RCBS Whisper Loading Die Question

[HotLead]

I have owned a T/C Custom shop Encore barrel in .300 Whisper for several years now, and love it (even though it is a 1:10 twist). I contacted SSK and purchased my first couple hundred pieces of formed brass and a set of RCBS .300 Whisper loading dies.

Now that I am in the process of building an AR upper in 300-221, will I be able to load for it with my Whisper dies and shoot safely? Or will I have feeding/ chambering issues? I don't know enough about the differences in chamber dimensions between all the variants. Thanks in advance for any answers.

[A62Rambler]

Hotlead,

I'm new to the 300-221/Whisper/Fireball caliber myself. In my reading I have found that, 300-221 chambers are the tightest with whisper next and fireball the largest. I think the differences in the chambers is pretty small and is just a way to keep from paying royalties on JD Jones patent. Are you planning on using necked up 221 brass or cut down 223 brass? I don't know what JD Jones was using. I think the only possible problem might be neck diameter. That can be corrected by reaming the necks. My redding dies using cut down 5.56 brass have a max case neck of .335 which I believe is right at the max for a 300-221 dimensions. This was without any reaming so I would think your dies and brass from JD Jones should work fine. Wow that was wordy! I'm sure one of the more knowlegeable folks will be along to correct me or verify soon. :welcome:

[HotLead]

Thanks A62Rembler,

I plan to form from 5.56 Lake city brass. (one of the reasons I love the whisper ctg) Lake City is what I purchased from SSK as well.

[Garrett]

From what I understand, 300/221 is the same thing as .300 Whisper - SSK has the Whisper name copyrighted.

I've used brass from both .221 Fireball (loaded and formed brass from Reid's Ammo) and Lake City brass (formed brass from SSK and loaded ammo from CorBon).

Both seemed to work just fine.

I believe the SSK barrels have a slightly wider chamber at the neck so you don't have to ream the necks when you resize military brass.