I have a EGW 20 MOA base on my SPS. The rear height of the base is .530 and its too tall for me to get the proper cheek weld. Are the better bases (NF, Badger, seekins) lower at the rear? I read where the seekins is .44 in the rear fro the 20MOA mount, which will help, but I wanted to find the lowest mount I can afford. I have a cheep weaver that is really low, but its also a 0 MOA base.
Rifle Scopes base height
- Thread starter badshooter
- Start date
Re: base height
Sloped bases will often present cheekweld/height problems.
My approach is to build a custom slope into the regular unsloped base. This method takes into account the actual relationship between the boreline and the particular scope's elevation adjustment mechanism.
Zero the rifle at 100yd, then run the elevation down to bottom and come back up around 3-5MOA. Using a small aimpoint at the top of a target, fire several shots, and plot the distance back up to the 100yd zero.
Now the math.
There are 3600 inches in 100yd. Measure the length of the base and divide that number by 3600. If it's, say, 4 inches, the result will be .0011111, etc.
So, speaking in rough terms, if the bullet impacts 20 inches below the aimpoint, the rear of the base will need to be raised .020" in order to bring the POI and POA back into correlation. Glass or Epoxy Bed the base to the receiver with .020" of shim beneath the very rear edge of the base, and now the base is custom configured to provide the perfect degree of slope to permit the maximum amount of available elevation adjustment.
Be sure to apply release agent to the contact area on the top of the receiver and around it for some small distance.
The advantages to this approach are several.
The slope is custom matched to the scope's capabilities.
Standard unsloped bases are a lot more available.
It's kinda unlikely that raising the scope's eyepiece by the required number of thousandths is going to cause any new and serious cheekweld problems.
Greg
Sloped bases will often present cheekweld/height problems.
My approach is to build a custom slope into the regular unsloped base. This method takes into account the actual relationship between the boreline and the particular scope's elevation adjustment mechanism.
Zero the rifle at 100yd, then run the elevation down to bottom and come back up around 3-5MOA. Using a small aimpoint at the top of a target, fire several shots, and plot the distance back up to the 100yd zero.
Now the math.
There are 3600 inches in 100yd. Measure the length of the base and divide that number by 3600. If it's, say, 4 inches, the result will be .0011111, etc.
So, speaking in rough terms, if the bullet impacts 20 inches below the aimpoint, the rear of the base will need to be raised .020" in order to bring the POI and POA back into correlation. Glass or Epoxy Bed the base to the receiver with .020" of shim beneath the very rear edge of the base, and now the base is custom configured to provide the perfect degree of slope to permit the maximum amount of available elevation adjustment.
Be sure to apply release agent to the contact area on the top of the receiver and around it for some small distance.
The advantages to this approach are several.
The slope is custom matched to the scope's capabilities.
Standard unsloped bases are a lot more available.
It's kinda unlikely that raising the scope's eyepiece by the required number of thousandths is going to cause any new and serious cheekweld problems.
Greg
Re: base height
Thanks for the info. Do I need to get a high strength steel ase for this to prevent the shims from warping the base? From the pictures, the NF and Seekins bases look lower than the EGW base I have now.
Thanks for the info. Do I need to get a high strength steel ase for this to prevent the shims from warping the base? From the pictures, the NF and Seekins bases look lower than the EGW base I have now.
Re: base height
Does anyone have a NF base they could measure the thickness at the back? I called Scott @libertyoptics and he measured a Seekins to be .440 and a Warne to be .400.
Does anyone have a NF base they could measure the thickness at the back? I called Scott @libertyoptics and he measured a Seekins to be .440 and a Warne to be .400.
Re: base height
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: badshooter</div><div class="ubbcode-body">Thanks for the info. Do I need to get a high strength steel ase for this to prevent the shims from warping the base?</div></div>
For the purpose of establishing the proper height to build a custom base, "No". In reality, the higher end aluminum rails are probably plenty strong to not warp anyway, especially if the base/rails have full support from the shims. The shims are going to crush before aircraft-quality rails will. But I would just buy a Seekins rail and be done with it.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: badshooter</div><div class="ubbcode-body">From the pictures, the NF and Seekins bases look lower than the EGW base I have now.</div></div>
The Seekins Picatinny Rail is definitely lower than the EGW. I don't have personal experience with a NF, but from seeing and/or shooting other shooters M700s' at the range, the NF also appears to be lower than the EGW. Another manufacturer that seems to make bases on the taller side is Ken Farrell.
Keith
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: badshooter</div><div class="ubbcode-body">Thanks for the info. Do I need to get a high strength steel ase for this to prevent the shims from warping the base?</div></div>
For the purpose of establishing the proper height to build a custom base, "No". In reality, the higher end aluminum rails are probably plenty strong to not warp anyway, especially if the base/rails have full support from the shims. The shims are going to crush before aircraft-quality rails will. But I would just buy a Seekins rail and be done with it.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: badshooter</div><div class="ubbcode-body">From the pictures, the NF and Seekins bases look lower than the EGW base I have now.</div></div>
The Seekins Picatinny Rail is definitely lower than the EGW. I don't have personal experience with a NF, but from seeing and/or shooting other shooters M700s' at the range, the NF also appears to be lower than the EGW. Another manufacturer that seems to make bases on the taller side is Ken Farrell.
Keith
Re: base height
The shims only establish the height and hold the alignment while the glass or epoxy bedding compound hardens. The entire contact area beneath the base gets coated/filled with the resin, so the entire base is supported by the cured resin, and not by the shims. Wipe off any excess oozage with a paper towel, and regular nail polish remover will clean up any residue as long as you get it before it cures. During the hardening, the base screws should only be snugged up firm, but not torqued, this ensures there will be no stress on the base/receiver once the bedding cures. After curing, the screws can be torqued, the rings mounted, and the shims could be removed if you so desire.
Greg
The shims only establish the height and hold the alignment while the glass or epoxy bedding compound hardens. The entire contact area beneath the base gets coated/filled with the resin, so the entire base is supported by the cured resin, and not by the shims. Wipe off any excess oozage with a paper towel, and regular nail polish remover will clean up any residue as long as you get it before it cures. During the hardening, the base screws should only be snugged up firm, but not torqued, this ensures there will be no stress on the base/receiver once the bedding cures. After curing, the screws can be torqued, the rings mounted, and the shims could be removed if you so desire.
Greg
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