350 Legend vs 300 BO

[DMW1116]

I’m looking for a new barrel and want to get away from 5.56. Are there any issues with either of these? I think I want a 0-200 yard caliber and these fit the bill.

I think I can load 350 L cheaper, but 300 BO related items are easier to find. Things like magazines, barrels, etc are more common and typically less expensive. Loading components are similar for powder and primers. Brass is way easier to find or make for 300 BO. 350 L has the advantage of loading with cheaper 9mm projectiles.

300 BO has a longer history and any issues are more likely to have been worked through.

All that makes it seem obvious but I’d like other opinions.

 

[BreechFace]

What’s the desired use for this?

 

[JohnMc]

What’s the desired use for this?

^^This.

I can say that I'd only go with .350 Legend if I lived in a straight-wall cartridge only hunting state but that's for me. Your decision will be personal to you.
Also, I've not needed special magazines for .300 BLK, USGI aluminum and Lancer mags have been fine. I read that some PMAGs don't work so I just didn't bother with those for it.
On a safety note, there is zero danger of a cross caliber kaboom with .350 Legend. If someone runs .300 BLK and has .223/5.56 guns, diligence is required.

 

[DMW1116]

To fill the hole in my soul that wants a larger caliber AR-15. Other than that it’s a new cartridge to reload, range gun, and the standard reasons for another AR: HD, media/politicians say they’re bad so they must be good, etc. There is a fairly small chance I’ll hunt with it.

 

[jonnyc]

Feeding issues with .350 in unmodified ARs, no issues at all with Blackout. The interchangeability of parts with .300 BLK settles the question for me.

 

[BreechFace]

Given that SD/HD is in the mix I would lean towards 300BLK. Not because the 350 Legend wouldn’t perform in those roles but 300 BLK has really good SD/HD loads and is used in the military in small amounts still, as far as I’m aware.

If you would have said hunting first and SD/HD second I would have been up in the air on my suggestion, but probably would have leaned towards 300 BLK. But this would have been more because I don’t have personal experience on how well the 350 Legend feeds and cycles.

The 300 BLK feeds very well out of magazines. The only caveat is if shooting heavies for subsonic one should get 300 BLK specific magazines. And personally I would regardless. The specific magazines have more tension towards the front of the follower to counteract the greater amount of bullet weight as the 300 BLK cartridge is front heavy.

It is also my thought that one is less likely to over penetrate through walls with a 300 BLK because of the bullet shape spire point versus handgun profile of the 350 Legend. Spire point bullets with long ogives will upset and tumble due to their unbalanced weight from front to back. Whereas, pistol bullets are weighted more consistently front to back and will not upset and tumble to any degree close to a spire point.

The above is why 5.56 makes for a good home defense round as it tumbles on contact when hitting a wall as it upsets the bullets stability due to shape and location of weight.

 

[JohnMc]

To fill the hole in my soul that wants a larger caliber AR-15. Other than that it’s a new cartridge to reload, range gun, and the standard reasons for another AR: HD, media/politicians say they’re bad so they must be good, etc. There is a fairly small chance I’ll hunt with it.

Flipping off the rich men north of Richmond is a great reason to get an AR!
.300 BLK is easy to reload and make the cases from .223/5.56. There are lists of which cases work best, just have a look before chopping.
The .300 BLK would be great for HD, IMHO.

 

[DMW1116]

If you dig around you’ll see several indecisive threads about my current project. The directions basically depend on whether or not I’m willing to get into reloading another caliber. I wrote 300 BO off for a long time because of the chance of mixing them up with 223 and that is still a concern. Some research on 350 Legend leads to some feeding issues and the need for caliber specific magazines.

If I’m willing to get dies etc and accept the risk of 300 BO in a 223, then 300 BO is the obvious choice.

 

[BreechFace]

If I’m willing to get dies etc and accept the risk of 300 BO in a 223, then 300 BO is the obvious choice.

I mitigate the risk by only using 300 BLK specific Lancer mags for my 300 BLK. All my 5.56 magazines are either MagPul or metal mags.

I don’t use Lancer magazines for anything else and I colored in the depressed 300 BLK molding on the side of the Lancers with a silver sharpie to draw attention to it.

If I’m understanding what you wrote you are getting rid of your 5.56 so in your situation the only concern for mixup would be when shooting with others and their 5.56. At which point extra vigilance is needed in what magazine goes with what gun.

 

[jmorris]

To fill the hole in my soul that wants a larger caliber AR-15.

