Diagonal stringing

[TeaRex]

Hunting season is upon us, and most of the bullets I shoot are not appropriate for hunting, so I figured I better load up a few hunting rounds and test them out. I did approximately zero load development for these rounds. I took a powder charge that I knew would be safe in my gun and looked reasonable in quickload and away I went. First few shots were dialing the elevation in, and then I shot this first 5-shot group at 100 yards. Not an amazing group, but it certainly meets the "minute of deer" criteria. I moved straight to 200 yards and shot the next group and the shots created a string from low right to high left, starting with shot #1 in the lower right, and finishing with shot #5 in the top left.

I've noticed that the groups on my rifle and loads always seem to suffer from strings like this when things aren't working quite right... usually a lot more vertical stringing than horizontal, which I interpret as either (1) a velocity variation or (2) unfortunate barrel harmonics. I am not sure about #1 though... I think you would need a pretty significant velocity difference to get this amount of stringing at 200 yards. Then again, I am using a $30 electronic frankford arsenal scale to measure my powder!

What are y'alls thoughts?

Thanks,
TeaRex

PS- I am fully aware that a lot of VLDs wont shoot well unless they are jammed, or set to a certain amount of jump... I didn't to go through the effort for this hunting load.
PPS- The other theory I had was that the barrel/ammo was heating up on the second group. For all shots, there I took a ~30 sec break before reloading another round, then took 10-15 sec with the round in the chamber to pull the trigger.... so possibly the ammo temp was increasing some and increasing muzzle velocity?

 

[308Gunner]

The first thing I would do is use a beam scale to check powder weights, I would bet they are off alot more than you think. Then do an ocw test to find a load that will group fairly good for hunting season and then fine tune from there.

 

[gvanhyning]

Best hunting bullet is a match grade bullet. They're consistent and accurate and when you know where the bullet will hit, the animal goes down.

 

[dustinoif3]

Last time I shot over the chrono I was at the 200y line and all ten shots were shot semi fast. Like as you mentioned above and my 10 shot group looked damn near like that. Looks like a good deer slaying load as it sits. Good luck!

 

[RyeDaddy]

What kind of scope?

Parallax is my guess.

 

[JGorski]

You think you got problems, this is just a lot number change in bullets, 178 HPBTs, first lot did just fine, note the 168AMAXs in the upper right corner, so you cant blame it on anything but the bullets.

 

[TeaRex]

The first thing I would do is use a beam scale to check powder weights, I would bet they are off alot more than you think. Then do an ocw test to find a load that will group fairly good for hunting season and then fine tune from there.

Thanks for the advice... I'm probably due to upgrade to a beam scale. I was looking at the RCBS 10-10 scale... what would you recommend?

Last time I shot over the chrono I was at the 200y line and all ten shots were shot semi fast. Like as you mentioned above and my 10 shot group looked damn near like that. Looks like a good deer slaying load as it sits. Good luck!

Yep, I don't think the deer will complain much. For target/match shooting, I can get loads with better groups, but these will work just fine for the current purpose.
Did you ever diagnose what caused that group?

What kind of scope?

Parallax is my guess.

Scope is a nightforce NXS 5.5-22x56... I was watching for parallax shifts and adjusted before each group, so hopefully that wasn't the issue. For my own information, could parallax be that far off to cause that much dispersion?

 

[dustinoif3]

It was due to increase in muzzle temp I believe. My next outing I took a 30second break between. Only shot 5 rounds and it measured just at an 1" at 200y

 

[jcampbellsmith]

It was due to increase in muzzle temp I believe. My next outing I took a 30second break between. Only shot 5 rounds and it measured just at an 1" at 200y

At this time of year I'm typically trying to shoot a group of three deer (or more) and not many groups of deer will stand around for a minute. I think you need to look again at your rifle. I want my rifles to be able to handle a number of shots without worrying about the POI moving.

Regards

JCS

 

[dustinoif3]

It was a 10 shot string fired in close succession on a 80 degree day. The vertical diagonal stringing didn't get over 2" at 200 so it didn't bother me. I could just relate to the OP.

 

[Pinecone]

Two things come to mind.

1) If there was not sufficient cooling time between shots, the stringing could be due to barrel heating. If the shots actually were shot in the order along the line 1 - 2 -3 - 4 -5, then I would think heating.

2) During the shot event, the muzzle moves in a figure 8 like pattern, but normally tilted some. If your load is exiting around the X part of the figure 8, you could be diagonal dispersion. But in this case, I would expect the rounds to be in a random order along the line. 1 - 3 - 4 - 2 - 5 or similar

 

[damoncali]

Was it windy? You'll see some vertical deflection like that in a good crosswind. It's due to the spin of the bullet.

Edit: Nevermind. I misread. the angle of your stringing is too steep to be from wind. I would guess it's unfortunate vibrations.

 

[samnev]

TeaRex Quote
"Thanks for the advice... I'm probably due to upgrade to a beam scale. I was looking at the RCBS 10-10 scale... what would you recommend?"
I have the RCBS 10-10 great beam scale. But I would recommend you go to the RCBS ChargeMaster setup. Best thing I ever did to produce accurate loads. It eliminated having to wait for the beam to become stable and by the time one load is dispensed and loaded the next is ready to load. Tested the drops against the 10-10 and either were dead on or at most differed by 1/10 of a grain.