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How to avoid the “rear bag” effect (i.e., vertical stringing)? Login/Join 
Freethinker
Picture of sigfreund
posted
I have a Tikka T3 chambered for 300 Winchester Magnum mounted in an MDT aluminum chassis. The gun seems to “want” to be accurate with Federal 190 grain Gold Medal Match, with horizontal dispersion of well under 1 MOA. But the problem I have had from the beginning with that and other loads, including Black Hills ammunition, is a strong tendency for vertical stringing. One of my “best” groups at 100 yards yesterday measured 0.5 inch horizontally by 1.7 inch vertically. At one point it was so bad (and frustrating) that I switched scope sights to ensure that wasn’t the problem (it wasn’t).

I usually shoot either from the bench with a heavy, rigid rest at the front or from the prone with an Atlas bipod. At the rear I usually use an Accu-Shot monopod that I was folding forward and grasping with my support hand. More recently I fold the monopod forward and rest it on top of the support bag, and grip the bag and rest over the top with my support hand. The last technique coupled with a “filler” bag under my chin (bench) or chest (prone) permits very tight control over the gun. I use a small Triad Tactical wedge bag for rear support, and it’s pretty firm when pressed down.

Most recently I have made very concerted efforts to press the stock and monopod down onto the rear support bag as firmly as possible and with minimum contact before firing in an effort to minimize its sinking under recoil. That reduced the degree of the vertical stringing, but didn’t eliminate it. The stringing doesn’t occur with every group, but I can’t determine that I do anything differently the times it doesn’t happen. What’s more, I have other rifles chambered for 308 Winchester and 223 Remington, and don’t have the vertical stringing with them. Unless it’s a problem with the gun or/and chassis, I assume the greater recoil of the 300 is what causes the effect (I usually shoot with a large Sako brake, though, and the recoil is very tolerable).

So, any suggestions? It seems logical that firm downward pressure onto the rear bag would be best, but I don’t know. Should the stock just make light contact with the rear bag instead for some reason? The MDT chassis has a separate forend that screws into the receiver cover, but the screws are as tight as I can make them. The stock isn’t absolutely immobile with respect to the front part, but it gets pressed down hard as well to minimize any movement when fired.

Thanks for all replies.




“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 36996 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Rear bag technique is likely my most frequent source of shooting errors.

I began shooting precision rifles in prone, on flat ground, with target elevation being the same as my shooting elevation. I used small TAB and FTW bags -- all was good. Except that the low position meant my neck got tired shooting long strings. And I that couldn't deal very well with uneven ground at my position, or with targets that were higher or lower than my shooting position.

I transitioned to a slightly larger str8laced bag, which helped. After watching offgrid hold vertical so well with larger bags, I transitioned to a larger Weibad Tod-Tac bag, which helped. The larger Weibad supports my shoulder as much as the gun, allowing me to relax my upper body a bit. Furthermore, it noticeably reduces the rise and fall of the reticle with my breathing cycle.

I have a problem of relaxing my squeeze of the bag as I break the shot. Thus the bag collapses slightly, the buttstock falls, and I throw a round high. A second way for me to throw a round high is by not pressing the buttstock hard into my clavicle prior to breaking the shot. When I don't do this, the recoil tends to drive the buttstock downward into my shoulder, and yet again a throw a round high. Sheep-dip me seems to do this in one stage a match, when I'm pressured by the clock and getting razzled.

I recommend using a slightly larger than normal rear bag. Keep the bag fairly well filled, and tighten its adjustment strings for any given shooting position so that you don't have to do much squeezing to maintain the proper reticle position. Keep the butt firmly into your shoulder and make certain the bipod is loaded.

Watch your breathing cycle -- the optimal place to break the shot is at the brief natural respiratory pause at the bottom of the breathing cycle.

All this is more important with a heavy-recoiling rifle. We can get away with more fundamentals errors with 223 bolt guns. Interestingly, I find good fundamentals are also really important with very slow moving bullets -- like 22lr and pellet air guns -- where the bullet spends so much more time in the barrel.
 
Posts: 4876 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
Freethinker
Picture of sigfreund
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Thanks, fritz; I was hoping you’d chime in. I will definitely review my techniques and try to remember your guidance, especially the part about the stock against my shoulder. I wasn’t sure what I needed to do in that regard. During my session a couple of days ago my best group was the first and possibly because I was freshest and controlling the stock position the best.




