Could this be excessive headspace?

[fguffey]

I have no ideal where Hatcher got the .147" case head protrusion, I have never found an 03 with more protrusion than the Mauser. The only part of the case head that protrudes .090" is on the side of the extractor, meaning the rest of the case head has less protrusion.

Jim Watson, ldlfh7. thank you, ldlfh7 for my part you are welcome.

F. Guffey

 

[Jim Watson]

I think the German innovation of the rimless cartridge to simplify box magazine design is at fault. A rimmed cartridge need have no protrusion other than the thickness of the rim, backed up by the solid case head, except at the extractor cut. My Remington 788 .30-30 headspaces the rim against the flat breech face and the flat bolt face holds it there. The extractor cut is .15" wide and maybe .050" deep. I think a US Krag is the same, although limited by its single locking lug.

As I cited in the previous thread, Neidner had it figured out long ago. The Mann - Neidner "Hamburg" rifle had interrupted thread locking lugs, screwing the bolt right up to the casehead with no clearance at all. Mann said the rifle would stand overloads that would bulge the barrel and not even blow the primer due to the firing pin design.

I referred to the "despicable Hatcher" because I do not recall having seen Slamfire1 say a good word about him until now.

 

[fguffey]

I am guilty of that, a very boring conversation, for me, starts when some one starts with "Hatcher said" It is not as much about what Hatcher said but someone telling me what he said.

From the beginning the length of the chamber from the shoulder to the bolt face could have been tracked, in thousandths, Springfield nor Hatcher noticed. The third 'exposed' safety lug in front of the rear receiver ring made it possible. All I have ever used on the 03 when checking the length of the chamber from the datum/shoulder to the bolt face is the feeler gage.

I had rather check the length of the chamber from the shoulder to the bolt face with the ammo I am shooting than a head space gage. I have no problem correlating all the measurements.

F. Guffey

 

[Slamfire]

"If all you can do is rely on authority, because you don’t have the education or smarts to understand firearms design, then the world is a very confusing place. All these divergent opinions."

I was considering a reply to the nastiness and arrogance contained in that statement, but decided that it would be pointless in the face of such absolute knowledge of one's superiority to ordinary humans who dare to have "divergent opinions."

Buck up buckaroo, why don’t you prove to this "genius expert" your vast knowledge on bolt design?

So do something easy, what is the design load for a 30-06 bolt?.

I will make it even easier: given that the 30-06 has a case head diameter of 0.470”, that comes out to a surface area of 0.1735 square inches. I am using the OD of the case, you are free to pick any dimension you want, just tell us why. Anyway, I am going to pick the MAP of 60 Kpsia, though it might be a better choice to use the MPLM or MPSM, what do you think?, which will give a bolt face load of 10, 410 lbs. This load is based on the assumption that the case carries no load, something that apparently, you disagree with.

To plumb this further, I will make it real simple: Just how much load are you assuming the case carries and thus by how much do we weaken the locking mechanism? Let’s make it even more basic, will the case carry 50% of the load, 40%, 30%, 20%,etc, etc?, thus we reduce the bolt structure by 50%, 40%, 30%, 20%, etc, and what is your rationale for that number?

I am not going to ask your opinion on what safety factors to use and I am not going to require a Von Mises analysis, I am of the opinion that early bolt lugs thickness were at best based on maximum shear theory.

Once you give your “opinion” we can call out all the "dancing girls" and strike up the band!!

 

[Jim K]

Your use of the OD of the case head shows a common mistake in talking about pressure on the breech face. The correct way to calculate pressure on the breech face (bolt head) is by calculating the area of the rear INTERIOR of the case, (using trig to figure out how much of the curved interior area is the "rear"). The result in area is then divided into the MAP to obtain the absolute pressure on the rear interior, which is then calculated for the area of the case head. If desired, that can then be converted to PSI for the bolt face load.

OK, return questions. I agree that you seem to be very knowledgeable about some aspects of firearms design. How many firearms have you designed? How many design teams have you been on? How many of your designs have been put into production by firearms manufacturers? I once suggested to Gene Stoner that channeling waste gas back through the bolt was not a good idea; he responded by asking how many military rifles I had designed. A good reply question and it left me more than a bit red in the face. But it didn't answer my question or explain why he had used that system.

Jim

 

[Slamfire]

Your use of the OD of the case head shows a common mistake in talking about pressure on the breech face. The correct way to calculate pressure on the breech face (bolt head) is by calculating the area of the rear INTERIOR of the case, (using trig to figure out how much of the curved interior area is the "rear"). The result in area is then divided into the MAP to obtain the absolute pressure on the rear interior, which is then calculated for the area of the case head. If desired, that can then be converted to PSI for the bolt face load.

Thank you for a polite and well considered reply.

