Great article on how a barrel tuner works

[lobo creek]

http://www.precisionshooting.com/psm_2005_03_issue.html I tried tapping the barrel with a section of cleaning rod and it seems that the node on my rifle is about 2 3/8" to 2 1/2" from the muzzle. (tried this little experiment with no sights or muzzle brake installed) The trick is to add a weighted extension to the barrel to move the node forward to the muzzle. The node doesn't vibrate during the firing cycle.

[bwraven]

Thanks for posting this.

[rutro]

That's a very good article Lobo Creek. I'm glad you posted it up for us. Pretty much confirms some of the conclusions I've been thinking about, especialy in reference to our skinny barreled minis'. It will help a lot of people understand what's going on with their mini14's accuracy, if they read it and understand it that is.;)

[lobo creek]

Before I read this article I couldn't understand how hanging a heavy muzzle brake on the end of a skinny barrel could be of any help. It makes a whole lot more sense now that the vibration pattern of a gun barrel has been explained. No two guns are exactly alike, so someone might have great success with a Mason brake while others might see only small gains in accuracy using the same brake.

[P-Shooter]

Lobo, my thanks also, I have been working on this problem like everyone else. The article will help and it reminds me of what I have done with a few bolt actions that might work on a Mini. People have been "free floating" the barrel, (sort of) by eliminating the pressure at the gas block and this could be the wrong approach. My Mini-14 shot great right out of the box for a hundred rounds or so unttil the action worked itself a bit loose in the synthetic stock. Maybe this affected the pressure point at the gas block?? I have a tuner that I have been working with, but the gains are hard to determine so far. I have considered adding pressure at the gas block before, it needs to be even, now I think I will try something along that idea. It is part of the game to try ideas. I had started to add pressure at the gas block until I read on here about others NOT doing this. The article helped to get the brain working again.....

[lobo creek]

P-Shooter, my mini is a stainless model with a fiberglass stock. I also think that a wood stock is more rigid but I'll continue to work with what I've got. Just as with you, the article made me stop and look at what others have done and where they have had success in improving accuracy. I think that since the gas block is a clamp, it probably is a node point. The other node point on my gun is about 2 1/2" from the muzzle. That would mean that the midpoint (where the barrel has it's little bulge) is the area that has the largest oscillation when fired. KKina"s front clamp on his accu-strut is mounted near that midpoint. He's dampening that part of the barrel's vibration. There's another poster that had success using that egg-shaped device that looks like a galoline line primer bulb (I don't remember the name of the product). He had good results with the unit mounted around the same area of the barrel bulge. Then we have another shooter using a steel clamp-on shaft collar. I believe these weigh around 1 3/4 oz. He had his best results with the collar mounted right behind the front sight. I think he was also using a Mason brake. It almost stands to reason that if his brake weighed an additional amount equal to the clamp, he might not need the clamp. A barrel sleeve mounted on bushings that closely fit the barrel could work in taming the mid barrel vibration. Getting a bushind to fit the barrel in front of the gas block seems impossible because of that midpoint bulge. A sleeve might work if the bushings were mounted with one up against the bulge and the other behind the front sight. The sleeve could extent all the way to the gas block but the rear portion of the sleeve would be free floating. Then you could add a brake or just an extension that looked like a brake to the muzzle. It's weight would have to be a process of trial and error. That's pretty much what I've come away with after reading the article. I'm sure there are al lot more ideas out there. I hope to hear them cause right now I'm stuck in idle.

[P-Shooter]

Lobo, After I posted to you, I worked on my Mini-14, I decided to have the stock put pressure on the gas block. I have it now where the stock is pushing up on the gas block. The whole front end is pretty solid now. after the "article" I now realize my barrel sleeve is really a stiffener and heat sink, and not really a tuner. It weighs about 10-3/4 ounces and it fits from the gas block out to 1.7/8" passed the muzzle. I removed the front sight. The weather was pretty nice today but I got into a project that needed for me to be outside so I haven't shot it since I added upward pressure on the gas block. I am going to get away from free floating the barrel and see what happens. I free floated bolt-actions and always ended up adding a pressure point under the barrels the way Remington and other do. After the "article" I now see why my Marlins with the tubular magazine under the barrel shoot so well. My Dad's Remington 141 has a tubular magazine and it shoots pretty good also. Bill Calfee's article might help us get these Mini-14s and 30s shooting better. We are having balmy weather here in PA, nice for shooting, so I will report if I get a chance to see if my latest mod works.

