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SAAMI specs makes sure commercial ammo and guns marked as the same caliber will fire safely.
Mil Spec makes sure ammo will fire even when hot and dirty.

I would suggest you buy reamers made to (much) tighter specs than either specification, otherwise you'll have case expansion near the base and over-sized necks. Look at the SAAMI drawings and specify a reamer be ground to the TIGHT side instead of the middle or high side. There's a surprising amount of real-estate within the tolerances that can be used to advantage.

The SAAMI drawings for cartridge cases and chambers are available on line as a pdf file. Compare the largest case with the smallest chamber and see how much slack there is left. It is surprising.
 

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Yes! Indeed, reamers are usually made on the assumption they'll be used even in semii-autos where some extra room is helpful to feed in some designs. They also anticipate regular use as by a busy gunsmithy or a manufacturer so that they will need to be resharpened periodically. Too much metal rather than too little makes that easier.

For the home gunsmith, though, getting a tight reamer saves your brass. Even a finishing reamer can chamber several tens of blanks before it needs resharpening. Dave Manson told me that with good care and handling, he thought 50 barrels was doable with no roughing reamer involved. So, if the reamer is for your own guns only, even if you kept a full match schedule and shot out a barrel a year, you'd be using that reamer for a long, long time before it got tired. You don't need any extra metal on it.
 

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My head is spinning!! As a new reloader, should I concern myself with this?
Isn't following the load data in the manuals good enough?
 

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No, you don't have to memorize Mann's bullet flight tables either, just be aware they exist. SAAMI is where the 'standards' come from. The reloading manuals take that into consideration.

Welcome aboard!!
 

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My head is spinning!! As a new reloader, should I concern myself with this?
Isn't following the load data in the manuals good enough?
Yes, with three caveats. Don't trust old manuals. Don't trust the top load in any data will be OK in all guns all the time (in other words, always work loads up from the bottom while keeping an eye out for My head is spinning!! As a new reloader, should I concern myself with this? Isn't following the load data in the manuals good enough?[/QUOTE]Yes, with three caveats.Don't trust old ones, don't trust the top load in any data will be OK in all guns all the time, and don't trust that you can have different non-powder components (different primer, different bullet, different case) from that listed in the manual and get the same result. The old data books were developed before they began to routinely pressure test at least the top loads for their books.(There are a few exceptions, like John Clarke's M1 Garand loads from the 1980's, which work because they are not what the manuals at that time were publishing as maximum and because the M1 Garand is an exceptionally strong rifle that Hatcher showed would withstand loads that destroyed some bolt rifles (Arisaka's, IIRC).Even with his data, though I would use one of the military sensitivity primers that have become available since he authored that rather than those Clarke used.)On top of that, in the 1990's, pressure test gear began to be married to computers and clearer, more detailed pressure curves and data appeared that showed some of the older peak measuring and data and copper crusher data were covering up spiky behavior and other factors that have caused some loads for some powders to be adjusted down.As to the maximums in current manuals, I would guess that 99% of the time they are fine, but every once in awhile you can run into an issue.I've seen three examples of a starting load (the lowest load in the manual) already being at practical maximum for a particular gun.One of those was because it was from an old manual (Hornady 2nd edition from the 1970's) for which the load data was developed in a heavier gun than the one I was using and not pressure tested in a standard barrel.Hence, one of several reasons for my warning about old data.One, however, was from the last Speer data book.It was a .243 Win load (I've forgotten which one) that was worked up to mid-level and was producing 200 fps more velocity than the manual said it should and was popping the action open with every shot, despite the action being carefully cleaned and inspected.I mention that one because when the gun owner called Speer, they said they had the maximum load pressure test result on file and signed by a ballistic technician, so they were standing by it.The next time someone tells you all the modern load data has been wimped down because of lawyers, you can point to that example of what having lawyers actually does: prevent them from owning up to a problem and just assuming it must be the customer's fault.Another, less direct, factor comes to mind as well:If you look at data that was developed in a pressure gun, like Hodgdon's, and compare it to data developed in production guns but with the highest load then pressure tested, like Hornady's, you see some discrepancies.The Hornady manual maximum loads routines run from about 1% to as much as 9% lower pressures than Hodgdon's.Why?Well, several reasons come up.One is that only the powder distributing companies have access to reference powder.That is, they have powder that very closely meets all the target specs they give to the powder factory to make for them.What they sell varies in burn rate by ±3%—±5% depending on brand, and we don't know if Hornady or any other bullet maker or manual author might have got their hands on a sample that was slower or faster than average for developing their loads.Second, the modern conformal pressure transducers can be shown to vary about ±5% from one set to another.SAAMI has example load tables that showed this for the peak reading equipment.The computerized equipment is probably better, but it's not absolute, so you can get a difference that way.Third, modern bullets vary more in construction than they once did, and M.L. McPherson has shown that shooting a .270 Winchester with the same load and same bullet weight, but switching between all bullets of that weight varied the peak pressure 30%.Finally, some data is more limited than is obvious at first glance.Alliant's data shows a lot of what they call load "recipes".Unless you read their PDF file manual, you aren't warned those "recipes" are all maximum loads and that you are expected to know to reduce them 10% to start your load workup. (And there are supposed to be lawyers that go along with that practice?)Secondly, a lot of their data is with Speer Gold Dot bullets (Alliant and Speer have the same parent company, Vista Outdoors).A lot of people will think that means it is fine with other jacketed bullets the same weight.It doesn't.A Speer technician told me the Gold Dot line uses jackets that are electroplated onto the bullet cores and that they are softer than conventional drawn jackets.As a result, he said, some Gold Dot data has starting loads higher than maximum loads for some conventional cup and core bullets the same weight, while some others are not.It depends on pressure range, bullet size and other factors.So, what's a fellow to do?Always look at three or more sources of load data and pick the lowest starting load among them.This will weed out those whose data was developed on obsolete pressure gear (anything that says CUP is not a modern measurement; copper crushers results can vary over ±10% from one setup to the next).Always start with the bottom load listed and work up in steps not exceeding 2% of the maximum charge weight you are heading toward while you watch for signs of pressure.Lots of folks skip starting loads and go straight to the middle of the range.Once in awhile that can be very hard on the gun and shooter.Avoid the temptation.You only need to fire one round at each level to reveal a gross pressure sign.That's just six rounds from bottom to top, so it's not a gross financial or time burden."]pressure signs). Don't trust that you can have different non-powder components (different primer, different bullet of the same weight, different case) from those listed in the manual and get the same result.

