I have 2 ARs, 5.56x45 and 7.62x51. I'm not worried. But I know lot of folks with this issue. Different colored or marked mags seems to be the cheapest and easiest.
Pretty sure Grendel rounds shouldn't seat into a 5.56 bolt face (Rim diameter .440" vs .378" nominal) so in theory there's no way the firing pin would reach the primer if someone chambered a 6.5 in a 5.56...
In practice, not 100% sure, but I wouldn't lose sleep about it.
As for .300, presumably the bullet width wouldn't allow the case to headspace into the chamber, so the BCG would be out of battery where the bolt stops, and in any lower that's close to in-spec, the hammer will hit the BCG shroud before the firing pin. If your bullet is seated deep enough that it won't hit the chamber shoulder before the bolt is in battery, I suppose that could be an issue....but I can't say for sure, as I haven't played with loading .300BLK.
I mean, if it's a major concern, just make sure you only have one out of it's case at a time, keep the ammo separate and clear any loaded mags before switching rifles.
How do you guys keep your non-5.56 ARs marked or separate so they don’t get blown up by mixing up ammo & mags. I have a 6.5 Grendel & I’m thinking about getting a .300 Blackout but I’m alway worried someone will mix up & kaboom my AR. Though or solutions?
Like having one powder, bullet and load at once when sitting at the reloading bench, just put one type of ammo and one gun out at a time if you have others shooting your stuff.
I learned this when a neophyte buddy loaded and fired his .45 Colt revolver after grabbing .44 Magnum loads out of the wrong ammo can. If it wasn’t an old model Vaquero that he was shooting, it could have been catastrophic.
Stay safe.
Buy a FAL, you wont confuse mags anymore!
In safety process design, we have two types of safeguards - physical/mechanical and procedural. Because procedural safeguards are ALWAYS vulnerable to human error - aka, ignoring, forgetting, or failing the procedure - procedural safeguards are never considered “Full Value ISL’s,” independent safety layers, for any risk identified as class C or higher, meaning an incident could result in significant injury or death. Such, procedural safeguards always require additional independent safety layers to create a full value safeguard. Also pointing out here, most A and B class risks require MULTIPLE ISL’s, not just one.
So given that paradigm, we could never rely upon any procedure - such as marking magazines, ammo, or uppers, or separating/segregating ammo, or only loaning out one rifle and matching ammo at a time, etc. Any procedure like this is not infallible.
For example - despite marking magazines, an unwitting shooter might not realize the meaning of the markings (different sized mags or colors), or the markings may fail (bands slipping off or breaking), or a person still might load the wrong ammo into the magazines, or simply grab the wrong rifle, or assemble a non-5.56 upper onto a 5.56 marked lower, or a person might put ammo into the wrong box, or put a box of factory ammo on the wrong stack or shelf, or… or… or…
However…
Physical/mechanical safeguards DO constitute full value ISL’s, so mechanical safeguards are far more reliable than procedural - human dependent - safeguards. We like to pretend in firearms world that our procedural 3 rules of gun safety are the highest safeguards, but statistically and factually, mechanical safeguards always promote greater safety than procedures. Bluntly, you are more apt to forget to activate a mechanical safety on a rifle, or inadvertently deactivate the safety than the mechanical safety is apt to fail - AND - good PSM programs require methods to regularly confirm function of safeguards.
But physical fit is a mechanism which can fail - so quite literally, owning the 300blk is the only real risk in this scenario. There is no other combination of cartridges between which the larger bullet diameter cartridge will fit into the chamber of a smaller bore cartridge. 6.8 SPC, 6.5 Grendel, 204 Ruger, 17 Rem, 20 Pract, 6 ARC, 223/5.56, 458socom, 450 bushy, 350 Legend, 224 Valkyrie, 22 Nosler, 25-45 sharps, 7.62x39… all of these have sufficient interference in cartridge dimensions such none of the larger bore cartridge ammunition will fit into a smaller bore cartridge chamber. For the few which CAN chamber into eachother such as 17 Rem being fired in a 223/5.56 rifle or 6 ARC in a 6.5 Grendel rifle, the under-sized bullet will rattle down the bore, with no greater severity of consequence. The 300blk is the only larger bore cartridge which is sufficiently short to successfully chamber into a smaller bore, 223/5.56 chamber, causing a bore obstruction and potential catastrophic failure in a single shot.
So mechanically, no combination of cartridges and rifle can present a significant risk if you do not own a 300 blackout. If you DO own a Blackout, then there’s really nothing beyond fallible procedures which can prevent a Kaboom, which then requires at least two procedural confirmations to promote a single layer of safeguarding.
It just comes down the "headspace and timing" of the operator, keep your gear basic and simple to what works for ya.Unless you end up with both inch and metric mags somehow!
Or worse, you end up like my buddies Century FN FAL. It wouldn't run with either inch or metric. Just the one mag it came with. 5-6 of both types wouldn't run more than 1-2 causes cartridges at a time if at all. That one mag it came with ran pretty well though. But it somehow didn't match up with either inch or metric. Just Century being Century I guess.