Airgun trajectory, how flat is flat?

[Airgunoregon]

Coming from the AAFTA Field Target game, which is played from 10 to 55 yards... A flat trajectory means to me the difference in clicks or hold over I have to deal with between those distances. The game is all about range finding and reading the wind.

When limited to a 16 power scope for range finding in the "Hunter Class" I try to set up the gun with the scope as low as possible to the barrel. A smaller diameter scope helps get the distance from center of scope to center of barrel lower. I try to get it around 1.5 to 1.75 "

With that setup shooting a 10.34 gr at 932fps I'm .73 low at 10 yards, .14 low at 20 yards, .02 low at 25 yards, 0 at 26 to 30 yards, .37 low at 40 yards, .74 low at 45 yards, 1.24 low at 50 yards, and 1.88" low 55 yards.

You can see that the pellet is really dropping from 45 to 55 yards ( 1.14" ) but, if you guess the distance wrong you still have a good chance to get into the 1.5" round kill zone. On 16 power, with my Bushnell 6500 4-16, I need to hold over 1.75 mil dots at 55 yards. I can get 1 and 2 mil dots in the kill zone at 55 yards, so if I guess wrong on the yardage, I still have a good chance to land in the kill zone.

Now if I mount my scope at 2.75" center to center above the barrel, then my point of impact will be 1.38" low at 10 yards, .43" at 20 yards, 0 from 30 to 37 yards, .06 low at 40 yards, .27 low at 45, .61 low at 50 yards, and 1.09 low at 55 yards.

You can see that the flat zero range has moved out from 26-30 yards to 30-37 yards, more yards in the "flat spot", and less drop from 45 to 55 yards. But from 10 to 25 yards, there is way more chance to miss if I guess the distance wrong. A 16 power scope just doesn't range very well, and there can be 3/8" kill zones out to 15 yards. It's easy to guess a couple yards off and miss that small kill zone, so keeping the height difference lower from 10 to 25 yards is more important in the Hunter class... in my humble opinion.

But in the 12fpe class, they often mount their scope 3" plus above the barrel to make that flat spot even bigger and moved even further out to give them less room for ranging error from 45 to 55 yards where their pellet is really dropping fast, ( 2" from 45 to 55 yards). They are allowed any power scope that can range really well in 1/2 yard distances out to 25 yards and 1 yard distances from 45 to 55 yards.

So to me, the flat spot is really more about scope height than anything else.

In the Extreme Field Target with higher power, but targets out to 100 yards, the things to consider are very similar.

For bench rest, I can't see any reason to even consider this topic. To me it's more about how your pellet gun combo will group at 100 yards... in the wind. I agree that a gun setup for real high power will often "kick" way more, and be very hard to hold steady and get good groups.. so if you go for high power and less drop, you often have a harder time getting good groups.

Wayne

Match Director,

AirGun Oregon

 

[Airgun-hobbyist]

Coming from the AAFTA Field Target game, which is played from 10 to 55 yards... A flat trajectory means to me the difference in clicks or hold over I have to deal with between those distances. The game is all about range finding and reading the wind.

When limited to a 16 power scope for range finding in the "Hunter Class" I try to set up the gun with the scope as low as possible to the barrel. A smaller diameter scope helps get the distance from center of scope to center of barrel lower. I try to get it around 1.5 to 1.75 "

With that setup shooting a 10.34 gr at 932fps I'm .73 low at 10 yards, .14 low at 20 yards, .02 low at 25 yards, 0 at 26 to 30 yards, .37 low at 40 yards, .74 low at 45 yards, 1.24 low at 50 yards, and 1.88" low 55 yards.

You can see that the pellet is really dropping from 45 to 55 yards ( 1.14" ) but, if you guess the distance wrong you still have a good chance to get into the 1.5" round kill zone. On 16 power, with my Bushnell 6500 4-16, I need to hold over 1.75 mil dots at 55 yards. I can get 1 and 2 mil dots in the kill zone at 55 yards, so if I guess wrong on the yardage, I still have a good chance to land in the kill zone.

Now if I mount my scope at 2.75" center to center above the barrel, then my point of impact will be 1.38" low at 10 yards, .43" at 20 yards, 0 from 30 to 37 yards, .06 low at 40 yards, .27 low at 45, .61 low at 50 yards, and 1.09 low at 55 yards.

