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hevyjunk01

Need help with my first LR308 build

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Hello to all,

I just finished my first 308 build. I took it to the range and had 3 issues develop.

#1- (Worst one) my BCG was making contact with the receiver, which caused it to dent the receiver in both the lower left and lower right, near the entrance of the buffer tube on the threads. This make's me think I have the wrong size buffer. I currently am running the Primary Weapon Systems carbine buffer tube for the AR15, I'm also running the JP Tuned & Polished Extra Power Buffer Spring for 308 Carbine, and I'm running the 2.5" DPMS 3.7oz buffer. Should I be using the 3.2" buffer in order to stop my BCG from impacting the receiver? Or is there another area I should be looking at?

#2- My BCG would jam one round after firing 2 or 3 consecutive rounds. Inspection of the jammed rounds and casings shown groves on the casing all the way up to the round as well as a dent in the casing bending the round as a whole. Not sure what is causing this. Any help is appreciated here.

#3- I also had an issue on the last round using two different size magazines. My BCG would ride forward on the last round and fail to lock back with the empty mag. Not sure if this and #2 are related. I used a 10 round mag and a 20 round mag and had the same issue.

If anyone could help I would greatly appreciate it. Thanks in advance.

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Hi Junk    What you need to get it going is a DPMS 308car buffer and a plain ol ar308 car buffer spring...that is if you are using a car type stock? Always do the single round bolt catch lock back on a single round first. you have a cycling issue because of the mixed up stuff in . After you put those parts in the rifle ...do the lock back check...then get back with us....you cant check mags and ftf's and fte's until you get those two parts installed  1  2 and 3 are all connected as problems in your questions...make sure your buffer tube is installed correctly...what particular car buttstock? what upper/lower? barrel?

:) Wash

Edited by washguy

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Hello to all,

I just finished my first 308 build. I took it to the range and had 3 issues develop.

#1- (Worst one) my BCG was making contact with the receiver, which caused it to dent the receiver in both the lower left and lower right, near the entrance of the buffer tube on the threads. This make's me think I have the wrong size buffer. I currently am running the Primary Weapon Systems carbine buffer tube for the AR15, I'm also running the JP Tuned & Polished Extra Power Buffer Spring for 308 Carbine, and I'm running the 2.5" DPMS 3.7oz buffer. Should I be using the 3.2" buffer in order to stop my BCG from impacting the receiver? Or is there another area I should be looking at?

Are you sure you have the AR-15 EBT and not the .308 EBT? If you pop off the upper from the lower and take the action spring out and then insert the buffer and BCG into the receiver extension fully can you see what's making contact? From the info you've given us about the configuration, wash is right that you should be using the short LR308 carbine buffer and LR308 carbine action spring.

#2- My BCG would jam one round after firing 2 or 3 consecutive rounds. Inspection of the jammed rounds and casings shown groves on the casing all the way up to the round as well as a dent in the casing bending the round as a whole. Not sure what is causing this. Any help is appreciated here.

Do you have a picture of the malfunction? I can't tell if it's a failure to extract, failure to eject, or double feed from your description. Are the scratches from the magazine feed lips as the round is pushed out of the mag?

#3- I also had an issue on the last round using two different size magazines. My BCG would ride forward on the last round and fail to lock back with the empty mag. Not sure if this and #2 are related. I used a 10 round mag and a 20 round mag and had the same issue.

If anyone could help I would greatly appreciate it. Thanks in advance.

Make sure the BCG is lubed up well for the break-in period. Also, what barrel and gas tube did you use (this can also be caused by people using AR-15/LR-308 gas tubes on barrels with AR-10 pattern gas port locations)?

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Washguy/FaRKle!

Thanks for your help on this. I will post pictures later today. I'm at work now however; I'm running a local company's upper and lower receiver's manufactured after DPMS. I'm running CMMG fire control group with a mega tactical single stage trigger. I'm running a DPMS 18" fluted bull barrel with DPMS gas block with LBE gas tube. I'm running a Cryptic Coatings mystic bronze 308 BCG. Let me know if you need anything else.

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   Issue # 1 sounds like the contact pads on the side of the Bolt Carrier , just to the rear of the Firing Pin, keeper pin , where the BC is larger & will not make it past the Lower Receivers Extension threads & its hitting the the Receiver .

  The DPMS 308 Carbine Buffer is about , 2.5 " long , I would think your Buffer spring is not right, first off , as said . Take care of one issue at a time , the BCG hitting the Lower Receiver is the first one that needs to be looked into .

 

  There is another possibility that we have been seeing a lot of late & that's out of Spec Receiver sets being made by new Manufacturers . Not saying yours are one of these , but it can't be taken out of the equation for trouble shooting your problems .

  You problems # 2 & 3 may have something to do with your other Components or can be related to the # 1 issue . Have not heard of you BCG Manufacturer.

http://www.crypticcoatings.com/bolt-carrier-group-coatings/

 

  Interesting coatings , but any coating on components can cause issues ( Extractor , Ejector ) with components , until broken in .

 

  Has the rifle had Head Spacing checked ?

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FaRKle!

