Chamber Reamers

Chamber Reamers

Let’s take a look at chamber reamers for metallic cartridges.  If you are new to gunsmithing, or a serious firearms enthusiast, this post will help enhance your understanding of these important tools.

What are chamber reamers?

Reamers are a metal working tools used to create precisely sized holes with smooth sides in metal.  Chamber reamers are a special type of reamer used by gunsmiths to cut chambers in rifle, pistol and shotgun barrels.  Chamber reamers are cartridge specific and typically constructed of high-speed steel, but are also available in carbide for production applications.

Chamber reamers are precision tools built to tight tolerances.  For most cartridges, prices typically range from $100-200 (2015) depending on the brand and features of the reamer.  Care must be taken when handling and using reamers to avoid damage; bumping reamers into one and other, or running one in reverse will often chip, dull or break them.

What is the difference between a finisher and rougher?

Finish reamers, or finishers, are sized to cut a chamber to the appropriate final dimensions.  These are the correct size to meet specifications for the cartridge.  Sometimes, roughing reamers, or roughers, are used.  A roughing reamer is undersized and used to make initial cuts in a chamber before use of the finishing reamer.  Roughing reamers are most often used in production environments when a large number of chambers will need to be cut in an effort to avoid wear on the finisher.  For the majority of hobby and light duty applications, only the finisher is needed.

Frank Green, from Bartlein Barrels, reported being able to cut 40-50 chambers with a reamer.  Once a reamer dulls, Bartlein will send it back to be resharpened.  After it dulls a second time, there normally isn’t enough material to sharpen it into a finisher, however, it can be ground into a rougher.

What is a solid pilot?  Live pilot?

The front part of the reamer that allows the tool to follow the bore of a barrel is known as the pilot.  Pilots can either be solid or live (interchangeable).  A solid pilot is ground to a specific size and does not rotate.  Live pilots rotate and are interchangeable.  Interchangeable pilot reamers cost more than solid pilot reamers.

belted rimless and straghtwall chmaber reamers

The photograph above shows three different Manson solid pilot reamers.  The top reamer is for a belted (300 Weatherby) Magnum (note the cutting surfaces towards the rear of the reamer to cut the cartridges belt).  The middle is for a rimless rifle cartridge (221 Fireball).  The bottom is for a straight walled pistol cartridge (.357 magnum).

Manson and PTG bushings

Manson 308 Winchester Match (above left) and PTG 260 Remington (above right) live pilots reamers.  The Manson live pilot is secured to the reamer with an e-clip secured in a slot.  The PTG is secured to the reamer with a small screw.  The Manson system is more secure, however, the PTG system allows faster pilot changes.

7 rem mag barrel for m700 with 250 lug

A 7mm Remington Magnum chamber cut on a Shilen Barrel for a Remington 700 with a .250″ thick recoil lug.  Note the step cut inside to the chamber to support the front edge of the cartridge’s belt.

What are coolant slots?

coolant slots on the PTG journal

Reamers can have coolant slots machined into their journals (spindles) to allow fluids to pass through when used with chamber flush systems on lathes.  A chamber flush system pushes a lubricant, typically cutting oil, through the barrel and into the reamer.  This fluid lubricates the reamer and clears chips from the reamers flutes.  Coolant slots are available as an option on interchangeable pilot reamers.

Do all reamers have straight flutes?

straight versus sprial chamber reamers

No.  Chamber reamers can either have straight flutes (top) or spiral flutes (bottom).  The straight flute reamers are easier to inspect and sharpen.  Spiral flute reamers cost more, however, some feel that they provide a superior surface on the chamber walls.   Having used both, I haven’t noticed a difference in performance.

What specifications are reamers built to?

Unless otherwise specified, if a cartridge has been adopted by the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI), the reamer will be cut to these specifications.  If a cartridge has not been adopted by SAAMI, but adopted by Permanent International Commission for the Proof of Small Arms (CIP), the European regulating body, the reamer will be cut to those specifications.  In addition to standard reamers, manufactures will also offer custom reamers with special throats (such as a 260 Remington) or necks (6mm BR with a turn neck), in addition to wildcat (non standardized) cartridges.  When in doubt about which reamer to use, ask the manufacturer.

What is a headspacing reamer?

Most chamber reamers are held by a shank in the rear.  A special type of reamer, known as a headspacing or pull through reamer (below) turned with with a handle that extends through the barrels muzzle.

headspacing reamerThis headspacing reamer (top left) is threaded to the handle (bottom).  The reamer is placed in the action with a thrust bearing (top right) against the bolt face.  The reamer is slowly turned on a short chambered barrel and when the bolt closes, the rifle is at the correct headspace (note: it is possible to continue cutting once the bolt closes however this would create excessive headspace).  Headspacing reamers are useful for military rifles like the M1A/M14 and M1 Garand as well as pre threaded short chambered barrels.

What do the industry professionals think?  How should my reamer fit the bore?  Should it have a solid or live pilot? was fortunate enough to have the opportunity to ask two experts, Dave Manson from Manson Precision Reamers and Frank Green from Bartlein Barrels their thoughts on pilot fit and type of chamber reamers.  Who better than a reamer and a barrel maker to answer questions about chamber reamers?   This is what they said: What is the recommended clearance between the bore and reamer pilot?

Dave Manson: Desirable clearance between the bore (lands) and the solid pilot of a reamer would range from .0003″/.0006″. Please understand that this is my opinion only, arrived at after a number of years fitting pilots to bores. In my opinion, a properly-fitted solid pilot will do no more damage to a bore then will one of the interchangeable design. That said, careless, or ham-handed mechanics seem to be able to damage anything.

