Stonecreek, machining a reverse tapered chamber is NOT an impossibility! Loading a reverse tapered cartridge into this chamber would be however. The concept of the inclined plane would still be valid, however. The difference would be that in the case of the reverse taper the additional thrust force created by the taper angle would reduce the thrust reacted by the bolt and redistribute this force to the cases shoulder, belt, or rim depending on the method used for headspacing.

A realistic values for coefficients of friction between brass and steel are:
Static dry: 0.13 to 0.18
Dynamic dry: 0.09 to 0.13
Static wet: 0.08 to 0.12
Dynamic wet: 0.04 to 0.09

These values have all been determined through experiment from clutch friction material studies in manual transmission locker rings. They should be applicable to this discussion though. The static coefficient of friction is ALWAYS bigger than the dynamic coefficient of friction. Using these values the 92.2 lb bolt thrust force generated by the case taper would equal 92.2*.18 or 16.6 pounds! This is from a perfectly dry chamber. This thrust is hardly worth considering, in my opinion.

Nickel on steel does have a slightly different coefficient of friction than brass on steel. This difference amounts to about 15% - 25% lower, so it is hardly significant.

I think this topic has been beaten to death.

Axel

I found where Harald blasted my notion of calculating bolt thrust, it is in his first post on this thread:
http://www.serveroptions.com/ubb/ultimatebb.php?ubb=get_topic;f=16;t=001741#000031

Here's my favorite part: "There is a popular misconception that bolt thrust will be less with a straighter case because the gas pressure won't be pushing back on as large a surface area as for a tapered case. This is due to a really goofed up understanding of fluid mechanics."

Axel, he also blasts your theory....

Thanks for the support Stonecreek.

Bill

Gas pressure within a cartridge case is not unlike hydraulic pressure within a cylinder and acts much the same. The pressure acts upon the area of the piston period. The shape of the piston and the shape of the cylinder ahead of the piston have no effect whatsoever on the force generated.
Radial forces, as stated, are miniscule and exist as calculated only in the total absence of friction.
In reality though, there is friction. The case does grip the chamber walls and what's more, the case shape has little effect on this grip (I don't care what Ackley said!). As for the effect this grip has on bolt thrust, I believe it is not much. Why not? Because the amount of force required to deflect the brass case an amount equal to the total deflection of the bolt is just that, Not much. There are some exceptions and I'll get to that.
Keep in mind that this isn't the same as the amount of force required to cause the brass to fail entirely. The actually requires a surprising amount of force. This was demonstrated by Ackley in his test where he fired the 94 with the locking block removed. The case was able to withstand the amount of force produced by the 30/30 cartridge. There was no measurement of the amount of deflection of that case however.
Quite a long time ago I grew curious enough about this that I made up a split chamber so that I could seat an empty case in it then clamp it in place. I made this so about 1/2 inch of the case (in this case a 30/40 Krag) protruded from my chamber. I then clamped the chamber in a vise and set up a dial guage on the chamber to measure the deflection of the case head. I stuck a rod with a generous knob on the end (to push on)into the case and pushed.I found that I was able to stretch the brass a measureable amount (about .001")by hand ( a darn hard push mind you). It sprung right back of course but it had deflected. Now it is doubtful that any good front locking action deflects any more than this under the thrust of firing so I figure the effect of the brass gripping the chamber walls is, as I said, not much.
I have said before as well that I don't think case shape has all that much effect on the grip on the chamber walls. If it did the nicely tapered 303 British would not grip the chamber wall well enough to seperate case heads which it does commonly. There is no denying that a straight case can grip the chamber wall better but even the tapered case grips sufficiently to exceed the strength of the brass.
Do the WSMs produce more bolt thrust than smaller diameter cases? Yes they do. Does the length of the case have anything to do with this? No it does not. The case length is more than sufficient to provide all the grip that is required to overpower the brass. On top of that it doesn't really matter anyway since the amount that brass adds to the strength of the action is negligible considering the small amount of deflection of the bolt face.
A lubricated chamber does increase bolt thrust probably by about 200 lbs or so in the average rifle. The dangers of a lubricated chamber arose from experiences with greased ammo used in early 03 Springfields. The truth was, failures occurred not from lube but from faulty heat treating. The slight increase of bolt thrust may have been the final straw but it wasn't the whole cause.
I mentioned previously, while the amount of force required to deflect the case head is quite small the amount that can be contained before total failure is surprisingly great. Anyone that has owned a 94 Winchester with excessive headspace (pretty common)will have noticed that this shows up first in the form of protruding primers. This is because the case is driven forward by the firing pin and, when it fires, grips the chamber walls sufficiently that the case is held forward while the primer backs out. This happens even if the case is not "improved" by the way. Now in this case, while the theoretical bolt thrust may be calculated, the real thrust is practically zero since the pressure was insufficient to push the case back against the breech face. Had the headspace been zero then the bolt thrust would have been as calculated minus the amount required to deflect the brass the amount that the bolt would have deflected.
How about if our WSM had excessive headspace? Well, in this case the pressures are much higher than with a 30/30 so it is fairly certain that the force would exceed the strength of the brass. No protruding primer here! Since the brass has failed it's contribution to the reduction of bolt thrust is now zero.
I'm sure it is entirely possible to set up a test gun to measure bolt thrust and to measure the effects of case shape, chamber finish, etc. but even then the results will be open to interpretation. Regards, Bill.

