Mossy 500 POA POI off with 18.5" smooth bore


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jpwilly
April 21, 2013, 07:58 PM
Hey all, thanks in advance for any help.

I have a POA POI issue with my new mossy 500 combo. It came with a 28" vent rib bbl and 18.5" smooth bore bbl. I tested the 18.5" bbl out today at the range with some 2 3/4" 1600fps 1oz rifled slugs (Federal Power Shok). At 50 yards I was shooting at a 12"x12" shoot-n-c. POA was dead center and impact was over 1ft high and 1ft left. I held POA at bottom of target (6 oclock hold) and next slug hit about an inch above the target on the right hand corner. Once I knew where it was shooting I held low and left and put one throught the center of the target. I was able to hit consistantly after that by holding low and left but I don't have any sights to adjust and this isn't going to be acceptable for me. What can be done? Is it the barrel, the gun or the ammo?

Regards,

JPW.

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Virginian
April 21, 2013, 08:46 PM
Where does the 28" shoot? I would try some different slugs but i doubt that's it, and then I would contact Mossberg.

jmr40
April 21, 2013, 08:56 PM
Is this a rifle sighted barrel? If not, it is meant for buckshot/birdshot, not slugs. You may get reasonable perfromance up close, but 50 yards is really pushing it for slugs and just a front bead. The way you are mounting the gun and sighting down the barrel can have a huge effect with just a bead. With practice, and learning just how to hold the gun you should be able to get an acceptable POI. Especially at 20-25 yards. If you want to shoot slugs much farher you really need rifle sights.

squid841
April 21, 2013, 10:10 PM
I have a 500 also, and there are no sites on the rifled barrel, but you said it was smothbore. Mine is rifled, and It has a picatiny rail for a scope. also, are you shooting it left handed?

natman
April 22, 2013, 03:11 AM
I was able to hit consistantly after that by holding low and left but I don't have any sights to adjust and this isn't going to be acceptable for me. What can be done? Is it the barrel, the gun or the ammo?


There's your problem. Expecting a sightless shotgun to hit to POA like a rifle is a bit much. If you took the sights off a rifle and sighted down the barrel, how near POA would you expect to hit?

frankenstein406
April 22, 2013, 04:47 AM
Might have to get a scope mount and a red dot.

MCgunner
April 22, 2013, 09:38 AM
Stock fit has a lot to do with POI when pointing them. I had to shim both my Mossbergs to lower the drop to get them to fit me proper. Now, they shoot where I look, shot loads of course, but they have to be centered, too.

allaroundhunter
April 22, 2013, 03:28 PM
Slugs shot through smoothbore guns typically print high and left. It is not your fault, it is not the gun's fault, and it is not the ammo's fault; it just is what it is.

ZVP
April 22, 2013, 04:58 PM
I read right here in a post that alugs are right=on @ 100yards with a bead. Now I don't mean "X" ring, but hits near POA @ 100.. Slugs are pretty darn accurate these days and I have read many accounts of 3-4" groups at long ranges.
Now be honest, a slug hitting anyone within 2-4" is gonna take ALL the fight out of em , don't ya think?
Hits on game will anchor them where they stand.
I can understand your frustration and want of tight groups butwe are talkingt a smoothbore and a very long range shot group.
Is there a "standard" for slug groups?
This is why I like Buckshot!
Good luck!
ZVP

jpwilly
April 22, 2013, 06:52 PM
Thanks for the replies, I have not patterned the shotgun with 00 or 000 buck loads yet so not sure how those do.

But I have shot smoothbore shotguns that hit clost to POA with slugs maybe I was just expecting too much?

Yes, I'm a lefty my right handed friends 3 shots all went high left, mine were all high right -interesting.

Maybe I'll just beat the barrel on a car tire till is shoots slugs where I aim LOL.

DNS
April 22, 2013, 07:25 PM
I run slugs through my 28" 870 and buck/bird through my Protectors 18.5" barrel. Your not alone in crappy slug accuracy through short smooth bores.

Virginian
April 22, 2013, 07:53 PM
I have seen lots of smoothbore shotguns that would shoot well enough out to 100 yards, with a bead sight. He is not talking about accuracy, he is talking about POI. Accuracy is group size. POI is where the group hits.

jpwilly
April 28, 2013, 11:19 AM
Need some math help here: I believe I have figured this out. I put a 36" level on the reciever and the muzzle end of the barrel is 3/8" lower than level and the front bead is approx 1/8" tall leaving it approx 2/8" lower than level with the reciever.

I know the bore axis and rifle sights are set for a trajectory to overcome the drop due to gravities immediate effect on the projectile once it leaves the bore so does anyone know how much taller my front sight needs to be? The slugs were 1oz rifled slugs shot at 1600fps and at exactly 50yrds they were impacting 12-14" high.

Any help appreciated - Joel

natman
April 28, 2013, 12:31 PM
Need some math help here: I believe I have figured this out. I put a 36" level on the reciever and the muzzle end of the barrel is 3/8" lower than level and the front bead is approx 1/8" tall leaving it approx 2/8" lower than level with the reciever.

I know the bore axis and rifle sights are set for a trajectory to overcome the drop due to gravities immediate effect on the projectile once it leaves the bore so does anyone know how much taller my front sight needs to be? The slugs were 1oz rifled slugs shot at 1600fps and at exactly 50yrds they were impacting 12-14" high.

Any help appreciated - Joel
How far apart are the front sight and the rear sight (your eye) AKA sight radius?

Pop it into the calculator here (http://www.brownells.com/.aspx/lid=13093/GunTechdetail/Sight_Correction_Calculator).

jpwilly
April 29, 2013, 01:03 AM
Thanks for the link natman. I took some measurements just today with my calipers. I found that using a 24" steel framing square that the distance between the top of the barrel and the sight plane that would run parallel to the reciever is a gap of .274" but the top of the bead sight is just .155" off the barrel leaving a .119" gap of air. I know the bore needs to be pointed slightly high to overcome gravity and dead level won't work. The distance between the bead and the reciever is 18" and since there is no rear sight I'll use that in the calculator.

The calculator said the sight correction should be .120" so .155+.120=.275" front sight height needed for zero at 50.

natman
April 29, 2013, 04:01 AM
Don't bother trying to figure out a point of reference to the receiver. Just plug the values into the calculator and make the new front sight that much higher than the old front sight.

The problem with trying to use just a shotgun bead with slugs is getting your eye (in effect the rear sight) in exactly the same place within a hundredth of an inch every time.

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