POA/POI Variation Question??

[Longshanks]

     You guys on this website are some of the most knowledgable about turkey guns so i figured it wouldn't hurt to ask.  I have noticed with the multiple turkey guns i have sighted in with numerous chokes per gun that the POA/POI for the most part seems to come into play with HTL.  For instance with my xtrema and four chokes PG .670, JH .660, Kicks .670, and Hevi Choke .671 there seems to be no variation with the POI when it comes to shooting lead( shot to shot, shell to shell).  The variation only seems to be an issue with HTL. Example: xtrema with hevi choke .671: shoots hevi 13 3.5/.2.25./7's high and left.  Shoots Hevi 13 3/2/6's right.   JH. 660 Nitro 3.5/4x5x7 shoots low left.  I have noticed with some of the most awesome patterns on this website that the POI is normally way off.  If this were the result of mis-centered chokes than my POI's would be off with lead but that is not the case.  Also there seems to be a greater variation when shooting 3.5's such as Nitro 3.5/4x5x7's and Hevi 13  3.5/2.25/7's.  My question is has anyone figured out why?? Would have to be flexing in the barrel just as a rifle barrel flexes..?? Interested in opinions.  Thanks

[jfair]

I see the same thing.  All leads from low brass to 3.5" 2.25 seem to shoot the same.  Maybe a little up or down, but that would be expected.  Hevi 6 and 7's shoot the same as lead for me, the Mag blend is 6" low and 6" left.  Can't figure it out.  I asked kind of the same question in another post, and the best answer I got was maybe barrel harmonics?  This makes sense seeing how the mag blends are a little hotter than the others.  But none of my hotter leads shoot different so I don't know a good answer.

[Snoody Bastid]

I have no answer for you. But I just had the opposite thing yesterday when I patterened my NOS 11-87 SPS-T (3"). The Hevi13 3-2-6's & Rem HD loads were dead center POA (2 1/2" high) and all the lead loads were over to the right 3 1/2". Thats with 2 different chokes (PG & JH).

[Longshanks]

    Yeah has to have something to do with barrel harmonics and the amount the barrel flexes which i would assume would be effected by the load, and environmental factors.  I guess if a gun has a consistent POI issue with several loads then it could be off center.
    Definately has me scratching my head..got my xtrema dialed in with h13  3.5/2.25/7's but it is a one shell gun for now.  I cant solve the riddle..beyond my knowledge of guns/chokes and ballistics.

[trkehunr93]

My 835 shoots the Hevi-13 about the same as lead, I guess I am lucky.  Some guys have to scope their guns to get the POA/POI lined up.  I still shoot the bead sights on mine.

[Longshanks]

Its strange..i have a rem 870 that the POA /POI is the same with all lead shells, H13, FW7's, etc.
Have a Beretta Urika 3in that i am able to still shoot the beads on it as well.  Xtrema has presented more problems with HTL than any gun i have.  It will shoot all the lead shells great  and some 3in shells HTL are close.  Once i go 3.5 POI/ POA become an issue. I guess it would make sense that the 3.5 heavier loads would create more barrel flex or whatever the terminology for that would be.                                                                                                                                                     Shoots right at 300 in a 10in circle at 40 with 3.5/2.25/7's so i guess i will just shoot those out of it.

[Reloader]

I've seen POI variations with various lead loads as well as HTL loads.  HTL shows more because the patterns are smaller.

Whether lead or HTL, one needs to sight in his turkey rig with the exact choke and exact loads he intends to hunt with.

[Longshanks]

 That makes sense that it is more noticeable with a smaller pattern. That can't be the only factor though. All patterns are tight at 20yds or less checking POI/POA and easily visible if it's centered. With my guns the variation becomes most apparent with the 3.5 HTL loads. Is that due to the hotter heavier load or the effect HTL has on the barrel?? I've never had lead POI differences in my guns but I always shoot 3 in shells..hmmm.       Sighting in with one gun/choke/shell for hunting goes without saying but it's a shame not to be able to shoot effectively with more than one load in a scatter gun. Got allot of shells in he cabinet.

[Reloader]

I see the most POI difference from the wad that's used.  HTL wads are very different from lead wads.  With lead you are usually pushing a column of shot down the pipe that's riding the bbl with a portion incased with thin wad petals on most loads. Some lead loads do have deeper cups for more protection.  With HTL you are pushing a fully incased load with thick petals for protection.  Vary that thickness, design, and speed and you have a differing POI.

