My first semi centerfire rifle was a stainless mini-14 that I bought brand new during the early ban years. But around 2010 my dad said he wanted one and I never shot it much so I gave it to him for fathers day he was stoked. (of course I will get it back one day so there is that)

Anyhow, a couple weeks ago I was in the EE and found a Troy MCS chassis for sale so I bought it (knowing that I would get the mini back, but hoping I never would)
About a week after that I found a 1979 production blued 181 series for cheap so I got it also.  So now I am back in the mini-14 game I guess

I always wanted to get a barrel stabilizer from Accuracy Systems for the stainless one back in the day (when they called it the HAR-BAR.) And, in doing some research now it looks like they have made an evolution to an integrated barrel shroud harmonic stabilizer.

I know a Mini is not an AR and will not compete at the moa or sub-moa level without a cubic yard of cash, but...

Here is my actual question.

For the price of the shroud option I could file a Form 1 and cut the barrel back to just in front of the gas block. Since accuracy is hampered by the harmonics and whip of the .562 18" barrel, would this do help at all?

I have seen a post on The High Road from a guy who said he has a factory AC556 13" SBR, and he said that his has about the same accuracy as the 18". 3-4 MOA

What do you guys think is the best way to go?

I'd like to see a pic of the 13" sbr. I've been told Ruger never made any in that configuration aside from the select fire version.

Anything you do to reduce the "barrel whip" of the older pencil barrel Mini's will help.
Even just cutting an inch or two off the factory length will in effect create a stiffer barrel.
After shortening, the muzzle will need a re-crown. Ruger's crowns are mediocre at best, you will see another slight improvement with even a re-crown using hand tools like those available from Brownell's.
Adding some weight on the end like threading for a flash hider will help as well.

Most all Mini's are way overgassed, and reducing that (and using Wilson 1911 buffers on each end of the op-rod will help.
Typical way to determine if that Mini is overgassed is how far the carbine flings brass, 40 to 50 feet is way overgassed.
However, as the 181 series were "pre-Ranch", they have a different method of ejection, and will eject a sane distance of 3 to 5 feet, no matter how the gas flow is changed.

I don't know if I'd shorten one to just ahead of the gas block, though, as you'll then have a tough time getting enough gas to cycle.
The shorter the barrel, the more gas needed.
The new Tactical Mini's with 16" barrels need a gas port bushing at least .020" bigger than the 18" barreled ones.

I shortened a Mini-30 to 16" for my daughter, and it wouldn't even cycle with the same .065" bushings I use in my two longer barrel Mini-30's.
I put the stock .100" one back in, and it now ejects the same distance as my 17" and 18" Mini's, about 14-15 feet.

Velocity loss will be more significant with the 5.56mm by going to a shorter barrel.
In the 7.62 x 39 Mini-30, I've found that I get MORE velocity out of the 16" barreled Mini than my longer ones.
Seems powders in the x39  are optimized for the AK, so the x39 likes short barrels.

If you cut back to just ahead of the gas block, you can find on E-Bay the top half part of the gas block that has a sight blade on it, and I believe Lee Hadaway of The Arms Room, in Trinidad (or is it Pueblo) Colorado makes one as well..
(Other factors would be increased muzzle blast and decreased sight radius, but you are already aware of that with any SBR).

Here are my 3 Mini-30's. The one on the left that I modded for my daughter now has the old style Ruger wood stock with shorter LOP, the Choate PG stock shown was fast to swing and light, but had fitment issues so was replaced.

If you like the Troy stock, it's your gun. But no way would I put a heavy, sharp edged stock like that on a Mini.
I seriously doubt anyone would ever need several feet of rail like a Troy or Sage stock has.
I put a 3 inch section of Magpul polymer rail on each side of the forend, plenty for a sling mount and flash light. Plus I have the Ultimak railed hand guard for an RDS, scope or laser if needed.

The Ultimak has the same barrel stiffening and heat dispersing qualities as a strut, but is also the best place to put an optic, out of the way or the action and rear sight.
If you were going to use a strut, I'd recommend the Accustrut over the Mo-Rod or H-bar.
Kevin was the originator of the strut for a Mini, and his have the cleanest lines and clamps.

