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Whats the real juice on how thin you can have the wall thickness of a barrel, The Winchester pre64Fw came in .358win, I also see a re-bored ClassicFW 35Whelen on Gunbroker, from memory ClassicFw rifles have about a .565"@22" muzzle dia. So whats the true mimimum wall thickness one can have? | ||
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[(a² x P)/(b² - a²)] x [1 + (b²/r²)] You'll need to supply material condition and known internal pressure and then calculate the safety factor. | |||
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But what do the letters represent? Formula is useless without them. John Farner If you haven't, please join the NRA! | |||
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If you are talking about wall thicknesses at the muzzle, then for your example above, .1035 should be sufficient. I personally don't feel comfortable with wall thickness below .100 at the muzzle. _______________________________________________________________________________ This is my rifle, there are many like it but this one is mine. My rifle is my best friend, it is my life. | |||
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The general number I hear on this forum is .100, which makes sense for single barrel rifle for balance and accuracy. As far as safety is concerned, a lot of doubles are substantially thinner for better balance. For example, my little Italian O/U 30-06 tapers to .470 about half way down the 26" barrels and finishes at the muzzle at .450 (.4450 for the bottom barrel) for .071 wall at the muzzle. "Experience" is the only class you take where the exam comes before the lesson. | |||
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Pressure decreases the further away from the chamber you get. You have to specify thickness at which point along the barrel. I'm with Malm, I set .100" as a practical limit at the MUZZLE. Obviously the barrel wall needs to be thicker the further from the muzzle you get.  Aut vincere aut mori | |||
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I guess peak pressure drops off very fast because the taper after the chamber is very abrupt and .470 at 13 inches is still only .081 wall. "Experience" is the only class you take where the exam comes before the lesson. | |||
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I wouldn't want to bounce anything less that .100 off a rock.  _______________________________________________________________________________ This is my rifle, there are many like it but this one is mine. My rifle is my best friend, it is my life. | |||
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I don't know how precisely Quickload calculates muzzle pressure but it shows 9100 psi at 22" and a whopping 17,100 at 13". Now I'm gonna flinch like Barney Fife every time I shoot the damn thing. Too much information! "Experience" is the only class you take where the exam comes before the lesson. | |||
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No wonder I am still reasonably functional given the number of times my head has bounced off a rock Mike Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue.  What I have learned on AR, since 2001: 1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken. 2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps. 3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges. 4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down. 5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine. 6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle. 7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions. 8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA. 9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not. 10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact. 11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores. 12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence. 13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances. | |||
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some time ago Ruger made a run of 20" barrels that were made from heat treated steel and were extremely light.....I don't remember the wall thickness at the muzzle but maybe if someone here has one he might measure it and report. I believe they called it an "ultralite" and were unbelievably thin! /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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Ackley's old rule-of-thumb was at least 0.125" at the chamber and a few inches further out, tapering smoothly from there. However that was back when factory cartridges were generally below 50K psi and even then I believe it's too thin. I feel fine with 0.175" at the chamber & a few inches further out and with a smooth taper from there, IF the barrel is good tough modern steel of known origin and proper composition & heat-treat. As pointed out, less than 0.080" is very dentable; a dent in a shotgun barrel is one thing but a significant dent in a rifle barrel could become quite interesting quite quickly. How thin are the old Winchester lever rifle Extra Light Weight Carbines? I've had a couple of '86 45-70s that seemed paper-thin at the muzzle, especially after touching off a 500-gr load! Regards, Joe __________________________ You can lead a human to logic but you can't make him think. NRA Life since 1976. God bless America! | |||
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Thought it was obvious... A = internal radius (inches) B = external radius (inches) P = pressure (PSI) Compare the result with your material strength to get a SF. Unless you have some sort of formula which models pressure/time/distance in the bore you'll need to supply measured pressures. | |||
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Tig, did they specify that you can fire modern factory high pressure rounds through your U/O .30-06 ??
