Tell your experience with throating

I have unrelated experiences that are all over the map.
Bought an aftermarket BBL for my Glock. It had NO throating at all. The rifling lead right up to the chamber cut. It was a PITA, and made for shorter COALs than were necessary or really advisable for the chambering.
FFW to last night's experience:
I have an old Ruger M77 in 22-250. It is a tack-driver of a rifle, and an old favorite of my Dad's, who had it given to him as a gift on completion of a special project long ago. I inherited it when he died, in 2002, and have shot it some, and loaded for it, but never really looked at it critically.
Last night decided to find out what kind of leade was in the throat. Neck-sized a cartridge for it, and just finger pushed a bullet in the neck far enough to stick there, then chambered & closed the bolt. Opened it and measured the COAL. 2.460"
SAAMI spec is 2.350" for the 22-250. I don't really care if I go outside the lines a bit on COAL, but there's no more than a diameter of bullet in the neck. Seems really long to me. I looked the throat over real close to see if it might be shot out, but it is bright as could be, so don't think it is eroded.
What do y'all make of this, and how much attention do you pay to bringing the ogive of yer boolit to the throat of the rifling? I realize that pistols are going to be different than revolvers, which will be different again from rifles. Autoloaders will have to have a bit of leeway that bolt guns won't need.
All in all, a very inexact science for such a scientific thing, it seems like..... :roll:

If the accuracy remains the same as far as you can tell for your application(s), then you are OK as far as the projectile mating to its surrounding throat. As you shoot, the throat will get longer because of the elongation of the freebore portion of the throat. The leade will conform to the projectile from now on once the throat is broken in. Keeping the throat concentric is the brass' objective as the throat elongates. This is why you never want to index your rounds, most especially after the throat is broken in, indicating perfect match of projectile with throat. Indexing causes the expansion of the circumference emphasizing throating error. A new barrel should have no freebore, just leade. The projectile bearing length should be within the neck entirely. Therefore, you need a longer neck for a longer projectile. When the freebore is increased by shooting, the projectile is seated out until it runs out of neck. Usually, the accuracy falls off too much before there is no more neck length left to hold the same projectile. ... felix

This is a very involved subject that amounts to other circumstances of the gun. Meaning that you have to pretty much live with what you have unless you are short. Then you can do anything you want.

There are so many theories on throating and even more realities. Every gun wheres differently for a whole host of reasons. But the hole purpose of a throat is as a bore guide for the slug. So if you go by the purpose, then it is easier to figure out what you want. So this is why some of this differes from Felix's position.

Still, you can pretty much fit up anything, so what I find more critical is the leade angle. The greater the angle on a side, the more a bullet is delayed during the engrave process. The longer the delay, the higher the pressure. And that can tip a slug and ruin alignment if a slug isn't fully supported by steel. Or it can deform the base if a bullet has air holes in it somewhere.

If you are trying to correlate freebore length to accuracy, I think you will be disappointed unless you look at benchrest class outfits.

The more sloping the case body and shoulder, the shorter the neck, the more overbore the case capacity, the longer the freebore will wear until it stabilizes. 22-250 is a prime example.

The REAL accuracy damage comes from muzzle pressure though. So the more over bore the higher muzzle pressure. The shorter the barrel, the shorter it's accurate life. Higher muzzle pressure will erode the steel in that area eventually creating a blunderbuss set-up. Cut off the worn muzzle portion and re-crown and the accuracy of that barrel will return to 98% of it's former level.

And looking at a throat won't show you the microscopic cracking that takes place from heat and powder impact. And they will look shiny. On the plus side, a worn throat usually amounts to a worn leade angle that generally improves cast performance.

You don't "need" a long freebore if you have a tight enough case neck. But I don't like relying on creating or trusting brass uniformity for alignment. I prefer steel to perform this task as long as I can still reach the leade with the lightest bullet weight I want to use.

in my experience, i usually take a bullet and measure (in the case of the 22-250) .225" up from the bottom and make a mark. .309 for 30 cals etc. If I can finger seat the boolit and the rifling push it in past that mark, I set my length for that distance -.003". That leaves me sitting my bullet .003 off the lands wich is where I typically get the best accuracy. I do not for any reason in a hunting rifle allow my seating depth to be less than the diamater of the bullet. In the case of the ruger's long throat, i usually seat out until i hit my bullet diamater or my magazine wont allow me to go longer. Not scientific, but works.

Also for rugers, allow around 10 minutes between shots. Watch em tighten up!!

FWIW, I get zero leading in my factory 21SF Glock barrel. Did you try that one first?

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Originally Posted by chris in va

FWIW, I get zero leading in my factory 21SF Glock barrel. Did you try that one first?

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I appreciate the feedback, and the Glock bbl has had some lead thru it. However, there are some differences in our programs. I am shooting a Glock 20, which, while the handle would be identical (OK, mine's not an SF, but otherwise...) is what I refer to as a high intensity cartridge. Everyone here will say fit is king, and I acknowledge that, but I think the pressure of the cartridge involved also plays a part. The 10MM (and sometimes 40S&W) loads I shoot have considerably more pressure than the .45ACP loads you use.
All that said, the Glock bbl WILL shoot without leading, if you do things right. The aftermarket bbl I referred to has a comp on it, and is just one reason it is in use instead of the stock Glock bbl. It still burns me that the aftermarket bbl has no leade in it at all. There should be a taper of the rifling at the business end of the chamber.
The throat was the reason for my post, not leading or lack thereof. It's good to know the stock .45ACP Glock bbls work well, tho! :Fire:

Pistol- Seating a lead bullet to touch the rifling will reduce end play making a more accurate round for shooting Bullseye slow fire. You must measure, as different alloys move the shoulder on a lswc. There is a very fine line between go and no go. Rifles- Centering the round in the chamber is whats important, the jump to the lands is over rated in most rifles as being important using J bullets. For cast, get a mould that has a bore riding type, big/heavy/long works. Don't overlook sizing only 1/2 of the neck with bushing dies or Lee Collet die. [IMG]http://i338.photobucket.com/albums/n...47inch_001.jpg[/IMG]