So I slugged the bore and determined ?????

[Bad Ass Wallace]

I am always taken me to task, when casters say "slug" the bore to determine the correct size cast bullet to use.

I say, all that determines is the size of the tightest spot in the barrel, better to start a bullet into the muzzle and make sure the rifling at that point (the last point of contact before exiting) contacts both the top and bottom of the lands. Then size your projectile to that dimension.

Take the humble 303 British;

According to the Small Arms Identification Series by Ian Skennerton "Magazine Lee-Enfield Rifle" Page 29

1) Lee Metford and Lee-Enfield Mk1:
Barrel Specification:
Barrel Length - 30.5"
Rifling Metford - 7 groove L.H. 1 turn on 10"
Rifling Enfield - 5 groove L.H. 1 turn in 10"
Bore Dia - 0.303"
Metford Rifling Depth - 0.004"
Enfield Rifling Depth - 0.0055
Metford Land Width - 0.023"
Enfield Land Width - 0.0936

From book "The British Service Lee" by Ian Skennerton Page 86
2) Short Magazine Lee Enfield Mk 3:
Barrel Specification:
Barrel Length 25.2"
Rifling Enfield - 5 groove L.H. 1 turn in 10"
Bore Dia - 0.303"
Enfield Rifling Depth at muzzle - 0.0065
Enfield Rifling Depth at breech and to within 14" of the muzzle - .005
Enfield Land Width - 0.0936

From book "The British Service Lee" by Ian Skennerton Page 158
3) Short Magazine Lee Enfield Mk 4 & 5:
Barrel Specification:
Barrel Length 25.2"
Rifling Enfield - 5 groove L.H. 1 turn in 10"
Bore Dia - 0.303"
Enfield Rifling Depth at breech - .005
Enfield Land Width - 0.0936

It would seem from this data that an Enfield 303 could be .303" over lands and a bore of up to 0.314" at the breech and up to 0.316 at the muzzle.

My Martini Enfield 303's shoot best with a .314 dia projectile which would seem to fit with the above specifications and bore diameter of .313"

[Der Gebirgsjager]

Well, just for the sake of conversation, if your bore has a tight spot, and the bullet passes through that tight spot, it's not likely to get bigger again after passing it. So I would say that is valuable information to have. If there's a gross difference between the tight spot and the average of the rest of the barrel, then for better accuracy I would consider re-barreling.

[Char-Gar]

One more time....Sugging the bore of a rifle to determine the proper size of cast bullets is an unmitigated waste of time. Whatever number you get will be irrelevant.

The size of the throat/leade/free bore ahead of the chamber is the only number of significance. Size the bullets as close to that as you can get without going over.

This has been said, over, over and over again, but some folks still have not gotten the memo. The old "slug the bore" myth persists despite all attempts to drive a stake through it's heart.

[gpidaho]

Do a chamber cast or next best what folks call a pound cast and determine the size of the throat. The barrel of a rifle is just a long sizing die. And as Char-Gar said slugging the bore doesn't tell you anything. Well it may tell you if there's a real tight spot I guess but not much else. Gp

[williamwaco]

one more time....sugging the bore of a rifle to determine the proper size of cast bullets is an unmitigated waste of time. Whatever number you get will be irrelevant.

The size of the throat/leade/free bore ahead of the chamber is the only number of significance. Size the bullets as close to that as you can get without going over.

This has been said, over, over and over again, but some folks still have not gotten the memo. The old "slug the bore" myth persists despite all attempts to drive a stake through it's heart.

yeah! ^ ^ ^ ^ ^ ^ ^ ^ ^ ^

what he said.

[KCSO]

I have a set of brass rods that I use to slug with, a short one and a long one. I put a round ball into the bore and expand one at the muzzle and one at the breech for the most accurate slugging. If I push a ball through and hit any tight spots in the middle that bore needs to be lapped.

[Larry Gibson]

One more time....Sugging the bore of a rifle to determine the proper size of cast bullets is an unmitigated waste of time. Whatever number you get will be irrelevant.

The size of the throat/leade/free bore ahead of the chamber is the only number of significance. Size the bullets as close to that as you can get without going over.

This has been said, over, over and over again, but some folks still have not gotten the memo. The old "slug the bore" myth persists despite all attempts to drive a stake through it's heart.

Exactly.....

[swheeler]

sugging? Take a case fired in the gun and measure the inside neck diameter of it, size to that.

[Jack Stanley]

What Char-gar said is the shortest way to get it right . I generally use a throat impression to find the size but I have bumped a bullet just into the throat to get close .

Jack

[Texas by God]

I kinda like to see what I see and feel what I feel by slugging the bore. Also if someone asks "What's your groove diameter"?- you can say ".358". That's knowledge even if It's of no consequence.

