First build Aero

[flyingfinn]

This is my first 308 build. Previous experience was assembling a few PSA 5.56 kits.

Aero Precision: M5 lower, M5E1 enhanced upper/handguard combo, BN BCG, lower parts kit minus fcg/grip

BA 18" heavy profile fluted rifle barrel

LaRue MBT

Ergo grip, Magpul PRS stock

SLR sentry 7 adj. gas block

Radian raptor CH, VG6 MD

I mistakenly ordered a AP M5 carbine buffer kit, so that will have to be shipped back. I called AP, but was too late order had already been processed for shipping. Great, helpful folks on the phone at AP by the way.

Forgive my ignorance;

What rifle extension tube would fit my AP application?

It was recommended to me to purchase a Armalite AR10 spring with part number ending in "1095". 

Also it was recommended to me for a buffer selection from DSGarms; ar15 heavy carbine H buffer p/n dsg-4201-0031. I am unsure of barrel length/gas system my buddy built. But this buffer sounds incorrect for my application. There isn't a length measurement on DSG's site only a weight of 3.779 oz.

From what I have read so far in research is that a Armalite buffer p/n ending in 1090 with length of 5 3/16" and weight of 5.4 oz would be what "I" need.

Thanks all! 

[flyingfinn]

Aero Precision does have a rifle buffer tube kit. But there is no dimension for spring length listed. Also the buffer length/weight differs from armalite. AP buffer length is listed at 5.3" and weight is 5.6 oz.

[jtallen83]

The Armalite buffer tube is longer and uses AR-15 size buffers while the Aero tube is the shorter AR-15 length and uses a short buffer that is usually lighter than the H3 buffer that Armalite uses. I always recommend using the Armalite buffer kit. Listed as out of stock but they are usually back with some pretty quick, sometimes a phone call will get a kit.

https://www.armalite.com/product/ar10rekit01-6-position-receiver-extension-kit/

[flyingfinn]

Thanks for the link!

With the Magpul PRS stock I wouldn't need an extension tube with six positions as it is not a collapsible stock. Correct?

 

https://www.aeroprecisionusa.com/m5-308-rifle-buffer-kit

This is the buffer kit the AP tech said would work for my application when I talked to him on the phone. I waited on buying it as I am still learning and bought the wrong kit yesterday. Any thoughts?

[jtallen83]

2 hours ago, flyingfinn said:

With the Magpul PRS stock I wouldn't need an extension tube with six positions as it is not a collapsible stock. Correct?

The only PRS stock I have used went on a rifle length extension, I don't know what they are available for now just trying to explain the differences in carbine extensions. Armalite also sells the buffer, spring, and extension in rifle length as a kit.

Edited March 2, 2020 by jtallen83

[unforgiven]

Rainneer has Armalite parts most of the time.

[98Z5V]

5 hours ago, flyingfinn said:

Thanks for the link!

With the Magpul PRS stock I wouldn't need an extension tube with six positions as it is not a collapsible stock. Correct?

 

https://www.aeroprecisionusa.com/m5-308-rifle-buffer-kit

This is the buffer kit the AP tech said would work for my application when I talked to him on the phone. I waited on buying it as I am still learning and bought the wrong kit yesterday. Any thoughts?

That rifle extention kit would work well - rifle receiver extention and buffer are good.  Spring is unknown.  Run it and see.  If the spring is an issue, just swap in an Armalite EA1095 spring and you're set. 

The MagPul PRS 3 will work on rifle receiver extentions or mil-spec sized carbine receiver extensions (OD = 1.14").

[flyingfinn]

Thanks all!

I don't have all the tools that I think I should have for my build. 

Go/No-Go gauges 

Also after reading some posts in the 308 tools section I followed a link to Brownells for a barrel nut torque tool. Seems to have some pretty good reviews.

https://www.brownells.com/gunsmith-tools-supplies/rifle-tools/barrel-tools/308ar-barrel-extension-torque-tool-sku080001040-72374-116250.aspx?sku=080001040

Any other tools did you find you couldn't function without? Such as ejector tool or gas tube wrench.

 

[flyingfinn]

A bunch of parts arrived today! I have a 4 day weekend coming up. Looking forward to some assembling!

 

[Radioactive]

Looks like fun

[unforgiven]

Just like Christmas

[willbird]

The Brownells tool is a good one. I have one for AR308 but not yet for AR15 :-).

The punch for driving in gas tube roll pins is handy :-).

 

Bill

[flyingfinn]

Rifle buffer kit arrived today. Inside depth of extension tube is 9 11/16". Spring length approx. 12", OD of coil approx. 7/8". I didn't measure wire diameter. Buffer is as advertised by AP; L=5 3/16" and weight=5.4 oz.

Trigger, gas block and tools should arrive tomorrow.

