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Discussion Starter · #1 ·
So I'm considering getting a 300 BLK conversion.

Are dedicated 300 BLK Pmags really required or do 5.56 mags work fine?

I've read early Pmags with the little nub at the top of the mag was problematic with certain bullets in .30 caliber and people were dremeling it out.

Thanks in advance.
 

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I'm honestly not sure as that would be something to ask a seasoned user of .300 BLK. But from my personal opinion, and you might have already considered this but, I plan to get dedicated BLK mags for my conversion just to differentiate them from my regular Pmags and reduce the risk that I put the wrong bullets into the wrong chamber as much as I can. We know that mixing up .300 BLK in a 5.56 barrel can have explosive consequences and vice versa, and humans can make careless mistakes, so I'm trying to eliminate that from happening by assigning one set of mags to be loaded with one and only one caliber even if they can do double duty. I didn't get my mags painted with anime girls (just) because the were cute, I also wanted to differentiate the ones I have loaded with the ones I've used. I'll get an entire set of .300 BLK dedicated mags and I plan to paint them completely different (maybe jets or robots, maybe just solid colors) so I can't possibly mix them up with the 5.56 Pmags and load the wrong bullets into the wrong conversion. The possibility of a barrel exploding isn't worth saving money on mags and even if there is a little benefit to using dedicated mags, then it's just a bonus. The fact that the Magpul mags say .300 BLK on them is worth it to keep 'em separated.
 

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Discussion Starter · #3 ·
I'm honestly not sure as that would be something to ask a seasoned user of .300 BLK. But from my personal opinion, and you might have already considered this but, I plan to get dedicated BLK mags for my conversion just to differentiate them from my regular Pmags and reduce the risk that I put the wrong bullets into the wrong chamber as much as I can. We know that mixing up .300 BLK in a 5.56 barrel can have explosive consequences and vice versa, and humans can make careless mistakes, so I'm trying to eliminate that from happening by assigning one set of mags to be loaded with one and only one caliber even if they can do double duty. I didn't get my mags painted with anime girls (just) because the were cute, I also wanted to differentiate the ones I have loaded with the ones I've used. I'll get an entire set of .300 BLK dedicated mags and I plan to paint them completely different (maybe jets or robots, maybe just solid colors) so I can't possibly mix them up with the 5.56 Pmags and load the wrong bullets into the wrong conversion. The possibility of a barrel exploding isn't worth saving money on mags and even if there is a little benefit to using dedicated mags, then it's just a bonus. The fact that the Magpul mags say .300 BLK on them is worth it to keep 'em separated.
I've heard the argument....not worried about mixing them up. If you get into XCRs very far, you'd better get used to the idea of checking things since you can swap parts/calibers so easily.
 
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Early in my 300 experience, I didn’t have any trouble with 556 mags…that was really before there were dedicated 300 mags and before I was shooting subs. I found a good deal on some Pmag 300s about 2 years ago and have used those since with no problems. Not sure they are really needed, but I ended up with dedicated. Can’t really speak to the question of certain bullet types and 556 Pmags.
 

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Don't think it would hurt but don't think it's a necessity either. I got a couple just because but never had any issue with standard pmags with mostly 147gr plinking in my 300xcr. I've shot subs for fun but never loaded more than a few at a time.
 

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Discussion Starter · #6 ·
Don't think it would hurt but don't think it's a necessity either. I got a couple just because but never had any issue with standard pmags with mostly 147gr plinking in my 300xcr. I've shot subs for fun but never loaded more than a few at a time.
And I don't plan any subs frankly....or very limited at best.

Sent you an email asking if you have any 9.5" bbl 300 BLK conversions in stock or parts to build one (will need the piston op rod and gas tube for the Type 3 buried block in a stnd L upper)....JFYI.
 

