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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/15/2008 at 17:40
Harriershot View Drop Down
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Today I was bedding two Burris  signature bases the traditional way. I would start with two layers of Kiwi neutral shoe polish on the top of the receiver, I would then lay a piece of sandpaper over the top of the receiver where the base would go and lap the base a little to scuff the bottom side of the base to get the Devcon 10110 to bond real good. I then would get the action level, apply some Devcon to the underside of the base and bolt down to about 50% of normal tightness all the while I will check with a level and make sure the base is going on level to the receiver (so as not to squeeze all the Devcon out from under the base) and let cure for 24 hours. I would then remove bases, take a dremel tool and remove excess Devcon from the bolt and dovetail holes.

Then it struck me, Why don't I just take the lapping the base on the top of the receiver a step further and just lap it until all the black finish is removed from the underside of the base. I would then do my contact check, this is done by wiping a very thin layer of white teflon grease on top of the receiver and bolting the base in place, then crefully remove the base without sliding it around and check to see if the base made 100% percent contact with the thin layer of grease.
It would seem to me a metal to metal full contact via lapping like I have described would make for a better contact than messing around with the Devcon.
 
What do you guys think?
 
Charlie 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/15/2008 at 20:33
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You have good mechanical aptitude.

Although "glass" bedding produces absolutely perfectly mated surfaces, the overall effect of thoroughly lapping the bases should produce an effect that, in a practical sense, is as good. Also, there would be nothing to chip or crack under recoil. Of course, the surface of the receiver would have to be almost perfectly consistant in order for it to work, i.e., neither a cast receiver nor one that has been mis-shapened during the polishing process. In all probability, you would get better results by lapping with the bore line, instead of lapping rotationally or perpendicular to the bore line. But, individual guns will vary. The thing to remember is that inconsistancies/sizing  in the receiver will have just as great an effect as inconsistancies and sizing of the bases. After lapping the bases, I would certainly smear a light coat of paste blue, as used by machinists, on the receiver and then put the base in place. Transfer of the blue is then checked in the same manner as the white grease you are now using. But, paste blue will allow you to smear a much thinner coat and see the results much more easily and accurately. When the results are in doubt, you might wish to then use the bedding compound. Yes, it's more hassle, but the results are flawless I hope this makes sense.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/15/2008 at 20:46
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Dallas, I concede, I took off the front base and removed the Devcon bedding. I tried lapping with a piece of sandpaper between the base and the top of the receiver. After a lot of lapping and removal of finish on the underside of the base I did my white grease transfer test. There was still a lot of non contact area between the base and the receiver. The rear base with it's Devcon showed a 100 percent transfer. Oh well I just put the front base back on with Devcon.
I guess everybody uses Devcon for a good reason.
Nothing ventured, nothing gained.
 
Charlie
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/15/2008 at 23:57
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Your idea was sound. It won't work in most cases, but trying each time can't hurt anything. All it can cost you is a little elbow grease.

You're wise to use the Burris bases. They're excellent. Moreover, the Burris Signature rings can't be beat. You're also wise to use a separate front and rear base instead of a one-piece windage adjustable base.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 02:55
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PerhapsI'm missing something, but I was wondering how this process would provde a centerline to the bore itself. If the screw holes were note square to the boreline, it would seem to defeat the lapping process.
 
Roy
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 07:09
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I agree with Roy.  I personally have never lapped bases.  I always lap horizontally split rings, but rarely use them, preferring vertically split Warne rings.  Talley light weight one piece rings I use occasionally and I lap those, but it does not take long.  A pair of Burris horizontally split Ruger style rings took me 30 minutes to lap to perfection they were so out of round.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 07:34
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If you are using signature rings (plastic inserts) there is no lapping of the rings. I was trying to lap the underside of the bases to get them to match the top of the receiver.
What I like about the two piece bases is that you can use the play in bolt to base space to locate the bases a little to the left or right. In other words when I am using my eye to look down the bore at a target 29 yards away, while I am trying to mount the scope to line up on the target. I will use the Burris inserts in different thickeness's to accomplish elevation changes. I will use the side to side play to accomplish windage adjustments. If the play is not enough I will then use the windage screws in the rear base.
Using the above method the results at the range usually yield a POI within a couple inches of POA.
All this while the scope is still in it's optical center. Typically I only have to use the scope turrets for just a few clicks to get the POI on the bulls eye. All this tells me that if I am getting near perfect alignment on my bore sighted 29 yard target  with the scope, then when I go to the range and am nearly right on target, I believe I am getting a nearly perfect scope to bore alignment.
 
Enjoy
 
Charlie
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 07:42
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Never had a problem with vertically split Warne rings and traditional bore sighting methods.  Only a few clicks of the turrets on quality rifles and I am there, of course with quality scopes.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 08:03
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Wow. I am amazed at some of the things that you technical folks do. Impressive.
 
I just put the blue loctite on the bases, if applicable, and lower ring screws and 'guestimate' tighten the ring screws on top. So far so good. With that said, i really don't mess w/ windage or elevation after sighting it in - and i vice the gun, look through the bore, and get the crosshairs 'close' and then sight it in. 
 
Do i need to be more careful?  I am careful to not overtighten the rings. But other than that, i just do it.
 
J
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 08:16
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That is an impressive bit of - wow, that's something.

