The 300 BLK is obviously picking up steam in the popularity contest ––––  i had heard tell that this was basically  JD Jones old .300 Whisper cartridge he popularized in silenced Contenders years ago ,  but given a more "black-ops" sounding name for the AR market.

Is there  a ring of truth to this or do the cartridges have some differences ?  

I'll try to do a little more reading outside ARFCOM too –– i  am contemplating building one up ––-  the cartridge's linege doesnt really affect my decision, but was just curious ––––  

As an aside,  i wish Remington's fat little  .30 RAR would pick up some steam  in the aftermarket ––- maybe the different bolt head is holding it back ,  but velocities are close to .308 category with that one

Just get a .300blk - it can fire .300 whisper. Things don't work out the other way around I'm told.

I have heard the same things too. Chamber pressure of 300 BLK is too high for 300 Whisper.

Any chance 300 BLK is going to get a spot on the caliber specific FAQ? I have lots of questions.

http://www.300blktalk.com/forum/index.php

I'll only quote part of what I've read hear and provide the link if you want to read the rest yourself. Like I said though, I don't have any experience with it, it is only what I have heard.


Ammunition Review

The 300BLK took all the problems that the whisper had and eliminated them. The biggest being the 300BLK is SAAMI approved so every 300BLK is the same as the other BLK. AAC also made the the throat a little larger to accommodate brass that is cut down from .223 instead of Necked up from .221 fireball. The 300BLK can also run a little hotter than the Whisper.

The best reason for the 300BLK for the consumer is that it now cost half of what JD wanted for his rifles and 1/3rd of what the ammo cost. There are now a ton of manufactures for the ammo, rifles, brass and barrels instead of just one or a couple knock offs.

THIS IS TRUTH

you can shoot a whisper out of a black out barrel but not the other way around

.38 special .357 mag kind of deal...

now you can take a whisper barrel and have it changed into a black out barrel for cheap.. like 50 bucks cheap if you have a gun smith into those things...

I'm a little confused here... Correct me if I'm wrong:
You Can shoot a Whisper out of a Blk Barrel, but you Cannot Shoot a Blk out of a Whisper barrel?

Looking at S&W's Whisper Upper:
http://www.smith-wesson.com/webapp/wcs/stores/servlet/Product4_750001_750051_799601_-1_772153_757784_757784_ProductDisplayErrorView_N
Model M&P15 300 Whisper® Upper Assembly
Features & Benefits
   Manufactured on the M&P15 modern sporting rifle platform.
   Chambered in .300 Whisper®.
   Will also safely fire .300 AAC Blackout

I claim now, I know Jack $hit about the 300s. I'm just wanting to get clarified information, because I'll be in the market soon to purchase one (with the future plans of a suppressor).

Some whisper barrels have a tight neck that cannot be used with cut down 223 brass as the neck is too thick. It usually wont chamber anyway. 300 Whisper made with 221 fireball brass does not have these issues. The 300 blk has a more generous neck for use with cut down 223 brass. Some whisper barrels including the 2 that I own will chamber cut down 223 brass just fine. It jusr depends on the barrel. If it chambers easily and you dont have to mortar it to get it out it is usually fine. YMMV................DV.......................

No one (including the dreaded-by-this-site Robert Silvers) knows why S&W decided to name their rifle a Whisper and pay JD Jones the royalty for a wildcat but it apparently is the one exception to the rule.  Think of 300 BLK and Whisper just like you would 5.56 and 223.  Here, 300 BLK is the more powerful cartridge just like 5.56 is.

300 BLK : 300 Whisper :: 5.56 : 223

Thanks for making that simple for me.

Now it's making sense. Thanks for the clarifying this up for us.  

The 300 BLK is the SAAMI spec chamber for the various wildcats based on a 221 Fireball case backed up to 30 cal. (300-221 Fireball, 300 Whisper®, 300 Fireball, 300 WTF (WhateverTheFuck) etc…). It is similar to the 22-250 REM started out as a wildcat that went by the handle 22 Varmiter. The 25-06 also has a similar history.

So to the question can one shoot 300 BLK ammo in a 300 Whisper? The answer is "It depends on the actual dimensions of your 300 Whisper chamber.

The 300 BLK is not more powerful than the 300 Whisper. The marketers (AAC and there agents/employees) may try and convince you of this but it is simply not the case.

I have four 300 WTF's and have tried various different factory 300 BLK ammo in my gun and my reloads match or slightly exceed the factory ammo. If I was going to buy another I would get the 300 BLK just because it is easier to find 300 BLK barrels now than 300 WTF barrels.

The Truth  ! ! ! !

I have not seen any statement to this effect from Robert or other "marketers."  What I have seen said is that shooting a 300 BLK round in a tighter 300 Whisper chamber has the potential to raise pressures above safe limits.  I think some are misinterpreting this as "the 300 BLK is more powerful."  Instead, it just means the 300 BLK SAAMI chamber is slightly wider in the neck than some Whisper chambers so (in part) that 5.56/.223 cases can be necked down for brass.