over pressure issue?

[atdski07]

built the gun myself,
Quentin Defense lower
Dpms Lower parts kit
carbine length buffer
Dpms upper receiver
Dpms 24" stainless steel bull barrel w/ rifle length gas system
Cmmg MKIII BCG.
That's the basics of it.

I was out in the desert doing some shooting. I had this gun and a few of my bolt actions also chambered in .308.

I was shooting some reloads I had gotten from the gun show, had a few that didn't want to eject and had to tap them out with a brass rod (did this with all guns), a few of them actually had the extractor rip them. Swapped over to some 308's that I reloaded myself and had dialed in for my bolt actions and issue disappeared with the bolt guns.

Swapped over to my LR 308 and loaded up some of my reloads and it seemed to be working flawlessly until my BCG basically got stuck in the buffer tube, not bad just gave it a light tap on the butt and it popped out, but it happened about 4 times out of 40ish rounds. I'm thinking that a couple of my reloads were a little hot, possibly causing it to be over pressured. These were not match reloads I basically dialed in my powder drop and would check maybe every 10th case.

This is pretty much the online issue I had other than the scope having to be maxed out on windage just to get it zeroed.( Nikon m308 and I figured out the fix for that today if anyone else is having a issue with that).

Anyways just looking for opinions and or advice on the issue with the BCG and buffer.

[ar15barrels]

I see two different issues with Picture G3.
First, your buffer detent is too far back which is letting the buffer run into the detent each time the carrier is cycling.
Second, you probably have the wrong length buffer or buffer tube as your carrier rails are striking the lower receiver.

[kcstott]

The other thing is "reloads from the gunshow" yeah bad idea.

You understand that semi auto rifles can not run just any old rounds through them right?? that the action is designed to run with a specific bullet weight and velocity??

what ever ammo you buy it needs to be 7.62 nato specs That means a 147 gr JHP @ 2700 FPS. You can't go over to the LGS and pick up any ol ammo dump it in the gun and expect it to work. Most ammo that is for hunting have heavier bullets and that means a heavier impulse on the weapon, a weapon that don't need that much gas to cycle. Granted the AR type gas system is not nearly as sensitive to load changes as say an M1 or M1A but attention still needs to be paid to the correct loads being used in your weapon.

[6mmintl]

The bolt carrier looks like there is no, or at least a minimum, chamfer on the rear edges of the bearing guide rails.

I deburr/ramp and polish front and leading edges to reduce receiver/lower wear/galling.

[atdski07]

The bolt carrier looks like there is no, or at least a minimum, chamfer on the rear edges of the bearing guide rails.

I deburr/ramp and polish front and leading edges to reduce receiver/lower wear/galling.

So i should chamfer the shiny part in the picture alittle,

I see two different issues with Picture G3.
First, your buffer detent is too far back which is letting the buffer run into the detent each time the carrier is cycling.
Second, you probably have the wrong length buffer or buffer tube as your carrier rails are striking the lower receiver.

I will check the internal length of the buffer tube this evening when i get off work. I got all the parts for the buffer from parallax tactical, told them what i had and those are the parts they gave me.


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[Ninety]

Almost looks like your buffer tube isn't screwed in far enough.

Is it capturing the buffer detent?

[atdski07]

I see two different issues with Picture G3.
First, your buffer detent is too far back which is letting the buffer run into the detent each time the carrier is cycling.

Could you please elaborate on this. It is currently set to where the buffer tube is just barely holding the detent inplace, should i thread in the buffer tube another turn?

sent from my tin foil tent via d.o.s. using a apple computer with a floppy drive

[atdski07]

The other thing is "reloads from the gunshow" yeah bad idea.

You understand that semi auto rifles can not run just any old rounds through them right?? that the action is designed to run with a specific bullet weight and velocity??

what ever ammo you buy it needs to be 7.62 nato specs That means a 147 gr JHP @ 2700 FPS. You can't go over to the LGS and pick up any ol ammo dump it in the gun and expect it to work. Most ammo that is for hunting have heavier bullets and that means a heavier impulse on the weapon, a weapon that don't need that much gas to cycle. Granted the AR type gas system is not nearly as sensitive to load changes as say an M1 or M1A but attention still needs to be paid to the correct loads being used in your weapon.

Yes im aware of this, dont worry im not shooting 180 grain match bullets through it.

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[Ninety]

Could you please elaborate on this. It is currently set to where the buffer tube is just barely holding the detent inplace, should i thread in the buffer tube another turn?

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Your bcg should make contact with your buffer before the retainer detent should. All those little marks on the bottom of your buffer is from it slamming into the pin. That shouldn't happen. Your said this was a qd lower right ? Very odd.
If that pin is too far back the bcg doesn't make contact with it until it cycles back. The bcg should always be in contact with the buffer.

[ar15barrels]

I got all the parts for the buffer from parallax tactical, told them what i had and those are the parts they gave me.

That does not mean that the parts are right.
That just means you are running what they gave you.
Measure the length of the buffer.
Measure the length of the INSIDE of the buffer tube.

[atdski07]

That does not mean that the parts are right.
That just means you are running what they gave you.
Measure the length of the buffer.
Measure the length of the INSIDE of the buffer tube.

And from the back of the bcg to where it hit

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[ar15barrels]

The buffer looks correct for the tube.
From the measurements, the carrier is JUST crashing into the receiver while the snubber bottoms out in the receiver extension.
I would clearance the rails on the rear of the carrier as mentioned above.

[atdski07]

Copy that.

Tomorrow ill pull out my DPMS bcg and compare it to the cmmg too, just to see if theres any difference, dont feel like digging it out now

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[BKTJ]

Your buffer is correct for the 308 carbine platform 2.50" overall (the 5.56 is longer 3.25). Next check your spring, the .308/7.62 spring should have 29 to 30 coils and be approx 10.75-11" long ( the 5.56 has 36-37 coils 10.25-10.50"). Also if your spring is longer than 11" you are running a rifle length spring.

[atdski07]

Your buffer is correct for the 308 carbine platform 2.50" overall (the 5.56 is longer 3.25). Next check your spring, the .308/7.62 spring should have 29 to 30 coils and be approx 10.75-11" long ( the 5.56 has 36-37 coils 10.25-10.50"). Also if your spring is longer than 11" you are running a rifle length spring.

If thats the case then yes i have the correct spring in it

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