This is my opinion so get your salt shaker.
First, [bleep] can the range rod. It's a waste of time and a false sense of security.
Here's why: If you are going to put a pin in a hole, there must be a clearance built into that interface. If we look at a gauge pin set (common in any well equipped machine shop) we quickly learn that the pins come in two forms. A "+" and a "-". What this means is a .500" gauge pin is actually ground to a dimension of .4998" They are 2 10ths undersize. The opposite is true for a "+" set.
How this applies to this exercise. If your using a range rod with a .236" bore for a 6mm and the bore actually measures .236" the only way that pin is going to fit is if you get a hammer and drive it in, or you freeze the pin and warm the barrel. The trick now becomes getting it out of the hole.
Now move onto straightness. Unless these pins are properly stress relieved they are going to warp over time. Rolling them over a surface plate with a light shined along the tangent contact point will illustrate this. A healthy human eye has a resolution of about .002" If you see daylight, there's an issue.
Hardness. These pins are typically very, very hard. They have to be for them to stay within tolerance and to avoid wear over time. Rule #1 with any barrel is be very, very careful when inserting a cleaning rod, etc. What happens on the off chance that you catch an edge and put an inclusion in the bore due to the rod? -You start over with a new barrel. That sucks.
Last, cylindricity. Grinding that pin perfectly round and free of any taper isn't exactly easy. Inspecting this requires some rather sophisticated equipment. Chucking it up in a Grizzly lathe with a dial indicator isn't how you do it.
In truth, these are all more than likely very, very small discrepancies. Where it becomes a concern is when they all stack up against you. It's been proven time and time again that range rods do not repeat.
So, now what? We simplify. Get yourself a high resolution test indicator. I like the Brown and Sharp with a .00005" resolution. That is an incredibly small value. I don't for a second actually believe that it will measure to that value. I don't care as all I'm looking for is movement detection. That is all we care about. Next, purchase a long stylus for the indicator.
Chuck your barrel up as you would and dial up into the bore in the vicinity of where the bullet will hit the lands. It just has to be close. Now adjust until the indicator is "riding the land" and the needle is returning to the same position each time. Some barrels make this impossible as there will be a land that's a smidge taller than the rest. It's ok. They still shoot great. (seriously, don't let it kick your behind)
Now, the opposite end with the spider. Snug everything up to where they make contact. Don't concern yourself with dialing it in, it's not important. Just snug the screws up and let the muzzle end flop around as it will.
The logic behind here is that the barrel doesn't magically take this set once you pull it out of the machine. It's going to go right back to wherever it wants.
The argument will be made that were not actually dialing to make the bore parallel. Your right, in truth, were not. Neither are you with your "witching rod". What you are doing however is exponentially complicating your setup and luring yourself into a false sense of security.
Given a choice between stuffing a hardened pin in a brand new $360 barrel and using a polished carbide tipped stylus, I'll take the stylus. This is as much a risk management strategy as it is an accuracy observation. I know with confidence the bore is running common to the spindle with an indicator. I can't guarantee that with a rod.
Your setup time will reduce, you'll be more productive, and that translates into more cash in your wallet. After doing it all sorts of ways for literally thousands of barrels over a 15 year period, I've settled on this as its simple, fast, and presents ZERO compromise when we start putting rounds on paper.
Regarding the clocking debate. It's been shown to me to be internet hype. I've yet to have a client bark at me because he's mysteriously having to dial "X" number of minutes/mils as he goes further away from where he's standing. Once the bullet leaves the muzzle, the barrel has zero to do with how the bullet travels towards the target. If you zero at a 100 and your barrel is say .05" from theoretical center, does the group magically wander the further you go out because of this?
No, it doesn't. There are other forces at play.
1. Magnus effect
2. Coriolis effect
3. Spin drift
4. Wind
The only one here I really give any real credibility to is wind. The other three do happen, but at the typical distances were talking the values are so small that it's little more than interesting conversation over beers after a match/hunt.
In all my years of doing this, I've yet to drop a point due to the coriolis effect. The wind however makes it a habit of eating my _ss.
Hope this helps.
C.
Last edited by C_Dixon; 08/13/15.
