base shimming?

Discussion in 'The Basics, Starting Out' started by CIG, May 12, 2005.

  1. CIG

    CIG Member

    Messages:
    5
    Joined:
    May 12, 2005
    Have a Howa 1500 in 270 with Luepold quick release mounts - two piece base with Bushnell 4200 elite 6-24. The release on these is on the bases - not the medium rings. The problem is that at 200 meters it is about maxed out. I need to go to 500 for silhouette. So the answer is shimming. How do I do it? How many shims, size, where to put them and where to get them. These bases fit Rem 700's. The load is Hornady 130 gr flat base SP over 45 gr IMR 4042 and Win primers in Win cases. Thanks for any help. <font color="white"> </font>
     
  2. CIG

    CIG Member

    Messages:
    5
    Joined:
    May 12, 2005
    The powder on that load is actually IMR 4064.
     

  3. HopSing

    HopSing Member

    Messages:
    18
    Joined:
    Apr 25, 2005
    [ QUOTE ]
    Have a Howa 1500 in 270 with Luepold quick release mounts - two piece base with Bushnell 4200 elite 6-24. The release on these is on the bases - not the medium rings. The problem is that at 200 meters it is about maxed out. I need to go to 500 for silhouette. So the answer is shimming. How do I do it? How many shims, size, where to put them and where to get them. These bases fit Rem 700's. The load is Hornady 130 gr flat base SP over 45 gr IMR 4042 and Win primers in Win cases. Thanks for any help. <font color="white"> </font>

    [/ QUOTE ]

    Your maxed out in elevation? You need to raise the elevation reticle, but ran out of room?
     
  4. abinok

    abinok Writers Guild

    Messages:
    877
    Joined:
    Nov 25, 2004
    CIG,
    First of all, welcome to LRH!
    Theres a couple of options other than shimming those bases, but ill cover shims first. The first thing id do if Iwere in your position would be to find out how much adjustment you have above your current zero. That way we will know how much adjustment you have in both directions, and you can optimize the location of your zero, inside the scope, so that your zero is towards the bottom of the adjustment, leaving you plenty of "up" adjustment.
    at the bottom of this picture you will find the formula for computing shim thickness needed for a given moa of adjustment wanted. [​IMG]
    The problem is that there is a limit to the amount of shimming you can do without damaging the scope. usually about .020 on a long action rifle. in this instance about 12moa, or just over 24" at 200yds. You can buy shims made of steel from any of the mailorder catalogs, or your local gunsmith will probably be willing to sell you a few, but its easier to make some yourself from a spare aluminum sodapop can you have around. It measures .004" thick. If you do decide to shim, don't be like one of the guys I saw at the range a while back. Put those shims under the rear base, not inside the ring /ubbthreads/images/graemlins/grin.gif!!!
    My suggestion would be to look at getting either a tapered base, or a set of the Burris Signature rings with interchangable inserts. Thats what all of the top portion of the above photo is. It gives all of the possible shim values with these rings, and these rings combined with a variety of tapered bases. Any of the tapered bases for the remington will fit the howa as you already mentioned.
    I believe that leupold makes a 20moa base that will fit your rings, and if I recall its only in the area of about 30 bucks.... worth a look.
     
  5. Brent

    Brent Well-Known Member

    Messages:
    2,537
    Joined:
    Jun 12, 2001
    If you need to shim, it will be needed under the "rear" base in order to gain more elevation.

    You can buy shim kits (Brownells) or cut out strips of a soda can (~.004" thick) and use multiple strips to gain the elevation you need in the rear.

    ~.001" shim in the rear equals "roughly" 1 MOA change in elevation, so if you want to bring it up 20" at 100 yards, start with about .020" worth of shim stock under the rear. .030 might be better in your case if you're already bottomed out at 200 yards.

    I highly recommend lapping the rings if you shim the base so you don't kink or bend the scope tube.

    The better fix would be to get a tapered base for a 700 and bed it, or buy some Burris posi-line rings with inserts.
     
  6. Brent

    Brent Well-Known Member

    Messages:
    2,537
    Joined:
    Jun 12, 2001
    Abinok,
    I posted late. /ubbthreads/images/graemlins/wink.gif

    Good advice and a nice chart! /ubbthreads/images/graemlins/smile.gif
     
  7. CIG

    CIG Member

    Messages:
    5
    Joined:
    May 12, 2005
    I can't really find any QR bases from Leupold that say anthing about 20MOA taper? I need to go about 38 inches or more, based on standard ballistic chart with 200 zero. I looks like I will try the .020 shim in the back. Will installing these and then lapping the rings have any adverse effect if I need to change shim height, or just relap them? I use this gun for both hunting and silhouette and using two different scopes. This means I have to use this system and it also means I am going to have to lap both sets. Any additional informations is appreciated. Thanks,
     
  8. Mysticplayer

    Mysticplayer Writers Guild

    Messages:
    1,459
    Joined:
    Jul 27, 2001
    Don't bother with a tapered based or shimming. Making the problem more complicated then it needs to be.

    Get a set of HIGH (extra high if it will make it under the scope bore distance rules) Burris Sig Zee rings with inserts. Buy a set of inserts (5 , 10 and 20 thou in one box). Put the 20 thou in the rear, 5 thou in the front. Raise the rear of the scope, lower the front. Rezero your scope which will be almost all the way 'down' now.

    Go have fun. This is the best and easiest way to shim. Absolutely no stress on the scope tube, don't have to muck about with lapping and all that calculations. Best part is if you change your load and the scope is now shooting too high, swap in less inserts and voila back at it again in 5 minutes.

    Oh, you can also rotate the shims to give a variable amount of adjustment. 5 min job at the range. Try doing that with shims - yuck.

    With the 270, shooting 500m will need less then 12 min of scope elevation depending on how 'slow' you want to run. That's a big case for silhouette...ouch. You have plenty of scope for the job.

    Definitely try the 130gr SST. Way higher BC and superbly accurate. Be careful about stringing. You are using very little powder for that case size and irratic ignition could really screw up your 500m groups.

    Jerry
     
  9. CIG

    CIG Member

    Messages:
    5
    Joined:
    May 12, 2005
    I think at this point I will shim and lap until I get the results I need. After I'm sure I want to shoot this sport more often I will go with a smaller round - .260 or 6.5 Swede and go with those Zee rings. That is the base powder for that load, but I get .8 7 shot groups with it. If I get stringing at 500 I'll know why. I was getting pretty good groups at 385 aiming above the plate, but stringing might be occuring.

    Thanks for the advice.
     
  10. CIG

    CIG Member

    Messages:
    5
    Joined:
    May 12, 2005
    Well I went to Gander Mt. and got Shims. Two .012's and one .006 for a total of .030. Lapped both sets of scope rings. Sighted both scopes in at 100 yards. Went to the silhouette range and at 500 meters I still have a turn plus left on the Bushnell. No stringing at 500 either with that load.