All of these threads on the topic have me curious...

Can someone explain it in layman's terms (no equations!) i.e. why I should care about it, what factors it depends on, and what it means practically for deciding what you're going to chamber your new rifle in?

My simple thoughts are that, no matter what the area of the cartridge base that sits on the bolt face, ALL of the rearward thrust bears on the locking lug surfaces. Is this incorrect?

Thanks in advance,
Todd

Here is an article about it:

http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm

Keep in mind that pressure and thrust are two different things. I think we all understand pressure, so I will not explain that. Thrust is more like a push. Imagine what a vice does as it bends a piece of metal. Then imagine it happening faster and that is thrust.

At the point of highest pressure the case certainly grabs onto the chamber walls especially the neck.If you were to fire a H&K G3 without fluted chamber the case would be torn in half.But as a practical consideration all bolt thrust would have to be absorbed by the locking lugs. The practice of lapping locking lugs to the reciever will help accuracy but also distribute stresses evenly to both lugs.But as long as the reciever is designed for that cartridge there won't be a problem don't worry about it.Its only when you ignore bolt thrust that you get into trouble like the 40 s&w.

The reason you should care about it is that if you are using a large diameter case, ie 500 Jeffrey, 505 Gibbs, 585 Nyati et al, and opperate at high pressures, you have the potential to cause the bolt lugs to fail, and the bolt to be impaled in your forehead.

As was mentioned in the other threads, the bolt thrust is not 100% of the force excerted on the base of the case, is exerted on the bolt, unless the brass is so soft as to flow. There are also the cases of excess headspace, where the cartridge case can impact on the bolt face, and thus transfer a much greater force to the bolt, and then to the lugs.

In general terms, if you stick with standard diameter cases, you don't have to worry about bolt thrust. It's when you try to create shoulder fired artillery on std sporting actions that you need to consider the forces involved. Kinda like plumbing nitrous in your daily commuter. The stock engine is wonderfully robust in std tune, but when you push it well beyond it's original design, breakage is a very real possibility. The difference is, a blown engine is typically just $ in the toilet, a blown rifle action has a high potential of causing a fatality.

I wonder if we could clarify a point with regard to how the HK delayed roller lock action works?

My understanding is that the gas system only holds the bolt locked, and then once pressure in the system drops enough so that the bolt is unlocked, residual pressure in the barrel acting through the fluted chamber blows the case backward out of the chamber, taking the bolt (and bolt carrier?) back with it to cycle the action. So if this were true and we rebarreled a delayed roller lock action with the gas port but without the fluted chamber, the bolt would unlock, but the action would not cycle (or only partially cycle) and the case would not eject and would not be torn apart. Have I misunderstood this?

Todd,

Paul H is correct. What you want to do is get an idea of what force you are dealing with. "Thrust" is just a name given for a force, the product of pressure times area is all (in this system). You can bogged down in endless speculation about stretching cases ect but the quickest and easiest way to again, get a good idea, is to multiply the maximum listed pressure for the cartridge by the area of its base.

Example: .30'06 has a max pressure of 60,000 psi, base diameter of 0.473". So the maximum force exerted on the face of the case base is 10,542.98 pounds and assume the max thrust.

This is the maximum, not taking into account the fact that the interior of the case is curved and only a small portion of the base is flat. In order to account for the curvature we would have to determine the radius of the curve from the case wall down to the base and then use the calculus to integrate this radius over the distance times radians in a circle. This would give us the area of the curve.
We do not take into account the resistance the cartridge case brass has to stretch. This too would influence force since we would have to subtract that value.

Now, the shape of the cartridge has absolutely no influence on the force exerted on the base of the case or the bolt face. I will elucidate:
Imagine a perfect system, you would drop a bullet into the barrel, followed by powder and Super Glue a primer over the firing pin hole. Now insert and close the bolt. Since this is a perfect system, there is no work lost in the system due to expansion of the chamber, friction of the bullet, heat lost to the container ect. When you fire this perfect system the maximum force exerted on the bolt lugs will be exactly equal to the maximum pressure times the area of the bolt face. This is a theoretical max.
Taking into account all the other variables can immediately be seen to be almost overwhelming but it can be done if you want to take the time for the math.
I like simply using the pressure times area since you want a number you can look at and think about and compare to other cartridges.

