bolt lug on mod 700

Discussion in 'Gunsmithing' started by jmason, Aug 22, 2008.

  1. jmason

    jmason Well-Known Member

    Messages:
    1,527
    Joined:
    Feb 6, 2008
    i wanted to check the bolt lug engagment on my 700 so icleaned the lug recesses and the rear srfaces of the lugs. I then colored threar of my lugs wit a black marker, and chambered a once fired brass and closed the bolt. Then I removed it and found that only 1/3 of one of the lugs is engaged in the recess. I definatly don't have engagment on both sides. This leads me to my question. I'm having a heck of a time working up a load with this gun. Will this cause me to have really poor accuracy, or is this one of those things thet gets you a 1/4 moa tighter gouping after it already shoots ok?
     
  2. NesikaChad

    NesikaChad Well-Known Member

    Messages:
    753
    Joined:
    Jan 28, 2007
    This is a great topic.

    Before you get too excited or worried, lets look at something.

    Think of your rifle with the bolt closed and the striker pulled to the rear. The sear is bearing against the cocking piece and all that spring pressure is trying to drive the striker forward. The bolt has the lugs locked up at the 6 and 12 clock position.

    The cocking piece is roughly at a 45* angle so the forward pressure exerted by the spring is trying to drive the bolt up and away from the sear. So what are your lugs doing? The bottom lug is being mashed against the receiver as the top lug is being pushed away. The amount of distance between the two is determined by how much clearance there is between the bolt body and bore of the receiver.

    You can machine and lap lugs for the rest of your life and never solve this problem.

    Not until you resolve the clearance issue and even then it'll only help so much because you must have some room for the bolt to cycle.

    The only two actions I know of that address this issue specifically and account for it are the ones produced by Jim Borden and Nesika Bay Precision. Even still, there are plenty of other high end actions still shoot just as well without the "Borden Bumps". I am a former production manager for Nesika and I have great affection for the product, so know that it's hard for me to admit that fact. But it is the truth. A hundred sloppy old Remmy's and Win M70's on the firing line at Camp Perry proves it.

    If your having accuracy issues, this would be the last place I'd get too excited over.

    Here's a simple check list for a stubborn rifle.

    1. Hold the thing in your hand at its balance point.
    2. With your free hand, smack the barrel and listen/feel for a nice "ring" that goes away on its own.
    3. What you don't want it doing is sounding like a cracked church bell. That indicates something is touching someplace that it shouldn't. Not very scientific, but it does work. I do it to every rifle I build as part of the QC.

    Next test.

    Make sure your action screws are tight. If it's a Remmy, I wouldn't go past 40inch pounds. Many will raise eyebrows to that and feel its too low a figure. I've done the research side by side with a man who makes a very nice six figure income designing nothing but aerospace fasteners for Boeing. I have the paper and the findings to qualify the statement. (But it's 7000 miles away in SD right now and I'm in Baghdad Iraq)

    Conduct a visual inspection.

    Is the crown damaged?
    Did something happen to the bore as a result of overzealous cleaning rod usage?
    Are the bases tight?
    The rings?
    Are the rings out of alignment and causing a bound up scope?
    Is the scope out of parallax?
    Is the scope serviceable or has something internal gone south?
    Is the magazine box "floating" between the floor metal and the receiver? If you can't reach into the loading port and wiggle it up and down the rifle will never shoot right.
    Are the guard screws binding at all when snugging up the barreled action, floor metal, and stock?

    Is the stock inletted deep enough to where the recoil lug isn't bottoming out, preventing the receiver from fully "nesting" in the stock?

    I'd go over all this before even batting an eye at the lugs not touching. use a dab of clay or even a piece of chewing gum to determine if the lug is bottoming out.

    Assuming everything above is right:

    Go buy some good quality factory loaded ammo. Make sure the bullet weight is matched to the twist rate on the gun.

    This takes your reloading out of the picture. Think of it as a "second opinion".

    Fire some groups. If the result is a nice tight group, then you know that your reloading practices need some revision. If its still a scatter brain, then it's may be time to weigh some more expensive options. (barrel, scope, receiver work, etc. . .) If it shows some improvement, then I think you can tune the gun with careful hand loading.

    Good luck.
     

