Should I Moly my bullets ?

[Berger.Fan222]

Pressure is reduced due to friction being reduced.

And where can the actual direct measurements of lower pressure be found?

I've heard the claim repeated many times, but no one has linked or cited the actual pressure data.

 

[JRS]

And where can the actual direct measurements of lower pressure be found?

I've heard the claim repeated many times, but no one has linked or cited the actual pressure data.

Possibly by contacting the companies that perform the testing. Not everyone has access to that type of equipment. When I was coating my bullets, I always had to increase the powder charge when using the coated bullets, to achieve the velocity the naked bullets exhibited. Those slick little buggers reduce friction.

 

[mikecr]

Well for sure friction change is the least benefiting of coatings for bolt action firearms, with rational load/twist/bullet combinations (for most shooters). Where friction reduction is needed to help out a broken situation (bullet blow-ups), then it's reasonable that bullet coatings may not help as much as some might think. If that's what the USAF concluded(I don't have the report), I can believe that.
But:
Friction reduction does not help barrel life, as barrels do not 'wear out'.
Friction reduction does not reduce pressure, as any failed test of the idea proves.
Moly reduces pressure only through latent heat of evaporation, and not friction. This can extend throat life a bit.
WS2 has a lower friction coefficient than Molybdenum Disulfide, and does not change pressure or MV one bit. This, blowing any 'friction reduction' benefit out of the water. It never was a benefit of coatings.

I already know and rely on other benefits of coatings -for my situations.
No expert, but I've observed coating results for quite a while.
I've personally been using WS2 in dry prefouling and bullet coating for over 30yrs.
Over the past 40yrs in reloading, I've watched use of other coatings, and seen success and failure with every one.

The notions with coatings here remind me of the standard default for barrel length discussions and testing. It always seems to land on muzzle velocity as the only potential in question.. Zero consideration or testing otherwise.
It's like the conclusions about one cartridge over another -purely because one can generate higher MV. Like nothing else matters..

 

[JRS]

Friction, or the lack of, reduces, or increases, pressure. It really is quite simple. Is the friction on a bullet the same between a .236 bore diameter and a .237 bore diameter? Which creates more pressure? The larger, or the smaller? I was using hBN, formulated by ROBAR for 2 years prior to David Tubb advocating the use of hBN. The proof is in the pudding!

 

[mikecr]

Friction, or the lack of, reduces, or increases, pressure. It really is quite simple. Is the friction on a bullet the same between a .236 bore diameter and a .237 bore diameter? Which creates more pressure? The larger, or the smaller? I was using hBN, formulated by ROBAR for 2 years prior to David Tubb advocating the use of hBN. The proof is in the pudding!

In this scenario the friction on a given bullet is higher slightly,, or greatly.
Pressure here is not really quite simple. Different bore areas present different confinement to expanding gasses(expansion ratio), which is independent of friction. By the time you increase interference fit of a bullet/bore to cause increased pressure, you've reached another of what I consider a broken situation, and coatings may reduce the number of failing bullets(unless USAF says it doesn't). This would be a friction reduction benefit that by far most of us will never need.
What was it Tubb's advocating of hBN proved anyway(can't find it)? A difference of pressure? I doubt it.

hBN has a Coefficient of Friction at 0.15 to 0.70
WS2 has a Coefficient of Friction (Dynamic @ 0.03 & Static @ 0.07)
http://www.lowerfriction.com/product-page.php?categoryID=1

WS2 is way way slipperier, and it does not change MV.
So hBN may be very useful, probably is, but any implication of pressure/velocity change as a benefit, do to it's 'low friction', would be hogwash. Just sayin..

 

[JRS]

 

[Berger.Fan222]

hBN has a Coefficient of Friction at 0.15 to 0.70
WS2 has a Coefficient of Friction (Dynamic @ 0.03 & Static @ 0.07)
http://www.lowerfriction.com/product-page.php?categoryID=1

Coefficient of Friction is defined in Mechanical Engineering (and intro Physics) in a manner much different from what is happening in a rifle bore.