What I posted is correct! As Stonecreek stated, in the real world bolt thrust is a dynamic event. This means the actual bolt thrust force changes with time. The approach I took is absolutely correct, however. If you want to adopt my approach to dynamics, you simply need to integrate it with respect to time.

If what you have posted about this gentlemen Harald, is factual. Then Harald is very wrong!

Edit - I have just read the link from Harald. Harald is saying, exactly, the same thing I have said. The difference is I used a mathematical example and he used only verbage.

Axel

[ 10-04-2002, 01:56: Message edited by: Axel ]

Axel,

The only thing that matters is pressure and area. As Bill Leeper pointed out, the shape of what is ahead of the breach makes no difference! Positive/negative (???) taper does not affect the pressure nor the area, so it does not matter.

I'm sure that Harald is a fine and knowledgeable gentleman, I just happen to disagree with him on the subject of bolt thrust.

Is it dead yet?...

Bill

Bill M, the pressure and area matter only in that they represent a FORCE. Force acting upon an incline plane will have X, Y, Z components if we are dealing with a three dimensional object. As I showed in the example I provided, with the taper angles in metallic cases the thrust force due to the taper angle is INSIGNIFICANT, but does exist!

As I said this is elementary mechanics and vector analysis. If you do not understand these concepts then I suggest you either 1.) accept what is said by those that do, 2.) educate yourself and then perform the analysis yourself, 3.) drop the subject as you are not qualified.

Mr Leeper is correct also. His experiments support my calculations. Could there be a connection...I wonder? In engineering terms this is referred to as correlation.

I think we have beaten this to an unreconizeable pulp, don't you?

Axel

Axel,

You are very confused. Go read some books on fluid dynamics and pressure vessels. Gases exert pressure equally in all directions!!!! Vector mechanics has absolutely no relevance here.

Bill

Ask a steam turbine specialist at General Electric why the interference or shrink fits associated with high pressure vessels may vary from 1 to 8 mills and he'll tell you it's most often the length or depth of a bushing that dictates the degree of tension required to maintain position @ operating temperatures and not diameter, even when the surface areas are comparable. When structural design precludes the use of a suitably long sleeve, bushing or guide, the component is fitted with a mechanical assist of some kind, such as endcaps, retainer rings or allen screws. Such are industry standards, worldwide.

I feel that not only does case design play a role in bolt thrust but so also does remnant case lube, action oils, nickel coatings, brass ductility, powder burnrate and a host of other variables not encompassed by simplistic, two dimensional equations.

