I'm building a pair of 9mm ARs, one pistol and one rifle.  The piston is using a new Stern 9mm upper, and the rifle is using an old Olympic Arms 9mm upper.   The 'lots of 9mm info' thread has some fantastic details about buffer weights, tubes, etc, but I have a couple of questions that I couldn't determine the answer to.

https://www.sponaugle.com/post/IMG_1769.jpeg

First - For the AR 9mm pistol build I'm using a strike industries 'Short Pistol Buffer Tube'. (blue in the above picture)  Its internal length is 5", compared to 7" of the standard carbine buffer tube.  With this shorter length I assume I would not need the buffer spacer that is required with the carbine buffer tube.  The only detail about that gives me hesitation is that the buffer spaces that I have seen are not 2.0" long, which is the difference between the carbine tube and this short piston tube.   I would also need a heavier buffer weight corresponding with the recommendations in that other 9mm info thread.  

Second - For the AR 9mm rifle build I noticed that the olympic arms bolt is close to the same length as the 5.56 bolt (this is an olympic arms upper from circa 2013).  Given that it is longer, would I still need the buffer space when combined with the standard carbine buffer tube (7" length)?  Since one of the reason for the buffer spacer is to restrict the rearward travel of the bolt given the 9mm cartridge size I would guess it would still be helpful.  An opinions on this?

Cheers.  Hope everyone is having a great christmas.

SI has their own compact buffer for that tube.  

The 9mm bolt is shorter than a 5.56 bolt, hence the need for a spacer or longer buffer in a carbine.  Not familiar with Oly so no help there, but there are guys here that are.

The Olympic Arms system was designed to use a standard carbine length buffer. You could use a 3/4" spacer in the tube, but I never found it necessary. The Oly setup doesn't have LRBHO unless you're using the latest polymer mags. My carbine uses the Sten mags.

You will want the Strike 9mm buffer for that tube. I made my own from a cut down carbine buffer. Use the Strike buffer spring. The short Strike 5.56 buffer will be way too light and short enough to cause problems.

Thanks!  I missed that part on their site, but there it is!

Thanks for the reply!  Good info on the Oly setup.

I found that 9mm specific buffer on the SI site, so I'll have to see if I can find it anywhere as it looks to be backordered.   Agreed that short buffer that came with the short SI tube is way too light. I think it was around 1oz.