Shortening the barrel

[dave-0]

I read Joencrew's post from May 2006 about cutting the barrel off at the 'index mark' that Ruger put on their factory barrels. I also read the article about how muzzle brakes work, and the importance of finding the 'node' at the barrel and using the muzzle brake to shift that to the end of the barrel.

Does anyone know why Ruger put the index mark on the barrel in the first place? I have had my mini for about 10 years and this is the first time I noticed it. Incidentally, I have a series 196 and it shoots horrible.

One thing I picked up on in the muzzle brake article is that you can hang a barrel (from a string, I guess, with the receiver still attached) and tap it with a brass hammer to find the spot where the barrel no longer rings. This should scientifically locate the nodal point in the barrel where the accuracy will be the greatest.

There was another group member who shortened the barrel in 1/4 inch increments, and stopped at 16.25 inches -- presumably because of ATF restrictions. Cutting the barrel off at the index ring would leave a barrel length of 14 inches, and a muzzle brake would be a permanent addition. So my theory is that the barrel node is somewhere between 14 and 16 inches. I'd like to keep the barrel as long as possible, but the index ring appears to be the limit for the type of muzzle brake I'll be installing.

Has anyone else experimented with the shorter barrel lengths?

[my1911s]

I cut my barrel to 16 5/16” and installed a Choate 07-07-13 flash hider. At that length, the muzzle bottoms just as the flash hider reaches the barrel step. This also places the last 2” of barrel into the flash hider, which I believe helps stiffen this area.
At this point, I’m getting close to 1 ½ MOA and I believe some final load tuning may get me below that number. My gun feels much better with this length barrel than it did stock.

[dave-0]

I'm still intrigued by the amount of accuracy claimed by Joencrew at .55 to .65 inches at 100 yards. I am going to be using a Black warrior style muzzle brake, which looks pretty heavy and a bit longer than most other muzzle brakes.

[my1911s]

Every rifle has a 100% probability of producing a one shot one hole group. With each additional shot, the probability of the group expanding increases as random variation in the process begins to manifest itself. If one were to fire twenty rounds from a gun capable of only producing a 4” AGR, several of the shots may produce a group of ½” AGR. Those shots would probability be randomly spread over the twenty rounds, but they could be consecutive. If they happened to be shots 1, 2 and 3, and the shooter stopped at that point, he might conclude that he has a 1 MOA rifle. If he were to continue firing, the true 8 MOA nature would emerge. A three shot .55” group means very little. Five – five shots groups of .55” means a great deal more.
With regard to the flash hider, heaver might very well be better. Only true test is to punch holes in paper.

[Jaybird]

I would think that every time you change the length of the barrel by chopping it, you also move that point. And that point probably moves towards the end of the barrel but would probably never reach the end as there would always be some harmonic until you ran out of barrel. But by cutting the barrel to a shorter lenth thus moving the spot further towards the end of the barrel, the weight required to dampen it would be less or the barrel weight would not require as much movement to zero the harmonic. That is strictly a guess!

[my1911s]

One explanation I read explained it this way: Adding weight (i.e. flash hider), creates the effect of lengthening the barrel and causes the node (area no little or no vibration) to shift further from the receiver. If the node can be shifted to the muzzle, the barrel will vibrate between the receiver and the muzzle but the muzzle will remain relative still.
This sounds as good as anything. All I care about is not sending rounds into the next county, a real possibility with a Mini.

[dave-0]

Doing a little further research on the internet, I found this:
http://accuracysystemsinc.com/mini_14_30_accessories.html

If you follow that, Accuracy Systems shortens the barrel to 13" with this type of muzzle brake (the same kind that I bought). I can't imagine any shop lopping that much off the barrel unless there is a genuine gain in accuracy. I think I will find out more about why they do this, and what kind of accuracy results.

[my1911s]

As you shorten a barrel you are changing the ratio of the diameter to the length, as this ratio decreases the barrel becomes stiffer. Stiffer barrel, less harmonic amplitude, greater accuracy. The issue is you never get something for nothing. Shorter barrel means less velocity. That’s why varmint shooters don’t use 13” barrels.

