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bolt lug on mod 700

 
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  #1  
Old 08-22-2008, 08:24 PM
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bolt lug on mod 700

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?
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  #2  
Old 08-23-2008, 01:09 AM
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Re: bolt lug on mod 700

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.
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  #3  
Old 08-23-2008, 02:39 PM
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Re: bolt lug on mod 700

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.
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Last edited by jmason; 08-23-2008 at 08:05 PM. Reason: add info
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  #4  
Old 08-23-2008, 05:07 PM
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Re: bolt lug on mod 700

"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.
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  #5  
Old 08-24-2008, 12:13 AM
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Re: bolt lug on mod 700

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.
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  #6  
Old 08-24-2008, 01:32 AM
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Re: bolt lug on mod 700

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.
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  #7  
Old 08-24-2008, 05:52 AM
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Re: bolt lug on mod 700

So Coyboy, if you and I are doing it wrong, how come the rifles shoot so good?
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