While barrel stiffness is a factor in node width and tunability, it's remarkable how predictable it is with my tuner. So much so, that I look for and expect there to be four marks between completely in tune to completely out of tune...on a typical short range rifle and barrel. I can even predict group size and shape at each mark within that range. I say that because there are several lengths and contours that fit with and are commonly used in short range...Like 19-1/2"23" LV barrels to 22-26" hv contours. Between those contours, I expect to see basically the same tuner mark values. When we step up to more popular long range lengths and contours, such as 28-30" HV and 1.250 straights, tuner value changes, but just a little bit., to typically five marks from in tune to completely out of tune. So, while stiffness does matter enough to quantify in this regard and on target, it's still a relatively small amount. But if you run the numbers through the stiffness calculator, it makes sense that there really isn't a huge difference there either. Keep in mind that with my current tuner, one mark is equal to .001" of tuner travel.
Now, lets say we start with a load that is giving us 3,000fps at 50° and as temp rises to say, 75°, it now gives us 3,020fps. Reasonable numbers IME, but I use them just as much for easy math...
So, that 20fps increase is equal to .6% velocity increase.
Lets also say that the bullet is in the barrel for nominally 1.5 milliseconds at 3000fps. That's a pretty tiny amount of time, I think we will agree. But, at 3,020fps, it's in the borefor less time...for .6% of 1.5 milliseconds less time! Now were talking REALLY tiny! So the bullet is reaching the muzzle sooner in time, right? How do we bring it back to perfect tune? We speed the vibrational frequency up by, guess what... .6%!! So it's calculable and tuners aren't voodoo, afterall!
That's relevant because a stiffer barrel vibrates at a higher freqency...or faster, with less space and time between nodes. A less stiff barrel, slower, with wider nodes that are spaces further apart. This makes staying in tune easier and less dramatic, to a degree. I mean, the less stiff barrel deflects more...or has more INITIAL amplitude.
I want to stop and clarify this statement before moving on. Physics teaches us that when we add weight to the muzzle that amplitude is decreased. This is true..OVER TIME! So yes, amplitude does decay faster over a period, netting a reduced amplitude during a wider time frame...But we're dealing with nominally 1.5 milliseconds and the amplitude is increased by barrel droop, even before we pull the trigger! Hopefully, we're together on this, because it can rightfully be a point of contention. Just remember that we are dealing with vibration for a VERY short period of time.
Back to my point about more muzzle deflection being a good thing...Since I can't tune for what I can't see on target, a muzzle that deflects more, make my "out of tune" groups bigger than they would be without a weight at the muzzle. That sounds bad but it's not, because I can't tune for what I can't see on the target, especially in real world match conditions. This is true whether you use a tuner or a barrel that is less stiff..same, same, in most regards, except the tuner is adjustable, at the bench.
I've been wanting to talk about this and want to while it's fresh on my mind and I'll stop for now....and I don't mean to make this thread all about tuners. It's just that barrel stiffness is a key in how they do what they do.
Anyway...There are two camps about how to tune when planning to use a tuner. One says to tune the load to the rifle before putting the tuner on. The other is to do load work up as normal, with the tuner on but don't touch it...forget it's there.
BOTH WAYS WORK!
Oh but how? Easy..The best way to look at things is, as the barrel moving in a simple, one dimensional sine wave pattern, where the nodes just appear the same...over and over again, repeating. Yes, there's more going on but the tuner being at the end of the barrel is adjusting the average of everything happening behind it.
Now, REPEATING is the key word because that's what takes place and it's how doing load work up works either way..on or off. Because the barrel crosses a sweet spot over and over again. Again, only .004-.005" tuner travel from dotting up to worse than you ever thought it could shoot....then it starts over, and over, and over..fore all intents and purposes her, forever.
It crosses these sweet spots that we call nodes with a tuner or without. My tuner lowers the frequency by nominally 30% over no tuner, yet it works both ways? Yes! The barrel crosses these sweet spots without any weight, or even a net loss of weight...as it does with the tuner but the nodes are about 30% further apart due to the lower frequency created by simply having a weight at the end of the barrel. Long story short, if you do load work up without the tuner on, you're loading to a node that shoots but is about 30% from the one where it will shoot the same way within about four marks at most, with the tuner. Is that clear? The sine wave example is the way to think about it...Bullet exit happens, ideally, just prior to the vertical apex of the barrel swing...with the tuner or without it. The fact that it works both ways just proves that tune repeats over and over, forever...from a net loss of weight at the muzzle(threaded for a tuner) to a net gain of several(many) ounces, with one. Bottom line here is two things...First, you can do it either way with equal results IME. Second is that it just repeats, over and over. That's important to remember. Other than positive compensation, there is no reason why one vibrational node would be better than the next...from the standpoint of which will shoot smallest...No difference. I've shot some tiny groups at the bottom of the barrel swing.
More later...
