Mossberg 100 ATR Problem..

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NitwiT

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Hey guys,

Some of you know me, and that I'm new to this hunting/range thing. So I'll do my best to describe what's going on with my dad's hunting rifle.

He's also a first timer, picked up his PAL before I did, and got a Mossberg 100ATR (.308) out of Kamloops for a first rifle. Comes with a 4-16 x 56mm barska on it. Not a bad price for a beginner rifle.

Anyway, I took him out to the range, to see what his rifle could do, and to play some more with my Tikka. Here's where it got interesting.

We got him close the the x ring at 25 yards, he was about an inch high and an inch to the right. I figured that was good enough, and so we set up a target at 100 yards in order to finetune his group.

First problem was expecting a group, his first shot missed paper entirely, second shot was an inch right and 4 inchs high, third shot missed paper, fourth shot landed two inches right and 8 inches high.

At this point I was confused, so he gave me his rifle and I fired two shots, neither of which landed on paper. Outta curiousity, I adjusted his scope 9 inches down, and we proceeded to land two shots 4 inchs high, 3 inch spread, and one at the right height, by wide to the left by 3 inces.

Now, I know its just a mossberg, with a chinese scope, but I'm kind of thinking there must be something screwy with it.

On target at 25 yards = 9-11 inches high at 100??

Btw, to rule out the shooter, I lent him my rifle, and with his ammo he placed two shots 1/4" moa about an inch farther to the right then normal but at the height I set it at.

And while I'm on the topic, he shoots with glasses on, could this affect anything?

P.S. - He's shooting 180gr Federal PowerShoks, with a 1:10" twist, which is more than enough
 
I would try and get them to be dead on at 25 yds if possible and then deal with the minimal elevation changes at 100 yds after that. Also worth keeping in mind, is that if you are zeroing in at 100yds, the bullet would still be on the upwards part of its flight at 25 yds, so if anything it should be sighted in a little low (I wouldn't do this because we're talking an inch or two max).

As to what is wrong, I would suggest that you verify everything is tight that makes contact between the scope and rifle. I used to have a 22 that shot awful (10 inch groups at 50 yds no matter what ammo), it shot fine with open sights so I changed scopes, same issue. Turned out the mounts kept loosening off and after correcting this, it shot like a normal .22 should. Also, after doing this I would check the scope. I used to have a deerfield carbine that missed one too many deer. I loved the gun but it couldn't hit a barn so I just thought there was something up with the gun, and a local gun shop had a 700 that I was interested in, so I made a trade. Put the same scope on it, same problem. The scope wouldn't hold zero.
 
If you were 1" high at 25yds you could easily be 9-11" high at 100yds.I would guess 1"
low at 25yds would have put you closer to the ball park at 100.This situation was also exagerated by the large objective of the scope(sight line that much higher above bore).

Next time bore sight the scope yourself at the range at 50yds. Nothing high tech here,
just remove the bolt, look down bore and center it on target . Next alternate looking between scope and through barrel while making your adjustments. Once every thing
looks good try shooting. Getting your gun on at 50 will save you lots of ammo and frustration at 100.

If the gun is still spraying them all over start checking your rings,bases,action screws,etc. By process of elimination you should be able to sort out if its the gun,scope,or ammunition.

Hope that wasn't to long winded.
Goodluck.
 
Are you shooting from a supported position? Take the shooter out of the equation as much as possible when sighting in.

Make sure everything is tight.

There would be different POI between you and your dad as everyone sees things / and thus aims slightly different. But it shouldn't be anything drastic.

If it keeps up, trying swapping scopes and see if that's the problem.
 
Ok, thanks for the inputs guys

Looks like we're heading out to teh range again soon! (Shucks!)

GSoD - Shooting from a benchrest, and we both traded rifles to test this.

Marcoman - My understanding of a 308 and its relevent ballistics is that at 25 yards the bullet is climbing, and at 100 yards it will be coming down, canceling out the rise.

I shouldnt be too concerned about the disparity between 25 yards and 100 yards then.. is that right?
 
You should be centered 1/2" low at 25 yds. I shoot at Mission, if you do too PM when you're going out and I'll give you a hand. I shoot most weekends.
 
scope height?

How high is the scope? On the off chance that you have very high scope rings being dead-on at 25m would mean being much higher at 100m than you would be with a very low mounted scope.

Group size - tough to say, lots of variables. Check all possibilities with the scope mounts (i.e. loose bases or rings) and then the muzzle crown for starters, try different ammo, let a few different capable shooters shoot a group...
 
I think it may have something to do with the scope mount. His Barska has a large objective lens and it's mounted in such a manner that it easily clears the barrel by a fair bit. (not sure how much)

I'll let you know what happens next time we go out
 
Sounds like that scope is very high in the mounts then...that would explain the huge elevation at 100m if your were dead-on at 25m.

I have never liked huge objectives, and feel anything over 40mm is totally unecessary on a hunting rifle.
 
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