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Rifle Scopes Only 8 Mils of adjustment after 100 yd zero

nic_bravo_whiskey

nic_bravo_whiskey

Sergeant
Full Member
Minuteman
Nov 30, 2008
554
6
El Paso, Texas
I zeroed my rifle last week at 100 yards. After setting the zero stop, I checked to see how much adjustment I had, and it's only 8 Mils. Rifle is a 10fp, base is a 20 MOA TPS base with low TPS rings. Scope is a PST 6-24x50 sfp. I did have to bed the base on the front side. The last base I had on this rifle needed to be bedded, and it wasn't. I bought the rifle like that. It was a zero MOA base, and it screwed up my IOR scope that was mounted to it.

Here is a pic of the bedding job that I did, and I'm wondering if this could be the cause of the problem.

ScopeBaseBedding.jpg
 
You bedded the front and not the back...

I think the fact that 2 bases with two scopes had issues, points to one thing... operator error.

How does a 0 MOA base "screw a scope up" ... it's a solid piece of metal, it can't screw a scope up.
 
Lowlight said:
You bedded the front and not the back...

I think the fact that 2 bases with two scopes had issues, points to one thing... operator error.

How does a 0 MOA base "screw a scope up" ... it's a solid piece of metal, it can't screw a scope up.
Click to expand...

When I tighten the two screws on the rear of the base, there is a gap between the action and the bottom of base at the front. That's where the bedding comes into play. Without the bedding, when the two screws at the front of the base are tightened, the base bends down, towards the action. This misaligns the rings, and that's what damaged my scope. I had to lap those rings to get everything to line up correctly.

The back didn't need to be bedded. When I tightened the screws on the front of the base (and not the back), there was no gap between the base and action at the rear.

I don't even know why someone would bed the front and back of the base? That doesn't make any sense to me?
 
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DFOOSKING said:
And is only 8 mils a bad thing?

That's roughly 850yds for a 175smk/308Rem.

A 260 could practically go to 1K.

Not sure if you should have bedded the front of the base so heavily. You may have removed the cant it provides.
Click to expand...

Yeah, I know. Just seems that there should be more adjustment with a 20 MOA base. I think I may have removed some of the cant as you mentioned with the bedding.
 
If you say so, I wasn't there, but figure 14 thousands of an inch at the action is roughly 20" at 100 yards. So what do you think happened.

You removed your cant, so you have a 0 MOA base again.
 
Lowlight said:
If you say so, I wasn't there, but figure 14 thousands of an inch at the action is roughly 20" at 100 yards. So what do you think happened.

You removed your cant, so you have a 0 MOA base again.
Click to expand...

I guess so. But, if I did remove the cant from the base, then that would mean that it is bent in the opposite direction? Or this Savage action is so fucked from front to rear that no base will be accurate on it? I don't know. 8 mils is not so bad, I would be upset with any less.
 
roggom said:
Your supposed to bed the rear of the rail not the front. The bedding material takes up any slop between the receiver and the rail.

Remove the bedding and watch John's video.




"Budget Precision" Pt.1 - Remington 700 Scope Base Installation - YouTube
Click to expand...

Not too sure how you gathered that from that video, but you should be absolutely sure that what you are saying is fact when posting suggestions. That particular rifle needed the rear bedded. That does not mean that all rifles need the rear bedded.

You should watch that video over again, then you hopefully will realize what exactly the bedding is supposed to accomplish and why it needs to be done in some cases.
 
Ok, first off, you're certain this base isn't for a flat rear savage? If the base is correct, the whole purpose of bedding a base is to keep it stress-free on the receiver. In order to be stress free, the front AND rear need to be perfectly in harmony...meaning bed both. If the rear meets up perfectly, then almost all the bedding material will squeeze out when you torque it down. Refer to the search function for proper base torquing technique.

Next, what is your total mil adjustment in the optic? Not what the manufacturer says, how many TOTAL elevation mils do you have to work with?

It is certainly in the realm of possible that you have a misaligned receiver, as Frank said earlier: 0.014" difference can equate to roughly 20" (~5.5mils) @ 100 yards. Lay a flat-edged ruler on your receiver...that would answer that question quick whether the receiver or base is off.
 
