Got his from another Forum ! Great INFO ! 
RJ
OK, just about everything I have read is that you must use CCI450 primers for this cartridge. So, I paid a lot of money to buy 1000 primers online. When they came, I immediately started testing. I had a previous AR15 of this caliber so I proceeded with old loadings that had worked well with it. I have a 20" Lilja 1-8 twist barrel. I had always used CCI400 primers in the past so I slowly worded up some loads with powders I had used before. These included Benchmark, RL15, CFE223, BL-C(2), TAC, VV N133, and XBR8208. In every case, velocity was less with CCI450 than with CCI400. Accuracy was marginal. I started loading 5 rounds with 400 and 5 rounds with 450 using my best-performing powders which were 1. Benchmark, 2. RL15. Benchmark being the fasted and RL15 the slowest of the powders I used. In EVERY case, the velocity was slower with 450 and the accuracy was better with 400. The velocity was only about -10fps slower but I would have expected it to be faster since most magnum primers add about 60psi. Apparently, the only difference between CCI400 and CCI450 is the dimensions of the primer cup. The differences are: 400/450, Cup thickness .020/.025 Cup Diameter .1753/.1750 Cup Height .109/113. I guess they call the 450 a Magnum only because it may be able to stand up to chamber pressure higher than the 400. The peak pressure for this cartridge is 50,000. In all the MAX loads I have used, none have shown any sign of overpressure using either primer. In "most" instances, 50,000 psi is not in the magnum category and would not necessitate the use of 450 primers in the 6.5 Grendel. One other clue is the primers look identical. Both have an identical yellow cup. This would tell me that there is no liability issue if you were to mistake one for the other. Apparently, Bill Alexander used CCI450 primers in the development and it just stuck. All of the Alexander Arms reloading information I have found always lists the primer as CCI450. Other manufacturers use different primers such as WSR. Just my thoughts!
A Reply :
No you did not read that. Nowhere has this forum said that "you must use cci450 primers" for this cartridge." Let's get that settled right now.
There is a lot of advice/opinions on which primers are better, or worse, for not only AR but also for a bolt action. You pays your money and you makes your own choices. With powders, brass, primers, bullet, rifle model, even reloading protocols. It is ALL under your own direction. And I believe if you are honest that is the tenor of the advice on here.
As to primers: The brisance of the 2 versions, 400 v 450, is different, as are the physical dimensions (several posts on this). That is the heat or flame ability. Each of the different primer versions, Mfr X vs Mfr Y, regulars and magnums, has a different brisance. Read about the tests online. CCI, Federal, Remmy, Winchester, Wolf, Mil-std, they are all different in their specific heat/flame.
No one, that I recall, is saying that you "must" use one primer or not, all of these are simply recommendations and you are in control of your own loading.
The 400 has a thinner cup and is more liable to a pierced primer or possible slam fire than the magnum, or than the #41 (for small rifle primers).
If you simply substitute a different primer for your "normal" primer/load combo, then for sure the MV will differ, and may or may not be more accurate, or even more or less scattered- SD-wise for MV. Same is true for substituting one brass for another. Or one lot of powder for another. Raw substitutions without proper workup - any bad impacts are on you because you did not start low and work up.
Now I personally have not had any slamfires nor any pierced primers from AR shooting but then again I do not shoot 1000's of rounds a year.
Others whom I respect have had the same.
You get to make your own choices.
another Reply :
Thanks for the post - always good to get more info as I try to learn as much as I can about this cartridge. You mention that the velocity is lower in comparison, but may I ask, were these side-by-side comparisons fired on the same day? Or is this in comparison to prior records? I ask, because most people don't really account for barrels slowing down as they age. I suspect it's the lengthening throat letting more gas leaks by, or the bore gets more loose. But in any event, it is known that barrels slow down as they age. Other possible factors include powder aging, if this is the very same jugs, and they are getting older. It won't really go bad or weaker with age, so much as it can accumulate humidity over time, even through the plastic. Not sure your situation, storage practices, etc, but gunpowder mass can change up into the full digit percentage point, depending on their humidity exposure over time. Someone who scientifically tested this, found as much as 3-digit velocity change, just based on the humidity of his powder exposure. Also, in my experience, the Chorny being used can matter as well, and I tend to find the precision of a chronograph can be good on any given day, but it's actually accuracy can move around by well over 10 fps, (or so I suspect).