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[rondog]

So, is there a tutorial or sticky here somewhere telling how to do this throat impression and chamber/pound casting? Not all of us know this stuff. And searching here - I always end up out in Google land......

[GhostHawk]

Very good sticky on chamber casting.

I will say this, I slugged several barrels, got them stuck, and unstuck.

And then I tried a chamber cast. Nothing got stuck. I got the most accurate cast shooting rifle I'd ever had. 50 yards 3 bullets in one hole sighting the scope in. Less than an inch at 100 if I can hold up my end. Which is often debatable.

I repeated the process on my next rifle, and got the same results. Cloverleaf's at 25, and 50. I would have had one at 100 but I pulled the last shot half an inch.

I know which one I use. The one that works. Chamber cast. YMMV

[Crash_Corrigan]

Ya can't go wrong with cerrosafe. However you must follow the directions and measure the casting at a certain time after making it. Over time the casting will change measurements and it is not a permanent casting for future reference. It is easy to do and it works. I have a couple of Enfield's which are very different from each other. Each chamber was different and calls for a different dia. boolit to be accurate. I have had to file a notch in the rim to keep the brass separate. Before casting I was guessing and had lousy accuracy in both rifles. Now I can put my rounds out there to 250 yds and slam the steel gong with regularity. With the standard Ed Harris Red Dot loading I have a very comfortable rifle to shoot and they are cheap to load for as I recover the alloy from the backstop and recycle it again and again.

[Texas by God]

sugging? Take a case fired in the gun and measure the inside neck diameter of it, size to that.I want to try this on the SMLE I'm fooling with. It slugs .312" tight the whole way through. I'm going to try some Sierra 180 .311" sp that are already loaded first. I've cleaned it up to sell for a friend but I'll probably buy it.......and a mould........
Best, Thomas.

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[Char-Gar]

sugging? Take a case fired in the gun and measure the inside neck diameter of it, size to that.

This notion has been floating around this site for a while now as a short cut. This will tell you the maximum size of a bullet that can be fired in the chamber and in that case, but will give you zero information about the throat. It also does not account for the variety of case neck thickness in various makes and batches of brass.

I have several rifles with either large or worn throats. I must neck turn to thin the brass, so it will hold the proper size bullet and still have some room for the neck to expand and release the bullet.

Measuring the inside of a fired case may or may not work. A cast or throat slug will always work.

[swheeler]

Oh it'll work

[Char-Gar]

Oh it'll work

Oh, I am sure the bullet will trundle down the barrel and strike the target. However that is not what I am after. I am after the smallest group possible.

[zymguy]

So, is there a tutorial or sticky here somewhere telling how to do this throat impression and chamber/pound casting? Not all of us know this stuff. And searching here - I always end up out in Google land......

im with rondog, how do we do it?

[Outpost75]

If you barrel has a tight spot, the answer is to lap it out until its dimensions are uniform.


https://www.google.com/search?rlz=1C1SAVA_enUS523US533&q=how+to+hand+lap+a+rifle+barrel+youtube&sa=X&ved=0ahUKEwjoyJ6elM3VAhVJVyYKHcM5BnMQ1QIIdigB&biw=1254&bih=894

[Hannibal]

im with rondog, how do we do it?

I don't know how to post links, but in the Cast Boolits sub-forum, there is a 'sticky' for 'how I do a pound cast'.

[zymguy]

I don't know how to post links, but in the Cast Boolits sub-forum, there is a 'sticky' for 'how I do a pound cast'.

http://castboolits.gunloads.com/showthread.php?218414-FYI-This-is-how-I-do-a-pound-cast

[Hannibal]

http://castboolits.gunloads.com/showthread.php?218414-FYI-This-is-how-I-do-a-pound-cast

Yes, that's the one I was referring to. As for a chamber casting, Cerrosafe is the product I've seen recommend most, and I believe it comes with instructions.

Hope this helps.

[Outpost75]

Here is a reposting of one of mine:

To determine the correct bullet diameter for a rifle, the groove diameter of the barrel is NOT the determinant.

INSTEAD you want to measure the throat, or the unrifled portion of the barrel forcing cone or "ball seat" ahead of the case mouth, before the rifling starts. The best way to do this is from a chamber cast or upset throat slug.

Most accurate for measurement purposes and easiest is to upset a throat slug, or as some people call it a "pound cast."
Start with a sized case with DEAD primer in its pocket. The way I do this is to heat the lead pot, then fill the sized case with DEAD primer plugging the flash hole, and generously overflowing the case.

After the lead cools, clean all spilled lead off the case exterior, then file the exposed lead FLUSH to the case mouth.

Take a piece of PURE lead buckshot or short chunk of pure lead wire and drop it into the EMPTY chamber, letting it fall into the throat of its own weight. (With very long throats you can use a longer piece of wire or a SOFT bullet with long bore-riding nose and not a long grooved section).