  3. jmason

    jmason Well-Known Member

    Messages:
    1,527
    Joined:
    Feb 6, 2008
    I'd run through your list and I colored a ounce fired unsized, and a brand new case with sharpie. Chambered both. Both chambered hard. Both have marks above and below the sholder crease on one side of them. Where the case body and sholder meet. At this point I don't think the lugs are the problem anymore.

    Chad, I do want to thank you for your persistance in answering the million threads I've posted. You've responded to damned near every post I've put in this section. I think some are tired of seeing me post. I will admit I can be a bit of a "wolf cryer" sometimes.
     
    Last edited: Aug 23, 2008
  4. Coyboy

    Coyboy Well-Known Member

    Messages:
    2,132
    Joined:
    Jan 30, 2005
    "you can machine and lap lugs the rest of your life and not solve this problem"

    Sorry Chad, not true, The recievers I "blueprint" are lapped in so both lugs contact when sear pressure pushes the back of the bolt up.

    Look at a real old rem reciever that has seen alot of use, You will see where both lugs contact fully due to years of wear-in.

    It can be done relativly easy.
     
  5. NesikaChad

    NesikaChad Well-Known Member

    Messages:
    753
    Joined:
    Jan 28, 2007
    Ok, so you lap them in when its in battery with the cocking piece trying to run over the sear, sooooo what happens when the sear drops and all the tension goes away?

    The same thing that happens when they don't touch while in battery?

    Also, do you machine the bolt face to be square while the gun is in battery too? Or is only the bottom side of it contacting your case head when in battery?


    Look, I'm not smart enough to make this stuff up on my own. I only learned about it after hanging out with some folks that have been doing this longer than I've been alive.

    My only point is I personally don't feel this makes near the difference some claim. That being said I've always done it because I'm smart enough to realize that if I didn't I'd have customers show up at my house with torches and lengths of rope.

    At Nesika, we treated lapping the lugs as more of a "quality control" issue than a performance one. We did it as a means of making sure the surfaces were square. It took longer to clean the stuff out of the action afterward than it did to actually do the job.
     
  6. linksmechanic

    linksmechanic Well-Known Member

    Messages:
    668
    Joined:
    Jan 16, 2007
    boy I hear ya on that one. I worked as a Golf course equipment manager where I bought 3 gallon jugs of lapping compound. I used mostly 80 grit. This was used on every mower everyday for the last 9 years of my life. It takes quite awhile to get the compound out and off of the metal as it imbeds itself.
     
  7. EddieHarren

    EddieHarren Well-Known Member

    Messages:
    1,045
    Joined:
    Nov 27, 2005
    So Coyboy, if you and I are doing it wrong, how come the rifles shoot so good?
     
  8. NesikaChad

    NesikaChad Well-Known Member

    Messages:
    753
    Joined:
    Jan 28, 2007
    Enough.

    I'm not going to get baited into a pissing contest with anyone over something this foolish.

    Never once have I said that my ways are the only way to do anything. Never once have I claimed that my rifles have a magical power to shoot better than anyone else.

    Finally, never did I say anyone was doing anything wrong.

    If I offended anyone, deeply sorry and yada yada. . .
     
  9. Coyboy

    Coyboy Well-Known Member

    Messages:
    2,132
    Joined:
    Jan 30, 2005
    Chad, by no means have you offended anyone. Simply suggesting there are other meathods to achive results. I have come up with this method, I'm sure others use it, and it is not lapping the bolt in with the cocking piece and sear assembled. I'm kinda suprised you seem to be getting a little testy when someone dosn't completely agree with you.

    Now as far as the sear dropping and all the tension goes away. Go dry fire your remi then push down on the rear of the bolt, there is still tension on the bolt pushing it upwards. It's not much but it is there.

    Sooo just as the trigger starts to move the bolt is pushed up, both of my lugs contact.

    Just a nano second after the sear drops the bolt is still being pushed up, both of my lugs contact.

    A nano second after that pressure builds and both of my lugs are still in contact.

    All I'm doing is eliminating a possible vibration induced by the bolt being forced to center in the raceway as the top lug slams into the top lug abutment.

    Now if your still up on your Trig you can figure out how out of square my bolt face will be with the base of my brass cartrige when in battery. Its less than the distance your top lug is going to have to move to contact the lug abutment.
     