“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 36996 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Picture of old rugged cross
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i don't precision shoot. When I go to the range and bench shoot to confirm zero I take a very basic approach with the range sand bags. Get the right height front. Get the rear bag support for proper
approximate poi on target. At that point I am pretty good to go. Your set up seems a bit complicated to me.

I find bipods to be a negative for accuracy. In my case anyways.

Good luck.




"Practice like you want to play in the game"
 
Posts: 11373 | Registered: September 21, 2005Reply With QuoteReport This Post
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quote:
Originally posted by sigfreund:
It seems logical that firm downward pressure onto the rear bag would be best...

I think firm downward pressure on many bags will contribute to vertical variation. On bags that are easily compressed, this could mean a lower than desired buttstock position somewhere in the firing/recoil cycle. But regardless of type of bag, it may be difficult to have the exact same pressure on the gun from one shot to the next.

Jacob Bynum of Rifles Only compares pressing the trigger on a rifle to tapping a tuning fork -- there are lots of vibrations occurring between pressing the trigger and the bullet's leaving the end of the barrel. If we shooters change those vibrations in some way during this brief process, the bullet will likely travel in direction that's different from our intent.
 
Posts: 4876 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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quote:
Originally posted by old rugged cross:
I find bipods to be a negative for accuracy.

There's a definite technique to using most collapsible bipods. Forward pressure on the bipod. Firm pressure of buttstock to shoulder. Solid follow through after breaking the shot.

But these fundamentals of marksmanship apply to virtually all shooting positions and support systems. In one precision rifle course we were instructed how to shoot a bipod (even a Harris) from a slick steel plate in the prone position, without bipod hop, and without affecting our accuracy. It wasn't easy, but it was doable. After that, shooting from some of the other alternative positions didn't seem so bad.
 
Posts: 4876 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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I read the OP a few times and then I read the very thoughtful and excellent responses. Diagnosing something like that sight unseen is not something at which I excel, and fritz's analysis and suggestions have been right on target.

I will offer a couple of things as just "food for thought," as this is really what these threads are about anyway.

I took notice of the fact you say the problem does not exist with milder recoiling cartridges but shows up when using the big boomer, I think that's a clue, but perhaps not the one people would expect.

I saw the other thread about rear bags and your responses to it.

Before I go further, let me tell you about my setup. For a rear bag, I used a Protektor model for many years, but not the piddly one shown in the rear bag thread. I used the bigger one, #41, in which I poured about 7 pounds of heavy sand. The stock of my rifle has a very shallow taper under the stock. It's not flat like an F-Open rifle, but its angle is very shallow making it possible to adjust the elevation without messing with the bipod elevation. A regular rifle has a much more pronounced angle on the stock.

I changed the rear bag to a bigger one that had a longer top in an effort to gain more control on the way the rifle recoiled during long strings of fire. It's not difficult to keep it nice for 3-4 or half a dozen rounds, but when you're string is a minimum of 22 rounds, things start moving after a while. All of a sudden you start getting elevation issues on target.

Most recently, I replaced the bigger bag with a humongous one which took almost 20 pounds of heavy sand to fill. I filled that bag to be very tight and it just does not deform on top it's so tight and the top is much longer than before. The rifle glides effortlessly and consistently for the entire 22+ round string. The distance between the bag and the bipod carpet is the same all the way through so the rifle moves the same way during my followthrough.

My thinking is that it's not so much that the rifle recoils more and digs inconsistently in your rear bag causing elevation issues, it's that the rifle is recoiling faster and longer and the toe of the stock is not supported the same way the further the rifle goes back. You're trying to hold it by grasping the Accu-shot, but I submit to you that is not consistent so the rifle will recoil more and drop off the rear rest or may not go back as far and thus not go down as much.

My feeble suggestion is that you are going to have to put more shoulder into it to prevent it from going back inconsistently.
 
Posts: 2603 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Freethinker
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Great!

You guys have definitely given me things to think about, and just from your discussion I had a few “Oh, yeah; I was probably doing that” moments.

I haven’t tried shooting the rifle much with a bipod yet. If I can’t do it from the bench first, I don’t know that I’d do it better lying on the ground.

Thanks again to everyone.




“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 36996 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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fritz,

After reading through this discussion, I took a look at the Todd-Tac bag which looks HUGE. The description leads me to believe that its purpose is for positional shooting but not prone.

