I want to save money on my 300 blk upper build when I buy it, so Will a 5.56bcg work in a 300blk upper are should I buy one with a bcg for the $100 more it will cost me. I’m building a pistol. Not sure what length I will get between to 8.5, 9.5 or 10.5. I think that’s the different sizes. Don’t want the 7 or 12 inch barrel.
Thanks Bob
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Yes 5.56 bcg will work for .300blk.
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Thanks. That will save me some money.
Same BCG, CH and mags will work.
Word of caution - Label your mags and keep separated !!
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Consider color coding or some other similar easy to quickly recognize differences between as many parts as possible. For example, magazines I buy the 300BLK PMAGs and label them with different colors in the dot matrix area. Blue for the standard 5.56 mags, yellow for 300 supers, red for 300 subs. All my 300 uppers have either upper receivers or hand guards or both that are FDE or grey. You can also label ejection port covers, or get a different color, or ones with the caliber printed on them. The Magpul polymer covers are ridiculously easy to install, too.
All this gets into the realm of being obsessive, I know. But it is useful to prevent problems and makes your firearms more interesting, too.
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All good advise. The color mag bands are cheap on amazon.
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basically what they are saying and what i subscribe to is do everything humanly possible to prevent yourself from having an accidential discharge of a wrong caliber in the wrong breach situation. That thought terrifies me, and I like these folks, am ultra attuned to making sure i have the right bullts for the right caliber gun im shooting. I try to make sure i have each mag labelled, color coded, or using different magazines entirely and labeled. Usually 2 forms of identification is MINIMAL. to ensure such a thing never, and i mean NEVER happens. and even still with the multiple marking, i still visually check at least 3 times before i fire the first round out of the firearm just to be safe.
Happy Shooting. and yes the mag bands re much cheaper online than in stores or at other “firearm Specific” locations.
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I am a FIRM believer using dedicated Lancer 300 mags, mine are 20 rnd. The follower is correct for the projectile and steel feedlips plus mag is marked 300BLK.
Goodluck on your build!
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Very good advice, never thought of color coding subs but I did know of marking 5.57 and 300 blk. Thanks for the great advice. It’s been very helpful.
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Thanks, just screen captureed your advice.
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Some operators may not have had experienced issues running other mags but l did.
Guitarguy steered me in the right direction for positive feeding! My 300 was my second PSA build which is a rifle mainly for Coyote or deer.
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You’re very welcome. Safety first just has been ingrained in me for so long on so many different levels its second nature now. which is a good thing. All it takes is that one round in the wrong place and you’re toast… and while i like toast, i dont think i’d like becoming it. lol
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i loaded a .300 round in a 556 mag once, luckily it didnt go off when pulled the trigger 
ive since moved onto a crack barrel .300, no more ar15 style LOL
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yeha. that woulda scared me straight too…
you’re lucky nothin went boom when you pulled that ol trigger.
dont have a need for simi-auto .300 anyway, i dont hunt
subs out of a closed action and can is so fun too