300 Blackout and 150 gr

A

a24296

New member
I picked up some 150 grain FMC .308 bullets (brand unknown) at a great price. I was planning to use them up in my Ruger Mini 300 Blackout rifle. Hornady lists the C.O.L. for a 300 Blackout at 2.235" but if I load the bullets at the cannelure the C.O.L. is 2.080". I would be using Hodgdon 300 BLK powder but at a mid-range load.

Will seating the bullet this low create unsafe pressures?

What about too much headspace?

Thanks.
 
Your cartridge headspaces on the shoulder, so COL has no effect. As to raising pressure by seating too deep, it's the seating depth, not the COL that matters. If you loaded a short roundnose bullet to the same COL as a long spitzer, the seating depth of the short bullet would be lower. Interesting that Hornady loads all of their 150s to the same COL, from the Interlock RN to the long sleek A-Max. If you are concerned, just seat to the COL you choose, and ignore the cannelure.
 
My guess is you can seat out to 2.260" like standard mag length for .223 AR . Of course shorter lighter bullets may not have enough in the neck . That's why I asked what max mag length is on a Ruger magazine.
 
On the Hornady 150 FMJ bullets I have, the shank below the cannelure is only about 1/4” long. Seating the bullet out 0.155” past the cannelure doesn’t leave much bullet to be gripped by the neck....




.
 
Thanks to all. beretttaprofessor, 17.0 grains of CFEBlk is less that I had originally planned but it sounds like a great place to start - and probably stay at.
 
I don't know all of what you are dealing with.

Is there a problem with loading to the tested book published length?(disregarding cannelure)

The bullet likely was designed for 7.62 X51 . There is no reason to expect the cannelure to be in the "right place" for 300 Blackout.

One factor I consider is seating the bullet base the full depth of the neck length.

The 300 Blackout has a short neck. I'd take full advantage of it.I'd want maximum bullet to cartridge neck contact. If its a boat tail,I'd hang the boattail into the powder space.

It needs to be not over 2.260 for magazine length. Beyond that,most of COL (in this case) would be feeding reliability.

I'd ignore the cannelure. Its irrelevent to 300 Blackout. Unless you have another specific reason not to,I'd load to Hornady's recommended 2,235.

You asked about headspace. Its apparent you are not clear on the meaning of the word. Bullet seating depth has nothing to do with headspace.

I suggest you study the topic in your reloading manual,or use the search function here to dig up past threads. Its a good subject to know about.

Headspace is all in the gun. Not the ammo. Its the distance from the breech face to the chamber feature(shoulder,in 300 BLK) that limits the forward travel of the cartridge in the chamber.

Head Clearance is the term used to describe the clearance from the cartridge case head to the breech face when the cartridge is full depth in the chamber,contacting the chamber feature (chamber shoulder in 300 BLK) that stops the cartridge from going deeper.

Headspace is in the gun,and only the gun. Short of gunsmithing,nothing you are going to do will change headspace.

Head clearance is about how your ammo fits the gun,and that can be affected by your handloading practices. But that is around resizing the cartridge case and sizing the shoulder *

The bullet seating depth is not a headspace item...or it should not be.

* Rimmed cartridges headspace on the rim. Belted cartridges on the belt. Straight wall rimless cartridges on the case mouth.Rimless bottleneck cases use the shoulder.
 
a24296 said:
I picked up some 150 grain FMC .308 bullets (brand unknown) at a great price. I was planning to use them up in my Ruger Mini 300 Blackout rifle. Hornady lists the C.O.L. for a 300 Blackout at 2.235" but if I load the bullets at the cannelure the C.O.L. is 2.080". I would be using Hodgdon 300 BLK powder but at a mid-range load.

Will seating the bullet this low create unsafe pressures?

What about too much headspace?

Thanks.
Click to expand...
You must have the old Hornady 10 book before the errata pages. According to the latest Hornady load data:
150gr FMJ-BT w cannelure seat to 2.090"
150gr Interlock SP w cannelure seat to 2.106" (same as 150gr Interlock BTSP
150gr SST (ballistic tip) w cannelure seat to 2.210" (longest listed 150gr COL)
 
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