Reamer dimensions
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Dave Tooley
Active member
What do you want to achieve by tightening up the reamer?
Dave
Dave
Dave Tooley
Active member
Yes I do tighten up reamer specs but only to accomplish a specific goal. It is very easy to blindly change numbers without knowing what the unintended consequences will be. I've learned that the $$$$ way. Tightening up the back of a reamer if taken to extremes can cause hard extraction and can render a FL sizing useless. I'm going ask this question again in an effort to make you think about the direction you're headed. What do you want to accomplish? Is there a problem or are you looking for a solution to a problem that doesn't exsist?
Dave
Dave
M
mike in co
Guest
talk to the reamer makers...they have seen it allll....
BTDT, does NOT work.
Understand what you're trying to do, it won't work.
I've tried to contain caseheads via tight chambers and tight boltfaces.
I've tried to reswage caseheads and primer pockets.
You CANNOT contain them.
Or fix them.
Concentricity is a function of fireforming, I currently have my reamers made FAT like .006 or more over the brass and concentricity is as good as it gets.
You ARE getting advice from people with longrange accuracy experience. I can't imagine anyone questioning Tooley's credentials, unless they don't compete long range??
al
Not quite a sentence.
In some respects, Al and his experience runs counter to others of us. But it is still experience.
Part 1: As far as case head expansion -- you cannot minimize any expansion of the case that is beyond the chamber -- there is no steel "containing" it. This is usually what is thought of as the "case head." But you can minimize expansion just ahead of the web, where the case is supported. Let's suppose you decide a chamber of .003 over body diameter is right. So, you measure a Lapua case, then buy Norma or RWS brass. Guess what -- they likely have slightly different body diameters, at least, for a number of cases. Norma 6PPC cases run about .003 smaller than Lapua .220 Russian cases. I've forgotten which is which, but Steve Shelp got Norma, Lapua, and RWS 6.5x55 cases. Differences in body diameter were significant.
So, buy your brass before ordering your reamer. Either mike it carefully, or if you cannot, send a case to the reamer manufacturer along with your wishes for clearance.
Part 2: As far as centering the bullet in the bore, read T.J. Jackson's article in Precision Shooting, October, 1985. Well, you don't have it to hand. Essentially, he proved, by shooting in the Houston Warehouse, that if the case necks were true to the bore centerline, and the case head was square to the bore (really, the boltface, which better be 90 degrees true to the bore), the rest of the case was irrelevant. Now most of us can't machine a case like T.J. did, but it does show that excessively tight chambers aren't the answer, good necks are -- and square case heads.
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Dave Tooley
Active member
Powers
Once brass is fire formed to the chamber the majority of concentricity issues come from the dies with some influence from the brass itself. Tight chambers have nothing to do the concentricity of a loaded round. If your depending on the chamber to straighten your loaded ammo you got other issues to address.
In order of importance
1. there has to be enough clearence between the brass and the chamber dimensions. .003" is bare bones minimum
2. Fl sizing die has to be matched to the chamber dimensions.
The closer the chamber diameter is to the brass diameter the more difficult it is to get a commercial sizing die to work. Most of the time I order a finish and resize reamer together. A matched pair and make my own sizing dies.
One more thing that doesn't work. Don't expect a sizing die to work if you have to size the brass down smaller than when it was made to get it in and out of the rifle.
Dave
Once brass is fire formed to the chamber the majority of concentricity issues come from the dies with some influence from the brass itself. Tight chambers have nothing to do the concentricity of a loaded round. If your depending on the chamber to straighten your loaded ammo you got other issues to address.
In order of importance
1. there has to be enough clearence between the brass and the chamber dimensions. .003" is bare bones minimum
2. Fl sizing die has to be matched to the chamber dimensions.
The closer the chamber diameter is to the brass diameter the more difficult it is to get a commercial sizing die to work. Most of the time I order a finish and resize reamer together. A matched pair and make my own sizing dies.
One more thing that doesn't work. Don't expect a sizing die to work if you have to size the brass down smaller than when it was made to get it in and out of the rifle.
Dave
JerrySharrett
Senile Member
Am I confused, or what?
Powers, are you thinking about tightening up the "headspace" dimension of a belted cartridge belt? Some people still consider the belt on a belted magnum as the principal headspace control. If this is your thinking, headspace to the case shoulder not the belt.
Powers, are you thinking about tightening up the "headspace" dimension of a belted cartridge belt? Some people still consider the belt on a belted magnum as the principal headspace control. If this is your thinking, headspace to the case shoulder not the belt.
Jerry, I disagree with you on that. Years ago Rick Picceretta showed me how to avoid head seperation, which you'd get if you headspace off a shoulder, which I was getting. If you headspace off the belt it works much better. I haven't had the problem since. This is with a 308 Baer.
JerrySharrett
Senile Member
Joe, if you are headspacing purely off the case belt and the shoulder happens to be bumped back too far, say 0.010" or more, you for sure will get case separation.
I don't know what method you and Rick Picceretta use but I'm certain the case shoulder is still in contact or very near contact with the chamber shoulder if that method fixed your case head separation problem..
G
Greg Culpepper
Guest
Hi Jerry,
I think Joe and Rick are right about this.
