POI shift revisited-long

POI shift revisited-long

Joined: March 8th, 2009, 4:24 pm

October 1st, 2011, 8:33 pm #1

i have been shooting in a new pro sport and a new Hawke sidewinder 30 with the tactical reticle with half milldots. Really like this reticle and I am going to a click regime from my previous holdover regime. the Tactical reticle is great for wind doping as well.

Yesterday i calibrated a new sidewheel in bright sun. Hector Alfaro was there and gave me a temperature strip to put on my gun. First the rangefinding "findings". This morning i was out early and i had open shadow. Ansel Adams, the great landscape photographer would have called it "zone four" on a 10 zone gray scale. In shadow my ranges were off around a yard. the marks said the targets, placed at a measured distance, were further than the day before in bright sun. As the sun came up and lit the lanscape it chamged back to the original marks. I figure that my pupils dilation effected the plane of focus of my eyes.

Now for the other POI issue. I started with a gun temperature of around 74 degrees. Of course the gun, a springer, creates its own heat and also absorbes heat from direct sun shining on it. I sat in direct sun for a couple of hours and the gun rose to 90 degrees. I then experieced a 5/8" POI shift. The gun started printing its still tight groups higher. not just one or two shots but all shots. there was no lateral shift. It was straight up. Great accuracy with 1/4" hole at 32 yards off the knee. Now, i can understand metal expansion causing this. The scope has a reflective insulating blanket on it and while i don't have a temp strip on the scope it has to have had a lower temp than the gun. This has been discussed before here. Somewhere, I think maybe Bill Day or some one else talked about this and how he fixed his front scope mount so it was a little loose and he did not have this problem any more. I would like some re hash of that fix if possible. Can't remember what he did.

Of course in a match we shoot four times and cover our gun so it does not heat up quite so much so most likely won't get so hot.

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Joined: December 23rd, 2007, 5:14 pm

October 1st, 2011, 8:51 pm #2

None of the scopes I have tested hold POI when sitting in direct hot sunlight for over 15min. compared to shade. List includes 3 Loup comps,4 Nikko 10-50x60 Dia. ,2 Bush 8-32 ,1 Bush 6-24 ,2 Tasco CS 8-40, 1 6500 2.5x16 Bush,1 Hawke 30 and a few others I forget. Least shifty All Bush front focus types. Worst Hawke and Tasco....c
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-bp
Joined: June 5th, 2009, 4:21 pm

October 1st, 2011, 10:14 pm #3

i have been shooting in a new pro sport and a new Hawke sidewinder 30 with the tactical reticle with half milldots. Really like this reticle and I am going to a click regime from my previous holdover regime. the Tactical reticle is great for wind doping as well.

Yesterday i calibrated a new sidewheel in bright sun. Hector Alfaro was there and gave me a temperature strip to put on my gun. First the rangefinding "findings". This morning i was out early and i had open shadow. Ansel Adams, the great landscape photographer would have called it "zone four" on a 10 zone gray scale. In shadow my ranges were off around a yard. the marks said the targets, placed at a measured distance, were further than the day before in bright sun. As the sun came up and lit the lanscape it chamged back to the original marks. I figure that my pupils dilation effected the plane of focus of my eyes.

Now for the other POI issue. I started with a gun temperature of around 74 degrees. Of course the gun, a springer, creates its own heat and also absorbes heat from direct sun shining on it. I sat in direct sun for a couple of hours and the gun rose to 90 degrees. I then experieced a 5/8" POI shift. The gun started printing its still tight groups higher. not just one or two shots but all shots. there was no lateral shift. It was straight up. Great accuracy with 1/4" hole at 32 yards off the knee. Now, i can understand metal expansion causing this. The scope has a reflective insulating blanket on it and while i don't have a temp strip on the scope it has to have had a lower temp than the gun. This has been discussed before here. Somewhere, I think maybe Bill Day or some one else talked about this and how he fixed his front scope mount so it was a little loose and he did not have this problem any more. I would like some re hash of that fix if possible. Can't remember what he did.

Of course in a match we shoot four times and cover our gun so it does not heat up quite so much so most likely won't get so hot.
mount the scope properly, but tighten only the back rings. then snug the front rings gently, so that the scope could slide fore and aft in the front rings as it expands/contracts. this would be best if the scope/mounts were lapped first (pain in the kiester).

you can also do this a different way, smearing a finger print full of RTV (silicone seal) inside the front rings and snugging them loosely so that the front mount has an effective 'cushion' between scope and rings, allowing expansion and contraction without torquing the whole scope. RTV peels off when you're done or if you change your mind.

-bp
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Joined: October 28th, 2003, 9:58 pm

October 1st, 2011, 11:21 pm #4

i have been shooting in a new pro sport and a new Hawke sidewinder 30 with the tactical reticle with half milldots. Really like this reticle and I am going to a click regime from my previous holdover regime. the Tactical reticle is great for wind doping as well.

Yesterday i calibrated a new sidewheel in bright sun. Hector Alfaro was there and gave me a temperature strip to put on my gun. First the rangefinding "findings". This morning i was out early and i had open shadow. Ansel Adams, the great landscape photographer would have called it "zone four" on a 10 zone gray scale. In shadow my ranges were off around a yard. the marks said the targets, placed at a measured distance, were further than the day before in bright sun. As the sun came up and lit the lanscape it chamged back to the original marks. I figure that my pupils dilation effected the plane of focus of my eyes.

Now for the other POI issue. I started with a gun temperature of around 74 degrees. Of course the gun, a springer, creates its own heat and also absorbes heat from direct sun shining on it. I sat in direct sun for a couple of hours and the gun rose to 90 degrees. I then experieced a 5/8" POI shift. The gun started printing its still tight groups higher. not just one or two shots but all shots. there was no lateral shift. It was straight up. Great accuracy with 1/4" hole at 32 yards off the knee. Now, i can understand metal expansion causing this. The scope has a reflective insulating blanket on it and while i don't have a temp strip on the scope it has to have had a lower temp than the gun. This has been discussed before here. Somewhere, I think maybe Bill Day or some one else talked about this and how he fixed his front scope mount so it was a little loose and he did not have this problem any more. I would like some re hash of that fix if possible. Can't remember what he did.

Of course in a match we shoot four times and cover our gun so it does not heat up quite so much so most likely won't get so hot.
One of the best scopes with one of the worst temp/ranging reputations is the Schmidt & Bbender FT scope. What I find very intersting about this is the fact that the S&B has a Titanium tube. The only commonly available material with a lower coefficient of thermal expansion is Carbon Fiber. If a scope with a titanium tube has a worse reputation than a scope with an aluminum tube then something else is going on. If it's expansion causing this problem the S&B should be 4x better than any aluminum scope.

So what could be causing this? I don't have a clue.

Turning to your POI shifting, let me say that I can't shoot 1/4" holes off the knee at 32 yards. I don't think I can offer anything of real help, but I'd be interested in how you sit. The reason I'm asking is that I went to a "floating gun" hold ( The butt actually rests under my armpit) a little over a year ago to eliminate/minimize that problem. As far as i can tell it worked. The problem is that now that my shooting is getting better I can't hold much better than 1/2" at 27 yards due to motion from heartbeat. I seem to be able to hold better by wrapping the gun and putting the butt on my shoulder, but I'm back to getting those pesky shifts like you're experiencing. The short version of my long sob story is that i wonder if we're not just making suttle changes in our hold as we progress in the shooting session. Anyway, that's my theory. So I'm trying to take no more than two shots at a time, separated by long breaks and see how that pans out.

Knobs
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Joined: March 8th, 2009, 4:24 pm

October 1st, 2011, 11:36 pm #5

but yesterday and today were particularly good. at the end of the session i went out to 55 and a 10 shot group was less than 1" wide and about 1/2" high with two unexplainable fliers that were about 1/2" and 1" outside if the group. had to be me althought i had a 3-5 mph frontal wind quartering right to left which may explain the width to height ratio. strangely the fliers went to hte right even though wind was right to left.
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Joined: March 8th, 2009, 4:24 pm

October 1st, 2011, 11:42 pm #6

None of the scopes I have tested hold POI when sitting in direct hot sunlight for over 15min. compared to shade. List includes 3 Loup comps,4 Nikko 10-50x60 Dia. ,2 Bush 8-32 ,1 Bush 6-24 ,2 Tasco CS 8-40, 1 6500 2.5x16 Bush,1 Hawke 30 and a few others I forget. Least shifty All Bush front focus types. Worst Hawke and Tasco....c
when practicing is very unlike what we do in a match. In a match I always cover my gun between lanes with a cover i made from one of those silver dashboard protectors you can get at walmart or the 99 cent store. In addition i am shooting over a hundred rounds, maybe 200 in a session and only 44 in a match. aAlot more continouous heat is involved and the gun and scope heat up more than in a match i think.

I went to pet store and got a couple more temperature tapes so i can monitor what is happening heat wise to both gun and scope.

I will also try the front mount idea. I do have one piece BKL mounts though.
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Joined: March 8th, 2009, 4:24 pm

October 1st, 2011, 11:44 pm #7

mount the scope properly, but tighten only the back rings. then snug the front rings gently, so that the scope could slide fore and aft in the front rings as it expands/contracts. this would be best if the scope/mounts were lapped first (pain in the kiester).

you can also do this a different way, smearing a finger print full of RTV (silicone seal) inside the front rings and snugging them loosely so that the front mount has an effective 'cushion' between scope and rings, allowing expansion and contraction without torquing the whole scope. RTV peels off when you're done or if you change your mind.

-bp
I wonder if you have to coat both sides of the mount or could maybe just do the top ring?
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Joined: March 8th, 2009, 4:24 pm

October 2nd, 2011, 2:39 am #8

One of the best scopes with one of the worst temp/ranging reputations is the Schmidt & Bbender FT scope. What I find very intersting about this is the fact that the S&B has a Titanium tube. The only commonly available material with a lower coefficient of thermal expansion is Carbon Fiber. If a scope with a titanium tube has a worse reputation than a scope with an aluminum tube then something else is going on. If it's expansion causing this problem the S&B should be 4x better than any aluminum scope.

So what could be causing this? I don't have a clue.

Turning to your POI shifting, let me say that I can't shoot 1/4" holes off the knee at 32 yards. I don't think I can offer anything of real help, but I'd be interested in how you sit. The reason I'm asking is that I went to a "floating gun" hold ( The butt actually rests under my armpit) a little over a year ago to eliminate/minimize that problem. As far as i can tell it worked. The problem is that now that my shooting is getting better I can't hold much better than 1/2" at 27 yards due to motion from heartbeat. I seem to be able to hold better by wrapping the gun and putting the butt on my shoulder, but I'm back to getting those pesky shifts like you're experiencing. The short version of my long sob story is that i wonder if we're not just making suttle changes in our hold as we progress in the shooting session. Anyway, that's my theory. So I'm trying to take no more than two shots at a time, separated by long breaks and see how that pans out.

Knobs
my left foot and right foot are separated as much as i can. (i find myself backsliding to "feet together" once in a while). I have a pad made from a small camera bag on my left knee. the gun is balanced front to rear on that. If i take my hands away it stays put. Neutral. I do not touch the front of the rifle with my left hand. The butt is against my shoulder but very light. I try not to touch the pistol grip except on the very back behind the action with my thumb. My trigger finder is on the trigger only. I try to avoid any kind of side to side input no matter how small. No matter how much i practice i sometimes deviate withouut thinking and that may be the source of some flyers. Bill Tramel also pointed out to me that my thumb pressure may vary and cause a downward pressure on the pistol grip throwing a shot high.

the reason i try not to put my feet together is because i am trying to create a plane. Three points establishes a plane and is most stable of all platforms. my butt is one point and each foot is another point making three points to establish the plane. if you sit with feet together you have a two point platform or at best a very narrow triangle but i think an equalateral triangle would be the most stable.
Last edited by LARRYPIRRONE1 on October 2nd, 2011, 12:07 pm, edited 1 time in total.
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Joined: July 24th, 2010, 1:44 am

October 2nd, 2011, 3:51 am #9

i have been shooting in a new pro sport and a new Hawke sidewinder 30 with the tactical reticle with half milldots. Really like this reticle and I am going to a click regime from my previous holdover regime. the Tactical reticle is great for wind doping as well.

