Vertical stringing

Hi all, I have been developing a load for my son's Rem 260 and it is very consistent sideways, about 20mm from side to side of the group (5 shots), however it seems to disperse on the vertical axis over 65mm at 100m. I am shooting from sandbags front and rear and feel comfortable with the technique. The action is a Brno 601 with a Trueflight barrel mounted. I am using Nosler Ballistic tips, 140 gns and feel it should shoot better. It is also action and pillar bedded with no barrel contact in the channel. I was wondering if there are any rules about seating depth which may help shrink the vertical dispersion? Any thoughts greatly appreciated.

Regards Ruger7mm

I know this will be obvious, but I would be checking your powder scales first. I run a very similar set up and the only time it gets out of line is when I'm a bit lax with my powder measuring, and it's always verticale.

I use RCBS beam scales and really took my time to ensure it was as consistent as I could get it. The velocities were spread across 24 fps so I thought was acceptable. Thanks for the thoughts and all variables need to be considered.

24fps Extreme Spread is good. It should not cause a vertical string on 3".

Seating depth will most certainly affect group sizes. Give it a play? Try 0.5 and 1mm jump?

If you are using a silencer try shooting a group without it?

I would normally start by looking as barrel channel clearance, action screws tight, scope bases as well as rings.

Try a different silencer?
Check for baffle strikes?

How many rounds has the barrel fired . . . Is it new or a take-off repurposed. If it's a take-off it's possibly got either carbon or copper fouling. A picture of the groups might also give some clues.

Even some variation in powder weights shouldn’t give that much vertical dispersion.
I’d Almost guarantee that pattern will be due to the rifles bedding. Is the action glass bedded and barrel free floating?


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Shooting off bags. Is rifle sitting level when firing at target. If sitting muzzle high, shots could be kicking in a high pattern.

Sit it on the bags as you would to shoot, stay clear of the rifle and slide it back say an inch while looking through scope. If you see vertical movement that's what could be happening on recoil.

All rifles jump with recoil before the bullet leaves the barrel. Variability from recoil is therefore about inconsistent replication of the same amount, and direction, of jump each shot. It is fashionable not to hold the rifle bench or rest shooting other than at the rear. You might try the more traditional hold of left hand (right handed shooter) holding the rifle firmly downwards at the forend "wood" without touching or interfering with the barrel. What in fact a traditional sling brace hold does.

Also is it possible you are experiencing a slight flinch on subsequent shots?

I ran into an issue with my 7x57mm last year, one of my goto deer rifles. Previously zeroed and accurate load went ape one day at the range. Difference was I was shooting prone off a bipod, something I don't normally do with this rifle as I normally shoot it off sticks or offhand. Turned out the somewhat soft/floppy forend was being pressed up onto the free floated barrel occasionally by my crappy prone hold.

Is there any predictable sequence to where shots are landing, ie start high and drop, or start low and climb, or just random up and down?

Hi all, thank you for your thoughts, and I'll try and answer them.
On the bags I use a solid hod on the fore end to minimise the movement, and I was shooting other rifles and they didn't string.
I have since bought a wheeler torque wrench and the screws seem okay at about 35-40 lbs, and it's also pillar bedded so should sit in battery okay. It was at 30 lbs" so will not change anything until I test that.
The barrel is new so shouldn't have any copper build up, however will give it a copper clean before the next session.
I have the projectiles about 20 thou off the lands, will try some ladder seating tests as well.
I don't think I am flinching, it is a lovely rifle to shoot, and I was shooting a 284 and a 30-06 that day with very acceptable results. I usually can tell when I stuff up a shot and pull it or get my breathing and trigger control out of sync.
Will try and test the suggestions above in a sequence to try and isolate the main protagonist, however it will probably be contributed to by all the variables. Will report back.

Many thanks for your thoughts and advice, very much appreciated.
Ruger7mm

Just randomly. Get a small block of wood and place it between stock and barrel in barrel channel so there is a slight pressure point. I had this problem with a newly barrelled and bedded rifle and tried it on advice. The final solution was a re bedding job.

Quote:

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Originally Posted by whanahuia

Just randomly. Get a small block of wood and place it between stock and barrel in barrel channel so there is a slight pressure point. I had this problem with a newly barrelled and bedded rifle and tried it on advice. The final solution was a re bedding job.

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Aluminum tape is another great way to adjust bedding, use layers to achieve the desired result. If you're like me and never get back to do a "proper" job it can be a good permanent fix.

Brnos were pressure bedded ,( slight upward load on the barrel at the foreend) if that's not there now it's could account for the stringing. As the two above posts suggest try adding a pressure point back in and see what happens.

How many groups have you shot that show that pattern?

You already said that you didn't have stringing with other rifles shot that day, but one of the biggest problems with vertical stringing is inconsistent cheek weld and shoulder pressure on the stock. The other things to check have already been mentioned in the thread with seating depth (barrel harmonics) and if the barrel is a heavier profile than the original, it is not touching any portion of the stock (even with pillar bedding).
Cheers

You have had a lot of variables pointed out, which are fair questions but here are a couple more thoughts.
1, I wonder during your load development towards your current load, whethet you recorded the shot sequence and powder charge per shot on your target. This helps to identify potential nodes for further refining. The questuon also arisrs ad to powder type and how close you are to max charge. All brass from same lot ,age and prep sequence?
Finally, the action screw torques may need to be closer to 59
0 inch pounds. Somr pics of your test targets showing shot charge and shot sequence would be helpful.

I have a (vague) recollection of a problem with my 601 vertical string, was, as I remember, the sheet metal magazine box not seated properly after a stock-off clean up. You are able to stick your fingers up the mag well and it should move a little. If not, it could be pinched like mine. Plays hell with the accuracy and difficult to suss. Could have been upside down even.... Simple things first.

A binding internal mag box has caught me out a couple of times. Easily fixed. But in my experience dispersion was random rather than vertical

Fire 20 shots. The horizontal will probably marry up with the vertical then.

Hi all this was the last of 4 groups I shot with the rifle, and felt like all shots were genuine and not pulled etc. It is a 5 shot string with two shots close together. I am going to do more testing and will take more photos and record the individual shots.
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