Chamber Throats, My Tirade On Subject

A Difference In Chamber Throats You Can See.... very important!

And you CAN see the difference!

No, not just "very important." It is crucial.... and very simple. DO take a few minutes and follow the steps described further down.

I get a lot of comments about what I write is "over my head," meaning over the reader's head. But it is all very, very simple IF explained in simple steps and in simple terms. It is above and beyond what the slick finish magazines pander all the time, and, frankly, it is totally ignored to the point it makes me wonder if in fact, the established industry does not want you to know what is inside the barrel.

Those of you who have had me do rechamber work recently or have gotten one of my custom barrels should take a hard look at the throat area. Use cheaters if you have to... like I do as the eyes get older.

Look closely at the ends of the rifling as your first focal point, then look back closer to you between the end of the chamber neck which will be the pronounced dark ring behind the rifling. In this area in between, you will see the rifling is cut away and you will also then see a smooth hole.... with no rifling..... blending in with the grooves of the barrel.

You may see a very faint line in the groove area connecting the ends of the rifling. This is where the throat reamer stopped and will only appear IF the groove diameter is smaller than the throat reamer. Otherwise, the throat reamer will only cut away the rifling.

F there is a line at all connecting the ends of the rifling, the degree to which it appears absolutely uniform in width indicates how well the throat is centered in the bore/grooves.

What you don't want to find:

Case in point and noted with a factory .308 Win. barrel I only cut a rim counterbore in the end of ... meaning no chamber work done....that I shipped yesterday. You can plainly see that this line between the ends of the rifling in this factory chamber was markedly deeper/wider at 5 o'clock and 180 degrees opposite this it was markedly thinner, fainter.

Experientially..... there is a big percentage of barrels with throats off-center substantially that still can be made to shoot satisfactorily. BUT.... when you plunk your money down, what do you prefer? Luck? Or something done right with the best chance the barrel will do what you want it to do?

I have proven thousands of times over that a minimal diameter throat centered with the bore does what it is supposed to do. And what is that, exactly?

The throat should be thought of exactly for what it is. It is, in FACT, a forming die that takes that "perfectly" made bullet made in ultra-precise expensive bullet forming dies in the pretty green, black, red, yellow, or whatever color box and gives it its final forming operation before it travels out the barrel.

It is in the throat that the bullet takes on its final shape as it enters the rifling, and the degree to which the bullet enters the rifling canted, cockeyed, off-axis, or whatever term you can relate to it is reformed out of balance. Its shape and center of mass are no longer concentric.

Bullets spin at tremendous revolutions per minute. A carpenter's router, for example, spins at about 30,000 rpm. Most car engines are redlined at something around a measly 8,000 rpm. Bullets on the other hand spin so fast that in the case of thin jacketed bullets at extremely high velocity, their centrifugal force will literally make them fly apart in mid-air before they even reach the target.

The RPMs can often exceed 200,000 rpm. Take the two .220 Swift rechambers I just did in factory Encore barrels. The factory still uses, I presume, 1-12" twist .22 CF barrel blanks. So for every foot the bullet travels, it makes one rotation. If the velocity is 4,000 feet per second, which it typically is with a Swift, then the bullet is rotating 4000 times EVERY SECOND! NOT MINUTE. Multiply this out, and it comes out to 240,000 RPMs!

Can you see better now why it is so vitally important to keep a bullet in balance? And why the emphasis on the throat?

Barrel harmonics are another issue of course, but so far as what can be accomplished with the chamber, specifically the throat, the better the throat, the better the chance for accuracy.

Yet, unfortunately, the industry at large screws this up royally from SAAMI right down through their minions that grind chamber reamers and tell the factories how to chamber barrels. Thus, you see some really bastard things come out of the factories in general. Maybe it is because I am so close to TC barrels, but in all my years doing custom rifle work and TC barrel work, it appears TC has been one of the worst about blindly swallowing some of the idiocy that comes from SAAMI.

The list of pure junk chambers is probably longer than the list of good ones so far as throat design and tolerances are concerned.

Look at what I do.

Look at what TC or other aftermarket shops do.


YOU CAN READILY see the difference!

"Co-Axial Throating." That is what I call my throating procedure. All it means is that the throat is lined up with the bore

What a novel idea?

Wonder why someone else in higher places with better technology hadn't thought of it? And if they have, then shame on them for not providing it to you in every barrel you buy!

My fist is sore from pounding the pulpit. :-o Sermon over.

Go in peace.

Mike Bellm

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