Calculating the Ballistic CoEfficient of your pellets

[milegajo 595]

As a follow on from my Self Reliant Airgunning - Pellet Production thread, I thought I'd post a quick method on how I've been calculating BC without getting too technical.

 

The theory is pretty straightforward. I don't have two chrono's, just a combro, so I am relying on Chairgun and its 'BC based on POI difference' calculator.

 

Ten shots in total were fired. 5 at the zero of 12 yards, 5 at 30 yards. This gives us two distances. The fall of the shot will tell us how the pellet is performing in the barrel, then the air as it reaches its target. Of course, the chrono is telling us how fast it is leaving the muzzle.

 

Now, this is important. The database BC was very different from my findings. This is due to manufacturers taking an average performance figure, in the same way they take an average pellet weight and print it on the box. It's convenient and accurate enough for most peoples needs. Evidently, not mine!

 

When I was weighing the pellets I made, then a manufactured tin, I saw how we take so many figures for granted with out bothering to check and measure for ourselves. So no wonder we all have those 'mystery' shots that take us aback. Especially when changing pellet brand.

 

After the shots were fired, the average fps was taken (703.9 fps with a 10fps variation possibly due to a strip down just prior to the test) then the groups analysed and measured.

 

 

 

Accuracy on the bull would come later, for now, a clear grouping was sufficient. (I couldn't help but fiddle with the windage, though not elevation)

 

I settled for a rise of 0.896" over 18 yards.

 

 

My old zero was 12.1 - 27.5 yards before the strip down and the RWS Supermags were calculated to be 0.0062 @ NTP already a big difference in performance (or calculations!)

 

 

Here we have the new zero and a graph that should accurately reflect the performance of my rifle and the pellet of choice. Chairgun will then update the pellet database for you with your BC calculation.

 

Yet another variable in airgunning to consider, measure and adapt to. Who said it was all 'point and shoot'?!

[Skot Ruthless Teale 1,701]

Theres a lot more to it.. to some people!

 

Point and shoot is all well and good..

But to get the best out of your kit you need to weigh,sort, wash,measure and lube pellets lol

 

if you can be bothered to do all that you will probably see better results.. but can still get great results just by 'pointing and shooting' each to their own i say!

[zini 1,939]

Point and shoot is all well and good, but to get the best out of your kit you need to weigh,sort, wash,measure and lube pellets.

 

True and funny you have just written that Skot because for the past 2 years or so I have been saying the exact same thing and getting some varied comments, some even thinking I'm crazy and going over the top with this kind of preparation.

 

Washing, lubing, weighing prior to calculating your own pellets REAL (not what Chairgun deems as standard) BC is the ONLY way to get the best out of your equipment.

 

This is how me and Davy calibrate our rifle now and the results we are getting is quite pleasing and better than ever before.

 

What people do not understand is BC plays a MASSIVE part of pellet accuracy especially at range.

 

You can go onto Chairgun and produce a software profile in 5 minutes and print it off and go out and shoot 30 yards past your zero and on what Chairgun deems as correct and miss massively by 1/2, 1 or even more mildots, mag depending, most do if they are honest.

 

To calibrate properly using Chairgun you NEED to calculate you BC after zeroing PELLET on PELLET (nothing less) at you max shooting range.

 

Only then will your data be 99.9% correct and you will be able to be within 1/4 of a mil dot through your whole trajectory.

 

The rest is down then to the shooters own skill level.

 

I wouldn't be able to achieve some of the shots I can with an air rifle without this preparation before hand.

 

True you can get good results also with just loading, pointing and shooting but on a % I would bet with better prep your % of good shots improves and with ease too.

 

As you say though each to their own.

 

Si.

Edited August 14, 2012 by zini

[Skot Ruthless Teale 1,701]

I dont have the 'tools' to weigh or measure mine.. but i do wash and lube.

 

when i get a hw100 after saving for a few months il properly go over the top finding the best brand.. exact size and exact weight lolwashed and lubed lol.

[milegajo 595]

Pellet on pellet! Ah dammit.

Double dammit as i just swapped the 97!

 

Good excuse to practice bc calculating.

 

For me, the technology we have today begs to be utilised.

 

The alternative is years of practice with one rifle and the seemingly best performing ammo. 'power' being measured by penetration of pages in a telephone directory...

