M788 .308 is vertical stringing

[Selmer]

I have a Rem. M788 in .308 that has started vertically stringing it's groups.  It used to be my go-to gun for itty-bitty groups when somebody started braggin about tight groups, but now it send them down range all over the vertical place.  Horizontally they are still less than an inch apart, but vertically I can shoot 6 shots and cover 10" with the bullets!  I did the dollar bill test on the barrel and it was tight, so I took just a little wood out of the channel to relieve it and I'll check it out this weekend with my proven accuracy loads.  I checked all stock screws, base and ring screws and everything is tight.  Is there anything else I should be looking for if the free-floating doesn't work?  Any tips are greatly appreciated.  This rifle used to put Nosler 150 gr. BT's into 1/2" at 100 yds. every day.  Please help!
Selmer

[vernonp]

Selmer      Every time I have had this problem it was from the barrell overheating. As much as you have probably shot this rifle, that may not be the reason. Anyway, overheating the barrell will cause vertical stringing.    I hope you find the problem        Vernonp

[Iowegan]

Your stock probably warped or swelled up from humidity. Try this: remove the barreled action from the stock. Find a washer with a hole large enough for the front stock screw. Put the washer in a vise sideways and squeeze it until the washer is arched. Put the front screw through the stock then place the washer on the screw. Tighten the front screw then install and tighten the rear screw. This should give you a free floated barrel. Your vertical stringing should go away unless you over heat the barrel. It won't hurt to leave the washer in place or you can do a real free float later.

[Selmer]

Well, I thought the problem was a barrel overheating also, although I couldn't figure why it would just start doing it all of a sudden, this rifle used to literally shoot 10 shot groups of 3/4" at 100 yds, it would just make a little bit bigger hole every time I shot.  So I took the time to shoot a 10 shot group from the bench, every shot from a cold barrel, I let it cool completely and it STILL vertically strung them out.  The first two were touching, then the next were 4 inches lower, but stacked right on top of each other, then the next three were 2 inches higher than the first two and stacked, touching, and so on and so forth.  That's when I checked the barrel channel for excessive barrel/stock contact and it was quite tight, so I sanded a little out and resealed it with tung oil and mineral spirits, and used 5 layers of black electrical tape drilled out and put over the front stock bolt to free float it, I have plenty of clearance now.  I'm going to shoot it this weekend, I'll post some pictures of the targets if I get some time, if it's still a problem we'll go from there.  BTW, it is a well-cleaned rifle, so that's NOT the problem, it gets regular treatment with Butch's Bore Shine and I also use Wipe-out, both do a wonderful job.
Selmer

[dave375hh]

Selmer,
In addition to floating the bbl check the recoil lug mortice to be sure it's not bottomed out. Grab some of the ol'lady's lipstick and put some on the bottom of the lug carefully reassemble the rifle and tighten the screws. Then take it apart and see if there's lipstick in the bottom of the mortice. If the forearm warped the mortice may have swelled also. Look at the wood behind the lug to see if it has cracked or compressed. Unless you damaged the bbl or crown I'd bet that the bedding has changed.

   I have four 788's and none have ever done this, but all of mine are glass bedded with the bbl's floated.

[Larry Gibson]

Selmer

There are two key indicators in your descriptions; it started verticle stringing "all of a sudden" and the last test had three different groups of two shots "stacked on top of each other" then would shift between "groups".  I have worked with a lot of M788s (still have a very nice accurate one in .308) and have found it always helpfull to free float the barrel.  However I have never seen one walk groups like yours either due to stock pressure on the barrel or the barrel heating up.  Your "groups are going it both directions and I have found that excessive stock pressure or barrel heating (warpage) causes groups to walk in only one direction.  Always can be a first time but I don't think so here.  

While you mention all the mount screws and stock screws are tight you have failed to mention the scope itself.  Even the very best of them can go bad, and for no apparent reason.  The erratic verticle shifting up and down of point of impact is a very STRONG indicator that your scope has gone south and will not hold zero.  Before the problem drives you too crazy I suggest you swap the scope with one of known performance and test the rifle for verticle stringing again.  Too many shooters put their trust blindly in the scope and look at the rifle or ammo for the accuracy causing problems.

Larry Gibson

[Selmer]

I've thought about the scope, I've never had problems with it, but who knows.  It's a Simmons Aetec, yeah I know, it's not a Leupold, but it has done well for me over the years.  I have a B&L Elite 3000 on my .30-06, I'll switch the scopes out this weekend when I shoot, I'll check the Aetec on the .30-06 and see if does the same as it does on the .308.  I hope I can get to the bottom of this, it annoys me when my rifles can't hit a paper plate at 100 yds and they get sold if I can't work them down to under 1" at 100 yds.
Selmer

[Larry Gibson]

Selmer

I know it's hard to believe but I've had a Leupold (along with numerous other makes) scope that "served me well for years" begin to do exactly what you describe.  Leupolds do and will go south, why else would they have or need a repair department?  

Larry Gibson

[Selmer]

I'm hoping it's not the scope, that's more expensive than fixing the gun!  We'll find out, I haven't had a chance to shoot yet, my cars are going to heck, one alternator went out, another has a leak in the heater line AND a seized rear brake, so I've been working on cars.  Maybe I'll get out today.
Selmer

[Redhawk1]

Also a suggestion is to check your mounts. It they are good, like you said try a different scope and see how it does. It is all a process of elimination. Good luck and I hope you find your problem.

[dave375hh]

One way to check the scope would be to turn the scope 90deg and see if it throws them side to side instead of up and down.

[Selmer]

Well, I finally figured out the problem, and LMG hit the nail on the head, I put my B&L Elite 3000 on it and my groups were under an inch again, I put the Simmons back on, and 6" was the best I could do.  Now the question is, will Simmons give me anything or fix it?  I've had it ten years on the same rifle, .308, and it looks fine, it's nothing I did to damage it, so should that be covered by the warranty?  Let me know what you think.
Selmer