You can see that the flat zero range has moved out from 26-30 yards to 30-37 yards, more yards in the "flat spot", and less drop from 45 to 55 yards. But from 10 to 25 yards, there is way more chance to miss if I guess the distance wrong. A 16 power scope just doesn't range very well, and there can be 3/8" kill zones out to 15 yards. It's easy to guess a couple yards off and miss that small kill zone, so keeping the height difference lower from 10 to 25 yards is more important in the Hunter class... in my humble opinion.

But in the 12fpe class, they often mount their scope 3" plus above the barrel to make that flat spot even bigger and moved even further out to give them less room for ranging error from 45 to 55 yards where their pellet is really dropping fast, ( 2" from 45 to 55 yards). They are allowed any power scope that can range really well in 1/2 yard distances out to 25 yards and 1 yard distances from 45 to 55 yards.

So to me, the flat spot is really more about scope height than anything else.

In the Extreme Field Target with higher power, but targets out to 100 yards, the things to consider are very similar.

For bench rest, I can't see any reason to even consider this topic. To me it's more about how your pellet gun combo will group at 100 yards... in the wind. I agree that a gun setup for real high power will often "kick" way more, and be very hard to hold steady and get good groups.. so if you go for high power and less drop, you often have a harder time getting good groups.

Wayne

Match Director,

AirGun Oregon

Great explanation of the different setups in each category. I like to set my scopes up fairly low and zeroed the way you folk's do in field target, even though I do a lot of long range bench shooting at silhouettes also. That "flat" shooting first fifty yards makes for good hunting rig and after that dialing the turret or holding over is a must-do situation anyways.

Altering and studying the ballistic charts found in the Strelok and Chairgun apps for speed, b.c., and actual drop over time (distance) gives a lot of insight into long range hold over amounts. As Vetmx, Centercut, and other's have pointed out, on long range shots it is always better to be accurate with the yardage estimation and use the correct holdovers with an accurate shooting gun even if it is a bit slower, rather than flinging a slug down range with a speedy, less accurate gun in hopes that the flatter trajectory will make up for the gun's shortcomings.

 

[ChRiSiS]

I realize I am late to the discussion here and a lot has already been mentioned. I see most people tying flat to BC and I couldn't disagree more. Yes BC will determine how quickly your projectile will slow down, but gravity is gravity and it is a constant downward acceleration of 9.8 meters per second per second. Your pellet is accelerating downwards the moment it leaves the barrel and gravity acts on it - so technically speaking there is no such thing as a flat trajectory, just varying tightness of a parabola based on how angled up your barrel is. So the speed of the projectile is the only thing which will determine how close to flat the parabola is. 

You can mess with BC to see that it's possible for a slug going slower than a pellet will have a flatter parabola, but that a comparison not an answer to Mike's question.

So how flat is flat? It isn't, there will always be a curve.

While I agree with this in general (actually, in totality) there is a role played by the BC of the pellet/slug. The BC will largely determine how quickly the projectile slows down from it’s initial velocity. So while CTshooter is absolutely correct that velocity is the critical determinant and that ”gravity is gravity”, a projectile that decelerates more rapidly will, over the distance travelled, be slower - thus giving more time for gravity to do its inexorable work at 9.8 meters per second per second!

 

[JimD]

Thanks Wayne for a good explanation.

To those thinking slugs are the answer to drop please play around with a trajectory program like Chairgun for realistic projectiles and velocities for your guns. I have and I do not see much drop difference. What is different is wind drift. Close to twice as much. But drop maybe 10-20% less with slugs. I suggest it isn't a huge difference in drop.

I'd been thinking of trying a .177 bullpup in hunter field target but thanks to Wayne I need to rethink that. I was wondering how close the targets get. A conventional rifle where the scope can be lower may work significantly better. I agree completely that the bullpup with it's high scope pushes out the point where you have to hold over but also makes you shoot really low up close. That would make range estimation critical at close range where a conventional rifle would not be nearly so far off - and thus a range error less of an issue.

 

[Kinetic45]

Hummmm having read this whole thread I thought I'd add that for hunting you might consider zeroing at 85 yards because in most airguns you'll be very close to the same height over at 50 yards as you'll be under at 100.

I like to tune my air rifles to 925 to 950 FPS for slugs so I'm +-3" high at 50 yards, on zero at 85, and +-3" low at 100. Sighting in all my air rifles like this helps me when I switch from rifle to rifle. Range estimation becomes a bit less critical.