New to Grendel - Why the QL difference between SAAMI and CIP?

[DDBTx]

Greetings all and thanks for the view. I am new to the Grendel but not to reloading, for example have done some OBT stuff to work up a Tikka Lite in 300 WSM, did my own 458 SOCOM loads for the then-new Barnes SOCOM bullet and others, and wildcatted a 30-25 WSSM AR using QL and a chrony, from scratch. I prefer working up loads to following recipes, and am pretty conversant with the eccentricities of QL and how and when to adjust it to fit your real world results.

Found a bargain on an unfired Sabre Defense fluted 22 inch Grendel upper, so here i am with my 3rd oddball AR project gun. And with one big question that I am sure must be obvious to the old Grendel folks here but the answer is not coming up in my searches after several hours.

Question: Why the CIP max pressure, both in QL and online, listed at 58740 PSI but the SAAMI max is 52000? That is a pretty significant difference! Usually the SAAMIs are higher in rifle rounds.... see 30-06 and 308 Win. for example but no other SAAMI vs CIP I can find have this big a difference.

Apologies if this is an old answered question i am just not bright enough to uncover with my search terms!

Best,
DDBTx

[bwaites]

The Max is the SAAMI pressure. That number for CIP must be a transcription error.

Welcome to the boards!

[JASmith]

bwaites is probably right.

The CIP and SAAMI organizations go to great lengths to ensure that their standards are equivalent even though the numbers seem different. Mistakes in translation do occur.

An example is the free-bore and throat description. For a long time, the CIP definition had an incorrect specification for this part of the chamber. Reamers cut to the initial CIP specification would not accept factory ammunition. That has since been corrected and we now see the 0.5 - 1.5 degree compound throat in both the CIP and SAAMI specifications.

Pressures are a bit more complicated. The measurement techniques and locations are different - see https://en.wikipedia.org/wiki/Small_...essure_testing for a comparative description of pressure measurement techniques. Also, the definitions of pressures are different. SAAMI uses a "Maximum Average Pressure" (52 ksi), a "Maximum Probable Lot Mean" (53.3 ksi), and a "Maximum Probable Sample Mean" (55.3 ksi). (Numbers in Parentheses are for the Grendel.) Statistical arguments are used to define these pressures so that a manufacturer won't reject, for example a lot if one set of ten shots shows an average of 54 ksi using a load that historically yields under 52 ksi provided multiple samples from the lot being tested average less than 53.3 ksi.

These same statistical arguments support Bill Alexander's position that load data be kept at 50 ksi and under. The folks testing individual loads are hard pressed to test enough samples to assure that the true average stays within the SAAMI Maximum Average Pressure of 52 ksi unless their samples are at 50 ksi and under.

Go here for a mid-level technical discussion of these pressures: http://shootersnotes.com/articles/saami-pressure/.

I have been told the CIP pressure number is referenced to a different statistical definition but that working pressures of ammunition manufactured for the Grendel are consistent with ammunition manufactured to the SAAMI standard. I have not yet seen a validation of this position so am passing it along as speculation.

Back to bwaites' comment: I would feel a lot better if the CIP number converted to something closer to 55 ksi... There may be another hiccup in translation.

[sneaky one]

I have sent a many test units to JASmith, for pressure tests. As a whole, I was maybe 1-2 k over on pressures. Bill A stated that the case can rupture at about 58k.

Running at known peramiters - on load charges will be fine. 50-52k is fine. Don't Hot Rod ! Unless you want to risk everything, . What is an eye worth to you? Yours.

Yes this is the safety nerd check. All the data provided is for us all to be safe . Don't push it.

I went outside the curve of reloading with my bullet trials of '09-10. I had a many behind me- engineers, ballisticians, etc., to find a pathway for a new ideal bullet. In the end- I found it on my own.

No, we do not want the curve at 55k. 52k is fine as a standard maximum.

It is the 95 GMX.