On the vortex website, the PST claims 19 mils total elevation. 19/2=9.5 mils for a 0 degree flat base. 9.5mils-1.2mils of drop for a 100 yard zero= 8.3mils of theoretic "UP" mils elevation remaining. Either your scope doesn't have a full 19 mils total travel, your base has imperfection or is a flat base, your rings a not aligned/imperfect, your receiver is untrue...or there is some other strange anomoly.
 
smokebomb said:
Ok, first off, you're certain this base isn't for a flat rear savage? If the base is correct, the whole purpose of bedding a base is to keep it stress-free on the receiver. In order to be stress free, the front AND rear need to be perfectly in harmony...meaning bed both. If the rear meets up perfectly, then almost all the bedding material will squeeze out when you torque it down. Refer to the search function for proper base torquing technique.

Next, what is your total mil adjustment in the optic? Not what the manufacturer says, how many TOTAL elevation mils do you have to work with?

It is certainly in the realm of possible that you have a misaligned receiver, as Frank said earlier: 0.014" difference can equate to roughly 20" (~5.5mils) @ 100 yards. Lay a flat-edged ruler on your receiver...that would answer that question quick whether the receiver or base is off.
Click to expand...

The base I have is the correct base. As far as bedding the rear, since it sits flat on the rear of the action, bedding it will pretty much do nothing. The rear screws are too close together. I don't see that having any impact on what I'm experiencing here.

I did mention that the receiver is most likely misaligned, and I do think that could be a problem.

8 Mils is not bad to work with, that's around 27.5 MOA. But I did use all of the shims for the zero stop. I was not expecting that with a 20 MOA base.
 
smokebomb said:
On the vortex website, the PST claims 19 mils total elevation. 19/2=9.5 mils for a 0 degree flat base. 9.5mils-1.2mils of drop for a 100 yard zero= 8.3mils of theoretic "UP" mils elevation remaining. Either your scope doesn't have a full 19 mils total travel, your base has imperfection or is a flat base, your rings a not aligned/imperfect, your receiver is untrue...or there is some other strange anomoly.
Click to expand...

And with the 20 MOA base, -5.8 mils? So I should have close to 13 mils of adjustment?
 
Yep, in a perfect world around 13.8ish mils of "up" with a 20moa base.

If you're ok with 8 mils "up" then you're good to go! You should be solid out to 750+ yards, and you have a reticle to work off also!
 
nicholas306 said:
Not too sure how you gathered that from that video, but you should be absolutely sure that what you are saying is fact when posting suggestions. That particular rifle needed the rear bedded. That does not mean that all rifles need the rear bedded.

You should watch that video over again, then you hopefully will realize what exactly the bedding is supposed to accomplish and why it needs to be done in some cases.
Click to expand...


I know what bedding is supposed to do, I am guilty of not reading the entire thread before I posted. If the front of the rail is indeed lower than than the rear, the bedding material took up the space, but of course took all but maybe a few moa of cant out of your rail. Probably would have been worse with a zero moa rail. Guess your stuck with the 8 mils or try a 30 in hopes of ending up with 10-15 after its bedded.
 
smokebomb said:
Yep, in a perfect world around 13.8ish mils of "up" with a 20moa base.

If you're ok with 8 mils "up" then you're good to go! You should be solid out to 750+ yards, and you have a reticle to work off also!
Click to expand...

Yeah, that's probably the way it's going to be unless I decide to go with a 30 MOA cant.
 
Nicholas you need to remove the bedding from the front, yes the front, and bed the rear, then this is a biggie, LAP the rings, by doing this the rings will be in perfect alignment, ensuring no damage to your scope, and you will have all the adjustment needed from a 100 yard zero.
 
Anyone who suggests that he can remove the rail and the bedding and then simply bed the rear instead of the front has a poor grasp of geometry.

With the mismatch I am seeing between the offset heights of the rail vs. the corresponding surfaces on the receiver, the only way I can see to mount that rail on that receiver and retain cant is to bed the front and the rear.

If that rail is straight, then letting it balance naturally on the receiver will have it touching the top of the receiver at the very front of the rail, with a wedge shaped gap opening up behind the point of contact, and touching again where the ejection port ends where another wedge shaped gap appears.

Bed the entire rail, filling those gaps with wedge shaped areas of bedding material.

You may end up with too much cant, though.

It would be good to know whether the rail or the receiver is machined wrong, too.

Joe
 
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scudzuki said:
Anyone who suggests that he can remove the rail and the bedding and then simply bed the rear instead of the front has a poor grasp of geometry.

With the mismatch I am seeing between the offset heights of the rail vs. the corresponding surfaces on the receiver, the only way I can see to mount that rail on that receiver and retain cant is to bed the front and the rear.

If that rail is straight, then letting it balance naturally on the receiver will have it touching the top of the receiver at the very front of the rail, with a wedge shaped gap opening up behind the point of contact, and touching again where the ejection port ends where another wedge shaped gap appears.

