Have a pencil 16" barrel 5.56 ar15 and it seems to be stringing vertically somewhat, but I havnt actually shot it enough to figure out in which direction
because I have been testing a variety of bullets and loads for hunting.

I think it is stringing up, at least I have a few groups do that to one degree or another, but my question is - is it typical for a pencil barrel AR to string in one direction or another ??

With a couple of loads - 5 shot group and 1 and 2 are pretty close then 3,4,5 are moving up somewhat as the barrel heats up. At least thats what it looks like.

How far were you shooting? In general, your shot  pattern should be fairly round at short distances.
Shooting really far can expose vertical issues, but not typical for  what I assume you are doing.

Bbl heating isn't likely unless you are doing all of that really fast and even then it wouldn't be very common for a normal bbl to go straight up and down.

Do you have anything special in terms of gadgets hung on the guard? Does your bbl float? Are your sights standard  or other?

Well now that I think about it the wind was up range which can push bullets down so that was probably more of it than anything.

Its a non floated pencil barrel and they heat up quick. In the past with a cold small diam barrel I could get off 3 shots before the pattern started opening up.

Guess I need to shoot it in dead calm.

What kind of sights or optics are you using? I just went through the same drama, but found out that the scope I was using was not as good as I hoped. (Springfield armory)
I swapped it for a Vortex and that took care of it.
What distances are you shooting? Try shooting separate groups with different gr's of ammo and find out which one your gun likes.
Shorter distances? Consistent point of aim? Open sights are tough at long distance when your trying to zero.
Its not 'typical' for barrels to string.
I'm sure that through the process of elimination, you'll get it figured out.
Have fun doing it.

It would have to be a helluva wind to do this at short ranges. If you were out at 300 or more, I could see this starting to shape the dispersion pattern, but you would have noticed the condition changes, no?

Keep at it, you will find it. In the long run, if you are going to shoot accuracy work at distance, you will upgrade the bbl and the sights.

Not looking for a bench gun, more just curios.
All 100 yards.

1st shot some ladders looking for something accurate enough to hunt hogs with at night with the 55 gr TTSX over CFE.

Had a Leupold 2-7x scope on it at first looking for tight groups.
Once I narrowed it down to the tightest group which was not that tight, 3 shots 1.25" with a couple of flyers, I swapped to a Pulsar N750 and proceeded to zero that scope for night hunting.

Got it zeroed and had some other ammo with me. Shot some of my old load, IE 53 gr TSX bullets over H4895 and that ended up shooting the tightest of everything.

All in all with my old 53 gr TSX load it is good enough to night hunt with. Just curious about the stringing.

I'm thinking about picking up one. When the target moves, how responsive is it to the movement- any delay? Quality of the image?

With a pencil barrel and non free-float handguard, differing amounts of pressure on the handguard can cause vertical stringing.  I have seen POI move over 6 inches at 100 yards with too much pressure.

If you are shooting off of a rest, not getting the rifle back in the same place for each shot will also cause vertical stringing.

I have to be careful to keep from resting on the sling stud.

Jack...

With the pencil type barrels they really need to be free floated to not induce any errors. I tried to go the easy route and used a set of M4 handguards that I had laying around on my 300blk build and it became evident that it needed to be free floated. Now it is a sweet eyeball plucker at 100 yards.

Okay - got it. Free float for sure. Shooting off a rest most likely caused this. Makes sense.

Right now I am having a 358 gremlin barrel made so if I decide to keep the 5.56 upper I will put a free float handguard on it.

Honestly I have not used it enough to give it a quality of image report but I will after Xmas.
The other day was the 2nd time I have used it, both in daylight.
You can use it during the day if its not too bright and I could see a 2" black target dot at 100 yards although fuzzy.
Well enough though to shoot that 1.25" 3 shot group.
I am not sure if it was somewhat washed out/fuzzy because it was really still too bright but all I wanted to do is site it in.

I was concerned about the image blanking out from recoil, but I saw none of that. That must have been the N550 that did that.
Not sure on lag but I did not notice it.

I also have a Pulsar R550 monocular and a Luna LED IR illuminator.

Previously I tried to run that behind a NV Eotech Sightmark knockoff and just looking through that around the house I thought that would work, and it did, but when I got to the field it was good for about 50-60 yards then it got too fuzzy.

This N750 should be good for 200 yards and my max will be 200 yards as that is about the end of decent trajectory for the 358 Gremlin and most fields I night hunt hogs are 100-200 yards max. Not sure if I will need the Luna IR yet with it, but it makes a huge improvement on the 550R. The other night I could see a fox squirrel clearly at 75 yards with the R550. Could see another tiny animal at abotu 200 yards, btu the rez was so low I could not make ti out.

I got this N750 directly from Pulsar as a refurb then they had a 15% off sale so the total was just under $1200 shipped. So far so good.

Will know more after Xmas.

Thanks for the info. I'll be looking for your update.