Choosing Throat Angle for 338-06 Improved

[Duvel]

Hi guys!
I'm in need of some advice. I just had new Winchester 70 rebarreled to 338-06 Improved. Well, when I started to put some fire forming/barrel break-in loads together, I came to realize that there is virtually no throat in this rifle. I have to seat bullets ridiculously short to even get the round to chamber. Instead of sending the gun off to have my smith lengthen throat(which means a bit of a wait), I am going to order a Uni-Throater from Pacific Tool & Gauge. The problem here is that I have to specify what throat angle I want, and since I am no expert by any means, I need your advice on what is the best choice. Being that this rifle is mainly going to be used for plains game, I plan on using several different bullet types. However I do plan to shoot lots of smaller game at medium ranges with the 250gr Sierra Gamekings AND Matchkings(they have their time and place). So lets just assume I want a throat cut for Matchings and extreme accuracy. I know I could just call PT&G and ask Dave, but I'm particularly interested in the wealth of knowledge you guys have to offer. Also, please specify if you are stating the cone angle of the throat or cone angle/2. Thanks again!

Cody

 

[B23]

You are absolutely correct, there is a wealth of knowledge on this forum but I certainly wouldn't pass, on any recommendation Dave Kiff gave you. He's a pretty sharp cat and knows his stuff. I'm pretty sure if you tell Dave all your particulars he will give you very sound advice. Best of luck to you with your new build.

 

[Duvel]

I agree with you 100%. Dave is a prince of a guy and I never take his advice lightly. I've never really looked into the subject of throat angles until now. I usually just supply a dummy round to the smith and he does the rest. This time I was overseas and was unable to get a dummy made up for him. Its interesting to think about the affect the throat angle would have on accuracy and throat life. Your right though, I should probably just give Dave a call and listen to what he has to say on the subject. He makes things too easy, yawn.... Thanks for the reply!

Cody

 

[Kevin Cram]

I use PTG uni-throaters to custom throat to a particular throat length and I typically run a 1 1/2 degree lead angle. I wouldn't hesitate to call Dave either though. I'm pretty sure you'll get the same angle.

 

[J E Custom]

Hi guys!
I'm in need of some advice. I just had new Winchester 70 rebarreled to 338-06 Improved. Well, when I started to put some fire forming/barrel break-in loads together, I came to realize that there is virtually no throat in this rifle. I have to seat bullets ridiculously short to even get the round to chamber. Instead of sending the gun off to have my smith lengthen throat(which means a bit of a wait), I am going to order a Uni-Throater from Pacific Tool & Gauge. The problem here is that I have to specify what throat angle I want, and since I am no expert by any means, I need your advice on what is the best choice. Being that this rifle is mainly going to be used for plains game, I plan on using several different bullet types. However I do plan to shoot lots of smaller game at medium ranges with the 250gr Sierra Gamekings AND Matchkings(they have their time and place). So lets just assume I want a throat cut for Matchings and extreme accuracy. I know I could just call PT&G and ask Dave, but I'm particularly interested in the wealth of knowledge you guys have to offer. Also, please specify if you are stating the cone angle of the throat or cone angle/2. Thanks again!

Cody

You should have about .226 free bore @.338 diameter and .189 length of cone to .330 diameter
(about 1.22 o) or very close for the 338/06.

Your smith may have short throated your chamber. I allways recomend a standard SAMMI chamber
for best results all round.

I have seen a few chambers that had no throat at all and pressures were the reason they were
brought to me to re chamber.

J E CUSTOM

 

[shortgrass]

Any chamber not cut to SAAMI specs should be marked with the variances, some how. We're liable to see lots of "interesting" stuff in the next few years, as rifles change hands but the important info doesn't. I see pleanty of barrels now with no makers (gunsmiths') name, town & state. If that's there (as it should be!) you can hopefully contact the maker for info.

 

[Duvel]

Pac-Nor actually did the work on this one for me. Chris has always done a great job so no complaints there. Its just my fault for assuming the chamber would have SOME throat to it. Oh well, live and learn. I'll give PTG a call tomorrow and get the throater ordered. Thanks alot for the help guys.

Cody

 

[Bullet bumper]

The exact angle depends on the freebore diameter which could vary from .338 to .340 in some cases.
At 338 x .189 x .330 = 1.2124 degrees , half angle .
At .340 x .189 x .330 = 1.5154 degrees , half angle.
It changes significantly with just a small change in freebore diameter .
I would be surprised if the chamber freebore diameter is right on .338 . They usually have some slight bullet clearance but not always .
How much freebore you need depends on the shape of the bullet you are using and how much you want to seat it in or out of the neck of the case.
I would make up a dummy bullet with the bullet you want , seated where you want and take measurments from that . Also you need to know what diameter the freebore if any is . The bore will be close to .330 but that may vary also.
With the exact diameter of freebore and bore and the length of the throat an exact throat angle can be calculated. If you play around with a few different bullets you may be able to settle on a good compromise length that allows seating of several ogive shapes on the lands that you may use by just seating more or less into the case neck . The limitation is usually the limited shank length of long ogive boat taill bullets .

 

[Duvel]

Thanks a bunch Bullet Bumper! The figures you have given puts me on the right track. So I assume the free bore diameter will be dictated by the throating reamer... Correct?

 

[Bullet bumper]

Well in this case that depends on wether the throating reamer is larger than what you have now in the chamber end. If you have say a parallel .340 now but the free bore part of the reamer is only .338 then you could get a slight edge at the start of the throat . You really need to know exactly what dimentions you have now in the chamber and stay with the freebore diameter you have , so the reamer just polishes the diameter you have but not increasing the diameter by any real amount . It would not hurt much if it was say .338 now and the reamer scraped it to .339 but if it is already .340 now then you don't want it any larger . I would make a Cerrosafe cast of the chamber and measure that . Even if there is no real freebore there now , I don't really know , it gives you the diameters at the end of the chamber to know what you are working with . Then you can decide on the reamer diameter you need .

 

[Duvel]

Just received a copy of the reamer print used to chamber my rifle. It has a whopping .016" of free bore at a diameter of .3385". No wonder! At least I have some good figures to give Dave Kiff. Thanks for all the help!

 

[Edd]

I found this old thread while searching for information on a 338-06.

I am planning on having one built and had intended to go with a standard 338-06 A-Square SAAMI reamer. When I looked at the reamer specs, I was a little surprised at the freebore specs. It is larger in diameter and longer that I think it needs to be.

Does anyone know why a 338-06 would need more freebore than a 338 RUM?

 

[J E Custom]

In My opinion, The free bore should not be more than .001 to .002 larger than the bullet.
throat length depends on the cartridge but should be generous if hot loads are intended for
it. Lead angle should be somewhere around 1''5'o to 2"0'o ( most are 1"22' to 1"30'o

SAMME specifications are intended for loads of many different sizes (Factory) and safety. but .016
is way to big and I suspect the reamer was not spec. correctly, or just a bad reamer.

This Link is a 338/06 A Square and would be about the right dimensions for the 338/06 in my opinion.

http://www.saami.org/PubResources/CC_Drawings/Rifle/338-06 A-Square.pdf

Maybe this will help with your get the correct chamber dimensions.

J E CUSTOM

 

[Edd]

That A-Square SAAMI drawing was the one I was looking at, the one I didn't like.

I found this non-SAAMI non-A Square one that makes a lot more sense to me.