Bill M, as I said you are not qualified to argue here. First in evidence you could not tell that Harald was saying the same thing I was. Second, you could not tell that Mr. Leeper's experiment said, essentially, the same thing my calculations said. Lastly, you do not understand the force distribution in the gun. The pressure is uniformily distributed, I have said this already, further it acts perpendicularly to the surface of the case, I said that already too. Now the vector analysis comes into play when looking at the reaction between the case and the chamber wall. Since these two surfaces are at an angle relative to axial thrust force, there is a very small rearward reaction force. You can believe what you want I really do not care. Since you have missed my statements and this Harald gentlemen's it is very obvious you are not a careful reader and are looking for a fight. I find it incredible that there are those here that call me a troll, when you, sir, are the aggressor.

Axel

I didn't start this thread to create another pissing contest. I value and appreciate ALL the fine input and hope it can end in the same spirit it began. Like I always say, "there are a lot of smart folks here".

Whoa, there folks. Let's not insist on disagreeing when we are mostly in agreement!

Bill M, Bill Leeper, Axel, and myself are all pretty much in agreement that the shape of the case is, in real world terms, totally irrelavent to "bolt thrust". I also agree with Bill Leeper that with low-pressure cartridges, there may be practically no bolt thrust, and that with higher-pressure cartridges the bolt thrust is essentially the same as chamber pressure acting on case head area. As several pointed out, it is a mistake to believe that "sticky bolt lift" is a result of excessive bolt thrust, since the bolt is "sticky" AFTER the pressure is relieved (as a result of stretched brass). An over-lubricated chamber can cause extremely sticky bolt lift by allowing the cartridge to back out against the bolt face rather than stretch against the bolt face, but lubricating a chamber has nothing (in practical terms) to do with bolt thrust.

Axel, I think the point of contention between you and Bill M is actually a negligible one. Perhaps you might make it clearer to all of use if you would comment not on the effect of the taper of the case walls, but on the effect of the shoulder angle. This area, especially in a large-bodied, small bore cartridge like a .270 WSM would, under your theory, have a great deal more influence on vectored forces than the case walls (which are much closer to parallel to the axis of the case).

I can believe that static fluid pressures are much different from intense dynamic pressures, as can be illustrated by the effect of a "shaped" explosive charge which exhibits much more force in one direction than in others. However, the "jillions" of theories which have been applied to brass cartridge cases like the Weatherby venturi shoulder (thought to smooth the gas flow from the cartridge through the neck), the long taper of the H & H style cartridges (thought to reduce pressure by "funneling" gas forward down the bore), and now the WSM (laughably said to improve efficiency by placing the powder closer to the primer or some such processed meat product), have all proven to be inconsequential to cartridge performance. (That's not to say the designs are not consequential to rifles -- the H & H feeds marvelously and the WSM allows long-cartridge performance in a short action gun, and so on.)

At any rate, Axel, you might comment on your view of the shoulder influence. You might also explain why you feel this is significantly different from Bill M's pressurized hydraulic cylinder.

I think I'd have to agree with Bill Leeper that if a fairly tapered .30-30 case doesn't eject itself from the chamber when fired un-contained by a bolt head that the effects, if any, of vectored forces can't be very great at all.

[ 10-04-2002, 23:29: Message edited by: Stonecreek ]

Stonecreek, I agree with your contention that "we" are all in agreement. It is amazing how minor technicalities can become so incredibly blown out of proportion. I apologize to Bill M for coming across in such a hostile manner. It was inappropriate on my behalf. I have been plagued with false accusation of trolling and I took it out on him. Again I apologize.

Personally, I feel that the shoulder angle hasn't much effect other than in regard to the gas flow characteristics of the gas. From the chamber pressure perspective, I would think that the highly shouldered cartridges would generate a larger stretching of the barrel shank than a straight walled or slightly shouldered case. This could, and I stress could, produce a greater potential to case sticking. I do not believe however, that this would be the case with any barrel contour currently employed. My reasoning is that the bolt lugs and raceways are not as stiff as the barrel shank so the deflection would occur there; therefore, reducing the barrel shank deflection.

The shoulder angle's only effect on bolt thrust, in my opinion, would be dynamic and due to the pressure time curve. The steeper shoulder angle may increase the time at higher pressure; therefore, increasing the time that the maximum thrust force is applied to the action locking lugs.