But with a barrel that ends just past the gas block, just where are you going to put that Strut ? Won't be enough barrel sticking out for even a one clamp Accustrut Socom . With an Ultimak, you can get the advantages of a strut, and not need 4 or 5 inches of barrel sticking out pas the gas block in order to mount a strut.
The 2 clamp strut (with dimple option) is by far the most effective at helping the old pencil barrel Mini's, but you'd barely have enough room to put one one a 16" barreled Mini, much less one that is 13" or so.
Here is the two clamp Accustrut on an 18" barreled Mini:


And I'd avoid buying anything (except maybe a 3 pack of gas port bushings) from ASI, they charge double, even triple for stuff that you can get elsewhere.

He said AC556

You are correct they never made a 13 inch SBR Mini-14, I should not have have called an AC556 an SBR as it is a 13" barrel machine gun

Thank you for your detailed response, I will dissent though, respectfully.

I am familiar with 5.56 velocity loss over barrel length, a 10.5 or 11.5 is still a good performer in my world with 55-62 grain where shots never exceed 250 yards/meters. I live in a jungle, no joke.

The only reason I bought this Mini was that I got the MCS at such a bargain. I come from the ban era so ultra heavy quad rails were the norm, and I have no fucks to give in that respect. So, I will stick with the MCS chassis as I can set it up like my Sig556 work rifle (other than rock and lock).

But since this is a tech forum, and not GD, lets get on some nuts and bolts.

A 13" barrel AC556 obviously has a measurement for the gas bushing as does a 16" tactical and a normal 18". A shorter barrel (10.5-11.5) gas bushing size should be be able to be backward extrapolated. Gas volume versus bushing and/or port size is just math, that can be overcome.

So here is where the hypothetical meets the road and I will think out loud...

If a mini can be chopped to 10.5-11.5  (which is just in front of the gas block-ish) an increase accuracy will be theoretically realized because all of the accuracy adders are therefore nil (aka tensioned barrel shroud or harmonic damping bars and crowning) since these only act on forces in front of the gas block (except for crowning). However, the mass the accuracy adders is then gone making harmonic vibration interference still a possibility (this vibration is why the target Mini got the sliding stabilizer)

Would harmonics still play in with a barrel at gas block length?

In my experience, My 13" cut down SBR Shoots as good or possibly better than it did with the full length GB barrel.

I haven't done a scientific study, but when I sighted in, I noticed that I was impressed with groups at 50 yds.

The groups were decent 1-3" groups open sights from bench and remained consistently good throughout a few mags.  I wouldn't SBR deliberately to improve accuracy, but i'd say it didn't hurt on my conversion.  On a 5.56 you are going to lose a bit of velocity and not redeem the ballistics the rifle cartridge was designed for.
Cut and crown quality probably matter a bit on the cut down.

Your accuracy will be fine. As I said a shorter barrel acts like a stiffer, less whippy barrel. Even just cutting off an inch from a standard 18 inch barrel is a help.
After shortening, you'll have to re-crown anyway, any decent crown job will be better than what the factory does.

An even gap between gas block and proper torque of the gas block screws, in a criss cross pattern is essential.
Most guys with a full 18" barrel can get away with a .045" gas bushing, the 16" Tactical needs more gas, like a .060" or .065'.
Your 13 inch, or whatever it turns out to be, might need a full .080" or larger.

Not sure what you meant by "the mass the accuracy adders". Good accuracy can be obtained without the goofy sliding dampener of the target model.
In a longer barrel, things like a strut and adding some weight on the end, like a flash hider reduce barrel oscillations (whip).
With the short barrel you propose, barrel whip will be non existent.
A strut will not be needed at all, and you wouldn't have enough barrel sticking out past the gas block to mount one anyway.

You could throw on a Flaming Pig/Krink Brake - that would add mass and gas pressure, and reduce the blast.

I also don't think shortening it will hurt accuracy on a 181 series.  in the 1980s, I shot an AC556K with a 13" barrel, and it gave the same accuracy as my 180 series Mini.  I do have a suggestion, though.  If you got a 186 series with a 1/7 twist barrel and SBRed it, you would get better performance with that shooting MK262 MOD1 77 grainers, than a 1/10 twist 181 series.  The MK262 MOD1 is effective even from the Spec Ops shorties (MK 18 Mod 1) they use.  My 186 LOVES MK262 MOD 1, and my 77 grain clone load.

