Micrometer is much less than min OAL?
- Thread starter Mattj4867
- Start date
That is the bottom line.
Each different type of bullet from any mfg has to be checked to be sure.
You can go with the overall recommended and in most cases it works ok.
Remington for (at least some) of their rifles are using deep throats that look to be for ELD bullets.
Just repeat the test if you use a different profile bullet.
Mattj4867
I also use the RCBS Precision Mic , great tool . You can size your brass by chambering a fired case into you chamber , most likely it won't chamber without resistance . Set up your sizing die long an slowly size and test in your chamber until the bolt closes with no resistance . Record that measurement with the Mic . Then with that case set up your seating die seat the bullet long test the same way as you did with the case , alittle at a time until your bolt closes , record that measurement with the ogive section of the Mic . That would be the start of the rifling , now you can jump or jam your reloads for what ever shoots best in your rifle . I tried different measuring tools and I like the RCBS Precision Mic the best . The tool measures from the base of the case to the datum line on the shoulder of the case , the other drum measures from the base of the case to the ogive on the seated bullet . Not the tip OAL. You have to be concerned with the over all length when loading from a magazine in your rifle , if so seat to OAL as listed in your load book for that bullet , then use that bullet in the Mic for the ogive measurement . The tip of the bullets may vary in size , isn't the best way to measure . Ogive is the way to go .
I also use the RCBS Precision Mic , great tool . You can size your brass by chambering a fired case into you chamber , most likely it won't chamber without resistance . Set up your sizing die long an slowly size and test in your chamber until the bolt closes with no resistance . Record that measurement with the Mic . Then with that case set up your seating die seat the bullet long test the same way as you did with the case , alittle at a time until your bolt closes , record that measurement with the ogive section of the Mic . That would be the start of the rifling , now you can jump or jam your reloads for what ever shoots best in your rifle . I tried different measuring tools and I like the RCBS Precision Mic the best . The tool measures from the base of the case to the datum line on the shoulder of the case , the other drum measures from the base of the case to the ogive on the seated bullet . Not the tip OAL. You have to be concerned with the over all length when loading from a magazine in your rifle , if so seat to OAL as listed in your load book for that bullet , then use that bullet in the Mic for the ogive measurement . The tip of the bullets may vary in size , isn't the best way to measure . Ogive is the way to go .
More than you really wanted to know...
This is actually not correct. You can pick any arbitrary location on the case shoulder to use as a reference to make a before and after resizing comparison to determine how far the shoulder is set back, but the fact this arbitrarily chosen diameter is a reference does not make it a datum.
As I mentioned before, there are several datums on a cartridge and chamber (marked with a "B" for Basic on the SAAMI drawings), and these are chosen by the cartridge designer or by agreement among SAAMI members. Their purpose is not just to define headspace. They are the dimensions that are the takeoff points for other dimensions that define the shapes of the cartridge and chamber; the taper of the sides and the locations of the intersections of the neck and shoulder. They allow you to accurately determine the dimensions of cartridge case forming tools and to set up a precision grinder to sharpen a chamber reamer with the right profile. An arbitrarily chosen reference point, by definition, does not provide that information so it is not a datum.
There is a complication that occurs resizing older rimless cartridges precisely that can be spotted in their case and chamber drawings. The .30-03 derivatives the 30-06 and 270 Winchester drawings, for example, show a difference between the case and chamber shoulder angles such that the angle of the case shoulder is slightly greater than the chamber shoulder angle is. This is because headspace used to be figured not to a shoulder datum (that's a SAAMI innovation; the CIP doesn't use it) but from the breech face to the intersection of the shoulder and case body. If you have a copy of Hatcher's Notebook it shows this as the headspace on the .30-06, and they wanted to be able to determine where the outer perimeter of the case shoulder before it touched the rest of the chamber shoulder because that's what defined excess headspace.
A result of that is that if you take a random reference point too close to the neck and try to find shoulder setback directly, you can actually set it back a thousandth at that location and not have set the outer edge of the shoulder back at all. This is because the resizing die is made to the case shoulder angle while a fireformed case is set to the chamber shoulder angle. Unfortunately, the difference in shoulder angles is one thing in SAAMI's drawing and another in the Garand blueprints and I've seen a couple of other old drawings suggesting still other angle pairings have been used. So your best bet for an unfamiliar chamber is to measure the case to whatever shoulder reference you please, then mark the case shoulder with a Magic Marker and set up your resizing die, slowly turning it in while checking the ink for contact marks to determine when shoulder contact is complete. Then you can take a measurement to the reference again to see how much it changes before shoulder setback actually commences.
