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Bullet engraving Force study

In general it is interesting but (always the but) may not be relevant to the competitive shooting disciplines.

First up is most projectiles used in competitive shooting vary significantly from the two test projectiles. Different jacket alloys, different core alloys, different bearing surface lengths and thus different bearing surface areas, different jacket thickness. For the newer solid projectiles now entering the market different material/alloy and bearing surface length/surface area.

Regarding the bullet coating technique. Spray on moly isn't used a lot, impact plating is which results in a much more durable coating and the coating is less thick than a spray on coating. Other materials such as tungsten disulfide and hexagonal boron nitride may give different results from spray on or impact plated moly. Not a lot of competitive shooters use any of the coating methods but prefer to shoot bare projectiles. I noted though that moly coating was effective in reducing forces with the Barnes solid but am not aware of anyone using Barnes competitively. Use of coating did reduce pressure deviations which could result in lower ES and SD in muzzle velocity although single digit ES and SD are common with bare projectiles in competition rifles and loads.

The common leade (forcing cone) used in competition barrels is 1.5 degrees which has become pretty much the standard for competition as is seems to allow the projectile to more accurately align with thee bore. At any rate some year back the AMU determined the 1.5 degree leade was more accurate during the changeover from 30-06 to .308 in competition.

True polygonal barrels have been a wash in competition. There are hybrid rifling profiles such as canted rifling but these are less common. Typically "standard" rifling is seen although that may be cut rifled or button rifled. It may be 4, 5 or 6 groove. Of importance seems to be the land to groove ratio, more lands more pressure (bearing surface contact) but longer life as there is more material to resist flame erosion and vice versa.

While the testing is interesting and the results are more or less what one would expect, the sample size is very small. Bore fouling was not considered which might have been an influence after say 100 or more tests of a given combination.

Anyway, while an interesting read it didn't really challenge any commonly held beliefs amongst the competitive community. A couple of pundits would take the study to task for the limited sample size and state any resulting statistical analysis should not be considered definitive because of that.
 
I use danzac but not necessarily for friction reduction. It makes a significant difference in how often I need to clean, however..and that is the sole reason that I use it. I never clean until the end of a match with is typically 150-200 rounds. I have won multiple grand aggs after around 400 rounds down the pipe. This is Benchrest, too.

I do not find there to be significant pressure difference, naked vs. coated. In fact, I don't find significant tune changes either. I use a tuner though, and it's nothing to need to nudge it a mark from one day to the next, depending on conditions.
 
My take from it is that engraving Force and bullet “resistance” to travel have more variables than are known. I remember polygonal rifling being sold as “less defomative” to the bullet and, therefore, having less pressure permutations and potentially better accuracy. We found out pretty quickly that the better accuracy potential was pretty elusive. Moly, and other “anti-friction” coatings also are similar although these coatings still have their followers. I never bought into it...seen too much “snake oil” in my time perhaps.

At any rate, while the methodology here seems a bit suspect, these results indicate that throat geometry is more important than coatings in controlling bullet engraving and I was a bit surprised that the forces are so low. I was expecting engraving forces in the order of several thousand pounds. It turns out they are an order of magnitude less.
 
riflewoman said:
My take from it is that engraving Force and bullet “resistance” to travel have more variables than are known. I remember polygonal rifling being sold as “less defomative” to the bullet and, therefore, having less pressure permutations and potentially better accuracy. We found out pretty quickly that the better accuracy potential was pretty elusive. Moly, and other “anti-friction” coatings also are similar although these coatings still have their followers. I never bought into it...seen too much “snake oil” in my time perhaps.

At any rate, while the methodology here seems a bit suspect, these results indicate that throat geometry is more important than coatings in controlling bullet engraving and I was a bit surprised that the forces are so low. I was expecting engraving forces in the order of several thousand pounds. It turns out they are an order of magnitude less.
Click to expand...
One man's snake oil is another man's treasure. That's all I can say about it. Try it for fouling reduction, if nothing else...before ya knock it.

I've used it in about 20 or so barrels over the last ten or so years, and in multiple calibers/chamberings. The result has always been the same without fail, for me. YMMV but I'll keep doing what's working for me.

Note that I don't make any outlandish or even popular claims of velocity and accuracy increases. I have not seen either. I have seen very significant fouling reduction and that is all. That's all I need.
 
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I've used moly and found it useful in factory barrels. While the loads have not changed, nor has velocity it does cut back on fouling a bit and actually improves the first cold bore shot. I always pre-treat the bore with an oil moly mix running a couple of dry patches through to remove excess. I'm thinking of trying HBN simply because it isn't as messy to work with.

