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Quote:No disrespect taken, it's just a nice discussion...Ackley did another experiment that you'd love... "To further prove the point, the locking lug was removed from the action entirely leaving the breech block or bolt with no means of support other than the finger lever...The rifle was fired several times with the barrel tight. All cases appeared to be normal except for excessive primer protrusion...but the test described seem to indicate that a very small percentage of the CHAMBER pressure was trasferred to the breech face in the form of thrust. In this test the barrel absorbed the pressure while the action merely furnished the means for detonating the cartridge except when the chamber was oily." He also goes on to show an example of a M94 that was accidentally blown up due to a double charge of Unique. "The action was not damaged except for the threads being expanded when the chamber section of the barrel split. The barrel separated completely just forward of the chamber...This shows how the high pressure could not be contained by the barrel, but the relatively straight standard .30/30 case did not back up against the breech bolt enough to harm any of the action parts..." Quote:Your statement proves nothing about the pressures being uniform all around a brass case. All it shows is that some folk found that the the inelastic expansion of the case web somewhat correlated to an overpressure or imminent overpressure situation. Plus you're still measuring the web radially which shows nothing about pressure in the axial (backthrust) direction. Bobby, I'm guessing that you're viewing the uniformity of pressures in a static condition where there's been time for pressure to equalize within the vessel. Not the case in a cartridge case even discounting case/chamber wall adhesion. Here's an excerpt from some e-mail correspondence I had with Dan Lilja (who IIRC is an Engineer with the PE designation) we had a few years back (which I amazingly kept!) The context of the correspondence was concerns about Moly getting in the chamber and causing lug battering. "...case grip can have a very pronounced effect. But it can also vary greatly due to the condition of the brass, lubrication, chamber wall surface finish, etc. Some weak rifles, such as a Win model 94, will show primers backed out of the case with fairly stiff loads. The reason being the breach block is springing back as the pressures move the primer out. The case stays stuck to the chamber walls while the primer moves outward. Chamber wall adhesion is the reason why. With milder loads the block is strong enough to resist the primer...The tensile strength of brass does not really enter into this." | ||
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Quote: You're very welcome. I've always felt that the answers to questions we have are often times out there. The works often been done (sometimes inaccessible since they're done by the US Gov't Arsenals) and we just need to find them...sometimes we need to string together several works to get what we're looking for, or sometimes we have to adapt old methodology to our specific situation to get to where we want. Here's another bit you might find interesting, from Harold Vaughn's "Rifle Accuracy Facts". In calibrating his strain gage barrel, Vaughn found that at 12,000 psi, "the case expanded so that it was in contact with the chamber" (consistent with his Lame's equation calculation). "Lames equation can be used to show that a pressure of 12,000 psi is required to expand the head region of the case so that it is in hard contact with the inner wall of the chamber." In this case, Vaughn was referring to a 270 case being fired in his Remington 721 test bed. I'm sorry I can't make a recommendation regarding your specific situation. I'm not a wildcatter and I can only arm you with what I feel is credible information on what's been done and found in the past. My shooting is fairly mundane with the bulk of it in Service Rifle competition. Load work up and pressure testing of bleeding edge AR loads is about as crazy as I'll get. | |||
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Ricochet, You asked, "Huh? Why would you think having the case head "slam into the bolt face" would stop the case from expanding? The case will expand in all directions." Of course, it would not stop it from expanding. You misunderstood me or I did not communicate clearly. Would you all agree that the pressure produced by a factory round would be less in an ackley improved chamber since there is additional surface area in the chamber? I don't want the pressures to exceed 45k PSI in my M336. Max pressure for the .307 is 52k CUP. But I want the convenience of firing factory ammo in my rifle sometimes. This is why I considered the ackley improved chamber--to increase chamber surface area, thereby reducing the pressure produced by the factory loads. I just don't know if the increase in surface area inside the chamber will lower the pressure enough to get me down below my 45k PSI max. FYI: I have no intention of firing 'hot' handloads in this rifle. I didn't mean to open up such a can of worms. Thanks for all of the input, folks. | |||
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I have always loved that passage from Ackley where he held the breech closed with his fingers. It is interesting but misleading in two ways: 1) The breech face being locked would have stopped the brass' elastic stretch, and the locking mechanism could get beat up. 2) The angle of the taper in an Ackley cartridge has almost no effect on gripping the walls of the chamber: my Ackley taper effect on friction calculation After having overloaded 100 guns in 40 cartridges just to see what happens, I have seldom had a problem with breech face support. One exception was a Colt Agent Aluminum framed 38 special with steel cylinder. I went 2 gr. past the 357 mag max load for Blue Dot a 110 gr., and the frame bent. It still shoots, but is shows that the chamber, brass, or primer are not always the first to go. Bolt thrust is real, but not a big deal. -- A society that teaches evolution as fact will breed a generation of atheists that will destroy the society. It is Darwinian. | |||
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The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Re: Breech/Bolt thrust during fireforming
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