Poor vertical dispersion.

[MrMusicMan]

Hello SH!

I'm not gonna lie, although I've been shooting since I was but a wee lad, I'm a total noob when it comes to precision shooting with higher power rifles. Hence, my joining this site in hopes of some education and direction.

I have a new Remington 700 SPS-T .308, Weaver sight rail and rings, Harris bi-pod, factory trigger tuned to 2.5# pull, and a cheap Vector Optics 8-32x50 scope with 1/8 MOA turrets. I've now put 45 shots through it. So far, I've used nothing but Federal Premium Gold Medal Match 168gr and have been super anal about cleaning the thing frequently during its break-in.

Here's what I'm running into and where I'm hoping for some help. I am getting around 1MOA accuracy horizontally our of the gun at 100 yds (or at any range, for that matter). However, vertically I'm getting anywhere between 2 and 4 MOA at the same range. I've had a couple of ideas but wanted to hear your input. If you look at the picture I posted below, you can see the scope is fairly high above the cheek rest on the stock. High enough, I can't actually get a good stock weld on my cheek, but have to move to my jaw in order to line up with the scope. Could it be that I am getting some serious up and down variance by the way I have to position myself on the stock?

With the exception of the stock weld, I feel pretty confident in my technique. I shoot my little Marlin Model 100T at around a half a minute at 100yds all day with reasonable ammo.

My other thought was this: The factory Hogue stock bends just enough to touch the end of the barrel when set on the bi-pod. Is that enough to jack the barrel harmonics by 1-3 MOA? Or am I just a poopy shooter when it comes to "real" guns?

Thanks for your help, and Happy Thanksgiving!
-MMM

 

[Seth8541]

Re: Poor vertical dispersion.

Your stock weld has everything to do with vertical dispersion as well as many other factors, but by looking at your picture the 1 thing that jumps out at me right off the bat is the lack of some sort of cheek rest that contributes to you having total muscular relaxation, and the ability for your stock weld to maintain a constant position from shot to shot. Consistency is accuracy. Being that you have no cheek piece on your rifle, you are forced to use the muscles in your neck to achieve correct sight picture and sight alignment. This is NOT consistent, and by no means promotes the same exact shot to shot position. You need to be able to rest the full weight of you head on the stock, close your eyes, take a deep breath, let it out, open you eyes, and have perfect sight picture, sight alignment. This is not possible if you are using your neck muscles to "Chase" the correct sight picture, and then hold it, and squeeze off a shot.

The verticle dipersion can be attributed to many factors to include:

The presence of scope shadow in the sight picture
Improper breathing techniques and not shooting during your NRP
Position of the buttstock in your shoulder is inconsistent from shot to shot
Poor quality ammunition

There are more, but I am leaning towards the first 3 in your case.

Get lower scope rings
Build a cheekpiece for your rifle
Practice you breathing, and firing during your NRP
Freefloat your barrel

I'm sure that if you do those 4 things your groups will tighten up. Hope that helps.

Seth

 

[timelinex]

Re: Poor vertical dispersion.

Personally, I doubt its the cheek weld. At 100 yards especially, that should be a distance that unless your doing something majorly wrong, you shouldn't have to much a problem achieving 1moa as long as the rifle and ammo let you. Your rifle and ammo are both reputable models that should easily achieve better than 1moa. So that leaves the "your doing something terribly wrong" part. The reason I say cheek weld isn't causing it is because as long as you adjust your parallax to be as close to parallax free as you can, different cheek welds should not cause 4moa of difference. I only recently got a cheek pad, before it I had a slightly uncomfortable position and used my neck muscles. I was still able to achieve much better than 1moa and in fact the cheek pad did not help accuracy in any way and just made it much easier,faster and more comfortable. So if you want to get a cheek pad, I highly recommend it, but don't expect it to fix your problem.

A high sitting scope shouldn't cause 4moa, but a cheap scope sure can fail to hold zero. If its not holding zero than you might as well just point your barrel at the target and shoot.
The other option is that it is totally possible that the stock touching the barrel is throwing off the harmonics. I would look into fixing that asap. This should still not cause 4moa though.

Unless its the scope, the most obvious answer is a major flaw in technique. First thing to make sure is that yu are pulling the trigger only at the bottom of your breathing cycle. Yes I know it might feel like its not important, but it is. The most likely thing that is happening is flinch. You are in some way flinching as you pull the trigger.. Video tape yourself and put it up here and someone will see it.. in fact you will probably see it yourself after watching the tape. You could be flinching by moving your head,moving your shoulders or even squeezing one of your hands. Looking through the scope at 100 yards you should see that any tiny movement causes your point of aim to shift alot, so it shouldn't be to hard to imagine that these would cause huge dispersion.

