Breech plug size chart

[Kiwi]

Gents.
Morning / evening depending on where you are.
G'day from Australia, great site you probably have this info posted but is there a size chart for breech plug vs bore.
Regards.
Kiwi.

[P.W.Berkuta]

There probably is but I use the barrel & breach plug info on Track of the Wolf's web catalog site.

[Kiwi]

Many thanks building one of Runar's sea service pistols but only in 50 cal.might take a while but with work interrupting.

[Old Ford2]

Hello Kiwi,
This stuff is more addicting than ( some ) women or drugs.
Great site here to get you started.
Fred ( Canada )

[Mtn Meek]

G'day from Australia, great site you probably have this info posted but is there a size chart for breech plug vs bore.
Regards.
Kiwi.

I don’t know of any such chart, but you can figure it out by looking at Tap Drill Charts.

Take a 5/8-18 breech plug for example.  The recommended tap drill size is 37/64” fractional or 0.5781” decimal.  The largest practical bore size to give a shoulder for the breech plug to butt against is .54 caliber or 0.540”.  If the bore is rifled with 0.012” grooves, the diameter across the grooves would be 0.564” giving you only (0.578” – 0.564”)/2 = 0.007” of shoulder in the grooves.  Basically, you would have some shoulder at the lands and practically no shoulder at the grooves.

The same exercise for 3/4-16 plug would yield a largest practical bore size of .62 caliber.  There would be a shoulder at the lands, but only (0.6875” – 0.644”)/2 = 0.022” of shoulder in the grooves.

Doing the same for 7/8-14 plug would yield a largest practical bore size of .775" caliber like on a Brown Bess.  You would have less than 0.007” shoulder in the grooves.

[John Archer]

There is such a chart on page 29 of Recreating the American Longrifle by Buchele, Shumway, and Alexander...if you don't have this book you should get it.
John