HELP! 20 MOA base question

Discussion in 'Long Range Hunting & Shooting' started by C-dub, Dec 10, 2011.

  1. C-dub

    C-dub Member

    Messages:
    10
    Joined:
    Nov 26, 2008
    Hope I'm posting this in the right spot.

    I got in my Rem 700 Milspec (.308 win) this week and wanted to try it out at the range. I put a 20 moa pic rail on it and headed out in the wind today to get her sighted in fairly close.

    Imagine my surprise when I was about 7 moa LOW at 100 yds. I was running Fed GMM (waiting on my dies) with 168 SMK. I zeroed it in relatively close, shot a 3 shot group and then called it a day to conserve ammo. I still have a lot to do to her yet (Timney, LOP increase, different rings, etc.).

    Anyway, I got back home and pulled the base to measure the difference front to rear and came up with .080". I then leveled across the front of the receiver and measured down to the rear and got, yep, .080" giving me a 'flat' base!

    This is my first experience with a canted base. Am I missing something here or was the base mispackaged at the factory? Shouldn't it be about .050" taller in the rear after mounting? Let me know your suggestions.

    I asked this on another forum but figured I might get better/faster info here. Thanks for your help.

    Chris
     
  2. AJ Peacock

    AJ Peacock Well-Known Member

    Messages:
    2,229
    Joined:
    Oct 7, 2005
    Where was you scope set, as far as elevation, was it near center or did you have to spin it up. If so, could you have had it installed backwards?

    AJ
     

  3. gcollins

    gcollins Well-Known Member

    Messages:
    51
    Joined:
    Sep 17, 2011
    Hi Chris,
    You are correct!! I am not quialified to be posting on this! But common sense tells you that the whole reason for a canted base is to give yourself more elevation gain that your scope might of run out before you got dialed in on the spot!
    I hope that I have not sterred you wrong. Just my 2 cents worth!
    Greg
     
  4. C-dub

    C-dub Member

    Messages:
    10
    Joined:
    Nov 26, 2008
    AJ,

    The scope was new from the factory (SWFA SS 10x42). I didn't spin to both extremes to ensure it was at the center of it's travel but according to the hash marks on the turret, it should have been centered.

    There's no way to install it backwards (first thing I checked when I put it on!:)) so that can't be it.

    Thanks for suggestions though.

    Chris
     
  5. AJ Peacock

    AJ Peacock Well-Known Member

    Messages:
    2,229
    Joined:
    Oct 7, 2005
    You need to see where the scope is in relation to it's travel when the base is installed. If it is near the center at your expected range, then you are good to go. With a 20moa base at 100yds, it will probably be nearer the bottom of travel.

    AJ
     
  6. Jm32526

    Jm32526 New Member

    Messages:
    2
    Joined:
    Dec 10, 2011
    I am currently building a rifle right now and I put a 20 moa base and I could clearly see the difference between the front and rear of the base. My guess is your base was mislabeled.
     
  7. WildRose

    WildRose Well-Known Member

    Messages:
    8,210
    Joined:
    Feb 3, 2011
    What was on it prior?

    Did you change rings as well?

    What base did you put on it?

    What scope have you got?

    Changing the height of the scope (Raising it) relative to the center line of the bore will make the rifle shoot considerably low at 100yds and will make an even bigger difference at 25yds.
     
  8. C-dub

    C-dub Member

    Messages:
    10
    Joined:
    Nov 26, 2008
    Wildrose,

    There was no scope previously on the rifle. I put a Weaver Picatinny 20 moa extended rail base on it with Warne Maxima low rings. The scope is a SWFA SS 10x42.

    On looking at the base it does have noticeable slant to it, BUT there is a .080" difference in height between the front and rear receiver on the rifle (from what I could measure). This 'uses up' any cant the base has rendering it 'flat' for all intents and purposes.

    Looking at Talley's website, they give ring dimensions differing by .110" for 700 SA rifles, again, showing the difference between the receiver mating surfaces.

    Perhaps I need to contact SWFA, or better, go right to Weaver and seek advice.

