No, stick a cleaning rod in with a patch on it. See how many inches it takes to make a revolution as you push it in. I would guess 14.

 

Or use a bore brush

 

For .30-30 rifles the Marlin twist rate has been 1-in-12" for many decades.

 

That was my understanding as well on the carbines, wasn’t sure about the 24” rifles. Thank ya!

 

The 1:10 / 1:12 twist rate will stabilize the 150 to 170 grain bullet weights, although, the original loading was a 160-grain bullet when the caliber was introduced. 125 grain factory loads are or were available but not sure if still on the market. There are heavier 190 grain proprietary loads available although, not sure if a 1:12 twist rate would stabilize that bullet weight.

 

My Marlin 336C chambered in 30-30 and made in 1979 has 1 in 10 twist.