If that were my goal I’d get another 458 socom.

 

[jmr40]

The only reason to choose 300 BO over 223/5.56 is if you want to use a suppressor. The only reason to choose 350 Legend over 223/5.56 is if you want to hunt big game in an area where straight wall cartridges are required. If not required I'm not convinced 350 Legend is a better deer cartridge than 223 loaded with 75 gr or heavier bullets.

I have considered both and decided 223 does everything I need to do with a lot less expense and drama.

If I wanted more performance from an AR platform the 6.5 Grendel or one of the 6.8's are the only ones that make sense to me.

 

[jmorris]

I mitigate the risk by only using 300 BLK specific Lancer mags for my 300 BLk.

I mitigate the risk by leaving my 300blk loaded, only removing the mag to put more in but I only use it for one thing.

Seems to me the highest risk situation is to have both .223 and. 300blk firearms and ammunition out a same place at the same time.

 

[AJC1]

I've been pondering a 300 bo for a long time, as a low cost option. My ability to run cast bullets has a lot to do with what I choose. I've seen strange things happen with lead rings in barrel extensions and other stuff shooting cast in a 300 bo. I don't know if it's a semi platform issue, an AR issue or just bad luck with the 300bo. I don't really intend on getting a silencer so I was comparing 300bo to 300 hammer. I still need to see if case forming works from 223. If I'm not going to run cast or use a can and can still convert brass that may be a better option in my situation.... figured it might be worth mentioning....

 

[BreechFace]

Have you tried powder coating your lead cast?

 

[DMW1116]

If that were my goal I’d get another 458 socom.

Those are for making holes in souls, not filling them. Besides, I didn’t know I needed a bigger ejection port and I already bought the stripped upper.

 

[DMW1116]

If 18” SPR barrels in 223/5.56 were in stock anywhere, my decision would be easier. Evidently they’re the thing to build right now.

 

[DMW1116]

If I didn’t have my 30-30, a bolt action 300 BO & some heavy cast bullets would be on my list. As it stands, some heavy cast bullets are still on my list.

 

[CraigC]

I thoroughly enjoy the .300Blk, it's almost too easy. Brass and bullets are plentiful and it's a cinch to go from supers and light bullets to heavy subsonics and back again.

I mitigate the risk by leaving my 300blk loaded, only removing the mag to put more in but I only use it for one thing.

Seems to me the highest risk situation is to have both .223 and. 300blk firearms and ammunition out a same place at the same time.

Yeah because mass never matters.

 

[mongoslow]

go 350L
that is the shoulder of a 170 lb 10 point I shot last year at around 65-70 yards, the bullet is a 170gr Hornady interlock, it destroyed that shoulder both lung ,broke the offside shoulder and I recovered the bullet under the skin on the opposite side of impact, get a purpose built 350L rifle ,it needs a pistol length gas system to insure proper BCG speed . Ruger MPR, Wyndham Weaponry, CMMG, use 350L mags, the only round I've ever had a feed issue with is the 150gr Deer season XP, that big plastic tip will hang on a feed ramp but everything else has fed, and no the 223/556 is not in its class for hunting or Sub 200 yard effectiveness on rampaging malcontents

 

[brewer12345]

If you plan to hunt with it, 350 is the no brainer choice. If you care about subsonic, 300BO makes more sense. Otherwise, sort of a tossup IMO.

 

[mavracer]

There is a fairly small chance I’ll hunt with it.

Then I'd probably say 300 BO. But they're both pretty nice rounds and can be reloaded on the cheap. Since I have both now I mostly load my blackouts subsonic Barry's plated 200/220 gr work nicely and leave the supers for the legend so far the only bullet I've tried are 147 XTP blems they shoot just like the WWWB 145 FMJ for accuracy.

 

[C-grunt]

If 18” SPR barrels in 223/5.56 were in stock anywhere, my decision would be easier. Evidently they’re the thing to build right now.

Ballistic Advantage has then in stock

 

[Telum Pisces]

I own all the above. When you ask the question of "which one," just get both.

I hunt deer with both. Both perform perfectly fine at supersonic velocity.

 

[earlthegoat2]

If your desire is subsonic and using a can then 300 BLK.

otherwise 350L for nearly every other possibility that does not involve subs and a can.

 

[Lo-Profile]

I have both, as well as a .450 Bushmaster. Sometimes magazines can be a issue in all of them, but it's a easy fix.
I prefer 300 blackout for ease of ammo finding and reloading components.