As I said recently on another thread, I get no lateral play at all in my Badger bases (Talleys might have a slight but not much.)

I shoot out past 600 yards with great regularity and have never lapped a base and haven't seen a negative effect to not lapping the base.

But, if that gives you confidence in your setup, go for it; confidence is the name of this game.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 16:04
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Perhaps I should have explained my point of view more clearly. When "accuracy gunsmiths" retap base screw holes on a reciever, their intended purpose is to make the base screws align with the centerline of the bore. While this is not often a problem with CNC machining used today, it does happen more often than most would like to believe. No amount of base lapping will make this happen. As I stated, it is not often a problem, but it does occur. For short range work, it would be rarely be noticed. But as the range increases, it becomes more apparent.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 16:20
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Harriershot, one important thing to consider, and most likely the reason why you didn't get full contact with your "lapped" base is because of the fact that when you place a piece of sandpaper over the top of the receiver radius, you are enlarging the radius by the thickness of the sandpaper.  So, let's say your sandpaper is 0.020" thick.  I'm guessing here, but that's probably not too far off.  If your receiver is 1.35" dia/ 0.675" radius (the diameter of a M700 action), then once you get total cleanup on the bottom of your base, it will have approx 0.695" radius minimum, which no longer mates with your receiver.  Plus, it's hard to keep the surface absolutely true, since the sandpaper can vary in thickness and it can have wrinkles on the surface.  True lapping involves using a precisely sized rod about 0.0005" smaller than the radius you want to impart onto the surface and lapping compound.  A true surface is important to precisely controlling the cutting diameter.  In that way, it is much like a very slow grinding process.

Edited by RifleDude - May/16/2008 at 18:11
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 17:50
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Just in addition to what I previously mentioned, I saw this re-grinding of the receiver top by a guy named D'Arcy Echo ls who is an absolute perfectionist for accuracy. After the regrinding process, he mills his own scope bases for absolute perfect alignment with the bore of his rifles. Most gunsmiths would not go to such great lengths. Moreover, most gunsmiths don't command 12 thousand bucks for a synthetic stocked rifle either. Most of his customers are probably better known as trust fund babies if you know what I mean. You know the type, folks who buy Hemi-Cudas for 200 grand. I, for one, don't see that in my immediate future. Us poor saps have to settle for sub-standard rifles like Hill Country Rifles.
Roy
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 18:06
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Originally posted by jonbravado jonbravado wrote:

Wow. I am amazed at some of the things that you technical folks do. Impressive.
 
I just put the blue loctite on the bases, if applicable, and lower ring screws and 'guestimate' tighten the ring screws on top. So far so good. With that said, i really don't mess w/ windage or elevation after sighting it in - and i vice the gun, look through the bore, and get the crosshairs 'close' and then sight it in. 
 
Do i need to be more careful?  I am careful to not overtighten the rings. But other than that, i just do it.
 
J
 
 
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 22:06
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Rifle dude, you make a redneck garage engineer like me feel like a bit of a simpleton. Your mathematic explanation as to why my lapping with sand paper over the top of my receiver did not work is rather impressive. I mean after I did all that lapping to get the bottom of the base shiny I thought for sure that I would have a 100 percent contact. My grease transfer test showed about 20 percent, much to my dismay.
When I was in tenth grade I barely passed an algebra 1 class with a D, this was with tutoring and a lot of extra credit homework. At the end of the semester my teacher told me you will probably never understand this stuff and you will probably never be a rocket scientest so I am going to pass you anyway. Rifle dude, my guess is you probably aced trigonometry.
Thanks for the explanation and I will stick with the Devcon.
 
Thanks
Charlie
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/16/2008 at 22:15
Harriershot View Drop Down
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As a followup. I mounted the scope on my A-BOLT with Burris signature rings. With the top of the bases showing level with the action and using 0 inserts in all four places the scope showed dead on elavation with my 29 yard eye down the bore sighted target. The windage was just a few inches to the right. I removed the scope loosened the rear base and pushed it over to right and tightened the base bolts. After reinstalling the scope she was dead on. for both windage and elavation. As soon as I get her to the range I will report back on this thread.
My past experience using this technique has yielded very good results.
 
Charlie 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/17/2008 at 07:05
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Originally posted by RifleDude RifleDude wrote:

Harriershot, one important thing to consider, and most likely the reason why you didn't get full contact with your "lapped" base is because of the fact that when you place a piece of sandpaper over the top of the receiver radius, you are enlarging the radius by the thickness of the sandpaper.  So, let's say your sandpaper is 0.020" thick.  I'm guessing here, but that's probably not too far off.  If your receiver is 1.35" dia/ 0.675" radius (the diameter of a M700 action), then once you get total cleanup on the bottom of your base, it will have approx 0.695" radius minimum, which no longer mates with your receiver.  Plus, it's hard to keep the surface absolutely true, since the sandpaper can vary in thickness and it can have wrinkles on the surface.  True lapping involves using a precisely sized rod about 0.0005" smaller than the radius you want to impart onto the surface and lapping compound.  A true surface is important to precisely controlling the cutting diameter.  In that way, it is much like a very slow grinding process.
 Great explanation of the problems he was getting into.  Truthfully, I was concentrating more on why he was doing it than anything else.
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