I just installed a cantilever type rifled slug barrel onto my Mossberg 500 20ga. I shot the first shot at the target starting at 50 yds, the gun was shooting in the dirt. I have since raised the crosshair adjustment so much that it is out of adjustment and it is still shooting 5'' low at 50 yds. The barrel came with the scope already mounted on it and it said it was laser bore sighted. I have mounted plenty of scopes but have never had this problem. any help would be greatly appreciated.
slug barrel shooting low
- Thread starter tball614
- Start date
It is a 3x9/32 bushnell that came with the combo. Mossberg #92010. I checked everything, all is tight. My son installed the barrel, he said when he tightened the barrel hand tight, there was a small gap between the barrel and the magazine tube he said like .015'' so he tightened the nut with pliers. I didn't know about this till afterwards and I told him this was normal and loosened the nut to hand tight. Is it possible that small amount put the barrel in a bind or something? Just taking a shot in the dark, no pun intended.
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Aim higher.
At the expense of burning up ammo on guess and check, try swapping the scope rings around, (front one to rear, rear one to front.
Try a laser bore sighter, it may help with scope alignment. It may at least show how much it's off anf help in determining what piece of the system is causing the problem.
Does the Scope rail look parallel to the barrel? Check it with a level
Does the Scope rail look parallel to the barrel? Check it with a level
Joe Porter
.22LR
I'm just curious;
As the cantilever and scope mount came from another gun; was that gun a 12 gauge?
Just wondering if there may be a specification difference between 12 and 20 gauge cantilevers as their reference point would be different for the center axis of the bore?
So, just perhaps both the scope and the catilever would be fine on a 12 gauge, but the difference between a 12 and a 20 gauge barrel would be enough of a difference as to not let the 20 gauge barrel zero with that mount and scope?
I've boresighted a lot of weapons systems, that might be something to look at.
As the cantilever and scope mount came from another gun; was that gun a 12 gauge?
Just wondering if there may be a specification difference between 12 and 20 gauge cantilevers as their reference point would be different for the center axis of the bore?
So, just perhaps both the scope and the catilever would be fine on a 12 gauge, but the difference between a 12 and a 20 gauge barrel would be enough of a difference as to not let the 20 gauge barrel zero with that mount and scope?
I've boresighted a lot of weapons systems, that might be something to look at.
Never thought about swapping the mounts, I will definitely try that. I will also check for level when the scope is off. It said on the package that it was factory bore sighted but I guess that could have been done incorrectly from the factory or it could have been banged around during shipping. I have shot 15 rounds of sabot slugs so far; getting very expensive. Has anyone ever put a shim between the scope and the bottom ring? Had someone tell me they did on a .30/30 once, but then I wouldn't know how thick of a shim to start with. Thanks very much for the input.
I thought it was funny, my wife thought it was very funny, didn't mean to seem snippy.All in fun.
No worry's, I didn't think you were (snippy). Sometimes hard to communicate stuff on the web.
. Anyway, welcome aboard.More seriously, I don't know how familiar you are with shooting (shotguns in particular), but from what you said, it may be that you are anticipating the recoil (bucking the shot) which typically will show up as shooting low. I've been shooting for about 55 years, and still catch myself doing that sometimes with a new to me gun. Pisses me off when I do, but it's a very common problem.
One way to find out if that's the problem, is to video yourself or have somebody else watch for it. If you can make or buy some blank shells, have somebody else load the gun with a random mix of hot shells and blanks so that you don't know which one is up next. If you're bucking it will be obvious when you fire a blank.
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Joe Porter
.22LR
Before you do anything else, figure out just how much adjustment in elevation you have by going to the full down and then counting your clicks up. once you have that number go to your midpoint. Sandbag that gun in and on a targe and get it set in as firmy as possible and fire one round at your target. That elemenates most of the possible human error. If your even close to being on paper figure your adjustment and try the same thing again.
If you're not even close at this point.
If you want to try something and have a 500 12 Gauge available.
Measure the distance from the bottom of the mount to the barrel on your 20 gauge. Now mount the catilever and scope to the 12 gauge and measure again. Add both numbers and divide by two, the difference would be the engineered offset. If this offset is too much, this would be what makes it not zero with your gun.
To proof this fire the 12 gauge as above and see what your results are.
The difference could be taken off of the bottom of the mount to make it work.
If you're not even close at this point.
If you want to try something and have a 500 12 Gauge available.
Measure the distance from the bottom of the mount to the barrel on your 20 gauge. Now mount the catilever and scope to the 12 gauge and measure again. Add both numbers and divide by two, the difference would be the engineered offset. If this offset is too much, this would be what makes it not zero with your gun.
To proof this fire the 12 gauge as above and see what your results are.
The difference could be taken off of the bottom of the mount to make it work.
@Joe Porter I'm confused buy this: "Now mount the catilever and scope to the 12 gauge and measure again." The cantilever should be semi-permanantly attached to the barrel. It really cannot be swapped.
I have the feeling that it may not be mounted to the barrel correctly or that the scope rings are not off from front to rear (swapping them around would quickly determine of this is the case.)
I have the feeling that it may not be mounted to the barrel correctly or that the scope rings are not off from front to rear (swapping them around would quickly determine of this is the case.)
Joe Porter
.22LR
Sorry about that, I didnt think this was permantly attatched to the barrel.
I borrowed a bore sight, dead batteries tho, now I need to get to the store for more ammo and some batteries. I am going to swap the mounts around and start from scratch. I have been shooting for 30 years, but everyone still flinches once in a while. I was shooting from a very good rest. I would think I was pulling of on all 15 rounds. The kick wasn't as bad as I thought it would be, my youngest son has a rossi 20ga single shot that is brutal to shoot even with 2 3/4 # 7 1/2 shot shells, this Mossberg shoots way smoother, always has since I got it in 1978.
Got back a little while ago from shooting the gun again. I used the bore sight and swapped the mounts. Bought the Remington sabots this time, $19.99 per box at my local wal mart. Really liked the way they shot tho. Shot it first at 25yds, it shot 3" to the right but dead center. Next I shot at 50yds, it shot 6" right and 8" low. I made the necessary adjustments and shot another round, it shot 1/2" low of the hole it made at 25yds so I took it a few clicks to the left. The next shot at 90yds, it shot dead center and 1" high, can't complain about that. Its a good thing too because deer season opens in the morning and my son really wanted to use this gun. Thanks for all the ideas and info, you guys were very helpful.
Glad you got it brought in. And I just realised something, I may have missed earlier, are you shooting sabots through a smooth bore? Because the shots still seem pretty erratic.