Rear Bag Settling Tricks?

[kvd]

Thank you for the information. Happy that you were able to improve your setup.

Ken

 

[Brians356]

Ken it worked out well, shot best score this year. Instead of fidgeting with bipod or bag adjustments during the string of fire, simply slide the rifle slightly to tune the elevation. The 1.5 degree was just right.

When you "slide the rifle slightly", does the bipod stay planted in place? That would want to flex or fold the legs slightly, but your results suggest no adverse effect.
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[CharlieNC]

When you "slide the rifle slightly", does the bipod stay planted in place? That would want to flex or fold the legs slightly, but your results suggest no adverse effect.
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Brian the legs on by bipod are rigid, the length of the leg adjusts by rotating it as a screw. The feet are designed to slide on the mat. So there are no issues with it. That would not be the case on my tactical rifle which uses a Harris with claw feet, which is what I think you are envisioning.

 

[memilanuk]

Ken it worked out well, shot best score this year. Instead of fidgeting with bipod or bag adjustments during the string of fire, simply slide the rifle slightly to tune the elevation. The 1.5 degree was just right.

...and now you know why the McM XIT stock has a slight taper to the toe - it's built specifically for FTR. The other option would be to switch to a SEB JoyPod, so you could do all the elevation control with the joystick. Sounds like you're kinda invested in your current bipod, so you're probably better off using a tapered stock like you did.

 

[noload]

The butt is straight and parallel to the forend, sliding it back and forth gives no vertical change looking through the scope. A quick calculation shows the settling is only around .01inch to yield 2 moa. Such little deviation is why I'm able to squeeze the bottom of the bag, and not really feeling movement, and restore the elevation. I was able to tamp 3 filling spouts of sand into it and will shoot next week to assess. Worst case I will squeeze bag to restore, as this is less disruptive than loosing position to adjust the bipod.

May be I'm missing something but I don't know how you can shoot with a bipod and a straight butt without having vertical setup issues. Or problems half way through your string. I would suggest a taper in the rear butt stock

 

[Brians356]

May be I'm missing something but I don't know how you can shoot with a bipod and a straight butt without having vertical setup issues. Or problems half way through your string. I would suggest a taper in the rear butt stock

Uh, he already did, and problem solved, unless I'm confused (not atypical.) Something about a 1.5-deg taper ...
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[memilanuk]

Yup. Just surprised me that he went with such a shallow angle (1.5°) rather than something more normal like 3 or 5°. But hey, whatever works. Getting the stock angle to match up with the angle of the top of the bag as closely as possible helps make everything play nice together.

 

[BoydAllen]

Some time back, a friend who was having issues with his bag base (one of the long tall ones filled with heavy sand) stretching had one made with double wall construction, cordura on the inside and leather on the outside. His bag was stretching because of vibration from riding around in the back of his pickup.

Out in my garage is an unfilled short range bag, from an estate sale, that is made entirely from cordura. I am going to be interested in how that works. It seems to have been made by Protektor, with a gap between the ears that appears to be suitable for a short range benchrest stock. I have several other bags so I should be able to make a decent comparison.

 

[CharlieNC]

Why 1.5deg? Upon recoil taper works against you as vertical moves during the shot, and inconsistencies by the shooter detract from the score. I would prefer straight, parallel but thats the topic of the thread.

The degree of settling while shooting a string was 1 to 5 moa max, quantified by observing the target rings. A little trig shows this is only a few hundreths of an inch in bag height, which I came to accept as unlikely to resolve. So how much taper to offset 5moa without undue impact during recoil? Recall 1.5deg = 90 moa. Over the length of contact between the bag and stock I figured the few hundredths in height could be recovered by sliding the rifle approx 1in. To me this accomplished fine tuning while not overly sensitive like a highly tapered stock. The result suits my shooting style well.

 

[noload]

Why 1.5deg? Upon recoil taper works against you as vertical moves during the shot, and inconsistencies by the shooter detract from the score. I would prefer straight, parallel but thats the topic of the thread.

