Here I will address the older thin barrel Mini's and the associated barrel harmonics which are not conducive to shooting good tight groups and vertical shot stringing when the barrel heats up. Most of the newer Tapered barrel Mini's are capable of sub 2-MOA with iron sights and we will not deal with them here.
The older, thin barrel Mini's have 18 1/2" barrels and are not very stable when fired causing harmonics (wave distortion) and erratic groups. When the barrel heats up, it also causes vertical shot stringing. These have been the chief complaints about the Mini-14 and it's lack of accuracy.
By shortening the barrel to 16 1/4" leaves a shorter, stiffer tube. The shorter, stiffer tube will shoot more accurately and consistantly and will not be as prone to vertical stringing. Loss in velosity will usually be 100 to 200 fps, I have seen as little as 50 fps loss with some loads, which is not too bad considering the gain in accuracy. The only shortcoming is the cost to have it done by a gunsmith. To properly shorten the barrel, it has to be removed from the action, in most cases, to be shortened in the lathe. Once shortened, it has to be re-crowned and the sight re-installed. This will usually have to be done by a gunsmith, as the home smith is not usually equiped with the skills or the equipment to do the job.............
Aftermarket barrel struts, properly installed will reduce group sizes up to 50% or more all by themselves. What it does in essesence, is stiffen the barred by being attached at three points. Two clamps on the barrel and one securing point on the gas block. This creates a very rigid mount that virtually elininates barrel harmonics and vertical stringing when the barrel heats up. The strut clamps also act as a heat sink, drawing heat away from the barrel. I machined my first barrel strut system back in the early 90s, before anything else like it was available. It, by itself, reduced my group size from 3-MOA scoped, to sub 1-MOA scoped. This prototype strut is still on my favorite and my go to first Mini. My struts today are basically unchanged, except for minor cosmetic changes and have always givin similar results on customers rifles.
If you have fabrication skills, tools and materials, you can fabricate your own strut for less than $20. If not, here are a couple of links for struts (not mine). The Original Barrel Strut for Mini-14s
The photos below show my original prototype strut and how it is mounted.
CRYOGENIC STRESS RELIEF:
Cryo stress relieving is a dry tempering process that relieves stresses in the barrel due to machining. It re-structures the grain of the metal and makes the metal more dense while at the same time, relieving stresses in the metal due to machining. It has been proven to reduce group sizes up to 50% and virtually eliminate vertical shot stringing when the barrel heats up. I can attest to this, as I use the process myself and personally know the before and after results. Barrel life will be longer and another plus of the process is that I have found that the barrel is easyer to clean.
If you choose to go this route, depending on the company you go through, it will cost anywhere from $35 to $85 per rifle. You have to send the barreled action, stripped of all other parts. Some companies will do small parts also. You can find several companies doing this by doing a Google search. I only use one company and they are the original. I won't post a link to it as I do not want to be accused of advertising a sole source. I don't think that would be appropriate here. I will answer PMs.