Horizontal Dispersion - Need Opinions

[masan]

I will have a spotter this weekend, a friend is bringing his new .260 over to work with some test loads he wants to try.

[sinister]

Excellent.

Try using as solid and consistent a rest as possible. A sand bag under the heel of the stock can help, as well as using a "Saddle bag" style system (kinda-sorta like this to minimize lateral spread):

[markm]

Those Geissele triggers can make me nuts when trying to stack holes. Great triggers, but after coming of a bolt gun, I feel like I'm bouncing the friggin gun all over with the AR/Geissele combo.

[opsoff1]

Everything folks have said above is dead nuts on. My knee jerk was trigger (operator induced) and wind (mother nature - that b*tch) but as I read more and more - this seems more like an equipment issue.
Couple of things to look at.
1. Gas tube to key interface - if your gas block has shifted ever so slightly, (rotated or moved forward) the movement will be magnified at the key. This does goofy things to barrel harmonics - inducing horizontal stringing and vertical stringing.
2. Be very aware of bench technique - AR's can be finicky off the bench - also - not a fan of bipods on hard surfaces - ditch the bipod and shoot off of bags. Put the bags right in front of the mag well.
3. Probably the most unlikely, but worth a check if the issues above come up blank - check the scope. I see you are shooting NF - but hey, shit happens. Scopes - even the best can go wrong. Run a simple box test on the scope at 100 yds moving the reticle 2mins for each side - see where you come back to.

Good luck.

[T2C]

It could be trigger control or the effects of wind or it may not be. Have a friend shoot groups with the same loads and see if you get the same results.

It could be the load. I developed target loads for my 8mm and 30-06 rifles and observed horizontal stringing with lighter charge weights. I incrementally increased the charge weights until the groups were concentric. The charge weights vary depending on bullet weight and bearing surface length.

[Colt guy]

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.

Or as I like to call it shooting a weather report.

Are you using wind flags?

[taliv]

my guess from looking at your target is
if you are right handed, it's cant
if you are left handed, it's wind

markm had a good point though. pushing the trigger is a possible culprit, especially when it starts at the center and goes one direction. but the direction could be different with freehand vs bipod vs bags. basically, is the front of the gun fixed and your finger is pushing the backend? or is the backend fixed and your finger is pushing the front end?

[masan]

Again, thank you all for the input. As of now I am planning to address as many of these points as possible during the holiday weekend. Some family members are IBS (International Benchrest Shooting) competitors and we are planning to get together at their home to try and figure this out once and for all. All shooting will be done from a solid concrete bench, bagged, with wind flags, spotter, etc. at 100, 200, and 300 yards. I plan to work up a number of rounds of this load, with slight variations to try and really pin this down. If you all are interested I will photograph and document our findings as we go.

[opsoff1]

my guess from looking at your target is
if you are right handed, it's cant
if you are left handed, it's wind

markm had a good point though. pushing the trigger is a possible culprit, especially when it starts at the center and goes one direction. but the direction could be different with freehand vs bipod vs bags. basically, is the front of the gun fixed and your finger is pushing the backend? or is the backend fixed and your finger is pushing the front end?

Cant will manifest itself with windage shots that are low - those groups do not show low or "corner" shots as they are referred. It very well could be a load tuning issue, but I'd make sure you rule out the mechanical issues before you start chasing load issues - that could make for some very frustrating bench time.

[taliv]

Cant will manifest itself with windage shots that are low - those groups do not show low or "corner" shots as they are referred. It very well could be a load tuning issue, but I'd make sure you rule out the mechanical issues before you start chasing load issues - that could make for some very frustrating bench time.

at distance, yes. at 200 yards, i wouldn't expect more than what's on his targets now