The degree of settling while shooting a string was 1 to 5 moa max, quantified by observing the target rings. A little trig shows this is only a few hundreths of an inch in bag height, which I came to accept as unlikely to resolve. So how much taper to offset 5moa without undue impact during recoil? Recall 1.5deg = 90 moa. Over the length of contact between the bag and stock I figured the few hundredths in height could be recovered by sliding the rifle approx 1in. To me this accomplished fine tuning while not overly sensitive like a highly tapered stock. The result suits my shooting style well.

Charlie I understand your theory completely. I don't know if you can have "NO Bag settle" shooting a larger caliber rifle in the prone position with a bipod. Even my Open class gun with a straight butt stock will settle. I've been trying to fix rear bag settle for yrs now ... I seem to get to a certain point and thats it. Then you have the ground settling also. ???

 

[CharlieNC]

Pat after determining the "settling" is a few hundredths of an inch, I decided that would not be corrected by any fill besides concrete! Hence a different tactic.

 

[memilanuk]

@CharlieNC something I copied shamelessly from others is putting a tab on the stock hardware that extends down and touches the rear of the bag (alternately, extends sideways to touch the back of the bag ear on one side). Use it like a lot of F-open and BR guys do the front stop on their front rest - after the shot, push the gun forward to where it touches, then ease it back a bit.

For my gun, I set it up so the crosshairs are around the bottom of the target @ 1000yd when the tab is against the bag. I ease it back to where they are in the middle, reload aim and fire. When/if the bag settles during the string (I do pound the stock in, but with a dead bottom, shooting mat and the squishy grass firing points @ Connaught or similar ranges, it happens) it might rise up to the bottom of the black at the forward position. If it settles much more than that I either adjust the bipod or rebuild the position (limited options for either during pair fire, less of a problem during string fire). If it gets high enough to where I catch myself trying to shoulder it just a fuzz (out of habit) to push the crosshairs down to center... STOP. That way lies weird vertical stringing. DAMHIKT

As an added bonus, the stop tab prevents the stock working it's way up to where the buttplate hardware gets between the ears and causes weird fliers. HTH

 

[CharlieNC]

@CharlieNC something I copied shamelessly from others is putting a tab on the stock hardware that extends down and touches the rear of the bag (alternately, extends sideways to touch the back of the bag ear on one side). Use it like a lot of F-open and BR guys do the front stop on their front rest - after the shot, push the gun forward to where it touches, then ease it back a bit.

For my gun, I set it up so the crosshairs are around the bottom of the target @ 1000yd when the tab is against the bag. I ease it back to where they are in the middle, reload aim and fire. When/if the bag settles during the string (I do pound the stock in, but with a dead bottom, shooting mat and the squishy grass firing points @ Connaught or similar ranges, it happens) it might rise up to the bottom of the black at the forward position. If it settles much more than that I either adjust the bipod or rebuild the position (limited options for either during pair fire, less of a problem during string fire). If it gets high enough to where I catch myself trying to shoulder it just a fuzz (out of habit) to push the crosshairs down to center... STOP. That way lies weird vertical stringing. DAMHIKT

As an added bonus, the stop tab prevents the stock working it's way up to where the buttplate hardware gets between the ears and causes weird fliers. HTH

Great suggestion, I will copy that too. Any suggestions for a good tab material?

 

[memilanuk]

I used what I had laying around... 0.125" x 0.500" flat aluminum that came out of an old filing cabinet system. Screwed the buttplate down to a chunk of MDF and put a carbide bit in the router table and nibbled away til it just fit.

 

[Cyclops]

I shoot FTR.
I use "zircon" foundary sand in my "Bigfoot" rear bag. This fine sand weighs about 2x more than ordinary sand. To fill a Bigfoot back takes about 11 kg (~22.5 lb) of sand. I glued the seams on the bag to prevent sand leakage from the seams. The bag is full and barely deformable as required by FTR rules.

I place the rear bag on an 8 mm steel plate when shooting. (The plate has a skateboard grip surface applied to stop the bag sliding.) I drop the rear bag onto the plate before shooting to consolidate the ground under the plate and consolidate the bag. Once the bag is placed the rifle stock should be dropped firmly on the bag to further settle the bag.

With this procedure on doesn't get a climb in evelation due to settling - unless the shooting mound is very soft. I've shot at Trentham (NZ) where each shot climbed 1 MOA as the mound was so soft. The plate under the rear bag finished up about 1/2 inch below ground surface at the end of the detail.