The time had come to re-zero the scope on my .22/250 to suit the load I've been developing: V-Max 55 grainer, 38.4 grains Hodgdon H380, cartridge oal 2.50 inches.

Up to now the rifle's been satisfactorily zeroed for Federal factory ammo at 200 metres and my home load in development was shooting consistently higher.

For convenience I started at 100 metres and settled on POI high by 2 inches - various ballistics s/w had suggested 0.91 to 1.19 inches high at 100 yards, so allowing a bit for the metric conversion etc....

I then moved back to 200 metres, (The land I zero over has a very gentle down gradient down range possibly 4 feet over 200 metres.) aimed at bull, expecting a drop from poi at 100 metres but guess what? Impact had RISEN by 3 inches. This was no fluke as I put two holes next to each other. I was able to bring poi back down using the scope turret but ran out of ammo before I could re-check at 100 and then calibrate at 150, 250 and 300, but why did poi rise in this way?

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Pete, perhaps you will find the following link useful:

http://www.huntingnut.com/

It has an excellent, FREE, external ballistics program for the download, which should help with this type of questions.

The short answer to your question is: at 2" high at 100 meters, assuming a scope 2" above the barrel, the bullet is still on the "rising" part of the trajectory. 200 meters should be close to the "top" of the trajectory. With a 22-250, you'd cross the line of sight again around 325? HTH, Dutch.

Dutch,

Thanks for your input. I already have that software and I've been using it for several months now. Though I suspect (and hope) you're right, pointblank and an excel spreadsheet available at www.jacksonrifles.com suggest that the round is on the down slope at 200 metres, theoretically at least. (Don't forget I'm trying to zero this load at 200 metres, having previously been zeroed on a factory load at this range.)

FWIW, Pointblank has it reaching the top of the trajectory at just under 150 metres, Excel is less "helpful", showing 0.91 inches high @ 100 yards, 0.97 high @ 150, my zero at 200 and -2.15 @ 250 yards.

One of those times when the "theoretical" caveat attached to ballistics s/w kicks in.

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Pete. It could be that your problem stems from the slant range. This shows up whenever one shoots either uphill or downhill. What it boils down to is this. You are shooting at 100 meters downhill, but the actual range on the level might be only 95 meters. I am a bit mathematically challenged, but I remember that aspect from rawinsonde operations using transponders while employed as a weatherman. (meteorologist) Granted, your slant isn't much, but the change in projectile may also be a part of it.
Just a possible aspect to look at.
Paul B.

Paul,

Thanks - I'd wondered about that enough to do some digging and:

1. I always zero over this land, so don't have the problem of zeroing on flat ground then shooting an incline.

2. I estimate the slope at 200 metres to equate to a fall of about 4 feet or 10 degrees (unscientific estimate using mk1 eyeball). I read that, typically, a 30
degree angle would send a 200 metre shot 2 inches high (100gr .243). So even if I weren't zeroing along the slope, (and had no such problems using factory loads) the impact should be somewhat less than 2 inches.

Don't let me put you off though - if you think I'm wrong and can learn something, or if you've got more data about gradients, I'd love to hear it.

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Wait a minute - I set my target about 4 feet off the ground, so there shouldn't be any gradient effect!

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Hey folks,

Shooting both uphill and downhill will raise the point of impact at a given distance from muzzle to target. Whether a slope of four feet in 200 yards is enough to account for your change, I do not know. I have no prayer of doing the math, but I am certain your POI will rise commensurately with an increase or decrease in elevation. It makes no difference whether you are shooting uphill or downhill - your POI will rise.

Best wishes,
Dave Wile

Pete, you wouldn't happen to have one of those Euro "Cyclops" scopes on that puppy, would you?

If your velocity is anywhere close to where it should be (say, 3450), that's the only answer I can come up with: increasing the distance between the center of the bore and the center of the scope in Pointblank gets me closer than anything else. HTH, Dutch.

I see nothing unusual about that, barrel viberations and each barrel is a inity unto itself...I'll bet it doesn't change much at a 100 when you try it...In many guns if your 2" high at 100 then your 3 or 4" high at 200 and dead on at 250 or 275..All the figures are "there abouts" depending on your barrel, caliber and a host of other varibles.