Bed the entire rail, filling those gaps with wedge shaped areas of bedding material.

You may end up with too much cant, though.

It would be good to know whether the rail or the receiver is machined wrong, too.

Joe
Click to expand...

That's actually a good idea. I could end up with too much cant like you said. And that JB Weld is going to be a bitch to get off.

I'm sure it's the receiver that's misaligned.
 
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427Cobra said:
Nicholas you need to remove the bedding from the front, yes the front, and bed the rear, then this is a biggie, LAP the rings, by doing this the rings will be in perfect alignment, ensuring no damage to your scope, and you will have all the adjustment needed from a 100 yard zero.
Click to expand...

I don't like the idea of lapping the rings. I would rather live with the 8 mils of adjustment.
 
nicholas306 said:
Exactly. I just don't know how much I should bed the rear, it would be a guess. I'm sure it's the receiver that's misaligned.
Click to expand...

Bedding is just filling a gap that occurs between misaligned surfaces. You don't have to know, the parts will tell you, just follow my procedure.

This assumes that you've chipped off the bedding material you've already added, of course.

Ensure that the rail is straight, first.
Ideally you would need a surface plate but if you have a granite countertop available that should do; the machines they surface them on tend to make them pretty flat.
Make sure the rail is completely flat, no ripple, bend, twist, etc.

These days if you use a straight rail and quality (unaltered) rings, lapping is unnecessary.

If the rail is found to be straight, apply bedding material to both mounting surfaces of the rail, install all 4 screws a few turns just to get the holes aligned, and finger tighten 2 of the screws just enough to squeeze excess bedding material out, the first screw (starting at the front of the rail) and the 3rd screw. Do not tighten these screws; you do not want to bend the rail at all, you just want the rail touching the receiver at 2 spots, one at the front, the other right at the end of the ejection port (the front of the 2nd mounting pad of the rail). The bedding material should harden to form 2 little wedge shaped pedestals that completely support the rail.

Joe
 
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While I dont have quite the same setup, I have the same scope on a Rem 700 308 with 20 MOA base(that required ZERO bedding to the action). When zero'd at 100 with 175g FGMM I have 11 mils up left in the scope(might be 11.3 or something). So if his base ended up at zero MOA or even with a + angle due to something being out of whack, 8 mil sounds plausible. Im not great with the mil's to MOA relationship, but what is 3 mils to MOA?
 
Captain Kirk said:
3.44 moa = 1 mil
Click to expand...

So potentially, he has lost 10 MOA of cant on his 20 MOA base, again using my setup as a reference point(which isnt a great comparison, but I have the same scope). I know there are a ton of other factors to consider too.

Since I have about 11 MIL up from my 100 yard zero with 175g FGMM(I dont know what he zero'd with) on a 20 MOA base and he only has 8 then 3 MIL*3.44=10.32 MOA that he is losing in his base with the bedding job/bent something/out of spec who knows what...

Again my numbers are WAG's at best since our setups are not 100% identical.
 
Savage put out a batch of actions a while back that were seriously misaligned front-to-rear. If yours is one of them, ship it back and I'm sure they'll make it right.

I have a 10FP action that with a 260 barrel pushing 130gr Bergers @ 3000fps only had 7.0mil from a 100yd zero, with Bushnell Elite Tactical 4200 6-24x50 optic in Burris XTR low rings on a Weaver 20MOA base.

My simple, easy solution was an EGW 25MOA base.

I now have a different optic (Vortex HST 4-16x44) and the barrel action/base/ring combo is good for something like (IIRC) 12 mils up from a 100yd zero with 140gr HPBT @ 2810fps.
 
scudzuki said:
Bedding is just filling a gap that occurs between misaligned surfaces. You don't have to know, the parts will tell you, just follow my procedure.

This assumes that you've chipped off the bedding material you've already added, of course.

Ensure that the rail is straight, first.
Ideally you would need a surface plate but if you have a granite countertop available that should do; the machines they surface them on tend to make them pretty flat.
Make sure the rail is completely flat, no ripple, bend, twist, etc.

These days if you use a straight rail and quality (unaltered) rings, lapping is unnecessary.

If the rail is found to be straight, apply bedding material to both mounting surfaces of the rail, install all 4 screws a few turns just to get the holes aligned, and finger tighten 2 of the screws just enough to squeeze excess bedding material out, the first screw (starting at the front of the rail) and the 3rd screw. Do not tighten these screws; you do not want to bend the rail at all, you just want the rail touching the receiver at 2 spots, one at the front, the other right at the end of the ejection port (the front of the 2nd mounting pad of the rail). The bedding material should harden to form 2 little wedge shaped pedestals that completely support the rail.

