Lubed pellets vs velocity spread

[Scotchmo]

I tested lubed pellets for accuracy in a single gun a few years ago but results were indeterminate. Since then, I have occasionally run strings of lubed pellets over the chronograph in the garage but always experienced velocity spreads that were 2x or 3x times as great as unlubed pellets. A tight velocity spread is an easily measured value that translates to better accuracy for far shots, so the poor velocity spreads in the lubed pellets caused me to investigate no further.

I'm currently working on a new gun and have been getting minor/moderate shifting in poi. I'm shooting CPH 10.5gr@900fps and had read that they are the most likely to benefit from lubing. I already determined that weighing and sizing gave some small accuracy improvements. I decided to once again try lubing.

Velocity spread of the lubed CPH was disappointing, but I decided to go ahead and do an accuracy test. My backyard range is 25 yards so velocity spread should not affect it too much. I did not have a lot of time, but initial accuracy tests showed a significant improvement over unlubed pellets. No wandering poi over a string of about 30 shots.

I shoot field target so need accuracy out to 55yds. I calculated the vertical poi variation from the increased velocity spread and determined that the accuracy improvements should more than compensate for that. I've got an FT match tomorrow, so I'll be able to get a better test at all distances.

If it proves out, I'll work to figure out how to reduce the velocity spread in the lubed pellets. That will likely involve a lighter hammer.

[elh0102]

I'll be interested to hear your results. I have always washed and lubed pellets for my PCP rifles, and now it's more out of habit than need. When I first started in air rifles about 20 years ago, I shot nothing but Crosman brown box Premier pellets, some of the best, but dirtiest pellets ever made. Now that I shoot mostly JSB, there is probably not a need to wash and lube, but I do it anyway, and seldom do I need to clean barrels. I don't know why the lubing process would result in larger ES, I have not seen that result.

[nervoustrigger]

Scott, I'm curious to hear more about the increased extreme spread...theories why, factors influencing it, etc.

I ran a little experiment today with a couple of rifles to see if I could duplicate your results.  The setup was:

• Two (2) regulated PCP rifles
• Shot 25 pellets from the tin (RWS Basic) with each rifle
• Washed and waxed the pellets (Purple Power->Dawn->tumbled with 10 drops of White Lightning)
• Shot another 25 pellets with each rifle
• Cleaned the barrels before each 25 pellets
• Considered first 5 shots as seasoning shots (plotted them but did not use them in ES calculation)
• Paced the shots about 15sec apart

Results:





Looking over it, this particular wash and lube process makes no meaningful difference in the ES for these two rifles.

[Hayfoot]

OK... now time for a stupid newbie question: 

then with the wicked barrels suggesting that you lube... does that still apply?
thanks,
M 

[bandg]

Absolutely no experience with washing or lubing pellets here but I'll speculate a bit.  Washing would logically seem to possibly improve consistency a bit for "dirty" pellets (those with casting swarf, etc.).  Lubing effect would seem to possibly be highly process dependent (viscosity of material, application method, and drying).  Any build up of material around the waist and especially in the skirt might effect performance.   Could the effect vary based on barrel finish?   Would probably take lots of testing to determine the effect definitively and might vary for shooter to shooter in any event.

[Scotchmo]

Scott, I'm curious to hear more about the increased extreme spread...theories why, factors influencing it, etc.

I ran a little experiment today with a couple of rifles to see if I could duplicate your results.  The setup was:

• Two (2) regulated PCP rifles
• Shot 25 pellets from the tin (RWS Basic) with each rifle
• Washed and waxed the pellets (Purple Power->Dawn->tumbled with 10 drops of White Lightning)
• Shot another 25 pellets with each rifle
• Cleaned the barrels before each 25 pellets
• Considered first 5 shots as seasoning shots (plotted them but did not use them in ES calculation)
• Paced the shots about 15sec apart

Results:

Looking over it, this particular wash and lube process makes no meaningful difference in the ES for these two rifles.

