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Mark's 300 Fireball Project

Quarterbore's Note!  What to see a video of this in operation?



 I too was fascinated by the concept of the .300 Whisper, but put off by the $1100.00 price tag for the upper alone. In comparison, Olympic Armsí upper is $529. For the price of the SSK, I could have my Fireball upper, plus another complete upper chambered in .17 Remington for varminting.

I did, though, find that the Oly upper, while very sturdy, had a few issues that needed to be addressed for reliable operation. I found two main modes of failure which initially made it rare for a whole magazine to fire without at least three jams. Some rounds, as the bolt stripped them from the magazine, would catch on the forward edge of the magazine. The resultant stoppage could usually be corrected with a good Ďwhackí to the left side of the receiver. I corrected this by applying a tiny radius to the inside edge of each magazine to be used with the Whisper. Only a minute amount of metal need be removed.

Typical jam with unmodified magazines:

Tiny radius applied to leading edge of mags:


I would strongly suggest setting aside some magazines just for the Whisper. Regular .223 rounds will not chamber in your Whisper upper. Conversely, a .308 bullet loaded in a Whisper/Fireball round could possibly chamber in your expensive upper, and cause extensive damage. You donít have to paint them bright orange, but donít get the ammo mixed up!

A second issue concerned the feeding of the larger bullets through the barrel extension. The AR-15 was designed for .223 rounds; the feed ramps do not well accommodate a bullet over twice the original size. I tried various bullets over 200 grains, but I never found anything that worked with the stock barrel extension. Clearly, some delicate, precision machine work would be in order. Like all real men do, I got the Dremel out, and installed the smaller grinding stone.

This is a photograph of the barrel extension on the original .223 rifle. Notice the triangle shaped locking lug:

For comparison, here is the barrel extension on the .300 Fireball after modification. I ground down the triangular part of the feed ramp, and blended the edges of the locking lug into the channels adjacent to the lug:

To sum it up, the Fireball upper will not run with the barrel extension supplied by Olympic Arms. Minor additional machining is necessary. Presumably, in addition to the adjustable gas port, this would be done already on the SSK Industries upper. I wonder if JD Jones would sell just the barrel extension? Somehow I doubt itÖ

I did investigate having a real machinist do this simple operation for me, but being a Real Man, I was not intimidated by the prospect of ruining hundreds of dollars worth of delicate equipment with my crude hand tools. I traded emails with a guy in Tennessee who was very professional, and offered to do the task for a nominal fee. He has a jig set up just for this task. If he agrees, Iíll addend his email address to this document, he will definitely do a better job than what I was able to pull off.

As for what lower to use, well, I only own one, here is a photo. This is originally made by Olympic Arms, how fitting that I would end up putting it together with Olympic parts! Notice that third position on the selector switch, and the top of the auto sear sticking out above the receiver.

Here is the whole thing, assembled and ready to go, complete with Gen 2+ night vision scope and American Manufacturing XXX suppressor. Apparently Mike Klos, the silencer manufacturer, didn't want any baffle strikes, and built in plenty of clearance in this excellent can!  For more information about the suppressor, try . My can was originally designed with very generous tolerances for the .223 round, but I have been using it on my .308 upper for hundreds of rounds without any problems. If you intend to use a .223 can on a .308 upper, be sure to check with the manufacturer first, not every suppressor has enough clearance for the big bullets. If you are interested in buying into the Class 3 world, have a look at or for more information. Contrary to common belief, you do NOT have to have any kind of license to own a machine gun or silencer, at least not in Texas. You will receive a tax stamp from the BATFE authorizing you to possess the machine gun or silencer. Do NOT try to make or improvise a silencer without prior permission from BATFE, even a Coke bottle taped on the end of an old .22 rifle is a felony, and will be prosecuted as such. You are guaranteed jail time for the first offense. Donít do it!

Silent is isn't, but it is definitely very quiet for such a high muzzle energy. I would compare it to my Crossman air rifle in .177 with about four pumps of air in it. I get excellent accuracy, even with that cheap BSA scope I bought on sale at CDNN. I shoot the Sierra 220gr HPBTs for plinking, and when I finally have a chance to hunt I'll use the 220gr LRNs. I have a night vision scope, but have yet to sight it in, there aren't too many rifle ranges open after dark in my neighborhood.

Overall, here are my impressions:

Itís BIG. Itís LONG. Itís BLACK. Itís HEAVY (probably total over 14 pounds as shown).

And best of all, itís MINE!


Special thanks to Mark for sharing his description, photos, and exceptional video!


Please Note: I am looking for additional images and descriptions
of 300 Whisper or 300/221 Fireball rifles. Please Contact Us if you
would like to see your rifle or pistol on this website!

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This site was last updated 03/26/04