Trajectory question

[Austin Hemphill]

I was shooting my limited gun today, seeing what kind of groups I could shoot.  I noticed that with my gun sighted at 15yds, at 40 the groups were about three inches lower.  I want to know if this is within the realm of trajectory, or is it me?  The load I am shooting is a 180gr Montana Gold JHP at about 950-960 fps.  I have begun to rethink my shooting, applying what Brian mentioned in Burketts video about the fundamentals, and have noticed a jump in the accuracy of calling my shots, so this would be of great value to me.

[Flexmoney]

Over half of that is you...likely more.

[Austin Hemphill]

Kyle, thanks for the info.  I thought it was mainly my fault.  What would be a reasonable drop?  

[Flexmoney]

With your zero distance...likely an inch is bullet drop.

I am pulling from a Sierra reloading Manual (4th edition) for pistol.  It has ballistic data.

Sierra does something that is interesting.  They calculate the the point blank range the bullet will hit to within two inches above/below line of sight.

For a 180gr., 40 caliber bullet, doing 950fps...you can get a point blank range of 80 yards by setting the zero to 65 yards.

For our purposes...a zero of 30 or 40 yards seems ideal.

A 30 yard zero will give:

(-.10) @ 10 yards

(+.15) @ 20 yards

(0.00) @ 30 yards

(-.56) @ 40 yards

(-1.53) @ 50 yards

A 40 yard zero yields:

(+.03) @ 10 yards

(+.43) @ 20 yards

(+.42) @ 30 yards

(0.00) @ 40 yards

(-.83) @ 50 yards

(The above is for a 180gr. 40 cal doing 950fps.)

[ErikW]

Hey Austin, Detlef and I have the same problem with our Limited guns. We have to hold high on those long targets. I don't think we ever figured out why. Look for the thread if you are interested.

[Phil Dunlop]

Kyle,

thanks for the trajectory tables, newer shooters might be interested to note that in both tables the range at which the bullet first crosses the line of sight has been ommitted.

Using the 30yd zero, the bullet will also be spot on at 12-15yds, and with the 40yd, at 8-10.

I zero my 40S&W at 15, which gives me point of aim at about 35 I guess, but the important thing is that I have no trouble shooting A's out to 50yds.

Its far easier zeroing at the closer distance.

Sorry to state the obvious,

P.D.

[Flexmoney]

Phil,

Thanks for adding on.  With you info in mind...

It is likley that Austin bullet is still on the rise when sighted to his 15 yard zero.  Meaning he would be on zero again at 30 yards as the bullet drops again.

So...he would actually be getting a bullet drop near .56 at forty yards, not my guestimated inch.

Right?

[Phil Dunlop]

Kyle,

absolutely!

The only other concideration is the ballistic coefficient of the bullet, though I doubt there is a huge variation in available 180's

The missing couple of inches of trajectory are much more likely to come from a less than perfect sight picture, and particularly the definition of the target.

I use a steel A zone for a lot of my practice, and find it a lot easier to hit than the A zone of an IPSC target simply because it defines itself.

Hope that makes sense

[Flexmoney]

Phil,

I'd have to do some re-reading...but, from what I recall, you are right.  The bc's (differences) are insignificant in our application.

I like the steel "A-zone" target idea as well.