If you are planning on reloading and are looking for subsonic loads with heavy bullets, the 300 Blackout might be a good option. I've had decent results with some of the heavy bullets (Mostly Berger) in mine. If you aren't looking for the heavy bullet options or need the subsonic loads, then a better option might be the 7.62X39 for more standard loadings with lighter bullets. The Whisper may have a slightly shorter throat, so using longer bullets might be problematic in some chambers. Do the research and talk to some shooters with similar interests that have sorted theirs out. I built mine out of a pile of Brand X Y and Z parts. My next one might include a suppressor, since the heavy bullet subsonic loads may be at their best when quieted down. I just don't know if it's worth the expense and trouble. Some of these subsonic loads are pretty quiet, when compared to lighter and faster bullets. Powder selection seems to have a significant effect. AA1680 seems to work pretty well with the heavy bullets, but there are a handful I'm working with and trying to get sorted out. Barrel twist is also a consideration. If memory serves me, Mine is a 1 in 7". The usual seemed to be 1 in 7.5" when I looked around for parts.
I've been waiting for availability of 300 Blackout AR15 uppers. Already have a .30 cal suppressor.
The .300 Whisper is a proprietary cartridge, so anything connected with it is going to have royalty fees built in.
The .300 Blackout is essentially the same thing, designed to get around the proprietary issue. The two cartridges are interchangeable.
Both .300's come in supersonic and subsonic loadings. The supersonics use up to 150 grainers. The subsonics use up to 220 grainers. The supersonic load is similar in power to the 7.62x39 and 30-30. The subsonic load is rather pointless unless you have a suppressor.
The subsonic loads initially used a 1:8 twist, but most manufacturers are shifting to a 1:7. There is a variety of gas systems. Some use a carbine gas system, while others use a pistol length gas system. The pistol length seems to match the pressure curve better, but few make a pistol length gas system with a 16" barrel. Barrels longer than 16" are not needed because the powder is burned within that length.
Carefully look at specifications. Some manufacturers will have a chart that indicates whether their upper is designed for supersonic, subsonic, or subsonic suppressed. Unsuppressed subsonic is the hardest to cycle properly.
Cycling is a moot point with bolt actions. The only real problem I see is that most 300 BO or Whispers have lightweight barrels. In my opinion they should have a short heavy barrel to prevent as much barrel deflection as possible when a heavy suppressor is screwed on.
EOTech makes a holosight that is calibrated for the .300 BO. And Leupold can make custom elevation knobs for their Mark AR scopes.
You can shoot a 300 whisper cartridge in a 300 Blackout but NOT the reverse. The 300 Whisper is a necked down 221 Fireball case and the 300 Blackout is a necked down a 556 case. Dimensionally they are different.
I have found that the subsonic rounds are about 2 MOA and drops like a rock in terms of trajectory over 200 yards. Supersonic they are ballistically better.
I had a 300 Blackout upper. (necked up .223 case) It functioned fine, but it is a really a short range cartridge. Still fun for 100 yard recreation. I hear people talking like they shoot out to 500 yards, but they must be satisfied with "minute of barn" accuracy, where I am a sub "MOA" type rifleman.
Since I am not interested in suppressors, the round did not hold my interest. They are not legal for hunting where I live, and not useful for competition It went the same way as my Desert Eagle pistol, sold to someone else.
Actually the issue of shooting 300 BO in a Whisper chamber is a bit more complex than a simple yes or no. It depends on who made the 300 Whisper chamber. See the link for an explanation.
The subsonic rounds can have better than 1 MOA accuracy if the twist is fast enough. This is why the industry is switching from 1:8 to 1:7 twist for their subsonic barrels, while some manufacturers are leaving their supersonic barrels at 1:8.
And yes, the 300 BO or Whisper makes no sense if you are not using a suppressor and subsonic ammo.
This is one of the better youtube videos showing what a .300 BO in an AR15 can do when suppressed. The audio quality is high, giving a good idea of the actual sound. The shooter is talking normally and the report is well below that.
He also shoots a supersonic round through the suppressor, and you can clearly hear how the bullet cracks loudly as it breaks the sound barrier. Any supersonic bullet is going to create a sonic crack or miniature sonic boom, and that will be about as loud as an unsuppressed .22 LR rifle.
You simply take .223 or 5.56 brass and run it into .300 BO sizing die without the expander.
Trim to 1.368.
Then run it through the sizing die again with the expander to finish sizing the neck.
Chamfer the edges if the expander and sizing die did not smooth them enough.
The reason this works is the process makes an odd looking case that steps down twice, But that's not an issue because when trimming the case the small neck and shoulder get cut completely off. The link has pics of the process and clearly shows the double necked case being trimmed to a single neck.
Some of these posts are real head scratchers? Why would anybody think a sub sonic round would be for shooting past 100 yards at the most is beyond me and owning one without a suppressor is POINTLESS... It's as if people are buying and building guns and then find out what they bought or built is a short range tactical weapon that has no real sporting purpose!
It's like buying a 10ga magnum shotgun and being surprised when it isn't as good for quail over a pointer as you would like.
A simple google search would have saved some of these guys a whole bunch of time.Jeff
I've built a fair number of .300's for customers and will throw this out there.
1) These are not long range rifles, but with 110-120gr ammo and a 16" barrel, they will perform as well as most factory produced .223's out to 150-200 yds.
2) At 100 yards or less, I generally get better groups with subsonic 220gr SMK's than with supersonic.
3) You can shoot Hornady .300 Whisper in any .300 blk. Other brands, beware.
4) IF you can afford it, and if you want to go through the process, buy an SBR with suppressor. This is what these were really designed for. I realize it makes these a two stamp gun, but it's worth it. If you can afford to add full auto, it's the most fun you can have with your clothes on.
5) If you want a quick add-on to your current AR, buy an AAC upper. They come in 9", 12.5" and 16", complete with BCG and ready to mount to any lower. You can buy these for around $900. Just remember that if you buy the short versions, you are breaking the law by putting it on a lower without the proper paperwork to make it an SBR - even just to see what it looks like.
6) If you want a nice turnkey rifle, AAC makes the MPW line, which is a great buy at around $1400.
7) Ammo is tough to find right now. That will change.
I have been shooting and reloading the 300 blackout and have used it for the last two years for whitetails here in MN. Have had great results with the 110gr-150gr bullets up to 150yds. Have not shot a deer past that. This has been on the AR15 that I built and also have a 223/5.56 upper that I switch out to go P-dog hunting by just removing two pins. Two guns in one