Just measured my buffer tube---WTF?

[dpete]

I've been reading with great interest all the threads detailing the need for proper length buffer tubes, springs and buffers, and the companies that manage to get them wrong.  I have always thanked my lucky stars to have put together my 308AR with parts from scattered sources not knowing what I was getting and having the rifle work perfectly from day one without any of the issues I have read about. 

Today I measured the inside length of the buffer tube that is on it and its only 6 7/8" inside length!  7 1/4" outside length!  WTF?   Was supposed to be a milspec carbine tube.

The spring is 10 3/4" long with 26-27 coils.  .078 wire diameter.

It ran fine with the original 3.8oz, 2.5" buffer but ejected out to about 1:00.  I recently put in a 5.4oz KAK 308 buffer to try to tame the ejection a bit and it worked to a degree. 

My questions are:

Has anyone heard of a tube this short?

Would getting a proper length tube give me any benefits?

Should I just leave well enough alone and be grateful that it eats whatever I put through it?

 

[98Z5V]

Never seen one short before, brother - that's weird.  That extra 1/8" that missing from the BCG travel will have an affect on your pile-of-brass placement.  I'd give a 7" internal depth extension a shot and see what happens.  Does it have enough travel to lock back on the bolt face?  And do so, on an empty mag?

[dpete]

I now have seen one other buffer tube/spring combination this short and it was a thread here.

From this post: 

FYI... PSA using 2 different buffer system lengths

 

andbfoosh006 stated:

Here are the measured weights and lengths between the "New" and "Older" versions.

Again, remember these parts do not interchange... unless you the complete buffer system ( DPMS v. Armalite )

New / Armalite / Longer.......................... Older / DPMS / Shorter

Supplied OEM PSA buffer ............ ( Both are way to light IMHO, they should be min. 5.4oz )

.....3.8oz / OAL 3.260"...................................3.8oz / OAL 2.5"

Supplied OEM PSA Buffer Tube......

.....5.0oz / OAL 7 7/8" ..................................5.0oz / OAL 7 1/4"

Supplied OEM PSA Buffer Spring.....

......1.5oz / OAL 11 3/8" / 29coils..................1.5oz / OAL 10 5/8" / 28coils

 

His buffer, spring, and buffer tube measurements are identical to mine or within measurement method differences.

When the BCG is fully pulled back with the charge handle the bolt is .1" - 1/8" behind the bolt catch.  

The rifle has functioned perfectly including hold back on empty magazine since its first shot. It just ejected brass about 8-10 feet out at 1:00.

[blue109]

Yup. Buddy just brought me a gun to troubleshoot (only time anybody calls me anymore lol). Buffer bump stop was chewed up and pieces of rubber were in the FCG. the pin holding the bumper was bent and it enlarged the hole in the buffer body. Internal depth was about 1/4" short. 

[dpete]

My original buffer was beginning to show signs of that.  The bumper section was beginning to flare over the top of the tube.

The buffer tube in your picture is even shorter than mine though.

[GoodByNAair]

Did you get the lower/ gun as whole or piece it together? That even seems short for an AR15 car tube, both mine are 7 1/8 - 1/8 tape end if memory holds true. = about 7 1/8 to 7 1/4

[washguy]

46 minutes ago, GoodByNAair said:

Did you get the lower/ gun as whole or piece it together? That even seems short for an AR15 car tube, both mine are 7 1/8 - 1/8 tape end if memory holds true. = about 7 1/8 to 7 1/4

Good   if its an ar15 buffer tube its 7 inches inside measurement...now the ar 10 buffer tubes are longer...   

Armalite AR-10 Carbine Buffer Tube Dimensions – 7-5/8″         Wash

[dpete]

I bought the parts for the rifle individually and assembled it myself.  The buffer tube, buffer, spring, and castle nut were purchased as a set designated for a 308AR and the original buffer was 2.5" and 3.8oz. 

I probably should have been clearer in my original post that the rifle always has and continues to load, fire and eject perfectly, as well as lock back on an empty mag.  But the shells eject to 1:00. 

I guess I am wondering why?   Is it because the spring is also shorter but heavier duty than a normal carbine 308 buffer spring? 

I recently added an adjustable gas block and even with the gas 3/4 turned off everything works.  Its the why does it work that has my curiousity going. 

[98Z5V]

It's got enough movement to lock back, and strip new rounds - but it's running short.  That brass is ejecting while the BCG is shorter in it's stroke - even by a little bit.  Mentally, that's what I can come up with on it.  If it cycled just a little further back, with more BCG travel, it would be running a little "less fast & harsh."   It'll be throwing brass in a different place.

Edited April 12, 2018 by 98Z5V

[dpete]

1 hour ago, 98Z5V said:

It's got enough movement to lock back, and strip new rounds - but it's running short.  That brass is ejecting while the BCG is shorter in it's stroke - even by a little bit.  Mentally, that's what I can come up with on it.  If it cycled just a little further back, with more BCG travel, it would be running a little "less fast & harsh."   It'll be throwing brass in a different place.

Ok that makes sense.  I will be having access to what will hopefully be a true milspec AR15 carbine buffer tube.  Once I have that, what spring is recommended to work with the 2.5" buffer I already have?

