View Full Version : What am I doing wrong with this Mossberg?

January 10, 2011, 11:06 PM
Ok folks, I'm scratching my head on this one.

I tried to get the daughter's Mossberg 500 Bantam 20 ga to shoot slugs. I invested in the Trophy Slugster barrel which was factory mounted with a cheap Bushnell scope (could be problem #1) after having great results with a Trohpy Slugster (on which I mounted a Nikon Prostaff) for my 12 ga Mossberg 500.

A couple weeks ago, I went to the range with 2 boxes of Remington Copper Solid Sabots, Winchester Partition Gold, Lightfield EXP, and Hornady SST and my Caldwell Lead Sled.

The Remingtons were not a grouping, but a pattern. Shooting at 50 yards at 8" rounds resulted in holes all over the place. Obviously this gun did not like those!

The Winchester Partition Golds produced a measured 3 1/4" group at 50 yards, 2" high and 1 1/2" right.

The Hornadys were running 2 3/4" groups 1" low, but on center.

Then the Lightfields came in touching, and just outside the black at 7:00.

So, I take the Lightfields out to 100 yards and get a 3" group before running out of ammo. Seems like that will do it!

I buy 6 boxes of Lightfield EXPs, go back to the range today, and begin the job all over again to get the scope dialed in. At 50 yards, the first grouping is touching. Yeah! Then the fun stopped!

Instead of grouping, I began getting vertical strings going down. I was giving it a minute rest in between shots, and it was 32 degrees out, so the barrel wasn't heating up. An ungloved hand touching the barrel in between shots confirmed it wasn't even lukewarm. I was still shooting off the Lead Sled.

Eventually I adjusted the scope to compensate for the last round's POI, set the gun down and switched to my 12 ga Mossberg 500, and it ate the Winchester Platinum 400 gr slugs like a champ, giving me 2 1/2" groups at 100 yards.

Back to the 20 ga. The first round at 50 yards was back to 2" high with the adjustment, about where I wanted it before going to 100 yards. So far, so good. I shoot another round, and its 2" lower. Hmmm. I shoot another, and its another 2" lower. Arghhhhhhhh:mad:

Back to the 12 ga. Everything's fine.

Back to the 20 ga. I took it out to 100 yards and the first round was off the paper low. I adjusted the scope for the last POI and the first round went right where I wanted it. Then it strung low again on successive shots!

I'm assuming the scope is bad. After all, it was a package deal from Mossberg for the scope/barrel. I checked the rings and they are tight. I checked the mounting bolt for the barrel and it was tight. A bad scope is the only thing I can think of. I've never had one go bad like this before, so I'm a little nervous that this might not be the problem and throwing $250 at the Nikon Slughunter I've been considering might be in vain (or it will go on my 12 ga :D)

Anyone got any other thoughts? After 6 boxes of Lightfield EXPs through that gun alone tonight, there's $72 out the window...

the rifleer
January 10, 2011, 11:51 PM
Is the scope secured tightly in the scope rings? It may be a bad scope too. try shooting it without the scope and using the bead.

January 10, 2011, 11:55 PM
I vote bad scope. Slugs recoil pretty hard and a cheap scope will have a wandering zero.

January 11, 2011, 01:17 AM
I have to agree, sounds like a scope issue.

January 11, 2011, 01:22 AM
I have a friend whose family hunts deer with slugs. They had a couple Leupold shotgun scopes that cost close to $300 each. Both scopes gave out around the same time and wouldn't hold a zero anymore. If these supposedly higher quality scopes gave out, I'd guess the same maybe happened to the package-deal scope you're talking about.

January 11, 2011, 06:34 AM
I would put a Prostaff scope on hers as well, they are great. Also if you want to try another ammo yet Federal Premium with the barnes expanders are great.

January 11, 2011, 06:58 AM
Did you use lock tight on the rings and scope base?

I assume the scope is mounted correctly for proper height and windage adjustment.

January 11, 2011, 08:03 AM
I vote bad scope. Slugs recoil pretty hard and a cheap scope will have a wandering zero.

I've had three shotguns with three different red-dot scopes. two held up just fine and the one in the middle blew out after about 4 shots and the "zero" wandered all over the place.

January 11, 2011, 08:27 AM
My Son's Bantam did pretty much the same thing. What I found out after trying two scopes was that you could not keep the barrel tight enough to get the same POI after firing ten or so rounds. It would start drifting down or moving from side to side. Gave up on it and got him an HR.

January 11, 2011, 08:32 AM
Sorry, Slugster barrel went right over my head, just saw Bantam. Probably right, Locktite and then new scope.

January 11, 2011, 10:22 AM
I very much appreciate the inputs. Thanks!

To address the questions:

@ rifleer, ammocrafter, and olddrum: The scope and rings are tight. I don't have a torque wrench to measure it, but they are tight enough to cause me concern of tightening them more. I checked that first off when I began troubleshooting.

@ rifleer: Because it has the cantilever mount, there's no bead to try.

Everyone else: Your suggestions are reinforcing the suspicions of the scope. I can't think of anything else, but since I am not the bastion of all knowledge, wanted to hear if I was missing something.