However, the slighter the shoulder angle the more the brass will be drawn into the neck/bore. The tensile force on the case due to this effect would be explained by this equation:
(pressure * area)* cos(shoulder angle).

Axel

I'm a bit out of my league here 'cuz I'm happy when the pointy lead thing comes out the end of the long tube after I pull the little spur under the handle you pull back to put a new brass thingy into the round tube with the hole in it but I did read Dan Lilja's article and I seem to remember his formula for "bolt-thrust" (sounds like something a stripper might do) is a function of pressure and the inside area of the case...period, exclamation point etc etc.

The other things being "discussed" quietly and in a genteel manner all seem to be off the point.

DBBill, I agree with you. If you are a physicist carrying everything to the 10th decimal point the Lilja equation is inaccurate.

I provided an example, which is accurate. You be the judge. Is a 16 pounds of force generated by body taper angle, which is including the effects of friction, matter when the other component of bolt thrust is 6875 lbs!

To put it in a clearer light the percentage of thrust from the body taper is: 0.2%

The standard deviation of the powder's pressure is most likely greater than that!

If you wanted to calculate bolt thrust I would use the approach stated in Lilja's website. That being pressure times the internal cross sectional area of the case at the base!

Axel

It reminds me of the old expression..."He's the kind of guy who would measure something with a micrometer....mark it with a grease pencil...and cut it with a chain saw."

You insist on using a simple formula as though you were dealing with a pre-sealed vessel. The "seal" in this scenario is a creation of pressure and a brass casing, subject to variables that no mathematical equation can embrace. The most obvious comparison, overlooked to this point, is that of straight walled cases, where case heads don't rest against the boltface, to bottleneck cartridges which headspace on the shoulder with the head firmly against boltface. Which would give the greater bolt thrust at a given pressure?

Quote:
Most designers believe that 'back thrust or breech pressure' is a more serious consideration than 'Chamber pressure' because it is working directly against the moving parts of the action. To calculate breech pressure one can take the chamber pressure in relation to the internal area of the case that put pressure on the bolt and whilst the 2 locking lugs on the bolt must bear the strain ... so that should be our focus.
The distribution of back thrust is shared by the case and chamber walls depending on its grip on the chamber walls as it varies between tapered cases and a more parallel type cases. The balance of the thrust, plus the full thrust of the primer goes onto the bolt. If there is oil in the chamber or on the cartridge case, the back thrust will be increased tremendously and may even approach that of full chamber pressure. If we ignore chamber-wall friction, but assume a 'dry' chamber, we can compute back thrust as follows:-
Max Inside (A) (B) Ave. Operating (A x B)
Cartridge Case Diameter Area Chamber Pressure Thrust in pounds
.30-06 Spr .400" .126 sq. in. 43,000 psi 5,418
.375 H&H .445" .156 sq. in. 60,000 psi 9,360
.458 Win Mag .463" .168 sq. in. 45,500 psi 7,644
.458 Lott .463" .168 sq. in. 63,500 psi 10,668
.404 Jeffery .493" .191 sq. in. 39,000 psi 7,449
.378 Weatherby .515" .208 sq. in. 59,000 psi 12,272
.460 Weatherby .532" .222 sq. in. 63,816 psi 14,191
.416 Rigby .539" .228 sq. in. 44,000 psi 10,032
.500 Jeffery .564" .250 sq. in. 46,412 psi 11,603
From a safety standpoint, the bolt lugs is of prime concern ... the factors are ... the strength of the metal, its dimensions as well as its ability to flex. In general then, the bigger the calibre, the greater the area that is affected ... this area is then multiplied with the actual pressure which is dependant on the actual load, comprising the bullet weight, the type of powder and the charge to yield a specific velocity. It is thus clear that a hotter load will increase the back thrust.

[ 10-05-2002, 08:03: Message edited by: Nickudu ]

Of all the pictures you have seen of a "blown bolt action", how many had the lugs sheared off. Have you ever seen such a picture?

If you were to machine say .003" of the back of one of the locking lugs, after firing lots of shots, would you then expect both lugs to be bearing?

