Precision Rifleman Magazine
Great article, in the August issue, by Dan Lilja discussing barrel rigidity. Nice to have a magazine with articles about accuracy concerns.
They are doing a great job with the magazine.
Dan's work on barrel rigidity is why both my LV guns have HBR taper barrels on 'em.
Good shootin'. -Al
If interested, Dan Lilja has a number of good articles at his site. Each one of the subjects on this page is further broken down: http://www.riflebarrels.com/articles/ There are many fascinating topics that he covers in detail. Nice man to talk with, too.
In the for-what-its-worth department, we're going to be chambering up a 30-PPC in the next couple weeks. The barrel has a Hunter taper, but will use the full 5-inch 1.250 section, as allowed in the Varmint classes.
Based on Jackie's earlier work, I also figure a 20-inch length is enough. That should be one stiff barrel, with enough available weight allowance in HV to add both an 8-ounce "tuner" (muzzle mass) and a heavy scope. Might make LV weight without the "tuner" & with a regular scope, but that's not a design goal right now...
Thanks to Dan Lilja for his ideas, and to R.G. Robinett & Al Nyhus (at least) for testing the idea out. Jackie too, for his testing on the .30PPC.
The shorter and stiffer that a barrel is, the faster its swing rate is on one of those graphs that Varmint Al published. In order to give the bullet time to exit the muzzle time to exit the barrel while the muzzle is on the rise, the whole issue is slowing down the rate at which it rises and then falls. It would seem that a short barrel can easily be too stiff for this to be accomplished, especially considering how much stiffer taking a couple of inches off makes a barrel. (I have spent some time trying different contours and lengths using Dan's program.) This whole issue will probably be made more critical by the lower muzzle velocity (compared to the 6PPC) of the .30 PPC. I know that very accurate rifles have been built in this caliber, and that the same can be said of rifles that do not have tuners. I am merely pointing out what I think that I understand about how tuners work, thanks mostly to studying the work of Varmint Al.
I had kinda thought of that, but I lack of ability to run the FEA analyses Al runs -- or anything even close, to be honest. So we're back to a threaded barrel & a bunch of different weights. Really different weights, all the way from 2 ounces to 16 ounces, and testing by trial & error. If it shoots good, maybe it won't be a waste of time for Al to run an FEA on what worked, which would really needed as evidence for anyone else do the same.
It's a good platform for that trial & error experimenting, a drop-port Viper, bedded by Jim Borden in a second generation Rimrock stock -- the one where he stopped going for absolute stiffness & more for vibration control.
I've read Varmint Al's posted test, and while he did do some testing on short barrels & accuracy -- even shorter than 20 inches -- I didn't see anything on short, stiff barrels and muzzle mass. Since I can't really model it, seems worth burning some powder.
I figure bottom line, if the "tuner" doesn't work -- by which I mean I mucked up the figuring, not that tuners don't work -- I'll still have a nice, competitive rifle in it's plain configuration.
Good for you. Additional details on Varmint Al's testing: There were three ways that he was able to have bullets leave to the left of center on the muzzle rise curve. One was to add weight to the muzzle (a tuner). Another was to increase the barrel length to 24" (which slowed the swing). The third was to thin out the middle of the barrel, making it more flexible, and slowing the swing. I believe that this option was in response to my mentioning a couple of other instances where this was done, both involving rimfire firearms. Looking at a picture (in PS) of one of Bill Calfee's rimfire conversions of XP100 pistols, I had noticed that the center of the barrel had been slightly reduced in diameter. This was back when he was posting here on a regular basis. I said that I thought that it was done to increase the flexibility of the barrel, so that a lighter tuner could be used, for better balance in the pistol configuration. I referred to this slight reduction as a hinge point, and when he posted after me, he liked the term and asked if he could use it in future writings. Of course I was quite pleased at his liking the use of the term and said that that would be fine by me.