 

Aids like the chrono and chairgun, with relatively little extra work (compared to a lifetime of practice) helps us leapfrog god knows how many years and kilos of lead.

 

I dont wash or lube though I do weigh and sort. Something girly about washing and lubing. Haha.

I've read an article of research by jim tyler on lubing with positive results so I don't discredit it.

Still sounds girly though.

 

[Skot Ruthless Teale 1,701]

lets face it washing up is a womans job.......

 

but if it makes my gun more accurate its worth doing in my books

[zini 1,939]

Pellet on pellet! Ah dammit.

Double dammit as i just swapped the 97!

 

Good excuse to practice bc calculating.

 

For me, the technology we have today begs to be utilised.

 

The alternative is years of practice with one rifle and the seemingly best performing ammo. 'power' being measured by penetration of pages in a telephone directory...

 

Aids like the chrono and chairgun, with relatively little extra work (compared to a lifetime of practice) helps us leapfrog god knows how many years and kilos of lead.

 

I dont wash or lube though I do weigh and sort. Something girly about washing and lubing. Haha.

I've read an article of research by jim tyler on lubing with positive results so I don't discredit it.

Still sounds girly though.

 

You would be very surprised Mike, try this:

 

Poor the whole contents of what you deem as the best batch and cleanest pellets you have into a glass see through jug.

 

Ensure that there is warm water in there first then gently mix the pellets with you fingers.

 

Hold the jug up to the light and see the amount of lead dust and crap that is at the bottom of the jug.

 

Finally poor the pellets into a siv and look at what's on the inner edges of your glass jug.

 

It can be surprising mate.

 

All that if not dealt with first, ends up building up over time in your barrel causing inaccuracies, especially at longer ranges.

 

People don't wash because they say it makes no difference when they shoot a say 50 unwashed and 50 washed, that's because its more a longer term effect and takes time to show.

 

Si.

Edited August 15, 2012 by zini

[pianoman 3,584]

I second Si's response.

 

A clean and spotless rifle is an efficient, accurate rifle. And shooting 50 washed/lubed and 50 unwashed is no indicator of pellet performance. I've shot alongside my mate Andy (AndyFR1968 here) and he is a REALLY gifted spring and gasram shooter. He doesn't wash and lube his ammo, nor actually thought there was any merit in cleaning a barrel, as I do...Until....

 

Funnily enough, he has been having accuracy issues recently with his (normally) superbly accurate HW90 .20cal gasram.

 

A scrub and clean of his rifle's barrel and he's shooting brilliantly with it again!

 

I wash my ammo in a glass bowl of warm water and, ahem. 'Fairy' liquid. Sieve, rinse, repeat. With H&N FTT this removes a pile of fine swarf. You can see it glint in the bottom of the bowl! No way is that going inside a precision barrel of mine.

 

Dry with a hairdryer, spray WD40 onto a paper towel and lube the pellets by rolling them in the oily paper to get a fine coating with nothing going inside the skirt. This prevents the lube dieselling when the pellets are fired.

 

Nothing girly about the sub qtr-inch groups and extreme range accuracy I can hit with my Weihrauch HW77 and lubed ammo I can assure you Miles.

 

Regards.

 

Simon

 

Edit to add. Weighing is something I have come to consider is crucial. H&N FTT are a beautiful performance accuracy pellet in my Weihrauch spring rifles. But, I have found some severe inconsistencies in the tins I've bought over the last few years.

 

Wash, lube and weigh.

 

A most necessary measure in my opinion.

Edited August 15, 2012 by pianoman

[Mawders 595]

So you still use a fine coating of wd40 then?

 

I thought that was the old school way of lubeing pellets as alot of other sites don't recommend using it as it can cause ignition.

 

Might have to give it a whirl.

[zini 1,939]

I use WD40 too and i have never seen ignition mate.

 

Just be sparing with it.

 

This is almost 3 years old now.

 

Sorry for the poor quality editing but i was only learning editing then.

 

 

Si.

[pianoman 3,584]

Hi Mawders.

 

Well, I'm an old school spring rifle shooter and I've lubed my air rifle ammo with WD40 for decades. I swear by it.

 

As I wrote above, you spray it onto a thick paper towel or rag. Not so it's soaking, just get it oily. Then roll the pellets a dozen or so at a time to get the thinnest coating (not wet) onto the pellet's surfaces.