    Thanks for the replies, guys.
     
  9. joseph

    joseph Well-Known Member

    Messages:
    1,238
    Joined:
    Jul 26, 2009
    I have used EGW. Two 20 MOA and a 40 MOA and now they are making a 20 MOA rail for my Browning BAR. Every one has fit perfectly. You can get steel or aluminum.

    When you open their web site click on the picture and you can see the base has two different thicknesses. I do not see where they say 20 MOA Pica tinny Rail, but If you call them they will tell you over the phone what MOA they offer for your rifle. They say out of stock, but they are getting a shipment in a couple of weeks I think.

    Steel HD Remington 700 Short Action Picatinny Rail Scope Mount: Evolution Gun Works Inc.

    This is one of mine with an aluminum 20 MOA EGW rail:

    Vortex Viper PST mounted with pics. - Georgia Outdoor News Forum

    joseph
     
  10. rscott5028

    rscott5028 Well-Known Member

    Messages:
    2,608
    Joined:
    Apr 18, 2010
    I suspect your method of measuring height difference of your reciever from front to rear relative to the centerline of the bore is flawed.

    Do as suggested and make note of your elevation turret setting for your zero. Then, run it all the way up and down. You will likely be about 20MOA closer to one than the other.

    -- richard
     
  11. C-dub

    C-dub Member

    Messages:
    10
    Joined:
    Nov 26, 2008
    Thanks for the suggestions guys.

    I found on Snipercentral where someone had the drawings for the Rem 700 receiver. He said the difference between the front and rear of the receiver is .114" That correlates well with the Talley info. Obviously, I didn't measure precisely enough.

    Here's the thing, that only exacerbates my problem. Interestingly enough, when I measure the diff in the base (.083"-.085") and subtract it from the receiver diff I end up with about .030" which subtends to very close to 20 MOA; HOWEVER, it's the wrong way! The base cants up!

    Arrgh! Anyway, I ordered a EGW (which is shorter anyway) and am going to return the Weaver. I did email Weaver but haven't heard back yet.

    We'll see how the new base works out-if I screwed up or had the wrong base.

    Thanks again for the help.

    Chris
     
  12. WildRose

    WildRose Well-Known Member

    Messages:
    8,210
    Joined:
    Feb 3, 2011
    My suggestion would be once you have the new base, just put everything together and snug it up then see where you are.

    If that then doesn't solve everything give the guys at SWFA a call and tell them your issues.

    They not only sell this stuff but they are all former soldiers and operators and use it as well.

    If it does however work then take it all apart and mount it back permanently with bedding and locktite.
     
  13. Sully2

    Sully2 Well-Known Member

    Messages:
    2,480
    Joined:
    Feb 28, 2011
    There is NO WAY Id ever "perm mount" a scope or rings or ?? to the top of a rifle receiver. Think of the poor SOB down the line that might own that weapon....no way.

    Clean the top of the rifle and the underside of the rail with acetone. Use Q-tips and acetone to get down in the screw holes. Clean the screws with acetone. Install and TORQUE the screws down TIGHT. Its not going anywhere!!
     
  14. Broz

    Broz Well-Known Member

    Messages:
    8,637
    Joined:
    Feb 3, 2007

    It is a "have to" is many cases. Not a choice. The tops of many actions are simply not true. Especially some runs of the 700 Rems. They will vary from rifle to rifle by as much at .010" So bedding the rail base to the action is the only way to keep the top of the rail true. If you do not bed it, it will flex as you tighten it and the rings will no longer be in plane. This will transer into you scope tube and bad things WILL happen. I have also found that this is also magnified by some of the cheaper rails being off on the reciever side as well. To remove a beded / epoxied on base is not that hard. A little heat will do the trick. If it is a fine rifle and there is worry of bluing damage under where the base sits , simply coat the reciver side with a release agent and snug it down and clean excess epoxy up. The next day remove it, clean the release agent and torque the base into place. This will now have a prefect interference fit and the top of the rail will be true and flat. I do every one with epoxy and I use high quality bases now too.

    Jeff