[98Z5V]

For that setup, I'd say Sprinco Orange spring.  It just works. It's specifically designed for the 308s with the 7" extensions and 2.5" buffers. 

[dpete]

Cool thanks!  I was hoping you would chime back in before too long. 

[xxlfitness@yahoo.com]

when you guys say 7" extensions?? what does that mean, do you mean 7" buffer tube or? 

His tube now is only an 1/8" or so short, are you advocating some sort of  extension of a whole new tube/ never heard of an extension for a short tube.

[blue109]

The proper name for a "buffer tube" is receiver extension. A correctly machined carbine receiver extension has an internal depth of 7". An incorrectly machined receiver extension with an internal depth of 6 7/8" should be thrown in the trash and replaced with a properly made part.

[xxlfitness@yahoo.com]

yep agreed, not withstanding differences between AR-15's and AR-308's

[blue109]

13 minutes ago, xxlfitness@yahoo.com said:

yep agreed, not withstanding differences between AR-15's and AR-308's

So why did you ask the question if you already knew the answer?

[xxlfitness@yahoo.com]

It was a test for you. lol

No just kidding. I'm aware the technical name for the buffer tube is receiver extension but I haven used that term in a long time and I had a temporary brain fart.

However I will say about your statement, 

The 7" is a nominal value in my opinion. Id say we all agree that 7" ID should be the minimum length, more often than now I measure actually 7 1/8" - 7 3/16" for this nominal 7" 308 buffer however, just to be sure we are all on the same page, this does not address the few buffer tubes (receiver extensions) that are specifically designed to be longer set ups and measure longer than 7" ID but still under 8" for certain specific set ups.

If you dont mention this, someone will measure their tube to be a bit longer and throw it in the trash also because it doesn't measure within that 7"-7 3/16" range

 

 

[98Z5V]

You gotta get your information right, because it's not.

I've seen receiver extensions on 308 setups that have an internal depth of 7.100", and it causes cycling issues.  So, no, "a little longer" isn't okay, nor is 7.000" a "minimum depth" for a DPMS-based LR-308-type carbine recoil system.

[blue109]

Internal depth of a carbine receiver extension is 7". You can probably get away with a bit on either direction and be fine. That doesnt mean its not wrong. I dont use wrong parts. 

This thread was about the internal depth of a standard AR15 carbine receiver extensions.  there are other threads for AR10, VLTORA5, And Magpul extended extensions with measurements for those systems and the proper spring/buffer compatibility for each platform.  

Edited April 15, 2018 by blue109

[dpete]

On 4/11/2018 at 9:27 PM, 98Z5V said:

For that setup, I'd say Sprinco Orange spring.  It just works. It's specifically designed for the 308s with the 7" extensions and 2.5" buffers. 

I got the Sprinco Orange spring on Tuesday, put it in my short RE figuring lets see what if any difference it makes, and fired 20 rounds today.  Manually pulling the charge handle to a complete stop lets the bolt come back behind the bolt catch about 1/16"+/- farther than with the original spring.

Everything functioned as it should.  Ejection has gone from about 1-2:00 to 3-4:00.  I'll have an extra RE in a couple weeks to measure and put on to replace this short tube.  Or isn't it really needed with the cycling I now have?

[98Z5V]

I would do it, anyway  - just to have it right.  It's still going to affect the ejection pattern, with the proper tube.  I usually don't give a shiit about ejection pattern  - as long as brass is getting out of the rifle, I don't care where it goes.  Just get out.  However, with that short tube, that has to be beating up the buffer bumper, on the end. 

Looking at blue's pics again, the end of THAT buffer is all chewed up, and that RE is damn near 1/4" short.  Same thing will happen to yours, over time.  I'd go ahead with it, Dion.

Edited April 20, 2018 by 98Z5V

[washguy]

My go to has been the sprinco orange spring and regular buffer for the last several months... Me likey... If ur tube ain't seven you be tearing up your stuff... Just do it like 98Z suggests    Wash

 

[dpete]

Thanks guys, I will. 

[mrmackc]

On 4/10/2018 at 2:15 PM, dpete said:

I've been reading with great interest all the threads detailing the need for proper length buffer tubes, springs and buffers, and the companies that manage to get them wrong.  I have always thanked my lucky stars to have put together my 308AR with parts from scattered sources not knowing what I was getting and having the rifle work perfectly from day one without any of the issues I have read about. 

Today I measured the inside length of the buffer tube that is on it and its only 6 7/8" inside length!  7 1/4" outside length!  WTF?   Was supposed to be a milspec carbine tube.

The spring is 10 3/4" long with 26-27 coils.  .078 wire diameter.

It ran fine with the original 3.8oz, 2.5" buffer but ejected out to about 1:00.  I recently put in a 5.4oz KAK 308 buffer to try to tame the ejection a bit and it worked to a degree. 

My questions are:

Has anyone heard of a tube this short?

Would getting a proper length tube give me any benefits?

Should I just leave well enough alone and be grateful that it eats whatever I put through it?

 

Well, think about it guy..... If you put a rifle together and it works fine from the get-go you and I don't post about it working, just the duds get posted about.  Probably well over (WAG) 75% work.