20MOA base question from a noob (update with pic)

I have a Weaver 20Moa Tactical extended base and TPS med rings with a Bushnell 6-24x50 Elite Tactical 4200 30mm Rifle Scope
T6245. I am not able to zero the scope at 100yards it bottoms out. It is on paper at 100 but still shoots high approx. 4-6 inch, is this because of the 20MOA base or is there another problem (i.e. broken scope) . Everything I have read said I should be fine, but it doesn't seam to be the case for me.

Am I right that It cants the scope down

Help is greatly appreciated.

4-6 inches High would not be because of the base.

The scope has 70 moa of adjustment if I am reading it right.American Rifleman review. You have the elevation screwed down or up all the way?

I turn it clock wise wich shows down on the scope

Does that scope have a zero stop ? If so, you may need to "unset" the zero stop.

Funny story, I have a Leupold Mark 4, couldn't get the thing to zero, was shooting feet low at 100 yards, blamed the guy that built the rifle.

Put the rifle / scope away for years. Literally like 10 years.

Years later (after watching Enemy at the Gates and getting all sniper motivated), decided to get the gun fixed, took it to the range to verify / validate the problem, RTFM, and then discovered I wasn't adjusting the elevation correctly.

Rifle / Scope has been a solid performer ever since.

If you have some way to put the rifle in a vise or cleaning stand do so. Pull the bolt and make sure rifle is unloaded. Look through scope and verify the direction the turret is making the cross hair move. You should dial the cross hair to the point of impact. With the rifle unloaded and bolt out set a box up 25 yards away. Look through bore and then through scope adjusting till they are together.
Best guess six inches should be about 1 and 3/4 mil up corrected from what you posted.


The brains will be along to correct me soon.

you have roughly 15MOA from center available to zero minus the offset of the optical axis to the bore axis. Yes, the optic is canted "down" so you are in effect "borrowing" adjustment from dialing POI down and adding it (20moa) to dial elevaton or POI up.
assumptions: 1moa = 1"@100yards
70/2 = 35
35-20=15
Its not unheard of for the sum of variance to require that much adjustment to zero POI @100yards from the optical zero. Make sure the rear ring is seated properly to the picatinney base.

If you can vice the rifle, run the elevation to the extremes in a safe fashion on a 1" grid @100yrds and verify the full vertical adjustment range of 70". This should satisfy the question on if the optic is faulty. My bet is that the issue lies somewhere else.

HTH

I agree. There's something wrong with the rings or their installation. Also, be sure the base is installed correctly with respect to front and rear.

Something is wrong with the install. Maybe just start again and, methodically, re-install each component.

What gun are we talking about here?

vbfg135-Why do you think it's not the base? Some people cannot get a zero with a 20moa base.

Its a remington 700 tactical I reread my post I forgot the part where I did bed the scope base the same way loanewolf did on the Budget Precision Build. I used the same process on mine and it had the same gap in the rear and no gap in the front.

Because it is adjusted all the way down shooting high. If it was all the way up and shooting high
I would say scope . I have seen some shoot low and left that had a back ring miss installed . This is just my best understanding of what the op posted I am not swearing I am right but I am fallible.

Eta spellin

That's what happens. You add a 20moa rail you lose some of your down elevation.

ETA: When you adjust a scope elevation up it moves the reticle down. You adjust it down it move the reticle up.

OP how much windage did you use to zero? It could definitely be the base. The scope should have enough elevation to use the 20 MOA base but if during zeroing you used alot of windage due to the bore and base screws not being true to each other, then you might not have enough down elevation to get your 100 yard zero.

Also can be that the scope doesn't have the advertised elevation which happens. Now that you are at bottom turn the knobs and let us know how much up elevation you have.

If your Bushnell 4200 has the green lettering on the Turrets it is not a 70 MOA scope.. The Green lettered was the earlier version which if memory serves they are around 48 MOA of elevation adjustment..The newer version has white lettering and is a 70 MOA ..

Rick

I understand that the 20 moa base changes angle of the of center line of the scope down. I do not understand how you loose anything other than travel above or below the center of scope. In a sense giving you more moa or mill to shoot out father than straight bases.

It does give you more for shooting farther. If the scope has 50moa total. You would end up with 5moa down and 45 up. So it can make zeroing at 100yds hard for some scopes. But chances of zeroing in mechanical zero is near impossible. You will have to move windage which will take from your total adjustment.

It does not take much variance off the receiver to equal 20 moa at target. Consider 0moa bases compared to 20moa, the difference in the base is not obvious to the eye.

1moa = 1.047" @ 100yards
(12" per foot x 3ft per yard) x 100yrds = 3600" @ 100 yards
1.047"/3600" = .00029" per 1"
considering a 6" long, 20moa base that is ~.04 in difference from one end to the other in height off the bore axis.

I hope I math'ed that correctly. I never considered it before.

