Effect of heat on elevation

[loadedbutbroke]

Hello I am quite new to reloading and shooting .45-70 Gov with black-powder. I shot yesterday, for the first time, in hotter weather and found that the elevation required for 600yrds went up 10 minuets on my previous sight settings. There must be a reason for this can anyone explain it to me? Is there some way to work out how much to put on? Wind was light but tricky sometimes head on.

Secondly I am told that these boolits drift and that compensation needs to be made on the windage to compensate for this, how do I know how much to put on and which way?

Spec which is the same for all 600yrd shoots

Pedersoli Silhouette 32"
Soule rear sight and adjustable front sight.

530 grn Postell
60 grn Swiss #4
neck sized

Many thanks
Adrian

[KAF]

Head wind causes shots to go low because of the trajectory at long ranges such as 600 yd. Wind hits the bullet on top on the way down. Light will also cause elevation changes to the sights, clouds moving over etc.
556gr bullet at 1000yds has a 67ft mid range trajectory, 600 yds a bit less. Lots of odd winds up there at the bullet is in the winds along time at long range, so more effect.
Check this site out for wind info and use the chart at the bottom, it is correct........ http://tmtpages.com/windvector.htm

[KAF]

Oh and YES the temps and barometric pressure will effect bullet flight. Hot air less denser then cold air. Try to find flight charts for what pilots call Density Air (da)

[JSnover]

If your point of impact was lower, there was something else going on. Higher temperatures and reduced air density should have flattened your trajectory, making the boolit strike higher at 600. The headwind would do it.

[Hickok]

Could be heat mirage if the target was close to the ground, or if the "heat waves" were rising up if front of the target. Can usually be seen with a scope, but not so easy with naked eye.

I also tend to shoot away from the sun with iron sights, i.e., sun overhead, I shoot lower, sun off to the left, I will shoot to the right, etc. Not everyone does, but I seem to find this happens with me.

[loadedbutbroke]

Hi again just to clarify I had to raise the sights by 10 minuets over previous shoots in cool/cold weather to get on target. Pressure at Bisley yesterday was high.

Had a quick look at the recommended site. Looks good and answers the question about bullet drift; however I still can't fathom why the bullets were falling short on the original sight setting I don't think it was the wind as this was variable and in my view too light to affect the trajectory by such a large amount.

Still I am here to learn!

Adrian

[chill45100]

If we could please have the temperature and atmospheric readings or approximations that might be helpful to solving the riddle. A thought I have is related to the wind velocity at the height of the ballistic arc. Sometimes the wind conditions at ground level are much different at say 10 meters up. This can be particularly true if the range is sheltered by short trees or low rolling terrain.
Chill45100

[runfiverun]

have the cases been annealed recently?

[JSnover]

I shot yesterday, for the first time, in hotter weather and found that the elevation required for 600yrds went up 10 minuets on my previous sight settings.

Many thanks
Adrian
How much hotter was it? If we could rule out everything but the weather, it would help to know how much the conditions changed from the first incident to the second.
Also, were you shooting on the same range each day?

[country gent]

How much hotter was it and also how much drier was the air? May have been fouing control failing. Also was it brighter or darker light wise. The old saying was lights up sights up light down sight down. Wind can affect elevation also but 10 mins at 600 yds is actually 60 inches + thats alot for just condition changes. Have you changed your load any? Diffrent powder, charge wieght, grease cookie, wads, seating depth, primer type, cases? As all of these will also affect poi / poa. Keep detailed notes and descriptions of conditions loads sight settings and use this for a refrence for the next matches as time goes and more matches add up data trends becomes more apparent. I shot a shilouette match this morning and 400 yds was good ( 8 rams hit) with the modified load from the last match. I had to come up 1 min more but had dropped velocity on the NASA bullet by roughly 100 fps to around 1250 fps estimated. WInd was some light changes but could keep ahead of it, Light was changing back and forth and was an issue as catvhing the dull was a miss out the bottom and bright was a miss out the top. Light was the issue today. You see a halo or ring around the bullseye andlighter conditions make for a bigger halo duller a narrower halo. Another thing to keep in mind changing a front appeture can have a big effect on zeros as they arnt always centered and diffrent sizes or posts crosses are seen diffrent also.

[loadedbutbroke]

Hello all

Hope the following helps with the detail asked for above.

Ammunition

Same brass Remington neck sized and then very slightly flared never been annealed so far fired 6 times.

Same boolits Lyman 535 grn Postell mine come out at about 527 to 530. I batch them according to weight and load accordingly. I have tried hardening them up a bit recently as I am getting a few little bits of lead coming out on final clean up. Anything outside the batch weight is discarded so for example a 526 or 531 would go.