I disagree with using ID. That was a convention by at least one design bureau and I don’t know why they used it considering they had the ability to actually measure case head thrust. I have examined measured bolt thrust data from a 2010 Army report. The Army “heavily” lubricated 5.56 cases and measured the actual cartridge thrust. The actual, not theoretical case thrust, was higher than the thrust based on ID, and less, than a calculation based on OD. I am of the opinion the lesser value must be due to frictional losses in the lube.Given that the actual case thrust values were above the ID and closer to the OD, I am of the opinion that OD represents a worst case and therefore is the appropriate value to use.

I took several measurements after sawing off a 223 case just above the case head. Sidewall taper just at the case head gives a number of different values, which are different from the ID just above the taper.



But, your calculation method was used by some, the firearms designed by that method have had excellent service lives, probably due to the safety factors used in sizing the lugs.

OK, return questions. I agree that you seem to be very knowledgeable about some aspects of firearms design. How many firearms have you designed? How many design teams have you been on? How many of your designs have been put into production by firearms manufacturers? I once suggested to Gene Stoner that channeling waste gas back through the bolt was not a good idea; he responded by asking how many military rifles I had designed. A good reply question and it left me more than a bit red in the face. But it didn't answer my question or explain why he had used that system.

His reply was an insulting misdirection: of course blowing waste gas through the bolt was not the best idea, but, based on a Guns Magazine from the 50’s, he did it to avoid paying patent royalties. I am certain he was insulting you instead of providing a serious reply because he knew that DI made for a maintenance heavy and dirty weapon. Issues he would have been reminded of many times in his attempt to sell his weapon system to the Army. As it is, while semi auto DI’s are excellent target weapons, DI is so dirty, the only active general purpose military weapon using DI is used by the US Army, and those countries who accept US weapons as foreign aid. No other front line design, no country which designed a weapon from the ground up, and is using it, uses DI, which ought to show that DI was not the best choice for a military weapon. The number of DI designs out of inventory are greater than the number of DI designs in active duty.

There are features of Stoner’s design I like, I think considering the shoe string development budget he had, he did well. Most of the problems with his AR design could have been worked out had the rifle under gone full scale development, but it did not. Instead good Americans had to die in battle and hundred’s of millions spent fixing what could be fixed given that an immature weapon design was base lined in form, fit, and function. Two problems that remain to this day are the DI system and the magazines.

I have one active firearm designer I talk to, planning to buy some guns off him, one of his designs is in production, and unlike Stoner, he is still alive. He was the bolt designer and he used OD. As an active target competitor, it is surprising all the people you meet, and one, whom I have kept in contact with, was an artillery designer. He told me the typical safety factors he used and he used OD in his designs.

And none of them weakened their design by assuming the case took some of the load.

 

[Jim K]

Sorry, but I do want to clarify something I said. Gene's reply was not intended as an insult or taken as one. He was a good guy and he was joking. I accepted it that way, even with chagrin, something I did not make clear in my post.

FWIW, I have long considered the AR-18/180 to be a much better rifle than the AR-15, and I think had it been ready in time it would have been selected as the M16 rather than the earlier rifle. It would have been more reliable, less fussy, and much cheaper to manufacture. (I would have made the buttstock connection a lot stronger, though.) But the political demand was to get something out there to counter the AK-47 and the AR-15 was all there was.

I considered the vaunted Stoner 63, though, as "simplifying" things in a very complicated way. It was a "tour de force" that wasn't needed, though it impressed the heck out of some generals with that "push-pull-click" stuff. But an army just issues rifles to some and machineguns to others - they don't need to be convertible or combinations.

As for the ID-OD issue, I am not sure which is "correct", and suspect that neither is, since what is involved is relative pressures, not necessarily absolute. The folks who write that cartridge X and bullet Y give 52,286.745 pounds per square inch are not in the real world. I once wrote that there can easily be 100 fps +/- variation in a box of factory cartridges and was taken to task by some guy who read the tables in the Gun Digest and believed the numbers.

I think the whole thing we can say for certain about things like cartridge pressure, is that there are few pat answers. Things just happen too fast and any variations (like the position of the powder in the case resulting from fast feed or slow feed) can change things drastically.

I once did a firing time line in milliseconds and there is not a lot of that "slow push" we read about going on. Bolt lugs get slammed back fast, no matter what the design is.

Jim

 

[Slamfire]

As for the ID-OD issue, I am not sure which is "correct", and suspect that neither is, since what is involved is relative pressures, not necessarily absolute.

It used to be a designer took the highest number, even though it is only reached for a millisecond, and that became the design load. With the advent of computer models, deflections can be modeled in real time, and that might affect the analysis.

The folks who write that cartridge X and bullet Y give 52,286.745 pounds per square inch are not in the real world. I once wrote that there can easily be 100 fps +/- variation in a box of factory cartridges and was taken to task by some guy who read the tables in the Gun Digest and believed the numbers.

Agree about pressures not being a point value: when I found actual pressure data, the spread is much more than we have ever been lead to believe in the popular gun press. An excellent read on this can be found at http://kwk.us/pressures.html.

