No question is dumb!!
Yes you can use a long action for a small round ,but it is not normaly
First look at the round you want to shoot.
Then decide what length to use.
If the round Has a Cartrige overall length (COL) of 2.825 to 2.865 then the
preferred action would be the short action. (243,260,7/08,308,7WSM, 300SAUM
If the round has a COL of around 3.600 or more then a long action is required,(
The next thing to consider is the bolt face dia.
Small dia. is around .378 ( 222,223,ETC)
Standard bolt face is .473 (270,280,3006,ETC)
Magnum bolt face is .532 to .537 ( 7 rem mag,300 h&h, 300 win mag,300 RUM.ETC)
So with all that said if you wanted to build a 270 Winchester you would want a
long action with a standard (.473 ) bolt face.
And if you wanted to build a 300 RUM it would need a long action with a magnum
bolt face (.532 ).
Or a 308 Winchester you would want a short action with a bolt face dia. of .473.
You can use a short action for long cartriges but you have to single load and extracting
a loaded round is very difficult.
If you use a long action for a short round (like a 308 ) the action just makes the overall
length of the rifle longer and is not nessary.
There are a lot more reasons for choosing the right action for the intended round.
Talk to a good gun smith and tell him what you want to build and he should recomend
the best action for the build.
J E CUSTOM