The defining equations for friction coefficient in Mechanical Engineering relate to a normal force between two surfaces and the relationship between the normal force and the force required to slide one surface along the other.

This definition is inapplicable in a rifle bore for two reasons:

1) The normal force between the bullet and the barrel is not known or defined.

2) There are really multiple forces resisting the forward motion of the bullet in the barrel, including a) the force of sliding friction b) the force required to engrave the rifling into the sides of the bullet c) the force required to swage/squeeze the bullet through a smaller diameter bore (sometimes) d) the force of air pressure on the front of the bullet (which is much larger than ambient air pressure once the bullet is supersonic) and possibly others.

In addition to the inapplicability of the common equations defining how coefficient of friction works, the role of a "bullet lubricant" in a practical sense would be to reduce the total of ALL the forces that resist a bullet being pushed through a barrel, not just the force of sliding friction.

To further complicate the situation, the friction coefficients of the lubricants themselves does not tell you much, because you don't really have a pure lubricant between the bullet jacket and barrel steel, you have a mixture or intended lubricant and untended fouling and residues (carbon, primer fouling, copper, etc.) Studies I've read seem to show that the resisting forces are much more dependent on the specific bullet type, bearing surface, etc. than on the applied lubricant, and also that things like the type of primer and sealant between the case neck and bullet can play a role.

 

[Brians356]

Forget about the head games. Dawn dishwashing liquid will remove the moly from your barrel…. and also from your hands

Yup. The legend that moly can never come back out of a barrel is completely bogus. And it defies common sense. I still use moly in certain rifles, but have gone back to plain copper in others, and it was not especially difficult to remove, I've had more trouble removing both carbon and copper from some barrels.
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[Brians356]

Thats what I was trying to say about smoooothing out the highs and lows. Nice one Mozella !
I have tried HBN and couldn't get it to stick, I still use the dry Moly coating in a tumbling machine I built myself and don't find it particularly messy. Tried the wet method and could not get the results that other have had.

Mike.

For myself (YMMV) moly coated bullets make removing carbon easier, in decent bores makes copper fouling much less likely, allows longer strings between cleanings, makes bullet seating more consistent (along with 0000 wool polishing of case mouth), and prevents "stiction" (alleged "cold weld") between seated bullets and case necks (especially good for long-term storage of handloads.) Moly does not necessarily produce better accuracy. I believe it probably does extend useful barrel life.

I moly coat bullets myself, dry, inside a plastic vitamin bottle (taped securely shut) inside a block of thick foam rubber, tumbled in a clothes dryer ("air" setting.)

My two most accurate rifles (Sako 222 Rem and custom R700 250 AI) both see only moly bullets. I have an unaltered R700 VS in 223 Rem that is accurate w/ copper bullets, and it now runs CFE 223 powder. For big game rifles, with older factory barrels with mediocre (or worse) bores, I just use plain copper bullets and copper fouling-suppressing Enduron powders.
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[jim_k]

I shot in Scotland in 98, owner of the rifle I used, Charles Young, swabbed the bore with moly grease first thing before the match, and utilized a greaser. When the bullet is pushed into the the greaser nose it puts a ring of grease at the end of the case into the bullet. Each round was greased before it was shot.

Hey, Bamban, good to hear from you.
My smallest group ever was shot with moly, and that was 0.022" for four shots. I get moly out of my barrel just fine, especially every 500 rounds or so when I diamond-lap the bore. I don't think moly or boron nitride actually make for smaller groups. F/TR world champion does not moly coat, does he? Also, I don't think any of the guys at Bayou Rifles who have shot clean 20-shot strings of F/TR at 1,000 yards moly coat.
Moly is very helpful in hunting season if you hunt with a tipped or hollow-point bullet, in that you can moly-coat the rifle bore, and do not have to clean the rifle until the end of the hunting season, and the cold-bore shot will be reliable. Maybe Bamban will post his hunting rifle test results and whether or not he coated, that is, the one-shot-in-the-morning-out-of-a-cold-bore hunting tests.
With a spitzer lead-tipped bullet, I do not moly coat, since the tip will deform. Now I only hunt with lead-tipped bullets, due to one too many episodes of "pencilling" through.