Well … this is interesting. My German k98 barrel, when installed in two different receivers, hand tight, is about 265 degrees short of the 10 degree angle (sight centerline to vertical) I was hoping for. Or, you could say it went too far by about 85 degrees.
The barrel contact surface appears to be original (not modified).
I only see two remedies (I don’t like either):
1. Machine .063 inch from barrel or
2. Place a .017 shim between the barrel and it’s contact surface on the receiver.
The issue, in both cases is head-space. I can ream the chamber deeper for #1 but #2 adds .017 to the existing head-space.
Anything that can be added in the way of advice would be greatly appreciated!
Do not put a shim between the receiver collar and the end of the barrel. Doing so will increase cartridge case head protrusion. Cartridge case protrusion is far more safety critical than headspace. Under no circumstances increase the amount of unsupported cartridge case out of the chamber.
To understand why, I do recommend reading the free book , or at least reading the blowback section of the book.
Volume IV, Design Analysis of Automatic Firing Mechanism, by LTC George Chinn.
http://www.ibiblio.org/hyperwar/USN/ref/MG/
http://www.ibiblio.org/hyperwar/USN/ref/MG/IV/MG-V4.pdf
LTC Chinn has these wonderful, simple, pictures explaining that cases are not strong, and there is a limited amount of sidewall that can be sticking out of the chamber.
I do recommend reading The Bolt Action by Stuart Otteson and the section on the Mauser 98. Mr Otteson explains the importance of cartridge case support, the allowable amounts in different actions, and why the good cartridge case head support of the Mauser makes it a strong action.
Mauser M98 barrel, case supported up the extractor groove, good design
M1903 barrel, sidewall unsupported in extractor cut, not as good a design.
something that happens with M1903's when the case head goes.
Mike Walker, the designer of the Remington M700 action, describes why his action is strong in his patent:
BREECH CLOSING CONSTRUCTION FOR FIREARMS 2,585,195
Merle H. Walker, lion, N. Y., assignor to Remington Arms Company, Inc., Bridgeport, Conn., a corporation of Delaware Application
Prior art firearms of the type employing fixed metallic ammunition have always been dependent upon the metallic cartridge case for securing obturation with the walls of the barrel chamber and preventing the rearward escape of gas from the barrel. As a result, the head of high intensity center-fire rifle cartridges has always been a massive chunk of brass of usually adequate strength to bridge over gaps between the end of the bolt and the chamber mouth, or clearance cuts for extractors, ejectors, and the like. However, in spite of this massive construction, the heads of cartridges, due to metallurgical deficiencies, barrel obstructions, or other difficulties, all too often fail in service, releasing white hot gas at pressures in excess of 50,000 pounds per square inch into the interior of the receiver. With some modern commercial and military rifles the effects of a burst head are disastrous, completely wrecking the action and seriously injuring or killing the shooter. One of the better known military rifles presents in alignment with the shooter's face a straight line passage down the left hand bolt lug guide groove, which, even though the receiver proper does not blow up, channels high pressure gas and fragments of the cartridge head into the location where they can do the most damage. It has been often, and truthfully, said that the Strength of most rifles is no greater than that of the head of the cartridges intended for use therein. The primary object of this invention is the provision of a firearm construction which is not thus dependent upon the strength of a cartridge head, ordinarily formed of a material of relatively low strength by comparison with the ferrous alloys used for the firearm structure.
I am confident that the well known military action that Mike is referring to is the M1903. That action is pathetic in its gas handling characteristics.
Mauser designed his action so the barrel fitted against the receiver collar. If the lugs were not set back, and neither the receiver seats, than the cartridge case protrusion would be correct with a replacement barrel. The Armorer would then run a reamer into the chamber to set the headspace.
I got to talk to a cartridge manufacturing project engineer at a Regional. He was totally frustrated with all the modern rifle designs that keep on increasing the cartridge case protrusion. If a case bursts, he is the one going to get the blame, because no one thinks supporting the cartridge case is all that important. It took a lot of iterations for 19th century rifle designers to create designs that adequately supported the case head during firing, and yet still fed from a magazine, and extracted quickly. That whole period has been pretty much forgotten, and why a cartridge case is weak and must be supported by steel.
It took the internet to embarrass the Glock Corporation to provide more case head support. Glock blowups had to be common before the internet, but without a means for shooters to talk to each other about Glock blowups, surely nothing would have happened. As it was, shooters compared blowups, and began to realize that Glock chambers provided inadequate case head support for all situations.
Shooters posted pictures like these:
And by comparing problems, figured out Glock chambers left a lot of the case head sticking out. Glock slowly responded, probably due to the aftermarket responding faster than the Glock Corporation
But eventually, Glock changed the amount of cartridge case protrusion
You can look at this case design, and figure if the joint is sticking out of the chamber, something bad is going to happen
And there are odd ball designs by guys who want to hot rod their rifles. The O’Connor steelhead was created to use steel in the case head, to allow even higher pressures than brass, before the case head blows.
The 277 Fury has a steel case head. It is supposed to be the Army round of the future, the case needs a steel case head because the thing operates at 80 Kpsia.
.277 SIG Fury Demystified
https://www.gunsamerica.com/digest/277-sig-fury-demystified/
The inprint crowd understands headspace, more or less, but in their writings, it is clear the idea of cartridge case protrusion is an unknown waste land to that group. But it is more safety critical than base to shoulder measurements.
Figure out a way to solve your problem without increasing the amount of unsupported case protruding from the chamber before you blow the receiver ring on your rifle.
