300 whisper start up

[ReAX222]

I am really interested in building a 300 whisper AR15. I will need to get a mold (I think I want to shoot about a 200-220 grain boolit), gas checks and an expensive set of dies. This gun will be mostly for fun and I don't expect to shoot it past 200 yards but I would like a decent level of accuracy.

The process I understand so far is:

Size .223 shorter but open the mouth or open a .221 fireball to .308.
Cast a .308 boolit and let it air cool.
Size, install a gas check and lube it up.
Prime, powder and seat the round.

Here's what I don't know yet and think I should.
Will my cheap lee challenger press (O-Frame) handle the resizing?
Will I need the gas checks since I am staying subsonic (I think I will try to stay around 1000FPS give or take for some accuracy.)
Will the White Label Lube BAC I am currently using suffice?

Is there anything else I should know about this cartridge?
Is there anything special I should ask for or use in building an AR around this cartridge?
Any suggestions on buying a barrel or complete upper?

[JIMinPHX]

Whispers usually use heavy for caliber boolits. You choice of boolit weights sounds about right. You will need to manually cycle your action for each shot unless you retune it with a gentle recoil kit. If you set it up so that you don’t need to manually cycle the action, then the gun will not be as quiet. Your reloading press is fine. No gas check should be needed for sub loads. If you can take 200-yard shots with a subsonic round, then you are a better rifleman than I. I wish you luck with that. The holdover should be massive at that range. Fast pistol powders in appropriately small quantities usually work best in that caliber for sub velocities. The best source of further info would probably be SSK industries in Wintersville, OH. That’s where J.D. Jones developed the family of whisper cartridges. The AR platform was already used by them for this round. The people there should know all about it.

[MakeMineA10mm]

I've never shot cast boolits in my 300 Whisper. (I have a Model 1 300/221 upper assembly on my AR.) It shoots just fine at super-sonic with 147gr FMJs as well as the sub-sonic rounds. My trouble with it is, I don't have a dedicated lower for it, so I get spotty cycling with the subsonic loads. It definitely needs a lighter buffer and spring, or POF, LWRC or another manufacturer needs to make a short-stroke piston style gas system 300 Whisper...

As far as the loading, you have it right.

The 221 Fireball brass is far easier to work with, because there are less steps. It also has greater internal capacity, so you can load the super-sonic rounds a tiny bit faster.

SSK is now selling 300 Whisper brass, and it is ALL made from 5.56 military cases. They cut them off, re-size them, ream the case neck, and remove the primer crimp for you. These cases are the most resilient for the slamming around an auto-loader gives brass. If you make them yourself, you'll have a lot of work to do. When I run low on 221 brass, I'm just going to buy brass from SSK...

For powders, I love AA#9 for the subsonic loads. for super-sonic, I have some surplus WC-680, which is absolutely perfect burning speed for this size case. AA#1680 could be used about as well.

Someone here at CB told me they cast for the Whisper and showed pics of their bullets. They are long-spire-points, so that the out-of-case length is right, AND so that they feed through the AR's feed ramp system. That is a quite important factor when looking for a 30-cal. bullet mould. I'd guess that 90+% of heavyweight 30-cal. moulds are blunt round-noses or flat points. Those, I suspect, won't feed at all through a 300 Whisper AR-15.

If you're interested, I've been thinking of selling my upper to fund another project. Shoot me a PM, and I'll give you the details.

[shooter93]

I have two supressed rifles...a 300 whisper and a 458 supressed round. In the 300 I shoot 250 grains and Veral is going to make me a mold to keep the lube groove and bullet base in the neck...A cast bullet that long wouldn't feed in an AR. One of you biggest problems will be OAL...most any cast bullet will be well into case and well below the shoulder. At subsonic velocities bigger is always better. In the 300 AA 1680 has worked the best...in the 45...Unique hands down winner. Once you learn the rifle though...300 yd shots aren't all that hard. I've put tons of rounds through these rifles and may eventuell get stadia lines put in the scope for different ranges.

[ReAX222]

While I really love the idea of the 300 whisper, is there a round that will work better with cast boolits in the AR?

[MakeMineA10mm]

At the risk of ruining a sale to you, I'd say the 7.62x39 isn't a bad choice when it comes to cast boolits in an AR. I haven't shot cast in that caliber in the AR, but I have shot several hundred Lyman #311410 (130gr tapered round nose) through my AK in that caliber, and it feeds pretty well. Accuracy and AK don't always compute, so it's more for savings than low-recoild precise shooting, but the AR should shoot nice little groups if you find the right bullet, load, and sizing diameter.