This all assumes, of course, that you want to be that precise. Most won't care, which is why I titled this post as I did.
jmorris said:
This is actually not correct. You can pick any arbitrary location on the case shoulder to use as a reference to make a before and after resizing comparison to determine how far the shoulder is set back, but the fact this arbitrarily chosen diameter is a reference does not make it a datum.
As I mentioned before, there are several datums on a cartridge and chamber (marked with a "B" for Basic on the SAAMI drawings), and these are chosen by the cartridge designer or by agreement among SAAMI members. Their purpose is not just to define headspace. They are the dimensions that are the takeoff points for other dimensions that define the shapes of the cartridge and chamber; the taper of the sides and the locations of the intersections of the neck and shoulder. They allow you to accurately determine the dimensions of cartridge case forming tools and to set up a precision grinder to sharpen a chamber reamer with the right profile. An arbitrarily chosen reference point, by definition, does not provide that information so it is not a datum.
There is a complication that occurs resizing older rimless cartridges precisely that can be spotted in their case and chamber drawings. The .30-03 derivatives the 30-06 and 270 Winchester drawings, for example, show a difference between the case and chamber shoulder angles such that the angle of the case shoulder is slightly greater than the chamber shoulder angle is. This is because headspace used to be figured not to a shoulder datum (that's a SAAMI innovation; the CIP doesn't use it) but from the breech face to the intersection of the shoulder and case body. If you have a copy of Hatcher's Notebook it shows this as the headspace on the .30-06, and they wanted to be able to determine where the outer perimeter of the case shoulder before it touched the rest of the chamber shoulder because that's what defined excess headspace.
A result of that is that if you take a random reference point too close to the neck and try to find shoulder setback directly, you can actually set it back a thousandth at that location and not have set the outer edge of the shoulder back at all. This is because the resizing die is made to the case shoulder angle while a fireformed case is set to the chamber shoulder angle. Unfortunately, the difference in shoulder angles is one thing in SAAMI's drawing and another in the Garand blueprints and I've seen a couple of other old drawings suggesting still other angle pairings have been used. So your best bet for an unfamiliar chamber is to measure the case to whatever shoulder reference you please, then mark the case shoulder with a Magic Marker and set up your resizing die, slowly turning it in while checking the ink for contact marks to determine when shoulder contact is complete. Then you can take a measurement to the reference again to see how much it changes before shoulder setback actually commences.
This all assumes, of course, that you want to be that precise. Most won't care, which is why I titled this post as I did.
That can happen to reloaders that are in mortal combat with reloading and other reloaders. I start with the datum, I do not allow myself to be driven to the curb by SAAMI and I do not get confused with thinking ever gage is a head space gage and I do not believe the case has head space. I off set the length of the chamber from the shoulder of the chamber to the bolt face with the length of the case from the shoulder to the case head.
F. Guffey
Reloaders have improperly seated cases with too much crimp. I understand to a reloader there is no correlation between bumping/moving the shoulder back and bulging the case at the case body/shoulder juncture; but the seating die does not have case body support, the full length sizing does have case body support: Meaning it is impossible to move the shoulder back when sizing a case it is possible to shorten the distance from the shoulder to the case head but the shoulder the reloaders starts with is not the same shoulder he finishes with.
jmorris said:
I'm not sure that is so. I've noticed they like to use the same diameters where they can and, in most instances, they try to avoid numbers that aren't multiples of five thousandths. I also have noticed that most (but not all) of the datum diameters are closer to the outside perimeter of the shoulder than they are to the center of the shoulder, which is where I would have put it. Perhaps its because the case is more rigid there, but I don't know. Considering that SAAMI is a manufacturing standards association, their members probably like to minimize the amount of different tooling they have to buy, so that may be an influence as well. Some of the Weatherby cartridges don't follow that, and I expect it is because of the large transitional radii linking the shoulder to the body and neck.
It seems like a good question to ask SAAMI.