You don't have to read this post any further if you are not interested in the reasons behind the above. I will point out that probably the single most common error that results in some degree of catastrophic failure is people double-charging pistol cases. Rifle powders normally fill a case too high for a double charge to fit without overflowing, so that mistake doesn't tend to happen with rifle loading. But pistols and revolvers have been known to let go from double charging, so always look at the powder level in each case or use a powder checking die.


The whys behind the caveats:

The old data books were developed before they began to routinely pressure test at least the top loads for their books. (There are a few exceptions, like John Clarke's M1 Garand loads from the 1980's, which work because they are not what the manuals at that time were publishing as maximum and because the M1 Garand is an exceptionally strong rifle that Hatcher showed would withstand loads that destroyed some bolt rifles (Arisaka's, IIRC). Even with his data, though I would use one of the military sensitivity primers that have become available since he authored that rather than those Clarke used.) On top of that, in the 1990's, pressure test gear began to be married to computers and clearer, more detailed pressure curves and data appeared that showed some of the older peak measuring and data and copper crusher data were covering up spiky behavior and other factors that have caused some loads for some powders to be adjusted down. Finally, almost all primer formulations, some powder sources and formulations, and almost all powder quality control has been changed and generally improved over the last three decades, so some of the materials used in the old manuals are too different now to match their original performance.

As to the maximums in current manuals, I would guess that 99%+ of the time they are fine, but every once in awhile you can run into an issue. I've seen three examples of a starting load (the lowest load in the manual) already being at practical maximum for a particular gun. One of those was because it was from an old manual (Hornady 2nd edition from the 1970's) for which the load data was developed in a heavier gun than the one I was using and not pressure tested. Hence, one of several reasons for my warning about old data. One, however, was from the last Speer data book. It was a .243 Win load (I've forgotten which one) that was worked up to mid-level and was producing 200 fps more velocity than the manual said it should and was popping the action open with every shot, despite the action being carefully cleaned and inspected. I mention that one because, when the gun owner called Speer to report it, they said they had the maximum load pressure test result on file and signed by a ballistic technician, so they were standing by it. The next time someone tells you all the modern load data has been wimped down because of lawyers, you can point to that example of what having lawyers actually does: prevent them from owning up to a problem and just assuming it must be the customer's fault. They must have had other complaints though, as there is talk of them re-firing all their data.

