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Dry fire deviation

Printed From: OpticsTalk by SWFA, Inc.
Category: Scopes
Forum Name: Tactical Scopes
Forum Description: Police and military tools of the trade
URL: http://www.opticstalk.com/forum_posts.asp?TID=43792
Printed Date: October/17/2017 at 06:37


Topic: Dry fire deviation
Posted By: MikieG
Subject: Dry fire deviation
Date Posted: December/29/2016 at 06:50
I have an FNH SPR rifle with an SWFA 5-20x SS scope mounted in Nightforce steel rings. I have noticed that when dry firing, the reticle will move downward on the target roughly .5 MOA upon breaking the trigger. Live fire results are vertical stringing usually all rounds touching.
What could cause this?



Replies:
Posted By: SVT_Tactical
Date Posted: December/29/2016 at 07:40

I would think that just the slightest movement of your finger, shoulder reflex/relaxation, and the mechanical happenings would cause it to move some...... the reticle is etched in glass so it ain't moving in the scope... just you're movement causing the whole gun to move.



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"Most folks are about as happy as they make their minds up to be" - Abraham Lincoln


Posted By: Sparky
Date Posted: December/29/2016 at 09:49
+1


Posted By: MikieG
Date Posted: December/29/2016 at 10:01
It's exactly the same thing. Happens when shooting off a bag or off a bipod. I have the same scope on my REPR. Rock solid. Hammer drops, perfect follow thru. No reticle movement.
Amazed me. Perfect shift. Everytime the trigger breaks. Reticle drops .5 MOA on the target.
As though something is loose. Everything is torqued. Action bolts are 65 inch pounds, ring nuts are 65 inch pounds, ring cap screws are 15 inch pounds. I plan to work on it today.


Posted By: supertool73
Date Posted: December/29/2016 at 13:39
Try another scope on that rifle and try that scope on another rifle

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Lifetime warranty and excellent customer service don't mean a thing when your gun fails during a zombie attack.

"A Liberal is a person who will give away everything they don't own."


Posted By: MikieG
Date Posted: December/29/2016 at 13:40
Ok. Before making blame of shooter/glass/mounting/ or rifle/stock torque, I checked torque and remounted optic. Off to the range to rezero.


Posted By: MikieG
Date Posted: December/29/2016 at 18:10
Ok. Rezeroed. We shall see how it goes. The new question is why does this 178AMAX drop 8 inches between 100 to 200 yards?
It is a 178AMAX pushed by 43gr of IMR4064. 11/10THS is unacceptable. My 168 only drops 4 inches. But this 178 is terrible!


Posted By: Urimaginaryfrnd
Date Posted: December/29/2016 at 18:58
try a 190 SMK or  200 Accubond or 200 Barnes


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"Always do the right thing, just because it is the right thing to do".
Bobby Paul Doherty
Texas Ranger


Posted By: MikieG
Date Posted: December/29/2016 at 23:55
Is it even worse? 175 is reasonably similar to 168. Wouldn't think 178 would be this different.


Posted By: Skylar McMahon
Date Posted: December/30/2016 at 16:32
Post that pic Mickie


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Amat Victoria Curam


Posted By: Rancid Coolaid
Date Posted: December/30/2016 at 16:41
8 inches from 100 to 200, that is way off.

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The plural of "anecdote" is not "data."


Posted By: RifleDude
Date Posted: December/30/2016 at 17:55
Originally posted by MikieG MikieG wrote:

The new question is why does this 178AMAX drop 8 inches between 100 to 200 yards?
It is a 178AMAX pushed by 43gr of IMR4064. 11/10THS is unacceptable. My 168 only drops 4 inches. But this 178 is terrible!


It doesn't. You'd have to be getting in the neighborhood of 2000 fps to get that much drop from 100 to 200.

If you're seeing that much shift in POI, something else is going on, because that bullet cannot drop that much at that distance with a starting MV of 2500-2600, which is what you should be getting with that bullet and powder out of a .308.

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Ted


Money can't buy happiness... but it's much more comfortable to cry in a Porsche than on a bicycle.


Posted By: MikieG
Date Posted: December/30/2016 at 23:49
Spoke with Hornady today. They said 43 is not enuf. 44gr is the magic number. So I will bump the charge up and retest. Looks like a chronograph is in my immediate future.


Posted By: RifleDude
Date Posted: December/31/2016 at 12:29
43 gr 4064 is a near max load for a 178 in .308. 44 gr is right at max pressure, so look carefully for pressure signs.

Regardless, 43 gr should give you around 2500 fps or so MV, which translates to around 4.5" drop from 100 to 200 with the 178 Amax. There's no way you're getting 8" drop due to the load, and even if you were, you won't see much difference in trajectory at that short a distance between 43 and 44 gr charge.

You have other issues elsewhere on your rig, because ballistically, your load simply cannot drop that much at such short distance with that bullet and powder charge. Try a different scope to see if it is the culprit, and if it is, SWFA will take care of you.

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Ted


Money can't buy happiness... but it's much more comfortable to cry in a Porsche than on a bicycle.


Posted By: MikieG
Date Posted: January/05/2017 at 14:47
I went to 44 at the suggestion of Hornady. The drop at 200 was 4.32 inches inches. .6 mil. There were no pressure signs.



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