Cartridge case shape. The shape of the container has no influence on the pressure exerted over any given area in that container. You can have containers shaped like stars, spheres, clamshells, cylinders or eggs: for a given area, as long as the area is the same for each container, the force exerted will be the pressure times that area. We assume the pressure is interior and greater than standard. In the rifle the case is inside the chamber. We have examined a perfect system previously, now insert a brass container into that chamber. If the brass container were a perfect fit then again we would have the same as a perfect system since we assume brass will have nowhere to flow, hence no work (force) is lost moving the brass around. We can compress brass but it is insignificant for this discussion.
Change this system slightly to allow for a little movement of the brass, say the gap between the chamber walls and a little between the case base and the bolt face. The case will swell (no work lost since max pressure will still reach listed max) but we have the tiny little gap between the case base and the bolt face. The brass will stretch towards the bolt face and that stretch is the only factor we would take into account and do so by subtracting it from the overall force on the bolt face. We would do this by determining the the elasticity for that particular case and subtract the force necessary to stretch it to contact.

As to accelerating cartridge cases in chambers due to excessive headspace I have no comment. If bolt lugs did fail and the bolt began to move rearward I believe you would have a very serious situation about to happen in front of your face.
This is why "bolt thrust" should be a mitigating factor to anyone who is contemplating a wildcat but I do not believe you should becomeoverly concerned. Just look at what has gone before you onto those receivers, calc the "bolt thrust" using the max listed pressure and don't go over that, don't remove material from the front lug, make sure the reciever is heat treated (should it need it) by a firm that is patronized by the top 'smiths and lastly make sure your work is done by a 'smith with a rep for working with large bore rifles and not having problems with them.

SDS, the H&K G3 does not have a gas port ,it is a delayed blowback action and the bolt starts to move back immediately. Fluting the chamber permits the case to move back also instead of tearing. In early tests of the P7 ( a fantastic pistol)they found that the extractor tore through the rim so they fluted the chamber.

From the E. Arthur Brown Company:

Dear Nick,
Regardless of any calculated bolt thrust value, most gun smiths should agree that the ability of a cartridge to grip the chamber during ignition will dictate how much the cartridge is driven rearward. P.O. Ackley's experiments with pressure (page 131 of Vol I P.O. Ackley Handbooks) demonstrate this pictorally. Chambers which were intentionally over headspaced by unscrewing the barrel a turn were fired with lubed cases and dry cases. The lubed cases drove back to the bolt. The dry cases stayed flush with the breech and popped out the primer. Anyone interested can order the P.O. Ackley books from our website on https://www.eabco.com/Esale0412.htm.

Sincerely,
Eben Brown
E. Arthur Brown Company, Inc.
4353 State Hwy 27 East, Alexandria, MN 56308 USA
Ph. 320-762-8847, FAX 320-763-4310
http://www.eabco.com, Email sales@eabco.com

Roger,
A good synopsis, yours. Where were you when I needed you? Review the earlier thread:

http://www.serveroptions.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=002520#000026

Roger, better late than never. Thanks for the excellent explanation. I too have been concerned a bit with bolt thrust after reading all these threads lately. You da man! It is nice to have INTELLIGENT people posting here again,

Casey

Nick,

In terms of E A Brown's reply, the problem I have with it is that if I fire a load with .010 to .020" headspace and with a plunger ejector to drive the case forward, after firing I will have a fireformed case without headspace.

What say ye?

Mike

Hi Nick,

The slippery case is can be an example of max force in a perfect system since all (we will assume) will be used to push against the bolt.

Without the lube the case will expand in the chamber and then it will stretch to fill the chamber. However much energy it takes to do that we can subtract from the maximum force (thrust) we'd calculate. This is why I just look at the case base that would fit into the bolt.