Much earlier, well before I had read anything about rimfire tuners, Merrill Martin wrote an article (that was published in PS, back in the blach and white days) in which he recounted modifying an old prone rifle by thinning the barrel, in the middle, to the point where a give amount of weight at the muzzle deflected the barrel twice as much as before it was modified. After the barrel modification, he had attached a couple of shaft collars to the muzzle (They did not extend past the muzzle.). After some experimenting with the weight configuration, he was able to make standard and high velocity .22 ammo print to the same elevation at 50 yards. At the time, I thought that this was interesting, likening it to the self regulation at long ranges that has been attributed to the flexibility of the old SMLE rifles. However it wasn't until much later that I put two and two together and saw the application to barrel contour selection for use of tuners in CF aplications.
Another more recent anecdote comes from the experience of a shooter that did well, a while back, at a group match in (I think.) Las Vegas. Brynn Boras (sp?) won with a Beggs tuner, and when questioned about his experience with it said that while it worked on his LV barrel, that it did not on his stiffer HV contour. Of course he might have tried using three, or even four discs to remedy that situation.
Good luck with your project. Let us know of your results. As always, I will be interested, and hope to learn something new.
I know this comes out of left field - but I'm willing to bet some large-dollar research into these sorts of things will happen in the near future. The ISSF is changing the rules for Olympic rifle shooting to outlaw "vibration reduction systems". Notwithstanding the fact that the rules have yet to be finalized and no formal definition for "vibration reduction system" has been proffered, the speculation is that barrel tuners are targeted. No tuners means people are going to start playing with barrel contours and deep counterbores to accomplish the same goals. And the people who will do these experiments will be folks with unlimited funds and motivation - like the Chinese national team.
It's just too bad that if they or anyone else usefully breaks new ground, the research will be kept top-secret and everybody else will be reduced to microscopically analyzing photos of their equipment taken at matches.
Or the scuttlebutt could all be wrong and it may turn out that all they're trying to do is outlaw gyroscopic stabilizers, something that could be accomplished using military air-to-air missile guidance technology (that's mostly where you'd have to go to find gyros small and fast enough) for the bargain price of maybe USD$50K per rifle. There are teams out there that wouldn't blink an eye at that sort of expense. We won't know for sure until the rules are finalized. :-)
You know, and I've not really mentioned this before -- the modeling that Varmint Al does cannot be the whole story. Many of us -- Boyd & I included -- can load ammunition with an extreme spread less than 10 fps. Now I can guarantee you that when this is done, we will just as often as not find loads that "shoot better." What I can't say for sure, because I didn't collect data, is that these "better" loads with a higher velocity spread, were better because of less vertical dispersion. But I'd bet on it.
The rimfire guys have a different problem. Factory ammo only, and the velocity spread can be rather horrendous. Compensation for that has to come from the barrel. I'm sorry the Olympics dropped 300 meter CF & now only has RF (and I believe air rifle?).
For us CF shooters, it is a different story. Of course, we've our own restrictive rules, dating from the 1960s. As Jerry Hensler pointed out in another thread, benchrest has become much more about competition than experimentation. In the long run, we'll pay dearly for that...
Don't be so pessimistic. They'll always be the Jerry Hensler and Gene Beggs type individuals. It's part of human nature. One of the better sides. It's interesting that they're both from Texas. Must be the water!
Originally Posted by Charles E
That's 'cause a Texan is doing the picking. You forgot TJ Jackson, Jerry Stiller, and a bunch more.
Originally Posted by abintx
...And those other great Texans, like Mike Walker, Sam Wilson, Seeley Masker, Ferris Pindell, Lou Palmisano, Geza Nagy, and oh, Lord, I'm leaving about 20-30 people out.
Texas does have a liberal adoption policy, right?
I purposely left out a couple Hall of Fame shooters who are innovative, too (well, you gotta include Ferris Pindell, even if he is in the Hall of Fame.) There are a few who are both competitors and innovators, but fewer than one might think.
It would be nice to have a Hall of Fame for the experimenters, too. Where would we be without them? I know it's not true, exactly, but I see the current mindset as being that if a good idea comes along, the first thing people do is consider a rule change to make it illegal. That's a competitors viewpoint.
To stay just a bit on topic, maybe an article or two on some of the innovators of the past would make a good article for the Magazine?
Last edited by Charles E; 09-21-2012 at 11:15 PM.