Pellet batch selection - a different approach

Introduction

As some of you know I've been kicking around a theory for a little while now and I had the chance to do a bit more investigation over the weekend, so I thought I'd post my findings and the conclusions I'm starting to draw from the results.

I should point out that this is theory and as such, it could turn out to be useful information or a complete dead end - I'm approaching it with an open mind, and welcome your thoughts and comments.

Not all JSB Exacts are created equal - there are in fact something in the region of nearly 50 slightly different die's used in the manufacture of Exacts and in addition to that, there are different batches of pellets produced on those 50 dies. If you wander into a shop and buy a random tin of Exacts off the shelf, you could end up with a mega die/batch or a not so mega die/batch. Most of them usually shoot pretty well in most guns, but I've found that some shoot better than others.

So how do you tell the difference between the mega batches and the not so mega batches? (or even the really crap batches for that matter)

My usual method is probably the same as most shooters - I shoot groups at distance 50m and pick the batch that groups the best. But is there a more objective method that eliminates shooter error and environmental factors such as wind drift?

The Theory - Accuracy and repeatability are the same thing.

If you can put a pellet through a bit of paper at 50m and repeat that process so that the following pellet goes through the same hole, that's accuracy!
When you get inaccuracy, a large part of the cause is down to pellet stability in flight and a consequence of poor pellet stability is a reduction in velocity, a reduction on ballistic coefficent and an increased spread in downrange velocity. So could this be measured and predicted by performing downrange velocity testing with a suitable chronograph?.

The tests.

I've run out of mega pellets, so I'm looking for a new mega batch for the coming season, so I thought I'd buy 3 batches of pellets and put them through their paces over a chrono and see if the theory holds up.
The 3 batches I bought were die 19 (4.51), die 45 (4.51) and for fun, I went for mega batch die 34 (4.52) shot through my TX200.

And these are my chrono readings :-
(Pellets shot straight from the tin)

Muzzle Velocity (fps)

	Shot	Die 19	Die 45	Die 34
1	1	788	772	779
2	2	790	777	782
3	3	792	777	785
4	4	788	775	783
5	5	788	793	777
6	6	779	776	781
7	7	783	774	779
8	8	787	783	784
9	9	785	769	781
10	10	782	781	781
11
12	Ave	786	778	781
13	Std Dev	3.9	6.7	2.4

Downrange Velocity (fps @ 50m)

	Shot	Die 19	Die 45	Die 34
1	1	611	535	621
2	2	607	593	575
3	3	609	590	568
4	4	609	555	586
5	5	606	526	570
6	6	609	541	615
7	7	605	536	616
8	8	604	542	566
9	9	609	532	614
10	10	606	548	615
11	11	608		611
12	12	609		576
13	13	609		609
14	14	608		615
15	15	608		611
16
17	Ave	608	550	598
18	Std Dev	1.9	23.4	21.2

My conclusions

The 4.51's are noticeably looser in the barrel than the 4.52 batch - no big surprise there, but curiously die 19 seemed to give the highest average muzzle velocity, but die 34 (4.52) gave the most consistent velocities with a standard deviation of just 2.4 fps.

If I was picking a batch based purely on how consistent the pellets were at the muzzle, I would have chosen die 34.

Downrange velocities tell a different story though...

Die 19 was mega consistent downrange with a standard deviation of an incredible 1.9 fps and a higher average velocity of 608 fps (BC of 0.027), die 45 was crap - so crap in fact I didn't bother taking more than 10 shots!. die 34 was ok, but quite a big variation with a standard deviation of 21.2 fps and an average velocity of 598 fps (10 fps less than die 19).

I didn't concentrate on groupings, I was concentrating on putting the pellet consistently over the chrono's sensors while not making the expensive mistake of shooting my chrono in a light but variable wind, but I did notice that die 45 grouped like a shotgun!.. I was struggling to put in a sub 40mm group at 50m (the reason I stopped at 10 shots was because I didn't want to hit my chrono!). Die 34 grouped ok, but die 19 was grouping very impressively - often going through the same pellet hole as the previous shot. Like I said, I wasn't concentrating on group sizes, but you do notice when a pellet hits the same hole as the previous shot.

Now you might think that an increase in average velocity of just 10 fps at 50m isn't going to make much difference here or there, but on doing some exterior ballistics calcs, it would seem that the pellet that has the highest average velocity and tightest spread 'should' also be fairly significantly better in the wind as well. Although this is difficult to prove with subjective grouping tests where human error can creep in quite easily.