Same lube which is softer than Alox and very messy to apply (although I have come up with a neat little method of applying it which makes life a lot easier) mostly bees wax and oil I believe.

Same Swiss #4 60 grns slightly compressed with a thin card disc on top.

Boolit set out so it is just short of the rifling and chambers easily. No crimp

CCI rifle primer

I wipe out after each shot

The Range

Bisley Century range this is a maximum 600 yrd range . It has 108 targets across the whole thing is more or less level with slightly raised firing points There are flags at 200 yrd intervals running down the range. There are trees to the right and behind the butts nothing to the left but open land roadway etc. before some taller trees and buildings . Behind the range is a wooded safety area extending some 2 miles over gently rolling hills In fact Bisley camp and ranges are built on natural heathland. If you look at www.nra.org.uk/common/photos/ranges/ranges-2.jpg
(http://www.nra.org.uk/common/photos/ranges/ranges-2.jpg)you can see Century range on a good day. This is a very wide angled shot which is why the 600 yrd firing point appears to have a right angled bend in it. It is of course completely straight.

The conditions/ Sight settings

10/5/14 Pressure Low, rain, bouncing off barrel and strong left to right wind 22 mph Visibility poor chilly say 14 degrees C. Got completely soaked laying in 1/4 inch water

Sight setting at end of shoot 88 minuets (sorry didn't get the windage setting)


31/5/14 Pressure Low cloudy wind all over the place mostly from the right sometimes head on say 18 mph Visibility fair Chilly say 16 deg C spots of rain

Sight setting at end of shoot 90 minuets Windage 9 mins right


21/6/14 Pressure High 1022 mil wind light about 8 mph mostly left to right but very variable sometimes head on, some times the flags were blowing in opposite directions so maybe it was coming straight down? Sunny about 25 degrees centigrade visibility good with a heat haze in front of target however this seemed to be quite still i.e. it was not running one way or the other.

Opening Sight setting 88 (shot under target) at end of shoot 98. Windage varying 2.5mins either way.


Over to you guys.

PS if you are interested in the ranges at Bisley Camp Google it there are loads of pictures where you can see what we Brits get up to.

Addendum

Just some extra points I have just thought of having reread all of this thread.

The weather on Saturday 21/6 was very dry for the South East of the UK; low humidity. The other shoots were in very high humidity due to actual rain or rain on the previous day. It was very wet in May.

I was not the only shooter having to put there elevation up by a considerable amount. We all shoot similar rifles mostly in 45-70 Gov. I however do use less of a load than the others (60grn) who could be using anything up to 90grns paper patched. 80-85 is common. I will see if someone else in the club can let me know how much they raised there sights by.

The wind on the 21st while not strong was very tricky with all shooters complaining about it (mind you they always do).

I was on target 24 on Saturday previous shoots on Century were on 79 and upwards.

The overall aspect of Bisley is very open with the prevailing wind coming over the safety area to the left over Stickeldown which is the 1,000 yrd range and is very exposed and then onto Century The right hand side of the Century range always seems to be windy something to do with the trees.

Adrian

[Tom Myers]

Secondly I am told that these boolits drift and that compensation needs to be made on the windage to compensate for this, how do I know how much to put on and which way?

Spec which is the same for all 600yrd shoots
Pedersoli Silhouette 32"
Soule rear sight and adjustable front sight.
530 grn Postell
60 grn Swiss #4
neck sized
Many thanks
Adrian

Adrian,

"Spin Drift" is a result of air pressure caused by bullet velocity and attitude during the trajectory. The spinning bullet is essentially a gyroscope flying through the trajectory path with a slightly nose up attitude.
Air pressure on the lower side of the bullet/gyroscope causes the bullet to move at a right angle to the direction of force. (In the case of a right hand twist, the direction of movement is toward the right)
So, to compensate for the spin drift, the rear sight will need to be moved the left.

A ballsitics expert (Bryan Litz) has devleoped formulas to calculate (estimate) the spin drift of an individual bullet at different velocities and under various atmospheric conditions.

A bullet stability factor is calculated using bullet dimensions, velocity and barrel twist rate and that stability factor is then applied to the time of flight to each range. The result is then modified by the atmospheric conditions at the range.

A lot of pencil and paper time is involved with the calculations with the attendant potential for calcualtion error. I have been working on an upgrade to the Precision Ballistics software (https://secure.tmtpages.com/catalog/) that incorporates Mr. Litz's formulas to calculate the spin drift and display the sight adjustments, for a specific firearm and sight setup, needed to compensate for the drift at various ranges.

Not sure of your velocity, but will estimate it at 1200 fps.

These images are from the, soon to be released, upgrades to the Precision Ballistics (http://www.tmtpages.com/Ballistics_Ver-4_Help/hlp_precision_ballisticsx.htm) and Precision Load Records (http://www.tmtpages.com/New_Prec_BR/PrecRec/Prec_Rec-Bas.htm)software.