On reconsideration, I think part of the reason for the location is they are subtracting the effect of the maximum corner radius at each end of the chamber neck before locating the shoulder datum. The chamber's shoulder/neck corner radius is normally larger than the shoulder/body corner radius so a range of cases can fit without jamming. But this also means that when you pick a location on a fired case to measure, you have to pick a diameter that doesn't overlap the ends of those radii and expect to get a valid setback measurement off your resized case.
In the 223 Remington, for example, the shoulder is only certain to be flat between a diameter of 0.2768" to 0.3514". The exact middle of that range is where I would put it, but that is 0.3141". They chose 0.330". 0.315" would be the closest multiple of 0.005", and they didn't choose that. So I am thinking 0.330" was already used on something else and they decided to give it double duty.
Again, it's worth asking them what the rationale is behind the choice.
In the 223 Remington, for example, the shoulder is only certain to be flat between a diameter of 0.2768" to 0.3514". The exact middle of that range is where I would put it, but that is 0.3141". They chose 0.330". 0.315" would be the closest multiple of 0.005", and they didn't choose that. So I am thinking 0.330" was already used on something else and they decided to give it double duty.
Again, it's worth asking them what the rationale is behind the choice.
This forum has at least three members that claim they called SAAMI, that started when they discovered SAAMI. I can only guess the first one was a speed reader and was not in the habit of looking for footnotes and directions for reading drawings. It has been at least 65 years since I took my first map reading class; :read right and then up": Nothing has changed, I studied SAAMI drawings, the chamber drawing has a symbol for head space, the case drawing does not have use a head space symbol.
Speak where SAAMI speaks and be silent where SAAMI is silent: I am sure SAAMI was impressed with all of the qualifications listed by our members, I would not call SAAMI.
I can not provoke most reloaders to push away from the keyboard to make room for a RCBS ROCK CHUCKER. They refuse to measure the amount of cam over for the ROCK CHUCKER. They insist the ROCK CHUCKER cams over because they heard it on the INTERNET. I have had 4 ROCK CHUCKERS, I am down to three; I do not own nor have I ever owned a ROCK CHUCKER that cammed over.
I have at least 11 Herter presses, every one of my Herter presses cam over because they are cam over presses, my ROCK CHUCKERS are non cam over presses. Being a good shot does not make a member an expert at reloading.
Read right and then up.
F. Guffey
It can not be done? This stuff is not for everyone; in the big inning I had more confidence in reloaders; and now? I do not.
I open a drawer, locate my datum and then use it to determine the length of the case from the datum to the case head. For me life and reloading is much more simple because my cases do not have head space and the gage I use to measure the case with is a case gage, it is not a head space gage and it is not a case head space gage because the case does not have head space.
Again: The L.E. Wilson case gage has been with us for over 70 years, there is a chance reloaders could now be running L.E. Wilson 'BUT' before internet reloading the case gage has always been a case gage.
The Wilson case gage is a datum based tool: Get a light, shine the light into the gage to aluminate the inside of the gage, for those that can push their way away from the keyboard can see the datum in the gage; It has a radius, I do not use the light. I use other methods but I have shop skills, I use a transfer method, when using the transfer method do not forget to lube the case.
F. Guffey
jmorris said:
He bought the RCBS Precision Mic. I have several. In each of them, the case shoulder thimble hole is reamed to the SAAMI datum diameter. Mine will all admit my pin gauges (-0.0002" sizing) that match the SAAMI number with slight rubbing, but not the one 0.001" larger. So it's very close. The PM's have a thimble micrometer scale, with the longitudinal coarse scale on the threaded barrel the case seats into and circumferential fine graduation scale the lip of the thimble that screws onto it. Inside of the case measuring thimble (there is a separate one for bullet ogives), the SAAMI datum size hole passes through a flat surface perpendicular to the hole. This allows them to QC accuracy with a parallel end straight cylinder gauge the diameter of a case head that is ground to the SAAMI chamber minimum headspace length. They drop that gauge inside in place of a case and the flat surface contacts it right where the edge of the hole would stop on an accurately made headspace GO gauge. The scales then ideally read "0" as they will on a headspace GO gauge, though the RCBS tolerance seems to be ±0.002".
This is the only logical way to get a direct reading on a case that mirrors the chamber size from fireforming. They could choose a different hole diameter, I suppose, but then they have to calculate a different length for their cylindrical gauge. It's much simpler just to stick with the SAAMI numbers.