Next step is to shoot some groups to see if grouping tests give the same result as my chrono tests - i.e. die 19 is mega, die 45 is crap.

Oh I should also say that all 3 batches seemed to land at about the same vertical height ( and none of them hit the chrono screen )

The bottom line (for those who don't want to read all the thread)

It's looking promising to use downrange chrono testing as a more reliable method of pellet batch selection. If this proves to be correct, it will give a less subjective testing process for trying out other theories such as - does weighing my pellets give me any benefit? Is that mega air stripper actually any good? Should I lube my pellets? Should I sort pellets with a BIC pen etc etc.. you get the idea.

Oh, just to state the obvious, these tests are likely to be gun and barrel specific - what works in my barrel might not work in yours.

And of course, my theory could very well turn out to be a complete waste of time - it only took me about 45 minutes in total though so no big deal really.

 

Interesting Brian. Ta.

 

Cheers chaps

To answer some questions - yup these were with my TX200 Mk1 (I've heard people say in the past that springers give a better BC than PCP's - I'm getting a BC of 0.027 for die 19 (based on average velocities), it'd be interesting to see what others get with a PCP. These were at 55 yards (not far off 50m) on my measured test range in my back garden.

I chose 55 yards instead of 45 yards - because I've found that even pellets that seem to group quite well at 45 yards can open up quite significantly when they get to 55 yards - they're dropping quite fast when they get to 55 yards, so I guess they're more susceptible to pellet instability the further you go out. (just a guess)

Now these were all shot straight from the tin (literally - I had the 3 tins labelled up and sat next to me).

But for a bit of fun with numbers - have a look at the downrange velocities for die 34. What would happen if I could somehow sort those pellets so that I only used the ones that gave me a figure over 600fps.

I don't think this is possible, but hypothetically lets say that if I weighed, washed, lubed, sized and selected my best pellets with a BIC pen - suppose I could actually filter out the sub 600 pellets from the figures.

These are what the new filtered figures would look like from die 34 :-

Downrange Velocity (fps @ 50m) - Theoretically selected pellets
This is hypothetical don't forget!.

	Shot	Die 34
1	1	621
2	2	575
3	3	568
4	4	586
5	5	570
6	6	615
7	7	616
8	8	566
9	9	614
10	10	615
11	11	611
12	12	576
13	13	609
14	14	615
15	15	611
16
17	Ave	614
18	Std Dev	3.5

The results over the chrono would be better - 6 fps on average faster than die 19. Better BC, but a greater spread.
Would that amount to much difference... well, in theory no I don't think it would - in fact the tighter spread of die 19 would theoretically give me more of an advantage than the higher fps and BC of the sorted die 34.

Again just hypothetical based on a very small sample (just 15 pellets) but that would support the theory that weighing, sizing and otherwise sorting your pellets is largely a complete waste of time, since I can get better results from die 19 straight from the tin unsorted.

Of course this could all fall completely flat on it's face when I've actually shot some groups with the pellets - interesting though I think.

 

Brian, that just can't work.

Surely washing, sizing, weighing and looking at the pellet in fine detail through a microscope will ensure the best results with your batch.

Imagine the results you would have had if you were using a JO wind defying air stripper.

 

That's sort of the idea behind doing this partly. Just how much of the things we do, or fix to the end of our barrels actually make a real difference and how much of it is just imagined?

It's a fun little hobby to take the piss out of Si for spending £180 on a tube with holes in it - but can anyone say with any real certainty that he's wasted his money? Who know's maybe he hasn't... it would be really nice to have a test we could do that would give us some real data, with opinion, pre-conceptions and shooter ability totally removed from the equation. We can really ramp up the piss taking then

 

If I've got the time I might have a go, I've got a few different batches of Express and some old Mozzies kicking around in my pellet crate that I could try.

It's interesting though.. because I reckon there are far fewer die's of Express than there are of Exacts ( around 12 different die's of Express compared to nearly 50 dies of Exacts )

Something I know about the tins of 7.9's I've got in my crate is that at the muzzle, my TX puts out less muzzle energy with the 7.9's than it does with my 8.4's. Last time I checked (about 6 months ago) 7.9's were coming out at around 795-800 fps compared to 8.4's coming out at about 780. I didn't check downrange though.

If I'm getting a BC of 0.027 with a mega batch of 8.4's compared to say 0.023 with 7.9's the 8.4's will actually have about the same trajectory and take less wind than the 7.9's (in theory).

