Is a Low ES Critical ?

[rsterne]

We continually get bent out of shape trying to get very low Extreme Spread in the velocity with our PCPs.... Just to put that quest in context, here is some data I lifted from a Firearm Forum, comparing 26 brands of .22LR ammo....

I recently completed a testing project during which I fired 26 different Brands / Types of .22 LR Ammo in my Ruger 10/22 rifle. Below are the results of the testing, with the ammo listed in order of the best to worst (in regards to accuracy). 5 rounds of each Brand / Type of Ammo was chronographed, and six - 5 shot groups were fired in the accuracy test.

.22 Long Rifle Ammo Test
Ruger Model10/22 Rifle, 20 inch barrel

The numbers are as follows: Average Velocity, Extreme Velocity Spread & Standard Deviation.

Wolf Match Target = 1043 / 25 / 6.00
Wolf Match Extra = 1020 / 18 / 6.32
Eley Standard (Brown Box) = 1071 / 55 / 8.12
Remingtom (Eley) Target Rifle = 1031 / 25 / 6.24
P.M.C. Rifle Match = 1009 / 33 / 6.08
C.C.I. Standard Velocity = 993 / 32 / 7.55
Winchester X-Pert Hollow Points = 1144 / 41 / 7.48
Remington (Eley) Club Xtra = 1038 / 26 / 6.63
Quick Shok Hollow Points = 1550 / 38 / 7.07
Winchester Dyna Points = 1109 / 22 / 5.00
Remington Thunderbolts = 1213 / 84 / 11.66
C.C.I. GREEN TAG = 1023 / 48 / 7.87
Federal Lightning = 1215 / 49 / 8.00
Federal Classic Hyper Velocity Hollow Points = 1465 / 11 / 3.74
Remington Target = 1125 / 32 / 8.25
Winchester Power Point Hollow Points = 1215 / 16 / 5.39
P.M.C. Sidewinder Solids = 1195 / 58 / 8.83
Winchester WildCats = 1185 / 37 / 7.35
Federal Bulk Hollow Points = 1247 / 65 / 10.91
C.C.I. Mini Mag Solids = 1246 / 30 / 5.66
Winchester Hi-Velocity Solids = 1187 / 24 / 5.57
C.C.I. Blazer = 1213 / 34 / 5.57
C.C.I. Stingers Hollow Points = 1567 / 49 / 7.68
Winchester T-22 = 1150 / 28 / 7.35
Remington High Velocity Solids (Golden Bullet) = 1272 / 61 / 9.85
Remington Bulk Hollow Points = 1246 / 31 / 6.63

(Temperature at Chronographing was 75
degrees & sunny)

Most of the ones with the best accuracy were subsonic, in fact only 3 of the top dozen were supersonic, and none of the target velocity loads finished in the bottom half.... The average ES of the subsonic rounds was 31.6 fps, and the average velocity was 1037 fps, which works out to a 3.0% ES.... The best had a 1.8 % ES, and remember, that was over only FIVE shots.... Geoff Kolbe tested ELEY Tenex ammo, and found that the ES varied from 25 to 45 fps over a box of 50.... so that is about 2.5-4.5% ES....

Obviously, the lower the ES, the less vertical dispersion we will see in our targets.... However, perhaps we should be taking a page out of the book of rimfire shooters, and using harmonic tuners to compensate for the velocity spread, instead of worrying about trying to get it down to under 1%.... Keep in mind that if you get the ES under 2% over a long string of shots, you are doing better than just about any box of .22LR target ammo you can buy.... Just a thought....

Bob

[Dairyboy]

Very interesting to know! Makes sense then to why I could probably not get as tight of groups with my .22lr then my PCPs. Never expected that large of a difference

[nielsenammo]

I think the other consideration is how far are we shooting.  If you are shooting field target for instance, is it going to matter much at your max distance of 55 yards?  If you are shooting long range, say 150 plus yards I can see wanting it as close as possible.  I think part of it is just the quest - no matter if makes much a difference at all in the end.

[rsterne]

Yes, the range you are shooting at is critical, for sure.... I have a rule of thumb I use.... I like to see an ES of less than 2/range, expressed as a percentage.... That means a maximum of 2% at 100 yards, 4% at 50 yards, etc.... I find that makes the vertical dispersion less than my shooting ability, even from a bench.... If you enjoy the quest for a single digit ES, then go for it.... Just don't obsess over it, would be my advice....

