Headspacing Pre- Cut Long Chambers

This treatise will cover headspacing a rimless cartridge chamber reamed longer than the 0.030 inches required for normal chambering of a "Go" headspace gauge or new cartridge case. Here the barrel shoulder must be moved forward to achieve proper headspace. This is essentially opposite of working with a short chamber where a reamer is used in attaining proper headspace leaving the shoulder unaltered.

Normally, a pre-threaded, longchambered barrel will be approximately 0.015 to 0.030 inches over length for the "Go" headspace gauge, so we must accurately pre-determine the actual amount of barrel shoulder to be removed.

Here I used shims placed between the bolt face and the headspace gauge to test for bolt closure with the receiver screwed From left, unfired .22-250 case, .22-250 "Go" headspace gauge, Remington Model 700 bolt, recoil lug and several of the shims used between the bolt face and headspace gauge as a means of determining the amount of shoulder metal to be removed. Alive tailstock center is used in addition to the steady rest to assure perfect center. onto the barrel.

The ejector and cocking mechanism should be removed for this phase of the work. To begin, I cut several shims of varying thickness to fit inside the bolt face and place the needed number of shims on the bolt face, held in place with grease. Two shims at 0.010" and the remaining at 0.002" is ideal. I then remove shims until the bolt closes with some feel and carefully record the thickness of the shims. Then the barrel is set in a lathe with chamber end centered in the steady rest.

At this stage, I place a well-sharp-

ened lathe bit in the crossfeed in preparation for cutting the barrel shoulder and bring the lathe carriage stop, set at zero, against the carriage. The first lathe cut at the barrel shoulder is just a shaving of metal with the carriage stop at zero. Then, remove a few thousandths of shoulder metal and check to see how many pre-measured shims can be removed for final bolt closure. Getting down to the last couple shims, it’s very close to arriving at desired headspace.

The final lathe cut is made with the last shim removed, which is controlled by carefully advancing the carriage-stop the thickness of the last shim removed. This should result in a light feel of the Go gauge as the bolt is closed on the torqueddown barrel. Remember, the total thickness of the stacked shims is the exact amount needed to move the lathe carriage stop, allowing the tool bit to reduce barrel shoulder metal.

It is necessary to actually screw the receiver hand-tight onto the barrel to try things as this gets close because there is no second chance if too much shoulder metal is removed. If you do, a chambering reamer would be required to successfully complete the job. Maximum headspace is normally considered about 0.003 to 0.004 inches over a minimum Go gauge, but I’ve never gone this far.

Regardless of the type of cartridge being chambered, 22-250 Remington chamber, as described in the text, show the result of correct headspace as determined with a properly used Go gauge. Note the precise flush fit of the fired primer with the plane of the case head. This is the result of correct use of a headspace gauge regardless of the methods used in headspacing.

Cartridge headspace, correctly defined, still means the space between the case head and bolt face of a fully chambered cartridge. rimmed, rimless or belted, headspace is the allowed space from the base of the cartridge to the closed bolt face. This term is sometimes confused by talking about shoulders and datum lines and case head belts, which do have control over headspace, however, the final measurement is bolt face to case head.

So remember in working with an over-length chamber, we are reducing the space between the bolt face and the headspace gauge as the shoulder metal is removed and not increasing such space as advancing a reamer into a chamber would

At this stage the amount of carriage travel is predetermined to arrive at the proper amount to reduce shoulder depth. 22-250 Remington long chamber using the "Go" gauge to proper specifications. The gauge is seen beside the fired cartridge case. be. The end result is the same: Proper headspace. Conclusions Given a choice, I would much prefer working with a short chamber in arriving at correct cartridge headspace. It’s faster and there is less likelihood for mistakes.

However, following proper procedure will produce a precision result ei- Complete your American Gunsmith collection. Or read up on a special subject! A limited number of the following