How is everyone doing? I have a question for you. I am building an AR-9 and I have a majority of the pieces.
This is what I got so far....
1. Anderson Manufacturing - Stripped Lower
2. Anderson Manufacturing - Lower Parts Kit
3. PSA - 10.5" Complete Upper w/ BCG
I need to find a buffer tube and spring. Am I able to use a regular AR-15 one or do I specifically need one for an AR-9.
You need a buffer to match up properly with the buffer tube you have.
9mm AR's need a longer buffer than a typical 5.56 buffer as they do not have a separate bolt and carrier.
9mm specific buffers are generally about 5/8" longer than typical 5.56 buffers.
There may be special 9mm buffer tubes which are shorter to account for this difference and in that case, you would want a typical 5.56 length buffer to work with the special buffer tube.
So without knowing exactly what you have, we can't give an good recommendation.
When you put it all together, here is the check you want to do:
With the bolt closed, pull the charging handle ALL the way to the rear and HOLD the charging handle all the way back and make a pencil mark on the top of the charging handle at the rear edge of the receiver.
Next, let the charging handle forward while actuating the bolt catch so that the bolt is locked back via the bolt catch.
While holding the charging handle back at the locked-back position, make another pencil mark on the charging handle at the rear of the receiver.
Now remove the charging handle and measure the distance between the marks.
You want to see a gap of 3/16" to 1/4".
If you have a little more than 1/4", you can use quarters in the bottom end of the buffer tube to take up the space. Each quarter is a touch over 1/16". Don't stack more than 4 quarters in the buffer tube as then you are shortening the spring length too much.
If you have less than 3/16", you can shave some rubber off the end of the buffer to get to 3/16".
If you have a LOT more than 1/4", you likely don't have the correct parts and the best solution is to get the correct parts or a special spacer that shortens the buffer travel without also shortening the spring.