Insert your lead-filled dummy case and GENTLY tap it into the chamber using a piece of brass rod until you can close the breech. You are using the lead filled dummy case to force the lead slug into the ORIGIN of rifling. In short throated barrels it helps to drive the slug first into the origin of rifling, far enough to chamber the lead dummy behind it, then close the bolt and upset the slug against the lead dummy using a Brownell Squibb Rod threaded onto the end of your cleaning rod.

You don't need to use a hammer, just let the weight of the rod make many light taps of the squibb rod against the slug until you get a clear "ringing" sound. It need go no farther!

What you want to measure is the diameter of the UNRIFLED portion of the chamber forward of the case neck BEFORE the rifling starts! Extract the dummy and GENTLY tap the lead slug out and measure it. THAT is the diameter you want to size your bullets to!

Using Cerrosafe, etc. is more trouble and you then need to compensate for shrinkage, etc.

The upset pure, dead-lead slug is exact and straight forward!

If you forget EVERYTHING you ever read about slugging barrels and simply cast chambers from now on, and get bullets to FIT THE THROAT you will be far happier in the long run.

The limiting factor in safe bullet diameter is neck clearance. You MUST measure the neck diameter of the chamber on the cast. Most chambers have enough clearance ahead of a fired case mouth that a properly upset throat slug will get you a portion of the case mouth and its transition angle to the throat or ball seat, so that you can measure neck diameter at the mouth and throat diameter of the ball seat.

The loaded cartridge neck diameter must not be larger than 0.0015" SMALLER than the chamber cast at that point, to ensure safe expansion for bullet release. This is absolutely essential for custom target barrels which often have tight-necked chambers which require neck-turned cases. As a general rule the largest diameter of cast bullet which chambers and extracts freely, without resistance, will shoot best.

For instance in a .308 Winchester target rifle with .339" tight-necked chamber and using case necks turned to 0.012," maximum bullet diameter is determined by"

[neck (.339")-2(neck wall thickness 0.012)] - 0.0015 = 0.3135" for a "fitted neck" in which fired cases do not require sizing, but bullets will be held by case springback only. For necked sized fixed ammo, subtract another 0.0015" or .312" IF the chamber ball seat is that large. In a new barrel chambered for jacketed bullets, probably not. Min. SAAMI throat as on the pressure test barrel is 0.3105".

Unless you know your throat is smaller, try .310". If the barrel has been fired more than 1500 rounds with full power jacketed loads .311" will be better. If you shot a couple seasons season of highpower with it, .312" will fit just fine.

John Ardito set all of his CBA benchrest records shooting .312" bullets in his .308 Win. and wildcat .30 cal. rifles.
This is seldom a problem in the Russian M91/30s and Chinese copies chambers are notoriously sloppy!

In a typical military 03A3 .30-'06 chamber the minimum neck diameter per the drawing is 0.340".

Typical case mouth wall thickness of LC, FA, TW, WCC or other USGI brass is 0.013," so .340" minus twice neck thickness (0.026") = .314", minus 0.0015 for safe expansion = .3125" max. bullet for a typical worn GI .30-'06 chamber in an 03A3 or US M1917. A new barrel will have a .3095-.310" throat and you should size to that diameter for a "new" replacement USGI or Criterion barrel.

As a general rule the largest diameter of cast bullet which chambers and extracts freely, without resistance, will shoot best.
For milsurp .30-'06 rifles showing ANY MEASUREABLE throat wear this is .311-.312."

[swheeler]

I want to try this on the SMLE I'm fooling with. It slugs .312" tight the whole way through. I'm going to try some Sierra 180 .311" sp that are already loaded first. I've cleaned it up to sell for a friend but I'll probably buy it.......and a mould........
Best, Thomas.

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Give it a try Thomas and report back.:drinks:

[leadman]

A slugging of the bore on an old mil-surp rifle can give you some valuable info. It can tell you if there is a loose spot or a tight spot in the bore. Without a borescope a pit or built up rust may not be seen. It will also tell you if the gun has been cleaned from the muzzle and suffers wear there. I do a slug of the throat area seperately and will normally size the boolit to match depending on the neck size of the chamber.
With my 71 Mauser the neck is .008" smaller than the throat so I use 3 grains of poly-fil in the case to help seal the gases in the bore.

[Multigunner]

SMLE Mk1 bores were "reverse taper lapped" for the last 14 inches of the bore to the muzzle.
This was an attempt to get the same velocity and range when using the MkVI cartridge as the longer LE barrel by reducing friction.
The Cordite Mk1 propellant used with the MkVI cartridge in use at the time reached maximum pressure at ten inches of bore travel.

Reverse lapping was dropped early on but replacement of those barrels was not authorized till around 1917.
The SC HV marked barrels intended for best accuracy when using the MkVII cartridge are most often encountered but reverse lapped barrels still show up occasionally.