Home Forums Hunting & Shooting Custom Rifles & Wildcats A Gunsmith Forum question but...barrel timing/setback question(s)

Example: When a factory barrel is reamed for an AI, say 243AI, and needs to be set back say, .004" (per another thread), that is approximately 24 degrees of barrel rotation at 16 tpi.

If my calculations are correct, if there is factory engraving on the barrel it will be out of place, maybe even under the stock.

How are barrels setback for headspace and the engraving re-aligned?

There are setback to get the engrving in the correct place. Then a finish chambering reamer is run it to reset the head space.

On a 16 TPI thread, like a Remington. I indicate the barrel in the lathe. Move the shoulder that touches the recoil lug forward .063" to allow the barrel to spin on a full turn farther. Then I shorten the barrel tennon the same and deepen the pocket for the bolt nose the same. Then I pick up the old thread and continue it so that it will screw into the action. Finally I ream the chamber for bolt closure on a go gage, but no closure on a no go gage.

If a person wanted to cut a corner a thread relief groove can be cut on the tennon instead of continuing the threads. This leaves you with one less thread holding the barrel on, but in reality it is still plenty strong.

If you're chambering for an AI version you should mention that the 'go' gauge becomes a 'no-go' gauge so you can get a crush fit on new brass.

....and I wouldn't take the full .0625" at once,......just to be safe....these things will sneak up and bite you,...remember Murphy's law,...and whoever Murphy was, he was a machinist.

Very helpful information...once the barrel is screwed on the action, is the barreled action installed in the chuck and the reamer placed in the tailstock or attached to the carriage?

That depends on who you ask. I usually set it up in the chuck with a spider on the back side and reamer in the tailstock. Lots of different ways to "skin the cat".

I just toss the original barrel, buy a properly Ackley chambered Pac-Nor for the Remington 700 with the Rem Nut, or a prefit Brux, Shilen or Pac-Nor barrel for the Savage action and assemble them myself. Not even worth my time and effort to screw around with a rechamber of a OEM barrel, especially the hammer forged stuff today.

Gotta question even bothering with Ackley Improved cartridges in the first place. Although my latest project rifle in .22-250 A.I. came out exceptional, especially using the Hornady hydraulic case forming die, it's not really something practical or ballistically superior to the standard cartridge(s) available. But it is a hobby for an obsessive tinkerer.

My question didn't apply to a Savage and it did not have to be an improved chamber, it could be a short chambered factory cartridge. I am simply trying to understand the machining process.

Factory barrels sell frequently on the classifieds and I have been curious about the engraving for years.

Using the numbers just like your original post. If the markings pass the show line, then the barrel shoulder has to be moved enough to make a full rev of threads. You understand the tpi to angle relationship, so its just math.

That right there is funny and altogether too true!

As stated it's just math ...1 / threads per inch on tenon = set back in thousandths. That will index the tenon in perzactly one turn.

YOU GOT IT...