So, just to tie a bow on the "Can you blow up your 223 with a 300 Blackout cartridge" side thread, I finally got out into the garage to do a bit of an experiment. I started with some 62 grain 223rem Federal ETSP that was given to me a couple of years ago. I also grabbed 3 different hand loads that I have made up for my 300 Black out.
View attachment 7730936
I measured the Base to Ogive for 5 cartridges from the Federal ETSP load using a Hornady comparator, a 0.220 insert, and a Cabelas brand digital caliper.
1.8585
1.8585
1.8565
1.8640
1.8625
Average 1.860
The hand loads that I had on hand include Hornady 208 gr BTHP (subsonic), Hornady 225 gr BTHP (subsonic), and a moly coated 125 gr solid copper hollowpoint bought from MidSouth SHooters' Supply as a blem (super sonic). I measured the Base to 0.220 measurement for 5 of each.
208 BTHP average 1.914
225 BTHP average 1.918
125 Copper HP avg 1.897
I also measured the COAL
208 BTHP average 2.249 (2.250 nominal)
225 BTHP average 2.248 (2.250 nominal)
125 Copper HP avg 2.035 (2.030 nominal)
I had 4 308 caliber bullets to try. While I realize that 308 is arguably the most common bullet diameter and there are probably dozens of bullets in this size, I feel that I have hit on a common bullet for supersonic loads (125 gr Nosler BT) as well as subsonic loads (208 gr Hornady ELD-M). I used the hornady comparator, the 0.220 insert, and a fine Sharpie to mark lines at 0.220 on 1 bullet from each of the samples. I then used the 0.300 insert to draw a line at the ogive of each bullet.
View attachment 7730940
As a first test, each bullet was seated in a S&B 300 BO case (300 BO head stamp, once fired and resized using a Hornady Custom Sizing Die) such that the Base to 0.220 mark mimicked the BTO measurement for the 62 gr ETSP load. No powder or primer was used in this test.
125 gr Nosler BT- 1.859
Barnes 168gr TSX- 1.8585
Hornady 168 gr AMAX- 1.860
Hornady 208 gr ELD-M- 1.8575
View attachment 7730950
I also measured the Cartridge overall length (COAL) for each of the "dummy rounds."
125 gr Nosler BT- 2.1835
Barnes 168 gr TSX- 2.126
Hornady 168 gr AMAX- 2.210
Hornady 208 gr ELD-M- 2.2545
Satisfied that each of were no longer than "magazine length," I attempted to chamber each. Each was loaded into an empty 10 round Magpul Pmag with the bolt of the rifle locked back. The release was dropped and the result observed. I made no attempt to force the issue with the forward assist. None chambered. In the picture below, you can clearly see a circular dent created in each bullet during the attempt. And, if you look, you can clearly see that each experienced significant bullet set back. The rifle for this test was a DPMS Oracle marked as 223/5.56.
View attachment 7730959
I had a momentary lapse and moved forward to the next step before snapping a pic. The ELD-M load did not set back as far as the picture would suggest. I had used the press to seat it further into the case before I remembered to take the pic.
COAL after chambering attempt
125 gr BT- 2.082, difference of 0.1015
168 gr TSX- 2.014, difference of 0.112
168 gr AMAX- 2.140, difference of 0.07
208 gr ELD-M- 2.216, difference of 0.0385
Finding that 300 BO cartridges loaded to more or less mimic the dimensions of a 223rem round did not chamber in my 223, the next question was "What if I seat the bullets to a 'functional minimum' with the ogive right at the case mouth?" And, that is what I did.
View attachment 7730967
All 4 of these dummy rounds DID chamber in my 223rem AR15- with a caveat. As observed in the picture below, 3 of the 4 experienced additional set back.
View attachment 7730969
Final overall lengths for ejected cartridges are as follows
125gr Nosler BT- 2.010
168 gr Barnes TSX- 1.962
168 gr AMAX- 2.010
208 gr ELD-M- 2.109
So, what is the conclusion drawn from this? Well, yes, it IS possible to chamber a 300 BO cartridge in a 223/5.56 chambered rifle. That should be obvious from the 223rem being the parent case of the 300BO, and the minimal forming required to make the 300BO. But, and this is a really BIG but- bullets common to 300BO usage need to be seated at or below the ogive in order to force them to chamber in a 223/5.56 rifle. To my mind, this makes it
possible- though HIGHLY UNLIKELY (bordering on willful)- to chamber and fire a 300BO in a 223.
www.thetruthaboutguns.com
Maybe trying to ram logic into small minds where it won’t fit? We’ve got a couple of those here. Lol.
