Common sense tells me that for best accuracy the chamber reamer, brass and reloading dies should all be cut to provide the best fit.What is the best way to accomplish this? Start with the dies, full length size the chosen brass and send a sample of this to the reamer maker? Not wanting a tight neck chamber that requires neck turning, but the most accurate set up short of that.Thanks for any guidance.Frank.
Within reason, the chamber dimensions are not that critical to accuracy except in certain areas. I'm speaking of accuracy expectations at around the 3/8 moa level. One area that is quite critical is the throat. The throat should be parallel and not more than .0005" over nominal bullet diameter. The angle in should be between 1.5 and 3 degrees. The length should be suited to the bullet Apart from that it is beneficial from a brass life standpoint to have the chamber made so it is about .001-2" larger at the base than the FL sizer. If the neck has .004" diametric clearance, I'm happy. The really important thing is not the dimensions of the chamber but it's alignment in relation to the bore and the relation of the bore to the receiver. A sizing die that reduces neck diameter to -.010 then expands it back up to -.003 is likely to produce crooked brass and ammunition. The best chamber won't be likely to compensate for this. Regards, Bill.
The only other thing I've found out that adds to the centering of the case is the base diameter clearance, this should be no more than .001 -.002" larger than the case. Some chambers are cut with up to .004 .005" clearance there. Dave Kiff at Pacific Tool and Gauge told me this. Your die reamer should be made accordingly in the area and the shoulder diameter is usually .003 - .004" larger.
Cutting the chambers body, neck and throat all ground on the same reamer will insure a concentric neck and throat to the body as well, no guarantee with a seperate neck and throater reamer, although they can be done concentric, just more room for error.
My method would be to use a freshly sharpened reamer and then use a Redding Competition bushing neck sizer. With the bushing kit you can change your die in .001inch increments until you get the exact size you need for your chamber. While your at it get the Competition seater which will allow you to quickly adjust the seating die .001in with almost zero effort. I use the Competition set for my 308 Target rifle and notice a difference compared to using premium ammo.
Posts: 593 | Location: My computer. | Registered: 28 November 2001
Mr.Leeper, where the heck were you when I needed guidance? Might have helped if I asked right! Actually I just finished my latest project using your ideas. I built a modified .300ultramag, shortened the freebore by .060" for use with Nosler partition golds, had the neck diameter changed to .338 due to the fact I neck turn rem brass to eliminate the vairance in neck thickness. First rifle I've done all the machine work myself, looks like a good 3/8" rifle with the limited testing I've done so far.
Why is it that I have to lower my powder charges by 4 grains on max loads, but still get the higher velocities? Dave Manson (Manson Reamers) warned me about this, and it shows up true to his word. Does the shorter freebore raise the pressure?
aj300mag, I find it interesting your getting the results from your ultra that follows my finding in a 270 win. I have a short throat, tight neck clearance (.003 on a win factory Round)26" barrel that gives me ~3000 fps with 56.5gr R22 and a 130 gr Hornady sp. I`m finding this to be a most informative thread and will be watching for replys to your question.
Posts: 2535 | Location: Michigan | Registered: 20 January 2001
AJ300MAG, what OAL are you loading your Ultra to? I'm seating my 180gr Ballistic Silvertips out to 3.710" where they are .050" off the lands.
My 30/338 Lapua 40 degree Imp. reamer was designed, throat wise, for the 180 too. It should be done this week.
The bullet momentarily stops when it hits the rifling from the primer going off, this length becomes the effective case capacity. The shorter the throat, the more bullet in the case at land contact, less effective capacity and higher pressure.
One approach that some of the 1000 yard benchrest and extreme longrange shooters are taking is to spec the reamer from the f.l. die. This has worked good by having the chamber reamer made to be .003/.004 LARGER than the die. Most of us prefer bushing neck dies and we turn necks, of course. Another route that works is to have the die made after the chamber is complete, die made to suit fired cases. That is expensive, though. Others just buy a die reamer based on the chamber reamer. These concepts require some advanced techniques and experience in several areas. Your milage may vary.
Posts: 275 | Location: NW USA | Registered: 27 May 2001
Brent, I checked my chamber with 180g Balistic Tips, at 3.695" the bullet is against the lands. That lenght is the max that will fit the magazine. Be interesting to see how your 30/338 shoots.
A shorter throat will usually result in higher pressures and velocities. Lengthen the throat and pressures will drop as will velocities. Increase the powder charge and you will regain the same velocity at the same pressure levels you had with the short throat. Jay mentioned using the dimensions of the FL die to spec the reamer and that is a good idea. As I said I like to have the reamer about .002 larger than the fl die. In use then the FL die will really just barely size the brass. This is not ideal for a hunting rifle perhaps but great for a target rifle. Regards, Bill.
