AR-15 now with 9mm upper and 9mm magazine adapter. I have Odin weights for the 9mm. Do I have to change my buffer tube and spring as well?
Based on answers and discussions from other forums, the general consensus from people who have built and run similar setups is as follows. This is a summary of community experience, not a statement of fact or a guarantee for any specific build.
Short answer:
Most posters say you don’t have to change the buffer tube, but you will usually want a 9mm-appropriate buffer weight (which you already have with the Odin weights) and a compatible carbine spring. The standard 5.56 buffer setup is commonly reported to be less than ideal for blowback 9mm.
Why people recommend this:
According to multiple forum threads, a 9mm AR operates via direct blowback, so users rely on bolt mass, buffer mass, and spring tension rather than a gas system to control timing. Many builders report that standard 5.56 buffers are too light and can result in harsher recoil or reliability issues.
Buffer:
Forum members commonly report success with dedicated 9mm buffers in the ~5.4 oz to 8+ oz range. Odin adjustable buffers are frequently mentioned as a workable solution, with users typically tuning heavier rather than lighter.
Commonly referenced discussions:
https://thegunzone.com/what-buffer-should-i-use-in-my-9mm-ar-15/
https://blowback9.wordpress.com/2021/08/09/what-9mm-buffer-do-i-need/
Spring:
Many posters state that a standard AR-15 carbine spring works well when paired with a proper 9mm buffer. Extra-power or .308 springs are generally described as optional and situational (suppressed use, hot ammo, or personal preference).
Example manufacturer/forum guidance often cited:
https://help.angstadtarms.com/article/56-buffers-and-springs
Buffer tube:
Most forum responses indicate that a standard carbine buffer tube can be retained. Some users choose A5 or extended systems for smoother tuning, but these are described as optional rather than required.
Representative discussion threads:
https://www.ar15.com/forums/AR-15/9mm-pistol-build-spring-and-buffer-recommendations/15-760626/