I need the barrel tenon and thread dimensions for the 1917 Enfield. I know it's 1.125 x 10 square type .020 deep, .800 long. I think they are .050 + .002 wide. I think the breech cone angle is 96 degrees. Can anyone put me on solid ground? Thanks.

What "they" are you talking about when you say you think "they" are .050 + .002 wide?

I'm going to assume that "they" are the width and space between the threads?

These square threads use a cutting tool with a tip .050" wide and the depth of the finished thread is approximately the same .050"...but you should always use your receiver as a thread gauge to assure proper fit.

Grinding these cutting tools will definitely increase your vocabulary so I just buy them pre ground from Brownells.

According to Frank deHaas' great book, Bolt Action Rifles, the major diameter is 1.125", the minor diameter is 1.085", and the length of the tenon is .800". The thread pitch is 10 TPI and the thread form is Square, this works out to .050" wide like you said. The breech cone angle is 45 degrees and the extractor slot is .410" wide.
Rick Bin is right about the thread cutter too.

I'm just a poster here (RickB) not the moderator (RickBin).

excuse me here, while this post still has "posters" is the Remington Model 30 along the same measurements?

Yes, same basic receiver...

My bad!
I apologize to the both of you.

thanks RickB

By "they" I meant the grooves. If I make the grooves .051, the lands would come out .049, which will work. If they are both .050 it won't fit, right? So the tool would be .050 plus, but it couldn't be .050 or less. Am I right? Roy Dunlap, in Gunsmithing on page 664 says the grooves are .020 deep. This seems awfully thin to me, and the one old P14 barrel I have shows grooves much deeper than .020. According to deHaas it works out to .040 (thanks nsaqam) which sounds more like it. Somewhere I seem to remember reading that a Springfield breech cone is 96 degrees. Just looking at the angle of the left bolt lug leads me to believe it has to be somthing like 90. If deHaas means 45 degrees from perpendicular, that will leave the breech cone 90 degrees. I don't think this cone angle is a critical dimension anyway. As long as it will feed and let the bolt close. Already figured on buying the tool from Brownells' (thanks RickB) I think I have enough to go on now.

I always use the receiver as a thread gauge and "sneak" up on the final depth for the barrel threads since all receivers are going to have slightly different major and minor diameters.

From John Hinnant's book: Precision Riffle Barrel Fitting.

Thanks. I've fitted barrels before, but this will be my first square thread. Always helps to talk to someone who has done it before.

I just checked an old 1917 take-off military barrel and the thread depth reads .034" with a depth mic.

Keep in mind that these old 1917 barrels were notoriously a very tight fit on the receiver.

So then deHaas must be about right at .040. Wonder why Dunlap got it so far off. Just measured that P14 barrel, says .036.

Books are valuable sources of information but nothing beats good old measuring tools.

Keep in mind that with a square thread as long as the minor diameter of the barrel tenon thread is smaller than the inside dimension of the receiver they will go together.
The dimension given in deHaas' book correspond with the .020" dimension in the Dunlap book. (1.125-1.085= .040 in diameter which you would then divide in half to get the dimension of .020 per side) I'd bet the military spec for these threads are just as given by both authors but in manufacturing the threads were probably cut deep in both the receiver and on the tenon to assure fitup since square threads are not depth critical.
I would accurately measure the ID of the receiver threads (it's minor diameter) and cut the minor diameter of the threads on your tenon to just under this dimension because square threads are not self centering and a close fit would help maintain concentricity of chamber to receiver.
Have fun with your project.

Yes, I see now. I should have caught that myself. Thanks for restoring my faith in Dunlap. I planned on sneaking up on it as RickB says.

Grinding the tool bit is really rather simple. Go slow and keep a mic in your pocket. Close really is good enough as long as the top side and front edges are square to one another and the bit is smaller than 50 thou. You can even grind a slight angle on the front of the bit if you intend to go a little below depth.

Set your compound at a right angle to your crossfeed. Work to depth with your crossfeed and width with your compound. In other words, you can easily reduce the width of the thread by moving the compound the amount you want to reduce the width.

I find square threads to be much simpler to cut than vee. And, the Springfield cone is cut at 41 or 49 degrees depending on how you lathe is made.

This is an Enfield, but I think they are the same. Can you explain the 41 or 49 degree part. Thanks for the help.

I understand this is for an Enfield, but the Springfield was mentioned in a post.

41+49=90. On some lathes, the compound zero is marked right in front of your belly button as you stand at the machine. On others that is 90*. So, as you swivel your compound "X" degrees, on one lathe it will move to "Y" and on another it will move to "90-Y". Basically some lathes are marked in degrees to the axis and some to the end of the work piece.

One thing we know is that everything is manufactured to a tolerance. So, your thread width is going to be 50 thou +/- that tolerance or more likely 50 thou -. The only way to sneak up on that is to use a bit smaller than .050. The only really critical measurement when fitting a square thread tennon is the major diameter, as this is what centers the chamber to the axis of the action bore. A couple thou smaller on your thread width is not going to make any difference.

The easiest way to find the actual cone angle of a barrel is to set it up in a lathe and zero a DTI as it is run across the cone. In practice, we know that the cone is also cut to a tolerance and a degree or two off of the call out will be okay. I have run a DTI across a small number of Springfield barrels, and they all came very close to 41* on my lathe. Since the call out for the Enfield is 45*, it will not matter how how your lathe is marked.

I bought the bit from Brownells. Pretty thing. I guess I could grind something that would work if I had to, but this one is nice. It's .050 wide. I understand the thread width must be smaller than the width of the groove it runs in. They both can't be .050. As I cut the groove wider I'm also making the thread narrower, so it won't take much to make it work. Actually, as I understand it, thread width isn't critical in the least, but major diameter is the only thing that will center the barrel in the receiver. So, we're going to match the outside diameter of the barrel shank, to the diameter at the bottom of the thread grooves in the receiver. Since everything is going to center on the bottom of those threads cut some 90 years ago, I wonder how they were cut. Single point on a lathe, big tap, big tap with a pilot? Wonder what the tolerance was for major and minor thread diameters in 1917. I never thought about the centering aspect of barrel threads before. Very interesting. I don't have the old barrel. I do have a P14 barrel. Hence the questions about the cone angle. Thanks again for the help.