Bob

[Tomg]

I think that list is missing one small but crucial piece of data, and that is weight. (and BC)

Simple mind experiment for you, if you divide the weight with the ES you get a number, the higher the number the less trouble with accuracy you will have.
You can invert it and divide the deviation with the weight, and then the lower the number the better.
For amusements sake, take an ES of 20.

On a 45gr .22 you'll get something like 0.44 (lower is better)
On a 18.1gr .22 you get 1.10
So if BC was the same you can have more than twice the amount of ES on the heavier bullet.

[mobilemail]

Lets just assume for a minute that I know diddly about precision shooting....

Could you explain harmonic tuners and the associated process of tuning one?

[rsterne]

Actually, at a constant range, the ES is the most important factor in the vertical dispersion, and the BC and MV are secondary.... There is a widget in ChairGun that will allow you to make comparisions.... If you run the average 3.0% ES and 1037 fps MV for the .22LR Target ammo above, using the RA4 Drag Model and a typical BC of 0.115 (.22LR) the vertical dispersion at 100 yards is 0.94".... If you do the same for an airgun, shooting a pellet with a BC of 0.040 (GA) at 950 fps, with a 2% ES, you get a vertical dispersion at 100 yards of only 0.83".... Drop the BC to 0.020, that increases to 0.91", still better than your average .22LR target ammo.... However, increase the ES to 3% (like the .22 LR), and the vertical stringing increases to 1.19", due to the poorer BC of the pellet (0.040), compared to the bullet (0.115)....

Remember, the BC is proportional to the SD (the weight, in a given caliber).... If the range is long, then the BC becomes more important, because the bullet slows more, and the average velocity is less.... Therefore, the longer the range, the more important weight becomes in minimizing vertical stringing....

Bob

[Ribbonstone]

They do have the advantages of a lot higher BC (like 3 to 4X as high as pellets) and likely fired at 50 yards (if they mentioned the range, I missed it).

Will agree that too much attention is placed on velocity spread for most uses, really takes a whole lot of pellet velocity change to actually be the reason for a 25 yard miss.

But for comparison between rifles or between tunes, we do have to draw the line somewhere.  Wouldn't really make a difference to the value of the comparison it you picked 3%, 5%, or 10%.

Am reminded of some pellets uses that gave some wonderful numbers though the chronograph, but wouldn't shoot worth a hoot.

[Back_Roads]

Lets just assume for a minute that I know diddly about precision shooting....

Could you explain harmonic tuners and the associated process of tuning one?

I think harmonicas are tuned at the factory.
BTW interesting read and seems my preference in 22 LR ammo choices is validated.

[ackuric]

PCP Air rifles are used primarily for two reasons. Small game hunting and bench/target shooting.

For both cases most people dream/desire for 1 MOA shot to shot consistency or better.

To achieve 1 MOA @  100 yards you need between 1-2% ES. In most cases a spread of over ~20(2%-2.5%) will put you outside of this. I wouldn't go taking a bunch of 100+ yard shots with a 2.5-2.7% ES, especially when its a matter of optimal fill pressure and I can keep it <2% ie: 1-1.9%.

Low ES is critical, and becomes more critical the further your shot placement is. We all have our rule of thumb, mine is to keep it within 1 MOA which requires between 1-1.9% ES, respectfully.

And to add, this is just one of the factors that effect vertical dispersion, the less room for error we eliminate from our shot placements the better imo.

[rsterne]

Mark, the basic principle of using a Harmonic Tuner to minimize vertical stringing, and hence group size, is that a bullet leaving the muzzle a few fps faster will drop slightly less (ie a flatter trajectory).... All rifle barrels vibrate.... If you tune the vibrations so that the bullet reaches the muzzle while the barrel is on the upswing, but very near the top of the vibration, then a faster moving bullet will arrive slightly sooner, and the barrel will be pointing slightly lower, relative to the sight line.... A slower moving bullet, arriving a few microseconds later, will exit the barrel on a tiny bit higher trajectory.... If you have the tuner adjusted just perfect, for the range you are shooting at, the two fractionally different trajectories will converge at the target, and the variation in ES will be cancelled out....