Joe
Click to expand...

I just might end up doing this. I'll probably end up with more than 20 MOA. Should I used longer screws than what originally came with the base just to make the job easier? Then discard them and use the original screws after the bedding job is done. Also, how does JB Weld release from threads when using Kiwi as a release agent? I didn't use any screws on the bedded side before.
 
Last edited:
If you tighten the rear screws first and there is a large gap at the front, but if you tighten the front screws first, there is not gap at the rear. If this is the case, when you tighten the front screws, you are probably bending the mount,

What it means is that the front and rear action area are on different planes or different angles. If you tighten the rear screws, the mount cantilevers off the rear action area and hangs in space. If you tighten the fronts, you bend the mount down. The center of the mount will be high.

If you tighten the fronts first, the mount is jammed down on the rear action area, bending the mount, but in this case, the middle of the mount will be lower than the ends.

You need to lap the mount to the action. Wrap a piece of sandpaper around the action, front and rear, with the grit out, then slide the mount against the sandpaper to adjust the mount to the action.
 
I think Lowlight hit the nail on the head. I just went through this exact same exercise when I had only 3.7 mils after zero on a 20 moa base. Well it turned out the part number on the base indicates 0 moa (I ordered 20moa and got 0 moa. Never noticed till now). Before realizing this I decided to bed my base to reach a mechanical zero at 100 yard zero. Calculating what can't I needed from my current zero ended up about 22 thousandths (looks about like the OP bed thickness). This came to 18.9 moa achieved. So I agree if the front has been bedded the cant is like removed. It doesn't take much; only a matter of thousandths to reach 20 moa.
I would just re-bed to compensate for ant imperfections in base/action fit to achieve the cant desired. Not a first choice but for me it was better than buying a $100 dollar base that may/likely need bedding anyway. Hope this helps. I know I was very frustrated until I figured out my issue.
 
nicholas306 said:
I like the idea of bedding the base better.
Click to expand...

In this case, there is a MAJOR mismatch between front and rear mounting areas. Bedding the rear only, will likely end up with a bent mount. Bedding the front has already shown to be a not good thing.

And even if he has a 0 MOA base, changing to the proper 20 MOA base will NOT fix the error in the receiver.

First drawing is what happens when you tighten the rear screws first, as he did already. LOTS of space at the front for bedding.

Second drawing is what happens when you tighten the front screws first. As the OP stated, no bedding at the rear. But I am saying it is likely that the mount is not straight in this condition.
 

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I believe pinecone is partly correct. If you bed it as he has described you will/can end up with a bent/stressed base. However, if you elevate the rear and bed with the front stress free (no torque on front screws just alinment) then go back a bed the front using the rear to set the previous cant you can bed with an angle stress free to the rail. This gives you whatever elevation you desire and a "unbent" or stress free base. I just did it this past week. Worked fine. Good luck.
 
Pinecone said:
In this case, there is a MAJOR mismatch between front and rear mounting areas. Bedding the rear only, will likely end up with a bent mount. Bedding the front has already shown to be a not good thing.

And even if he has a 0 MOA base, changing to the proper 20 MOA base will NOT fix the error in the receiver.

First drawing is what happens when you tighten the rear screws first, as he did already. LOTS of space at the front for bedding.

Second drawing is what happens when you tighten the front screws first. As the OP stated, no bedding at the rear. But I am saying it is likely that the mount is not straight in this condition.
Click to expand...

This is exactly what's going on.

As stated above, I need to remove the bedding at the front. I need bed both front and rear of base. If done correctly, the bedding will be a wedge shape at the front and the rear. This will relieve stress, and then all four screws can be tightened. I'll probably end up with more than 20 MOA when it's all done.
 
I say go for it! I got 4.1 mils (~14 moa) from a 22 thousands rear lift on a 3.5 in ring spacing. I should have gone around 40 thousandths, but played it conservative as I had never performed the calculation a measure the result before. I'll know neat time. I still need about 4 mils to be where I want.
 
Again. I would lap the base to the receiver BEFORE bedding.

It doesn't have to be perfectly lapped, but at least get it close.
 
Pinecone said:
Again. I would lap the base to the receiver BEFORE bedding.

It doesn't have to be perfectly lapped, but at least get it close.
Click to expand...

Really? Why? The bedding will take up all of the space between the base and the receiver.

