What types of issues will create radical shift in POI

[Coop453]

I picked up a old H&R single shot turkey gun. 3.5” 12 gauge, short and handy with a factory full choke. Had a bawl with this thing today checking POI on the pattern board and blasting horse apples. Patterned almost everything from 2 3/4” #6 steel and lead on up to 3.5” steel #4 Federals about centered give or take, maybe a smidge high and centered. Except for Heavy Metal 3.5” #4, and the 2 3/4” slugs I tried. Those slugs are hitting more than a foot low from a mere 15 yards. Same deal with the 3.5” heavy metal load. I would have completely missed a squirrels with that heavy metal load.

I can put just the corner of my chin on that buttstock and about centered the pattern, compared to a good tight stockweld looking straight down the barrel with all other loads.

i probably have more than half a dozen other loads I tried that all shot good. At least half a dozen steel #4 loads, plus a frw different game loads, and even a couple buckshot loads. All pretty much centered on that bead and laying the smackdown.

That Heavy Metal load shoots good in the old Mossberg. So I wonder, what types of things create these radical shifts in POI?

 

[BeeMaa]

The most obvious thing I would look at is the action and how tight it is, especially if the loads you tested pattern well out of other shotguns.

The break action on the older shotguns can wear significantly. In essence, the gun is trying to open when the charge goes off pushing the load low. This will be exaggerated as the charge gets larger. I would highly recommend that you have this old shotgun looked at by a competent gunsmith before you shoot anymore of these loads.

 

[Firebird]

Curious what the barrel is marked to shoot. Mine for instance is for 2 3/4 only and since it’s quite old, I would not challenge the integrity of the barrel with anything outside of the norm.
Mine does shoot very tight patterns a long way out, a rather impressive single shot 20 gauge.

 

[Wyatt Smith]

Most of the H&R single shot 3.5 guns I’ve handles were loose as a goose.

 

[BRICKBURN]

Full Choke and slugs.
Slugs do not require choke. I would hazard a guess that it will not be aiding accuracy.

 

[Ridge Runner]

My guess is the slugs you used have a thicker cup that compresses tight around the slug as the slug exits the muzzle.

As for the Heavy Metal shotshells:

How close are the Heavy Metal shot loads compared to the Federal shot loads? ie 1 oz vs 1 oz, etc. Same for velocities.

Since shot is measured by volume, and Heavy Shot is heavier than both lead and steel, and that Heavy Shot doesn't compress the same as lead and steel, the full choke and velocity of the Heavy Shot could be factors in the low POI.

 

[Ontario Hunter]

How long have 3.5" shells been around? I certainly never heard of them when I was a young man. So how "old" can this gun be? Is the barrel actually marked 3.5"? My experience is H&R made very cheap junk. Failure to maintain accuracy would be the least of my concerns with one of those.

I have shot 3.5" ammo out of a much heavier auto made to shoot that ammo. Extremely punishing! How in the world does anyone manage to hang onto one of those flimsy single shots shooting that stuff? Better make sure the gun is properly shouldered or it could break bones.