For some reason, I am not allowed to view your pictured results, even when logged in.

I care more about SD. ES is not as good a predictor and can vary more depending on the number of shots.

I shot a CASA FT match today. It was setup as a springer friendly match so the targets were not extremely difficult. I shot 44/48. 3 of the 4 misses were on offhand and kneelers so that was all on me. Don't know why I missed the one sitting shot as the gun was keeping a fairly consistent poi throughout the day. I did not adjust the scope for sight in or during the match.  I was pleased with the results. I've got another match tomorrow and a big match next week. I'll keep shooting the same lubed pellets for those matches and get more empirical data.[/list]

[Motorhead]

OK... now time for a stupid newbie question: 

then with the wicked barrels suggesting that you lube... does that still apply?
thanks,
M 

They DO SO because the TJ barrels they use are tighter in bore and tight choked.  The Fp-10 lube recommended is to help with reducing fouling primarily

[nervoustrigger]

Scott, I added the SD and am posting the images using GTA's reply editor so hopefully they'll show for you.

[Scotchmo]

Scott, I added the SD and am posting the images using GTA's reply editor so hopefully they'll show for you.

I can see those graphics. The SD was 50% worse for non-lubed pellets in your 2400kt. Opposite of what I experienced with the CPH in my Gauntlet. I think it depends on the aspects of the initial pellet release. As the valve opens and pressure builds behind the pellet, the moment/timing of the pellet release is determined by a combination of static/dynamic friction and pellet inertia (pellet mass). Waxing/lubing might reduce the initial friction. And head size variation can cause a large variation in friction. It can all interact in ways that increase the total amount of variation. Inertia providers a more consistent/reliable resistance. I'm guessing that a lighter/faster hammer will bias the release to be based more on pellet inertia rather then friction/fit - and hopefully make the SD less dependent on friction values. The pressure would build faster behind the pellet even if it was already starting to slip.

[subscriber]

Just for grins, weight the same 10 pellets as they come out of the can; after washing and drying; after washing drying and lubing.

Apart from changes in friction, lubing may make pellet weight less consistent.

You are measuring only velocity variations.  You should also measure point of impact variation to see if the slower pellets land low, or not.  If the velocity variation is due to mass differences (and the lube is not dumped in the barrel or in flight), then the slower pellets may still print with the faster ones because their extra weight has increased their sectional density.

By the way, I like to lube pellets by rolling them on a uninked stamp pad:  
That way, they get only a trace of lube, and mostly on the bearing surfaces.  Tumble lubing may be faster, but lube inside the "tail" on some pellets only can't help consistency...

[Motorhead]

Just for grins, weight the same 10 pellets as they come out of the can; after washing and drying; after washing drying and lubing.

Apart from changes in friction, lubing may make pellet weight less consistent.

You are measuring only velocity variations.  You should also measure point of impact variation to see if the slower pellets land low, or not.  If the velocity variation is due to mass differences (and the lube is not dumped in the barrel or in flight), then the slower pellets may still print with the faster ones because their extra weight has increased their sectional density.

By the way, I like to lube pellets by rolling them on a uninked stamp pad:  
That way, they get only a trace of lube, and mostly on the bearing surfaces.  Tumble lubing may be faster, but lube inside the "tail" on some pellets only can't help consistency...

Yup ... SO, if your going to add a lubricant to otherwise dry & prepped pellets that i ever read about and tried is the pellet tin w/ foam pad way.
Dry foam pad in a pellet tin, few drop of lube / wax etc on pad then finger smeared some .... drop in a modest quantity of pellets, place lid on and rotate /agitate circularly.  this places a trace amount on pellet OUTSIDE surface only and nothing gets into the tail to cause imbalance.

[nervoustrigger]

Just for grins, weight the same 10 pellets as they come out of the can; after washing and drying; after washing drying and lubing.