To answer your other question I thought I ordered the 308 EBT but upon further measurements after the problems it looks like I got the AR15 EBT. It measures 7.25 from the back of the buffer tube to the anti tilt lip.

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Survivalshop

Since this is my first build I had it finalized by a local gunsmith and was told it was torqued to spec and had the headspace checked as well. He also fired 2 rounds in succession without mishap. I have these shells and after my mishaps I inspected them and noticed they have slight scraping on the brass from the bolt and a shallow dent on the opposite side. My thought process is leading me to believe that my spring is too strong causing my BCG to ride forward too fast for the proper cycle time.

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FaRKle!

To answer your other question I thought I ordered the 308 EBT but upon further measurements after the problems it looks like I got the AR15 EBT. It measures 7.25 from the back of the buffer tube to the anti tilt lip.

well crap, now I see what you have...you bought the pws high dollar enhanced buffer tube( the inside length)...which is adding to your problems

and then adding a hi power spring....with a wrong buffer.....get yourself a dpms car 308 buffer and spring and a 40 dollar ar15 buffer tube and go shoot  lube it up!   :) Wash   the enhanced pws tube,the one you have... if its 7+  its gtg with the right buffer and spring

Edited by washguy

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well crap, now I see what you have...you bought the pws high dollar enhanced buffer tube( the inside length)...which is adding to your problems

and then adding a hi power spring....with a wrong buffer.....get yourself a dpms car 308 buffer and spring and a 40 dollar ar15 buffer tube and go shoot  lube it up!   :) Wash   the enhanced pws tube,the one you have... if its 7+  its gtg with the right buffer and spring

I'm confused, how is the EBT adding to his issues? He's using the appropriate length spring and buffer with it.

Edited by FaRKle!

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I'm confused, how is the EBT adding to his issues? He's using the appropriate length spring and buffer with it.

 

I think the internal depth is off. 

 

FaRKle!

To answer your other question I thought I ordered the 308 EBT but upon further measurements after the problems it looks like I got the AR15 EBT. It measures 7.25 from the back of the buffer tube to the anti tilt lip.

 

For rhe components you're using, you should be using a receiver extension that has an internal depth of 7".  If that 7.25" measurement you got is the internal depth, that's your problem.  To verify, stack quarters in the end of the receiver extension until you close that internal depth to 7", then insert spring and buffer, and try it out with live ammo.

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Nobody's gonna give you grief, man. 

 

You don't have enough receiver extension to install a longer buffer.  Something significantly longer than the 2.5" shorty buffer isn't going to work with your setup.  Best thing to do is measure that receiver extension's internal depth, and see where it's at.  let us know what you come up with.  <thumbsup>

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I think the internal depth is off. 

 

 

For rhe components you're using, you should be using a receiver extension that has an internal depth of 7".  If that 7.25" measurement you got is the internal depth, that's your problem.  To verify, stack quarters in the end of the receiver extension until you close that internal depth to 7", then insert spring and buffer, and try it out with live ammo.

The lip of the EBT extends further than a standard receiver extension because it was designed to support the rear of the carrier while in battery. I'm pretty sure that's where the extra .25" comes from.

hevyjunk01, when you do measure the internal depth, measure to the edge of the buffer detent cutout, not to the end of the lips.

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Next step after that will be:

 

Measure how far back the front of the bolt face is from the rear edge of the bolt catch - you need to determine how much over travel there is with this setup.  The greater the amount of over travel, the higher the chances are of breaking the bolt catch on the last round.  You'll need to fine tune that gap, and reduce that distance with - yep, you guessed it - stacking quarters.

 

Or, buying new parts.

 

Excessive over travel is the entire reason your BCG is slamming into your lower receiver.

Edited by 98Z5V

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All here is the rifle complete with the damage and measurements along with quarter spacing in buffer tube.

#1 Complete Rifle

#2 Damage to receiver

#3 Buffer w/ BCG in tube without quarter ( it's impacting the receiver in all locations)

#4 Spacing between Bolt face and Bolt catch without quarters

#5 Buffer w/ BCG in tube with (2) quarters - 1/4" (looks like good spacing to me)

#6 Spacing between Bolt face and Bolt catch with (2) quarters - 1/4" (looks like good spacing to me)

Sorry having an issue with loading pictures.

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Can you screw the receiver extension in another rotation or two? Pic2 makes it seem like you can, and it looks like you've got the EBT backed off A LOT with its set screws. How long did the internal depth of the receiver extension end up being?

Edited by FaRKle!

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After checking my stuff at home I think you need to snug your EBT up more.

In this pic you can see too much gap between the end plate and the EBT.

post-15881-0-32352300-1427923828.jpg

Back off the top two set screws and large lower screw on the EBT, install it as far into the lower receiver as you can (while still allowing the buffer detent to come up into the channel) and then tighten the screws down (lower screw first, upper ones second).

My EBT sits very flush against the end plate.

Edited by FaRKle!

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 I count 25 coils on the Buffer spring . 

 

  So you are saying an AR 15 buffer would work with this Receiver extension ? That spring is not like a LR DPMS or AR 10.

 

  I don't think you can get another 360 rev. from the Extension  <dontknow>

Edited by survivalshop

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