The data entries and calculations are from my own target and chronograph records of groups fired from my Pedersoli Sharps 45/70, 525 gr. Postell, 70 gr. Swiss 1.5 combination. I recently used the Pedersoli in the Harris, Mn. BPCR 800, 900 & 1000 yd match. Although we were rained out after the 800 yard shoot, the sight adjustments for elevation and spin drift were very close to the computer estimates.

The estimated spin drift at 600 yards would be approximately 14 inches to the right and the sight windage would need to be adjusted left by 5 graduation marks or one complete turn of the adjustment knob.

The calculations indicate that, at 600 yards, the 18 mph headwind would cause a 16.9 inch drop and an atmospheric pressure change of 1.7 in/hg would cause a further 8.5 inch drop for a total drop of 25.4 inches or 4.3 points on the vernier sight.

That leaves 5.7 points of your sight variation unaccounted for but the previous posters have offered enough to probably account for the remainder.

http://www.tmtpages.com/LinkSkyImages/forum_images/PrecBalRec-5/PrecRecSystem.png


http://www.tmtpages.com/LinkSkyImages/forum_images/PrecBalRec-5/PrecRecBullet.png

http://www.tmtpages.com/LinkSkyImages/forum_images/PrecBalRec-5/PrecRecTargetRec.png

http://www.tmtpages.com/LinkSkyImages/forum_images/PrecBalRec-5/PrecRecShotRec.png

http://www.tmtpages.com/LinkSkyImages/forum_images/PrecBalRec-5/PrecBalDataEntry.png

http://www.tmtpages.com/LinkSkyImages/forum_images/PrecBalRec-5/PrecBalTrajectory.png

http://www.tmtpages.com/LinkSkyImages/forum_images/PrecBalRec-5/PrecBalSights.png

[loadedbutbroke]

Hello Tom

Thank you for a very comprehensive response to the thread. A lot is clearer now and combined with the ideas from others I certainly know a lot more about the theory behind this ballistics business for these big calibre black powder guns. My previous experience has always been with .303 and .308 at long range. Completely different animals of course.

I am away at the moment so can't get to check anything but I think the next thing is to check everything that I have done prior to and up to the last shoot when it all seemed to go wrong. One thing that I am beginning to wonder about is if the back sight has moved in some way, I can't say that I am over impressed with the Pedersoli sight.

I did check with one other far more experienced shooter who confirmed that the wind was tricky but they did not have the same massive variation in elevation.

Unfortunately my next shoot is not until end July at 600yrds and I do not have the opportunity to experiment before then.

Adrian

Ps I shall let you know how I get on or if I find anything.

[loadedbutbroke]

Hi again

Ok, I have been through and checked all three main components and have found as follows:

Ammunition.

I had some rounds left so dismantled a couple to check that I had not under-loaded them by mistake. Both were spot on 60grn.

Sights

The front sight seems to rock very slightly on the adjustment mechanism (Pedersoli adjustable with level) but I don't think this could a/c for such a large variation in point of aim. It always returns to its resting position.

Rear sight (Pedersoli Soule with adjustable apertures.) now this does concern me a bit as it does not always seem to return to exactly the same position once the rifle is fired and swabbed through. There appears to be a little bit of lean backwards or forwards once the bottom ratchet is engaged. This could account for a minuet or two either way but I would not have thought 10 minuets. I am beginning to think I need a better rear sight, any ideas of what and would I be able to get it over to the UK?

Records

I keep records of each shoot but the problem here is that my shooting activities since acquiring this rifle have been disjointed and therefore comparing across the range of limited data is quite difficult.

I went back through each shoot and put them on a spread sheet and compared what I believe is the best elevations I have at each range from 1,000 yrds down to 300 yrds. It became apparent that the data for the shoot on 10th May is wrong. Of course this is the data I used for the sight settings on 21st June! Therefore instead of being 10 minuets over I now believe it is only 3 to 5 minuets higher in elevation than I would expect.

So it would appear that the reasons for variation that fellow shooters, who are far more experienced than I am, have posted could easily explain the difference.

Light up sights up, The higher temperature etc.

Finally I checked as best I could my sight settings against a fellow shooters settings (in general not for that specific day). They use 85grn Swiss 3 for all ranges where as I am down on 60 grn No 4 up to 600yrds and 68 grns up to 1,000.

So it looks as if the main problem was my record keeping.

I hope contributors don't think I have wasted there time; I have learned a lot from the previous posts and will take it all into account on the next outing for which I am confident I shall be better prepared.I am shooting again 3 and 600yrds on 26th July.