Even with lead you can have very different POIs from one brand to the next due to varying wads and MVs, but not as much as HTL as the HTL wads are of much different designs.  Some guns will not show this as much as others.

Chokes have a large impact on POI as well.

I do not feel it has to do with bbl harmonics, I feel it has to do with components.

Some guns and chokes will have the same POI with certain lead and certain HTL loads, but you never know until you run them.

Turkey shells are pretty cheap in the big scheme of things, so it makes sense to stick with the good stuff and use the cheap stuff on hand for getting optics close.

Reloader

[Longshanks]

Thanks for the info reloader..i just learned something about all this.  That explains whats happening with my guns.  I was starting to think it was going from 3 in to 3.5 in shells or even the hevi shot itself.  I was headed the wrong direction with it.  Didnt consider the difference in the wads.  Thanks.

[mossy835]

I too am lucky when we sighted in my Mueller scope I used Low Base lead Estate shells to center POA to POI. When done the 3 inch HM #7's were right on with the lead. Now that was 25 yards but that was what happened for me.

[3" 870 Shell Shucker]

Chokes have a large impact on POI as well.

I've seen one choke shoot 6" low, and another choke shoot either dead-on, or a little high in the same gun, on the same day, with the same shells.

BTW, I've never kept and used any chokes that shot low.  I use the factory bead on both of my 12 gauges.

[drenalinld]

I suggested the barrel harmonics idea to jfair a few days back. I have seen different chokes, atmospheric conditions, or component changes cause POI variations. I can't understand how a wad change alone would cause POI to move horizontally. Certainly not the only thing I have trouble understanding.  To be clear, I've never handloaded a single shotgun shell yet, but 1,000's of centerfire rifle cartridges.

In my way of thinking, the barrel oscillates in some sort of oval pattern. A component change could vary the position of the muzzle when the shot exits or even change the oscillation pattern all together. If the barrel is ridgid and a component can cause the POI to change, I would think POI would vary depending on orientation of that component in the barrel. I know component changes affect POI, but IMHO it is only b/c it changes the barrel harmonics. I think this is why some rifles will have similar POI with almost any load and some will have to be sighted in again with a different load.

I can't say this is correct, but it makes some sense to me.

As for choke changes, a different piece of metal in the end of the barrel, where it moves the most, will change the oscillation pattern, even how tight the choke is threaded into the barrel can change performance. Some chokes are not concentric to the bore of the barrel and some choke threads and recesses are not aligned properly.

If barrels did not oscillate, I don't think POI would ever change.

Whether lead or HTL, one needs to sight in his turkey rig with the exact choke and exact loads he intends to hunt with.

RIGHT ON.

Reloader, you have have a ton of shotgun hand loading experience and I have none, so please don't think I'm trying to discredit what you have said. I'm just stating my opinion. I hope to understand it better one day. I need those cameras from Top Shot so I can see what's happening as the wad/shot exit the choke.

[Reloader]

drenalind,

I suppose harmonics could play a role in it.  I place more in the components as that's what I've seen play the largest role. 

Lets take HTL for instance.  I've taken the same powder to produce the same MV with two diff wads and had different POIs.  This probably has to do with the way a certain choke reacts with a certain wad.  The release of the shot plus the braking of the wad is most likely different between the two. Maybe the whip as well. 

OTOH I've taken two diff powders to achieve the same MV with the same wad and seem to get the same POI or very similar.  Those two different accelerations would make one feel the whip would be different between the two, yet the POI is not noticably effected.  When thinking rifle, that's definitely the case due to diff exit points in the vibration cycle.

You also have to consider the fact that the same load in a shotgun seems to give the same impact.  Although it wouldn't be near as prevalent in shot patterns as in rifle groups, you don't seem to hear much on grouping problems in shotshells. Another reason why I feel harmonics is not the major factor in POI with shotshells.

On that same token, but alittle different subject. You can take two different powders with the same components to achieve the same MV in the same gun/choke and achieve a tighter pattern with one load vs the other.  Acceleration rate plays a role in pattern density.  I have also found that shot size can be effected by acceleration, IE 7s may pattern bettern than 6s with a certain powder, yet 6s pattern more efficiently than 7s with a different powder. It's a head scratcher at times, but just like rifle you have to go with what works.


This is merely guess work, so you just have to rely on what you know causes the differences.

Have a good one,

Reloader