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With out a doubt, this has been the single most educational thread I've started anywhere. ---------------------------------------------------------------------------------------------------- If the 270 won't do it the .338 will, if the 338 won't I can't afford the hunt! | |||
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Proving that boattail bullets cause more wear/erosion at any point in a rifle barrel is a non-starter. There are studies that show that flat base bullets were more detrimental to barrel life than boattails and vice versa. So we cannot look to those for a conclusion. In most cases, those conclusions were secondary observations, because the object of the study was another aspect of the ballistic subject and not wear/erosion caused by a particular style of bullet. I do not pretend to have mastered the subject but engineers who deal with gas and fluid dynamics and internal ballistics have given some input: 1. The boundary layer in a rifle barrel (ahead of the chamber) cannot be laminar. It is always turbulent, regardless of the style of projectile afterbody. In the powder chamber or artillery case, this may be different but, we are dealing with a different set of circumstances (rate of fire, pressure levels) with shoulder fired small arms and differences are unproven and probably insignificant. 2. The boundary layer ahead of the chamber and behind the projectile varies in depth from 30 micron to zero. This means that the style of the bullet base can only influence the characteristics of the boundary layer if the base radius approaches two or three times the boundary layer depth. All bullets with a base radius of 90 micron or more will therefore have the same influence on the boundary layer in the barrel and that is pretty much all bullets, flat base and boattail. 3. Gas flow is stationery relative to the accelerating bullet afterbody, unless the bullet is under size for the barrel and gas flows over the afterbody to escape past the shank. 4. In such a case, the highest temperatures that are atributable to turbulent flow, actually occur on the bullet base and not on the barrel wall. With a boattail having more surface area, to absorb and transfer heat than a flat base, an argument can be made that boattails are better in this regard. It cannot be proved in practise and remains theory. If there is a difference, it would be insignificant as it would dissapear in the magnitude of erosion that occurs with gas leakage past the bullet. 5. Flow over a curved surface reduces boundary layer thickness and becomes turbulent in high pressure areas. See the illustration below of supersonic gas flow over a sphere.  6. All bullets allow gas leakage, from the point when the bullet is released from the case neck, to the point where the barrel is completely sealed. If a monometal or solid shank bullet is under size, it never seals the barrel and gas continues to leak past the shank. 7. With boattail bullets, the highest level of heat transfer, due to turbulent flow over the bowed surface, is not at the circumference of the bullet, but mid way along the boattail. With flat base bullets, the same flow occurs except that the cooler area in the center is larger and the base radius acts as the bowed surface. 8. Properly designed drive band bullets are the quickest to seal gas leakage, of all bullet types and, therefore, allows the least gas leakage. As gas leakage is the greatest contributor to throat erosion, the conclusion is obvious. Alf,
Can you elaborate on this because all the information we see shows that, with a boattail projectile, more heat is transferred to the projectile and not to the barrel once gas leakage is halted. Does your example not refer heat transfer to the chamber as the projectile starts to move? The distinction is made that, while gas leaks past the projectile, as it comes into motion, a smooth or grooved projectile may allow more or less leakage, depending on the afterbody shape. Either way a drive band bullet, of the correct dimensions, will halt leakage earlier than any style of standard or grooved bullet. Bottom line: It is not provable that either the use of boattail or flat base bullets (in the rifles we use for sport and hunting) promote erosion. There is a difference between barel wear/erosion with drive band bullets and other bullets. Barrels last longer with drive band bullet use. | |||
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ALF - thanks for the information. Question: How do these findings apply to powders like the "high-energy" (500-series) VV powders out there now? Should we avoid them for loading ammo that is fired a lot? "Bitte, trinks du nicht das Wasser. Dahin haben die Kuhen gesheissen." | |||
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Thanks Alf I look forward to learning more about the subject. Chris, Not much has changed, I see. You still take facts out of context, attribute stuff to me that I have not said and the agenda is still alive and well. Here is what I said regarding bullets touching the rifling: Start load development with the bullet touching the rifling if throat, magazine box and case dimensions will allow it. HV and FN bullets do not raise pressure levels like jacketed lead and standard and grooved monometal bullets do, when seated against the rifling. After that comes: Once the desired speed is achieved, then tune the accuracy of the grouping by experimenting with overall cartridge length. So I do not give a blanket recommendation to seat bullets against the rifling as you imply. My remark was in the context of new load development. Your irrational zeal to find fault with GSC product is showing again. Pressure inside a closed system is transmitted equally to all surfaces exposed to that pressure, so there are no high pressure wedges in the corners anywhere. If there were, it would still be equal for a flat base and a boattail bullet because all flat base bullets have base radii. If there were strange high and low spots of pressure in different places in the barrel and chamber, how would we reliably measure chamber pressure? I think I know what kind of wedgie is worrying you and it is quite suitable. | |||