[lobo creek]

I re-read some of guncat's posts where he experimented with shaft collars clamped to the barrel as a tuning weight. He was able to improvise a way to add varying degrees of weight to the collar. Anybody using a Mason pin-on brake could try the same thing by clamping a shaft collar on the brake itself. The middle area of the brake, where the six vent holes are, measures 0.745" on my dial calipers. A 3/4" bored collar will fit snugly. McMaster-Carr has steel and aluminum clamps in this size. By adding and removing weight you could find the optimum weight for a tuner for your particular rifle.

[guncats]

Good post.
still have to explain some of my observations though:
* on my 14 and 30 the sweet spot location was both at about 2" ahead of the gas block. The 14 has a long and thin barrel (factory 18.5" pencil barrel), the 30 has a thicker and chopped 16.5" barrel. Supposedly the stiffness should be quite different, then why do both have the same sweet spot location?

* I was able to change spread pattern by changing the shape of the tuner (verticle tuner -> verticle spread, horizontal tuner -> horizontal spread), the article explained " more accuracy by moving the node to the muzzle crown", but not exactly how it is done. It is more than just the mass that is changing the vibration mode. The auxiliary vibration torque induced by the shape of the tuner also affects the muzzle direction.....:wacko:

[lobo creek]

I may be wrong, but I get the impression from the article that you have to add both mass and length (overhang) so the barrel thinks it's longer but the muzzle remains in the same place. The new target mini has a sliding tuner that overhangs the muzzle. It weighs 11 oz. according to the article that was posted on this site. The barrel is heavy and, I think, needs a heavier tuner. I believe the standard mini with its light barrel wouldn't need anything quite so heavy to move the node to the muzzle.

[guncats]

so the "overhang" is the key.......huh<_<
Now somebody just have to figure out a way to do a fully adjustable "overhang" weight then we will be in good shape.

[lobo creek]

Yep, I think that's what we need. According to the article, a barrel, no matter how long or short or how heavy or skinny, has the same vibration pattern with the node a short distance behind the muzzle. Add a tube to the end of the barrel of the right weight and it acts like a longer barrel with the node still behind its end and hopefully where the muzzle ends. That's why the use of muzzle brakes helps to some degree the accuracy of the mini. Adding incremental weights to a brake like the Mason should prove or disprove this theory. Did you drill and tap a hole in your shaft collar in order to add weight to it? The two-piece 9/16" collar for use on the barrel uses 10-32 cap screws and the 3/4" collar that would fit on a Mason pin-on uses 1/4"-28 sized cap screws. If you replace the cap screws with threaded rod sections of say about 3 inches long followed by a spacer and a nut, you could attach the collar and have two pieces of threaded rod extended below to which you could add pieces of flat brass bar stock bored on each end for the threaded rod. A couple of nuts would hold these in place and you could add or subtract weight pretty easily. McMaster-Carr has on page 3492 of their catalog some alloy 260 brass in thin strips of varying widths (1/4" to 2" wide) and varying thicknesses (0.016" to 0.064" thick, about 1/16" ). It woud probably be better to start off with an aluminum collar as the steel one probably weighs better than two ounces.

[rugmar]

Very Interesting. Great article with lots of valuable info. Thanks for posting!

[cajungeo]

Thanks for the article lobo. It makes sense to me. I'm posting a link in the Mini Links Sticky under Articles

[P-Shooter]

Here is an update on what is happening. I haven't shot it enough to make any definite conclusions. I tried my Mini-14 first with the pressure point at the bottom of the gas block and the barrel sleeve off, five shots and only one touched the top of the target, it was shooting that high at 100 yards, at least a foot. I installed the barrel sleeve and adjusted the scope and the next five shots were in the black, two were still flyers away from the other 3 which formed a 1 & 1/2" triangle. I really need to decide on which spotting scope to buy so I can check after each shot. I don't know where in the string the two flyers were. I had gone to the range late and couldn't continue that day. (I had another project, a shotgun, to test also.) After about the first 100 rounds out of the Mini, it seemed that the flyers started to appear. Flyers is what I am going to try and eliminate. I haven't given up on the pressure at the gas block yet, but I know it might not pan out. My barrel sleeve does weigh 11 ounces as I said. With the sleeve's weight besides adding pressure to the gas block, I have too many variables at once. I need to get back somehow to conducting a controlled experiment. It is easy to have too many variables as you all know. I keep waiting for this Mini to "settle" down and start showing some consistancy. I will just have to keep at it. I will settle on consistancy. As far a grouping, I guess that will be a compromise. After all its not a target rifle, but its fast and fun, and that should be enough. (It has gotten me back to shooting more and that's good.)