Mike

Again, this is the fourth link that supports my position. What will it take to demonstrate that a simple bolt-thrust calculation is not the whole story? 3rd or 4th paragraph down

http://www.beartoothbullets.com/tech_notes/

[ 10-05-2002, 09:18: Message edited by: Nickudu ]

[QUOTE]Originally posted by Stonecreek:
[QB]"Whoa, there folks. Let's not insist on disagreeing when we are mostly in agreement!

"Bill M, Bill Leeper, Axel, and myself are all pretty much" - WRONG.

Guess I had to say it for ya! just playin'

[ 10-05-2002, 09:53: Message edited by: Nickudu ]

Nick,

For whatever it is worth.

Back in the very early 70s I had both a 340 Wby in Mark V and a 375 in a Model 70. Back then, many of us in Australia used a straight line neck sizing loading too and full length sizing was done with a vice die, as it became necessary. Since it was a vice die, cases had to be quite tight before you would resize them.

Cases for the 340 were made from the Winchester 375 H&H brass and this is what I observed.

The 375 cases needed full length sizing after less firings. Also, the 375 cases got real tight to chamber real quick. On the other hand, the 340 cases got gradually tighter to chamber.

Now in my opinion there could be two reasons for this, assuming of course the observation was valid given there were two different rifles etc. and etc.

Firstly, back thrust was greater with the 375 H&H, hence the action stretched slightly more and therefore cases became tighter quicker.

Secondly and I think this one is possibly the reason, the 375 being much more tapered would be harder to drive into the chamber because of less leverage on an inclined plane basis. One must keep in mind that some of the difficult chambering will be because of the fit of the chamber around the body of the case, not just case length and as we know it takes less impact to drive a very gently tapered wedge into a piece of wood.

Mike

[ 10-05-2002, 10:05: Message edited by: Mike375 ]

In relation to my post above on 349 Wby and 375, I just weighes a Mark V bolt and it was 18 ounces anda Rem 700 was 12 ounces. Did not have a a Model 70 handy, but a push feed M70 I guess would weight about the same as the Rem 700 bolt.

Obviously the intertia of the bolt must have some bearing on action setback. So therefore does a Mark V resist action set back more than a Rem 700 or M70.

Mike

Well, I'll be! If it's not Todd E and his latest identity, Axel, still pretending he's a firearms expert.

Let's see Todd, first you were a LEO...then you confessed to just being a college student, child psychology wasn't it? Then after several hundred other confessions and protracted good-bys, you morphed into the clone SRS until people got sick of you and your BS in that disguise and after about 100 protracted good-by's you finally flaked off THAT stupid persona. What did you claim you were as SRS...a loading dock hand, i.e. fork lift driver? Well I guess they WOULD know something about hydraulics.

And now you have promoted yourself to the great "German" firearms expert and "engineer" Axel Dimple. ROFL

The names change about as often as you change your underware, Todd E....but it's always the same old crap. Pretend you know everything. Babble a lot of meaningless numbers and equations and try to hide behind your sophomore physics book and hope no one figures you out.

Axel/Todd E/SRS - Your too funny...in a sick sort of way. Child psychology is definately the right field for you.

[ 10-05-2002, 10:37: Message edited by: Pecos45 ]

Nickudu, I get the feeling you are picking a fight. All the threads that you have posted say precisely what I have stated. The fact is that the thrust created by the body taper is SMALL! That does not mean that this thrust force does not exist. I have also provided an explanation for case stretching due to small shoulder angles. This entire discussion is basic mechanics and I am sorry if you find it hard to believe that the equations are so simple.

The shrink fits you discussed earlier are based upon the same principals. The equations are slightly different, however. In a shrink fit we consider the tangential stress in the "bushing". The actual interference pressure is therefore a function of the spring rates of the bushing and the housing into which the bushing is fitted.

We are not discussing an interference fit here! A cartridge is NOT shrunk fit into a firearms chamber, is it? Again this thread has been beaten beyond recognition, in my opinion.

Pecos45, perhaps you could persuade your friend ToddE to post his opinions on this subject. He seems to be the resident expert on these scientific discussion, at least according to you!

