Issue fixed. (Can delete)

[xfer42]

So whats going on?
Ive cut out a few of these DPMS 308 lowers and have yet to fire them. Im curious as to what is off. The ones Ive cut seem to rack smoothly. Im going away for a few weeks and looking forward to testing them when I get back. I bought a few of those $95 DPMS .308 Ares lowers ($99 now).

[kcstott]

Well looks like it's my LOWER!!! Colfax tactical lower(is a joke) doesn't line up to DPMS upper so failure to allow BCG to fully cycle. Causing the BCG to rub and slow down. Yup upper worked fine one friends lower... Now back to drawing bored. Might just sell it and go for custom bolt action!

I'm willing to bet you machined it out of spec.

[gemini1]

Well looks like it's my LOWER!!! Colfax tactical lower(is a joke) doesn't line up to DPMS upper so failure to allow BCG to fully cycle. Causing the BCG to rub and slow down. Yup upper worked fine one friends lower... Now back to drawing bored. Might just sell it and go for custom bolt action!

So you're no longer interested on buying a new lower? I'd be interested in your upper if you're planning to sell.

[MIGUEL RUVALCABA]

I used a CNC machine which was to spec! And it's not the machining I had 3 guns that had no clew other than to keep trying different parts or at end of day lower since they could tell it mite be having issuers since not linking up correctly. At this moment already have a good amount of $$ into it so might just go Bolt action way or all JP enterprise. I would sell it if the offer at least made me brake even. Only 70 rounds on it now since I fired 10 rounds without any failures on buddy's lower.

[67Cuda]

I have a Colfax LR-308 lower. When using a DPMS lower kit, the trigger would give multiple fires with one trigger pull. Luckily I was only loading two rounds at a time.
This was my first time out with it.

Put in a CMC drop it trigger to rectify that and now works great.

More to the point of fitment between the DPMS upper and Colfax lower. If I had to use the standard take down pins, the two would not have gone together.

The holes did not line up, I'm guessing it was the lowers fault. Being a machinist, I found the best pin size combination for them to fit together, machined the take down pins and everything is fine.

So it was certainly not smooth sailing with the Colfax lower.

Edit: I also had to fiddle fart with the bolt release as well to operate smoothly.

[ar15barrels]

I used a CNC machine which was to spec!

Then the lower should work fine...

[Central Coast Gunsmithing]

Ok so if you are having failure to extract this is what i do when i check ANY GAS OPERATED RIFLE
Put in a Dummy round and see if the bolt will cycle and extract without being fired.

Does it? Good.
Check your chamber and see if it is rough. If it is polish it

Now AR Specific check your gas hole in barrel alignment with the gas block hole if they are correctly lined up then there should be a even circle of powder burn around the gas block hole if it is not lined up then the circle will be ofset to one side or the other of the gas block. Next check your gas tube alignment inside the gas block i.e. look in the hole and see if its a strait shot to the gas tube.

Next if all of that is ok check the gas key on the bolt carrier

If it is loose then that can also cause problems

Another problem can also be caused by the bolt carrier binding in the upper receiver you can check that by using a rod and pushing the bolt carrier group strait back in the hole that the gas tube goes into.

There are tons of other issues but those cause the most of your failure to extract on a very consistent bases even a poorly shaped extractor will extract as long as it snaps over the rim of the case If i could see pictures of your brass or you can at least explain what clean brass looks like after being fired in your gun once it would help

(btw I,m a gunsmith not a English major as you can tell)

Also af far as 67CUDA's problem that is normally caused by a ill fit primary and secondary sear surfaces with their respective surfaces on the hammer and can be fixed by a competent gunsmith for less than a (drop in trigger) also said fixing can give you a really nice 2 stage trigger like feel

[kcstott]

I used a CNC machine which was to spec! And it's not the machining I had 3 guns that had no clew other than to keep trying different parts or at end of day lower since they could tell it mite be having issuers since not linking up correctly. At this moment already have a good amount of $$ into it so might just go Bolt action way or all JP enterprise. I would sell it if the offer at least made me brake even. Only 70 rounds on it now since I fired 10 rounds without any failures on buddy's lower.

Just because it was done in a CNC does not mean it was done to spec.

The offset could have shifted. chips in the vise etc, the set up is only as good as the guy putting that parts in.

