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"Chisel" case extraction is a hopeless matter.

"Chisel" Case Extraction Is A Hopeless Matter

A city gun shop quoted a fair enough price to a customer for removing a ruptured cartridge case from an old Mauser 7mm that had been converted to a .308 Winchester -- by shortening a 1903 Springfield .30 caliber barrel, threading and chambering.

Apparently the customer had failed to realize the extent of the damage he (or someone) had inflicted on the chamber walls by either digging, pounding or prying.

He wanted a second opinion so he brought it to our shop. We attributed the case separation to a combination of excessive headspace, plus the likely possibility that a handloader had excessively full-length sized the cartridge cases.

Initially, I presumed the barrel shank was properly measured and threaded, and that there was room for facing off the rear of the barrel, setting the shank shoulder forward -- and at least partially cleaning up the gouged chamber with a finishing reamer. However, upon discovering that the thread shank was a full .005" under diameter -- and that the previous barrel workman had left a 1/4" of barrel unthreaded between his threads and the barrel shank shoulder -- I contacted the customer and gave him a "visual" explanation.

Fortunately our shop still had a few 1903 surplus military barrels around. This allowed for a moderately-priced new barrel installation for an old knock-about rifle. The customer was assured of correct headspace, and a correctly-fitted barrel shank.

Installing A New Springfield Barrel

This chore is an "oldie" for most gunsmiths of my vintage. Younger graduating school gunsmiths might have difficulty, however, finding surplus 4-groove Springfield barrels. (2-groove barrels in both Springfield and Enfield will likewise do nicely, as well as 5-groove surplus Enfield barrels.)

The call for this type of conversion is no longer out front, only occasionally. If this situation does present itself, removing the original Springfield 1-10 square tread barrel shank is easily done with a sharp hacksaw. This will avoid the jerky cutting of a lathe bit jumping the extractor slot. It also takes less time than making a separate lathe set-up.

One thing to remember: The barrel shank diameter of M-93 and other Mausers can differ. We've found it to our advantage to cut barrel shanks a few thousandths of an inch oversize, if the foregoing barrel is loosely fitted.

Criticism Justified

Too often members of a profession band together in a protective net, refraining from participating in any critical comments about each other (even to the slightest mention of poor work, judgement or error). This might be a guild insurance tactic, but if it causes additional customer expenses and misery, then it is wrong.

Criticism can and should be directed in a constructive manner, offering kindly help via corrective information, from which we can all benefit. The original aforementioned conversion of the 7mm Mauser to .308 Winchester was probably done years ago, when many gunsmiths were learning and experimenting with WWII weaponry conversions. So this fellow ended up with a slightly loose shank diameter, slightly too short, with yet a short thread on the shank. It would still have been acceptable, provided he had chambered it to the correct headspace. Careful measuring and thinking can avoid such mistakes.

I want to re-emphasize the importance of correct headspace when doing chambering. As all qualified gunsmiths know, this is the measurement from the bolt face front to the shoulder of the cartridge chamber in semi-rimmed cartridges; and in rimmed cartridges is the distance from the bolt face to the front of that rim, to assure a safe lockup.

For those bully belted magnum cartridges it amounts to the distance between that bolt face and the front of the cartridge belt as it faces into the belt cut in the chamber.

These are all critical dimensions. All novices should be extremely careful in acquainting themselves with all the details. Any extra space allows cartridge cases to expand and possibly separate (especially after a few reloadings). Dangerous gases and particles can escape, causing injuries, and hopeless conditions in the field, where no tools are usually available.

Factory Headspace Usually Correct

During my approximately 40 years of gunsmithing, I've never found a factory built rifle with a loose headspace. (This is not to say it can't happen to some degree, but it has never happened to me.) On the other hand, I recall a new 7mm magnum bolt-action rifle that was brought into my shop. It required a heavy pressure on the bolt to close it on any new factory ammunition. Although this was a miserable situation for the owner, it was certainly safe. The problem was solved by removing the barrel and carefully extending the chamber to close on the GO gauge and ammunition (about .003").

Taking out a barrel for such a slight cut sounds needless when it can also be done by using reamer extension handles by hand. However, a more uniform, and thorough clean-up cut can be done in the lathe, plus polishing the chamber after the reaming. The quality of a truly finished chamber is well worth the extra time.

Sometimes cartridge case variations can confuse young gunsmiths. Don't worry. Often it also bugs a lot of older `smiths. Those belted cartridges seem to have the greatest variations. We've become accustomed to this. The larger, longer cases can take more expansion, thus some variation is not usually quite as critical. Often we've chambered to one make of cartridge cases (along with headspace gauge checking), and found that reloading from there is easier and more accurate.

Better Tight Than Too Loose

If headspace is a little tight, causing a "pinchy" bolt closing on some cartridges, it is far better than that fall-in sloppy feeling. In military chambers machining for easy chambering is purposely done to allow positive functioning under heavy heat, stress, and lack of cleaning.

During WWII we experienced functioning difficulties when over-ambitious armorers failed to back off the barrels two or three clicks from the gauge setting. In some instances this was catastrophic. There is no time for gunsmithing during combat (especially for the fellows who are tucked into those bomber belly turrets).

Of course, this doesn't pertain to our civilian firearms in severity, but it is still relative. It is well for both gun owners and gunsmiths to understand this. A slightly tight bolt closure on a bolt-action sporting rifle, doesn't stop you, but it can and will stop many semi-autoloaders.

There was a time when it was suicidal agony and death of everyone on some WWII bombers. Under certain conditions there was such a thing as adhering to the book too closely. Once the ordinance experts learned from experience, they never forgot!

PHOTO : A hacksaw can quickly remove a Springfield barrel shank.
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Article Details
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Author:Schumaker, William
Publication:Shooting Industry
Article Type:column
Date:Mar 1, 1989
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