Welcome to the forum.
There are plenty of threads that detail the differences in receiver extension (buffer tube) depth and the appropriate buffer and spring. An approximate depth is not good enough for these rifles. A rifle length receiver extension (RE) is the same across all platforms - AR15, AR10, LR308. An Armalite AR10 carbine RE will be 7 5/8 inches deep, not more or less. A DPMS pattern carbine RE will be 7 inches deep just like an AR15, again not more or less. The buffers and springs are also not interchangeable. Here is a great reference chart for that.
If you are still having an issue with your rifle, you might be better served by starting a new thread with your details.