If you are talking High Powered shoots, than the NRA or CMP websites will have the appropriate info. Most ranges have 3 position shoots and almost any rifle is welcome. For timed events, the norm is for bolt guns to receive some additional time, 15 seconds or so. There are so many folks that shoot from the bench only these days that keeping your 3 position skills tuned can really make a difference in competition or in the field. For most competition shooting a heavy barrel is most desirable. These are a couple of mine. 1st a Bushmaster DCM, 2nd a Howa 1500 .308.
Now, if you want a cheaper type of competition shooting, Military shoots are great. The rules of each shoot will specify the types of Military arms allowed.
I'm a TXDPSA member and we do carbine matches on occasions. They are similar to the IDPA type rules so you have to shoot from cover, on the run transition from rifle to pistol etc... They use different scenarios all the time. Some are even done out of vehicles and on motorcycles. Nothing is ever stationary. You have limited ammunition on some stages and you are forced to reload all the time. Keeps you prepared for the worst case situation. None of us are pro's, just being safe and having fun.
In NRA highpower Or CMP matches you shoot the following.
200 yards... offhand (standing) with NO sling used..but the sling is on the rifle. 2 sighters on the front end for 2 minutes. 20 rounds for the record slow fire. single load (one round at a time even in the AR-15 etc....) 20 minutes.
200 yards sitting... RAPID Fire. You have 70 seconds to go from standing to sitting and shooting 10 rounds total. You are required to load a TWO round magazine first, and an EIGHT round magazine next. (requires magazine change and takes nothing away from those shooting an m1 garrand).
you do this 2 times for a total of 20 rounds. YOu also use the sling.
You get 2 minutes on the front end for 2 sighters. (your eyeball is in a different place relative to the sights from standing to sitting to prone so you adjust your sights).
300 yards prong... RAPID fire. You have 60 seconds to go from standing to sitting and shooting 10 rounds total. You are required to load a TWO round magazine first, and an EIGHT round magazine next.
you do this twice for a total of 20 rounds. You also use the sling.
you get 2 minutes on the front end for 2 sighters.
600 yards prone SLOW fire. you have 2 sighters on the front end.
you have 20 minutes to fire 20 rounds SINGLE load again. you also use the sling.
Total of 88 rounds down range (with NO alibies) 80 for record and 8 for sighters.
Max score is 800 and 80 X
an X is a bullseye and is worth 10 points. X's are used as tie breakers.
if you were to shoot 727 and 42 X and i were to shoot 727 and 41 X you would win!
Lots of fun.
You are requiered to perform PIT duty in a TIMELY fashion (go with an old timer to teach you.... it is really easy).
You are required to score for the other shooter. (this is easy also)