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Discussion Starter · #7 ·
Early in my 300 experience, I didn’t have any trouble with 556 mags…that was really before there were dedicated 300 mags and before I was shooting subs. I found a good deal on some Pmag 300s about 2 years ago and have used those since with no problems. Not sure they are really needed, but I ended up with dedicated. Can’t really speak to the question of certain bullet types and 556 Pmags.
They are cheap enough....$10 a piece right now....just don't know if I should pony up for 22 of them (tend to buy in 11's for mag for rifles) just to have on hand since I have hundreds of 5.56 mags as it is.

Thanks for the feedback.
 
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They are cheap enough....$10 a piece right now....just don't know if I should pony up for 22 of them (tend to buy in 11's for mag for rifles) just to have on hand since I have hundreds of 5.56 mags as it is.

Thanks for the feedback.
I’ve got too many 556 to count as well. Think I’ve got 10 of the 300…pretty sure that was the deal at the time and I want to say they were around $6 or 7 per…haven‘t seen anything close since.

Why 11? What about handguns?

For me, it depends on the gun and use…fun, but a safe sitter usually 2 to 5 mags. Competition guns 5 to 15. SHTF guns or platforms that share mags…lots…many more than are likely practical…might be a good currency as well though! 🤔
 

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Discussion Starter · #9 ·
I’ve got too many 556 to count as well. Think I’ve got 10 of the 300…pretty sure that was the deal at the time and I want to say they were around $6 or 7 per…haven‘t seen anything close since.

Why 11? What about handguns?

For me, it depends on the gun and use…fun, but a safe sitter usually 2 to 5 mags. Competition guns 5 to 15. SHTF guns or platforms that share mags…lots…many more than are likely practical…might be a good currency as well though! 🤔
1 in the gun and 10 in my plate carriers if I go with a full load out...but on a carrier, that necessitates double stacking the mags which I don't like that tall of a profile for prone, but it's a worst case scenario.

Same as you though....more 5.56/7.62 AK/Stanag/AR10 mags than I can count...if it shares it, I have a ton. But with one off calibers, I have at least 11 per weapon.

Handguns, at least 5.....but generally, anything I carry with have tons of those too.....P320, Glock and M&P mags a plenty.

Since this would be my first foray into 300 BLK, if I wanted dedicated mags, I'd get 11....but I was getting 11 more in anticipation of a mag ban and 2 is 1, 1 is none mantra when it comes to guns for me. If I like something, I usually have 2 at least. I can see that happening with 300 BLK in the XCR.
 
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I'm not too sure on the pmags, I usually run .300blk through aluminum mags and have had zero troubles. I know that pmags are wonderful, but having lived through thermold mags, just makes me nervous. If it ain't broke, don't fix it.
 

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I've heard the argument....not worried about mixing them up. If you get into XCRs very far, you'd better get used to the idea of checking things since you can swap parts/calibers so easily.
I myself am not worried about a mix up but. . . I have 3 sons who will inherit (they have access now) all of my firearms and accessories. I use the 30 round Lancer translucent tan with the coyote brown bases and marked .300 BLKT. They are distinct and match my tan XCR pistol very well. I also have a couple of same 20 round mags for compact carry in a bag.
Air gun Machine gun Trigger Gun barrel Gun accessory
 
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@Col Maddog Is that a 1x prism scope? Does it actually cowitness with the back up sights? (I’ve read that that doesn’t work but don’t know anyone who has tried).
 

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Discussion Starter · #17 ·
@Col Maddog Is that a 1x prism scope? Does it actually cowitness with the back up sights? (I’ve read that that doesn’t work but don’t know anyone who has tried).
I have the old 1X PA Cyclops prism that cowitnessed with Troy Micro irons....on the shortest Aimpoint t1/t2 mounts.
 

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Discussion Starter · #19 ·
Sean, good to know, thanks.
Well, that said....I like the new 1X Cyclops a lot better and it too seems to cowitness with my Troy Micros (haven't shot it yet though) on the lowest ADM mount for a mini-ACOG. Planning to buy at least 1 more (have 2 Cyclops now).....really nice optic for the money.
 
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