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base shimming?

 
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Old 05-12-2005, 12:04 PM
CIG CIG is offline
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base shimming?

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>
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Old 05-12-2005, 12:17 PM
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Re: base shimming?

The powder on that load is actually IMR 4064.
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Old 05-12-2005, 01:28 PM
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Re: base shimming?

[ 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?
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  #4  
Old 05-12-2005, 01:39 PM
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Re: base shimming?

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.
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 [img]/ubbthreads/images/graemlins/grin.gif[/img]!!!
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.
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Old 05-12-2005, 01:43 PM
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Re: base shimming?

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.
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  #6  
Old 05-12-2005, 01:49 PM
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Re: base shimming?

Abinok,
I posted late. [img]/ubbthreads/images/graemlins/wink.gif[/img]

Good advice and a nice chart! [img]/ubbthreads/images/graemlins/smile.gif[/img]
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  #7  
Old 05-12-2005, 03:13 PM
CIG CIG is offline
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Re: base shimming?

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,
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