Noob .308 build almost finished

[JimK1075]

I’ve been lurking and reading a lot of info mostly from here because I like the feedback from this forum. I’ve built 3 AR15 rifles using complete uppers and now I’m on my first complete build. It’s an AR308 and I started with Ballistic Advantage lower, upper, BCG, and the barrel which is a 16” mid length gas .750 journal with the BA gas tube. I’m running an adjustable gas block by JP and it’s not suppressed, with a Midwest industries comp. The gas port looked very small so my radar went up. It measures a hair over 1/16” and it doesn’t seem right based on my reading through these forum threads. Anyway the buffer system I picked is a 2a armament AR10 buffer tube 8” with an H3 buffer 5.1oz. And a Tubbs flat wire spring for 308. I know I could go shoot this and troubleshoot the setup but I’d rather start somewhere close and I know you guys can help me with this gas port size. Any feedback is appreciated. I have read tons of stuff but I’m running in circles with all the info. My best guess is I need to drill to 3/32 or 7/64”.

[shooterrex]

Welcome from KY.

Go to Amazon and get a set of numbered drill bits. That lets you make smaller increments in hole size vs fractional bit sizes.

Hopefully the inside buffer tube measures 7 5/8". At 8" internal depth you BCG will more than likely be slamming into the receiver ears.

[BrianK]

Welcome to the forum! 

[JimK1075]

1 hour ago, shooterrex said:

Welcome from KY.

Go to Amazon and get a set of numbered drill bits. That lets you make smaller increments in hole size vs fractional bit sizes.

Hopefully the inside buffer tube measures 7 5/8". At 8" internal depth you BCG will more than likely be slamming into the receiver ears.

Not understanding your comment. Are you saying I have too much room?

[98Z5V]

3 hours ago, JimK1075 said:

16” mid length gas .750 journal

Gas port needs to be 0.080"~0.085".  Since you're running adjustable gas, just to to 0.085" and be done with it.  It'll eat anything you throw at it.

3 hours ago, JimK1075 said:

2a armament AR10 buffer tube 8” with an H3 buffer 5.1oz. And a Tubbs flat wire spring for 308.

Rex nailed it already.  Don't measure the OAL of the extension, measure the internal depth of the extension.  The number you're looking for is 7 5/8" internal depth.  If it's not that, state what it is in this thread.  Buffer needs to be 3.250" long.  That spring wouldn't be my first choice, I'd rather see an Armalite EA-1095 spring or a Sprinco Red spring in there. 

Rex also hit the nail on the ehad with the drill bits.  Don't use fractional bits to drill out your barrel.  Used numbered drill bits.  You can pick up the one you need from Ace Hardware, the Irwin numbered bits.  0.085" is a 44 bit.

https://littlemachineshop.com/reference/numberdrillsize.php

Also, H3 buffers should weigh 5.4oz. 

Edited December 3, 2022 by 98Z5V

[shooterrex]

Yes if your buffer tube is really 8" Internal depth the bolt carrier will slam into the rear of your lower receiver. Not good.

 

[Albroswift]

I like to screw the tube into the receiver, line up the retaining pin slot, then measure from inside bottom of tube to face of ears. Welcome to the forum!

[Rsquared]

Welcome aboard from Maryland.

What the other guys have already stated is gonna put you in the right direction.

[JimK1075]

6 hours ago, Albroswift said:

I like to screw the tube into the receiver, line up the retaining pin slot, then measure from inside bottom of tube to face of ears. Welcome to the forum!

Ok I got that but what are the “ears” ?

[shooterrex]

The rear part of the receiver the buffer tube screws into.

[jtallen83]

Welcome from Iowa!

[Cunuckgaucho]

Welcome from BC

[98Z5V]

5 hours ago, JimK1075 said:

Ok I got that but what are the “ears” ?

Here's the bottom line.  Measure the INSIDE of the receiver extension.

Measure along the TOP of it, as it would be installed.

Shove a tape measure down that thing until it bottoms out, and measure the top surface of that extension, at the tape. Take a picture.  Post that picture here.  Show us the internal depth of your receiver extension.  We move on from there.

Lower receiver, "ears" all that - the extension should be flush with the lower receiver, when it's (#1) manufactured correctly, and (#2) installed correctly.  Fuk all that, for now.

Just measure your internal depth of your extension, for now.  Don't worry about all that other shiit - for now.  If you have an extension with an 8.000" internal depth - that's fixable, but it's fucked up.  It wasn't manufactured correctly, by ANY standards that are out there. 

Get the internal depth of your extension in here, and don't get wrapped around the axle with all the other references.  Numbers matter. Get the internal depth up here - we move on from there.

Edited December 4, 2022 by 98Z5V

[Albroswift]

6 hours ago, JimK1075 said:

Ok I got that but what are the “ears” ?

Ha!

If you google it it comes up with the part of the receiver the trigger guard roll pins to. But what we call ears is what the BCG slams into if the buffer is too short or the extension too deep. 