I am far from an expert, and I'm sure someone more knowledgeable will chime in... But we aren't talking about going from .6moa to .25moa. If you are having trouble at <1moa it doesn't take an expert and is usually something huge.

 

[Seth8541]

Re: Poor vertical dispersion.

Chances are that it isn't just 1 thing, but multiple things as I stated above. As I'm sure you probably know, or maybe not, bucking, jerking and flinching does not give a repeated consistant impact, ie verticle stringing. Although scope shadow in the upper or lower portion of the sight picture will, as will improper breathing techniques, aswell as the position of the buttstock in the shoulder being inconsistent, couple that with a possible improper point of aim, fouled barrel harmonics due to an improperly floated barrel, and its definately possible to see that amount if vertical stringing.

That's just my personal opinion, but what do I know.

Seth

 

[MrMusicMan]

Re: Poor vertical dispersion.

I can get easy .5 MOA groups on my cheap .22 without issues, so I've been kind of bummed with the results from the .308 I'll tackle each of these thoughts over the next week and I'll post the results! Thanks!

 

[Seth8541]

Re: Poor vertical dispersion.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Music Man</div><div class="ubbcode-body">I can get easy .5 MOA groups on my cheap .22 without issues, so I've been kind of bummed with the results from the .308 I'll tackle each of these thoughts over the next week and I'll post the results! Thanks! </div></div>

Yes, improper stockweld can cause vertical stringing. So, can a cheap scope. Good glass is every bit as important as good ammo, good gun, and proper fundamentals of marksmanship. Remove 1 of those from the equation, and your grouping and accuracy goes out the window.

Float your barrel properly, get some lower rings (optional), build a cheekpiece, apply the proper fundamentals, and then see how it looks. If it is still taking place, start looking at the scope, and ammunition.

Hope this helps. Keep us posted.

Seth

 

[RFtinkerer]

Re: Poor vertical dispersion.

Also make sure you're pulling in the rifle firmly into your shoulder, and that your shoulder is dead meat behind the rifle. I recently "graduated" from a .22 to a 300 WM, and I had problems with stringing until I realized I was not properly maintaining support through the initial recoil pulse (moving while the bullet was still in the barrel.) Press the rifle firmly into your shoulder, load the bipod, breathe appropriately, pull the trigger straight back.

 

[MrMusicMan]

Re: Poor vertical dispersion.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Seth8541</div><div class="ubbcode-body">That's just my personal opinion, but what do I know.</div></div>

P.S. - Just noticed your sig. I'm gonna go with "You've probably got this precision shooting thing pretty well down."

Thanks for the help! I'll let you know the results!

 

[Seth8541]

Re: Poor vertical dispersion.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Music Man</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Seth8541</div><div class="ubbcode-body">That's just my personal opinion, but what do I know.</div></div>

P.S. - Just noticed your sig. I'm gonna go with "You've probably got this precision shooting thing pretty well down."

Thanks for the help! I'll let you know the results! </div></div>

Hahaha. That wasn't directed at you bud. Just trying to help. Do as the last poster said as as well, ie loading the bipods. Please do let us know the results.

Happy Thanksgiving
Seth

 

[Greg Langelius *]

Re: Poor vertical dispersion.

A poor cheek weld is capable of increasing vertical spread, especially if its combined with poorly compensated parallax. Barrel/stock contact from flexible forend can add to the problem.

A quick and dirty cheekweld adjustment can be accomplished using flexible foam (like from pieces of a mouse pad) and masking tape. When you can set up in position, close your eyes and rest your head so the pad takes the full relaxed weight of you head, then open your eye to a perfectly unshadowed scope image, you're there.

The barrel/stock flex issue can be temporarily eliminated by folding the bipod and supporting the rifle on a solidly stable, padded support that is placed back further along the bottom of the stock, so the rifle's weight is not flexing the stock.

This process of elimination can allow any other issues to be defined and addressed, assuming there are any. There may be, but it's a good start toward defining the problem(s) so they can be resolved.

Once you've done this I'd/we'd certainly like to hear back on it all, right here in this thread. I think we can take this all a bit further (ala parallax, making temp fixes more permanent, etc.), once these two basic issues have been dealt with.

Greg