Buffer tube question and SOTAR Larue Upper review

[pag23]

So I watched SOTARs video on the Larue Upper kit and he was concerned about the Buffer Tube and Castle Nut, being a Level 1 grade, on the example he got.

If this is the case, should I just get a Vltor buffer tube and FCD castle nut? I was also looking at the BCM A5 kit as well.

Rifle will be set up for range shooting under 300 yds for the most part...caliber 5.56

Thanks!

[everready73]

Not sure what Level 1 grade means? I am sure larue i using 7075 for the buffer tube. TDP calls for rolled threads i believe

The Vltor or BCM A5 kit (or any a5 system) is a good idea in almost any ar15 IMO. FCD makes great stuff and high quality. Nothing wrong with a quality RE kit from BCM, SOLGW, or Sionics either

All that being said i have NEVER heard of a Larue Ultimate Upper kit Buffer tube or any of the components having an issue

[pag23]

Not sure what Level 1 grade means? I am sure larue i using 7075 for the buffer tube. TDP calls for rolled threads i believe

The Vltor or BCM A5 kit (or any a5 system) is a good idea in almost any ar15 IMO. FCD makes great stuff and high quality. Nothing wrong with a quality RE kit from BCM, SOLGW, or Sionics either

All that being said i have NEVER heard of a Larue Ultimate Upper kit Buffer tube or any of the components having an issue

He talks about the threads on the buffer tube extension and castle nut... there are 3 levels, Mil Spec is 2, Level 3 is better. The issue wasn't the material but the threads on both parts...It was an interesting video..

I already went ahead and ordered the 2 parts from FCD, I didn't order an A5 system.....

[Joe Mamma]

So I watched SOTARs video on the Larue Upper kit and he was concerned about the Buffer Tube and Castle Nut, being a Level 1 grade, on the example he got.


Can you post a link to this video?

Thanks.

Joe Mamma

[pag23]

https://m.youtube.com/watch?v=tBbnBTSui0k

Here you go..skip to the 10:45 mark which talks about the buffer tube and castle nut...

[Duffy]

CNFs have been made on Swiss machines since late 2019, each CNF has its threads checked with a class 3 gauge.

These days we make upward of 2.5K CNFs a month, they're still individually gauged, and will continue to be verified this way. In 2019 Chad told me some of the CNFs didn't pass gauging, they still worked but I was duly concerned. I think the percentage of these that didn't pass was small, but we nevertheless started to look at other ways to make them. Being we make everything in small batches, we were able to quickly make changes (not to the design, but manufacturing methods).

We credit Chad Albrecht of SOTAR for the improvements we subsequently made on CNFs :)

[pag23]

CNFs have been made on Swiss machines since late 2019, each CNF has its threads checked with a class 3 gauge.

These days we make upward of 2.5K CNFs a month, they're still individually gauged, and will continue to be verified this way. In 2019 Chad told me some of the CNFs didn't pass gauging, they still worked but I was duly concerned. I think the percentage of these that didn't pass was small, but we nevertheless started to look at other ways to make them. Being we make everything in small batches, we were able to quickly make changes (not to the design, but manufacturing methods).

We credit Chad Albrecht of SOTAR for the improvements we subsequently made on CNFs :)

Got my order today! Very impressed so far and I can't wait to install it when the other parts come along..

[everready73]

Got my order today! Very impressed so far and I can't wait to install it when the other parts come along..

Cant go wrong with FCD. I have never been disappointed with their stuff. Function over form and you know they are using the best materials possible

[SOTAR]

My video is an example of one.

Using class 1 threads can allow the castle nut to loosen even if staked.

Milspec is class 2 or better.

FCD castle nuts are now Class 3 and a vltor tube will likely be class 2 or better.

[curious1]

My video is an example of one.

Using class 1 threads can allow the castle nut to loosen even if staked.

Milspec is class 2 or better.

FCD castle nuts are now Class 3 and a vltor tube will likely be class 2 or better.

Pretty sure the lower and nut are supposed to be 3B not 2. Tube I believe is a 2A.

[Disciple]

FCD castle nuts are now Class 3 and a vltor tube will likely be class 2 or better.

How about a BCM tube?

[pag23]

Well I called Larue today on the status of my order...they are back logged 4 to 6 months! So I guess the original person mispoke when they told me 4 weeks.

I am just going to have the lower built and keep the Larue parts when they come in as spares...

[Curlew]

What’s the minimum pitch diameter for a class 2A buffer tube thread? I’m guessing around 1.140”, but if someone could sanity-check that, I’d be grateful.

[curious1]

I think the numbers after finish are the same as the standard for a 1 3/16"-16 UN 2A. So 1.1403" is the chart number in the one I looked at. Numbers are different before it is anodized.

[Curlew]

...1.1403" is the chart number in the one I looked at.
Thanks for that. I finally managed to dig up a table myself, and it agrees with what you found: for class 2A, the PD should be 1.1403 min, 1.1454 max.

Over the years I’d noticed (by feel) a lot of variability in thread fit, and I’d even taken to measuring the buffer tube with a thread micrometer, but I hadn’t known what the actual spec is. But using 1.1403 now as a reference point, it seems that many of the examples I have are on the small side, and they don’t necessarily line up according to the general reputation of the manufacturers.

Two that seem to meet 2A specs are from Colt (no surprise) and Bushmaster (!), but both only barely, at around 1.140 to 1.141. Three others are are in the range of 1.138–1.139, so a little too small, and these are from manufacturers that you would normally think of as making good stuff. Two more are so small (1.134–1.135) that I don’t think they even meet 1A. But the best fit of all: an old commercial tube from Olympic Arms, which at 1.142 lands squarely in 2A. Go figure.