[JimK1075]

Thanks for all the welcoming comments! I took my buffer and spring out and weighed my buffer and it weighs 5.3 oz. The inside measurement of my buffer extension measures 7 3/4”. If I push my bolt carrier into the tube with the spring and buffer it does hit the lower ears. However there is a couple more threads exposed so I’m assuming I’ll be threading the buffer extension in until it’s flush or before it binds on the locating pin. It’s possible the bolt carrier won’t hit at full rear travel if I move the buffer tube further in but they make spacers for this I’m sure. I appreciate the pointers as I want a reliable smooth shooting and accurate rifle and these mechanics are exactly what I need to learn. I’ve located the #44 drill bit at the local ace hardware that I’ll be buying tomorrow. 

[cowenox]

loving the forum so far. Nice, knowledgeable people. Hard to come by it seems.

[jtallen83]

13 hours ago, JimK1075 said:

they make spacers for this I’m sure.

A quarter works perfect, two if needed, they get a little smooth and cupped after several hundred rounds of beating so it becomes a maintenance item, maybe a steel washer would last forever.

[JimK1075]

On 12/3/2022 at 7:14 PM, 98Z5V said:

Here's the bottom line.  Measure the INSIDE of the receiver extension.

Measure along the TOP of it, as it would be installed.

Shove a tape measure down that thing until it bottoms out, and measure the top surface of that extension, at the tape. Take a picture.  Post that picture here.  Show us the internal depth of your receiver extension.  We move on from there.

Lower receiver, "ears" all that - the extension should be flush with the lower receiver, when it's (#1) manufactured correctly, and (#2) installed correctly.  Fuk all that, for now.

Just measure your internal depth of your extension, for now.  Don't worry about all that other shiit - for now.  If you have an extension with an 8.000" internal depth - that's fixable, but it's fucked up.  It wasn't manufactured correctly, by ANY standards that are out there. 

Get the internal depth of your extension in here, and don't get wrapped around the axle with all the other references.  Numbers matter. Get the internal depth up here - we move on from there.

I posted the pic you asked for. Waiting for the solution 

[DNP]

He’ll be back. Hard to read that tape pic, but you’re positive it’s 7-3/4”?  How long was your buffer?  Is it 3-1/4”?

 

@98Z5V

[DNP]

Also, did you say the tube isn’t against the retaining pin?  It should be on top of it, holding it in place. It rides up and down on the spring so you can pull the buffer out.  I may have misread the comment about being able to thread in a little more and hitting the pin. 

[JimK1075]

2 minutes ago, DNP said:

He’ll be back. Hard to read that tape pic, but you’re positive it’s 7-3/4”?  How long was your buffer?  Is it 3-1/4”?

 

@98Z5V

Yeah I’m  Positive it’s 7 3/4” but I’m thinking there’s another 3/32 or 1/16”of threads because my buffer tube isn’t all the way forward. I did notice marks where the bolt carrier did hit the lower ears on assembly and hand cycling. The buffer tube is rated at 8” oal. The company states it is for the LR308 with the H3 buffer 3.25”

[JimK1075]

43 minutes ago, DNP said:

Also, did you say the tube isn’t against the retaining pin?  It should be on top of it, holding it in place. It rides up and down on the spring so you can pull the buffer out.  I may have misread the comment about being able to thread in a little more and hitting the pin. 

Yes it looks like I can get 2 more turns on it

[jtallen83]

44 minutes ago, JimK1075 said:

Yes it looks like I can get 2 more turns on it

I've used a needle file to cut a notch so I could get that one more turn, still had to add a quarter to get the distance the bolt travels before engaging the catch down some, keeps it from slamming too hard on it.

[JimK1075]

18 hours ago, jtallen83 said:

I've used a needle file to cut a notch so I could get that one more turn, still had to add a quarter to get the distance the bolt travels before engaging the catch down some, keeps it from slamming too hard on it.

Yeah I thought about that. I’ll take the tube in to where it’s flush and I’ll file the pin slot if need be. Not quite sure how much clearance is needed but once I have the buffer tube all the way in I’ll see how far the BCG will push in and if it still hits I’ll add a quarter as some of you suggested. Really appreciate the feedback because there isn’t much available information regarding this carrier hitting the lower “ears” and what the clearance should be. I’m glad I didn’t take the rifle out and fire it without some understanding of the mechanics.

[98Z5V]

On 12/5/2022 at 8:19 PM, JimK1075 said:

Yeah I’m  Positive it’s 7 3/4” but I’m thinking there’s another 3/32 or 1/16”of threads because my buffer tube isn’t all the way forward. I did notice marks where the bolt carrier did hit the lower ears on assembly and hand cycling. T

7 3/4" is too much, and the max you can run is 7 5/8" internal depth, without problems.  So, you have a 7 3/4" extension. 

Stay with me here.  7 3/4" = 7.750".  7 5/8" = 7.625".  That means your extension is not correct, but milled another 0.125" too deep.

A quarter is 0.069" thick.

You need to drop TWO (2) quarters down your extension, THEN put your spring in there and buffer.  That's the best solution for your receiver extension, instead of buying one that's machined correctly.

What brand of receiver extension is this, or where did you get it?  Everyone needs to know to stay away, so it's pertinent details here.

Edited December 7, 2022 by 98Z5V