Another, less direct factor comes to mind as well: If you look at data that was developed in pressure guns by a powder company, like Hodgdon, and compare it to data developed in production guns but with the highest load subsequently pressure tested, like Hornady's, you see discrepancies. The Hornady manual maximum loads routinely run from about 1% to as much as 9% lower than Hodgdon's. Why? Well, several possible reasons come up. One is that only the powder distributing companies have access to reference powder. That is, they have powder that very closely meets all the target specs they give to the powder factory when they order a lot made. What they sell varies in burn rate by ±3% to ±5% depending on brand, and we don't know if Hornady or Lyman or any other bullet maker or manual author might have got their hands on a sample that was slower or faster than average for developing their loads. Second, the modern conformal pressure transducers can be shown to vary about ±5% from one set to another. SAAMI had example load tables in the 1992 standard that showed this for the peak reading equipment. The computerized equipment is probably better, but it's not absolute, so you can still get disagreement from one test setup to the next, plus the SAAMI standard allows for two standard errors of variation from one sample of ten to the next even with the same equipment. Third, modern bullets vary more in construction than bullets used to. M.L. McPherson has shown that shooting a .270 Winchester in a pressure gun with the same load and same bullet weight, but switching between all bullets of that same weight caused peak pressure to vary over 30%. Fourth, they aren't using the same brass and primers and lot of the time. In some instances this makes little difference and in some it makes significant difference (especially with small rifle primer cartridges).

Finally, be aware some data is more limited than is obvious. Alliant's data shows what they call load "recipes", leading many to think you just load to that data and forget load development and work-ups. Unless you read their PDF file manual, you aren't warned those "recipes" are all their maximum loads and that you are expected to know to reduce them 10% to start your load workup. (And there are supposed to be lawyers involved?) Secondly, a lot of their data is with Speer Gold Dot bullets (Alliant and Speer have the same parent company, Vista Outdoors). A lot of people will think that means it is fine with other jacketed bullets the same weight. It doesn't. A Speer technician told me the Gold Dot line uses jackets that are electroplated onto the bullet cores and that they are softer than conventional drawn jackets. As a result, he said, some Gold Dot data has starting loads higher than maximum loads for some conventional cup and core bullets the same weight, while overlap or even coincide. It depends on pressure range, bullet size and other factors.

So, what's a fellow to do? Always try to look at three or more sources of load data and pick the lowest starting load among them. Online data makes that easier than ever to do a cross-check. This will weed out those whose data was developed on obsolete pressure gear (anything that says CUP; copper crushers results can vary over ±10% from one setup to the next, but some older rounds only have a copper crusher standard and no conformal transducer standard, so we are sometimes stuck with it). Always start with the bottom load listed and work up in increments that are 2% (or less, if you want to shoot more test rounds) of the maximum charge weight you are heading toward. Watch for pressure signs at each increase. Lots of folks skip starting loads and go straight to the middle of the range. Every once in awhile that can be very hard on the gun and shooter. Avoid the temptation. You only need to fire one round at each level to reveal a gross pressure sign. That's just six rounds from bottom to top, so it's not a big financial or time burden.

Finally, everyone wants everything to be easier than it is. Don't be discouraged that you have things to learn here. Enjoy it. It's a hobby. Just be aware that neither the Nanny State nor even the legal profession have guaranteed you can't find a way to hurt yourself with this activity if you aren't prudent. Indeed, be grateful for that.
 

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I noted that using the conversion formulas on post #10 on page one: CUP to PSI: =-17902+(1.516*(CUP)) and PSI to CUP: =((PSI)+17902)/1.516, seems to work fine for pressures above 33,000 PSI or CUP, however below that, the formulas produce questionable to nonsensical answers as one gets to lower and lower pressures.

As an example, using the formula on the following lower pressure pistol calibers, I got these low PSI results when converting CUP to PSI. Further, as the pressures approach 10,000 CUP, the calculated PSI are stupid.