  10. Coyboy

    Coyboy Well-Known Member

    Messages:
    2,132
    Joined:
    Jan 30, 2005
    Eddie, must be pure luck, or really good barrels, or one day we decided to look at things a little differently.


    Like any other trade or industry, Ask someone why they do it that way? "because thats how they showed me to do it."
     
  11. specweldtom

    specweldtom Well-Known Member

    Messages:
    1,064
    Joined:
    Jun 7, 2004
    jmason, I have checked the lug engagement on my rifles with blue dye. If they needed it, I lapped them until I got at least 75% engagement on both lugs. Then spent a lot of time cleaning the compound out until I couldn't see any of it anywhere and had no gritty feeling anywhere on the bolt travel or lockup. I honestly don't know if they needed it or not, but it made me feel better about the safety and accuracy of the rifle. Be sure and have the headspace checked if you do lap them.

    Nesikachad said that he does it to satisfy customers and had done it as a quality control measure. This discussion got too complicated for me, but I would definitely be one of those customers who would want it done.

    Good thread, both opinions well stated. Tom
     
  12. James Jones

    James Jones Well-Known Member

    Messages:
    2,854
    Joined:
    Jul 1, 2002
    Just to throw in my two cents and thats about all its worth

    I personaly don't see a benifit in going through the effort in lapping the lugs without squaring the bolt face unless one lug is making no contact at all. I just can't get my head around going through all the effort of making a perfect chamber dead strait with the bore then going through all the bells and wistles doing case prep and loading strait ammo then firing it with a bolt face that not holding it square..
    I have disscussed this at length with a smith who builds and shoots guns that hold world records. When he builds a factory action he simply cleans out the factory threads with a tap , then lightly laps the lugs with 80 grit compound and thats it !!! he laps the lug by applying pressure on the bolt face with the firing pin assembly removed. This smith builds some damn accurate rifles and swears that the accuracy is in the barrel and chamber and that you could set it off with a hammer and as long as the chamber is strait and the barrel is good then it'll be accurate. Again I just can't get my head around doing a job like that and expecting it to shoot as well as possible.

    If I'm the gun plumber doing the job and I'm installing a good barrel I'm gonna make sure that the action is trued to the bolt race way and the bolt lugs (front and back) and the bolt face are true to the bolt body this way everything is making solid contact. Now the only way I can see making both bolt lugs make full contact is to have the bolt body fitting solidly in the rear bridge and the only way to do that is by having a bolt that has full contact top and bottom and this achieved via the "bump" system like Jim Borden is known for and I have never done that so I guess that my rifles are in the group that only has one lug making contact.

    I'm not sure that anybodys way is better than anothers but I feel that as long as all possible varibles are eliminated then the chances of the gun shooting are far better
     
  13. Coyboy

    Coyboy Well-Known Member

    Messages:
    2,132
    Joined:
    Jan 30, 2005
    James, I hear ya, I have some customers who see no need for putting money in trueing an action. Some of those guns flat out shoot. I suspect a good barrel and quality fitting go a long way in and of itself. I have seen mauser shoot amazingly well with no other work then a skim cut on the reciever face, go figure.

    When someone wants a "blueprinted" action and bolt, and after all surfaces are single point recut, I lap the lugs the way I do knowing that when there lapped in that way the bolt is up in the rear and both lugs contact. If there is .003 bolt clearance at the back reciever ring, that means The bolt is pushed up .0015" from it's true center. When you do the trig for a triangle that is roughly 4" long and raised .0015" and then transfer that angle to a bolt face that is aproxiamatly a 1/2" you end up with a bolt face that is out of square by about .0002" (in a perfect world)
    I don't know anyone who is measuring there loaded cartrige runout to the ten thousandths of an inch.

    Now spread that angle out to the tips of the lugs, as if they were lapped in to be square with the center of the bolt raceway. With the bolt pushed up in the rear you now have close to a .0004 gap between the top lug and top lug abutment. AND your bolt face is still out by .0002".

    I'm just lapping out the .0004" gap between the lug and abutment, Hopfully eliminating one more variable.

    Jim
     
    Last edited: Aug 25, 2008
  14. EddieHarren

    EddieHarren Well-Known Member

    Messages:
    1,045
    Joined:
    Nov 27, 2005
    Sometimes I'm overwhelmed by peoples sincerity. Yada yada!