I do not like lapping because the base and/or rings are worthless on any other rifle. Bedding can be removed.
 
nicholas306 said:
I need to remove the bedding at the front. I need bed both front and rear of base. If done correctly, the bedding will be a wedge shape at the front and the rear. This will relieve stress, and then all four screws can be tightened. I'll probably end up with more than 20 MOA when it's all done.
Click to expand...

I think you need just what you mentioned above! Wouln't lap base nor action either.
You'll see what cant exactly will you achieve.
 
If I needed more than the 8 mils, in this situation, I'd remove material on the bottom rear of the base until I had clearance and bed the back.
Or, remove bedding in the front and bed back and front with the screws just barely touching the base as stated above. Either will work.

Trilogymac
 
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nicholas306 said:
Really? Why? The bedding will take up all of the space between the base and the receiver.

I do not like lapping because the base and/or rings are worthless on any other rifle. Bedding can be removed.
Click to expand...

Because the angles are so screwed up.

You can relap them to another rifle it needed.
 
nicholas306 said:
The base I have is the correct base. As far as bedding the rear, since it sits flat on the rear of the action, bedding it will pretty much do nothing. The rear screws are too close together. I don't see that having any impact on what I'm experiencing here.

I did mention that the receiver is most likely misaligned, and I do think that could be a problem.

8 Mils is not bad to work with, that's around 27.5 MOA. But I did use all of the shims for the zero stop. I was not expecting that with a 20 MOA base.
Click to expand...

Can you take a picture of the back of the action and base then post it up?
 
nicholas306 said:
I can't do that, there is no gap between the rear of the base and action. I would be guessing at the correct distance if I did so.
Click to expand...

Correct nicholas. Pyro don't bed the rear just for the sake of bedding the rear.
 
I think you said there could be a problem with the receiver. If that is the case, why wouldn't you pursue that first instead of some cobble job on the base? That would have been my first option. If I missed it and you determined it not to be the receiver then disregard my comment. Good luck
 
MagnumSecurity said:
I think you said there could be a problem with the receiver. If that is the case, why wouldn't you pursue that first instead of some cobble job on the base? That would have been my first option. If I missed it and you determined it not to be the receiver then disregard my comment. Good luck
Click to expand...

I'm not to sure how I would correct the issue with the reciever. It's made like that, nothing I can do about that.
 
Pinecone said:
If you tighten the rear screws first and there is a large gap at the front, but if you tighten the front screws first, there is not gap at the rear. If this is the case, when you tighten the front screws, you are probably bending the mount,

What it means is that the front and rear action area are on different planes or different angles. If you tighten the rear screws, the mount cantilevers off the rear action area and hangs in space. If you tighten the fronts, you bend the mount down. The center of the mount will be high.

If you tighten the fronts first, the mount is jammed down on the rear action area, bending the mount, but in this case, the middle of the mount will be lower than the ends.

You need to lap the mount to the action. Wrap a piece of sandpaper around the action, front and rear, with the grit out, then slide the mount against the sandpaper to adjust the mount to the action.
Click to expand...

Or he needs to bed the rail at both ends as I suggested above.

Ideally, Savage should make it right, but I'm not sure how long the OP wants to wait. I'd be happy to see manufacturers being held accountable for the products they sell, but I'm several months now waiting for FNH to make my FNAR right, which they decided to replace... but that's all they've done is decide. So when I get it back (and if the OP returns his to Savage) we're both going to have to pay transfer fees to an FFL for the replacement rifles, in my case, for a rifle I'm pretty much over.

Joe
 
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scudzuki said:
Or he needs to bed the rail at both ends as I suggested above.

Ideally, Savage should make it right, but I'm not sure how long the OP wants to wait. I'd be happy to see manufacturers being held accountable for the products they sell, but I'm several months now waiting for FNH to make my FNAR right, which they decided to replace... but that's all they've done is decide. So when I get it back (and if the OP returns his to Savage) we're both going to have to pay transfer fees to an FFL for the replacement rifles, in my case, for a rifle I'm pretty much over.

Joe
Click to expand...

I'm not going to send it back. I just want to shoot. I'm going to build a 700 soon. This is my learn what the fuck I'm doing in long range shooting rifle.

I'm just going to bed both front and rear. I tried to start last night, but I broke both torx bits that I have trying to remove the base. I torqued them to 25 lb/in. Fucking thing.
 
Anybody ever use scope base shims (Brownells) rather than JB Weld, etc? Looks like shims would be a hell of a lot easier to swap out than JB Weld would be to remove.
 
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