Headspacing off the belt keeps the head of the case against the bolt regardless of the space between the case shoulder and the chamber. As you are well aware, the technique of headspacing belted cases off the shoulder can overcome sloppy belt controlled headspace which is almost universal in production rifles. Factories use very liberal belted case clearances so customers can get any ammo in their rifles. Just like non-belted cases only worse. After all , you can crush a slightly long shoulder with the bolt but you aren't going to crush an interfering belt.
There is a lot of variance in head to belt dimensions on brass. A custom chamber can be fitted to the belt on the brass you intend to use. Headspace can be controlled by the belt and the striker can't push the case head forward to produce the case stretch that results in case separation. If the shoulder gets bumped back too far, it just blows forward as it would in blowing out a wildcat only much less. You can, and most people do ignore the belt and just headspace of the shoulder, but the belt is also available for this purpose. This approach eliminates any necessity to create a false shoulder on the case neck to prevent case stretch on the first shot on a virgin case. The limitation of this approach is that you can manipulate the shoulder of a case anywhere you want but the head to belt dimension of a case can not be so easily manipulated. So if you change brass on a belted chamber, who knows.
My 308 Norma mags are chambered by Mark King with a reamer that he got from Rick. I use only Norma brass. It works good for me.
Greg
I think Joe and Rick are right about this.
Headspacing off the belt keeps the head of the case against the bolt regardless of the space between the case shoulder and the chamber. As you are well aware, the technique of headspacing belted cases off the shoulder can overcome sloppy belt controlled headspace which is almost universal in production rifles. Factories use very liberal belted case clearances so customers can get any ammo in their rifles. Just like non-belted cases only worse. After all , you can crush a slightly long shoulder with the bolt but you aren't going to crush an interfering belt.
There is a lot of variance in head to belt dimensions on brass. A custom chamber can be fitted to the belt on the brass you intend to use. Headspace can be controlled by the belt and the striker can't push the case head forward to produce the case stretch that results in case separation. If the shoulder gets bumped back too far, it just blows forward as it would in blowing out a wildcat only much less. You can, and most people do ignore the belt and just headspace of the shoulder, but the belt is also available for this purpose. This approach eliminates any necessity to create a false shoulder on the case neck to prevent case stretch on the first shot on a virgin case. The limitation of this approach is that you can manipulate the shoulder of a case anywhere you want but the head to belt dimension of a case can not be so easily manipulated. So if you change brass on a belted chamber, who knows.
My 308 Norma mags are chambered by Mark King with a reamer that he got from Rick. I use only Norma brass. It works good for me.
Greg
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JerrySharrett
Senile Member
Greg and Joe, you guys are in a unique situation. The way you are using the belt on controlled tolerance brass will work but generally on run-of-the-mill belted cased with excessive shoulder setback can cause case separation just ahead of the belt. And, the belt will work for blowing cases out the first time but I'll bet you don't set shoulders back over 0.002" even on your application.
Come on Jerry, this is still Benchrest Central. Anybody shooting a belted case in *benchrest* should have a custom chambering reamer, and custom dies to match that reamer.
Ideally, the reamer is based on the particular brass, so if the manufacturer has the shoulder .015 shorter than SAAMI for his cases, so what? You have a reamer ground to fit. But if you have to blow the shoulder forward once, that's not too bad. Just so you don't have to do it for every reload (or twice, whichever comes first).
Headspacing off the belt isn't so bad an idea, if the belt/case head dimension is constant. When I "headspace off the shoulder" with a sharp-shouldered case, it is obvious that the body/shoulder junction is doing all the work. That's the only point on the shoulder that the FL die seems to move. As Greg says, the belt offers more contact.
G
Greg Culpepper
Guest
Jerry,
Joe and I aren't in a unique situation. Anyone shooting a belted case can do the same thing. Powers was looking for a way to improve something about a belted case application and this is something that can be done.
Excessive headspace will lead to case separation belted or otherwise as you point out but since Powers wants to go to the trouble and expense of a custom reamer and chamber, this approach is an improvement.
I use a standard Redding full length die (not a bushing die) and hit the shell holder hard. The reamer was ground with this die in mind, tight neck, mild size and bump and no need for an expander. Cheaper than making and hardening custom dies. I also have a standard neck die that gives me another half thou or so neck tension but I never use it. If the cases start getting a little tight for length because of work hardening and spring back I just anneal and the cases run through the gun just fine. I'm sure that you are correct that my shoulder clearance never reaches 2 thou but if it did I would not likely lose cases to stretching.
Best regards,
Greg
Joe and I aren't in a unique situation. Anyone shooting a belted case can do the same thing. Powers was looking for a way to improve something about a belted case application and this is something that can be done.
Excessive headspace will lead to case separation belted or otherwise as you point out but since Powers wants to go to the trouble and expense of a custom reamer and chamber, this approach is an improvement.
I use a standard Redding full length die (not a bushing die) and hit the shell holder hard. The reamer was ground with this die in mind, tight neck, mild size and bump and no need for an expander. Cheaper than making and hardening custom dies. I also have a standard neck die that gives me another half thou or so neck tension but I never use it. If the cases start getting a little tight for length because of work hardening and spring back I just anneal and the cases run through the gun just fine. I'm sure that you are correct that my shoulder clearance never reaches 2 thou but if it did I would not likely lose cases to stretching.
Best regards,
Greg
G
Greg Culpepper
Guest
Charles,
What you said!
Greg
What you said!
Greg