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Borden bumps.

 
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  #1  
Old 01-12-2004, 05:30 PM
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Borden bumps.

I was hoping that someone would be nice enough to give me the long version of what "borden bumps" are.

I read about them on the borden rifles website and on the nesika bay website but all it says is that they are there to reduce up the clearance on the bolt to receiver fit.

I emailed borden rifles and got an equally vague response.

Precisely where on the bolt are they located and how does a .0005" clearance help anything? It is my belief that if it ain't touching then it ain't touching. I always thought that it was contacting surfaces that held rounds tightly in the chamber.

Thanks
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Old 01-12-2004, 07:38 PM
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Re: Borden bumps.

To explain let's back up to your average action like a Rem 700. With a round in the chamber and the bolt closed is the position we are concerned with. Like this the sear spring is pushiing up on the sear which is in contact with the angled surface of the cocking piece. This is forcing the back of the bolt up in the action. Can be as little as 0.001" or as much as 0.007" give or take a little. Reason is the Rem bolt is around 0.690" in diameter, while the raceway in the action is 0.705" roughly. This provides clearance for dirt, etc...
The Borden bumps are on the bolt behind the lugs and I think in front of the handle also. Using the same Rem #s for simplicity, they make the bolt 0.704" in diameter. That way in the locked up position, the sear/CP can't push the bolt out of square with the bore axis more than 0.0005" unlike the standard Remmy bolt being pushed out of square by several thousands. Clear as mud?
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  #3  
Old 01-12-2004, 08:12 PM
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Re: Borden bumps.

Chris Mathews, actually that was very clear, This site has been very helpful for the learning curve.

thank you, John
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Old 01-12-2004, 10:44 PM
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Re: Borden bumps.

Chris thanks for your reply. You hit the nail on the head. I did a google image search for borden bumps and came up with this page- http://www.snipersparadise.com/tsmag/Feb2001.htm

The bigest bummer is that for some reason none of the pictures would open up for me but now I have a better idea what they are and why a "clearance" dimension is important on a bolt lock up.
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Old 01-13-2004, 12:04 AM
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Re: Borden bumps.

If you didn't know, the 700 can be bushed front and rear to accomplish the same thing.
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Old 01-13-2004, 07:56 AM
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Re: Borden bumps.

Last time I spoke with Kevin Jenkins, he installed the bushings on the Rem bolts as well. Thing is, it pushes the price of the Rem action to that of a Nesika. Why not just start with a Nesika or a BAT, or one similar?

It seems that these would make the rifle less reliable under field conditions. For my purposes, I don't see the bushings or Borden bumps making any practical differnce.

For the bench rest crown, this may be very appealing.

FatBoy...
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Old 01-13-2004, 04:56 PM
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Re: Borden bumps.

Chris,
I don't understand the no clearance while woking the bolt statement you made? The bushing takes up extra clearance but still leaves some, and when the bolt is worked the bushings at the rear are actually withdrawn from the bolt bore completely and the original bolt body clearance forward of the bushings has plenty of clearance. I don't like the idea of bushing the front end tho, I think you're just asking for a binding condition just as soon as the bolt is withdrawn far enough that the rear bushings leave the bore. If it were me, I'd build up the rear bolt body with a Tig in several spots and turn it back down to the exact diameter it needed to be. All one really needs is maybe a bump on top and two on the bottom to keep the bolt centered in the cocked and uncocked position both. I haven't asked Dave yet what he'd charge me to put the bumps on, but he agrees it's a better idea than bushings and would take a lot less time.

I agree, I don't like the idea of anything soldered either, soft or siver. Bolt handles included. I like the bumps design that leaves clearance for grit to escape into.

I don't see the need to have damn near zero clearance on the "whole" bolt body itself, except for fast cycling on a bench gun, just the opposite in the field is what I want.

How much "accuracy" is gained by this mod? I've got no idea, but I do think it's slim to none. If the bolt body allows the lugs seat square when sear spring pressure is released and the bolt face is paralell to the lugs, the thrust from the casehead is more than enough to seat the lugs firmly upon firing, thus no out of square caseheads ever develop. JMO at this point.

From what I gather, the BAT and some of the other customs are machined too tight to be 100% reliable in the field, that's the impression I get from people who own them anyway.

When Dave puts this 30-338 Lapua in the stock for me, I'll have him put the bumps on my bolt and find out what he has to charge to do it.
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