I was impressed enough with the little information I could find on a bullet to reload for the 300 Blackout that I bought a box of them to try, but I need some help.

The bullet is a Sierra #2124 135gr HP.

I manipulated a case enough to be able to insert and remove a bullet and still chamber but holding the bullet firmly.

I then dropped a bullet into the chamber, inserted the case and pressed it forward with a dowel.
After doing this several times I kept arriving at an overall length of 2.152". This is contacting the rifling.

Case length is 1.360".
Bullet length is .900".
Only .108" of bullet is in the case neck.

In order to get a reasonable amount of bullet into the neck I arrived at an arbitrary COAL of 2.080".
This is .180" of bullet in the case and .072" off the rifling.
A Lee factory crimp die will be used.

Other than contacting Sierra (where's the fun in that?), anyone have any suggestions or comments?


I've not yet arrived at a charge rate for this bullet but am guessing something around 13.5gr to 14.5gr of 2400 might be reasonable.
In my 16" barrel I was hoping for close to 2000fps with this bullet but I don't believe 2400 will safely do it.
One more powder type on the shelf is likely.