I have owned my Savage Enfield mk1* since I was 2, bought back in the early 90s. My grandpa purchased it for me to enjoy when I grew up. 

Anyways, I did a pound cast on the throat and here's the measurements. 

THIS IS A 2 GROOVE GUN

.200 in front of the case mouth measures .318

.400 in front of the case mouth measures 315/316

.750 in front of the case mouth measures 310

The groves in these areas seem to be 318/320 but the rifling on this gun is really dirty, like, after a few days with penetrating oil in it and suddenly patches come out black again. At the muzzle I get a consistent measurement of 319 groove.

The muzzle is 308.5/309 bore and I can personally tell you that section of the barrel is very clean. 

I'm paper patching for this gun, and I'd like a bit of guidance as to how thick a bullet I can swage into the rifling. I am optimistic that the paper patched bullets will help clean out those grooves to get a better measurement and obviously better performance. This gun has never been shot by me so I have no idea what it's capable of doing. This barrel is not pitted in any way shape or form. It's actually very very smooth

A local cast bullet guru here in town told me to start with 316 and see how things go. Work up from there essentially. His knowledge was slightly limited as far as enfields go and I know they're kind of their own unique monsters as far as bullet size.  

So what do the experts out there think about the erosion on this barrel? Will I be more than likely be going up in bullet size? I guess in general I've always thought you cast a bullet to fill the grooves in the barrel. That's what I do for 3006 & 3030. Where things get weird is knowing you have a bullet compressing in your barrel .010 by the time it reaches the muzzle. 

Thank you all for your time Hope to hear from you all soon. For what it's worth I would like to attempt to make this gun accurate enough for hunting out to 200 yards maybe three? All of my lead bullets are essentially hunting bullets except for one or two molds

First off, CLEAN the barrel thoroughly with either J.B. Bore paste or at least a strong copper solvent. Keep cleaning till it comes out with no blue/green or grey crud on the patches.

You can't remove the layered on laminated fouling copper/carbon/copper/carbon/copper/carbon/ with penetrating oil & secondly shooting it will just add more layers so you're defeating your own goals.

NOW make your measurements.

After a day at the range with paper patched ammo, my barrel has nothing left in it besides a mirror polish. So, I see your point about not shooting over a foul barrel but for whatever reason paper seems to do the trick on the stuff you can't get out with a brush or jag.

.303 barrels made during WWII had quite large tolerances.  Those original 2 groove barrels are likely quite rough by now from firing cordite loaded ammunition, worse if corrosive primers were used and  not properly cleaned.  

My new throatcast has the exact same dimensions as my old one did. The barrel was not dirty in that area so I knew this wasn't going to change. 

The muzzle of the gun was also clean. So my muzzle dimensions are the same as well. He used his calipers and got the exact same dimensions I did. 

For every other rifle that I cast bullets for I always go 001-002 over the groove diameter. 

So the reason for this post is if I base that directly off of my throatcast I would be putting .320 bullets in this rifle. I'm having a hard time processing that as this is only a two-groove barrel and It seems like an awful lot of metal to swage down. If it's the right thing to do I will work up to that point. 

Right this minute I am loading 317 paper patch bullets to sit over 21 grains of 3031 powder. 

So am I the only one out there that thinks a 320 bullet being sized down to 309 is crazy? That bullet is going to swage down .010 within 1 1/2 inches in the barrel.

These are cast lead then paper-patched, yes?

That doesn't seem too out of this world to me. I wouldn't trust that with really hard-cast ones though.

I ordered some Lee push through sizers today so I'll be able to manipulate things up to 320. 

I don't know any other way to describe my muzzle dimensions. The most NARROW width of my barrel is 309.5. I'm describing this as the bore. If you go get a rod that's 3095 and slip it into the barrel it's going to hardly fit. 

The grooves of this two groove barrel are 319. It almost seems like after the deep clean we did I got an extra .0005 out of it. Making my grooves 319.5

If I have the wrong terminology somehow I apologize but that's the dimensions at the muzzle. I have one factory 303 round and the bullet completely slips into the muzzle all the way to the brass and tries to swallow the brass with it

She's tired I guess

Gun managed 4moa shooting off the hood of my ram charger ( 2" @50 yards )

I have 50+ properly patched bullets waiting to be loaded up and load developing 4895 powder. Bullet diameter was 316. 

You may have a "Cord Worn" muzzle caused by improper pull through usage.

Maybe slug the entire bore from breech to muzzle so you get the dimension further into the front. Cord wear tends to be just the first couple of images

3095---310 were consistent 

I have a set of ridiculously accurate calipers that have longer measuring edges on them and 1 in below the muzzle surface measures 309.5

I stopped half way down the barrel, from beech to mid barrel, and it was 310

That rifle is shooting a lot better than I would expect for such a worn barrel at the muzzle. 

For reference, the bore diameter is the width across the lands (smallest diameter), the groove diameter is the width across the grooves (widest diameter). It’s easy to check on a 2 groove barrel, a bit harder to check on the 5 groove barrel.  Nominal is .303 bore and .314 groove. 

OP, when you mention pound casting, are you describing the filling of a cartridge case with lead alloy and then half the neck with a long lead bullet and upsetting it with a steel rod to the throat and ball seat or simply slugging the bore by driving a lead ball through the length of the barrel?

I'm just curious to your method that your using if you would describe.

Thanks

I'm thinking this gun might be getting my 200 grain bore rider bullets. The ranch dog bullets I'm using were made for big fat throats so maybe that's why it's shooting good. 

I even put a 160 grain bullet ON TOP OF THAT when I was getting these huge measurements. 

So far, the only person who's confirmed 316 and bigger bullets for this type of 2 groove is Ed Harris

Manufacturing tolerances, particularly in war time, were quite large.  

The post war new BSA barrel installed on my Fulton Regulated Long Branch Mk I/3 slugged at .315.  Unfortunately, I didn’t record the 6 or 7 other No. 4 barrels I have (not including CBI and Lothar Walther recent production barrels), but IIRC, they are all larger than .314, I think one was .318. 

Keep in mind that the two groove barrel has the same width of cut grooves as the 5 groove, it just eliminates the cutting of the additional 3 grooves. So the mean diameter (average diameter around the circumference) is quite a bit smaller than a 5 groove barrel (just 1/5 of the circumference is at the groove diameter, 4/5ths of the circumference is at bore diameter).  This is why the 2 groove barrels shot .308 jacketed bullets reasonably well. 

Only way to find out what shoots the best is to test bullets of different diameters. I’d probably start at .314 and go up to .317. 

The measurements I was getting were so bizarre that I thought it was error. The grooves in front of the throat are 322. That's why I made this post

I also wanted to he how quickly the barrel erosion went down to 310 or 309. 

I've had this rifle since I was a toddler so I'm not fond of blowing it up over not understanding what 2 groove barrels like eating

To be honest, I'll probably stop at 317 and start over sizing gas checks. 

Thank you got validating these barrels can be huge and sloppy. The groove area in front of the blasting cone/throat are as high as 324. I sent 3 313 cast bullets down the muzzle to the chamber and they were all 309.5

I was literally clueless as to what to do with those measurements.

Give me a any " normal " barrel and I wouldn't have questioned a thing. But a2 groove? .324 to 309? No way!!! That's why I started researching