I thought I was good guess I have just been lucky.I will have to lurk back and study more.I put a twenty on a 700 308 with a WOTAC and was dead on no issues. I have Nightforces on a 700 and a REPR both have 20s as well.No issues zeroing.My Brother has two 3200 R700/H1500 they have 75 moa and run out just fine on 20 moa bases. Guess I need to find one that does not and play with it.

My Nightforce zeroed just fine and had a lot more down elevation to go. If you want to find a scope that won't zero at 100yds with a 20moa rail just buy one of the cheap $100 tactical scopes.

Well if I did it right it looks like about 48 moa from bottom to the top the clicks are .25 this must be an older model.

Check your windage. From where it's at now how much do you have left then go back to zero then how much do you have right?

about 20 clock wise and 25 counter clock wise

That's pretty close to center. I'd still say the base is the reason you can't get a 100yd zero.

I am with you on that one I have a new one ordered I'll report back when it comes in.

Did you order another 20moa base?

Rick for the WIN!

You could also use Burris Signature Zee rings to dial in extra/reduced cant.

New scope or new base?

I think he ordered a new base. But it's not going to fix his problem.

depends on if he ordered another 20MOA (no help) or a 0MOA base (should work fine). If he ordered the newer model of the same scope he should be ok with the 20 moa base, but he'll have to try it to find out.

No after finding out it only has 48 MOA from bottom to top I am trying 0 MOA base it cheaper than a new scope. If it works I get trigger time on this scope and save up the money and up grade the scope later down the road.

You said at 100yds it was shooting 4-6" high. Why not try a 10moa rail?

sorry i just saw this.
I am who sold you the scope. I had a 15MOA base and only had 4 moa down left in the scope. I think the new base should solve your problem. The turrets should still be "zeroed" from when i sold it to you. how far was it from my "zero" settings when it bottomed out? down 4 (reads 8 since that turret goes to twelve)
When i researched buying that scope originally the biggest complaint was the vertical adjustment was very limited. our difference in zeros may very well be the reason your having trouble. 20 MOA is alot for a scope that only has 48 moa of total adjustment and is low biased. FWIW that scope tracks great and always returned to zero after shooting to 1k several times. I found a sweet spot though B/C at 1k i only had 3 MOA left to top out max (168 gr bthp @ 2690fps).

t_kothmann thanks for the help I should have asked what base you used with it.

You said at 100yds it was shooting 4-6" high. Why not try a 10moa rail?[/qu

I would but at this point since I am a noob i'll run the 0 moa till I get some Experience/trigger time. The range I go to only goes out to 250 yards but I have places that I can go to so I can get out to 500 plus yards. My thinking is if I use the 0moa base I get full range of the turret adjustments to learn on.

If I look at my ballistics calc. ( with my info) There is 20 moa between 1k and 700. Really starts adding up towards the end. You should be fine to 600-750 depending on your load. But a 10 moa base you could probably squeeze out to 800. Im blessed with a 1 k range at my house. Most guys think and talk about 1k but to be honest shooting small 1-2 moa prices of steel at 500 is much more impressive and fun to me.
What caliber/bullet wt/velocity/bbl length are you shooting? I'll throw it in my calc and give you an idea of your expected range.

20 inch barrel 1/12 twist

308 Win. 168grain muzzle Vel. 2650

The gap would suggest you have greater than 20 moa cant in the final set-up.

I was thinking the same thing. RugRat

I agree with the above post but FYI

Thanks guys for all the help. t_kothmann what program is that on your phone?

Isnipe. Alot of people don't like it but I've had a couple and like this one the best. They are all honestly close to each other up to 500. Isnipe let's you save your ammo stats, range characteristics and rifles. Just choose from your saved lists . It also uses your accelarameters for inclination degrees ect. It's tuff to swallow 9 bucks but I bet I have saved more than that in ammo using it.

If you have a specific set of points you want let me know. I'll screen shot a couple of pages for you.
By 168 I'm assuming you meant sierra hpbt. (bc will be a little different)

That is the round I listed the specs for

OP, you might try removing the base and cleaning the bedding from it and the receiver, then install the base with no bedding. That might take care of the problem.

Actually, bed just the front of the base in order to reduce the cant.

I just want to say thanks to everyone who gave me input. I went to the range today with the 0OMA base installed and here is what I did at 100 yards. Now, This is my second time shooting a bolt rifle, the 308 round and out to 100 yards its not perfect but I am happy. I still think It needs fine tuning and me to get more trigger time on this rifle.

Thank you guys

Looks good. Just curious have you looked to see how much down movement you have now?

No but I do see 2 of the lines now where before I could not there are 4 total I could see when i top out the scope I will check later

I have 20 MOA down adjustment left

assuming you have 28 moa left, when you consult the ballistic chart i took for you it looks like you should still be fine well out to 800 yards. 850 is 28.52 moa according to isnipe.

Glad you are back on track.

TK

Interesting. Glad ya figured it out.

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