Measure the length of the buffer tubes internally and springs. There were some proprietary lengths out there at one time, I ended up with a rifle cheap that wouldn't run. Turns out that the carbine buffer tube was 3/8" short.
I was building my first AR10. When it came to the stock/buffer tube assembly, I figured, "Hey, a buffer tube is a buffer tube."
The rifle (.308) would load and fire, but WOULD NOT function.
Yes sir, I had installed an AR15 buffer tube in an AR10 rifle.
As my kids would later explain to me, "One thing is not like the other....!" LOL!
That was just part of my lesson on "AR15 parts are generic. AR10 parts are proprietary."
