Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

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Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

Post by starlingstalker » Mon Mar 09, 2015 11:13 pm

I load quantity test ammo on a Super 1050 for mil 5.56, 300 Blk with 125 gr. flat base Sierras and Sierra 220 gr. subs with occasional 458 Socoms for the function check ammo in newly built AR uppers. There are more than a hundred uppers testing daily and the builders test fire for cycling and bolt hold open and then apply the rails. One of the builders had a very senior moment and loaded a mag of 300 Blk 125 gr. Sierras to test fire. The 1st round did not seat so the forward assist whacked it into battery. He launched a 125 gr. bullet down a 5.56 barrel with a moderate charge of my favorite race car H-110 powder. Needless to say, the pressure was near catastrophic with the brass case welded into the chamber and its base separated completely.The upper and the bolt held up pretty well,required a shop hammer to get apart and the barrel nut actually unscrewed. The venting of the pressure blew out the Pmag and put a deep deep dent lengthwise in the next bullet to fire.
Spread the word. Seeing was believing - a new 125 gr. former 30 cal boolit now at 0.224 groove diameter. sharp lands were even visible the length of the OD. Near an inch and a half long. Near fell out with a lite tap.
H-110 WILL surely swage 30 cal.bullets instantly with a LOT of else. MOSTLY bad........ :shock:
Wish I knew how to post the pic out of my phone. You would be pleasantly pleased...... :roll:

Lucky for the shooter that he was wearing the EXPECTED PPE-shooters gloves and glasses and got a numbing concussive blast diffused into the glove fabric instead. A minor superficial nick in the web of the hand was the only injury. If the glove had not been in use, there would have been significant powder burns, embedded pulverized brass shrapnel with expected possible thumb fracture.
The moral of the story is if ANY fired round makes a beer fart or coughs, pops with reduced recoil or sounds Funny - INVESTIGATE.
Keep a rod handy to check for squib loads. If not, check out all the much wiser U-Tube idiots that learned the hard way - and got the lesson they Deserved. :mrgreen:
I told the tester THAT he got a MAJOR Blessing from Heaven Today. And was literally able to walk away. He's Been There, Done That!!!!
So, educate Your mag loading friend helpers and check your 5.56 ammo and or mags for a devil in the details, especially if You have both calibers for an errant 300 Blk. disaster that could happen. Saw what DID happen today.
starlingstalker :D
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Re: Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

Post by 66427vette » Tue Mar 10, 2015 7:23 am

He got lucky. Stupid is suppose to hurt.

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Re: Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

Post by ThaDoubleJ » Tue Mar 10, 2015 7:58 am

He might be smart and was just thinking about a cheeseburger.

There are a couple pictures of this event online, not sure where to find them, but one is an exploded upper as expected, the other is a bolt gun with like a 3" long 30 cal bullet stuck in the 22 cal bore. They milled the side off the barrel, looks pretty cool in there.

I bought Lancer mags for my 300blk, they feel and sound funny, so I'm trying to make it a habit that little bullets go in regular mags, big bullets go in weird mags. I've also been using a product called Brass Black to discolor my 300blk cases and try to add an extra visual cue to them.

Hopefully I never have a story to tell.
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Re: Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

Post by SpeedyR » Thu Mar 19, 2015 11:00 am

scary. I reload many calibers and even though some calibers are easy to convert from one to another, I try to never have something that isn't headstamped for the correct caliber. I don't do anything with blackout (yet!) but I already have a bunch of proper headstamp brass so when i do go that route I don't have LC stamps on two calibers. Hopefully not an issue for me to recognize the difference but just in case someone else grabs a box of something, I'd hate for mis labeled headstamp to be the issue.

32 Winchester Special formed from 3030, 218 bee formed from 32/20, 300BO from 556, 243 from 308, etc. I know it costs more and may be harder to find (like 35 remington these days!) but I like the peace of mind from having proper headstamp. I do like the idea of loading up specific magazines (metal vs. pmag or something similar) to lessen confusion as well. good idea.

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Re: Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

Post by Artful » Mon Oct 19, 2015 2:12 pm


maybe worth the investment for Mag Bands
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Re: Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

Post by BadKarmaZeroSix » Mon Oct 19, 2015 7:20 pm

I use separate mags (Lancers for 300 Blk and Pmags for 5.56), plus i purchased several of the bands for my Lancers that say "300 BLK" on them for my fiance to be double-sure when she is shooting with me...i have tried "blackening" the brass with SOME success, but then i lose them more often in the grass, so i'm trying nickel-cases for 300 and brass for 5.56 now...the black cases i have left are bolt-action specific loads (not enough gas to cycle AR) since i can control their ejection better...
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Re: Beware- swaging 300 BLK in 5.56 upper with H-110 - NOT recommended!

Post by eastern_hunter » Mon Jan 16, 2017 10:34 pm

I picked up some plastic IMI mags that have a protrusion at the base as part of the means for closing the spring in the magazine. They are visibly different from all other magazines I have that can be used with 5.56 ... and the difference can be felt in the dark.

I load 300 BLK in ONLY those IMI mags!!!!

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