Hi all,

I use a 270, and load Sierra Prohunter 110g projectiles.

A couple of weeks ago, I shot military at 500yds, and adjusted the elevation so that POI was the same as point of aim at that range.

Went to the range today to re-sight for upcoming hunting trip, and I'm puzzled.

At 50yds, I adjust the elevation to place the POI at about .75" above point of aim. When I fired at 50yds with the '500yd' setting, the bullet was hitting about 7" below point of aim at 50yd. BC of bullet (according to Sierra) is .318.

Is it possible to work out velocity using this info? I'm a bit intrigued because according to Point Blank, my bullet should have been hitting about 30" low at 500m, which it wasn't!!

TIA

Velocities estimates based on bullet drop can be pretty wild and confusing, as you have discovered, especially at only 50 yards. A friend had a similar experience which led him to believe that his bullet was actually rising instead of dropping.

Chronographs are cheap and accurate.

I shoot a .270 also and know first hand the accuracy potential but am not familiar wih Point Blank. Will have to agree with popenmann about chronographs. My experience using the chronograph and ballistics software has shown that there is sometimes a good bit of variation in velocities published in the reloading manuals. I use the Sierra Infinity 5 ballistics software. Using this software, the bullet drop calculations will be based on your bullet type/weight/ and velocity readings from the chrony at whatever distance you choose.
Also, I have had some problems with elevation settings that caused some very strange POI when all other factors were correct.

quote:

about 7" below

Huh?
7" high at 50yd would be approx 2716 with the Sierra 110gr .277 bullet (assuming a 1.5" scope height and standard atmospheric conditions.
The way I used to do it BC (before chronograph) was to use my 100yd scope setting, and hold steady on the aiming point at various ranges (say 100 to 500 in 100yd increments) and than match the measured group centers to the projected curve, varing only velocity. Of course I knew the atmospheric conditions I had been shooting in, so that variable was eliminated for me. With enough points on thecurve, you can get fairly close.

Tailgunner,

"huh?" was also my reaction!! I've always used the method you describe (ie, set the scope for 200, and then learn hold over, windage etc.,)... I HATE resighting rifles (even though all my rifles have Leupold scopes on them )

I'm not a great fan of sending bullets downrange to get back to where I was in the first place!!

However I needed to adjust the elevation so that my 14 yr old son would have a reasonable chance of competing at 500yds, and thought it would be interesting to see the results of the adjustments I made.

I've never relied on software to replace actual experience... in 40+ years, this is my first time at comparing 'actual' with 'theoretical' trajectories.

I also think I might have been using PointBlank the wrong way...

Bugger the software... my groups are accurate, repeatable, and in general I know where the bullet will hit out to any reasonable hunting distance...

I'm by no means a 'Luddite', but I'll stick with actual from here on in...

quote:

Originally posted by rugeruser:
Hi all,
When I fired at 50yds with the '500yd' setting, the bullet was hitting about 7" below point of aim at 50yd.

Are you sure you don't mean 7" ABOVE POA at 50?
At a wild guess, I THINK full bore rise in minutes for 500 yds from 100 yds would be about
9, so 7" at 50 sounds reasonable.
John L. (Wait till you see my new .458 W.Mag.)

quote:

Originally posted by rugeruser:
...At 50yds, I adjust the elevation to place the POI at about .75" above point of aim. When I fired at 50yds with the '500yd' setting, the bullet was hitting about 7" below point of aim at 50yd. ...

Hey rugeruser, That is indeed a bad sign. None of the things I can think of for having it happen are good.

Either the scope broke, the adjustment quit "tracking" properly(aka also broke), someone re-adjusted the scope and did not mention it to you, you readjusted the scope and forgot doing it and then did it again, you got mixed up on the number of clicks, the scope suffered a huge impact and got "out of whack"(technical term for broke), you somehow got moscow bill Targets which are Lieing to you, you were laying on the bench upside-down doing the shooting, you had the rifle scope "down" instead of "up" during the firing, or you originally adjusted the scope the "wrong direction" and had the bullets hitting the ground at 100yds and then bouncing into the target at 500yds(aka bank shot).

Doesn't matter which one it is, but you do need to figure out what happened before you go flinging bullets at Game.
---

By the way, real good to see you are actualy verifying the Point-of-Impact instead of just believing the External Ballistics software. NOTHING replaces a real Drop Chart.

What is the altitude?

What is the humidity?

What is the temperature?

What is the air pressure?

And most importantly, how close is the published Ballistic Coefficient to the actual B.C., and at what velocity, since B.C. varies with velocity.

Bottom line, attempting to make a reasonbly close interpretation of velocity based solely on trajectory is a crude art, at best. A ballistic pendulum, while itself something of an art to use, is much better. But with dependable chronographs available from a hundred mail-order sources for less than $100, isn't this a purely hypothetical question?

My fault, I reversed point of impact with point of aim... I also used Point Blank from the wrong (?) perspective.

Problem has been resolved...

Thanks for all your help and input.

RU

First, get a 45$ chrony, and that will end your issue.

PBR (Point blank range) is defined as a given height (call it a circle, it's easier on your mind) that the radius is the MAX you will stand for your rifle to raise/fall.

For example, say you want a rifle with a 6" PBR... Take 1/2 of 6.. that's 3... You will be sighting in for a max of 3" rise and a 3" fall, and will still have a rifle sighted in for deer.

A rule of thumb is that from 2600-2800, it's ABOUT 265 yards. Which is a good place to start at.

Here's the funcionality... a scope (line of sight) is a flat plane. A bullet travels in an ARC, and is "falling" the instant it leaves the barrel. So, if you sighted in for say 265 yards, 3" low, your bullet would cross the sight plane TWICE... once on it's way from the muzzle to the max height, twice on it's way down. (this is that neat function that allows you to get on paper at 25 yards and be close at 100)

You would then need to shoot, at various ranges, to know where it's actually EXACTLY hitting, but with a +/-3inch (better than most people can shoot without a good rest) it's "point and click"

a 30/30 with 6", iirc, is just shy of 200 yards, and a 30-378 is just shy of 300.

jeffe

Probably the best course of action to determine bullet drop or trajectory is the point of impact at the desired distance. The only way any of us are going to find this is by shooting the load and adjusting the sights for POI. Granted, the chrony is an excellent tool and when combined with a ballistics software program MAY give the shooter a good starting point to determine POI. The actual POI is going to be factored by so many variables that it would not be within the scope of this discussion to even go there. Trajectory AND wind drift are equally important to the firing solution at longer ranges - provided the line of sight is 15 degrees or less horizontal. In the field, my shots at game will be limited to 250 yards or less.

quote:

Originally posted by jeffeosso:
First, get a 45$ chrony, and that will end your issue.

jeffe

Yeah, I got one for sale right now (see classifieds).