I did a search and did not find any discussion of this on this forum, so decided to post this.
I am a new 300BLK shooter and I discovered something a little disturbing about the design. With the exception of the barrel, the 5.56 and 300BLK are identical. I did a plunk test and the 5.56 cartridge will not seat into the 300BLK chamber. However, the 300BLK cartridge happily seats into the 5.56 chamber! They both fit into the same magazine so the chance of error is real. If the mistake is made, then a 30 caliber bullet will be fired into a 22 caliber barrel. One internet poster said he saw a video of this scenario set up with a 10 foot string used to pull the trigger. He said the result was the expected exploding rifle.
I currently have two 20 round magazines, and all others are 30 rounds except one 10 round magazine. For now I am designating the 20 round magazines as 300 BLK only. I have put blue painters tape labeled 300BLK on the sides of them. I have always used the 10 round magazine for dry fire training, so will continue that practice with the 10 round serving dual 5.56 and 300BLK dry fire roles. All my ammo cans are labeled and stocked with one caliber only, so mixing of the 5.56 and 300BLK can only occur if I either load the wrong cartridge into the wrong magazine, or put a 300BLK magazine into a 5.56 rifle.
I use these on all my 300 BLK magazines as a visual and tactile indicator and also use different color mags for the 300 BLK. They come in lots of different colors so you can contrast the bands with the mags if you want to make it even more obvious. They also make some of these bands that say subsonic on them so you can keep from grabbing those when you really want the high speed rounds.
I also only take either my 300 BLK or my 5.56 gun and ammo to the range. Never both at the same time just to be extra safe.
Pulling the trigger on a 300 BLK round in a 5.56/.223 barrel would be very very bad for the gun and most likely the shooter as well.
I can’t imagine confusing my personal 300BLK with my 5.56, but this is not a bad idea for people that have so many they could get them confused:
“Will also fit around many hand guards for quick gun identification.”
I could imagine somebody going as far as putting different color marking bands on their 5.56 magazines with matching colors on their respective handguards. I can also see if you need to go that far down the rabbit hole, then maybe a 300BLK isn’t a good idea for you.
Edit:
I have re-thought this comment and have changed my mind. I will be taking all steps that can help prevent me from inserting a 300BLK magazine into a 5.56 firearm.
I don’t have enough firearms to get all that confused between them:(
My 300blk is a different color and size than my .223/5.55 rifle so I wouldn’t ever confuse them. My only concern is grabbing the right magazines for the right firearm in a rush or in the dark in a self defense situation.
Rather than using bands, that could fall off, I’ve marked all my magazines with these permanent markers. I have a similar issue having both .40 and 9mm Glocks that otherwise look identical.
Mine are different sizes as well, but 5.56 is sporting an LPVO vs. the 300BLK with a Red Dot.
I am not commenting for your benefit, I am sure you have a well thought out plan, but I am commenting for potential help to others …
The “experts” I have read recommend keeping bedside firearms already loaded to ensure no stumbling. I personally depend on a loaded, chambered pistol with a weapon mounted light, spare loaded magazines, and a bright flashlight beside the bed. I keep them arranged such that I can grab the flashlight first.
I can see the rational of both permanent labeling as well as removable bands. I would vote for permanent marking for 40S&W and 9mm as one can never become the other.
However, I am leaning towards the bands for 5.56 vs. 300BLK as I might change my mind and make a 300BLK magazine a 5.56 magazine by simply swapping bands. I have already ordered both 5.56 and 300BLK bands today. The 5.56 are black with white letters, and the 300BLK are black with green letters.
Same here except in a quick access safe since I have young ones around.
My 300blk and .223 firearms aren’t part of my immediate home response plan. They are in the safe cruiser ready in case I need to respond to outdoor trouble. But I have spare mags for the .223 and 300blk in mag holders and would want to make sure I leave the house with the right ones if I needed to.
I use the magazine bands that @Shamrock mentioned but in RED. Plus my 300bo has a red charging handle, red forward assist cap, and 300 BLK OUT script on the dust cover. Probably overly redundant but better to not make that explosive mistake and potentially keeping someone else you’re at the range with from making the OOPS.
May I recommend to all who have various weaponry which you commonly use together at the range, etc., as I do, that you label your ammo cans and pre-loaded magazines? DO IT!
I have re-thought this comment and have changed my mind. I will be taking all steps that can help prevent me from inserting a 300BLK magazine into a 5.56 firearm.
mistake and potentially keeping someone else you’re at the range with from making the OOPS.