I need wisdom on how to throat a barrel the old way.

[goodsteel]

I have in mind to make a rifle of .375 or larger caliber with the express purpose of shooting paper patch boolits with smokless powder.
I prefer to make my own reamers for cutting chambers because sometimes I cant resist the urge to tweak the cartridge into a wildcat (ie. I like being able to control every aspect of the chamber.) that, and in my specific situation, it is a lot cheaper to make the reamers than to buy them.
The only problem is that I have no knowledge of throat angles or how gently the rifling should lead into the projectile.
Is it better to have a long barely noticeable lead?
Should I keep it fairly abrupt?
Can it be too long?
What were the characteristics of the old sharps, trap door, or rolling block rifle's throats?
Any answers to any of these questions, even if its just conventional wisdom, would be appreciated.

[Frank46]

From what little I have read you should have the throater cut .002 over bore diameter with a 1.5 degree lead. Check out the PTG web site to see what they say. Hope this helps. Frank

[goodsteel]

checked out ptg, not much help, but it did remind me of why I make my own reamers.
Frankly, I am surprised that there is not more information on this subject. I would think that picky target shooters would be weighing in saying that it has to be this way or that. I mean realy? nobody knows?

[felix]

I don't know. But, I do know BR reamers are built with the pilot out in front of the neck portion. ... felix

[goodsteel]

I pilot my reamers as well, its just too easy to get 'em off center when you are busting through button rifling. Actualy, grinding the pilot is the easy part, hand stoning the relief on all the cutting edges is what gets the sweat dripping off my nose.

[Casting Timmy]

Recently I was reading gunsmithing Kinks II and it was talking about the angle for a revolver barrel. It said that cutting the barrel angle at 11 degrees was better for cast bullets, I have no clue what's best for rifles though.

I guess my suggestion would be doing a little extra searching to try and find out what's the best for cast bullets, as it could be a little different than current angles.

I think you;re on the right track with trying to find out about the old trap doors and sharps angles.

[largom]

Not a BR shooter but I have followed their technic's for several years. Most say a gentle leade of 1.0 to 1.5 is best. I would go with Frank on the .002 over bore Dia. for the throat. You could also determine the boolit you want to use, acquire the mold, and grind the reamer throat to fit your boolit.

Larry

[Mk42gunner]

I don't know the correct answer, but I do recall that one of the main Sharps replica makers had some problems when they tried to use a very gentle angle for paper patch throats.

Since you make your own reamers, what about starting with a short angled lead, then gradually working your way out a degree or so at a time? The potential problem I see with a shallow angle is the boolit getting off centered during accelerationonce the neck expands but before it is gripped by the rifling, make sense?

While Trapdoors are from the paper patch era, I don't think the US Gov't issued paper patched rounds, so that might not work so well.

Robert

[405]

Just about every old, original BPCR throat and leade I've looked at appears to be fairly long, continuous taper beginning at the chamber neck and extending into the bore- (probably the simplest to ream). In effect a single taper with no distinct throat or distinct leade. I also don't know if back in the BPCR era most, some or any makers made a specific distinction between or compensated for the throats or leades when chambering a rifle for either conventional grease groove or paper patched bullets. I would imagine some did experimentally or by special order. They likely just chamber reamed for one size fits all as both types of ammo was available and used simultaneously.

The best luck I've had with paper patched bullets is with a conventional two-step throat and leade with a fairly short throat and a more or less "standard" leade angle as is found in the modern C Sharps chamber. I shoot a tapered, swaged PP bullet with the final PP diameter about .002-.003" larger than bore diameter so when chambered/seated the forward part of the bullet's paper patched ogive-shank transition lightly engraves into the lands for bullet support and minimal runout.

[Cap'n Morgan]

I would grind the reamer to exact bore size. No point in bumping the boolit to oversize and then swage it down again - 0.002" over bore size is probably okay for jacketed bullets, but unless you want a free bore section I don't see any reason to go larger than bore.

[405]

I would grind the reamer to exact bore size. No point in bumping the boolit to oversize and then swage it down again - 0.002" over bore size is probably okay for jacketed bullets, but unless you want a free bore section I don't see any reason to go larger than bore.

If that is done there wouldn't be any throat- only a relatively short, angled leade. Then seems like, depending on bullet nose style and dimensions, most or all of the bullet shank plus some of the nose section would have to be inside the case neck in order to fully chamber the round. Are you talking "bore" diameter or "groove" diameter of the bore? By definition, the throat section of a chamber IS the free bore and the leade section is simply the entry part of the lands that has been angled to ease the bullet transition during its travel between the case and full land engagement in the bore upon firing. Guess I'm a little confused.

