Opinions on 181s are as plentiful as the ammo shot through them.
I have a low-serial number 181 built in 1977. I bought it in early 1980 and was my first firearm. I still have it and it is my favorite firearm. In the 37 years I've owned it, it has never even given a hint of a failure of any kind. Were I one to name my weapons, its would be "Old Reliable"...
It is a "GB", with a flash hider and front sight/bayonet lug. Some report that the combo of flash hider and front sight/bayo lug dampens the barrel harmonics that the infamous stringing is often complained about over "pencil barreled" Mini-14s. That stringing in mine is not noticeable, and it is about a 3-4 MOA shooter, which is about as good as I am. I don't bench shoot, but prefer a bi-pod.
Some considerations, though...
1) they have no provision for a scope or other optic. They were not designed with a scope in mind. There are two ways you can address that if you decide to mount a scope or red-dot.
- One is a funky side-mounted rail that requires no drilling, is reversible, easy to install, and pretty inexpensive (less than $30). I have one on my 181GB and - after some judicious use of blue loctite, is rock solid, but it took a while to get it that way as it would often work loose. There are two problems with this, though: a) it mounts the optic somewhat high, which results in a "chin weld" rather than a "cheek weld" (and also makes the Mini a bit top heavy with a scope) and b) it sits over the receiver. Early Min-14s eject brass more vertically than horizontally and quite often - if there is a rail and optic installed, the ejects will hit the optic (usually the windage knob). Mine occasionally does that - perhaps once or twice in a 20-round mag, and it is usually just a glancing blow to the bottom of the rail. Others have worse problems ("every Mini is different"). A nice feature, though, is you can switch from optics to irons by merely switching from a "chin weld" to a "cheek weld". No need to remove the optic to use the irons.
- The other option is a scout rail that replaces the hand guard and fastens to the barrel and gas block. The most popular is Ultimak. Sandog (on this forum) swears by them, and he knows his stuff! They're a bit pricey (about $110) but place the optic forward of the receiver (away from the ejects). They sit low and if you don't use an optic, you can still use the irons. An added benefit is that it both stiffens the barrel somewhat and helps with heat dissipation. A red-dot sight is the preferred optic to keep the weight and balance down. Were you to want to mount a scope, it would need to be a long-eye-relief scope. Mounting it is something you can do yourself and is reversible should you change your mind.
2) Ruger support is still available, but I have doubts about how much longer. The good news is that the 181 is essentially the same up through the 197 series non-ranch rifles, which were made through 2004. Parts are readily available.
3) The 181s have a 1:10 barrel twist, so lighter bullets generally do better. I shoot exclusively 55gr FMJ (either 5.56 NATO M193 or .223 REM), but it can shoot 62gr fairly accurately, too. Wouldn't go much heavier than 62gr, though.
4) In my opinion, the 181s have superior workmanship and finish. I also have a new 583 series I got last summer and the quality of the finish is much poorer.
5) If you decide the barrel whip is too much and accuracy stinks, you can address that with an AccuStrut (about $100), but I'd check to see if it is a big problem for you before planning to get one. I decided my 181GB was good enough for my plinking purposes without one - after I bought one... It drops man-sized silhouette pop-up targets at 300 meters from a supported prone position reliably. A 6" Accustrut will generally reduce shot groups by about half.
Hope this helps!