The .425 Westley Richards is a perfect example; how much would this beautiful little monster make?
Well we sure can't look at the base and use that since it is recessed so far so we have to take the bottom of the cylindrical portion. I haven't had enough coffee. I cannot remember what that is called!! Ken Howells book sez it is 0.545 and the base is 0.473. So that works out to 9,331.3 pounds. I used 40k pounds as pressure, I am just guessing since I've never seen reloading data on it.
Now looking at it I don't think the thrust would even be that high on the .425, the brass must be pretty thick there at the base no? It doesn't blow out and if the cases last for reloading, well, there you go, the perfect example of (as Paul said) thrust will be lower than in real life.
I come full circle back to my original statement that I like using a calced max for ease and simplicity. I am not the authority nor will I ever be, I am not an engineer either and I know there are plenty on this board with that background. I am using the physics that I learned and in particular the thermodynamics being shoved down my throat right now this semester.

Roger,
I have said all I am going to on this subject in the "WSM Bolt Thrust" thread. If you read through it thoroughly, you'll see that I was the only one to provide links to articles that supported my thinking. No mathematics will encompass all that is involved with a gasketed (shell casing), imperfect vessel, which itself, relys on variable pressure curve to provide an instantaneous seal. Case taper, chamber surface condition, brass properties, residual lubrication, primer strength, powder burnrate, powder charge weight and a host of other valid possibilities, can certainly undermine the simplistic formulas appropriately applied only to perfect vessels. Whether or not these variables amount to much, in a given rifle, is NOT my argument. Those who emphaticly state that their mathematical equations cover all the bases is my bone of contention. I'll stand with Ackley, Epps and the other experts I have alluded to, on the subject.

[ 11-10-2002, 00:18: Message edited by: Nickudu ]

All this exists no doubt about it.. I shoot a 375 and 300 H&H, that qualifys for a lot of bolt thrust I suspect, but all it does for me is make me trim cases, so be it, as this syndrome also allows for easy ejection and no stuck cases...It simply isn't one of my big worries...

Pecos,
I distinctly recollect someone asking you just where and when you have made a positive contribution to this Forum. They mentioned that, invariably, your posts were sorely lacking in anything, other than contentious banter. While few are losing any sleep over the issue of "bolt thrust", that surely doesn't diminish its' relevance as a point of discussion for interested persons. If you aren't among this group, why not simply ignore it, rather than insult the originator of the thread?

Nickudu, who said that about Pecos?

I kinda agree with Pecos in that this topic is somewhat indifferent to reality unless someone is designing a new action. I for one though, find the entire discussion interesting. That alone qualifies it for me as acceptable subject matter and NOT troll fodder.

I also think that Roger's highly knowledgeable post said it all about bolt thrust. Now I am no expert in these things, so if Roger has missed something please enlighten us.

Casey

Nickudu said:
"Roger,
A good synopsis, yours. Where were you when I needed you?"

Just what is it you're talking about Casey? Do you know?

As for Pecos45 - Do a search on his posts. In the process of assessing the value of his posts, you'll find out who said it ... and when you do, know that I agree with him.

This isn't about me and Nick or anything like that, please don't anyone take it that way!!! This is the way threads go to feces!!!

KB - The fluted chamber is a grand way to ruin cases or at least shorten the hell out of their life to a reloader. As one whose been building his own for almost 50 years, you couldn't run fast enough to give me a fluted rifle chamber.

Didn't this whole fluted chamber idea come up more as as aid to full-auto weapons? I've never seen that it had any value in the world of hunters.

Roger - It's no problem to me. Everyone just seem so serious and working up to a battle on a topic about as important as "front sight alloy."
Whatever turns you guys on is fine with me.

Pecos, fluting is needed in a roller action becasue of what mete said, the bolt begins moving the instant of firering. Semi-auto or select fire, it is a nessesity of that action type. The P7, I would imagine the slide starts moving the instant of firering aswell, untill gases are ported to the piston, which I guess is the reason they fluted those chambers aswell.

Fluted chambers my not be the problem many think they are. I know some one who claims he reloads for his HK91 with brass shot thru it many times, but only when their is not cheep surplus ammo around. It may reduce the total number of reloads you get out of cases tho. I have not reloaded for one, so I can not say for certin.

In a bolt rifle there is no need or reason for a fluted chamber. And it probly would be a danger aswell.

