Gunsmithing Reamer size vs Chamber size

[mdesign]

So if I use a reamer with a .316 neck how close to .316 will the neck of the actual chamber be?

Seems it out to be very close if the machining is done correctly but I wondered if any have ever measured to see how close it is.

 

[Revenge Seeker]

Re: Reamer size vs Chamber size

It depends on your method of lubrication, tool runout, tool wear, alignment, material(hardness AND consistency)... etc...

But if i had to venture a guess, i'd say somewhere within .0005 reasonably under ideal conditions. but with "perfect" conditions... Id say within .00005,

 

[257speed]

Re: Reamer size vs Chamber size

If the barrel is setup properly ie. dialed in precisely, then the neck could only be .316. Where you run into a problem is if the smith does something wrong and the reamer does not cut straight. That is when you would get a sloppy chamber. Just remember, the reamer can only cut the size it is, if all is done right.

 

[wnroscoe]

Re: Reamer size vs Chamber size

Depends on the initial set up and how the barrel was indicated in. If chambered between centers or in the headstock/chuck, 3 jaw or four jaw. Outboard spider or not, live pioleted reamer or solid pilot, reamers held in a floating reamer holder / pusher or Jacobs chuck.

Bushings have .0002" clearance between them and the bore. They also have approx .0002" clearance between them and the reamer.

Reamers tend to follow the hole so it's hard to say but I'd say in a perfect set up a reamer that has a .315" neck will produce a chamber that has a .315" neck. Hold the reamer wrong, chamber in a suspect manner or chamber a barrel that was set up incorrectly, who knows..........the sky's the limit.

When chambering a barrel the reamer must track straight with no wobble. When you’re about 75%+ finished, the reamer will be snug in the chamber when removing to clean chips off and re-lubricate. When chambering is complete if the reamer is loose in the chamber, felt movement, the chamber is oversized from throat to web.

I won’t even mention bad or worn bearings in the headstock, misaligned bed ways or tailstock........we'll save that for another day.

 

[Victor N TN]

Re: Reamer size vs Chamber size

I can only echo what's been said above. If it has an even number of flutes you can measure the flutes for the real OD of the reamer. If it is in fact .316", that's the smallest it can be if everything else in the setup is correct.

If you want to double check everything set up a piece of scrap and do a partial on it then cast the neck area and check that.

 

[DAVETOOLEY]

Re: Reamer size vs Chamber size

As everyone has stated a proper setup is critical when chambering but you're assuming the reamer measures exactly what you ordered. In many cases they aren't. +-.0005" is not uncommon. Not very many smiths have flute mic's or an optical comparator in the shop to check behind the reamer manufacturer. Also you can't just chamber a short barrel stub and measure the neck area. Because the reamer is not fully supported when it starts cutting, the neck area tends to be slightly larger at the start of a chamber than when the final pass is made and the reamer is supported it's full length. Also on a reamer with an even number of flutes the flutes are not 180 degrees apart, they are staggered a few degrees to prevent chatter so measuring across the flutes while it will get you close it won't give you a 100% accurate reading.