[goodsteel]

Don't feel bad, everybody is confused on this subject.:veryconfu:D


Since you make your own reamers, what about starting with a short angled lead, then gradually working your way out a degree or so at a time?
The problem with that idea is that, unless I get lucky, I will answer my question here by scrapping a barrel. That's a very expensive way to find out what somebody else might already know. It might be my only alternative though because most folks in this day never worry about the design of the breech. I could write a book on info about headspacing, but what about all the other dimensions that the reamer controls? Its true that a few of them dont matter, like body angle, shoulder diameter, and shoulder angle. But everything else seems kind of important to me. Things like neck diameter, neck length, angle of transition from neck to throat, throat diameter (if it has one), throat length (if it has one) and finaly, the subject in question: lead angle. Maybe I am making a mountain out of a mole hill, but I figured that the lead is the last part of the breach to touch the boolit before it is fully engaged in the rifling and must be important.

I would grind the reamer to exact bore size. No point in bumping the boolit to oversize and then swage it down again - 0.002" over bore size is probably okay for jacketed bullets, but unless you want a free bore section I don't see any reason to go larger than bore.


Then seems like, depending on bullet nose style and dimensions, most or all of the bullet shank plus some of the nose section would have to be inside the case neck in order to fully chamber the round.
Great discussion here fellas! You're not just warm, you're hot! realy hot!

[B R Shooter]

Most off the shelf reamers come with a 1 1/2 degree leade, that is 3 degrees included. For lead bullets and paper patched, from what I know, they prefer a more gentle angle. I chambered a few barrels for cast bullet guys close to me, and I got a 1/2 degree INCLUDED throater. It's long, but they had a mold made to cast a bullet where the nose matched that angle. I would think a gentle leade angle would be best for cast.

The length of throat should be close to what your bullet needs, how much does it extend beyond the brass. Long throat and short bullet makes the bullet jump before engaging. Long bullet short throat and your jamming the case in, if you can get it in.

For jacketed bullets, the throat/leade is about .0005 to .001 over bullet diameter, usually. For cast, I would do the same, but it is relevant to the bullet, not the GROOVE diameter. In the case of a 30 caliber, the groove diameter is .308, but most cast bullets are sized to .310. The bullet will travel through the leade, so it has to have room. The idea is to have the bullet swage itself into the groove/bore, thus the tapered leade. If the leade diameter was groove diameter, the bullet would be swaged before it ever got to the rifling.

For paper patched, doesn't the bullet stay in the paper through the barrel then strip off? Your throat diameter would have to accommodate that I would think.

[Cap'n Morgan]

Yup! That's groove diameter, of course.

[303Guy]

... and I got a 1/2 degree INCLUDED throater. It's long, but they had a mold made to cast a bullet where the nose matched that angle.This would be my thinking. With a boolit with most of its length outside the case the chambered boolit can be fully supported in the throat for an accurate launch. I have one or two worn and rust damaged bores that chamber in this way. These fired boolits show no sign of slip or shear on the forward portion of the boolits (higher velocity boolits can't be captured intact so easily). The disadvantage of an oversized throat and boolit is the tendency for the 'swaged' base to form a cup which may or may not cause base edge irregularities and accuracy loss. A rebated boolit base seems to solve that problem.

A shallow tapered throat does seem to limit boolit weight selection as the boolit essencially seats up against the throat taper but on the other hand there is no undersize bore-ride nose section (assuming patching the nose to bore-ride).

The 1/2 degree include taper may not be optimum for paper patch because of the nose core section being a little under bore-size but I would think it to be a good idea for plain cast.

Just my thoughts.

[405]

Yup! That's groove diameter, of course.
Thanks! That makes much more sense. I was beginning to question my sanity :veryconfu

[goodsteel]

That's why its so hard to discuss these things! You have to learn the lingo before you can even carry on a conversation. The last time I started a thread dealing with this, I had to look up the term for every single part of the breech. Then I had to deal with the fact that most folks didn't know what I was talking about.:groner: I am thrilled that you guys have all got a good grasp of the internal workings of a rifle!!! There are so many users but so few makers.
Thanks for all the good discussion. It gives me many things to ponder on.

[Cap'n Morgan]

That's why its so hard to discuss these things! You have to learn the lingo before you can even carry on a conversation.

Then imagine what it's like when the conversation is held in a foreign language :shock: If it wasn't for The American Handgunner and Guns & Ammo, we who speak English as a second language would be totally lost. As an example; over here we don't use bore/groove size. The distance across the lands (felter) is the "kaliber" (caliber) To simplify the matter, grooves are named "riffelgange", twist is "stigning" and groove depth is "gængedybde" :veryconfu

[405]

Cap'n
Well said and understood.
I think for these type discussions the best method would utilize CAD images so everyone could see exactly the finer points about such as chambers, throats, leades, etc. Unfortunately, my antique computer along with my lack of ability with it prevent transferring or posting CADs. The devil is truly in the details and using a common "language" like CAD imagery would surely help communications- not just for those whose second language is English but for all who may use different terms for certain things.