Yesterday i calibrated a new sidewheel in bright sun. Hector Alfaro was there and gave me a temperature strip to put on my gun. First the rangefinding "findings". This morning i was out early and i had open shadow. Ansel Adams, the great landscape photographer would have called it "zone four" on a 10 zone gray scale. In shadow my ranges were off around a yard. the marks said the targets, placed at a measured distance, were further than the day before in bright sun. As the sun came up and lit the lanscape it chamged back to the original marks. I figure that my pupils dilation effected the plane of focus of my eyes.

Now for the other POI issue. I started with a gun temperature of around 74 degrees. Of course the gun, a springer, creates its own heat and also absorbes heat from direct sun shining on it. I sat in direct sun for a couple of hours and the gun rose to 90 degrees. I then experieced a 5/8" POI shift. The gun started printing its still tight groups higher. not just one or two shots but all shots. there was no lateral shift. It was straight up. Great accuracy with 1/4" hole at 32 yards off the knee. Now, i can understand metal expansion causing this. The scope has a reflective insulating blanket on it and while i don't have a temp strip on the scope it has to have had a lower temp than the gun. This has been discussed before here. Somewhere, I think maybe Bill Day or some one else talked about this and how he fixed his front scope mount so it was a little loose and he did not have this problem any more. I would like some re hash of that fix if possible. Can't remember what he did.

Of course in a match we shoot four times and cover our gun so it does not heat up quite so much so most likely won't get so hot.
I set up my HW77 and scope a couple days ago in North Carolina in my back yard wooded practice range under bright sky and 80-85 degree temps. All was well when I left for DIFTA, however when I got to DIFTA this morning it was overcast, threatening a shower that never arrived till after the match, and the temps started in the low 50s.

At the sight in range I had to adjust my scope a few clicks to return the zero to it's 30 yard setting, shot a few groups from 10 yards to 50 yards to verify my settings and then started the match. Well....after a bit the skies got darker and it was difficult for me to even determine when the kz was in sharp focus. I then noticed that I was missing some normally "consistently doable" targets by hitting 12 o'clock high.

Before I even shot the course I commented that it was going to be an interesting match for me since I set up my scope range markings in a brighter lighting level and a 30 degree temp differential, plus wind was added to the mix. LOL........judging by the "gaggle of pellet splats" concentrated in an area outside the kill zones it seems that others were having the same issue.
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Joined: October 28th, 2003, 9:58 pm

October 2nd, 2011, 4:55 pm #10

my left foot and right foot are separated as much as i can. (i find myself backsliding to "feet together" once in a while). I have a pad made from a small camera bag on my left knee. the gun is balanced front to rear on that. If i take my hands away it stays put. Neutral. I do not touch the front of the rifle with my left hand. The butt is against my shoulder but very light. I try not to touch the pistol grip except on the very back behind the action with my thumb. My trigger finder is on the trigger only. I try to avoid any kind of side to side input no matter how small. No matter how much i practice i sometimes deviate withouut thinking and that may be the source of some flyers. Bill Tramel also pointed out to me that my thumb pressure may vary and cause a downward pressure on the pistol grip throwing a shot high.

the reason i try not to put my feet together is because i am trying to create a plane. Three points establishes a plane and is most stable of all platforms. my butt is one point and each foot is another point making three points to establish the plane. if you sit with feet together you have a two point platform or at best a very narrow triangle but i think an equalateral triangle would be the most stable.
the only contact i make with the pistol grip is on the lower front with my pinky and ring finger in order to keep the rifle from tilting. Very light pressure only. I first balance the rifle from side to side and use the fingers to fine tune only with light pressure. When the gun recoils, it recoils out of grip with the fingers so they can't ( in theory ) shift the gun from side to side.

I seldom have my thumb anywhere but off to the side of the pistol grip. I find that the slightest pressure during recoil will move the shot.

My foot width varies depending on terrain etc. Usually fairly wide. I also found that if I get my knees too close to my chest it aggravates heatbeat. As I move my forward knee closer to get the gun up so i can use my shoulder on the buttpad my "off" knee seems to be naturally moving out. I don't usually have problems with stability, just the regular rythmic motion caused by my heart.

I no longer have any problems bending over the gun from a flexibility point, but I'm thinking this may add to the heartbeat problem.

I'll be trying a shooting pad off the knee I guess. It'll help ge the gun up a bit. I see a lot of guys using them that shoot springers.

K
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