Horizontal Stringing

[Barossa_222]

I know there is a few clever guys on here and I'm asking on behalf of a mate who had some odd results on the weekend. Will certain barrels show very good vertical dispersion, but throw 2 or 3 mintue horizontal at long range?

[johnk]

From what I've seen, groups approach tune from either horizontal or vertical spreading, come together, tighten then string on the opposite axis as tune is approached then passed.

[Malcolm Hill]

There were quite a few rifles that displayed issues with horizontal stringing at the Port Pirie OPM on Sunday with all sorts of rifle related reasons being blamed. I don't think tuning problems were to blame though, but there were plenty of those 2 to 3 minute sideways shots happening and it was only 700 yards. I just put it down to atmospheric conditions at the time.
Regards Malcolm.

[Barossa_222]

I did hear that also Malcolm, I only ask because this particular rifle has shown the same sort of thing on other occassions during development.

[jcinsa]

I was at Pirie as well.

My elevation was excellent, some of the best I've ever had.

I just assumed that the 4's and 5's i got, left and right, was due to the switching weather.

Regards John

[DenisA]

JohnK's description of load development is spot on. The quickest way to see with certainty is to shoot some groups with the current load at 100y where wind won't give you a false result.

This is the reason why I struggle to convince myself to load develop at the longs.

Some ranges such as North Arm, have conditions that regularly look uniform and manageable, but 4's and worse appear out of nowhere for every one and no one could see why.
If that can happen with 4's, how are we supposed to tell whether 3:00 - 9:00 5's and 6's are a condition or load.

[RDavies]

Yes I have seen it. Often it has been a seating depth change which rectified the horizontal stringing. Not sure why, maybe the boffins on here can explain it

[williada]

Barossa you describe this problem as a long range problem and in the magnitude of 2-3 minutes. This sort of magnitude tells me to firstly look at rifle cant. As Jim Sweet wrote, “A 6 degree cant will give you a bird at 900 yards”, with a factory load in .308. I assume this rifle has had reasonable load development.

The cant can be exacerbated with a changing head pressure due to the mound position to get the right elevation for long range and you can actually put sideways pressure on the butt trying to get the right eye relief. It can also mean the butt length is inappropriate and can lead to the flawed position. It can also mean the front rest is not in an optimum position and sliding on recoil on an angle if you are not observant. Just watch how Alan lines up his bags to track properly.

Inadvertently muscling the rifle into position will also exacerbate your cant. Check that your scope bubble is in the right position. It should match your crosshairs, which in turn are aligned with the horizontal axis of the action which in turn should be matched with the base of the forend, which should in turn be matched with the horizontal position of the rest. If anyone of these is out of alignment you will experience cant when you move the sights and your shots will be wide. If you are aiming off, cant will not be induced. This is very important for team shooting when coaches move the sight and you are expected to have a centre hold.

The cant will be noticed more on those fishtail days because the sight movement is at its maximum point. A wide shot is often mistaken for bedding or loose fixtures but they tend to be in angular in dispersion or in clusters. Of course altering on a canted shot implies the conditions are really knocking you around.

I don't dismiss the tune aspect entirely as group patterns at short range tend to enlarge and hold shape even with variable air density. You have noticed this problem at short range. Even if you had a crook crown, the pattern of dispersion would be noticed. If you had crook locking lugs the problem would be noticed at all ranges. A very poor tune component tends to be no greater than 1 1/2 minutes and would be picked up in short range testing which we assume was better than that. But condition judgement can add to that wide pattern the rifle shoots in testing. An apparent aiming mark shift due to lateral mirage giving you a lateral component of that magnitude can also be ruled out in higher winds because the apparent movement is at its weakest. In light lateral winds though, with dense mirage, you can add to a little cant or barrel induced horizontal dispersion. If the winds are fishtailing, then there is an element of vertical due to mirage which reduces the lateral component and so I would discount that too unless the mirage disappeared.

It is possible that due to the extra time many shooters take at long range to get their shots off, it allows the barrel to cool. Then there is the possibility of a poor action/barrel joint or a barrel that walks laterally. This is a good reason to do 45 second shots in round robin style to test for these weaknesses or fouling. It is also a good reason to have the natural barrel bend fitted to your action in the vertical plane and certainly not the lateral one.

This brings me to scope problems. Your zero will be out if the scope is not mounted in the same direction as the bore by greater amounts with distance. The scope mechanism can also play up. Loose screws give angular dispersion rather than lateral.

These are some of the key things to consider.

Rod is tricking, he is a closet boffin. I think he knows why the seating depth changes the horizontal in the normal range of load development that is closer to 1 minute than 3 minutes. I for got to add before and it is very important for long range that the lower velocity nodes can string you horizontally if gyroscopic stability is not suited to conditions.

[Brad Y]

Agree, Ive had the same thing. I belive it was 500m and was getting horizontal stringing on a dead calm morning. No flags were moving, no mirage on the clear sunny morning, slight dew and people were shooting possibles left right and center. Not me. I had only tuned loads at 900m looking for the least vertical before this. Load was 43.6gr 2209 in an improved (not ackley) 260 with 140gr hybrids jumping 40 thou and travelling about 2860fps.

I re tested seating depth in the following weeks and actually found the gun to shoot much better at a lower charge of 43.2gr 2209 but with the bullets jammed 10 thou (later switched to 140gr vld's and they performed equally well) still around the same velocity. From there I kept up with throat growth and made sure I always had the same 10 thou jam and the gun shot brilliantly.

With an adjustable tuner you may be able to change group shape as well. Otherwise if your unsure of it, a few groups of different depths at short range where the condition cant affect you as much might show you something.

[RAVEN]

The load is probably not quiet tuned
Try 5 shot groups at 300
+.2gr then back off .2gr and shoot another group see if the group is rounder
Pete are they small holes @ 300 like I mentioned the other day

RB

From what I've seen, groups approach tune from either horizontal or vertical spreading, come together, tighten then string on the opposite axis as tune is approached then passed.

Spot on John

[williada]

Below are some groups of three different shooters who remain unnamed. This is not about how good the groups are or are not but the relative dispersion of varying charge and seating depth of rifles of varying target rifle quality in combined tests. It’s what their rifles did at the time before further development. n.b one barrel was discarded.
The circle in the groups was one minute. It takes a bad barrel setup to toss groups well outside the 1 minute zone.
Please note that with charge development testing, as separate to seating depth tests I prefer 5 shot groups. At the moment I am not in a position to do more of this by additional advanced stuff, but comments on sheets may assist others in a basic way.







Edit. Raven's point below about yaw is just so important with our stuff. Forget 100 yards. All the above groups we shot at the minimum practical distance yaw settles at 140 yards in order to minimise light, mirage and wind effects too.

Edit2. The second illustration contains information that is not shown visually as it was part of a conversation with the shooter and refers to a charge test as well which is not posted. It is the charge test you must do in Round Robin style.

[Brad Y]

We need a like button for the above post.

[RAVEN]

Great info Williada
I hope Mr Barossa can extrapolate what he needs to do
as the groups shown are a great example of in tune out of tune loads all these are at short range and at long range these groups would amplify.
I always tell ppl I help to do their testing at 300m as our long bullet can have some yaw at close range and this will not give you the right info to progress in the right direction.

RB

[plumbs7]

We need a like button for the above post.

Yep to that one!

[Tim N]

Just wondering if people using adjustable tuners have a different setting for each range?