Cartridge: - - - - Pressure PSI - - Pressure CUP (PSI should be higher than CUP)
.30 Luger ............24,546............. 28,000
.25 ACP .............. 19,998............. 25,000
.45 Colt (Ruger)....19,998............. 25,000
.45 Auto Rim......... 4,838............. 15,000
.44-40.................. 1,806............. 13,000
.38 Colt................... 290............. 12,000

And it also doesn't work well when converting lower pressure from PSI to CUP where the calculated CUP is higher than PSI, not lower. Further, as the pressures approach 10,000 PSI, the calculated CUP are stupid.

Cartridge: - - - - Pressure PSI - - Pressure CUP (CUP should be lower than PSI)
.45 ACP +P.......... 23,000............. 26,980
.32 ACP............... 20,500............. 25,331
.380 ACP............. 21,500............. 25,991
.45 ACP............... 21,000............. 25,661
.44 Special.......... 15,500............. 22,033
.45 Colt............... 14,000............. 21,044
 

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That's correct. You are not using the formula as its originator intended. When Denton Bramwell derived that correlation it was only for rifle cartridges, and only when their peak pressure was 28,000 psi (45-70) or more. No handgun cartridge data were involved in the calculations and in forum posts Denton himself pointed out it was only for rifles and only at 28,000 psi and up.

Even within Denton's constraints, the correlation is not always great. For example, if you use the CIP copper crusher number for 223 Remington, 53,664 psi (3700 Bar) and apply the factor, you get 63,453 psi; very close to the CIP transducer rating of 62,366 psi (4300 Bar). But if you apply it to the SAAMI copper crusher number for .223, which is 52,000 CUP, you get 60,930 psi, which is not very close to the the SAAMI conformal transducer MAP of just 55,000 psi. He considers it an insturmentation problem in the article. Overall, there are a number of instrumentation anomalies involved.
 

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Why is it when I am researching a load I will sometimes come up with load data for the same caliber (test rifle for that matter) and one bullet might have a max load with a pressure of 60,500 and a bullet by the same manufacturer in the same weight will have a max pressure of 51,000.

I've been told not to screen shot load data. You can see what I am talking about by doing a search on the Hodgdon site for 308 Winchester 150 gr. bullet with H4895 powder.

Both 150 gr. Nosler bullets of different design.

Also, with a max SAAMI pressure of 62,000 PSI, why are loads that produce pressures much lower (49K-55K) listed as max loads in the book.

Thanks.

Edited - I came across a bunch of 150 gr. Hornady FN bullets and wonder how pressures might vary with Varget or H4895 between the load data on the hodgdon site?

I cannot find any Hornady data for that bullet in that chambering...even old books. Closest is my Hornady #2 has data for the 170 gr. Flat Nose and 168 gr. Match. Data is almost identical for Min/Max even though it does not show pressure.
 

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Why is it when I am researching a load I will sometimes come up with load data for the same caliber (test rifle for that matter) and one bullet might have a max load with a pressure of 60,500 and a bullet by the same manufacturer in the same weight will have a max pressure of 51,000.
Look at the ends of the numbers at the Hodgdon site. One is in units of psi and the other is in units of CUP. The two kinds of instrumentation that produce these two numbers do not tend agree when:

a) the numbers are much over about 30,000 psi, or

b) when the diameter of the case body is small.

c) and sometimes they disagree for no clear reason.

For this reason, SAAMI has two separate sets of maximum pressure standards for each active cartridge, one in psi and one in CUP. For the .308 Winchester, the psi maximum average {peak} pressure is 62,000 psi, while the CUP maximum average pressure is 52,000 CUP. So, for the examples you gave, the 60,500 psi number is 97.6% of maximum, while the 51,000 CUP number is 98.1% of maximum. Neither goes to 100% because Hodgdon tests 10 rounds and the pressure variation they saw would have put the highest pressure cartridge in the test sample over the maximum.

In general, the copper crusher that produces the CUP number reads lower at high pressure than the conformal piezoelectric transducer does. The numbers get closer for large diameter cases at lower pressures. They two agree on 45-70, for example, which is rated at 28,000 psi and 28,000 CUP
 

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Thanks....on newer data I generally assume that pressures will be listed in PSI. Older data I pay better attention.

That's on me. :D
 

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Just remember that if Hodgdon tests it themselves, it's most likely in CUP. :)


Cheers
 
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