I had a tang 77.308win ultralite with 20"bl, it measured about .550" at the muzzle. | |||
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Macifej, Ok, say one has a rifle with modern steel in the barrel and one intends to load to modern high pressures of 63kpsi,...can one safely do so in that rebored classicM70fw 35whelen?, .... could one bore such a modern fw barrel to 9,3 or .375/06 and still be oK at 63kpsi? | |||
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The strength of the tube is one thing, what about the elasticity! A thin barrel will expand behind the bullet by an alarming amount! This probably won't matter much with a free-floated barrel but what does it do to accuracy? How would it effect barrel harmonics? Regards 303Guy | |||
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The take-off barrel from my tang ultralight 308 measures .495" at the muzzle. The barrel on my tang 35 Whelen measures .560" at the muzzle. Cliff LaBounty rebored a few rifles for me and he too used the .10" a side rule. | |||
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Understand your question but not enough information. You need to know the material strength of the barrel. This could be 90,000 PSI or it could be 130,000 PSI. I have no isdea what Winchester used on an M70 back in the day. You need to know the pressure curve for the particular cartridge/load etc you plan to shoot in your rebore. You need to know the precise ID (groove diameter) and OD of the barrel at the location where you wanna do the calculation. You could make some assumptions about material strength and work backwards from the current bore. Calculate the value of material being removed in the rebore but this would be just that - an assumption. My advise - find a rifle or barrel in production that has a similar profile in a similar chambering and duplicate the dimensions. The other thing to consider is that removing that little bit of material at the end of your barrel isn't going to save much weight (a few ounces maybe) but will have a dramatic effect on safety factor. Personally, I would not spend the money to rebore any barrel. New barrels are very inexpensive and readily available. | |||
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F.Y. John Farner If you haven't, please join the NRA! | |||
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Did I miss something...?? | |||
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Yes, it does and it was proofed in Europe so I have no reason to feel there is a problem however, it obviously won't take the same abuse a heavier wall barrel can take. OTOH, the fully soldered ribbing on both sides adds a significant amount of stiffness to what would otherwise be a whippy and likely inaccurate single barrel. I am in no way suggesting because I have a double rifle with barrels this thin that it would be a good idea on a bolt or other single barrel gun.  "Experience" is the only class you take where the exam comes before the lesson. | |||
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Funny; I thought it was obvious. John Farner If you haven't, please join the NRA! | |||
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| One of Us |
Many double rifle barrels are around .080" at the muzzle. And the rifle barrels on Drillings seem even less. Something else to consider is whether it is a cut rifled barrel or button rifled. I've been told by barrel makers that with button rifling you run the risk of the bore diameter expanding when turning wall thicknesses of less than .125" | |||
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From a Google search I find my own post 7 years ago:
I have tried to blow up allot of guns. If one takes the RC hardness of the barrel, the yield strength based on that, and then puts the kind of pressure one would calculate would cause the gun to fail...the gun does not fail. It always takes more than calculated to wreck a gun. It may be that the one mili second of stress gets into a dynamic that has a different yield point. Pistols have chamber walls 0.1" thick, and I push the loads until the primer falls out. At the muzzle, rifles have dropped the max chamber pressure of 70 kpsi down to 10 kpsi when the bullet goes by, and the duration at the muzzle is even shorter. The only muzzle I wrecked was a .385" choke in 410 shot gun with .452" jacketed 230 gr bullet pushed with 45.5 gr H110 and 7.62x54R brass. | |||
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I love your posts, Clark- flaco | |||
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Jason "You're not hard-core, unless you live hard-core." _______________________ Hunting in Africa is an adventure. The number of variables involved preclude the possibility of a perfect hunt. Some problems will arise. How you decide to handle them will determine how much you enjoy your hunt. Just tell yourself, "it's all part of the adventure." Remember, if Robert Ruark had gotten upset every time problems with Harry Selby's flat bed truck delayed the safari, Horn of the Hunter would have read like an indictment of Selby. But Ruark rolled with the punches, poured some gin, and enjoyed the adventure. -Jason Brown | |||
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This is why larger guns ie cannon, have sleaved barrel construction. A thick walled cannon barrel would split near the breach if it were made in one piece due to surface hoop stressing. There must be a graphic description of it on the net somewhere. Regards 303Guy | |||
