05-21-2011, 02:28 PM
ss355 Wrote:Gents, thanks to you both for the replies. LR, I'll answer the questions you posed.
1. Smallest possible group? From a bench, most of the groups I shoot hover around 1 to 1.5" at 100 yards (this with not only the heavy bbl Grendel but with a HB .223 and .308, too). I believe my HB Grendel with Les Baer tube should be consistently sub-MOA capable. Though I'd like to shoot 1/4" group after 1/4"group, I think a more realistic, consistent number is in the 3/4" range, with the occasional group into the .5" range. This at 100 or similar MOA at 200 because those are the only distances to which I have frequent access.
2. Breathing pattern? Inhale deeply a few times to oxygenate my blood (but not to the point of lightheadedness), final full breath, exhale half breath and hold, squeeze trigger.
3. Reticle pattern? From point of hold at 100 yds, the reticle jumps toward 2:00-ish approximately .5" to 1" with every heartbeat. However, after the beat, though the reticle settles, I find that it doesn't always settle exactly to my point of hold, perhaps another .25" of slop. Even if I do manage to time the break of the shot between heartbeats, I'm still dealing with anywhere from a quarter to half inch of uncertainty in shot placement at 100. Does that make sense?
4. What have I done to eliminate the heartbeat artifact? Bagging the rear of the gun as solidly as possible minimizes but doesn't eliminate the artifact. Even letting the gun free recoil, contacting the gun with hand on pistol grip and cheek on stock only, shoulder not touching the buttpad, still doesn't eliminate the artifact. Shooting the gun in a field-type position, with the aid of a bipod only while supporting the butt or grip with my off hand/arm, significantly exacerbates the artifact.
My intent is to try to test the mechanical limits of the gun as best I can so when I am in the field I know, in theory, what margin of error I need to accept with my aim. I don't feel like I'm quite there, yet. That last 1/4 MOA sure is elusive!
Scott:
Yes, you should be holding about 3 / 4 minute pretty consistently with a LB Grendel providing you are using ammunition that will give performance, have a trigger that will give the performance, a stock that is ergonomically and mechanically designed to allow for the performance, an optic that is not only very good but also adjusted properly, and an aiming point that is the right size and color for performance. If your Grendel and .308 are top end using top end components, and you shot ten each, five shot groups, and culled shots that were way out but did go to your call, - you can expect your mean to be a minute or slightly less with 1 SD being somewhere around 1/4 or 1/8 of a minute. A exceptional AR in .223 with the perfect loads will probably have a mean of .75 MOA with one SD being about 1/8 minute. Why? Lighter recoil.
If you want to shoot groups that have a mean of 1/4 minute, buy a bench rest rifle chambered for a 6mm BR or PPC and get into the bench rest sport. You can shoot 1/4 minute groups with a gas blaster or a .308 but the few times it happens for five consecutive shots will be primarily due to chance.
I think you also need to define some sort of way of measuring your performance both from a bench and from what ever position you will be using in the field. What you must decide on is how to identify and deal with outliers. In this case, you set your own conditions and standards. So, set your conditions and standards and if you want I am sure we can all offer advice.
OK -- right now your attention is being taken from what you must do to get consistent performance and is being directed towards seeing the effects of your heart beating through your optic. Not a problem. Accept its movement. It is obvious you believe you have done everything possible and it remains to an extent so you have two choices. Either accept it or let it destroy your performance. Can you eliminate it completely? From a bench rest position you certainly can and that will take experimenting until you have found a position and method of control over the rifle that either totally mitigates the effect or eliminates it. A hard hold is a good start point but right now -- either accept it or let it ruin your performance.
What most guys do when dealing with movement caused by heart beat is to shoot when the reticle is at its apex or bottom of its range of movement. Just note that we will adjust our position until the movement is mitigated as much as possible given the conditions we are shooting. We will depend on controlled breathing -- be it slow or fast -- as a means of getting our attention focused on what is happening with the sights -- shifting attention towards sight picture so we can see if we need to do other things in order to reduce movement or if our movement is just fine for the task. When your attention is focused outwards on the sight picture, you note the pattern of movement while you breath and see basically two things that tend to make guys believe they are in control. One is that the pattern of movement is very consistent and second that the speed of movement is slow enough that the shooter believes he is more than capable of getting shots off at the right place in the movement area. I prefer to break shots at the bottom of the range of movement but understand that I am controlling the rifle so if the movement doesn't stop at precisely the same place, I literally shift the rifle's point of aim by letting out more air from my lungs or relaxing my upper body a bit more or a combination of both (most likely).
Let me suggest that you practice this technique of putting yourself back in control of your rifle so you can see how it works and perhaps gain some confidence that you are in control -- totally and without an iota of question.
So, take out your .223 blaster, ensure it and your optic is mechanically sound, and get some proven ammo. Get your bench set up to fit you and give you a good point of aim. Use a black dot for an aiming point. Try a two inch black dot at 100. Adjust your magnification until the center of your cross hair or dot covers enough of the black so that 1/4 of the black can be seen around the center of your cross hair. The center of your cross hair or dot will cover a large amount of the black dot.
Load five, get into position and breath while watching the cross hair and its movement. Yes, the center of your movement will be around the center of the dot. When you have let out the air in your lungs at a comfortable point for you, see where your heart beat is taking your cross hair. Most likely it is taking it in the same direction as your breathing. See where it stops and for how long. Most likely you will see it stopping at the low point for the longest amount of time so adjust your position so when you go into your respiratory pause, the dot or cross hair is pretty close to the center of your dot. Dry fire and adjust more as you see fit but do the process very quickly. When you see the cross hair center in your dot (after you have held your breath), fire the shot.
Dry fire ten or fifteen times and develop your technique. Then go live.
For live, fire a five shot string in fifteen or at most twenty seconds. Shouldn't be hard to do with a .223. Run a couple of strings like this and adjust your thinking and position as you see fit. Avoid looking at each bullet hole as it appears. Do not use a Shoot-N-See for this one as it will cause too much stimulus that will shift your attention. Just a plain black dot. Do not adjust your magnification so you see more than about 1/4 of the dot around the center of your cross hair. I want the cross hair to blot out about 3/4 of the dot to reduce stimulus. Also, if you shoot bullets into the center this time, you won't see the holes because your cross hair is covering them. Shoot quickly and confidently and do not look for holes until you have fired all five shots. After firing the five and before looking -- call each of your shots please. Then compare your group to your calls.
Practice this with your .223. Reflect on action, adapt but maintain your focus on the process of shooting consistently well and not an outcome. If your process is perfect and the outcome isn't -- you need better equipment.
LR1955