Home Forums Hunting & Shooting Gunsmithing Indexing a Fluted Barrel

I'm having a brain fart, or at least over thinking this.

What's the best way to index a fluted barrel on a Rem 700 action? Turn the tenon, recoil lug shoulder and thread, then creep up on the proper alignment by turning off a few threads and the shoulder?

I've got as fluted barrel that has a blem on one flute. I want to make certain that the blem is faced down (6 o'clock) and yet have the remaining flutes indexed/timed properly.

Face off the shoulder to clock the flutes to how you want them indexed (stop short to allow for torquing the barrel up tight). Set the tendon length and depth of the counterbore after indexing the barrel, ream chamber to correct headspace.

At worst clocking would take off one thread.

fit the tenon first to the action (with the tenon length left long), face the tenon shoulder until the barrel indexes properly, THEN face the tenon to the proper length, and finish chamber.

How much longer do you cut the tenon, if its 16 tpi one rotation is .0625.... Would you go at least one full rotation longer just to be safe and have enough in case you need to turn 3/4 of a rotation.

Another question do you index the bore to 12 O'clock first? Then cut tenon long, thread, then try to index bore to the closest flute that lines up with the muzzle end on the high side or 12 O'clock position.

Seems like you can only index one or the other not both. Or am I over thinking it too much?

Why cut the tenon long first? If you are real lucky, the barrel will index the way you want it, and you're off to finish the rest. In the world of the rest of us, you will have to start cutting the shoulder to get it to index, which you will then have to shorten the tenon, and finish. It makes things a lot easier if the action face has been trued, and the recoil lug surface ground. There will be take-up when tightening, so don't fit it dead nuts in the lathe.

It's easy. It's even easier to screw it up.

First, use a narrow permanent marker and with a scale, extend the flute onto the cylinder for visual reference. Time that mark to one of the jaws on your chuck. Pay attention and do your best to accurately index the position. Note the number of flutes on your barrel. (6,7,8, etc)

Next, thread your tennon as you would. Leave the breech face features alone for the moment.

Now screw your action onto the barrel, get it tight enough by hand so that you can gauge where you'll end up once torqued to final value. Next, back off the receiver until it clocks with the indexing jaw on your chuck. If you are using a chuck that has a number of jaws divisible by the number of flutes (evenly) then back the receiver off to next closest jaw. Measure the gap between the lug and the shoulder.

A little math:

Lets say you have six flutes. On a 16 pitch thread that pencils out to .0104" of linear (z axis) travel between flutes as you "climb" the threads. (1 / 16 ='s .0625. .0625 / 6 ='s .0104")

So, you back it off till it times and find that your gap is .006". .006" subtracted from .0104" is .0044".

.0044" is how much you want to peel from the shoulder to get the flute timed.

NOW understand if you do this, you will screw it up everytime. Threads crush. Parts compress under high load more than they do when your hand tightening. There is a fudge factor here. It varies from receiver to receiver and barrel to barrel.

I generally leave a few .001's as a safety margin. It is far easier to solve an underclocked flute than it is one that's gone past. Sanding a .001" off a recoil lug is pretty easy with a good piece of emery paper and a flat surface. (surface plate being the optimum tool, but a slab of granite tile will work too)

Headspace concerns. Again, easier to squeak a thou' or two afterwards than to pull it past and have to take ten or more to get everything back in sinc'.

The best answer:

Stop ordering fluted barrels. Buy them as a regular blank, fit and chamber, index the 12 o' clock position, then send them out for fluting. (what we do is use a small spring loaded center punch through the front base hole. It puts a tiny nick in the thread crest that we can use to index in the rotary axis on the cnc later)

This is how we do it here at LRI. We never buy fluted barrels for customers. The fluting operation is one of the last things we do (in house) after all the other work is completed. It solves the entire problem.

Good luck and hoped this helped. This is the exact process I came up with prior to deciding to bring all the fluting services in house. The biggest voodoo is sorting out the crush your going to have. There's no real magic formula for it. least not that I've found.

Fun!

C.

Chad thanks for that info that is a great tip!

I do have another question though I will be setting my barrel up through the head stock with an outboard spider and 4 bolt spider fixture on the front.

I will dial my barrel in with a range rod as best i can with the .0001 indicator.

NOW what if i have runout on the out board side of the barrel lets say as much as .030" on the muzzle end.

Usually you want to clock the barrel to the 12Oclock position to have your bore point up.

How do you index both the bore and the flutes as to line up the bore pointing up and the flutes strait up and down?

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.

To index a barrel no matter whether fluted or not, you take one inch (1.000") and divide by the pitch (TPI) of the thread. The answer is the distance from the crest (or root) of one thread to the next. This is how much material you need to remove from the breech of the barrel (and shoulder) to set the barrel back one turn. Divide this by the number of flutes and you get the amount of material to index from one flute to the next. So you see it is easy to calculate moving from one flute (or flat if working with an octagon barrel). I usually allow .001-.002" for crush fit when the barrel is snugged up, it is easy to remove that little bit rather than having to go to the next flute/flat or have to go all the way around another turn. Partial turns from flute to flute can be interpolated (guestimated) once you gain a little experience with the process.