Took this from ar15.com. Seems like a legit issue and not just some crazy dude. Several guys three-gun with BLK and it would seem from anecdotal posts that some special ops guys are trying out 300 BLK. Any reports from those two groups of movers and shakers of this happening?
Went shooting this weekend and IMHO, P-mags don't work very well with 300 Blackout. Ever time I pulled a P-mag loaded with 300 BLK out of my pocket, shells went spraying everywhere. Tilt the mag and give it a little shake and watch the rounds drop out the front like you're holding a 300 BLK pez dispenser.
I tried 6 different P-mags and 2 different ammo types. The heavier bullets were more prone to go flying uncontrollably out the top of the mag like a jack in the box. The Lancer mags were a little better, but still a problem. Shells 1 and 3 allow shell 2 to slacken and then to fall out, next, shell 1 pops out and the cycle continues.
Spent my time firing my other rifles after I got tired of dumping 300 BLK shells all over the ground. Hopefully, someone will make an actual 300 BLK mag with out all the front to rear slop and ribs pushing into the front of the bullet.
And a follow-up post.
Came home and tried to duplicate the P-mag failures I experienced on Sunday. I was able to repeat the problem with the P-mags but not my Lancer mag. Some mags were more resistant than others but one was especially bad. None of the mags have ever had any feeding issues once they are loaded in the rifle.
To get the mag to dump shells, I would lightly tap the mag on the left side with an odd numbered shell at the top of the mag. This forces shell #1 and #3 to the far left side of the mag and into the left feed lip. Shell #2 can now rattle around freely and if the mag is tilted and the bullet is a heavier grain (147-220gr) it will fall out of the mag as pictured in my post above. Shell #1 can now be thrown free once the feed lip looses it's grip.
Under the right circumstances, this pattern can repeat rapidly, launching 5-6 or more shells from the mag if the mag is facing down as it is being swung forward into the rifle receiver, which is what I experienced.
I bet it's due to leaving a mag loaded without using the pop in dust cap.. it probably causes the feel lips to bend a little allowing the rounds to pop.... in terms of 300 BLK the brass has the same dimension since it's made form .223 ....
and i've had one problem with a pmag I had left loaded without the cap (223) , not only rounds would fall out , but the mag was tight in the magazine well ...
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"Are you gonna pull those pistols or whistle Dixie?" --- Clint Eastwood --- The Outlaw Josey Wales
Sounds more like an issue of plastic/polymer fatigue in the P-mag and not an issue with the round itself.
I don't own poly mags but prefer the British steel mags myself. I have a ton of GI Issue mags as well so I don't plan on purchasing poly mags since I don't plan to use more than 5 rounds at a time in the mags anyway (I don't get excited by the idea of blowing off 30 rnds at a time...)
I'm thinking the OP is using older mags improperly and that explains the shaker magazine issue.
This is most likely caused by the internal rib. The rib is made for 556 and will make a 300 stack unevenly in the mag, forcing the nose of the bullet into the front groves and causing a bind. Without proper pressure on the top rounds they would fall out easily. The solution is simple, file down the rib appr. 1mm.
Just wanted to be clear that I haven't actually had that issue before. Someone posted that on ar15.com.
After I read that last night I loaded up some of my 110 Vmax handloads in a Pmag and was unable to get them to pop out no matter how much I shook or banged the mag. They wouldn't even move in the mag with a COL of 2.08. I'll load up some 147 and 225 grainers to test further.
I suspect that gentleman has something wrong with his mags but was curious if some of the more serious users over here had had the same issue.
It would probably depend on the bullet and COL, but a friend with substantial experience with the 300 has experienced this binding to be common with unmodified Pmags. And it is pretty obvious when you look at it, the mags are made for 556 so the rib has to push the cartridge towards the center of the mag. And with the COL at max the nose will easily catch at the front groove.
Fulmen wrote:It would probably depend on the bullet and COL, but a friend with substantial experience with the 300 has experienced this binding to be common with unmodified Pmags. And it is pretty obvious when you look at it, the mags are made for 556 so the rib has to push the cartridge towards the center of the mag. And with the COL at max the nose will easily catch at the front groove.
I know, but Remington and Hornady do not have this problem. We did R&D to develop ammo which is compatible with USGI and P-Mags. In fact, removing the rib is bad, as the ammo as designed for the existing rib.
I'm not one to argue with experience, and the reports I have are with heavy handloads and long COLs. I'm sure the Rem and Hornady work, but you must agree that the mags technically are wrong for the round and reducing the rib would be the correct modification?