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

Pete

I think you can forget about gradient, 4ft over 200yds is less than 1 degree. What velocity are you getting and how high is the scopes centerline above the bore?

Regards

Ray

To answer those who've asked, the scope's 1.8" above bore and my average velocity @ 12 feet from the muzzle last time out was 3520 fps.

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Dear Pete, according to my QuickTARGET software and based on your data plus an assumption of standard ICAO metro data, your load should have been 3.6 cm high at 200 m if you were 5.2 cm high at 100. Midrange trajectory would have been 6.1 cm at 139 m. The only explanation for such a high POI might be that the "compensation" (ask an Enfield shooter what this means) for your rifle/ammo combination had the bullet exiting at the top of the barrels vibration cycle. This and your relatively high scope mount serve as "cheaters" to get you a "flatter" trajectory than book figures could otherwise account for. BTW, the easiest way to increase point blank range for any rifle is to mount the scope higher above the bore! Run the numbers and you will see what I mean.

Okay DAvid, spill the beans about "compensation"?

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Pete,

What he means is that if the barrel is vibrating, and is on the way up when the bullet exits, it exits with both a horizontal velocity and a vertical velocity.

The vertical velocity might be 2.63 ft/sec (not a big number) which would give you a 3.6 inch rise in .114 seconds which is the difference in flight times from 100 meters to 200 meters.

Thus a traditional trajectory with no starting vertical component says your POI should have dropped 0.6 inches (to 1.4 inches above LOS) at 200 meters, while the linear offset caused by vertical barrel velocity added 3.6 inches, causing an impact 5 inches above LOS.

This is why you must always test a trajectory at at least two ranges, and preferably out to the maximum range used.

If you find the node where the barrel is at the top or bottom of its vibration, it has no vertical component and this effect disappears. It also makes your groups least sensitive to minor bullet velocity variations.

Don

[This message has been edited by Don G (edited 07-06-2001).]

Don, thanks for the explanation.

So, assuming this is what's happening, and doing so consistently, and I zero my scope (have done) to the poi at my preferred zero distance, 200m, what problems lie in wait for me?

Am I right in thinking that I've got more elevation to contend with than would be the case if the bullet exited when the barrle was at the botom of its cycle - or somewhere else?

I've still got to test the load at 250 and 300 metres but it's rare for me to have to take a shot at much over 200m.

Don't rush me on this - I'm getting theere and my brain's not far behind!

The cool thing the British found out about compensation was that ammo Vo variations were compensated for by barrel vibrations so that the service ammo, at very long range, not only shot better than at closer ranges but also shot flatter. To this day at Bisley, Mausers are preferred for ranges 600 meters or less, No.4 rifles for 600-1000 meters. But the queen of the 1000 meters/1200 yds matches is still the old SMLE which manages to compensate its bullets right into the V. Every rifle/ammo combo has some sort of compensation but it may not be noticeable without careful testing. Compensation explains how some rifles shoot 1 MOA at 100 yards but 1/2 MOA at 300. The only way to eliminate compensation completely is to first develop a load that has the lowest possible SD in velocity. Then the barrel is tuned (a Swiss fellow does this using the aid of acoustic microphones) so that the angle of exit of the bullet is the same every time. That is BTW how the Browning BOSS system works if you have the patience and knowledge to utilize it to the max. The rifle will then shoot its very best and will keep group size in terms of MOA constant at least up to the sonic/subsonic transition. Then all bets are off.

For the official explanation of compensation, see "Textbook of Small Arms, 1929", HMSO. This is now reprinted and available from Jeremy Tenniswood http://www.militaria.co.uk/selous.htm

[This message has been edited by David J. Moses (edited 07-06-2001).]

Pete,

I'm assuming you were 2 inches high at 100 meters and 5 inches high at 200.

If you sight in for zero at 200 meters you should be:

-1.8@0 -.5@100 0@200 -1.0@300 -4.5@400 -12.0@500

That is a weird set of numbers for anybody that knows trajectories!

According to my calculations your muzzle is moving up at 20.54 feet/sec when the bullet leaves the barrel and you must be using almost all of your down adjustment on the scope, as I estimate you need -21 MOA down angle on the muzzle to make it work out.

If you have any velocity variation at all I would expect to see a lot of vertical stringing in the groups.

