Throats, Good, Bad, Ugly?

[flmason]

Can someone explain to me the basics or thoats and/or what makes one good, bad or indifferent? Why and when you might ream one, etc.? Or point me to some good info on it?

Have to admit, years ago I never heard or read much about the topic... so I don't much of an understanding of the issues.

As regards Handi's (45-70 at the moment), what is know about them?

[thejanitor]

I believe the throat on the Handi is a little short if you want to shoot heavy cast bullets.(45-70)
on the 38-55 I believe the bore is slightly off to the chamber size so to shoot a bullet that fits that bore it is actually .382 (mine) so to get an accurate round you may want to run a reamer in so you can use bullets to fit and fill the rifling properly.
And when people ream the .357 mag  to Max the new taper in the throat is said to improve accuracy in .38 spec   .357 mag   and the maximum.
If I misunderstood the topic I am sorry,    thejanitor

[nanuk-O-dah-Nort]

I believe the term "Throat" is used in different context by different persons.

I consider Throad to be the area from the end of the chamber neck, to the minimum bore diameter.

this includes the freebore, and leade.

freebore being a parallel sided cylinder, leade being the tapered portion from Max diameter to Min diameter.

but that is just me...

now, as for Good throats?   they and your bullet need to match up near perfect for best accuracy.
but they can vary in shape/design depending on what you want accomplished.

Weatherby used  a long freebore to reduce chamber pressure, as does the military 5.56.

whereas some target rifles have throats cut to match the specific bullet you plan on shooting.

[quickdtoo]

Most H&R 45-70 barrels made prior to 2008 had short throat depth and the reason for throating, starting around 2008 from those I own they seem to have corrected that issue, both my 2008 SS Ultra and 2011 Talo Trapper have decent throat depth so bullets bigger than 350gr can be seated to book specification. The one advantage of throating is it creates a gradual tapered leade instead of the abrupt start of the lands, very evident in the case of the 357 Mag to Maxi rechamber when a PTG rifle reamer is used that cuts that leade even tho the throat is already deep.

Tim

[gcrank1]

Think of the chamber, it is of the shape of the case. At the mouth of the case is (should be) the reduced dia. to the bullet dia., this 'ball seat' or throat ( ball meaning bullet) carries forward to the origin of rifling where a transition (hopefully) is made in varying angles per the bullet design intended to be used. The length overall of this from the case mouth to the rifling is also intended for a certain (match rifles) or several popular and common (hunting) bullet designs (a compromise to fit many).
Now some cartridges have better designed chambers than others. Some have no apparent reduction in dia. from the outer case mouth wall to the bullet dia. inside that neck. When it gets launched out of there it is unsupported, gas can get around it and it slams into (sometimes) basically the almost squared off origin of the rifling. Not exactly optimum, that! This is all before it even gets into the bore to run on down and out........If it doesnt start good right there on launch it isnt going to improve downbore. It is probably a wonder we get ANY kind of accuracy given the poorly designed and executed chambers many guns have. But we do, and this is what we do, ring one out for what it can do and give it (pun intended) our best shot.
Have Fun 

[quickdtoo]

Bullet runout is an aspect of accuracy that is very important when it comes to the 45-70, as GC stated, how the bullet starts out is very important, short/fat 45-70 bullets aren't easy to seat straight, very evident when you can see a bulge on one side of the case where the base of the bullet is seated cockeyed, insuring the bullet is seated with .003" or less runout will be a big step in making an accurate round.

Tim

[flmason]

Sounds like we have at least two problem cases...

1) Rifling starts too close to the bullet. Not sure why that's a problem since I thought I've read that bench rest shooters try to do exactly that... seat the bullet out almost, but not quite to the rifling. On the other hand... if it *prevents* seating the round, that's a definite problem.

2) The Leade is too large permitting blow by gas cutting and/or erratic paths to the rifling. Sounds like it should ideally be exactly or minimally larger that bullet diameter, and only long enough to allow the round to seat fully?

Sounds a bit like we'd want the rifling to taper in smoothly also?

[gcrank1]

Depending upon the actual 'curve' of the bullet nose (the ogive) it may or may not fit when seated to the crimp groove, but sgl shots often dont need to be so located as they do in a repeater that must feed cartridges of a given length. My HB Lee 405 chambers up fine.
The throat dia. to SAAMI specs does have some +/- as does the chamber reamer from new to resharpened. One may be 'close chambered' , more like a match chamber and another more loose as in a 'field chamber'. The nice thing about lead bullets is you match the bullet dia. to your gun and the nature of softish lead is it bumps up and conforms to the throat to create the seal if it is reasonably close to the throat dia.
There are differing opinions on the exact 'best' angle for the transition, and likely the truth is that if it is sorta close to right, exactly this or that angle doesnt matter so much. Some guys have messed about with different throats, C.E.Harris for instance when at Ruger and after, and have preferences due to that great experience. If you ever want to do likewise the info is out there.

[nanuk-O-dah-Nort]

most of the shooters who strive for ittybitty groups with cast, suggest a perfect fit of bullet in the throat, from case end, to bore diameter, with little bullet freewheeling out there with no support.

lined up straight, pushed slow and accelerated gentle, and fully supported down the bore, gives you the best shot at accuracy