Once You Go 300 Blackout

Okay so I just figured it better I start a new thread then hoop on another one. I can't believe this is only happening to me. Just got a new 300 blackout upper and shot it for the first time over the weekend. A problem came up that has to be a problem everyone who shoots the Hornaday 110 gr. V-max. I keep getting a "smoke stack" with a round in the chamber every 3 shot or so and the bolt keep locking back after only a round or two as if the mag was empty. I think the problem is the ammo and how it sits in the mag. (pictures below). What do you all think?
Attachment 52165Attachment 52167Attachment 52169

The first photo is the mag with the v-max ammo tapped forward, second is with mag tapped back and third is Remington 220 gr. ammo. Being that the v-max is shorter I can tap it back and forth in the mag leaving a gap in back with ammo tapped forward. This gap I think make the gun see it as empty thus locking the bolt back. I was pretty pissed so I never got around to shooting the 220 gr. stuff but I assume it would run fine. I was about ready to sell that bitch right then and there but no one was around. Anybody else have this problem?

That's.....not supposed to happen. Can you try those magazine in another gun, like a .223? How about that BCG in another gun? Does it do it with other magazines? How does the bolt catch compare to other guns?

seeing as the bottom half of the bullet, and the entirety of the operating system, is the same as a .223 I ask about localizing it to the magazine or the bolt catch being loose, out of spec, too big, etc....

I'll recheck all that, but everything except for the new upper was running fine with my .223 upper, same lower, same BCG, same mags.

It doesn't make sense!!

Was told I needed lighter buffer. We will see

I can't see how it could lock the bolt back when there are still rounds in the magazine. The magazine follower is what locks the bolt when the mag is empty. With rounds still in the magazine (even shifted forward) the follower is too low to catch the bolt.

I'm thinking you might have other issues.

That isn't a 20 round pmag, is it? I had some feed issues with those. Seems that internal rib comes up higher in the 20 rounders than the 30 rounders. It was catching the edge of the case mouth and causing feeding problems for me.

I think you need to give me the upper and just give up.


Sent by a free-range electronic weasel, with no sense of personal space.

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Originally Posted by ray1970

I can't see how it could lock the bolt back when there are still rounds in the magazine. The magazine follower is what locks the bolt when the mag is empty. With rounds still in the magazine (even shifted forward) the follower is too low to catch the bolt.

I'm thinking you might have other issues.

That isn't a 20 round pmag, is it? I had some feed issues with those. Seems that internal rib comes up higher in the 20 rounders than the 30 rounders. It was catching the edge of the case mouth and causing feeding problems for me.

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See what you are saying. They are 30 round 3rd gen PMAGs

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Originally Posted by Monky

I think you need to give me the upper and just give up.


Sent by a free-range electronic weasel, with no sense of personal space.

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Monky, we need to put together a fund for you so you can get that 300 Blackout you keep asking for.

I've got three. Two are fraternal twins. Attachment 52177


Sent by a free-range electronic weasel, with no sense of personal space.

300 BLK is so different and varied from 5.56 and .223 that the gas system and recoil system can fail like this. I am tuning mine to work reliably on my loads of 150 grain FMJBT at 2000 fps. But when I shoot Fiocchi I get shorted cycles and other issues.

I'm on my third 300. I will definitely say that each one kind of had its own personality. I say if you can find a load that you like and the weapon functions with it just stick to that load.

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Originally Posted by Artema

300 BLK is so different and varied from 5.56 and .223 that the gas system and recoil system can fail like this. I am tuning mine to work reliably on my loads of 150 grain FMJBT at 2000 fps. But when I shoot Fiocchi I get shorted cycles and other issues.

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wow, 2000 fps is pretty hot for a 150 gr projectile in 300blk. can you elaborate? im closer to 1500 with 150 gr. and would like to get a little faster.

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Originally Posted by gta_spec

wow, 2000 fps is pretty hot for a 150 gr projectile in 300blk. can you elaborate? im closer to 1500 with 150 gr. and would like to get a little faster.

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I load 19.5 grains of Accurate 5744. It is a compressed load, meaning the brass is full to the top and you crush the large pieces of cylindrical powder down inside when the bullet is seated. That'll cycle just about any gun, lol.