View Full Version : Fluted / round ??

Steve Huff
01-15-2008, 08:36 PM
1 of my guns is a round bolt and the other is fluted.

The fluted opens and closes alot smoother than the round.

I assume this is because of friction ??

1 is a bat
1 is a grizzly

01-15-2008, 10:43 PM

A couple things come to mind though... The flutes remove surface area where the bolt would contact the bolt way, and thus reduces friction...

But a bolt that is too loose, bolt body much smaller than bolt way has the chance to get scewed in there and bind, a bound bolt is a lot of friction, flutes or no flutes.

a good fit and a good surface finish will give least friction.

I have one polished panda that has bound since day one, It has a beautiful pollish job, nice fit, real nice gun, but I go for the bead blasted one everytime because it functions. Bead blasted bolts are like millions of random flutes right?

Does bead blasting increase the outside diameter of the bolt?

Does bead blasting decrease the Inside diameter of the bolt way in the action?


01-16-2008, 05:02 PM

The force of friction has nothing to do with surface area. Bolt binding and surface finish issues are of importance, however.

Bead blasted finishes will hold lubricant better, but like knurling, will change the diameter by increasing it (within reason).


01-16-2008, 07:36 PM
I believe friction does have to do with surface area, and in a big way.

I'll put this in ironworker terms, because thats what I am. Take a 15/16" Barrel Pin for instance (pointed at both ends, but straight 15/16" in the midsection) and drive it through a 15/16th" hole in a 2" plate. The pointed part goes in easy, and as you get into the area where the hole is the size of the pin, it gets tighter. The more the pin goes into the plate, the tighter it gets, until the straight section is out the other side of the plate. Thats because as you drive it in, you have more and more of the surface of the pin contacting the hole, until you reach the other side. At this point you have total contact, and there is no way more surface area contact can occur. As you continue to drive it through you continue at the same tension, until the rear taper is now entering the hole, now with every drive you have less and less surface area contact and the pin gets easier to drive. This is because the constant friction is now applied to less surface area.

The idea of ball bearings, roller bearings, etc. is the same. The ball only contacts a surface at the tangent point, so friction is only applied at that point, a bushing used in a similar application however has much more surface contact and would build much more friction and heat.

So cutting down on the surface area by cutting flutes in a bolt reduces the amount of surface contact in a bolt action. thus reducing friction.

I wonder though, how much the diameter of a bolt that is not bead blasted would increase if it were bead blasted without turning it down some first?


01-17-2008, 12:22 AM
When you say open/close, is that up and down or in and out?

Bob Kingsbury
01-19-2008, 05:02 PM
When you bead blast a bolt, the dia increase is very small. generally
less than a thou. Some aggragate remains in the surface and will
act as an abrasive, wearing the inside of the action. Beware

Steve Huff
01-19-2008, 06:52 PM
back and forth only, still think it is friction, even more
lube/oil does not help.no problem, but can shoot
alot faster with less drag.