How to Measure/Ream 11 Degree Throat in Uberti Colt 1851 Navy?

[Head Tomcat]

Guys,

I am a bit confused on how to properly cut an 11 degree throat into my Uberti Colt 1851 Navy barrel and am looking for advice.

My Brownells 11/18 degree throat gage arrived and I dropped it into the mouth of the barrel. I was surprised to find the gage go all the way into the barrel and in fact went in .115” further which is shown in the left picture.

The gage was then slipped into a second Uberti Colt 1851 barrel which had been previously reworked by a respected black powder gun shop – including cutting the forcing cone to 11 degrees - and the gage went in even deeper at .190” as shown in the right picture.

I thought this gage should protrude above the barrel mouth and then the 11 degree throat reamer would be used to carefully cut away the factory throat until the ledge on the top of the gage fell even with the mouth. What am I missing, or do these Uberti barrels have a different geometry and the gage is supposed to drop some distance into the barrel before you do the measurement and start reaming? If so, how deep should the gage go into the barrel before the forcing cone is considered properly reamed to 11 degrees?

Thanks!

The Olde Tom

[JRD]

Whatever your forcing cone currently is, it's already way bigger than what the gauge measures.

Are you having spitting problems, or just cutting a new forcing cone for the fun of it?

You could possibly use molding putty to get an impression of the forcing cone and get some dimensions off the impression.

[JRD]

Did you buy a forcing cone gauge for 38/357 revolvers based on a .357 groove diameter and you are using it in a cap and ball revolver with a .375 groove diameter? If so, that could explain why the gauge drops way in.

[HWooldridge]

What JRD said is a distinct possibility...

In addition, I can't really see the gage too well, but most taper gages have a GO-NOGO window - either on the gage member or just above it. The GO range is within the window; not above or below.

[Gtek]

Kind of in the camp with the above. Drop a .375" ball on mouth and you should see about half of it, maybe a .380" depending on your groove.

[Head Tomcat]

Guys,

It appears JRD hit in on the head and I am a bit embarrassed having not thought of it!

The 11 degree throat gage measures .3436 on the micrometer so that explains why it fell so far into a barrel slugged at .3703". Essentially, what stopped the gage from falling completely through the barrel was the 11/18 degree flange. Below is a picture of a Hornady .375" lead ball inserted into the barrel and you can see it easily sticks out about 1/3 of the diameter.

The reason I am wanting to cut an 11 degree throat is simply to experiment on accuracy. Which brings up the question....what commercial gage is needed to correctly fit the barrel and show how far to cut an 11 degree throat? I would think a gage whose diameter is very close to .370" would be the way to go...but any thoughts on where to find one?

Finally, while it is not shown in the two pictures, the gage does have a shelf on it and I understand the proper range would fall between the upper/lower surfaces of that shelf.

Thanks!

The Olde Tom

[HWooldridge]

You can turn a gage on a lathe if you have access to a machine (or a machinist friend).

However, one thing to determine is taper length and finished mouth diameter. You don’t need a big entry unless cylinder indexing is real poor. That being said, and I’m estimating here, a .390 mouth opening is probably sufficient, then just let the reamer finish wherever it falls. No real need to spend money on a gage if you determine the entry size.

[Gtek]

My 2 cents, that barrel entry is a touch past sufficient, usually a non issue of blowing cones in these. Chasing accuracy in these things IMHO is more related in cylinder to groove. You stated you found .3703" in barrel, now mic the cylinder bores. I bet if you were to open cylinders to about .371" or so up front and used a .375" ball you and accuracy might run into each other.

[Jackrabbit1957]

When I cut a forcing cone I go only deep enough to clean up the existing one, I work on blackpowder revolvers exclusively, or if it doesn't have a forcing cone like the Walkers and early Dragoons , I will generally cut the length to about .200 give or take. Accuracy generally improves. Other things like correcting the arbor length and tuning the action help as well.