That tally's up with a side by side test that Andy Calpin did with 8.4's vs 7.9's a couple of years ago.

Of course that's very barrel dependant - if you're lucky enough to find a gun/barrel combination that really likes 7.9's (tested downrange with grouping and a chrono) then I think you're onto a real winner. But the odds of finding a mega batch out of 12 dies is lower than finding a mega batch out of 50 dies and the stumpy 7.9's might end up being less stable in the wind when they reach 50+ yards.

I know people that swear by 7.9's and people that do very well with 8.4's - how much of that is real and how much of it is imagined I couldn't say.

I'll see if I can give it a test later on when I've stopped stalling on shooting some groups in the garden - I fecking hate shooting groups, but I'm going to be honest with my findings, even if it exposes just how crap a shot I really am

 

Dunno (shrug) - it's difficult to say really, but at 30 yards unless you were getting a massively higher BC the difference in kinetic energy would be tiny.

If I had to put money on it, I'd say you were hitting the reset paddle a little bit lower than they were perhaps.

That's the trouble with the subjective tests we do really - we see something tangible happen and then come up with theories about why they happened. Before long we start to convince ourselves that our theories are correct and make decisions based on them.

Truth of the matter is, no one really knows why you could reset the target and they couldn't - it could have been BC, could have been where you were hitting the paddle - we could probably come up with half a dozen other reasons too if we tried. With the absence of any real data, it's largely a guessing game.

Anyhoo.. I've just shot some groups in the garden, just scanning and measuring them now. Not sure exactly what to make of the results, but I didn't do as badly as I thought I was going to, so I'm happy about that at least

 

Bri, are you using two chronos, or moving one down range?

 

I'm using 1 chrono and moving it downrange. So you can't compare shot 1 at the muzzle with shot 1 downrange and get an accurate BC figure - When I'm quoting BC's I'm going with the average MV against the average downrange.

Not a great way to do things, but for what I'm trying to test it doesn't matter too much. It was less hassle than calibrating my combro against my pro-chrono and then trusting that taking a shot with the combro fitted wouldn't alter my poi ( and cause me to hit my pro-chrono )

I'm not really trying to measure BC accurately, just demonstrate that consistency at the muzzle doesn't necessarily mean consistency downrange really.

Not really laboratory conditions I know, but hopefully better than our usual subjective tests

 

Right o.. just shot some groups at 55 yards in my garden range.

I was shooting next to a fence line that blocks out a fair chunk of wind, but there was still a bit of wind getting through - a fair few shots went straight with some drifting to the right with a left to right wind. ( I didn't measure the wind speed, couldn't be arsed ).

Oh and I think I lost count of how many shots I took with die 45 - I thought I'd taken 10, but I did lose count at one point and looking at the target afterwards I'm pretty sure I can count 12 holes.

( I'd make a crap scientist wouldn't I )

Anyhoo - have a look for yourselves at the result and see what conclusions you draw from them.

The blue 8 ring is 40mm, the red 9 ring is 25mm and the centre blue dot is 11mm (odd I know, but that's what my ruler says). These were shot off the bag. (I was quite pleased with all of them to be honest)

Notes about my groupings.. there's a pellet strike low and left on the die 45 group. You might think that was just a bad shot, but it felt like I good one to me, so make your own mind up. On the die 19 group there's a shot that went high, can't be sure but that might have been a bit of pilot error. The rest of them all felt like good shots to me (well good for me with a springer anyway).

My conclusion - Die 19 and Die 34 both put in pretty good groups I'd say - I could completely cover the Die 19 group with a £1 coin (and that's my benchmark of success with pellets). I'm not good enough to put in tighter groups than that, I'd say these groups are probably better than my average attempts. The first shot with die 19 went almost smack bang through the centre of the 10 spot. I was so tempted to just stop there and say I'd put 10 shots through

They all seemed to be going a little bit high at 55 yards, maybe my zero's off, but then again this is a bloody springer and they just do what they feel like from one day to the next.

Going on group sizes - it looks to me like die 19 was the winner (marginally) followed by die 34 and lastly die 45 - which actually wasn't quite as bad as I thought it was going to be, apart from the flyer out to the bottom left.

Not very scientific, but the groups do tend to agree with the downrange chrono results - and oddly enough, all the pellets were tending to land at about the same average height despite die 19's slightly higher BC and velocity. (Go figure?)