him a few loaded 220gr Sierra match kings, and apparently that's what he'd brought for the job. When we dressed her, we found the MK entered and tumbled, leaving a sideways wound track through the heart and lungs that looked as if someone had run it through with a large sword.

[320pf]

The 220 grain rounds will get sorta tilted in the mag due to the bullet curve hitting the indentation of the mag. I don't know if you can get full capacity using those bullets. They seem to feed OK though.

If you pick any good match barrel with 1x8 twist or faster you should be OK. Getting it to cycle with powders like H110 and N110 or faster in subsonic loads can be an issue without changing the spring and/or buffer weight. You will most likely need a RP spring and lighter buffer.

I would definitely get some sort of reliable gas adjustment in case you want to turn it off.

I used 221 fireball cases but you can trim 223 cases and turn or ream the necks. I will also turn the necks on the 221 if I need accurate loads.

I used an ordinary catalog chamber reamer that has a shorter throat so I can't load to mag length with the 220s without throating it.

AT the time I was using Lilja barrels but today I would go with a Broughten 5C.

I haven't heard of any body shots on deer with the 220s but my friend shot one in the neck with great results.

Nick

This is readily corrected by seating the bullet deep enough into the case so that the magazine rib rides on the bullet ogive where the diameter is approximately the same as a 223 case neck. (see this figure)

This information is a bit dated and is based on the experience people had with rifle builds that had the gas port in the standard carbine position. With the standard carbine position, the gas port needs to be about 0.1-to-0.12". With this set-up you will need an adjustable gas block if you want to be able to shoot both super-sonic and sub-sonic loads.

You can build a 300-221 aka 300 whisper that can shoot both super-sonic and sub-sonic loads without an adjustable gas block and uses a standard rifle buffer and recoil spring. It is all dependent on the location and diameter of the gas port. The best location for the gas port is the standard pistol position. A port diameter of about 0.80-to-0.85" seems to work best. I like to start with the gas port at about 0.73" and open it up so that the rifle will cycle 150g sub-sonic loads.

As far as how sub-sonics work on game cas if correct. The sub-sonic load will not expand... They do their damage because they are sub-critically stabilized when shot from a 1:8 twist barrel at sub-sonic velocities and tumble upon impact. The most effective sub-sonic bullets are >200 grains.

Super-sonic loads will expand and work well in game. (see this discussion thread):

http://www.quarterbore.net/forums/showthread.php?t=1768

320pf

Added after original post:

221 Fireball brass is hard to find and when you can fine it, the cost is too high. I make all of my brass from 5.56/223 brass. You will want to make sure that your barrel/chamber is cut with the an up-to-date reamer that will allow you to use 223 brass. These reamers have a slightly larger neck diameter to accommodate the thicker necks that you get with 223 brass. I am not too particular about my brass. It is mixed brands and I can routinely get my Noveske barrel to shoot < 1 MOA groups. Right now, one of the best 300-221 fireball barrels are being made by Noveske. These are other quality barrels out there but I am not familiar with all on them. I would avoid Modlel-1. They make OK blaster barrels. But the gas port on these barrels is in the carbine position, so you might have to work on getting the rifle to cycle reliably. In addition, the specs on the bore diameters is a bit greater than I like.

Edited September 16, 2008 by 320pf