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What modifications are you doing, and why?

 

I recently had a new world opened to me when I visited one of the running game simulators (movie theatre where you fire live ammunition, computer calculates strike according to range game is presented). I knew stock fit was important with shotguns, but didn't realize it would make such a difference with rifles.

 

With a standard rifle my results was pretty mediocre. When they gave me a Blaser fitted to my size, my results went through the roof - one miss, one poor hit, all other shots took the animal (screen) properly.

 

So the change is simply to have the stock lenghtened to copy that rifle. I have also re-fitted the cheekpiece to get perfect alignment to the new PMII 3-20x scope - it is definitively more finicky on the eyebox than my older PMII 4-16x.

 

Was out shooting today and also had to change my technique:

The rifle now gives best results with very little bipod load and the stock placed almost on the neck.

 

Not sure yet if the change was for a better allround rifle or if I'll revert to original lenght.

 

Absolutely no idea on what shifted the POI, everything is re-done and re-glued and verified with a couple of hundred shots now. Can't track it down to any single cause.

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Thanks Thomas, As i mentioned in the PM, i've ordered the adjustable stock for the blaser. i found the same with my recent revelations in sweden on the cine-range. I've ordered the standard stock length, which i would imagine is a little short for me, if its anything like other european rifles.

 

Glad to hear that you have confidence in the Blaser mounts etc. i was starting to have a mini-panic!

 

How do you find the new PM2, with the new turrets? I see on one of your blogs that you have altered them, with that in mind, what does the new PM2 give you over and above the PMII (2)? apart from the different levels of magnification?

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Nothing. The new PMII 3-20x has definitively been a step down in user experience for me. I lost two routine chances on deer in twilight due inability to properly ID - had to switch .

 

I absolutely trust the Blaser mount. I have simply not had any issues with it (other than price). Also the picatinny system with NF, Seekins or Spuhr mounts have worked well.

 

I glue (Locktite 243) all my mounts/ scopes

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Absolutely no idea on what shifted the POI, everything is re-done and re-glued and verified with a couple of hundred shots now. Can't track it down to any single cause.

 

My thought, especially on realising this was in the UK, not your usual shooting area, was that it could simply be temperature. I saw this article http://longrangeshooter.com/2009/02/temperature-effects-on-zero/ a while ago when trying to understand why my zero wandered so much with one rifle. It is a long article, the only record of such an experiment I have ever seen. One very interesting result, for an AI rifle, was:

 

"Below the 15 - 20 °C mark, there was a ¼ MOA shift for every 3 °C change."

 

That is a large difference, for a quality rifle, it surprised me. Could your zero shift be simply, or primarily, down to temperature change?

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My thought, especially on realising this was in the UK, not your usual shooting area, was that it could simply be temperature. I saw this article http://longrangeshooter.com/2009/02/temperature-effects-on-zero/ a while ago when trying to understand why my zero wandered so much with one rifle. It is a long article, the only record of such an experiment I have ever seen. One very interesting result, for an AI rifle, was:

 

"Below the 15 - 20 °C mark, there was a ¼ MOA shift for every 3 °C change."

 

That is a large difference, for a quality rifle, it surprised me. Could your zero shift be simply, or primarily, down to temperature change?[/

 

 

 

 

Thomas will no doubt confirm/not actual-and indeed the how hight the shot(s) were.

 

Temperature/altitude/humidity do indeed affect ballistics (same for any rifle,of course quality or otherwise),essentially via air density,but the three interact-higher up is usually colder,for example

 

It's unlikely that Scandinavia-Scotland/UK differences were more than 12 centigrade degrees (assuming we are in the sub 15C zone for which the data is available).

 

If so then we'd have 12/3x 1/4 moa max shift which is 1moa and that's about 3 1/2 inches at 350y (High..assumed,but should it be?)

 

It did look as if the shots were a bit higher than 4 inches...(depending on point of aim,of course)....twice that...?

 

So temperature might contribute ( IF Thomas didn't allow for it),but maybe not a full explanation?