By all means try it at 300 meters!

Were you the guy with the "long whippy barrel"?

Don

[This message has been edited by Don G (edited 07-07-2001).]

You guys are both right and wrong on this compensation thing. Barrel vibrations tend to disperse group size, but in a near circular manner, the idea that barrel harmonics stay mostly up and down is erronious. However the Enfeild phenomenon is a proven fact. But it has to do with recoil movement and time in bore. Upon firing the muzzle begins to rise, since a slower bullet will exit later than a faster one, it exits with the barrel pointed more vertical than a faster bullet will. Like previous posters have said the result is tighter groups with less vertical dispersion at longer ranges than at shorter ones.

David,

If you call it muzzle motion rather than "harmonics" you take in all effects.

In a typical rifle with the recoil lug below the barrel the recoil will excite the barrel with a mostly vertical component.

Usually in load development you will see that the movement in POI with velocity is mostly vertical. If the pattern is more than 20 degrees or so off of vertical I start checking out the lug and bedding to find out what is wrong.

A bent barrel can really cause an odd shape in the pattern.

Don

Okay guys, here's the update on re-zeroing my scope to match this load (with turret adjustments between shots),

200 metres:
1. 2" low, 3564 fps (I discount this as a first shot of the day flyer)
2. 1 1/8" high, 3584 fps
3. 1 3/4" high, 3627 fps (wound turret the wrong way!)
4. 1 1/16" high, 3608 fps, overlapping hole 2
5. 5/8" high, 3630 fps and turret lowered 1 more click then walked to 100 metres where:

1. 3/8" high, 3621 fps.

So I appear to have a load which shoots very flat at 100 and 200 metres. I'll let you know what happens at 250 and 300 metres!

Pete,
It's raining out so I recalculated using your latest figures. Here's the predicted POIs from your latest data. 3623 fps/ 55grVMax/ .375@100m/ .125@200m (after scope adjustment)

Range// POI// POI w/No muzzle flip
0 -1.8
50 -0.5
100 0.4 +1.0
150 0.6
200 0.1 +0
250 -1.2 -3
300 -3.6 -8
350 -7.1
400 -12.1
450 -18.8
500 -27.4

The vertical component of the muzzle velocity (muzzle flip) is 10.5 fps upward. The angle between your scope and your barrel is -7 MOA, or about 1/2 of a typical scope's adjustment range.

Note that these numbers changed fairly dramatically from the first set of data. On the first day was the POI at 200 meters 5 inches above POA or 3 inches above POA?

That muzzle rate is fairly high, I think it will be hard to reproduce with the slightest change in bedding or load.

It certainly is shooting very flat,but it is an interesting way to get there. I hope it all works out for you.

I would be very interested in seeing a plot of POI (not changing the scope) at 100 yards for a load progression from 36 to 38.4 grains in 0.2 grain steps. I'll bet it is all over the map. I would do that, then load for the point where the POI was at the highest point(bullet exits at maximum of the vertical muzzle velocity.) This gives you the type of muzzle velocity "compensation" that DJM was talking about.

Can you give us a detailed description of the rifle, barrel, stock, etc? Perhaps I am easily entertained, but I am fascinated.

Don
{I had a sign error, do I get partial credit? Changed lowest to highest}

[This message has been edited by Don G (edited 07-08-2001).]

I love this Forum!!
"Compensation"??
I have not been so puzzled since the discussion on the "Magnus force"

Barking Mad/
PerN

PerN,

Yep, It's great, ain't it!

Don

Don,
Where to begin? Firstly, I'm not "whippy barrel"!
Secondly, my scope elev turret still sits mostly at the bottom of its range of adjustment, but I haven't counted the clicks, it's probably up from dead bottom by not more than 2 full turns - I'll look tomorrow for you.
Third, the rifle? Tikka M55 heavy factory barrel, wooden biathalon stock (I belive it's basically as made by Tikka, though the previous owner had the barrel bedded and probably other stuff.) I shoot off a bipod on this rifle, with left hand stock support against right shoulder.
Lastly for now (just got in - had a hard day, I'll be back tomorrow), just looked back at my targets and
25th May: 38.4 gr was 3" high @ 100, 4 1/2" high @ 200.
22nd June: 4 3/4" high.