How to determine freebore for a reamer

J

JerryK

Member
I'm drawing up a short 6.5x284 case and getting ready to order the reamer, and would like to spec the freebore. I pushed back the shoulder (using a 300 Win Mag die) on a standard 6.5x284 case, and have the water capacity where I want it. The shoulder is 25 degrees at this stage.

Is there a method to determine the freebore with the bullet I want to use? The lead angle will be 1.5 degrees. I want to specify when ordering the reamer.

I have a shop but no lathe or mill.

Jerry
 
You can get a close approximation by taking a 1" micrometer and setting it to .001" smaller than bullet diameter. Slide it down the seated bullet and then meaure from the end of the case neck to where the micrometer stops.
 
I would form three cases.

Then seat three bullets of my choice.

Then send all to the reamer maker, followed up by a telephone call.

A good reamer maker will offer some great advice, suggest changes and check your drawing:)=

That been said I would choose more than one bullet and bullet weight all seated the same length from the base of brass to the bullet's ogive.
 
In those instances I use a throating reamer with my reamer made with a shorter throat.I like the range it gives me if there is a different type bullet I want to switch too :D
 
Ive never gone in with a throating reamer on an already cut chamber. How do you determine exactly how much deeper your actually going and how do you measure your results.
 
You can take the desired bullet and seat it to desired depth in a prepared case. Take that dummy cartridge and place it in the muzzle end of the square cut barrel blank. The bullet ogive will touch the lands and then you can measure from the face of the barrel to the case mouth. That will approximate the depth to set your free bore. Now we can start the argument on how much if any clearance is needed from the ogive to the lead in. :)
 
I been working with 6.5 wsm's the last couple of years. The PT&G reamer was fine for 100-120 grain bullets. I wanted to shoot 129's and 140's ,so I setup a dummy round with those and measured with a comparator. Seating them out as far as the magazines would allow. Use the throater to make up the difference.Works perfect.
Of course some mags will permit you to seat them further out to keep the bullets from being seated deep in the case.Some will not
 
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