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I read some years ago about the substantial difference in burning temperature between single en double based powders. Just to be on the safe side, I stopped loading rifle ammo with double based powders. | |||
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Gerard, Your paranoia shows again. I am not taking anything out of context nor did I criticize. The fact that your bullets can be seated to touch the rifling is rather a compliment than a bad thing as it cannot be done with other monolithics without pushing up the pressure. You just want to see the bad. We know that your bullets have a lower engraving force by virtue of the driving band design. And normally the closer to the lands the more accurate the bullet is. So there are 2 plusses for you. We all know that we can play around with seating depth; nothing new to that and so there is no blanket statement. Your silly statement of .... "Your irrational zeal to find fault with GSC product is showing again" is hereby rejected with the contempt it deserves. Your product is well designed and innovative - I said that a thousand times. All we debate here is some aspect of the base end if there is any real evidence to prove the one condition over the other in terms of throat erosion; that is all. You are way too sensitive. We are here to share info, and that was all that Alf did. And by asking questions we learn from each other, as we can see the conflicting articles and so-called tests that were done. My question was ... "Also what about the propellant gas and unburnt particles that attempt to pass the bullet which gets wedged in the corners that the boatail form with the barrel - is there not an erosion effect?" In other words I want to know about the abrasive effect of particles slamming into the corners, as they are blown out of the case much faster than what the bullet is moving, and that means they must be halted somewhere. That is all. There is no need to start name-calling or to make derogatory remarks. On a more positive note, it would be informative to explain to us how your bulllet seals the bore better or quicker than say a lead-core bullet, like a Nosler Partition and how you determined it. Warrior | |||
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This is the confusion that exists, and we are trying to unravel it, as poor mortals !!! Will we ever be able to to fully understand or is it going to be shrouded in a cloud of darkness till doomsday? Warrior | |||
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Thank you Alf, for a clear statement. Chris/Warrior/Truvelloshooter This is a direct reference by you, to the discussion of boattail v flat base of September last year. You made a number of mistakes then and now you call the references I gave "tests" in a derogatory manner. Your animosity in that thread was clear, so do not pretend now you meant no ill. You must think we are stupid. You follow this with a photo of a GSC drive band bullet. There have been very few discussions around the fact that boattails are used to manipulate cg position and I have participated in most of them. You were not involved, because you were too busy getting yourself banned from AR with your comments on the political forum, but it is clear that now you are trying to scare up imaginary problems with GSC products again. Do not try to play the innocent, aggrieved role, you are much too transparent. I have no doubt that the confusion you suffer on this subject will persevere. You will try to discuss this topic for the next 5 years, without approaching a conclusion or gaining any understanding, as you have done with the bullet length/twist rate thing for the past 5 years. You are happy when you can argue for the sake of arguing. Leave me and GSC out of your dishonest, uninformed, argumentative discussions, until such time as you have grown up into a rational human being, without an axe to grind. Hell will freeze over before that happens, I am sure. | |||
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Gerard, This is basically in line with the question I have asked, and it seems to share the feeling I had all along. I also hinted that there should be a question of degree for boatial bullets with different dimensions and design. Only by intelligent probing can we get to know more about the subject. And sometimes new information comes to hand and we have to change our views. Science is full of this. Alf shares with us in his above post how opinions changed over time and most interesting the experiment with the stepped boatail so as to overcome some of the inherit negatives. I have referred not only to your bullet, but also to the other bullet that I published alongside your bullet - I guess you have not noticed that in your blind rage. Your bullet just features a much longer and rounded