Gunsmithing Lets talk Barrel timing...curve of bore @ 12oclock

[USW.260]

So, to the powers that be, wroscoe, C.Dixon, Mark Gordon. Whats your tricks of the trade for this. When you cut the length/depth of Barrel Tenon how short of exact deminsion do you make it to time it out... Say for a Surgeon 591 @ .954". And how does this effect chambering. And how do you find the "high" spot?

 

[wnroscoe]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

To be honest, I've done it both ways and spoken to several builders about the same. I haven’t seen a difference in accuracy. The general consensus was this, use good barrels and good machining practices and all else will follow.

Usually, with the Bartleins and Kriegers I use, TIRO at the muzzle is less than .010" 99% of the time. Once dialed in and the machine is running you can hardly see the muzzle moving.

Here's something else, when I install a new blank in the lathe I dial the OD in first just to get close. When I change over and indicate the bore in, most of the time it's already within .005" or less TIRO. Had a Bartlein bore the other day run .002" TIRO off the OD.

Bottom line, use high end, good barrels.

 

[eddief]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

It's no different than timing a brake. If you are going to time a barrel it's best to do it before you chamber.

Find your high point at the muzzle end with your indicator and mark it. Screw on your action and note where the "mark" is, in relation to the action. Lets say the high mark is at 9 o'clock on the action.

If the threads are 16 tpi. take 1/16=.0625".... now we know .0625" taken off the shoulder will rotate the barrel 1 full revoloution.

We need roughly a quarter of a turn to get our mark where we want it. Take .0625"/4 = .015625"....so .015" off the shoulder will be roughly a quarter of a turn. Don't forget about crush when it will be tightened. Keep your cut a little short to compensate for it. This is something you'll have to get a feel for, so just go easy the first time and you'll be fine.

You can divide your full revolution into whatever is easiest for you. I usually divide into 1/4 or 1/8 to get me where I want to be depending on where the initial mark is, in relation to the action.

With all this being said, I only index barrels that look like they need it. Pretty easy to tell by eye after the bore is indicated in.

I don't believe indexing or lack of will affect the accuracy one bit as far as the barrel goes. Maybe in an extreme case it may cause the rifle to torque in a certain direction, but it's just a guess.

It can give you a little extra MOA and help from eating up windage in your scope for your initial zero.

 

[LRI]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

Mine is prolly the most scientific. NASA called and offered me a job when they learned of it.

It involves a lathe and a sharpie marker. Just grab onto the cylinder of the barrel in the chuck and spin it up to say 200 rpm.

Now grab your marker and remove the cap. Start moving the felt tip towards the muzzle. When it makes contact its going to put a mark at the largest swept arc the "krooked" barrel is creating.

Split that mark in half and you have your "high" point. Time that to 12 o clock and blaze away.

No fancy tooling required.

My purposes for doing this isn't accuracy related so much as it is getting a long range gun to hold a windage zero as you stretch your legs. Seems to work, but I personally have never tested it. More of a feel good monkey see/do kind of thing.

FWIW I never worked on the shuttle program.

C.

 

[USW.260]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

Very nice! Thank you Guys!

 

[HuskerP7M8]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

Chad’s method of finding the bore curve is essentially the same as the one Dr. Geoffrey Kolbe of Border Barrels has explained to me for an easy method of making a determination.

It’s also possible to use inserts with a very small iris placed in both ends of the blank and observe the concentric rings of light to see the bend and mark it. This is probably the most popular method used by some production barrel manufacturers. The barrel is then placed in a “Mariner’s Wheel” and straightened. A few smiths I work with use this method but I know of only one who has attempted to straighten a crooked bore….with mixed results.

I and a few others prefer to “live fire” in rigid (no recoil) fixtures and rail-guns to detect and measure bore curve. There are even some who shoot while the barreled action is in the lathe but only with rimfires.

I use a rail-gun with barreled actions or differentially threaded bushings with conventionally stocked rifles for my indexing tests.

Landy

 

[LRI]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

Landy,

Yer a sick one mister!

BTW: Your stock is at Terry's being finished up. Were rockin it together soon as it gets back.

Later buddy,

C.

 

[JJones75]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">FWIW I never worked on the shuttle program.

C. </div></div>

Having worked for the Shuttle program and currently with the Orion i can verify that everything ive seen you do for guns is light years ahead of what the space program requires.
im amazed we dont have shit falling to earth daily

 

[mdesign]

Re: Lets talk Barrel timing...curve of bore @ 12oclock

Very nice "test" station you got there Landy.