300 Blackout question

[mauler]

I hadn't really thought of it, but the shorter .300 case might allow the action to close enough on a 5.56 chambered rifle to get the firing pin to hit the primer.  I bet a free floating .30 caliber bullet exploding in a 5.56 chamber makes for all sorts of unpleasantness.  On a related note, I had a buddy who inadvertently loaded a .223 round into his AK 47 mag.  Yes, it fired the round, and gave a college try at ejecting the exploded case.  I love Mikhail Kalashnikov.

[bafsu92]

I hadn't really thought of it, but the shorter .300 case might allow the action to close enough on a 5.56 chambered rifle to get the firing pin to hit the primer.  I bet a free floating .30 caliber bullet exploding in a 5.56 chamber makes for all sorts of unpleasantness.  On a related note, I had a buddy who inadvertently loaded a .223 round into his AK 47 mag.  Yes, it fired the round, and gave a college try at ejecting the exploded case.  I love Mikhail Kalashnikov.

No, I tested it on mine to see, close but it won't go into full battery.

[mauler]

No, I tested it on mine to see, close but it won't go into full battery.

Cool.  Good info to have.  I wonder how the Kaboom pic Tyler referenced happened.

[fightingquaker13]

When I get a chance I'll take some pics of what I did. I dedicated all my FDE P-Mags to 300aac. I then took some number stickers and put "300" on the bottom 3rd of all the mags. I taped off the rest so there is just a small stripe exposed about 1/4" above and below the 300 stickers. I then shot them with flat black duracoat and took off all the tape and stickers. I basically have a 1.5" black band around the bottom of the FDE P-Mags with 300 in the stripe in FDE. It looks really good and reminds me what they're for. When I shot grendel I used all Foliage P-mags for it and had a little blue "G" on those mags.

Might be better to leave a little tape on there. That way you don't screw up in the dark and have that extra tactile fail safe. Ahh, duct tape, there are so very few problems that it can't solve.
FQ13

[robheath]

Great info guys now i'm glad i asked.  When I get mine built I'll use some dummy rounds and give a full report.  I can just see the bolt jamming that 30 cal round deep enough in the case to let it go into battery.  That would suck !!

[Sponsor]

[bafsu92]

Cool.  Good info to have.  I wonder how the Kaboom pic Tyler referenced happened.

Maybe they were using whisper ammo or a handload that was slightly shorter. It was very close, I walked the bolt in softly since I didn't want to jam in an mess up my chamber. I guess if you let it slam and/or used the forward assist you could probably get it into battery. Plus with so many AR homebuilds out there you'd be shocked how many aren't properly headspaced. If you were off a little there and your load was off a little here it could all add up to a big crap storm.

[Magoo541]

Maybe they were using whisper ammo or a handload that was slightly shorter. It was very close, I walked the bolt in softly since I didn't want to jam in an mess up my chamber. I guess if you let it slam and/or used the forward assist you could probably get it into battery. Plus with so many AR homebuilds out there you'd be shocked how many aren't properly headspaced. If you were off a little there and your load was off a little here it could all add up to a big crap storm.

I haven't built an AR-YET!, but I will partly because the headspace and timing are the things I haven't messed with since I ran the M-60 or M-249 20 years ago.  Even then all we did was check it with a GO/NO-GO gage and set it to the unit armorer if it was a NO-GO.  How do you set up the HeadSpace on an AR?

[Big Frank]

Just check with go/no go gauges. The headspace isn't adjustable. A new barrel and bolt will almost always be good together. Used parts... no so much.

[bafsu92]

Just check with go/no go gauges. The headspace isn't adjustable. A new barrel and bolt will almost always be good together. Used parts... no so much.

Yes and no, quality parts installed properly and this is 100% correct. I've seen some new barrels that don't have the barrel extension properly installed. I've also seen new barrels and new receivers that weren't manufactured completely square or true. It doesn't take a lot to throw things off. You can use go/no go gauges to make sure everything lines up but if it doesn't they don't really tell you where the problem is. That's why you buy quality parts or from a reliable source. Say you buy a upper and barrel from someone like PSA or BCM and you have an issue, you send it to them and they will make it right.

[robheath]

Yes and no, quality parts installed properly and this is 100% correct. I've seen some new barrels that don't have the barrel extension properly installed. I've also seen new barrels and new receivers that weren't manufactured completely square or true. It doesn't take a lot to throw things off. You can use go/no go gauges to make sure everything lines up but if it doesn't they don't really tell you where the problem is. That's why you buy quality parts or from a reliable source. Say you buy a upper and barrel from someone like PSA or BCM and you have an issue, you send it to them and they will make it right.

Exactly.  I've built 14 now and never had one not headspace...I have my local smith double check them ( he's a buddy of mine ) if you stick with quality parts, they are not at all hard to build.  About $100 bucks worth of tools and a little info and just about any body can build one.