Factory 300 Blackout in a SSK 300 Whisper
 

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I put some factory Remington 300 Blackout 125 gr OTM through my SSK 300 Whisper to see how different this ammo really is. I disassembled five random cartridges from the box. The composites were weighed.
The bullets weighed 125, 124.9, 125, 125, and 124.9. The bullets resemble a Hornady 225 Match with the back half cut off. They have a little less curve in the ogive, but they both have a compound ogive. They are consistent and well made.

Hornady 225 300 Whisper on the left 125 OTM Blackout on the right
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The brass weighed 85.3, 85.1, 85.7, 85.6, 85.8. The cases are lightly crimped and the necks are annealed. One piece of brass was completely annealed. That case will be discarded. Case lengths were 1.361, 1.3615, 1.3595, 1.361, 1.361. The AOL of the cartridges is 2.227. The unfired brass is dimensionally identical to factory 300 Whisper brass and the 300 Whisper brass I make except the head stamp and trim lingth.

The powder charge was 18.7 gr of unknown powder that resembles one of our favorites.
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The chronograph was not cooperating today so the test is not complete. It was very windy and kept blowing the sky screen over. I did run three shots through the gun.


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The cartridges that were unloaded were neck sized and reloaded back to factory spec. The only difference was that I charged it with 18.7 gr of H110. I will shoot these through the chronograph next to the factory loaded ammo.

Fired cases tell the story. The outside diameter of the Blackout necks comes in at 0.336. 300 Whisper = 0.335. Thickness at the shoulder for the Blackout = 0.362 300 Whisper = 0.360. The cartridges shot soft and cycled flawlessly. Primers are nice and round. There are no extractor marks. The Blackout has slightly less body taper which equates to the thicker area at the neck. Essentially the Blackout ammo is dimensionally 300 Whisper spec. The Blackout chamber is opened up a bit to facilitate feeding.

300 Whisper brass shot out of a 300 Blackout on the left. 300 Blackout brass shot out of a 300 Whisper on the right.

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Mr. Alleycat , would it be OK to ask for specific dimensions?

Diameter at shoulder before and after? W & Blk
Diameter at neck/shoulder before and after? W & Blk
Length of brass before and after? W&Blk
Best est. of neck length before and after? W&Blk

Case volume before and after W&Blk ?

I have a stack of reamer prints I'd like to compare this to, if its not too much of an imposition. No hurry either.

The slightly less body taper on the unfired brass is to maximize the shoulder. Keep in mind, I am *not* saying it has less body taper than 221 Fireball, 223, or 5.56mm. I am saying we shoot for the shoulder being toward the larger end of the tolerance range that would be still be in spec for those other cartridges.

The bullet is actually a Sierra 210 chopped off in the back, and then with the nose struck closed like a Sierra 155 Palma - and while it is long, the weight is kept down by having the nose hollow. So, it actually uses as much copper as a 150-ish grain bullet.

What exactly is it you hope to gain with a shoulder thats .002 larger?

More shoulder.

No I meant truthfully.

More shoulder - why not optimize for the most of something?

well if that were the case why stop at .002 when you could have Ackleyed it and gained something measurable?
(please dont suggest feeding becoming an issue, we both know better)