Vertical Groupings

[rayatphonix]

I need some help here. I've worked hard on my loads and am getting close with several rifle/bullet/powder combinations. My problem is that in several instances my groups spread out dead vertical. Left to right may vary by 1/4 to 1/2", but vertically the spread is more like an 1" to maybe 2".

One person told me that's evidence of uneven neck tension and/or crimping between one round and another. I have this problem with both bolt-action and AR rifles. Can someone give me an idea of what I'm doing wrong?

Thanks!

 

[LiveLife]

These are groupings at 100 yards shot with the same load out of both bolt and AR rifles?

 

[jaysouth]

My single shot rifles exhibit vertical stringing when the barrels overheat.

 

[rayatphonix]

bd, these are at 100 yards. My bolt and AR's have different calibers, so it's not a case of taking a good load from one rifle and trying to make it work in another (if that's what you were wondering).

jay, I have thought of that and it may very well be the problem. However, there's no sequence to the pattern; my second shot is as likely to be high as my 5th shot. And if the second shot is high, number three and 4 might be right back on target. That could be a sign on an over heated barrel, but I don't know.

My AR has a 24" bull barrel and my bolt guns are old Tikka's with sporter weight barrels.

 

[rayatphonix]

Upon further reflection, perhaps I ought to let the rifle sit for say 5 minutes between shots and see if the problem persists? I've always tried to never shoot a barrel that's too hot to hold comfortably (by the barrel), but maybe that's not enough.

 

[LiveLife]

I am old school when it comes to 100 yard shot grouping and barrel cool down.

I will let the barrel cool until I could touch with my hand between 5 shot groups.

I have 20" HBAR and slight heating don't seem to affect shot groups much ... but I am a lousy marksman even with a scope. I strive for MOG - Minute of Gong at 200-600 yards.

 

[blarby]

My single shot rifles exhibit vertical stringing when the barrels overheat.

Not alone there- BBL harmonics and all.

Upon further reflection, perhaps I ought to let the rifle sit for say 5 minutes between shots and see if the problem persists?

Not a bad idea.

 

[mr16ga]

if you want to know what is going on you got to use a chronograph. You will be able to sort out gun vs. load you are using. A high standard deviation causes vertical strings.
Joe

 

[788Ham]

Is the barrel on your bolt a free floating barrel? See if you can slip a dollar bill under the barrel, between stock and barrel, almost up to the action, if not, this might be the cause. When barrel heats up, its touching the stock, which in turn will push against the barrel.

 

[Walkalong]

Inconsistent shoulder pressure, or inconsistent pressure on the forearm.

 

[splattergun]

Several possible causes have been listed, all valid points. Try changing 1 thing at a time, beginning with those those that do not make physical changes to your weapon (that comes last). For instance, walkalong suggested inconsistent shoulder or forearm pressure, which is a good place to start, by reviewing your shooting position and making sure your hold is consistent. Next, bbl cooling, chronograph, load adjustments, etc.

Making difficult-to-reverse changes to the gun, like floating the bbl, is what I would do only after trouble shooting my techniques and loads.

 

[helotaxi]

The old time wisdom is that vertical due to breath control. Lateral stringing is due to trigger control. All over the place is due to either a combination of the two or inconsistent sight alignment.

 

[rayatphonix]

mr16ga: I thought of that and have chronographed my loads. SD was 11 on my last load through my Tikka... Typically my SD is about 20; don't know if that's good or bad, but measuring each charge, that's what I typically find. Chronograph showed what a bad job I was doing reloading and I've tightened up my groups considerably since I bought one. It was a very good investment.

Barrels on my Tikkas are free-floating. I had thought of that one.

FWIW my velocities aren't at the top end. I get better horizontal groupings mid-charge. This wouldn't have an effect would it?

I'll work on technique next week at the range. At this stage, that's very simple to do. I'd not thought of breath control but have worked hard on my trigger control so that makes sense.

Thanks for all the ideas!

 

[helotaxi]

An SD of 11 isn't great. Working on uniforming your neck tension will do more for reducing your SD than measuring every powder charge.

There are several other possibilities on why your groups are stringing as well.

 

[Walkalong]

An SD of 11 isn't great.

But it won't show at 100 yards.

 

[helotaxi]

True.

 

[twofifty]

What may show up as vertical stringing at 100 when using bags/rest is the effect of inconsistently placing the forestock on the rest.

If the rifle sling stud is allowed to contact the rest -either by plunking it down on the bag before the shot, or during the recoil impulse- you will get noticeable vertical stringing.

 

[gamestalker]

I've encountered that on several occasions and have resolved it by either floating the barrel, or bedding the action. But that is contingent upon other contributing factors as well, one being velocity consistency.



GS

 

[helotaxi]

Velocity differences, unless there are gross max spreads, don't typically manifest at 100yds and then usually not as vertical stringing. Velocity changes from inconsistent burn or wildly varying powder charges typically work out as diagonal stringing up and right for a right handed shooter and up and left for a lefty.

Vertical stringing with minimal horizontal deviation is usually a shooter technique problem. The fact that you're having it with both bolt and semi-autos points to technique as the issue. Shooting good groups requires you to be as consistent as possible from shot to shot, from holding your breath at the same point to a consistent cheek weld to consistent pressure on the stock and forearm to consistent front rest placement.

 

[rayatphonix]

After reviewing these posts, I'm pretty sure the error lies in the Indian, not the arrow. I'll need to work on technique which is much cheaper than continuing to assemble loads.

 

[Andrew Leigh]

Hi,

other reasons for vertical stringing;

Weak and or broken firing pin causing variable ignition.
Poor breathing technique is another culprit for vertical stringing.

It does help to see a couple of group patterns along with the sequence of the shots.

 

[popper]

Inconsistent shoulder pressure, or inconsistent pressure on the forearm.

Try a bag under the butt of the stock, the shoulder just to absorb recoil. Position the rear bag for elevation correction. You may have to single load for the AR depending on the mag or grip.