.300 Fireball (Whisper) SBR

[cohiba]

This was something I always wanted to build as I really like the cartridge. My first experience was with a T/C Contender. The cartridge is pretty potent in its full bore loading as Corbon made. The round shown is a 150 Nosler Ballistic Tip just for looks sake. For this rifle, it is subsonic only, probably 220gr or 240gr SMKs with a suitable charge of PB powder.

The build was one of those that goes together in your mind perfectly but not anywhere else. This was as much a nightmare as building a AR upper can be. Certainly has the right components I thought. I can't envision any better pieces:

LT Stealth upper
LT 10.0 rail
Noveske 10.5 CQB barrel in .300 Fireball. Pistol gas system, SS, M4 cuts, 1/8 twist, tuned for subsonic only
Colt M16 MP bolt and carrier, nickle teflon coated
HK 416 type sights
EoTech 553
Gemtech quick connect for HVT suppressor
SF M900 w/ LT lever

Problem one: Gas block would not allow rail to slide over it my just a wee bit.

Solution: 1. Mill the rear of the rail
2. Just kiss the bottom edges off the GB
3. Take the GB off (it is pinned and set screwed) and reattach it IN the rail through the holes. Holy mackerel Bat-Man, #3 worked.

Problem two: Bilock does not cinch all the way down as Noveske leaves room for a washer.

Solution: Make a washer. (Sounds simple. It's NOT) Done.

Problem three: Rail is just a shade too long to allow can to attach as Gemtech pointed out. DOH!

Solution: 1. Return LT 10.0 for 9.0. They would of course do it as they're customer service is excellent but nah, too easy and I want this NOW.
2. Mill front of 10.0 down to like a 9.8. MUCH harder but I pick this.

Problem four: Bought a SF M961 for this on ARFCOM. Some guy had a remarkable deal on these. Uh, too long. I have to set it forward enough for my thumb that the can will hit it. Double DOH!

Solution: M900. Jeez, that was easy for once.

Other than that, nothing went wrong. We assembled the upper for now and will mill the rail when the can gets to the shop. In the mean time, it runs fine. I had about 40 rounds of the 220 SMKs that last clocked about 1080 out of a 18" barrel.

I have to chrono this some day but a 220-240gr SMK in close must hurt a whole bunch or at the very least ruin someone's dinner plans. The hot Corbon loads really scream but I have to be careful about stabilization because of the twist. With the coming can, this will be quiet, whisper quiet in fact. :cool:

http://i20.photobucket.com/albums/b243/conndcj/300sbr001.jpg

http://i20.photobucket.com/albums/b243/conndcj/300sbr002.jpg

http://i20.photobucket.com/albums/b243/conndcj/300sbr003.jpg

http://i20.photobucket.com/albums/b243/conndcj/300sbr007.jpg

http://i20.photobucket.com/albums/b243/conndcj/300sbr005.jpg

Bonus pics. Teaser shots of KAC SR25K I'm running this weekend. Schweeeet.

http://i20.photobucket.com/albums/b243/conndcj/300sbr004.jpg

http://i20.photobucket.com/albums/b243/conndcj/300sbr006.jpg

[Impact]

looks great..do you reload or did you buy the ammo from someone else?

[AR15barrels]

This was something I always wanted to build as I really like the cartridge. My first experience was with a T/C Contender. The cartridge is pretty potent in its full bore loading as Corbon made. The round shown is a 150 Nosler Ballistic Tip just for looks sake. For this rifle, it is subsonic only, probably 220gr or 240gr SMKs with a suitable charge of PB powder.

The build was one of those that goes together in your mind perfectly but not anywhere else. This was as much a nightmare as building a AR upper can be.

Now you can fully appreciate what I go through sometimes on these kinds of projects...

You did go with an adjustable gas block right?
If not, add a setscrew.
Then open the gas port in the barrel and meter it at the block.
This will let you tune the gas system to function with a specific LOAD rather than choosing loads that FUNCTION.

[C4IGrant]

Looks very cool! Can I ask what the ammo costs and if you have to modify the mags in any special way to get the rounds to work in them?



C4

[RWBlue]

Looks very cool! Can I ask what the ammo costs and if you have to modify the mags in any special way to get the rounds to work in them?



C4


You can buy the ammo at reedsammo.com, but I think most people shooting the 300-221 will be reloaders. It is just too costly to buy and as a reloader I can tweak the load to the gun.

From my demo, the 300-221 should work in my gun without modifying my mags. YMMV.

[shootmovecomm]

Randall, I am checking on the status of a work order. I sent a flat top upper with a 16 inch barrel in to have it shortend to 14.7 inches, threaded, and the A2 flash hider permanently attached. If you have started work on it great, if not I was looking to revise the work order and have it shortened to 13.7 inches with a Noveske KX3 flash hider permanently attached that I will supply unless you have one on hand. What would be or what is the turn around on this item?

[cohiba]

Looks very cool! Can I ask what the ammo costs and if you have to modify the mags in any special way to get the rounds to work in them?



C4


Thanks Grant. HK mags work fine, just have to pay close attention to OAL.

Cost is tough to tell you for reloading only because I stocked up on brass and SMKs years ago then didn't use them anymore. Cost of SMKs have skyrocketed. When I run out (about 2500) I could give you a better answer. This round is definately for reloaders right now.

[JaxCatm]

Very neat build. Are you going to put a can on the rig?

[steezo757]

Had to bring this thread back to life.

How has it been running? Any issues? Have you played around with any small grain bullets 165gr/180gr? Reason I ask is because SMK are pricey and am wondering if there is a cheaper alternative.

[Marc]

Mr. Rausch,

I am also going to build a .300W upper starting on a S.S. barrel Blank in 1/8" that I still have.

I think I am going with a 10,3" lenght.

In your last post you recomment to open up the gas port and to adjust the gas with a screw setting in the gas block.

I would like to go with that, but what gas port do you recomment to do so?

Many thanks.

[AR15barrels]

I am also going to build a .300W upper starting on a S.S. barrel Blank in 1/8" that I still have.

I think I am going with a 10,3" lenght.

In your last post you recomment to open up the gas port and to adjust the gas with a screw setting in the gas block.

I would like to go with that, but what gas port do you recomment to do so?

As you will be adjusting the gas flow with the gas block, you can open the gas port in the barrel all the way to 3mm which is roughly the same as the inside diameter of the gas tube.
Then the restriction will occur only at the adjusting screw.

[Marc]

Thank you very much for your very fast answer!