[44man]

Light and wind. Targets are just not where you see them as the sun moves. You can actually aim where there is no target. Mirage makes it worse.
The best after market sight I have ever seen is made by Kermit Hoke, shoots Shippensburg Pa. I have his E mail as kshoke@comcast.net. Price is very reasonable.
BPCR shoots let you sight in before record shots, conditions are the reason. IHMSA does not allow sighters.

[loadedbutbroke]

OK shot again yesterday and am pleased to report that my sight settings were spot on for both 300 and 600 yrds which is very pleasing.

I also had the front sight tightened up by a Gunsmith. I am uncertain what they did but the front sight no longer rocks.

Going back to where this thread started re the effect of heat on elevation it was interesting that yesterday was the hottest range time I have done yet it seemed to have very little if any effect on the elevation. What did seem to make a difference was the light right wind which swung round to head on every now and then . This did cause the elevation to rise by a couple of minuets or more.

The light was in my opinion not as good as one would have expected considering it was sunny, perhaps there was a slight haze down the range. I did not see any appreciable mirage. Probably a function of my less than perfect eyes but I did have a problem focusing on the small targets, at times the image dropped out altogether.

Next shoot will be long range and I hope my new proven sight settings will be a good start point.

I use 60 grns Swiss #4 for mid-range, seems fine: 68 Swiss #4 for long- range 900/1,000, also good: any suggestions for an increase for 1,100/1,200 yrds? I was thinking of 76 grn. The boolit will be the same 530 odd grn Postell.

One of the problems I have is getting to test my ammunition before I shoot in earnest .

Thanks to you all for your help

Regards Adrian

[dave roelle]

Hi Adrian:

What kind of accuracy are you experiencing ?

I am betting the sight problem was a major contributor to the vertical---------shoulder position and shoulder pressure also have significant vertical effects -----Mirage can easily add or subtract 2 minutes.

Shooting prone ?-----cross stick height and barrel position on the sticks effects vertical !!!

Dave

[loadedbutbroke]

Hi Adrian:

What kind of accuracy are you experiencing ?

I am betting the sight problem was a major contributor to the vertical---------shoulder position and shoulder pressure also have significant vertical effects -----Mirage can easily add or subtract 2 minutes.

Shooting prone ?-----cross stick height and barrel position on the sticks effects vertical !!!

Dave

Hello Dave The accuracy is in my opinion is not too bad. I am getting pretty good groups at both 300 and 600 yrds depending of course on how well I am reading the wind! At 900/1000 I could not say as the conditions have been so bad each time I have shot. What I should do is go to 100yrds and test both my loads bench rested. Unfortunately this is not easy to arrange at the present time.

I always shoot prone using some very stable, adjustable cross sticks and use the same height for each range according to the relationship between the firing point and the target. Now your point about the position of the barrel on the sticks is something I had not considered. I usually have the sticks just over 1/2 along the barrel but yesterday it was nearer 3/4 of the way along.

I always try to get the position of the rifle in the shoulder at the same point if for no other reason than to minimize the felt recoil, but I have to confess that getting comfortable is not easy; this was the main reason I swooped the Rolling block for the sharps and I have to say I do find the Sharps more comfortable to use. I think on reflection that one of the main reasons for this is the relationship of the barrel to the butt. The rolling block butt appears to sweep away lower below the receiver than that on the Sharps, it all feels more in line and I find the right hand is more comfortable in relation to the rear sight and of course the triggers. The whole thing seems better balanced.

Thanks for the info

Adrian

[dave roelle]

Hi Adrian:

Certainly barrel/sticks position isn't all of a 10 minute difference but perhaps 3 or 4 minutes !!!

There are other listings on finding the "null" point of a barrel-----------hanging the rifle and tapping the barrel-----talcum powder dusting when shooting-------------i have tried both and they get closer than just guessing-----------what your actually trying to achieve is "barrel axis recoil"----if the barrel/rifle is jumping on the sticks ---move along the barrel until you find the spot that results in the "straightest" recoil.
Bet you find a difference-------------------now windage there's the hard one to dope out!!!!!

I shoot a Shiloh #1 30 inch 45/2.1

Onward thru the fog

Dave

[Scharfschuetze]

An interesting thread! I'm glad you got your sight worked out and are back to "zero" again. Having been in the long range business in the military for several years, I just couldn't quite get to grips with a 10 minute or 60 inch (152 Cm) difference in your zero at 600 yards, even with Tom's excellent screen shots of his ballistic programs. It now makes sense and I'm sure that it is a relief to you as well as a boost to your confidence in your rifle and load.

I'd love to see those old British ranges of lore. Lots of shooting history made on those ranges.

I certainly agree with you on your evaluation of the Rolling Block v. the Sharps. I have a US Navy Model 1870 RB in 50/70 and it always takes a while to get used to it's stock geometry.