Based on this, and basic statistics, given a standard deviation, the frequency of a high pressure shot is surprizingly high.

Page 1-9 AMCP 706-110 on page 1-9 gives pressure data, which is either taken from the 30-06 or the 308 Win. The book gives the example of a 50,000 psia cartridge with a std deviation 5,000 psia. I have seen pressure tested data on the 308 National Match ammunition, with the 168 match bullets, and the limited tests showed 1719 psia standard deviations, so I consider a 5,000 psia standard deviation reasonable over a large lot.

Based on this standard deviation:

15.9 % cartridge have pressures above 55,000 psia

2.3% have pressures above 60, 000 psia (about 2 in every one hundred rounds!)

1.2 % will have pressures above 65,000 psia. (about 1 in every one hundred rounds!)

So I believe the short hand calculation that SAAMI uses for Maximum Extreme Variation (MEV) to be quite reasonable. From http://kwk.us/pressures.html

Maximum Extreme Variation (MEV). There is a small chance that in a very large lot of ammunition, a single sample might test much higher than the averages. From statistics, SAAMI recommends an MEV no more than 20.6% above the MAP.

338 Win Mag 1.206 X 65, 000 = 78, 390 lbs/ in ²

It can be seen that at least once or twice in every 100 rounds, you can expect an 78,000 psia shot with 338 Win Mag factory ammunition!.

Just imagine the extreme high spreads on some people's reloads! Might be some 90,000 psia rounds going down the tube on the rare occasion.

When people raise the bolt loading flag, which they often do, I believe my best advice for that concern is to "cut your loads". Nothing increases bolt loading faster than a couple of extra grains of powder. Believing that case friction is a panacea for high pressures (Ackley anyone?) is about as realistic as believing you can survive a 100 mph car accident, because you put a pillow between your chest and the steering wheel.

I once did a firing time line in milliseconds and there is not a lot of that "slow push" we read about going on. Bolt lugs get slammed back fast, no matter what the design is.

Agree, I think Chinn calls it an impact load. Based on discussions with a number of people, treating the load as an impact load has greatly changed my view of heat treatments, and the great importance of looking at Charpy impact test data.

FWIW, I have long considered the AR-18/180 to be a much better rifle than the AR-15, and I think had it been ready in time it would have been selected as the M16 rather than the earlier rifle. It would have been more reliable, less fussy, and much cheaper to manufacture. (I would have made the buttstock connection a lot stronger, though.) But the political demand was to get something out there to counter the AK-47 and the AR-15 was all there was.

Once something is type classified, goes in to mass production, is issued, it gets very hard to replace. The logistics cost simply overwhelm all other considerations and the political will was not there to force the issue, as there was on replacing the M14 with the M16. Maybe once burnt, twice shy? I have handled an original AR180, looked like a better mouse trap to me, but, “good is the enemy of better”. Currently the military is requiring any replacement candidate to the M4 to be 200% better. I don’t know if there is anything using current materials, technology that will ever be 200% better. These sort of standards cannot be met unless Captain Kirk beams down a couple of phaser rifles for evaluation.

I considered the vaunted Stoner 63, though, as "simplifying" things in a very complicated way. It was a "tour de force" that wasn't needed, though it impressed the heck out of some generals with that "push-pull-click" stuff. But an army just issues rifles to some and machineguns to others - they don't need to be convertible or combinations.

The early M16 had a slamfire problem: primer sensitivity was not specified and exactly what accidents happened, not in any record, but the military reduced firing pin weight and went to a less sensitive primer: the #41. The M16 firing mechanism was not altered as there was enough energy margin to fire the less sensitive primer even down to -40 F. (or -40 C) But, Stoner's 63 version had misfires with the #41 primer!, he must have changed something.

 

[fguffey]

Based on this standard deviation:

15.9 % cartridge have pressures above 55,000 psia

2.3% have pressures above 60, 000 psia (about 2 in every one hundred rounds!)

1.2 % will have pressures above 65,000 psia. (about 1 in every one hundred rounds!)

So I believe the short hand calculation that SAAMI uses for Maximum Extreme Variation (MEV) to be quite reasonable. From http://kwk.us/pressures.html

It can be seen that at least once or twice in every 100 rounds, you can expect an 78,000 psia shot with 338 Win Mag factory ammunition!.

And the spread of pressures had no noticeable impact on the case head thickness and or diameter. When I find case head upset caused by high pressure I do not fined 1 case out of 20 or one case head out of 100 fired cases with upset case heads. I do find cases in groups as in 10 our of 10 or 20 out of 20 cases that were returned to the original box after firing.

F. Guffey

 

[gamestalker]

Even if it did have a head space problem, and it doesn't appear to, if it's doesn't have a serious head space issue, it can often be managed very well after the brass has been fire formed, by not bumping the shoulders back more than necessary when resizing.

GS