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I think cannon barrels were sleaved for lack of equipment capable of processing the large tube with precision. Older cannon were cast. More material in the breach area does not increase hoop stress. | |||
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Actually, it does. The idea of the sleaved barrel is that there is a stress between the sleeves. When a barrel is put inder internal pressure, the inner surface is subject to compressive stress which causes it to expand outward. This expansion causes the outer surface to expand circumferentially, so the nature of the stresses change characteristics. If I can find a graphic description, I will post it or give a reference. It's not a simple principle. Even if I still had my text books, it would take a lot of typing and it's like a foreign language!  Regards 303Guy | |||
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Why don't you scroll up to the top of this page and look at the second post..?? That, my friend is the fomula for calculating hoop stress. See if you can get it to show you an increase in pressure or an increase in stress with an increase in material thickness... | |||
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Mmmmm.... It's not quite that simple. That formula only applies to thin walled cylinders. I have been trying to download and post something from the 'net. This is a basic 'text' copy without the diagrams and fonts to go with it. Try this link; http://www.engineeringtoolbox....lled-tube-d_949.html "Stress in Thick-Walled Tubes or Cylinders". Stress in Axial Direction The stress in axial direction at a point in the tube or cylinder wall can be expressed as: σa = (pi ri2 - po ro2 )/(ro2 - ri2) (1) where σa = stress in axial direction (MPa, psi) pi = internal pressure in the tube or cylinder (MPa, psi) po = external pressure in the tube or cylinder (MPa, psi) ri = internal radius of tube or cylinder (mm, in) ro = external radius of tube or cylinder (mm, in) Stress in Circumferential Direction - Hoop Stress The stress in circumferential direction at a point in the tube or cylinder wall can be expressed as: σc = [(pi ri2 - po ro2) / (ro2 - ri2)] - [ri2 ro2 (po - pi) / r2 (ro2 - ri2)] (2) where σc = stress in circumferential direction (MPa, psi) r = radius to point in tube or cylinder wall (mm, in) maximum stress when r = ro (outside pipe or cylinder) Stress in Radial Direction The stress in tangential direction at a point in the tube or cylinder wall can be expressed as: σr = [(pi ri2 - po ro2) / (ro2 - ri2)] + [ri2 ro2 (po - pi) / r2 (ro2 - ri2)] (3) maximum stress when r = ri (inside pipe or cylinder) Trying to understand all this can be fun but can also drive one insane! Hey, I had to write exams on all this! Hoo boy!  Try Mohr's stress circle! (I passed!)  I still haven't found the graphic explanation I am looking for. It must be out there, somewhere.  Regards 303Guy | |||
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Your long ass formulas say the same thing as the simplified version I posted above..... My clarification of your point was only that Hoop Stress decreases with an increase in material thickness - not the inverse. But then the formula just proves what we all know. Fat barrels are stronger than skinny barrels. Here's a graphical calculator or two without the formulas to back them up. Pipe Strength Circumferential Shells Under Internal Pressure | |||
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Aah... yes, that's accepted!  I was hoping to find something to illustrate what I meant by 'sleaved' barrels for strength as opposed to "sleaved for lack of equipment capable of processing the large tube with precision" which no doubt also came into it - although I did not know about that one.It's frustrating when one wants to utilize this wonderful world of information called the 'net, only to to find a total absence of 'knowledgeable' substance! (Taken from "Antiquated Mother Hubbard who preambulated to her inner storage cavity to obtain for her canine quadruped, an ossified fragment , only find upon making an optical observation that the inner storage cavity was predominated by a total absence of edible substance!") Hee hee.Regards 303Guy | |||
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The last sleaved barrels produced that I know of were installed in the Iowa class BB's. If you look at all modern high pressure tubes they're once piece forgings. Of course the're quite a bit smaller too... | |||
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I remeber those 'sleaved' tubes. Rifled 'pellet gun' barrels were made the same way with a brass bore. The reason for the sleaved construction of the cannon barrel is that the compressive loading in the bore deminishes toward the outside where tensile hoop stresses are set up so to increase the strength for weight, the outer sleave is shrunk on to preload the inner sleave. The shrink fit interference is quite heavy! But this is a large gun - the G5 and G6 (same gun, different carriage). This barrel is sleaved the whole length. It may or may not have a third breach end sleave. I know I had to do a three sleave calculation for my exam! Whew! Anyway, nobody is going to sleave a rifle barrel for strength. Regards 303Guy | |||
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I will, when I splice my two 7mm barrels to get a 40 incher (out of boredom). | |||
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