300BLK OAL and pressures - discussion

[throttletony]

Hi all -
I've recently picked up an AR pistol in 300 blackout - and I love it!! I've fired it with some factory ammo and some handloads, no hiccups, and it's a very cool addition to my collection.

I've also converted about 125 pieces of 223 brass to 300BLK. Most of them, after trimming, measure about 1.357 - 1.360, with a few oddballs that are closer to 1.353 after smoothing them out w/ chamfering/deburring. Recommended trim length is 1.360/1.363 depending on manual.
My trimmed cases are on the shorter side of recommended trim length (I use the Lee lock stud and cutter w/ guide in a hand drill, so it's not adjustable)

I loaded a few rounds (150 gr Hornady FMJBT) and when I get the recommended length, the cannelure is fully visible and just above the crimp.

SO -- what's the lesser of two evils???
1) load them a hair "short" just a bit under recommended COAL in order to put crimp in cannelure (I am doing these with a beginning load, 14.9-15gr of W296, which cycles gun fine) The COAL is about 2.195 with the recommended min length being 2.230-2.235 (in different manuals and websites)?
-OR-
2) Load them "long" and ignore the cannelure (it would be fully exposed). THere's no real harm in functionality, right? Would I have to worry about jacket separation or a weaker crimp?

Again, these are not max loads, much closer to min/starting loads, so there is a little wiggle room to keep it within safe pressures, but I don't wanna find out the hard way that with 15 grns of W296 and 2.210" COAL is just fine and 2.200" COAL is too short and causes a pressure spike.


P.S. I'll probably just buy a batch of converted brass later and I'll make sure they're trimmed on the long side -- but that might not be until the fall. I'd like to use the brass I already have as long as I can do so safely.

 

[throttletony]

lots of questions there --
I guess I'm just wanting to start the discussion with fellow INGOers (who I generally trust as an initial sounding board)

Any input is welcome

 

[rg1]

Several 300 BLK shooters load the Hornady 150 FMJ-BT to 2.065" for better reliability feeding from AR magazines. Info I've read since getting into 300 BLK last year is to measure the bullet ogive and mark the spot where it measures .250" diameter and seat the bullet to where the .250" mark on the bullet aligns with the bump on the inside of a standard AR 15 magazine. That helps start the bullet straight into the chamber because .250" is the approximate diameter where the bump contacts the .223 case. Your load is very mild and the shorter oal won't cause high pressure. The 150 FMJ-BT isn't protruding deep inside the case. Common data for that bullet in 300 BLK is up around 16-16.5 grains of H110/Win 296 but do work up to that.

 

[Bfish]

 

[throttletony]

Several 300 BLK shooters load the Hornady 150 FMJ-BT to 2.065" for better reliability feeding from AR magazines. Info I've read since getting into 300 BLK last year is to measure the bullet ogive and mark the spot where it measures .250" diameter and seat the bullet to where the .250" mark on the bullet aligns with the bump on the inside of a standard AR 15 magazine. That helps start the bullet straight into the chamber because .250" is the approximate diameter where the bump contacts the .223 case. Your load is very mild and the shorter oal won't cause high pressure. The 150 FMJ-BT isn't protruding deep inside the case. Common data for that bullet in 300 BLK is up around 16-16.5 grains of H110/Win 296 but do work up to that.

Thanks for the info

 

[JTScribe]

Several 300 BLK shooters load the Hornady 150 FMJ-BT to 2.065" for better reliability feeding from AR magazines. Info I've read since getting into 300 BLK last year is to measure the bullet ogive and mark the spot where it measures .250" diameter and seat the bullet to where the .250" mark on the bullet aligns with the bump on the inside of a standard AR 15 magazine. That helps start the bullet straight into the chamber because .250" is the approximate diameter where the bump contacts the .223 case. Your load is very mild and the shorter oal won't cause high pressure. The 150 FMJ-BT isn't protruding deep inside the case. Common data for that bullet in 300 BLK is up around 16-16.5 grains of H110/Win 296 but do work up to that.

Ditto on this, that's exactly the load and COAL I use on my 300 Blackout. Once I got the right buffer in it, it runs like a top.