300BlkTalk

I am new to this forum and new to AR 15’s. Not new to shooting. I recently completed my first AR 15 build from a Daytona Tactical 80% complete kit chambered in 300 BLK. The problem I’m having is with Magpul 1st gen 5.56 30 round magizines. When trying to chamber the first round the bolt seems to be dragging the top cartridge when retracting the charging handle, and the first round doesn’t chamber fully. But after I clear that round, everything works as it should. This happens with factory ammunition 125 grain bullets and 150 grain bullets from a different manufacture. Is this typical for the 300 Black out? Or do I need different magazines?

Sounds like a magazine issue to me. If you don't fully load the magazine does it chamber the first round?
Try loading 28 rounds and see if the first will chamber.

I have tried loading 28 rounds and everything functions normally, I might try talking to tech at MagPul.

Load the same magazine with .223 rounds...note the vertical ribs near the front in relation to the bullet. Now load the magazine with 300blk rounds...see the issue with the vertical ribs on the bullet? On a full mag, that changes the height of the stack of bullets.

I sent a message to MagPul tech today, when I hear ( or if ) back from them I will let you know what they have to say. As you can see I am less that enthusiastic about how Some companies handle customer service now days! As of yet I am not talking about MagPul this is the first time I have had to contact customer service with them!

Magpul makes a mag for the 300BO. The only difference is the rib in the standard 5.56 mags is thicker.
The thicker rib causes the bullet to sit incorrectly, but I think that only applies to the heavier bullets used for subsonic.

I talked to MagPul and they didn’t help at all!
Also I sent a return authorization request toPalmettoand no response! I guess I won’t be buying from them again!

How you load the magazine can make a difference.

Top round should be tip up. The round stack can bind the top round if you push down hard into the magazine.

Load a a full mag, pay attention to how the top round looks.

Pull the charging handle back THEN insert the loaded magazine,make sure the bolt face is well behind the top round. Probably about 1/'8". See if that loads the first round.

After the top round is stripped form the top, pull the magazine and note the position of the new top round. If it is tip up and it was not before, the problem is likely how you load.

Generally you can take the fully loaded magazine and smack the primer end on the palm of your hand and it will free up the round stack in the magazine and cure the type of problem you are describing.

I've learned to lock the bolt back, and then insert the magazine. Otherwise, in some instances when the bolt is NOT locked back before I insert the magazine, the pressure of a fully loaded magazine against the closed bolt doesn't allow the magazine to fully insert. It may catch and stay, but the top round may not feed properly.

So, I always do things in a certain order:
1) Pull the charging handle and lock the bolt back.
2) Insert the magazine and give it a tap to ensure it's properly installed.
3) Release the bolt.

That has solved the problem for me.

Get some of these mags https://www.midwayusa.com/product/1022346310