Kristofer

My apologies ... I get buggered when someone, ANYONE , blows into a thread on the coat-tails of a respected poster, degrades its' value in accordance to THEIR own standards and blows out again. It's called a cheap shot in my town.

Nickudu, I am in agreement with Roger and I think you?

Regarding Pecos, I did as you suggested. I think I know who you are talking about now! I also have a deeper understanding of Pecos' complete and utter lack of posting anything MEANINGFUL! He does seem to just go around starting trouble. KBGuns seems to be involved in most of his trouble making as well. At least they are OFTEN posting on the same topics and are in total agreement with each other.

It is too bad that some individuals have to go around and sabotage threads just because these threads are of no interest to them! Why can't they just not respond?

Casey

KB - I would have to SEE someone reloading brass fired in a fluted chamber over and over to believe it, KB. Personally, I wouldn't waste my time on it.

The roller action is something of very questionable merit in my little mind to begin with. The world has had some damn fine machineguns and selective fire weapons without this design. Come to think of it almost all auto guns running around today are STILL either blowback or gas/pistol design.

Alright CASEY, you troll turd, have it your way. I may not have been answering the topic of this thread, but I was not detracting from it either. I discussing something that came up over the course fo this thread, fluted chambers. But since you feel the need to drag this thread down, down we go:

CASEY said:
" I also think that Roger's highly knowledgeable post said it all about bolt thrust. Now I am no expert in these things, so if Roger has missed something please enlighten us ."

CASEY, you dont know what you are talking about, but shit continues to dribble from you mouth. You admit you are no expert, but act as tho you are qualified to say who the experts are! This is you typical moronic behavior.

You never replyed to your "anneled Brass" thread after I called you out. Pretty much every one who was involved in that thread agreed with me. You have not clue about what you speek about, but continueally make anoucements as to who does!

How the hell can you know who knows what they are talking about, if you dont knwo your self? You are an ignorant trouble causer.

CASEY said:
" Gato, with regard to your statements to Pecos...DUH! He is worse than that POSeur TEG! Pecos screwed up a few of my posts with his asinine attacks on TEG! I could easily ignore TEG, but no one seemed to be able to ingore the combination of TEG, PECOS, JEFFEOSSO, RBG, RAB, KBGUNS, ETC, ETC! !"

Here you are, CASEY, bitching about trolls and how evering one needs to ignore them. Every one but you. You get to keep ragging on it like some damn 6 year old. I hope your dad takes you out back and beats you with a rubber hose.

CASEY, you are IMO, still a jackass.

Kristofer

[ 11-10-2002, 03:11: Message edited by: KBGuns ]

KB - I wish you hadn't answered my post. Casey is threatened by anyone who agrees with me.

It has reached the point on the Big Bore forum where it is just that...very boring. There are some really fine fellows with a lot of PRACTICAL, first hand knowledge here, but it gets harder and harder for them to get by the trolls.

Sometimes I think we should rename this forum BIG EGO, rather than big bores. Some of you are so threatend by anyone who dare to question anything you say it's pitiful.

I have NEVER claimed to be the ultimate authority on anything on this website...but I am smart enough to know bullshit and bullshitters when I meet them .

Now, since my presence here is so threatening, I'll bid you boys adieu and repost my question on "roller actions" to a separate thread. I hope you'll join me there KB. Perhaps you can respond there without making Casey wet himself each time.

Thanks to the responses from all... I have a better understanding of this issue as pertains to building rifles with larger-than-original case heads on Mausers, Enfields, etc.

WRT Pecos45, a thread that may be "silliness" and a non-issue to you may be interesting and useful to others. Fortunately, these forums are not simply for your convenience and enjoyment. I resent you implication that I am a 'troll' and suggest you look to your own behavior on this forum; beyond that I really don't care what you think of me.

Todd

Bolt Thrust (bolt trust would be a good pun)
Becomes important more than I used to think.

While this is anecdotale, it might be interesting

About 8 years ago, I wanted a contender in the worst way. I thought that a 35 rem barrel, 14", rechambered to 358, would be the perfect hogslayin gun. This is when I started talking to JD Jones, emailing bullberry, and talking with the gunsmiths at TC. They told me all about it, and, what my little mind could comprehend was, you have thrust against a defined area, that can break or pierce(!!!) a TC. Nice, so, I forgot about the TC in 358.