boatail than the other bullet, and as such, makes for a good illustration. Both bullets were just to represent that genre of bullet. It is the principle involved here Gerard, if you can just undertand that, and not one particular bullet. Amazing that you cannot see your derogatory remarks, and that is normally so in a severe case of paranoia, which is perhaps beyond your control. Whilst I have explained 2 virtues of your bullet just in this context, and there are more, you missed the opportunity to share with us a 3 rd potential virtue, which has to do with your claim that your bullet seals the bore quicker. Instead we have to listen to your rantings that carries no information nor any value. If your bullet indeed minimizes gas leakage, I will be the first one to praise you for that. You just need to explain to us the logic, and how you came to that conclusion, and by what method. Please could you do that for us. Warrior "If we don't change, we don't grow. If we don't grow, we aren't really living" ... Gail Sheehy, Amercian author. | |||
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Whether large-bore or small bore the principle should be the same, if it has to have universal truth. Perhaps just more noticeable where powder quantities are higer. Warrior | |||
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This was indeed my concern, as it seems to be so obvious that it will cause erosion to the throat area of the barrel that gets hotter and hotter after each shot, aiding the erosion process with its abbrasive shot blasting effect. Warrior | |||
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Yes, this is a fascinating thread. Wayfareing Stranger, congrats on starting it. Has anyone brought up [b]ball powder vs. stick powder vs. stick powder[b/]? I’ve heard there it could be relevant. There must be some reason why militaries often use ball powder (in addition to it being, as I understand it, cheaper to produce). | |||
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I agree that there is a lot of great info in here, thanks to both Gerard and ALF for their patience with those of us who are new to this subject, the pair of you should get together and write a primer on the subject to be posted as a sticky. Also thanks to them for explaining this in simple terms for me as I can see that the hard sums to model this are going to be very hard indeed. | |||
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Alf, I have been revisiting some literature on this subject and, from Lloyd Brownell's "Pressure Factors", the conclusion is that gas leaks past the bullet until the bullet obturates the bore. With jacketed lead, this is normally at the point where the bullet has expanded sufficiently, or is of sufficient size to start with, in circumference, and has proceeded far enough past the leade to effect a seal. Although Brownell did not work with anything other than jacketed lead bullets, when we look at recovered bullets under magnification, it shows that under size solid shank and mono metal bullets do not obturate the barrel, because the surface finish that existed before firing, is unchanged upon recovery. There is no evidence of friction/contact between the bullet and barrel groove bottoms. Gas therefore leaks past such bullets for the entire time the bullet spends in the barrel. See the example below.  This brings up the following question: In the statement below, mention is made of the jetting of gas along the boattail. "The arguement surrounding this theory is claimed to be the jetting of gas along the tapered rear of the bullet allowing the gas to concentrate at the point where the rifling cuts the tapered boat tail of the projectile leading to a concentration of heat and thus erosion." Gas can only flow over (jet along) the boattail, if it is also flowing over the length of the shaft and passing the bullet. The moment the bullet seals the bore, gas stops flowing and, the only change that can happen, is the increase in pressure that drives the bullet. An increase in pressure acts on all exposed surfaces equally and there can be no difference in heat transfer to the barrel wall, between a flat base and a boattail, except if we turn to what we know of internal combustion engines. In cylinder head combustion chambers, protruding edges are avoided because they heat to the point where they glow and cause detonation. Similarly, sharply recessed corners are avoided because they are known to be cooler than surrounding flat and curved surfaces. This brings us back to the fact that a boattail bullet absorbs more heat from the combustion process than a flat base and would form a deeper recessed corner between bullet and barrel, than a flat base bullet. This suggests that boattails would cause the barrel wall to run cooler but, if anyone can prove this in testing, I would like to see it. Transfer of heat, through conduction into the bullet material or the barrel steel, is just not fast enough to allow a meaningful difference to develop, in the time the bullet spends in the barrel. I think that the following statements can be made with a fair amount of confidence: 1. There is no difference in barrel wear/erosion between different bullet afterbody designs alone. 2. Under size, jacketed bullets will result in more wear/erosion than correctly sized bullets, because they obturate the barrel at a later point. 3. Under size, solid shank and monometal bullets will result in the most wear/erosion because they never obturate the barrel. 4. The quicker a bullet seals the barrel, the better. Of course the original comment I made would also still be true: "To address the original question: Yes, "magnum" caliber barrels have a shorter life span than slower calibers but magnums can be made to last longer, with the right choices, than slower calibers with the wrong choices." | |||