[DDBTx]

Good stuff, my thanks JASmith and sneaky one. I am not an engineer, though I think i have a decent grasp of basic powder engineering and have spoken with a few such folks in "strict confidence", meaning outside the realm of lawyers, about other loading issues. I have no desire to risk a weapon much less an eye or finger or my life on a load. A 6000 psi difference between CIP and SAAMI in QL seems abnormal unless it is bolt action vs. AR action stuff. I will stick with 50 - 52k in my QL calcs. Anyone have any input on what to look for as far as AR pressure signs, from actual experience with the AR based grendel, since those hard small mag rifle primers will not crater as easily?
And now sneaky one i will do a search to find your 95 GMX load!

[JASmith]

...Anyone have any input on what to look for as far as AR pressure signs, from actual experience with the AR based grendel, since those hard small mag rifle primers will not crater as easily?

There is a nice discussion of pressure signs in the 6.5 Grendel Reloading Handbook. The two volume set can be ordered at http://www.ar15buildbox.com/shop.htm and at http://www.shopalexanderarms.com/6_5...Reloading.html.

These books also have a couple of hundred loads between them. Also more than 600 loads are on the 6.5 Grendel page at http://ammoguide.com/?catid=456.

Enjoy and keep us posted!

[DDBTx]

Just dropped 42 bucks to read that discussion, sir, as well as 2 volumes of data; and glad to pay you and the others for your good efforts. Cheap at that price! I would have spent hundreds or thousands to replicate.

[DDBTx]

Vols 1 and 2 arrived, and were a great read. I will be referencing them often. Many thanks for your efforts and replies!

[mseric]

The difference is in the pressure testing devices and how pressures are determined.

CIP places their pressure transducer further forward than SAAMI, as a result CIP (NATO) rounds will read higher pressure than SAAMI tested rounds.

Testing a CIP round and a SAAMI round in the same test barrel either CIP or SAAMI will result in identical pressures.

[DDBTx]

So I went through QL's most up to date cartridge list and found some weird data on CIP vs. SAAMI max pressures.
22-250 CIP 58,740 SAAMI 65,000 Delta: SAAMI is 6,260 psi higher
223 Rem CIP 62,366 SAAMI 55,000 Delta: CIP is 7,366 PSI higher
270 Win CIP 62,366 SAAMI 65,999 Delta: SAAMI is 2,644 PSI higher
30-06 Spg CIP 58,740 SAAMI 60,000 Delta: SAAMI is 1,360 psi higher
30-30 Win CIP 46,412 SAAMI 42,000 Delta: CIP is 4,412 higher.
300 Blackout CIP 50,763 SAAMI 55,000 Delta: SAAMI is 4,237 higher
308 Win CIP 60,191 SAAMI 62,000 SAAMI is 1,809 higher.
6.5 Grendel CIP 58,740 SAAMI 52,000 Delta: CIP is 6,740 higher.
7mm Mag CIP 62,366 SAAMI 61,000 Delta: CIP is 1,366 higher

Half the time SAAMI is higher; the other half it is CIP. Variations go from not much (308 Win, 30-06, 7 Mag) to alarming (Grendel, 22-250, 223, 300 BLK).

Anyone have any wisdom as to what is going on there?

That is some odd results. I dont see a pattern there.

[mseric]

Under SAAMI proof test procedures, for bottlenecked cases the center of the transducer is located .175"
behind the shoulder of the case for large diameter (.250") transducers and .150" for small diameter
(.194") transducers. For straight cases the center of the transducer is located one-half of the transducer
diameter plus .005" behind the base of the seated bullet. Small transducers are used when the case
diameter at the point of measurement is less than .35".
Under C.I.P. proof test standards a drilled case is used and the piezo measuring device (transducer) will
be positioned at a distance of 25 mm from the breech face when the length of the cartridge case permits
that, including limits. When the length of the cartridge case is to short, pressure measurement will take
place at a cartridge specific defined shorter distance from the breech face depending on the dimensions
of the case.
The difference in the location of the pressure measurement gives different results than the C.I.P.
standard.

https://www.docdroid.net/shd8/the-truth-about-308-win-and-762-nato.pdf.html

[mseric]

http://kwk.us/pressures.html