[Casting Timmy]

Actually from reading all the posts, it might be best to draw it out.

Start with the bullet you want to shoot and knowing the throat will start your .002" larger and that you want a bullet jump of .03", see what the angle would be for that scenario. Then compare to what has been said for angles here. Of course you will have to change the dimensions above for what you really want, but that would also give you a good starting point to look at.

[leftiye]

That 1/2 degree leade may or may not work with boolits that don't have matching noses with the same taper. Though it probly is still better than a sharper leade angle (within reason). Though my guess would still be that less sharp angles are better, especially better than the really sharp angles. Original 45-70 chambers had no freebore, and maybe 45 degree leades (almost no leade). Some marlins and H&Rs are still this way.

Freebore cannot be too tight or as has been stated swaging can occur. Probly more to the possibility, the cartridge wouldn't go into the chamber and lock up. Freebore must be more than boolit diameter. - and then some to allow functioning if fouling is present. .001 is not much room for dirt.

[lmcollins]

Throats and leads very all over the map.

Get the SAAMI specs that are available on the web, and look at them. Newer cartridges like the 222 by Remington often have 3 degree included angle leads, and I don't remember the throat diamiter over groove diameter, but the newer the cartridge the less the throat diamiter is over bullet diameter.

If you think that I'm full of it take a look at the various 7MM rounds: Look at the old 7x57, and them compare it to the 7MM-08. The neck of the old 7x57 is like a funnel, and the early cartridges were loaded with 175 grain round nose bullets. In 1892 or 1895 it was even hard to produce a barrels of a consistant diameter: land and groove wise. I would imagine that bullet diamiters varied more than todays also.

I find the entire subject very interesting, and think that if I were ever to have a custom 7x57 made up it would only be with a reamer with its neck made straight, and throated with a separate throating reamer .001 over bullit diamiter (.285) to a loaded sample round of something like a 160 grain Nosler Partition. Or: I'd just have a reamer made up with the neck, throat, and lead as per the 7mm-08 Remington. I believe it has a 5 degree included angle.

Get the figures from the SAAMI reamer prints, and compare the neck diamater, throat diameter, throat length, and lead angles of the 7x57, 280 Rem, 7x08 Rem, and 7mm Rem Mag. Compare them all. Very interesting. Especially for a cast bullet shooter.

[B R Shooter]

SAAMI specs are all over the place. So many cartridges come from quite a few years ago, and were made "standard" for them. Things change. Uses change.

The whole idea of doing a custom chamber is to get what you want, not what was standard 50 years ago. In competition, it is very common to have a chamber tailored around a particular brand of brass, neck thickness and a specific bullet.

[calkar]

www.bellmtcs.com is a great read on this subject.

[Tokarev]

Goodsteel,

Why don't we take a look at the drawings of some famous barrels for the throat angle?
I have one example drawing on my workbench: 7.62x25TT barrel.
Its throat is a 0.0183" reduction in radius by an 2" arc.
Being math challenged, I can't tell you what angle it is.

[goodsteel]

Interesting, its a radius! I'll just bet that the best boolit for that rifle matches that radius. Thanks for the info buddy!

[B R Shooter]

In the "extreme" benchrest world, some are doing this, matching the throat to the bullet ogive. While it may have merit, I doubt it will last long, the wear will eventually bring the throat back to a straight taper, or something.

[HollowPoint]

Just yesterday I was measuring the dimensions of a new 303 British chamber reamer I bought from midway. I believe it's made by Pacific Tool.

Since I'm installing a new 30 caliber barrel to replace the original barrel I had to lap and re-sharpen the neck and throat sections of this reamer to work for what I had in mind.

I do recall that the area of the throat did have a .002 difference from the mouth of the neck to about 3/8" forward of the neck-mouth. (according to my digital calipers)

I never knew that it may have been possible for the throat to have a slight curve to it. If that was the case- on my reamer- it doesn't any more. It's just a straight .002" taper from back to front.

HollowPoint

[goodsteel]

I used a reamer for the last rifle I barreled and it was the same way, strait taper from bore diameter to groove diameter and no freebore at all.

[uscra112]

There was a good article by Ed Harris in American Rifleman, going back into the '70s I think. "Proper Throating is the Key to Accuracy". (Heaven knows where my copy is, or I'd scan it for you.) IIRC his position was that 2-3 degrees included angle was about right. For longer boolits, a straight section .001 over boolit diameter was recommended. He was, of course comparing to SAAMI throats for .30-06 / .308 / .30-30. Only the .308 met with approval, FWIW.
I don't see much advantage to a 1/2 degree included angle. That wouldn't be far from simply freeboring, nicht war?