I removed ejector assy. today in preperation to measure head space with the go/no-go gauges I ordered. I have not measured for headspace on any firearm before and may have questions when I perform the procedure. But as I understand it I can and should check headspace before I install the barrel in the upper receiver. I've read some threads that mention the use of a field gauge (did not order one).

I also read some informative posts by 98Z5V on gas tube length. I ordered one from Aero P. as it is listed as a rifle length gas tube. It is advertised as 15.125" in length, which is contrary to the 15.5" dimension that I read about, guess I'll see where it ends up in relation to the cam pin cutout when installed.

Edited March 6, 2020 by flyingfinn
sp.

[jtallen83]

3 minutes ago, flyingfinn said:

But as I understand it I can and should check headspace before I install the barrel in the upper receiver. I've read some threads that mention the use of a field gauge (did not order one).

You can check when assembled , just easier beforehand. The field gauge isn’t really necessary, if the no go gauge fits you check the field gauge, if it goes then it’s not safe to fire. Even if it doesn’t go you could see some issues with the case due to the excessive headspace, myself I just call it a fail if the no go fits. Field gauges are generally used to check older used rifles, with new parts send it back if the no-go fits. Sometimes different bolts will give different results, I have a few spares and have swapped bolts to get the correct fit.

[flyingfinn]

Thanks jtallen83!

[willbird]

Also if you ever "needed" a field gauge you could find the equivalent dimension and cut a disk of shim stock and affix to to the rear of your no-go with some grease. 

Looks like "Field" is an extra .004 for  SAAMI 308 and an extra .006 for milspec M14 7.62 nato.

SAAMI 308Win:
GO 1.630"
NO GO 1.634"
FIELD 1.638"

7.62NATO (M14 US MILSPEC):
GO 1.6355"
NOGO 1.638"
FIELD 1.6445"

 

[flyingfinn]

 

Thanks willbird!

[flyingfinn]

Oops! My Brownells order showed up sans barrel extension torque tool. Instead I got the go/no-go gauges AND a field gauge instead of the torque tool. Apparently I did not "review" my order well enough during checkout. My fault. I blame it on tooooo many items in my wishlist, along with a fevered happy clicking to get this project assembled. 

Oh well. I'll get the barrel/bolt checked with the gauges and probably the lower assembled on my long weekend. 

[flyingfinn]

The go/no-go gauges worked just fine. All is well.

Putting the ejector back in the bolt was fun without a 3rd hand. I improvised with a cutoff case, some wood blocks and bench vise.

The rear takedown pin detent spring is NOT fun. Trying to get that tiny set screw to stay on the allen wrench while compressing the spring without launching the spring is difficult. I used a pin with a hole a bit bigger than the set screw as a guide. I could not get the set screw threads to start before I slipped off the spring. Several times. I even launched the spring into outerspace once. Of course I found it on the floor not far from the workbench. I have spare springs, so of course I found it.

I lost the set screw (no spares). While searching for it I did find a detent pin that I launched during a previous lower assembly! Hopefully the local hardware store has some 4-40-1/8 setscrews in stock.

Any tips to install that pesky booger of a spring/setscrew?

 

[98Z5V]

1 hour ago, flyingfinn said:

Putting the ejector back in the bolt was fun without a 3rd hand. I improvised with a cutoff case, some wood blocks and bench vise.

This is exactly what I do, too.  I made a jig to work, and didn't buy a jig to get it done.  Well done, man.

[flyingfinn]

Here is a pic of the improv.

For the rear takedown pin detent spring I skipped the set screw (for now). I figured the grip is already the retainer for the safety detent spring. I did a search earlier and discovered as you pointed out years ago it was the builders that started tapping and installing a "keeper" before the manufacturers of lowers did it.

[98Z5V]

58 minutes ago, flyingfinn said:

 I did a search earlier and discovered as you pointed out years ago it was the builders that started tapping and installing a "keeper" before the manufacturers of lowers did it.

 

4-40 set screws.  If you found the info I posted - that I can't even find now, good work...      I've used 6-32 set screws with good effect.  You can just tap the hole for a 4-40, but for the 6-32, you have torun a drill bit first, ream that hole size up, before you run the 6-32 tap in there. 

Good work, man.  Good job researching all this stuff, too - you're putting in the work to make your gun run, and that's appreciated here, more than you know. 

[flyingfinn]

I did finish the lower assy. yesterday evening. I couldn't resist mocking up the upper with the lower. I wanted to check fitment of the upper anyway, so I temp installed the barrel, handguard and muzzle brake. 

I am impressed with the machining and fit. I am not a gunsmith or a well experienced tinkerer of firearms. I only have my career in aviation to compare how things are built. Aero Precision makes an excellent product. I would certify their stuff to fly at 40000 feet.

 

[Radioactive]

Lookin good 

[RedRiverII]

I'm pretty sure that Aero is an aeronautics manufacturer first and guns second.