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100 atr, major accuracy problems

C

chukarguy

Copper BB
Hi everyone, I am new to the forum here and new to Mossberg rifles in general, although I have been around Mossberg shotguns for the last 15 years.

I recently purchased a used Mossberg 100 atr with a synthetic stock in 308 in part because of the great reviews I have read, and also because I liked the way it looked and felt. After several trips to the range, 4 different brands of ammo, and replacing the scope with a brand new Vortex scope, the best I can do with this gun is between 5" and 8" (100 yards) groups regardless of scope or ammo. I know this is not a common problem with this rifle because I cant find any complaints of accuracy problems with this rifle anywhere on the web. I dont think it is my shooting because I shoot sub 1/2" groups with my savage axis at the same distance with factory ammo.

I am not necessarily expecting sub 1/2 inch groups out of this gun, but I don't think its unreasonable to think it should shoot 1 1/2" groups with its preferred ammo although I believe most people are getting 1" groups or better with this set up.

I am hoping there is something stupid that I have overlooked that I could fix myself. I did take the stock off to look for something out of place and I didnt find anything real obvious. I tightened up the action screws, but I did not torque them properly. One of the threads on the rear action screw seemed to slip on me at one point so I took it back out to examine it and saw no signs of stripping or cross threading. My groups are totally inconsistent, they do not "walk" from one point to another, but move all over the place. I will have some groups that are totally vertical, followed by groups that are vertical and several inches off on windage.

I have tried allowing adequate time for the barrel to cool down between shots, 15 min. between each shot, and all the results are the same. At this point I am thinking it could be the mounts and rings, although they seem pretty sturdy and I have tightened them up as well, or something to do with the action screws, or the barrel.

Any thoughts?
Thanks in advance for any replies.
 
That sounds like it could be a barrel defect. One thin you could check is to make sure that the barrel is actually free floating and that the stock isn't touching it. Slide a dollar bill in between the stock and barrel to check this.
 
Yes, the barrel is contacting the stock for sure. I would gladly dremel some stock out to float it, I just didnt think that explained the severity of my problem with a synthetic stock. I am not very experienced in working with rifles though and my "thoughts" could be off. Do you think that would explain accuracy issues of this magnitude?
 
I think that is probably the cause of your problem. I'm not sure about the atr, but on my 4x4 there is a pressure point underneath the barrel towards the end of the stock. You'll want to leave that but free float the rest. The stock touching the barrel can change the harmonics of the barrel and cause the horrendous accuracy your getting. There is a thread where someone else on here had this problem but I am not able to locate it.
 
What type of scope mount and rings are you using? Is there a possibility that something there may be loose? You also mentioned that one of the action screws "slipped". Is that screw still loose or is it holding?

True that an irregular point of contact along the barrel could affect harmonics, but if the contact is consistent then so should be the shot placement and groups. You usually only end up seeing changes in point of impact when a wood stock swells or shrinks against a barrel that is not properly bedded or free-floated. Even in those cases it's temperature/humidity related and the changes occur slowly. With your situation it is looking more like there is something loose either in the optics or the barrel/action.

I'd start eliminating one variable at a time and if everything checks out I would send the rifle back to Mossberg with a detailed description of your issue. An out-of-spec barrel or chamber isn't entirely out of the realm of possibilities...
 
Thanks for the replies. I called Mossberg and to my suprise, they said they would be glad to take a look at it even after I told them that I had purchased the gun used. I think i will try a few more things before I send it in. The rings are tight and holding, but I need to take them off and check the bases. If they are loose I will use some loctite. I may even have a smith look at the barrel. I must say that I am impressed with Mossbergs willingness to look at it even though I purchased it used, and the nature of the problems I am experiencing. I will keep you posted on how it turns out. Thanks again
 
One thing that hasn't been mentioned, nor tried that I can see, is if you have taken scope off and tried it on another rifle that you know of that shoots good. This will determine if scope's W/E are holding. I know Vortex makes very good scopes, but that doesn't mean the scope can't be bad.
I had a brand new Weaver scope that cost $300. It wouldn't hold POI from the minute I mounted. Had to send back to Weaver to have whole interior mechanism and all springs replaced. So a bad scope can get through QC--no matter how expensive.
Del
 
I had the same major accuracy problems when I got my Night Train 2. Ultimately, I found that one of the stock scope rings had a twist in it. In the end, I replaced the stock picatinny rail with Weaver bases. A "35" and a "36". I also replaced the rings with Leapers UTG swat style 6-screw tactical detachable rings. I also bought two sets of the detachable rings so that I can remove the Barska 6-24x60 scope, and put on a smaller 3-9x32 scope that I use for hunting. (reduces the weight, dramatically).

...and just to add to that, I had made a rookie mistake at the range. While using a bench rest, I strapped the barrel down. (in my mind...to reduce the jump from recoil). After 20 shots, I had seen a nice tight grouping of about 3" @ 100yds. lol.(not near the sub-moa that I think this rifle is capable of). That led me to find some more information about free-floating and bedded barrels.

Long story short, I changed the rings and bases. Used a shooting bag at the range and got way more consistent groupings, (not sub moa), with both scopes. While accepting a certain amount of shooter error, I am now satisfied.
 
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I am in a similar situation. 100 ATR Night Train in .308 s/n BA245195 (bought used in 2013) and my accuracy is ridiculous. Whenever I think I am getting it close, it jumps 5 or 6 inches at 100 yards. I have since loctited my rail (those screws were mad loose) and just now after joining the group have disassembled my firearm to ensure it is a free floating barrel. I think that at some point, the owner before my tightened down the front allen screw completely before doing the back screw near the trigger. My barrel is now much more obviously sitting higher off the stock. Once I get out to the range, I will let you all know how it shoots.
 
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