I find that it doesn't take longer than about 20 shots to start noticing some fatigue in my shoulders and neck. If there is something in addition to exercise and stretching that could help, I'd love to understand that and incorporate it into my prone shooting.

Thank you,
Henryrifle
 
Posts: 430 | Location: Atlanta | Registered: November 11, 2009Reply With QuoteReport This Post
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Originally posted by henryrifle:
After reading through this discussion, I took a look at the Todd-Tac bag which looks HUGE. The description leads me to believe that its purpose is for positional shooting but not prone.

There are some who prefer the smaller bags, such as FTW and TAB. These work well for those who shoot from flat, prepared surfaces -- like a square range. That's not how I shoot. My practice "range" is rolling pasture land. My competitions are on whatever type of surface the match director decides to toss our way. Occasionally we get to shoot from smooth, flat surfaces. Most of the time we're shooting up, down, sideways, with various dips and bumps in our prone positions. At lets not forget the rocks, sticks, and pointy desert plants that seem to be strategically placed near our sternum or nether regions.

Wiebad's tac pad works really well as a prone rear bag when you place part of the bag under your shoulder and part of the bag under the buttstock. I've used mine enough now that the poly beads have compressed a bit, and I'm thinking of having a seamstress add some more filling.

Wiebad's Pump Pillow is a true positional shooting bag. It is....big.

As for neck and shoulder strength, two things come to mind. First, practice dry firing in you home. No ammo costs and you can build familiarity with whatever shooting positions you use. Two, physical fitness. I exercise almost every morning before going to work. On the weekends I ski, climb, bike, and do a boatload of physical labor on our ranch. I recommend some type of workout program to help with the pounding we take while shooting.
 
Posts: 4876 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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Thanks, fritz. I've seen your practice range in some of your posts. It looks amazing and you are a fortunate guy. Bags are not expensive unless you have 10 or more and it seems like finding one that works for you is somewhat subjective. Thanks again for the explanation and insight into your preferences.

Henryrifle
 
Posts: 430 | Location: Atlanta | Registered: November 11, 2009Reply With QuoteReport This Post
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Picture of 3/4Flap
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Seems counterintuitive, but try grasping the forearm to eliminate vertical stringing. See if that helps.


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Posts: 4736 | Location: Idaho, USA | Registered: May 20, 2005Reply With QuoteReport This Post
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Hey fritz:

I have a follow-on question for you. I have a WIEBAD Tac Pad and think I might be using it as you suggest above.

From prone, most of the bag is under my chest with about two inches sticking out for the rifle stock to rest on.

Here is the part I am less sure about. I am also still using a much smaller squeeze bag to make very small adjustments. This has made a noticeable improvement in consistency.

I am not sure that I could eliminate the squeeze bag though. I feel like I am cheating the rifle has become so stable.

Can you comment on the correct use of the Tac pad and thoughts on using a squeeze bag too?

Thank you,
Henryrifle
 
Posts: 430 | Location: Atlanta | Registered: November 11, 2009Reply With QuoteReport This Post
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I've gone through many bags over the years and have finally settled on the Reasor Game Changer. It's meant to be used when shooting off of barricades, but I've found that it makes a nice rear bag when shooting prone as well.
 
Posts: 1553 | Location: Ohio | Registered: October 17, 2007Reply With QuoteReport This Post
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sigfreund,

I plan on shooting at Chaffee next week, glad to watch you shoot, help you figure out what's causing the vertical stringing. Likely it's a combination of things...

Shooting your other rifles mostly prone?
 
Posts: 2317 | Location: 9860 ft above sea level Colorado | Registered: December 31, 2008Reply With QuoteReport This Post
Freethinker
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Out the door now, offgrid, but I will be in touch; thanks.




“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 36996 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Originally posted by henryrifle:
I have a WIEBAD Tac Pad and think I might be using it as you suggest above.

I am also still using a much smaller squeeze bag to make very small adjustments. This has made a noticeable improvement in consistency.

If it works for you, then that's the preferred setup. Two bags takes more time to setup than one, and could produce some variability in positioning. It's probably not the most forgiving method if you have to move from one position to another rapidly.

There's nothing that says you can't use 3, 5 or 8 bags -- it's all about how and where you shoot. The target doesn't lie -- if you're shooting more accurately, then a given setup is a step in the right direction.
 
Posts: 4876 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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