That's not really a concern with a dry lube (wax) like White Lightning or Krytech.  The one I'm using is less than 1/3 solids.   The majority of its volume (and mass) is a solvent which helps distribute a uniform film and then it evaporates.

Pulling some figures for specific gravity of wax and the volume of a drop, I added about 2.4 grains of wax to 450 pellets.  Evenly distributed, a 7.0gr pellet would be increased to 7.005gr.  Poorly distributed, perhaps some have 10x as much...so those weigh 7.05gr .  Not a magnitude that matters compared to the typical weight variations of the pellets themselves.

You should also measure point of impact variation to see if the slower pellets land low, or not.

Well, I didn't do that this time but I have tried before to correlate slight weight differences at 40 - 50 yards (e.g. JSB 18.1gr that weigh 18.1gr and 18.3gr) and it just gets lost in the group size.  Perhaps at a 100 yard indoor range and with a supremely accurate benchrest rifle, it would be possible to tell but I will probably never know

[subscriber]

Not a magnitude that matters compared to the typical weight variations of the pellets themselves.

Good point.

[Tonykarter]

Scott, all things being equal among two populations of pellets, one lubed as you describe above i.e., in the pellet tin and the other using your 16:1 two-cycle mix method, which of the two methods achieve the greatest repeatability?

[Motorhead]

Scott, all things being equal among two populations of pellets, one lubed as you describe above i.e., in the pellet tin and the other using your 16:1 two-cycle mix method, which of the two methods achieve the greatest repeatability?

Full wash and 2 stroke ... it does not pool either, but does have the advantage in oil filming the entire pellet which can be of benefit if your having high lead oxidation happening during storage.
Tho as stated many times my lubing is nearly always with hard lead pellets like H&N / Crosman  etc ...  JSB generally Don't require added lube unless required such a MM's TJ hammer forged barrels.

[subscriber]

Apart from lubing pellets to prevent pellet oxidation, who lubes pellets to prevent oxidation of barrel steel?

PCPs seem to spit moisture clouds on every shot, and some of that may condense on the barrel steel, and promote rust.  A thin film of grease, oil or wax should seal the barrel from such moisture...

I don't always lube pellets, but I always shoot perhaps two or three very wet (oily) pellets at the end of shooting for the day, in case it ends up being  awhile before I shoot again.  Oil in the base cavity and around the skirt get thrown off onto the barrel wall on the way out.

The idea that you can use a cleaning rod to pass an oily patch through your airgun barrel in preparation for long term storage is all well and good.  However, if you have a few airguns, then exactly when "long term storage" starts for any given airgun can be a little unpredictable.  Hence, I treat the last shooting session of the day as if it is the last one before long term storage...

Iron is slightly more reactive than lead, so lead is not going to protect steel from corrosion the way zinc would: https://en.wikipedia.org/wiki/Electronegativity.  And lead dust is hardly a water tight barrier, unless it is soldered to the steel in a continuous film, formed at high temperature...

[Motorhead]

Not a metallurgist and not sure to what degree non rust additives are added to steel other than nickel, it does appear we don't have issue of barrel rust from expelled moisture.
But DO get rust on exterior surfaces due to SALT ... from our own bodies.

[dan_house]

Scotchmo, your shooting the Gauntlet for FT?

[Scotchmo]

Scotchmo, your shooting the Gauntlet for FT?

I have been for the last few matches. I shot it at the Nevada state match, and a few local matches, including Saturday at CASA and yesterday in Cambria
https://www.gatewaytoairguns.org/GTA/index.php?topic=50078.msg1482915#msg1482915

It is still a work in progress, but it gives me a good platform to experiment with a lot of 3D printed parts.

[subscriber]

But DO get rust on exterior surfaces due to SALT ... from our own bodies.

Handling pellets with sweaty fingers would seem a nice way of dosing the bore with salt...

Also, lead oxide is a water soluble salt.  That suggests it would draw water, rather than repel it...