Generally speaking, you don't want the bullet to arrive at the muzzle in mid-swing, that leads to a large amount of stringing.... The barrel pauses momentarily at both ends of it's swing, so if all the bullets had identical muzzle velocities, having them exit at either end of the vibration would be just fine.... However, if you tune to the UPPER end of an oscillation, you can additionally partially (or completely) cancel out the ES.... Of course if the barrel is oscillating sideways, or on an angle, you will be left with a small amount of horizontal stringing, which you can eliminate by tuning to the absolute end of an arc.... In order to use the tuner to help cancel the ES, the barrel should be oscillating only in the vertical plane.... That is achieved by INDEXING the barrel, which is rotating it in the receiver until you get the smallest groups, usually at the 6 o'clock position (but sometimes 12 o-clock).... but that is another subject....

Bob

[rsterne]

Yep, Matt, I agree 100%.... Keeping the ES small enough that it stays (well) within 1 MOA is absolutely my goal as well.... When shooting at 100 yards, I generally use a pellet with a BC of 0.035 or greater, and if you do that, the BC makes little difference.... and I would be shooting at 900-960 fps MV, with an ES of less than 2%.... As with the example I gave above, that keeps the stringing within about 0.8 MOA, and if the ES is half that, so is the vertical dispersion.... That is exactly why I prefer regulated PCPs as my gun of choice at 100 yards, for their low ES....

By following my rule of thumb, when I miss, I can pretty much be assured either I messed up, or I didn't allow for the wind.... and that blaming the ES is unrealistic.... for me, at least....

Bob

[Tomg]

Apropo, and a little sidelined from the ES, but indexing a barrel, as far as I can surmise is not to combat the oscillating itself being canted/angled (which really cannot happen) but rather the fact that the bore is not aligned to the OD of the barrel which causes the POI dispersion to become angled due to the exit deflection caused by it. Keep in mind that depending on the bore misalignment direction can cause the vertical dispersion to be more than what the ES indicates, or even less (6 vs 12) (most barrels are off a little bit, just the nature of barrel making) We are not talking about much, but it adds to the dispersion in the other end. Generally speaking you want the alignment to be in the vertical plane, preferably at the 6 o clock position (recoil push at the imaginary bore line pushes it into alignment, if its at 12 o clock its pushes it away from the alignment - I can explain better if someone wants to know)
When you index the barrel you turn it 90degree, take a few shots at the same bull. you will see a ring forming, large or small, you want your barrel in the 6 o clock position.
For most airguns this is not possible due to the transfer port is pre drilled (some rifles uses a thimble, which do make it possible) If you get a new barrel without a transfer port, have the gunsmith index it for you on the lathe before doing the transfer port in the right position.

[scrane]

In a .22 rimfire ES defines  the quality of the ammunition. In an airgun ES is an indicator of the quality and condition of the gun.

[rsterne]

Yeah, I didn't get into the details of indexing, but thanks, Tom, that was a good explanation.... If the bore at the muzzle is not aligned with the OD, it "kicks" the muzzle to the opposite side, and the vibration tends to be in that plane.... When we index it, we want it to vibrate vertically, not horizontally.... I use 6 o'clock, but I have read many prefer 12.... which is why I mentioned both....

Bob

[shorty]

Here is something else to consider with how we calculate ES ((MAX-MIN)/MAX) in regards to "velocity range" using our airguns.

[Tomg]

Shorty, yes, the ES max number expressed in fps is not as accurate in telling the story as a percentage is.
As you can see from the table, the lower the muzzle fps, the higher the percentage is for any given ES.
Good catch.

[shorty]

Here's some more to chew on with ES and POI at 50 yards.

+/-10 fps or what we air gunners call a tuned a gun.

[shorty]

What the tables show is a 1" kill zone is perfect for any small game at a 5% or less ES at 800 fps to 900 fps without wasting our valuable air when shooting at 50 yards. For some reason it feels like anything over 900fps and the air usage goes down with all out PCP's.

So,
Match your pellet weight to your power level and the gun should "theoretically" out shoot you.

[Tomg]

Anything above 950 with pellets has been proven over and over as a very silly goal as it just uses air with very little benefit in speed down range due to very poor BC numbers.