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Gerard: I do not believe there is a system out there in our current ballisitics setup that has the ability to totally obturate the barrel and completely negate gas blow by.  Gases escape via rifling groves , prior to the projectiles exit . Expanding gases are far faster then any projectile . Interesting Info posted by " El Deguello " . a 30-06 was completely shot out at 2000 rounds using propellant with a 30% nitroglyserine content and about 4000 rounds using 20% nitroglyserine, using nitrosellulose the accurate bore lifetime was increased to 12,000 -15,000 rounds the same as the Mauser 8mm using German nitrosellulose flake powder. When in liquid state Nitroglycerine is Highly Acidic however when converted to nitrocellulose or Gun cotton I E gun powder it's far less acidic ; although it's still acidic . Flame temp coupled with high acidic values equals Chamber & barrel erosion . Elementary Chemistry fellow shooters . Shoot Straight Know Your Target . ...  | |||
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...Elementary Chemistry fellow shooters... Well if it's so elementary, could you explain to me why so much of the military ammo uses double-based ball powder? That's not a snotty comment; I'm genuously curious. Thanks. | |||
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I'm not sure as to the question your asking . Here is the best reasoning I can give . Military are in the business of extermination not the loss of their own . Hopefully below answers some of your questions . Nitrocellulose deteriorates with time, yielding acidic byproducts. Those byproducts catalyze the further deterioration, increasing its rate. The released heat, in case of bulk storage of the powder, or too large blocks of solid propellant, can cause self-ignition of the material. Single-base nitrocellulose propellants are most susceptible to degradation; double-base and triple-base propellants tend to deteriorate more slowly. To neutralize the decomposition products, which could otherwise cause corrosion of metals of the cartridges and gun barrels, calcium carbonate is added to some formulations. To prevent buildup of the deterioration products, stabilizers are added. 2-nitrodiphenylamine is one of the most common stabilizers used. Others are 4-nitrodiphenylamine, N-nitrosodiphenylamine, N-methyl-p-nitroaniline, and diphenylamine. The stabilizers are added in the amount of 0.5-2% of the total amount of the formulation; higher amounts tend to degrade its ballistic properties. The amount of the stabilizer is depleted with time. Propellants in storage should be periodically tested on the remaining amount of stabilizer, as its depletion may lead to autoignition of the propellant. Smokeless powder burns only on the surfaces of the granules, flakes or cylinders - described as granules for short. Larger granules burn more slowly, and the burn rate is further controlled by flame-deterrent coatings which retard burning slightly. The intent is to regulate the burn rate so that a more or less constant pressure is exerted on the propelled projectile as long as it is in the barrel so as to obtain the highest velocity. Cannon powder has the largest granules, up to thumb-sized cylinders with seven perforations (one central and the other six in a circle halfway to the outside of the cylinder's end faces). The perforations stabilize the burn rate because as the outside burns inward (thus shrinking the burning surface area) the inside is burning outward (thus increasing the burning surface area, but faster, so as to fill up the increasing volume of barrel presented by the departing projectile). Fast-burning pistol powders are made by extruding shapes with more area such as flakes or by flattening the spherical granules. Drying is usually performed under a vacuum. The solvents are condensed and recycled. The granules are also coated with graphite to prevent static electricity sparks from causing undesired ignitions. # Propellants: * Nitrocellulose, an energetic component of most smokeless propellants * Nitroglycerin, an energetic component of double-base and triple-base formulations * Nitroguanidine, a component of triple-base formulations # Wear reduction additives, to lower the wear of the gun barrel liners USA 16"/50 (40.6 cm) Mark 7 * Wax * Talc * Titanium dioxide * Polyurethane jackets over the powder bags, in large guns # Other additives * Graphite, a lubricant to cover the grains and prevent them from sticking together, and to dissipate static electricity * Calcium carbonate, to neutralize acidic decomposition products Shoot Straight Know Your Target . ... | |||
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So does weatherby Freebore thier rifles to extend barrel life? ---------------------------------------------------------------------------------------------------- If the 270 won't do it the .338 will, if the 338 won't I can't afford the hunt! | |||
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Dr. K, To resurect this thread, are you saying that the military's primary purpose for using double-based powders is that they are more stable in long-term storage? | |||
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