[p35bhp55]

"A three shot .55” group means very little."
Ok, but I'll take it anyway!
:)

[my1911s]

Take it away. Any gun is capable of firing a small 3 shot group, the question is one of probability. Many shooters will fire a small 3 shot group and take it as proof their gun is “capable” of that level of accuracy. Doesn’t work that way.

[p35bhp55]

If you mean I have to fire 20 then pick the group out I agree. If you mean my gun will only do 3 then spread, for my use that will do. I don't picture myself mowing down an armed mob at long range. besides that's what they make .308s for.

[my1911s]

The reason all rifles do not fire all shots through the same hole is random variation in the process. The process is defined as the rifle, ammo, shooter and environment. All of these contribute some degree of variation to the process. In order to accurately measure this variation you must have a statistically reliable sample. A sample size of three is not reliable, as it may represent only a small part of the total process variation. For me, I would not trust a sample size less than 25 and then use the AGR method of group measurement not extreme spread. This is much more involved but the number will actually mean something.

[dave-0]

The reason all rifles do not fire all shots through the same hole is random variation in the process. The process is defined as the rifle, ammo, shooter and environment. All of these contribute some degree of variation to the process. In order to accurately measure this variation you must have a statistically reliable sample. A sample size of three is not reliable, as it may represent only a small part of the total process variation. For me, I would not trust a sample size less than 25 and then use the AGR method of group measurement not extreme spread. This is much more involved but the number will actually mean something.

I agree; this is part of what we teach. But, as I originally posted, I am intrigued by the barrel shortening techniques developed. They do seem to be supported by hard evidence, and even some theorists have developed mathematical models of how barrels respond. BTW, I still haven't heard back from ASI on why they reduce the barrel length to 13 inches as opposed to 14 stated by Joencrew.

Personally, I would trust 3 or 4 groups of 5 shots each, allowing some rest period to cool the barrel and maybe even clean it. When the weather decides to cooperate, I should be prepared to head out to the range (too cold, blowing, icy right now).

[my1911s]

I would guess that longer barrel length probably has more of a negative effect on accuracy than a positive one. That is to say, the longer the barrel the more potential for harmonic vibration. Once the bullet has engaged the rifling for an inch, the stabilizing rotation would have occurred. After that point it’s just a matter of velocity. In one article I read on harmonics, the author cut a 22 barrel to ¾” and was shooting surprising 50 yard groups. I’ve cut 2 3/16” off my barrel and while I haven’t had a chance to chronograph my loads since the cutting, I expect to loose 200 – 250 fps.

Addendum:
What I’ve read on barrel length vs. velocity, as the barrel is shortened; the drop in velocity is not proportional. As the barrel is shortened each inch, the velocity drop becomes larger after each cut. The first inch cut may yield a decrease of 75 fps. The second inch cut may yield a decrease of 110 fps. on top of the 75 from the first cut.

[p35bhp55]

"I would not trust a sample size less than 25 and then use the AGR method of group measurement not extreme spread. This is much more involved but the number will actually mean something."

We use 100 parts as a sample at work, but I have to admit laziness, if I ever go to that much trouble with a rifle it won't be my mini. Also there would have to be a rest and trigger device involved, I'm thinking the shooter part of the process is too big a piece at least for me.

[benson00]

Im not sure if this will help for your ballistics out of your shorter barrels.

http://www.winchester.com/lawenforcement/pdf/LEPDF/2006%20Poster_Front.pdf


look under rifle ballistics

[dave-0]

Accuracy Systems got back to me on my question. They shorten the barrel to 13" and add the big stabilizer to bring back the length of the barrel to over 16". They indicated that the accuracy depends on you barrel but they have shot sub-MOA groups by cutting the barrel.

On my Mini14 the barrel index mark is around 14.5 inches from the end of the barrel So I will likely try cutting at the index mark. The overall length will look to be about 17 inches or so.

[my1911s]

Are you going to have AS do the work? Just remember, if you do the work yourself, the flash hider must be attached in a way that meets ATF regs.

[dave-0]

I can do it. The muzzle brake has to be pinned or can be tack welded in place. Someone mentioned silver brazed (hard silver solder) but that much heat might warp the barrel.