The thing with types of rifling is how much of the projectiles bearing surface is in actual contact with the barrel and how deep is the engagement meaning how much pressure is exerted. I can see the less compressible Barnes requiring a lot of force. Probably the reason Barnes started cutting relief rings on the bearing surface to decrease engraving pressure among other things

A lot of pretty sharp people have been working on small arms for a lot of years. Most modern firearm designs have been originally military in nature, and yet virtually all improvements in accuracy have been driven by the civilian community and not the military. Some guy (or gal) with a lot of experience sitting around thinking "what if". Old Parker Otto, Harry Pope, Phil Sharpe and the like.
 
Friction is a curious beast. Anytime it is involved the problems get to be extra exciting.

I believe Moly takes a little time to build up in a barrel. Did I miss the part where they "seasoned" the bore with moly?
 
I’ll have to look up the details because I can’t remember them off hand, but Harold Vaughn’s book contains a brief passage where he speculated that moly’s contribution was *not* due to anything to do with friction at all, but is a chemical/thermodynamic effect. (this is where my memory is fuzzy- I’ll see if I can find it in more detail if someone else doesn’t know).
 
damoncali said:
I’ll have to look up the details because I can’t remember them off hand, but Harold Vaughn’s book contains a brief passage where he speculated that moly’s contribution was *not* due to anything to do with friction at all, but is a chemical/thermodynamic effect. (this is where my memory is fuzzy- I’ll see if I can find it in more detail if someone else doesn’t know).
Click to expand...
Harold sprinkled powdered moly equal to that present on the base of the bullet and observed the same velocity drop as coated bullets.......
 
riflewoman said:
I was expecting engraving forces in the order of several thousand pounds. It turns out they are an order of magnitude less.
Click to expand...

Lead and copper are very malleable metals, which may account for the difference. Monolithics, or steel-jacketed bullets, probably would give higher numbers given equivalent profiles.
 
riflewoman said:
My take from it is that engraving Force and bullet “resistance” to travel have more variables than are known. I remember polygonal rifling being sold as “less defomative” to the bullet and, therefore, having less pressure permutations and potentially better accuracy. We found out pretty quickly that the better accuracy potential was pretty elusive. Moly, and other “anti-friction” coatings also are similar although these coatings still have their followers. I never bought into it...seen too much “snake oil” in my time perhaps.

At any rate, while the methodology here seems a bit suspect, these results indicate that throat geometry is more important than coatings in controlling bullet engraving and I was a bit surprised that the forces are so low. I was expecting engraving forces in the order of several thousand pounds. It turns out they are an order of magnitude less.
Click to expand...

It may be an issue of semantics, but I'm not sure the longitudinal force required to push the bullet into/through the lands is actually "engravement force", as opposed to an actual measure of the compression force required to engrave the bullet to a specific depth. Clearly, monolithic copper alloy bullets are much harder to compress than a traditional lead-core bullet. Because the copper alloys used in monolithic bullets can be very similar in composition to the copper alloys used in bullet jackets, I think it's safe to say the major difference in compressibility is due to the lead core material in the traditional bullet.

Regardless, I'm not sure what data in the article brought you to the conclusion the forces were an order of magnitude less [than thousands of pounds]. According to Fig. 13, the resistance pressure for an uncoated lead-core bullet peaks at about 27.5 MPa, or ~3990 psi, whereas the the solid copper projectile peaks out at approximately 100 MPa, or ~14,500 psi. The value obtained for the lead-core bullet is fairly consistent with the shot initiation pressure (factory preset) used by QuickLoad (3626 psi). So it seems to me from the article as though the forces are in the thousands of pounds (psi). Am I missing something? In any event, thank you for posting the article, it was a good read.
 
You’re welcome.

The force is given in Newton’s in Figure 12 on page 8. The pressure in MPa was derived from the force. In figure 12 the forces for the M80 bullet were around 1200-1300 N. At 4.45 N/lb that give about 350-400 pounds. The Uncoated Barnes had a peak push force of just under 5000 N or say 1000pounds. I was expecting 3000-4000 pounds for the ordinary bullet.
 
I still haven't had a chance to read this through, but for what it's worth, I have seen data that puts the engraving force in the hundreds of pounds range. Unfortunately, I cannot for the life of me remember where. And Greg's point as to the difference in "core" material (since solids don't ahve cores, exactly) makes a lot of sense. the piosson effect (lateral deflection due to a longitudinal force) would certainly be different. (...and complicated, as I'm guessing that lead plastically deforms a little, whereas I'm not sure about the copper - but the yield points and spring-back would be different even if both deform plastically).
 
Harold Vaughn (an engineer who knew when to convert to USEFUL information ;) ) used a figure of 600lb of actual force required to push a 270 bullet into the rifling lands using a setup with a push rod.
 
alinwa said:
Harold Vaughn (an engineer who knew when to convert to USEFUL information ;) ) used a figure of 600lb of actual force required to push a 270 bullet into the rifling lands using a setup with a push rod.
Click to expand...

Newtons are useful but like most SI units are either too small or too large to be meaningful.
 
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