7MM-08 cycling issues

[R4CETECH92]

Hi Guys, new to the world of building an LR7MM-08. I have finally completed my first build and it turned out pretty amazing until it came time to go to the range. The first visit was shooting and cleaning over and over again. It performed great if it was a bolt gun, the problem its having is failing to cycle the bolt isn't coming all the way back when firing but i have no issue locking it back manually.

The build consists of Juggernaut tactical upper and lower, cmmg internals, 20" X-Caliber  7mm-08 1/9 twist barrel rifle length gas system, 3.8 oz buffer carbine length. and a non-adjustable gas block. 

My question is there something I need to change in the buffer system or is it a gas system issue. 

Thanks in advance.

[shepp]

Welcome to the forum to feel free to tell us about yourself in the intro section

[R4CETECH92]

2 minutes ago, shepp said:

Welcome to the forum to feel free to tell us about yourself in the intro section

Will do I appreciate the help in advance!

[jtallen83]

17 minutes ago, R4CETECH92 said:

20" X-Caliber  7mm-08 1/9 twist barrel rifle length gas system,

My 16 inch rifle gas 308 X-caliber barrel came seriously under-gassed. Maybe measure the gas port in case someone here can give some guidance on what the size should be.

[R4CETECH92]

7 minutes ago, jtallen83 said:

My 16 inch rifle gas 308 X-caliber barrel came seriously under-gassed.

Sounds like what I've been hearing. I will measure it accurately tomorrow at work, I checked with a set of bits tonight. It was between a .0625" (1/16) which fit and a .078" (5/64) which did not fit.

Edited December 27, 2017 by R4CETECH92

[98Z5V]

There's no way that gas port is large enough, but you might have some recoil system issues as well.  Need to get measurements on the following:

Receiver extension internal depth/length inside.

Buffer length

Relaxed length of the buffer spring, and how many coils it is.

[R4CETECH92]

It's carbine buffer tube will measure tomorrow.

Buffer is 2.5" long, spring was just under 11", and spring was 28 coils.

[98Z5V]

Also, collapsible stock or fixed stock?  Had to ask...

EDIT - Disregard, we posted at the same time.

Internal depth on that receiver extension should be either 7.000" or 7 5/8".

Edited December 27, 2017 by 98Z5V

[R4CETECH92]

Collapsible, I'll measure that as well thanks.

[washguy]

R4  welcome to the forum from Texas        Wash

heres some pics      standard mil car buffer tube 7"   an ar15 spring car vs a 308 car spring yours  is too short

these pics no particular order....lol  standard car buffer length but you can get em heavier     heres a heavier buffer but same 2.5 length   .... with a rifle length gas system you have  you are prolly undergassed.....all of my 308's are mid length and ive had to drill em out sometimes myself....xcaliber has no clue as to what size your barrel needs....ask JT about that....lol...... bit #45 is a good start .0820  but it will prolly need a lil more like a #43 .0890     but before you start drilling get the right spring and make sure you have the correct buffer too

also check to make sure your gas block port is centered over the gas port hole on the barrel and you are getting the flow to the gas tube....make sure your gas tube is aligned to the bcg and charging handle...but I think its a mismatch spring...and undersized port....put a wooden dowel in the barrel and get you the numbered drill bit...the dowel protects the barrel from you going too far to the other side....hmmmmm lyrics from a song poppin up in my head.....    Wash

 

Edited December 27, 2017 by washguy

[survivalshop]

 Here's some info on Gas Port sizing .

https://forum.308ar.com/topic/15037-barrel-gas-port-size308338260243-etc/

 

[washguy]

R4 since you are prolly gonna develop a load for your rifle this creates another problem because of the bullet weights and the burn rates of powders.....I see an adjustable gas block in your future....but first and foremost lets get a 308 car spring in there....if it were me I would spend the 9 bills for a standard ar308car buffer spring,but have a Tubbs flatwire car spring on the way...it will help most all of your cycle probs . you cant mess up he sells a spring that fits a car or rifle same one.......I do see a lil drilling in your future...easy peasy...your port size is too small......always wanted a 7mm 08     Wash     always start one round in mag...shoot itand then check to see if if the catch holds....   Wash

http://www.davidtubb.com/ar10-tubb-parts/bufferspring-sr-ar10

Edited December 27, 2017 by washguy

[R4CETECH92]

Thanks for the help guys I appreciate it. Those springs are on back order, I'll order one regardless. Then if that doesn't fix it time to drill.

[R4CETECH92]

7 hours ago, survivalshop said:

 Here's some info on Gas Port sizing.

 

Thanks, by the looks I will definitely need to drill, or find someone who can local.

[washguy]

1 hour ago, R4CETECH92 said:

Thanks, by the looks I will definitely need to drill, or find someone who can local.

R4   you don't even need a drill press for this...just have a wooden dowel in the barrel so you don't hit the other side

drill with a #45 and a 308 car spring...that just might be all you need   if Tubbs is out  go here https://www.larue.com/products/tubbs-buffer-spring-ar10-sr-25-buffer-springs/

[R4CETECH92]

9 minutes ago, washguy said:

if Tubbs is out  go here https://www.larue.com/products/tubbs-buffer-spring-ar10-sr-25-buffer-springs/

Ordered! Will shoot it when it comes in then find some good numbered drill bits.

[survivalshop]

 Out of caution , drill in stages , if you get to that point ,where you have to drill the Port out . I would think the 7mm'08 would be close to 308 Port sizes . 

    Run the Action wet , don't be shy on the Lubricant.

Edited December 27, 2017 by survivalshop

[R4CETECH92]

18 minutes ago, survivalshop said:

 Out of caution , drill in stages.

    Run the Action wet , don't be shy on the Lubricant.

Thanks for the advise! And the bcg is lubed!

Edited December 27, 2017 by R4CETECH92

[survivalshop]

2 minutes ago, R4CETECH92 said:

Thanks for the advise! And the big is lubed!

 Testing in-between those stages would also be a good idea .

[R4CETECH92]

I planned on it so I don't over drill.

[R4CETECH92]

Wash, I measured my buffer tube it was 7" even and I'll double measure gas port in the morning thanks again. The drilling is still making me nervous...

[98Z5V]

36 minutes ago, R4CETECH92 said:

Wash, I measured my buffer tube it was 7" even and I'll double measure gas port in the morning thanks again. The drilling is still making me nervous...

You have the right buffer length, then, for that receiver extension.  2.5" buffer is the correct one for a 7" internal-depth carbine receiver extension.  I was thinking that spring was too short - even AR15 carbine buffer springs are longer than that.

Don't be nervous about drilling that gas port up - just go slow.  You don't need that drill turning 10-million RPM.  Stick a 1/4" wooden dowel down the barrel, like wash said, and you'll be alright.  Use light pressure on the drill - you don't need your bodyweight on the drill to get a larger bit through that gas port.

Edited December 28, 2017 by 98Z5V

[R4CETECH92]

Sounds good I have a drill press at the shop I'll use, new spring is ordered as well. When it comes to the drilling I grabbed a dowel rod from Lowes tonight and will do it on a press if the spring doesn't work.

[R4CETECH92]

Start with a 5/64 drill bit then go to numbered bits, or do I buy a set of # bits (49) and go down from there?

[98Z5V]

You'll only need a few, and you can pick them up from Ace Hardware or Lowe's.  The Irwin numbered bits, sold individually.  Focus on the bits between 0.080" and 0.095".  I highly, highly doubt you'll need to go higher than 0.095".

Looks for these:

(Number 47 through number 41 will do what you need done.  )

Edited December 28, 2017 by 98Z5V