Ok so if you are having failure to extract this is what i do when i check ANY GAS OPERATED RIFLE
Put in a Dummy round and see if the bolt will cycle and extract without being fired.

Does it? Good.
Check your chamber and see if it is rough. If it is polish it

Now AR Specific check your gas hole in barrel alignment with the gas block hole if they are correctly lined up then there should be a even circle of powder burn around the gas block hole if it is not lined up then the circle will be ofset to one side or the other of the gas block. Next check your gas tube alignment inside the gas block i.e. look in the hole and see if its a strait shot to the gas tube.

Next if all of that is ok check the gas key on the bolt carrier

If it is loose then that can also cause problems

Another problem can also be caused by the bolt carrier binding in the upper receiver you can check that by using a rod and pushing the bolt carrier group strait back in the hole that the gas tube goes into.

There are tons of other issues but those cause the most of your failure to extract on a very consistent bases even a poorly shaped extractor will extract as long as it snaps over the rim of the case If i could see pictures of your brass or you can at least explain what clean brass looks like after being fired in your gun once it would help

(btw I,m a gunsmith not a English major as you can tell)

Also af far as 67CUDA's problem that is normally caused by a ill fit primary and secondary sear surfaces with their respective surfaces on the hammer and can be fixed by a competent gunsmith for less than a (drop in trigger) also said fixing can give you a really nice 2 stage trigger like feel

Nope he has his mind made up. It's the crappy lower
Machined correctly on a CNC machine that could not possibly make a bad part

Listen up!! check your lower to the print then tell me whats fouled up

[Central Coast Gunsmithing]

Now i admit i don't have a ton of experience with AR platforms but most extraction problems are going to be in your upper unless you have that upper pinned so god damn crooked that it just can't function anymore.

I would check out the upper before you scrap that lower just to give yourself more experience at the leaast

[kcstott]

Now i admit i don't have a ton of experience with AR platforms but most extraction problems are going to be in your upper unless you have that upper pinned so god damn crooked that it just can't function anymore.

I would check out the upper before you scrap that lower just to give yourself more experience at the leaast

He said it runs fine on a different lower so it probably is the lower

The problem he describes leads me to believe the FCG pocket was machine off center and shifted the BCG over at the rear causing it to bind up.

Now I find that hard to believe as the front take down lug would have to shift as well. The only other issue is the receiver extension thread could be off center but that would be easy to identify.

Once again Brake out the calipers and get your print and check the damn thing.

[ar15barrels]

The problem he describes leads me to believe the FCG pocket was machine off center and shifted the BCG over at the rear causing it to bind up.

I'm trying to comprehend how moving the FCG pocket in the lower would move the BCG in the upper.
Have you compared the hammer width to the width of the hammer clearance cut inside the BCG?

Perhaps you are thinking of an old style armalite carrier with the really narrow clearance cut?
If the FCG pocket was grossly mis-located, the hammer would just strike the bottom of the carrier instead of the firing pin.

[kcstott]

I'm trying to comprehend how moving the FCG pocket in the lower would move the BCG in the upper.
Have you compared the hammer width to the width of the hammer clearance cut inside the BCG?

Perhaps you are thinking of an old style armalite carrier with the really narrow clearance cut?
If the FCG pocket was grossly mis-located, the hammer would just strike the bottom of the carrier instead of the firing pin.

No just that the rear lug pocket is typically machined with the FCG pocket and if it was shifted over say .030" may cause a bind with the bolt rubbing the buffer tube. Yeah all your BCG now a days have a mile of hammer clearance. and you've been doing this far longer then me. I had no idea about a "old style Armalite.
but like I said that can't happen as the front lug would have to shift as well.

[ar15barrels]

No just that the rear lug pocket is typically machined with the FCG pocket

If you had said above that the rear lug pocket location in the lower would shift the upper, I would agree, but you specifically said FCG pocket...

[ar15barrels]

I had no idea about a "old style Armalite.

I did a google search to find a photo of the old style and new style 308 carriers and it turns out the damn photo was on my own website...

[kcstott]

If you had said above that the rear lug pocket location in the lower would shift the upper, I would agree, but you specifically said FCG pocket...

Yep i did but I would consider it one and the same. although technically not.