How to measure the slug on a No. 1 MK III Enfield

[cropcirclewalker]

Ok, them Brits.

Today I cast up some 319247s in pure lead and slugged the barrell of my Lithgow SMLE No. 1 Mk III*.

So 5 grooves might be cool, but when you put the calipers on one groove they come in on the land on the other side.

It read .310.

So, then I got my micrometer and I read around and around the slug. Sometimes it would read .310, .311 and sometimes it would read .315.

I assume that the .315 was reading from one edge of the corner of a groove to the opposite corner of an opposite groove. Not exactly the actual diameter.

Here is the question........What is my bore dimension?

or......

How do I really measure it?

PS I hope this is the correct section to post this question. If not, mods, feel free to move it.

Thanks

[StarMetal]

You have to make a little V adaptor. Take some metal that is about anywhere between 1/16 to 1/8 inch thick, cut it so it's 1 inch long and about 3/8 wide. Then bend it a perfect 90 deg in the middle. Now that outside V point....flile that so it's flat and level/square like the V can stand perfectly straight up on it. Don't file too close to the inside corner as you don't want to weaken it. Okay take a 30 caliber jacketed bullet if you have one. Mike it a few times to get an average. Let's say it mikes out exactly at .308. Okay now place the bullet in that V you just made and mike the two together. That flat part of the V you filed should rest against the stationary anvil of the mic and the moveable one against the bullet. Get an average. Now substract those two measurements you got...the bullet alone, then the bullet with the V tool. Okay...drive a slug thru your Brit barrel. Now measure it with the V tool like you did the jacketed bullet...EXCEPT make sure two rifling ridges touch the V 's legs, that is one rifling ridge on each leg of the V. That means a rifling ridge will be dead center for the anvil to rest against as you screw it in. Get an average and then substract the number that you got from when you did the other two measurements. Let's see if I can write that out. Jacketed bullet diameter equals .308, the measurement of the .308 bullet with the V in place equals say .323....you subtract the bullet diameter from that number .323 minus .308 equals .015. Okay now you measure the bore slug with the V and you get say .329. Substract that .015 from that . That would be .329 minus .015 equals .314...that would be your groove diameter for your Brit barrel.

I had a picture of this tool and how you use it, but I lost it. If you have a hard time understanding this let me know. Basically what you have turned your regular mic into is a V Mic for measuring round tubing or rods.

Joe

[StarMetal]

I drew a picture in Paint real quick. The first one on the left is the V tool. Then the one on the right is the V tool with a bullet in it. Just place it with the bullet in it between your mic jaws and measure. Don't forget to get that correction number first with a known jacketed size so you can subtract it when you do the lead slug.

Joe

[NVcurmudgeon]

Another way is to slug or Cerrosafe cast the throat. If you fit boolit diameter to the throat, you don't need groove diameter as the boolit must go through the throat first. Throat dameter is usually slightly larger than groove diameter. One trick I used to get me by until I could get a slug from my No. 4 Enfield properly measured, was to drill a 5/16" hole in a piece of metal. Then I enlarged the hole with emery paper wrapped around a dowel until a slug would barely pass through the hole and measured it with calipers.

[cropcirclewalker]

Thanks for the replies. They helped me to understand the problem.

So this afternoon there I was sipping on my favorite cereal malt beverage and thinking about it.

:drinks:

That's when it came upon me... :idea:

I finished my CMB, got out my scissors and cut a strip about 3/4" wide out of the can.

Next I miked a 311284 which I had just shoved through my Lee .309 sizer and it read .3090. good.

then I wrapped the CMB can strip around the boolit just miked and read it again only this time it contained 2 layers of aluminum can. She came in at .3174.

Now......I subtract .3090 from .3174 and come up with .0084, which represents the thickness of the two layers of the can.

Now I mike the slug wrapped in the aluminum and she comes in at .3227 and subtracting the .0084 from the aluminum, I come up with .3143.

Violla! and with copius coolery I know my groove depth.

You see, the aluminum is rigid enough to hold its shape and let us not forget that the rifling is twisted, which further helps to hold.

Thanks, Fellers.

PS Fer grins, I miked 2 layers of aluminum and it came in at .0088. Close enough for .gov work. :)

[Bob S]

I wrap the slug tightly with thin brass shim stock, carefully mike the result. The groove diameter is the mike reading minus twice the thickness of the shim stock.

Most 5-groove Britsh Enfields tend to run .315 and up, in my experience ... which is one reason it is hard to get them shoot acceptable well with anything except a properly fitted cast bullet. The nominal spec was .303 bore, .0055" groove depth. If you do the math, the nominal groove diameter should be .314. Even the Brits did not make bullets to fit that!

Resp'y,
Bob S.


Resp'y,
Bob S.

[mag_01]

:castmine: ---- Iwould say ur bore is about .316or so---I have been thru this myself and now use a fat 30 boolit that comes out of bore at .317 (beagled mould)---I opened up a .314 sizer die to about .3155 and now use it gas checked in my SMLE -works well indeed---I also tried a .317 boolit as cast---it would not fit in throut area---.316 will---also If you have case seperation or primer back out you have a headspace problem--I wellded lugs on bolt and fit to just close down on case on closing---0 headspace or so to speak-works well ----case life is very good---results have been good working with AA5744---180 lead----24 or 25 grs. as well as 2400---18 grs.--work these loads to get the most from your SMLE ---good luck ------Mag---:castmine:

[cropcirclewalker]

Following my previous conclusions,

I lapped (wrapped a 5/16 dowell with a couple of layers of clear wrapping tape and coated it with valve grinding compound and chucked it into my cordless drill and set it to rotate backward and sat and watched NCIS on the TV and valve ground my spare Lee .311 sizer die out to .315

I yam on board with the fatter 30 group buy but in the mean time since I don't have a boolit mould that will drop anything bigger than like .313 (Beagled) I cast up a bunch of 319247s and sized them down to .315.

The missus has me doing honey dos.

I haven't had enough shots through my smelly to confirm and I have been playing with mostly Bluedot loads. I just bought a lb. of 2400 and will be soon making some shots over my chrony with the 319247 to figger out what may work.

Hurry up on the fatter 30. [smilie=1: