I am curious about the process of cutting a chamber, particularly in a new barrel that wasn't previously chambered, but details on a re-chamber are interesting too. It would seem to me, having some experience reaming pre-drilled holes in steel with a straight reamer, that a chambering reamer really has its work cutout! Usually when reaming a hole with a straight reamer, the hole is pre-drilled to just a few thousandths under the reamer size so the reamer removes only a small amount of metal, and the chips are very small and short curls. But starting with a 30 caliber rifled tube and reaming a 300 RUM chamber is definitely a different story. Is the new chamber typically roughed-in with a drill bit or end mill, then cleaned up with the chambering reamer? Does the reamer dig up large chamber-length chips? I imagine a lot of heat is generated during the process. About how long does it take to make a finished chamber (using the 300 RUM example)? Is the chamber completed with the reamer, or must it be polished after reaming?

Appreciate learning from any and all with this experience. Its just for curiosity's sake.

the smiths i use for chambering both use the chambering reamer all the way through.

the thinking behind that was that the pilot at least has a centered guide to follow all the way through the chambering process as opposed to having a pre bored hole which may not be perfectly centered to enter with the pilot reamer.

once you enter a chamber that was started with an end mill or drill, you my start hitting the chamber walls near the shoulder before the pilot can center itself in the bore correctly and that can cause wobble which can break reamers, cut uneven chambers, and possibly scratch the chamber too badly to continue with that barrel.

i am no expert, but this is what i was told by my smith buddies as to their reasoning.

You have a couple ways to attack it, drill then single point it to dead true with the bore, or ream from the start. If you try to drill then ream without single pointing.....you just wasted $350.00

Good stuff this.

Although many a chamber has been cut with a finishing reamer alone, a roughing reamer followed by the finisher is much easier on tooling.

First we dial in at the throat and 2" farther in to get our chamber lined up with the actual path the bullet will be taking.

We drill to bulk out some material and make way for the boring bar.


Then single point to correct the bore so the reamer can follow our newly established centerline.


Our pressure flush coupler


Then we bring in the reamer.

I always chamber my barrel with the finishing reamer and never pre bore. If i was going to use a roughing reamer i wouldn't pre bore any deeper than the finishing reamer pilot would take to reach the bore or rifling and alternate the reamers until the chamber was finished, but this is me and what i personally would do. I do polish after cambering, but very little.

Slow and steady wins the race..... Finish ream the whole way... About a million ways to screw it up. 1 or 3 to do it right..

W

This is the only way to chamber a barrel in my opinion to get it right and get the best accuracy.

Great stuff folks. Thanks, and keep it coming.

Frankly, I'm fascinated with anything related to 'smithing. I do minor stuff on my own rifles, or for a buddy that begs. I have made some stuff on a friend's machines, like scope mounts, escutcheons, and little custom parts. I aspired to be a gunsmith in my youth until I learned how little money many guys make doing it, and that many guys have real jobs with benefits and do 'smithing in the evenings and on weekends. I worked on small arms in the Army, mainly machineguns, but there isn't much call to fix machineguns in civilian life. I went through the small arms repair course at Aberdeen Proving Grounds in 1977. Of course there's a lot more to gunsmithing than replacing worn parts, tightening rivets, and wire lacing bolts on military stuff.

Indicate the barrel in, drill and bore the hole right up the body/shoulder junction leaving .010" stock in the bore. Step ream the chamber if you don't use a pressure flush system. The reamer will follow the bored hole, no need for a pilot bushing.

There are many ways to do it i know, but I only build for myself and my way works for me, so will stick with it.

Yup...

It's the target that counts!

you are right about that

What do the chips look like when cutting with the chamber reamer?

For the lack of a better term, the look like short fine strands of wire. They don't come out looking like a chip you'd see off of a drill.

When nearing the end, do you screw the action on the barrel while chucked in the lathe to check headspace?

Just as a final check. I use a bushing that slips over the barrel tendon and then depth mike from the face of the bushing down to the headspace gage. When I reach a predetermined measurement the chamber is finished. I set the depth of my chambers to where the bolt will close with slight resistance on a "go" gage.

The only issue if it really is an issue is if you use a reamer whether a roughing or finish without pre boring and single pointing the chamber is the reamer will simply follow the bore. With a tight fitted bushing the throat will be well centered in the rifling but may not be very square or perpendicular to the path of the bore. It also may be prone to cutting the chamber oversize as the tip of the reamer follows the curve of the bore it must cut the corner, if you will, and put a taper larger than the reamer in the chamber area. You will see this on your fired brass as a little bulge just above the base. This is how factory chambers are cut and I have seen many that were way out of square. Even out of square if the rest of the rifle, mainly the crown and bedding were in order still shot pretty well. An effective floating reamer holder will help eliminate the oversize chamber at the expense of a little run out. Our method leaves us minimum spec, zero run out and perfectly square to the 2" of bore the bullet will be introduced too. Lots of guys don't go to the trouble of all this and have very competitive rifles. Our reasoning is we will control everything we can to minimum tolerances to get as straight as possible and help eliminate the luck factor. These methods along with our pre fit inspection has cut our "bad barrels" to zero.

We use a depth mic to get us to the last 10 thousandths and then we use a precision reamer stop to allow us to take cuts as small as .0001".

This gives us really precise headspace control. For a target gun we can get a true zero headspace or for a field gun we can set it to .0005" over to a max of .001" based on the customers preference or our recommendation. If you get snug or under the go on a torqued up barrel you may find the full length sizing die may not set the shoulder back enough to allow easy chambering. A little long headspace is easy to compensate for at the loading bench. A little short may require modified dies.

I agree the real thing that counts is the results on target.

We just did a 17 Hornet for a guy on a Ruger that shot in the 2�s on the test fire with factory ammo using a 12 power scope. I wish we would have put a 20 power on that one to see what it really could do.

Very fine chip and most follow the reamer out , but i cut very slow 50 thousands at a time and then clean reamer . I use Mineral Spirits, I have two jars one marked dirty and the other clean, then i blow the reamer dry with compressed air, blow out the chamber and then dip the complete reamer in cutting oil and repeat until i get close or almost to head-space and then cut 5 thousands or less and measure after every cut until the bolt will just barley close on the go gauge with slight pressure. The secret to cutting a chamber is to not get in a hurry no matter what method you use. You can take metal off but you sure can't put it back.
Screwing the action on with the head space gauge is how i check after measuring with the depth mic and this is when I'm just a couple of thousands off from head space.
Measurements are fine but nothing like cutting to fit.
Here is the target results from the 222 i just built for myself using the method i use for cambering. Three shot groups 100 yards. Leupold 14 power scope. I'm not a Real Gunsmith who barrel for a living just a amuture who now build his own rifles and learned how from reading books and listening to real smiths on how it is done.

The absolute last thing you want to do is pull it from the lathe. Most of the work is getting it dialed.

you have that right. When i remove from the chuck , everything is done except barrel polishing cutting to length and crowning

If you have the proper tooling and measuring tools, you do not need to screw the receiver on to check headspace. You ever tried screwing on an action that is glued into the stock to check headspace when the barrel is in the headstock?

no i haven't. I have had a couple that were glued in but they were barrel before the glue in

What pumps are you guys using for High pressure flush systems?