I don't think shortening the barrel has quite as much effect as people think it does.  For example, I bought a 184 series Mini-14 for $350 after a prior owner had attempted to improve accuracy by shortening the barrel.  It was in great shape, but it was obvious why he sold it when I took it to the range. It was a 3-4 MOA carbine and obviously shortening the barrel didn't help, and didn't get the former owner where he wanted to go.

However, when I added an Accu Strut to it (the short SOCOM version) along with a Choate Browning style flash hider/front sight combination, a .045" gas port bushing, a shock buffer, and a Tech Sights rear sight.  I also added a Choate hand guard and did some shortening on the rear to ensure it did not contact the receiver (as you do with a NM Garand or M14) to ensure it doesn't change the stress on the barrel as the barrel heats up.  Once done, it demonstrated 1.5 MOA accuracy with Hornady 55 gr FMJs.   That's the same accuracy I get with my pencil weight AR-15 SP1 and my M16A1 clone built with a police surplus M16A1 upper half with the same load.

A year or so later, I also picked up a 187 series Ranch Rifle  that had been sold as surplus by the state of North Carolina.  It had a very heavy combination flash hider/front sight/bayonet lug device on the muzzle.  It gave me 3/4" groups at 50 yards on the trip home - but shot about 18" low with the rear right as high as it would go and front sight filed about as low as it was prudent to go. It was obvious they had a scope on it. Once I removed that muzzle device it shot to a normal point of aim, but was again a 3-4 MOA rifle.



The extra, and excessive, muzzle weight took care of the barrel whip/harmonics issues, but significantly lowered the point of impact.  However, the idea of adding some muzzle weight has historically worked well with the Mini-14 and that was why I chose to add the Choate front sight and flash hider to my other Mini-14 as it improves the accuracy by helping the harmonics but without excessive POI change.

I gave my 187 series ranch rifle the same accuracy treatment as my 184 series Mini 14, but kept the 18" barrel length and once again got the same 1.5 MOA accuracy as my 184 series Mini-14.

In short, both my early pencil weight barrel Mini-14s/Ranch Rifles give me the same 1.5 MOA accuracy after the same accuracy treatment and in that condition there is no difference between the 16" and 18" barrels.



Personally, I think 18" is pretty much the sweet spot for a .223 barrel on a tactical style rifle giving you a good compromise between ballistic efficiency and length/handling. I added a scope to my 18" 187 series ranch rifle to take advantage of the accuracy (and I have the 16" Mini 14 when I want a shorter carbine) and it ends up being about the same length as a 20" AR-15.  Any difference is due to the stock. With the Revolution stock's longer length of pull it's the same length as an A2, and with the standard Ruger stock its the same length as an A1.



My recommendation would be to make the same accuracy mods to your 181 series Mini-14 and only shorten the barrel to 16" if you want to reduce the over all length of the barrel with the Choate flash hider to the original 18" length.

-----

As an aside, I wasn't a big fan of drilling another channel in my barrels, especially in in the barrel on my 187 since it already had 2 cut in to it, so I used green Locktite 620 to attach my flash hiders.  It's designed for slip fit applications with clearances up to .015" with a shear strength of 3800 psi, and temperatures up to 450 degrees F.   I used tape to temporarily hold/adjust the rotation of the front sight to zero with the rear sights mechanically centered, and then used index marks on the tape to re-orient the sight after I applied the Locktite.  The end result was perfectly indexed rear sights that have stayed solidly in place, even after full magazine dumps.

450 degrees F is the rated temp, but practically speaking you'd have to heat it up to about 600 degrees and then maintain it for about 30 minutes to get it loose.

I should also add that when I installed the Accu Struts on my Mini-14s I carefully pre-assembled and then center punched the locations for the Allen screws that secure the strut to the gas block.  I then used an end mill to create a divot that fully captures the Allen screws and creates a very solid fit.  In fact if you remove the clamps the strut itself still won't move.  Consequently, my results might be better than with the strut installed with just screw pressure.