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POI changes with Bi Pod, groups going crazy.

 
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  #1  
Old 09-08-2006, 09:36 AM
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POI changes with Bi Pod, groups going crazy.

I just bought a couple Harris 6-9 Swivel bi pods with the notched legs. I have tried them on 4 different rifles. My 3 Accumarks and my ever faithful Ruger 77V. All 4 rifles it changes my point of impact 1 1/2" up and turns 1/2 inch grouping guns off of the bags into 1 1/2 to 2" horizontal stringing messes. The 22-250 is not that bad but it still changes the poi by an unacceptable amount. I have tried a variety of rear rests, different holds and nothing seems to work. I bought them after reading about all these precision shooting results I have seen on this sight and others. I tried the same Harris in the 9-13" model before I bought mine. On the bench it was just too tall but it did the same thing. I thought it was because it was too tall. The 6-9" seem very steady. Looking through the scope and dry firing they are more stable than my sand bags. 2 of my Accumarks are very generously free floated clear to the action. There is no stock pressure on these two at all. Right now the only thing they are good for is taking pictures and holding the guns for cleaning. I have had several other people shoot them with the same results. Their Harris bi pods seem to work fine. What the heck is going on with mine?

I always cover my shooting table with a blanket. Could that be causing the problem?
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Old 09-08-2006, 10:22 AM
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Re: POI changes with Bi Pod, groups going crazy.

I know what you mean about impact shifting. It bugs me to. I however dont have the same problem w/accuracy as your stating. This is what I usually do. I work up loads from a bench and a lead sled. The bi pod is on my stud on the rifle, but I work up loads and zero off the bench. Now the funny thing is, when I shoot off the bipod, its no longer perfectly zeroed, especially as the range increses. I think what one needs to do is sight in how he will be shooting. So I will be working up loads off the bench and lead sled still, but when I zero the loads, I need to zero off the bipod because they impact differently. Example being that my 270 takes 6 more clicks of elevation to get to 800 yards when I am using the bipod vs. shooting off my leadsled. It does make a difference and you need to account for it or you'll be missing at longer ranges. Its all a headache at first as to why your not hitting where you want, but everything has to be the same every time when shooting. I guess it goes for rests to, it has to. Usually my groups are bigger off the bipod because its not as steady as a bench rest. Thats why I dont like to zero off the bipod that much because its not as perfect of zero, but when you zero off the bench and then take a shot in the feild laying prone w/bipod, chances are your not gonna hit where you thought you were.
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Old 09-08-2006, 12:36 PM
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Re: POI changes with Bi Pod, groups going crazy.

I would think that the swivel part may be the problem , you hight not be able to see it but your gun moves alot when you pull the trigger even on an empty chamber were talking thousandths of an inch but that makes a differance. and when the rifle is being cradeled in bags it kinda hold it still where its just siting on the bi-pod , with rubber feet no less.
I've found that 99% of bi-pods will make your gun bounce from recoil , one way to help correct this is to rest the feet on small sand bags so some of the bounce is soaked up.

If your not contacting the barrel in any way with the forend then theory what ever the forend is resting on doesn't matter , but guys don't relize somtimes what all happens and just how much movement goes on from the time the trigger is pulled to when the bullet leaves the barrel
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Old 09-08-2006, 02:36 PM
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Re: POI changes with Bi Pod, groups going crazy.

That might explain why I had a zero shift when I added rubber feet to my AI bi pod that previously had metal ends.
I thought it was coincidence but it has never shifted zero before or since.
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Old 09-08-2006, 03:56 PM
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Re: POI changes with Bi Pod, groups going crazy.

Jeza , make no mistake , they will bounce a little with steel feet also. I feel that the problem is that the gun moves backward and the legs "load up" and cause some bounce and with rubber feet it may slide some rather than sticking like rubber would.

I'f I get time I may do an experiment between rubber feet and some polished SS balls as feet and I'll rest them on a polished SS plate with some lite oil so they will slide easy and compair this to the regular feet shot off of a
Line-X coated table
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Old 09-08-2006, 04:46 PM
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Re: POI changes with Bi Pod, groups going crazy.

Don't laugh, but I read on this forum or another that someone's answer to the problem was placing the bipod legs in an upside-down frisbee. Might work if it is flat enough across the top.
The plus side to that is on a slow day shooting groundhogs you could play catch or try for a record distance throw in the open fields. [img]/ubbthreads/images/graemlins/grin.gif[/img] Or maybe hit groundhogs with the frisbee, sort of like catch n release. hmmmmm [img]/ubbthreads/images/graemlins/wink.gif[/img] BC would probably be terrible though...
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Old 09-08-2006, 04:55 PM
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Re: POI changes with Bi Pod, groups going crazy.

I dry fire a lot to practice. It's dead steady on the dry fire or shall I say that at 300 yards the crosshairs won't leave a 3/8" aiming point. Now when I fire that is a whole new thing. On the recoil it will lift the bipod 3-4" straight up and the gun torques over sideways on the swivel. I have my swivel so tight it takes two hands the tilt the rifle. I bought these as a quick alternative to setting up front bags that always need a slight adjustment after each shot. Since I can't shoot prone without the help of a small crane I won't have much use for at least one of the bipods. Looks like I'm in for a Caldwell BR rest next.
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