Horizontal Dispersion - Need Opinions

[masan]

Gents, I am hoping that a few of you will weigh in on this.

I finished the build on this rifle about a year ago and have been working with it a lot, as it is a damn fine rifle.
https://www.m4carbine.net/showthread...likely-my-best

I have found that at 100 yards the gun really likes the following load:

77gr Nosler Custom Competition
22.0 gr H322
Wolf SRM Primers
Federal Brass (not a fan)
O.A.L 2.255

At 100 yards, the rifle and this load will repeatedly shoot under .25 minutes, and if I am doing my part, under 0.2 minutes.

As I move further out, the vertical dispersion of my group stays nearly the same, right around 0.2 - 0.25 minutes. The horizontal dispersion, however, keeps growing, at 200 yards it is roughly 0.5 minutes and at 300 yards the horizontal dispersion is approaching 1 minute, while the vertical dispersion is still staying around 0.2 - 0.25.

TgtGfx.jpg

Am i correct in thinking that this is a neck tension issue? I want to keep pushing the distance but I want to solve the problem with the horizontal dispersion before I do. Any insight at all will be greatly appreciated.

[markm]

We get that from time to time as well. It's shooter induced... although I don't know exactly what causes it most of the time.

Are you getting a good straight back trigger break?

[masan]

Thanks for the reply markm, was hoping to hear from you. Yes, I believe that I am, and I usually am good at calling my shots and fliers. If this is shooter induced, in regards to trigger manipulation, have you found a way to overcome the problem?

I do a lot of dry fire with my Glocks for ipsc, but not as much with any of my ARs/Geissele triggers. Also, in my 300 win mag, out to 600 (cant go much further around here) I do not see horizonal shifts like this unless I am completely neglecting to take into account the wind.

[Onyx Z]

Do you wrap your thumb around the backside of the grip? If so, I bet you are pulling the rifle when squeezing the trigger. Try keeping your thumb on the same side of the grip as your fingers and see what kind of results you get.

Completely off topic, but did you see much of a difference with the adjustable GB on the rifle gas? I thought about getting one for my intermediate barrel, but I didn't think it would make much of a difference on the longer gas systems... it makes a world of difference on my carbine though.

[masan]

I had two goals in mind when I decided to use an adjustable gas block, one to reduce the impulse from the BCG movement, and also to try and get the rifle to use just enough gas to cycle properly, and keep the rest of the gasses pushing the bullet. In both respects it seems to have worked well, the gun is very "soft" shooting, and I can squeeze a little extra velocity out of my loads.

That said, if I had to do it again, I do not think I would.

Load development was tedious while trying to make sure the rifle was using only the minimum amount of gas to cycle. Using a chronograph and ladder testing allowed me to get an idea of where the barrel liked to be velocity wise, but after adjusting the gas block, I would need to re-test loads to see how fast they were with the new gas setting, then adjust them again to get the velocity required.

All in all it was a lot of work (which I didn't mind) and a lot of material (which my wallet did mind) for what I feel is ultimately an underwhelming amount of gain.

TL/DR: Little gain for a lot of effort, likely would not do again.

[markm]

Thanks for the reply markm, was hoping to hear from you. Yes, I believe that I am, and I usually am good at calling my shots and fliers. If this is shooter induced, in regards to trigger manipulation, have you found a way to overcome the problem?

Not really. Is this happening a lot/consistently? Do you have a nice, fast trigger, etc? I try not to over-react to occasional grouping issues.

There'll be days were it's a friggin fist fight to hold MOA. It just happens. There's guys that'd be thrilled to shoot the group you posted.... but with that vertical is so nice that it does beg to get the horizontal improved too.

[StingerDan]

If reloading is your issue, horizontal dispersion is, as a general rule of thumb, caused by seating depth, as vertical is powder charge. Providing you have proper case prep, and are not overcrimping, or some other improper technique. Dan.

[sinister]

Vertical dispersion is generally a result of variations in pressure and velocity.

Horizontal is a result of wind.

Remove the human element (i.e., shoot from a secured machine rest) and you'll see rifle-ammo group trends.

In team rifle shooting (4 shooters) it is the responsibility of the shooters to hold for the tightest group they can. If rifles and ammo are consistent then all shooters should be able to hold a half to a minute of angle group height. The shooter is responsible for elevation.

It is on the coach and his wind reading abilities to keep the shooters' groups centered within a half to a minute of wind, keeping everyone synchronized and inside the 10 and X-ring.

Most folks will never experience this because they are shooting, loading, and proofing on their own and scratching their heads trying to figure out what is voodoo vice science.

[markm]

Yeah... can you have a spotter watch each and every shot?

In other words... if you're back and fourth from left to right in an unchanged wind, you can get an idea where the issue is.

[masan]

Thanks for all of the replys!

Markm, this does happen consistently with this load, but not with any other rifles. Trigger is a Geissele SD-E.

SingerDan, That would normally be my first thought as well, as I have found that to be the case many times loading for bolt guns. For this rifle I am loading for mag length, well out of the lands, which is what ultimately has me thinking it could be a neck tension issue.

Sinister, when this first started happening (any time I took the rifle past 100) I too thought it must be the wind. Nearly all of my shooting past 100 up to this point was done with heavy, long 6.5mm and .30 cal pills. So I initially took it as an opportunity to improve my ability to read the wind, quickly becoming frustrated as a result of making what seemed like no progress.
I have made a point of shooting in as close to zero wind conditions as possible, shooting the "let up". Ultimately, the horizontal dispersion remains.

I plan to do more work with this tonight and over the upcoming long weekend and will post any results I find. Thank you all again for your help.