 

We'd expect some effect of temperature on wind drift too,though that seemed spot on,so maybe no wind?

 

I'm sure Thomas can confirm the missing jigsaw pieces.

 

gbal

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Temperature/altitude/humidity do indeed affect ballistics

 

I appreciate that it is a long article and I don't expect you to have read it, but it is absolutely NOT about exterior ballistics, this is about the temperature of the rifle, they used a temperature controlled van at the range to set the temp of the rifle, keeping ammo temperature and air temperature constant, I think they even tried to keep the scope temperature constant, but I don't remember exactly how, it's all there in the article.

As such it is an effect that is individual to the rifle and not predictable (direction or magnitude) without measuring it, which is pretty difficult to do.

 

I suppose the proof of whether this was a factor for Thomas would be if the opposite error was observed, i.e. the zero shifted back, when he got home and shot in the usual environment....

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I appreciate that it is a long article and I don't expect you to have read it, but it is absolutely NOT about exterior ballistics, this is about the temperature of the rifle, they used a temperature controlled van at the range to set the temp of the rifle, keeping ammo temperature and air temperature constant, I think they even tried to keep the scope temperature constant, but I don't remember exactly how, it's all there in the article.

As such it is an effect that is individual to the rifle and not predictable (direction or magnitude) without measuring it, which is pretty difficult to do.

 

I suppose the proof of whether this was a factor for Thomas would be if the opposite error was observed, i.e. the zero shifted back, when he got home and shot in the usual environment....

 

 

OOPs,my apologies...the basics I think stand,we need more info from Thomas,which would also apply to external Ballistics (or at least say whether they might be involved),or data that individual rifles can vary x3 the figures given,and short of testing Thomas' rifle it is unknowable. Is the internal effect consistent-eg always POI down when colder ? If it isn't consistent....?

 

Interesting though,if it's consistent within a given rifle.

 

gbal

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OOPs,my apologies...the basics I think stand,we need more info from Thomas,which would also apply to external Ballistics (or at least say whether they might be involved),or data that individual rifles can vary x3 the figures given,and short of testing Thomas' rifle it is unknowable. Is the internal effect consistent-eg always POI down when colder ? If it isn't consistent....?

Interesting though,if it's consistent within a given rifle.

gbal[/

 

 

Thinking on just a moment more,lower internal temperature is likely to reduce velocity (as is external),usually reducing POI,though I take the point that both may interact in individual rifles,and not be consistent rifle to rifle. The effects might also be cumulative in the same direction-here it would need to be vertically up.Probably unlikely for the internal effects to be consistently high POI,given steel tolerances etc,could easily be quite variable,through 360 degrees,though perhaps rifle consistent.

More info from Thomas should confirm/not any temperature changes etc.I think I am even less confident of a full explanation based on temperature,in the one off case...

...but It would help to read the original again (I seem to recall controlled,but completely unknown wrt representativeness,ie one rifle-once-it's a start) but it was a cold day when I read it,and memory might be fallible.) :-)

 

gbal

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The shot took 5 clicks or 0,5 MRAD high which is about 1,75 MOA.

This had nothing to do with the temperature of the rifle or ammunition.

 

The turrets used in Scotland are set up specifically for that location (I use different ones for autumn/ spring) and I shoot with an "offset" trajectory calculation at home.

 

I have "above average" track of the V0/ temperature relationship with my ammunition, so those changes are very predictable and successfully compensated for.

 

In the below video I shoot my "Scotland trajectory" and as predicted the strike is 1-2 clicks low due the differences in weather. Air pressure was 32 hPa higher and air temperature 10C colder. I run a very temperature stable powder these days (Hodgdon H1000), so the V0 change is significantly reduced from what it was with MRP and N560/570

 

https://www.youtube.com/watch?v=sV2OyM5WEwQ

 

I would not expect my rifle do anything unexpected (lower/higher V0) in temperatures from -20C to +25C where I have tested it. I have no background to say much about such issues, but I'd guess there's "stress" somewhere in the rifle if POI changes more than can be expected for the ammunition issues.

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