A moron and his uni-throater...

[can1010]

View attachment 375687

Ok, looks like I've achieved a freebore increase of . 010 by running the stop collars up to the point where the centering sleeve just barely covers the step in the tapered cutting surface.

In order to achieve the depth desired, I'd need to have the reamer shoulder cut back . 225 as shown.

This would give me plenty of length to keep pushing freebore forward. I can confirm that only the first 1/3 to 1/2 of the cutter is cutting.


Our theory is correct-ish I think.

all my uni throaters are 1.4" from the back of the bushing to that shoulder what is yours? also the actual cutting surface stops just before that, yours looks like it has cutting surfaces all the way up to and even on the shoulder. did you have PTG check the part # on your reamer to verify it is what you think it is. mine will cut a 1.100"+ freebore before that shoulder ever touches the chamber neck on A 26 Nosler

 

[Rflshootr]

My goal is to increase freebore. Yes it cuts fast. The point of tangency is not moving towards the muzzle end as I cut. I guess the questions is...

If I continue to increase the depth of cut but do not see a correlated increase in freebore length, what is going on?

You're cutting the wrong end of the barrel.

 

[tobnpr]

all my uni throaters are 1.4" from the back of the bushing to that shoulder what is yours? also the actual cutting surface stops just before that, yours looks like it has cutting surfaces all the way up to and even on the shoulder. did you have PTG check the part # on your reamer to verify it is what you think it is. mine will cut a 1.100"+ freebore before that shoulder ever touches the chamber neck on A 26 Nosler

This.
It's been a long week...but running out of adjustment makes no sense to me on this. Disclaimer- never used a unithroater (usual reamer micrometer stop collar in a lathe) but it isn't adding up to me.

It's only about .570 from the shoulder datum to the forward end of the leade on the 26 Nosler. The stop collar may not be sitting right on the datum line in your chamber but it's going to be close enough... how you could run out of reamer? You need well under 1" of reamer (not incl the pilot) to hit whatever freebore you're looking for. What am I missing here?

Remember you can also confirm your numbers by case protrusion with your dummy round (assuming you don't have a coned breech) with a depth mike since the barrel has been pulled.

 

[StumpyJohnson]

Bear with me....

 

[StumpyJohnson]

 

[StumpyJohnson]

 

[StumpyJohnson]

 

[StumpyJohnson]

From my CRUDE mechanical drawings I'm seeing roughly 1.1236 of length needed from the point the shoulder of the uni-throater affects the point of tangency/ogive contact point to where the end of the cutter would be...

 

[StumpyJohnson]

In other words over an inch of tapered cutter length is required before CBTO is affected. Around this point the shoulder of the reamer comes into play and you're stuck...the CBTO is relatively unchanged put you've pushed the 1.5* lead angle pretty far down the barrel.

Am I crazy? Or is this not bad for a window licker?

 

[StumpyJohnson]

Whelp, after a convo with the fine people at PTG I'll be sending the throater back to have more cowbell ground into the jobby. To be continued....

 

[Willys]

Meaning what? Sharper angle or longer cutting surface?

 

[StumpyJohnson]

Longer cutting surface. The step in the throater will be ground back approximately .250"

 

[Rflshootr]

Longer cutting surface. The step in the throater will be ground back approximately .250"

Or, maybe the existing free-bore diameter is already larger then the reamer free-bore diameter, which also would require more depth to clean it up.
Ever think about a Cerrosafe cast of the throat and free-bore area?

 

[StumpyJohnson]

Or, maybe the existing free-bore diameter is already larger then the reamer free-bore diameter, which also would require more depth to clean it up.
Ever think about a Cerrosafe cast of the throat?

Nope