 

This prevents getting the lube inside the skirt and keeps the ammo lubed enough to perform without being so wet they will ignite.

 

Try it and see what you think!

 

Regards.

 

Simon

 

Edit to add.

 

That film of yours Si is a spot on demo except, I wouldn't spray directly onto the pellets. Any of the wet lube in the skirts can cause dieselling and inconsistent velocities, if not actual ignition.

 

But, in over 30 years of lubing this way with WD40, I have yet to see an ignition caused by it..

 

Regards and compliments mate.

 

Simon

Edited August 15, 2012 by pianoman

[milegajo 595]

Pellet on pellet! Ah dammit.

Double dammit as i just swapped the 97!

 

Good excuse to practice bc calculating.

 

For me, the technology we have today begs to be utilised.

 

The alternative is years of practice with one rifle and the seemingly best performing ammo. 'power' being measured by penetration of pages in a telephone directory...

 

Aids like the chrono and chairgun, with relatively little extra work (compared to a lifetime of practice) helps us leapfrog god knows how many years and kilos of lead.

 

I dont wash or lube though I do weigh and sort. Something girly about washing and lubing. Haha.

I've read an article of research by jim tyler on lubing with positive results so I don't discredit it.

Still sounds girly though.

 

You would be very surprised Mike, try this:

 

Poor the whole contents of what you deem as the best batch and cleanest pellets you have into a glass see through jug.

 

Ensure that there is warm water in there first then gently mix the pellets with you fingers.

 

Hold the jug up to the light and see the amount of lead dust and crap that is at the bottom of the jug.

 

Finally poor the pellets into a siv and look at what's on the inner edges of your glass jug.

 

It can be surprising mate.

 

All that if not dealt with first, ends up building up over time in your barrel causing inaccuracies, especially at longer ranges.

 

People don't wash because they say it makes no difference when they shoot a say 50 unwashed and 50 washed, that's because its more a longer term effect and takes time to show.

 

Si.

 

Funny you should say that as yesterday I had to wrestle a silencer adapter off the SMK. After only 50-100 shots the lead dust had it jammed on solid.

 

Will certainly give it a go. I do pull my barrels through regularly but thats a habit from the infantry, from what i read, few bother. Prevention must be better than cure.

[milegajo 595]

I second Si's response.

 

A clean and spotless rifle is an efficient, accurate rifle. And shooting 50 washed/lubed and 50 unwashed is no indicator of pellet performance. I've shot alongside my mate Andy (AndyFR1968 here) and he is a REALLY gifted spring and gasram shooter. He doesn't wash and lube his ammo, nor actually thought there was any merit in cleaning a barrel, as I do...Until....

 

Funnily enough, he has been having accuracy issues recently with his (normally) superbly accurate HW90 .20cal gasram.

 

A scrub and clean of his rifle's barrel and he's shooting brilliantly with it again!

 

I wash my ammo in a glass bowl of warm water and, ahem. 'Fairy' liquid. Sieve, rinse, repeat. With H&N FTT this removes a pile of fine swarf. You can see it glint in the bottom of the bowl! No way is that going inside a precision barrel of mine.

 

Dry with a hairdryer, spray WD40 onto a paper towel and lube the pellets by rolling them in the oily paper to get a fine coating with nothing going inside the skirt. This prevents the lube dieselling when the pellets are fired.

 

Nothing girly about the sub qtr-inch groups and extreme range accuracy I can hit with my Weihrauch HW77 and lubed ammo I can assure you Miles.

 

Regards.

 

Simon

 

Edit to add. Weighing is something I have come to consider is crucial. H&N FTT are a beautiful performance accuracy pellet in my Weihrauch spring rifles. But, I have found some severe inconsistencies in the tins I've bought over the last few years.

 

Wash, lube and weigh.

 

A most necessary measure in my opinion.

 

I'll try it out. I certainly want to keep my rifles tip top in both performance and condition. It is a hobby, but also a tool for a job for me.

 

Cheers!

[milegajo 595]

Might try a roll as describe with veg oil.

[milegajo 595]

When i weigh mass produced pellets i tend to find at least 4 variations. This increases as you get down to the cheaper brands. What do you chaps do? Fire off the most common weight first, then work down adjusting as you go?