About the same time, I was reading ol' Parker's both on bolt thrust and the 30/30 improved. Seems that the same system can take a higher pressure (that I thought was the endall deamone of all guns) if the bolt thrust was decreased. Interesting, makes sense, but interesting. Seems that the "system" can be modified to placing it's energy in different ways/directions. Which explains, partly, why weatherby improved the 300HH and the guns's didnt blow up. See, Ole Roy used mauser actions to get started, right?

Whoever said, in this post, that if you stick to the "conventional" cases, you are fine, is perfectly correct. And I think that takes us up to the 470 capstick, the largest of the standard mag casehead rounds.
But, step into a 460 w, 500 anything, or 585, then you are going to be entering an arena that will require quite a bit more care and feeding than my 376 or 416 rem. I find these to be pretty useful, and interesting, to think about. I am just about convinced, however, that i am too much of a wussie(PC- that's a FANNY) to have one bigger than a 470 mbogo, and I would only load that to 470 NE or a tad better

As for fluted chambers rifles, this is actually only fluted necks. I have or have had or shot quite a bit,many semiauto battle guns The guns with a fluted chamber, even the tokarov/draganov that has a HUGE rim, are meant to decrease the size of the neck and push the case back, releasing some of the "grab". It's hard on cases, but these aren't designed for reloading. Turn the gas off, on those that you can, and you just have ugly necks, unejected, that will resize.

jeffe

What happens to the case when fired in the fluted chamber depends on pressure and case hardness.The P7 cases are usually just marked by the gases though I had Nyclads that were so soft that the brass acually flowed into the flutes. The Johnson auto in WWII used delayed blowback also and they used a waxed case ,not my choice especially for military.

Comments about the Johnson were from memory.That one used oiled pads. It was the Pederson that used that used waxed cases.

At the risk of getting into another cuss fight, which seems to rideing just under the surface here, I'll offer this.

The case thrust is only important when one is building a rifle on a particular action,used to decide what cartridge is best suited for that action. If, say, you are about to build, or re-chamber a double rifle, then case thrust is a VERY important thing to consider. With a Bolt action it is less important, but still is something to keep in mind. In the double the thrust may be a factor, even with standard loads, but it is only a real problem in a bolt action when useing very high pressure chamberings,or very over size rounds for the action, for the most part.

The action of a double is naturally springy, and is suceptable to damage with too much case thrust, both to set it off face,by bending the barr, and to cause a concave dent in the face behind the cartridge rear surface, where the steel is either too thin, or too soft for it.

Nickudu is right about the shape of the case, and it's surface, haveing as much or more to do with the actual thrust action, as the mathmatical surface area of the case butt. The simple mathmatical formula to determine the area of the case head, is only one thing to consider, and in, and of it's self is not definetive. Two very differently shaped cases with the same case head area, and chamber pressure will yeald different results, as PO Ackley found 50 years ago. Simply because the information is old, does in no way take away it's validity.

The thrust is a very short event, in time, when the cartridge is fired, and the case's ability to grab the chamber walls for this nanosecond of the event, makes a lot of difference, as to case thrust's actual effect on the face of either the bolt, or standing breech.

Folks, this is only opinion, and is not law, but has been beared out to my satisfaction, by some of the best firearms experimenters of all times, and my own experience, when adhearing to their reccomendations! I don't, for one minute, down play what those have found to the contrary!

I think on the other thing concerning suspected trolls, I'll simply say nobody here has shown me any evidence of being a GOD, so anything they or I say is open to debate, without all the cussing!

Just a thought!

MacD37,
Good points as to the practical reasons to be concerned with bolt thrust. I don't know if I agree with the tapered case statements, but what the hell.

Out of curiosity, have you ever seen a double rifle with a bent action bar?

Thanks for satisfying my curiosity MacD37. I take it since the bar has been bent that a double rifle, which has been "shot off the face" is junk? If not, how does one "fix" a double rifle, which has "shot off the face"?