Bag vs Bipod

[Geno C.]

I went to my first long range match today and it went less than stellar.. It's a cold bore shoot so no fouler or sighters. I knew this so this last week I took out my 300wsm that I have been shooting for a while and had a proven load at short range (100-200yrds). I have a farm that I went to to test to 500yrds. The dope came up with a velocity of 2650. I confirmed this to 500yrds almost perfectly. 10.1 moa up from a 100 yard zero a half inch high. Seemed simple enough. Got to the 600 yard line, dialed 13.75 moa up, 16" high!!! wtf!!!

I always normally shoot off a bipod, either bench or prone. They required that I shoot off their sand bags on a bench. I didn't think it would be a problem. What gives? Is it possible the different shooting platform caused this?

Equipment and load;
300 wsm
210gr Berger hunting vld
61.6gr RL22 2650fps
M70
31" rock barrel
5.5-22 NXS
Yhm Phantom QD
40degrees
29.9 pressure
1300ft

 

[Sterling Shooter]

I went to my first long range match today and it went less than stellar.. It's a cold bore shoot so no fouler or sighters. I knew this so this last week I took out my 300wsm that I have been shooting for a while and had a proven load at short range (100-200yrds). I have a farm that I went to to test to 500yrds. The dope came up with a velocity of 2650. I confirmed this to 500yrds almost perfectly. 10.1 moa up from a 100 yard zero a half inch high. Seemed simple enough. Got to the 600 yard line, dialed 13.75 moa up, 16" high!!! wtf!!!

I always normally shoot off a bipod, either bench or prone. They required that I shoot off their sand bags on a bench. I didn't think it would be a problem. What gives? Is it possible the different shooting platform caused this?

Equipment and load;
300 wsm
210gr Berger hunting vld
61.6gr RL22 2650fps
M70
31" rock barrel
5.5-22 NXS
Yhm Phantom QD
40degrees
29.9 pressure
1300ft

O.K. so I assume you eventually were right-in-there. What was the corrected sight setting? This information would be helpful to discern your error origin. Nevertheless, it appears you were speculating on velocity rather than confirming with a chronograph. Remember, just a 50 fps change in velocity is worth about a minute of angle. In addition, your relationship between the gun and ground being divergent from when earlier zeroed would certainly allow for angular error; and, the relatively heavy recoil of your rifle would accommodate such error if control of the rifle was not consistent. One more thing, looking at your score book does your grouping have a pattern, and did shots eventually go on call? Answers to these inquiries will help get to the source or sources of error. Otherwise, all you can do is focus on proper application of the fundamentals.

 

[Geno C.]

It was a cold bore shoot so only one shot was taken. All my practice was simply a cold bore shot then a separate group on another target. I didn't use a chrono, just back calculated from the hits I getting. I confirmed this at 500 yards the day before in a 7-10mph wind. Dialed 10 moa and help 2 moa into the wind and hit 1/2" low dead center. Followed by a 2.5" group of 5 shots centered around that point of aim.

 

[Sterling Shooter]

It was a cold bore shoot so only one shot was taken. All my practice was simply a cold bore shot then a separate group on another target. I didn't use a chrono, just back calculated from the hits I getting. I confirmed this at 500 yards the day before in a 7-10mph wind. Dialed 10 moa and help 2 moa into the wind and hit 1/2" low dead center. Followed by a 2.5" group of 5 shots centered around that point of aim.

Since observation and grouping assessment are not possible you need to analyze the call/strike corollary. A shot on call but not right in there suggests position issue. A shot not on call suggests the sight not adjusted properly for effects of drag, gravity, wind, and weather.

 

[Graham]

Bag vs Bipod

Your zero was off: You were high because you shot from the bench. Have a look at Frank's comments on the thread here discussing potential zero shift from prone to bench, and its causes.

But the rest of it, to make a total of 16", was you.

 

[Geno C.]

I was afraid of that... I'll have practice more off bags and then put the bipod on and see if I can repeat this.

Thanks for your help.

 

[Sterling Shooter]

I was afraid of that... I'll have practice more off bags and then put the bipod on and see if I can repeat this.

Thanks for your help.

Remember, from any position, there is a line of bore at rifle rest and another line of bore as bullet exits bore which creates an angle and arc between the two lines. For bullets to have the same point of impact, the angle and arc between line of bore at rest and as bullet exits bore must be the same from shot to shot. Even a miniscule divergence in recoil resistance will spoil results, that's to say, if anything about the position is different from shot to shot the shot grouping will be bigger than what would be possible from a shot to shot Princess And The Pea position. Shooters who work on making their positions consistent shot to shot will eventually recognize as they perfect their positions to produce smaller groupings there will still be a change in point of impact when there is any sort of change in the shooter's relationship between gun and ground, or characteristic of bone/artificial support. Even when the shooter is shooting from a specific position using a specific support mechanism, let's say prone with sling, moving from one ground location to another will encourage bullet displacement.

Also, when I know my no-wind zero for a particular distance and position/support, as based on corrected zeros noted in my score book, I will still be receptive to quickly adjusting my sights for any newly created position when a shot called "right-in-there" is not right-in-there. The bottom line is that zeros are as fleeting as they are perishable.

 

[Geno C.]

Thanks Sterling. This is pretty much what I was figuring what happened. I'm going to have to see if I can take a video of me shooting in both positions to see what I can do to make my hold and follow through more consistent in both.

 

[Irokcrawl]

Videoing your self is a good idea. Ive done that with many other things that require exact repetition and it will help point out your flaws as long as you are honest with yourself. I personally shoot about an inch higher when shooting from the prone position at 100 which then of coarse grows as I get out towards 1000 yards. My dope cards have that listed in there and I try to stay conscience about it but from time to time I will find my self using the data for prone which then messes me up when I'm shooting off a platform and vise versa.

 

[Geno C.]

That would seem to be a pain in the ass in a comp so I'm going to try to get both positions to have the same poi.