Frank Green: I start with .0004″ under bore size. I check the bushing fit by feel. If it feels to tight drop down another bushing size (they normally come in .0002″ increments).   .0002″ under bore size I feel is to tight.  A good gunsmith will have a set of bushings for each caliber.  I just went thru this with a local guy yesterday. He ordered is 6.5mm (.260 Rem. reamer) with the standard .2560″ bushing size. I showed him three different barrels. One barrel it would barely start. That told me the bore size was right at .2560″ to .2561″. The next barrel the bushing went in smoothly but snug. On the second barrel most likely the bore size is at .2562″. So on this barrel using a .2558″ bushing would probably be just fine.  After you thread the barrel and breech cone it like on a Pre64 model 70 or you do the counterbore on a Rem.700 that’s when I check the bushing fit. Before chambering.  Some good smiths that I’ve talked to in the past have said that up to a .001″ under bore size won’t hurt anything at all. I tend to agree but just for my own comfort I don’t go that far down. Do you prefer solid or live pilot reamers?

Dave Manson:  If I had the barrel in-hand and was grinding a reamer for myself, I’d make a solid pilot with the fit I liked to the specific barrel. On the other hand, if the barrel had been ordered–but not received–I’d grind the reamer to accept removable pilots and choose an appropriate pilot bushing when the barrel arrived. When using removable pilots, I’ll choose a bushing that’s a slight drag-fit in the bore so it will revolve on the reamer, rather than revolving relative to the bore.

Frank Green:  Live reamers all the way. I don’t like the solid piloted reamers. By using a live reamer you can change the bushing so it properly fits the bore of the barrel. I’ve seen to many times with a solid pilot reamer where the pilot portion is basically the same size or just a .001″ under bore size and it scores the tops of the lands. With that part of the reamer going the furthest into the barrel that after the barrel is finish chambered in front of the throat area the lands are all gouged up. Your just asking for trouble.

Since Dave Manson makes some of the best reamers on the market, I also took the time ask him some additional questions: What is the typical clearance between the reamer and the bushing?

Dave Manson:  Depending on tolerance stack-up, there can be as little as .0001″ and as much as .0005″ clearance between the pilot bushing ID and the spindle’s OD in tooling utilizing interchangeable pilots. What spindle speed to you recommend for turning barrels?

Dave Manson: Optimum spindle speed depends on many variables, including reamer and barrel material, reamer profile, set-up rigidity, alignment and method of holding the reamer, as well as the coolant system employed. With less-rigid chambering systems, such as with a steady rest, we recommend keeping spindle speed below 100 rpm in order to reduce any tendency to chatter induced by vibration. Rigidly held barrels (in a 4-jaw chuck or collet, with muzzle-end spider) can be turned up to 350 rpm. Optimum spindle speed often is lower than this, but speeds up to this figure can be used to improve finish/eliminate chatter without damaging the reamer.

How are reamers held on a lathe?

Normally reamers are held in a reamer holder.  Here are a few I use:

13 reaming set up

A floating reamer holder (above) is the most common method for securing a reamer on the lathe.  This one, from Brownells, is made by Manson Precision.


GTR Tooling makes a non-floating reamer holder (above).  While the reamer will still follow the barrels bore, the rear of the reamer doesn’t move as much as the Manson holder.  Greg Tannel, owner of GTR Tooling, recommends this holder for a lathe set up for secondary (plunge cutting) operations.

reamer held with pliers

The most basic method is to hold the reamer with a set of pliers (or a tap handle) and use the tail stock to feed the reamer into the barrel.  Be careful not to hold the pliers with your hand, if the reamer breaks or binds injury can occur. Surprisingly, this method is used by some top rifle builders as well as the USMC Precision Weapons Section.

I’ve used the three methods shown with great success.

What is a chamber flush system?

A chamber flush system forces pressurized cutting fluid into the barrel to remove chips from the reamer.  In most applications, the fluid is pumped into the muzzle and exits the chamber end of the barrel (I know of some production set ups with the coolant flowing through the reamer).  It is captured, filtered (so chips aren’t introduced to the chamber) and recycled into the barrel.

cutting chamber

Chamber flush systems (above) allow for a higher spindle speed, longer tool life and a require less time to cut a chamber.

What is a reamer stop?

The Kiff/Lambert Micro Adjustable Reamer Stop is a micrometer adjustable collar that attaches to the shank of a reamer to control the depth of cut.

A close up view of the reamer stop.  The stop allows depth of cut adjustment in .001" intervals.

In the photo above, note the reamer stop limiting the depth of cut against the end of the barrel.  The stop can be adjusted in .001″ increments to precisely control the depth of cut.

Reamers stops aren’t mandatory, however, they make chambering barrels easier.

What kind of reamers do you use and prefer at

I own a mixture of solid and live pilot reamers from Manson, PTG and Clymer. I’ve had great luck with solid pilot reamers, but have encountered barrels where they won’t fit.  When this occurs, I normally send the reamer to Manson to be ground for an interchangeable pilot (he will work on other manufacturers reamer).

As far as brand, I prefer Manson reamers, however, the PTG and Clymer reamers work fine. I have heard great things about JGS, but don’t own any.

PTG is the largest company and is continually expanding in size.  This has resulted in some growing pains- intermittent customer service, and incorrectly cut and hardened reamers.  I had a 6×47 Lapua reamer that exploded (broke mid flute- I’ll try to find a picture) in a chamber because it wasn’t properly hardened.  PTG replaced it, however, the process was fairly involved and took a few reminders directly to the owner.  The replacement reamer worked well.

If you have any other questions you’d like addressed, please reach out to on the contact page.

A special thank you to Roy Hill from Brownells, Dave Manson from Manson Precision Reamers and  Frank Green from Bartlein Barrels for their assistance in this post.

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