Axel Dempel

PS Pecos45, please note the spelling of the last name. You continue to mispell it.

Axel, My reference to shrink fits was merely an attempt to convey the principles of linear engagement as a way to further demonstrate the thought process of the E. Arthur Brown Co., Elwood Epps, P.O. Ackley, the Beartooth Bullet company and countless others, on this issue of ACTUAL bolt thrust. I am not spoiling for a fight.
I am one of the few persons at this Forum who has arbitrarily treated you with respect, throughout your tenure here, and that, despite allegations as to your identity and/or veracity. If you can't see that I am merely trying to engage in an exchange of ideas with others who hold interest in such things, it not my problem.
However, as I am getting tired of all this, I hope I may allowed to make my exit. Good Day to you and all the best.

[ 10-05-2002, 18:41: Message edited by: Nickudu ]

Axel Dimple, Axel Dumple, Axel Demple - What difference does it make Todd E.? They are all you trying to pretend you're the greatest firearms expert who ever lived.

How do I know? Easy! Your style and stupidity never changes. "Dazzle them with irrelevent numbers and BS," that's you. But practical experience....you ain't got it.

Now why don't you go reinvent yourself AGAIN and come back as a Rocket Scientist this time. Maybe people will believe your crap then.

OH, you just pissed Nickudu off...time for one of your famous "apologies." He was one of the last guys nice enough not to treat you like the idiot you are.

Nickudu, I did not mean to sound hostile toward you. As I understand it, everything being stated on the links you have posted agrees with what I have said. I guess that is all I am trying to say. It is ultimately my fault if you can not see that my statements and those made on these various links are in fact saying the same thing. I cannot figure out a better way of explaining it. I agree that case taper angles have an influence on bolt thrust. Can we leave it at that and part on good terms?

I do appreciate the fact that you have behaved like a gentlemen toward me, as well, thank you. If however, you feel as though I deserve it, please treat me as the others do. For some reason I believe that you are more mature than that, though.

Axel

[ 10-05-2002, 21:29: Message edited by: Axel ]

Axel/ Todd E. / SRS - How did I know your apology was coming? Duh, because you never change your stupid routine.

You are SOOoooooo predictable.

Get a life and go away. You're the one with the maturity problem. Not Nickudu.

Oh, Yes, Axel ... I am very mature as I now weigh 260 pounds and have hair in my ears. I thought I last told you to have a "Good Day". Obviously, you're still not listening! Later ....

Nickudu/Pecos45, excuse me. I am gullible aren't I? I fell so completely for your trolling. Foolish me I thought you actually wanted to learn something. It is quite obvious by your statements that you were baiting me all along. You would truly need to be dense to not see that what several people had stated, besides myself, and the information in YOUR links was indeed a match!

Good day, INDEED. I hope you enjoyed your fun. Why must grown men take advantage of others kindness?

Conversely, I hope that others DID learn something from the knowledge put forth on this thread, by Stonecreek, Bill Leeper, and Myself, with a little help from Bill M and Harald I may add.

Axel

Axel,
Surely, you must be joking???

[ 10-06-2002, 05:43: Message edited by: Nickudu ]

Nickudu,
Re your question as to whether a straight walled case or a shouldered case would produce the most bolt thrust. The answer is that with all else being equal the bolt thrust would be the same. There are scenarios wherein the grip of the cartridge on the chamber walls may effect bolt thrust and I tried to explain some to you. I may have failed in that attempt.
The component of bolt thrust as produced by the taper on the case is indeed slight. In fact I strongly suspect it is zero. This because ALL cases grip the chamber walls regardless of body taper. The only exception is if the case is lubricated. Even then, if it were not for the rearward thrust of the pressure within the case, it is unlikely that any rearward movement would be produced strictly by pressure acting upon the sides.
Ackley may have known a lot about a lot of things but he was wrong in his contention that less taper meant less bolt thrust. That others continue to believe and repeat this fallacy makes it no less wrong.
Now, there are situations wherein the cartridge's grip on the chamber walls can affect bolt thrust and even make it effectively zero but this happens at pressures that are low enough that nobody cares. Regards, Bill.