300Whisper trim to length 1.355 not 1.400!
 

About once a month, someone is trimming down brass for their 300 whisper to 1.4". It's a pretty common mistake since that is the length of the .221 fireball; but not the 300 whisper. The real trim to length for the 300 whisper is 1.355".
Don't feel too bad. Even the Hornady book got it wrong.
The new Sierra book got it right.

How about a sticky for the trim to length before someone gets hurt trying to chamber a case that is too long in a 300 whisper chamber?
Gos.

The funny thing is I had a brain fart and trimmed all my brass to 1.450", and loaded them up. They fed and functioned perfectly in my upper. Hell, I even loaded them another 3 times without trimming them again and they still worked perfectly. I must have a big ass chamber!

I've loaded for some guns that did accept the 1.4 with no problems, but I have seen others that did not. I'm just wanting to see this thing set to a standard length.
It would be interesting to see with a casting what your chamber length really is. What brand is your barrel?
Gos.

I have no idea. The seller told me it was an Armalite SS barrel. I never heard that Armalite ever made any Whisper barrels, but that's what the guy told me.

What we need is some technical Specs and FAQ....

Here is a related thread from the past:

http://www.quarterbore.net/forums/showthread.php?t=147

case dimensions
 

ammoguide.com shows the following dimensions for the .300 Whisper:

Case length: 1.40"
Neck id.: .308"
Neck od.: .330"
Neck length: .228"
Shoulder angle: 11 degrees
Body dia. @ shoulder: .369"
Shoulder to base: 1.070"
Body dia. above rim: .375"
Rim dia.: .375"

Which measurements are inaccurate, other than case length?

I'm looking at my hornady reloading manual, it shows case length of 1.4" but it has a 1.355 case trim length.

Case length: 1.40"
Neck od.: .335"
Shoulder angle: 23 degrees
Body dia. @ shoulder: .361"
Shoulder to base: 1.070" - if you do the math its 1.071
1.101 ot the front of the shoulder
Body dia. above rim: .376"
Rim dia.: .378"

Thats from the hornady book by copying and pasting yours and changing the numbers, I deleted the numbers that weren't there.


Jon

Case Length
 

Hmmmm ... I'm holding a page I printed off the Internet (I think it's from Accurate's website, as it only lists their powders) showing the 300 whisper (note: not named as 300 Fireball, and the description quotes JD Jones) and all of it's dimensions. The dimension from the rear surface of the case to the end of the neck is lsted as 1.360 inches, with an overall loaded round length of 2.245 inches.

Miker

I have cut my chamber with a 30/221 chamber from ptg, and I need to trim my brass at 1.350 otherwise it does not chamber.

Nic

The Sierra manual lists 1.365 as the case length and calls it 300-221 but also mentions Fireball and Whisper as alternate names. :eek: I'll say this. After starting the process of making my own brass, buying suddenly doesn't seem so expensive. :wink:

Edited to add My Sierra manual shows 1.360 as the trim length.