300BO stuff

So, I know I have some kind of compulsion n this stuff, but I do not even own a gun yet but want some guidance on, mainly, dies. The deal is I plan to eventually get something in 300BO, probably will start with another upper for my PSA pistol, if I like screwing with it maybe a carbine upper, maybe a Ruger American Ranch.

But at this point I have a bunch of cases I screwed up that are going to be perfect donors. I bought the Squirrel Daddy trim fixture. I figure size then trim, I like the lee dies, any reason not to get these?
https://www.amazon.com/dp/B006T3JJD6...v_ov_lig_dp_it

I am caught up 12g, and 20g, and almost on 9mm, so I just need to do a few 45s and I can screw around with this the rest of the winter.

Lots of folks here know this, but am specifically thinking @LittleLebowski might be in the know on this.

Those dies look good, I've had no problem with Lee dies.

The Squirrel Daddy fixture is good to go.

Before you buy an upper in .300 BO, decide on a method to segregate / discriminate between your 5.56 magazines and your .300 BO magazines. Firing a .300 BO in a 5.56 is no bueno.

Personally I use Lancer mags exclusively for .300 BO as they both look and feel different than the GI and PMAGS I use for 5.56. Plus the Lancers allow a little bit longer OAL for subsonic rounds.

Quote:

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Originally Posted by HCM

Firing a .300 BO in a 5.56 is no bueno.

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I know this, but thanks for reiterating.

Quote:

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Originally Posted by HCM

The Squirrel Daddy fixture is good to go.

Before you buy an upper in .300 BO, decide on a method to segregate / discriminate between your 5.56 magazines and your .300 BO magazines. Firing a .300 BO in a 5.56 is no bueno.

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Coincidentally, I just saw this. I don’t know the guy, and can’t vouch for the specifics, but apparently a 300blk in a 556 gun. No bueno, indeed.

https://www.instagram.com/p/Bq5yuHqH...d=c386cxbts6gl



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This was awhile ago so I don't have pictures.

A couple years ago, at my old job, we had a S&W MP15 that came in as part of an LE seizure. It was bound to be ground into scrap metal so we decided to experiment.

We braced the rifle in a rest and tied a piece of 550 cord to the trigger. Then we chambered a round of 300BLK and torched it off.

It took a couple drops of the bolt to get it to go into battery. Once the bolt was fully closed the hammer was able to set off the primer as normal.

The result wasn't a catastrophic failure but was probably pretty close. The case blew out and basically destroyed the ejector. The magazine base plate (and mag guts) were blown out of the lower. The bolt carrier stayed intact but the upper was bowed out slightly along the stretch of aluminum just below the ejection port.

We sectioned the barrel and found the bullet was about 2" long. It had been stretched and squeezed down the barrel and was lodged just ahead of the gas port.

This was using a handload. I don't recall the exact load but it was with a Nosler 110gr Varmageddon bullet and H110. I usually load for reliability rather than max velocity so it was likely probably a grain under published max. Was that slightly reduced charge what kept the bolt carrier together or was it just a fluke that the carrier didn't crack along the bottom?

Either way it would have been no fun to actually shoot!

On the plus side, I apply a heavy crimp using a Lee Factory Crimp Die. The round didn't chamber without a fight so I'm fairly confident I'd be able to catch a round that got mixed into my 223 ammo by mistake.

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Quote:

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Originally Posted by HCM

Firing a .300 BO in a 5.56 is no bueno.

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Quote:

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Originally Posted by Tokarev

The round didn't chamber without a fight so I'm fairly confident I'd be able to catch a round that got mixed into my 223 ammo by mistake.

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Have loaded some rounds at this point, mostly using the Speer TNT 125g and reread this and I had a wonder how close these rounds could come to chambering and had the thought to drop one into my 223 case gage:
Attachment 42062
That seems like enough OAL to stop it getting chambered. Though I may stick to a mental rule to not take both to the range on the same day, or at least not have both out of the truck at the same time.

Most people recommend a good crimp with something like the Lee Factory Crimp Die to help avoid any bullet setback.

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