Vent placement - checking my calculations

[Jerry V Lape]

I have figured to center the vent 11/64" forward of the breechplug face to allow for the diameter of the interior cone which is 20/64".  This will be a coned interior, not a liner.  However I do have a White lightening liner, which should I need later would take up the 1/64" margin I left between the breech face and the cone. 

This position leaves me with the fence 3/16" forward of the rear of the barrel which seems as good as can be done without notching the breech plug face which I do not care to do. 

Have I got this correct?  Is that 3/16" forward of the barrels rear edge an acceptable compromise?

[Dennis Glazener]

I have figured to center the vent 11/64" forward of the breechplug face to allow for the diameter of the interior cone which is 20/64".  This will be a coned interior, not a liner.  However I do have a White lightening liner, which should I need later would take up the 1/64" margin I left between the breech face and the cone.

I would feel better with 12/64 or 3/16 just to be on the safe side.

This position leaves me with the fence 3/16" forward of the rear of the barrel which seems as good as can be done without notching the breech plug face which I do not care to do.

Have I got this correct?  Is that 3/16" forward of the barrels rear edge an acceptable compromise?

Its the best of two bad situations. Having to notching the breech is worse, in my opinion. Personally having the fence forward of the end of the barrel is no big deal.
Dennis

[Birddog6]

I don't actually use any precise measurements.  I don't like notching the breechplug face or having the breechplug threads & vent liner threads intersecting.
I lay the breechplug on the outside of the barrel on the flat the vent liner is going.
I take an Exacto knife & using the back side of the blade tip, I scribe a line across the flat to indicate where the breechplug face will be.
I sit a vent liner on that flat, move it forward of that scribed line about 1/16" & then mark the center of the vent liner on the barrel, remove it & scribe a straight line across the barrel flat on that mark.
I always scribe the lines as marks come off to easy & I end up redoing the above 2-3 times if I don't scribe it.

Now I know that is nothing precise as some would like, as no actual measurements taken. However, when using dif barrel makers, dif calibers with dif breechplugs, I am not going to keep a chart of every one to have actual measurements. Plus sometimes I shorten the breechplug & barrel, so the charted measurements would work in that case anyway.

So, this works for me & some others as well, lots of dif. ways of doing it.

As for the pan fence being at the end of the barrel, some are, some are not on the Originals I have looked at, so I never have concerned myself with that. I will agree it may look neater to have it that way, but for me it is not worth it when it means grooving a breechplug.

Keith Lisle

[msw]

I agree with Keith.  Rather than running the risk of 'getting wrapped around the axle' over measurements, just go with siome plain old empiricism.  Most probably what worked for the originls, and will work for us, too.

Make good smoke!

[Jerry V Lape]

Actually guys I did the positioning exactly as Keith described.  The measurements were taken afterwards so I could be sure I had space to fit in a liner if required at some future date and as a means of describing the setup in this question.  Dennis input that a little wider margin between breech and cone addressed one aspect of the question, the issue of final position of the fence with respect to the rear edge of the barrel was the other.  I think I am good with the setup as described.  Thanks for the help.  

Keith's description of how to do the physical layout might be a good thing to put in the tutorial for new builders.  I know the first time I built, before this site existed to find advice, I spent quite a lot of time cogitating on how to get the vent in the correct location and the method as Keith described was how I finally resolved it.