Just trying to point out some items to ponder, as 10 fps isn't that much of a velocity difference.
As to primer impact on round performance - to be honest, with 6.5Grendel, I don't think it matters that much. Over the years, I did test and find with a really slow blue-dot powder in 9mm, magnum primers gave a measurable change in velocity. But that was a really slow pistol powder that's difficult to ignite and leaves lots of unburned powder when used; primer hotness mattered. Rifle is another matter. I personally haven't noticed much difference when switching primers at all in Grendel, to be honest, aside from a couple learning experiences I'll note below.
As to primer choice, I like CCI450 in the 5.56 AR15 as a general purpose primer, but have run pretty much everything under the sun. The only time I had issue was running surplus H335 at below-minimum load in 5.56 (trying to be "safer" doing a test on something), using weak CCI400 primers. With that much void space with a difficult to ignite ball powder - those rounds would hang-fire. That's where I learned void space matters. I repeated that experience running faster 4064 in 6.5CM in small primer brass. This had a decent amount of void space. CCI450 would 1/4 second hangfire almost every single shot - cost me a deer-neck shot ending up being a gut-shot - that sucked (yea yea, "it wasn't my fault"; but I made the ammo, so still my fault). CCI41 would fire per normal. There are Johnny's youtube video's on this very topic (that I discovered AFTER). Void space in a casing matters a lot, and frankly, I consider that a factor on my primer selection first - as only use your hottest primer, if it has a lot of void.
But 6.5 Grendel does not have hardly any void. It's a small case, and in the end, it's the gun-powder that makes it go. Point being, no, I personally don't have issue with CCI400 in 6.5 Grendel, and would run it if I had it. It's a low pressure round, with low void-space, and usually fed with faster powders that are happy to ignite, like 8208. I've never had a slam fire with a CCI400, or know anyone who has.
As to your slower velocity difference, my own suspicion is it's either a more worn barrel when tested, or other system experimental error (such as the calibration scale being .1 gr off, or sizing neck tension of this brass was different, or the chrony was mounted just a time bit different), than actually due to the 450 sending a weaker shot than a 400.
One More reply :
My experiment with .223 Rem
CCI #400
2861
2871
2872
2875
2873
Average 2870
SD 5
ES 14
CCI #450
2947
2925
2925
2933
2936
Average 2933
SD 8
ES 22
RJOK, just about everything I have read is that you must use CCI450 primers for this cartridge. So, I paid a lot of money to buy 1000 primers online. When they came, I immediately started testing. I had a previous AR15 of this caliber so I proceeded with old loadings that had worked well with it. I have a 20" Lilja 1-8 twist barrel. I had always used CCI400 primers in the past so I slowly worded up some loads with powders I had used before. These included Benchmark, RL15, CFE223, BL-C(2), TAC, VV N133, and XBR8208. In every case, velocity was less with CCI450 than with CCI400. Accuracy was marginal. I started loading 5 rounds with 400 and 5 rounds with 450 using my best-performing powders which were 1. Benchmark, 2. RL15. Benchmark being the fasted and RL15 the slowest of the powders I used. In EVERY case, the velocity was slower with 450 and the accuracy was better with 400. The velocity was only about -10fps slower but I would have expected it to be faster since most magnum primers add about 60psi. Apparently, the only difference between CCI400 and CCI450 is the dimensions of the primer cup. The differences are: 400/450, Cup thickness .020/.025 Cup Diameter .1753/.1750 Cup Height .109/113. I guess they call the 450 a Magnum only because it may be able to stand up to chamber pressure higher than the 400. The peak pressure for this cartridge is 50,000. In all the MAX loads I have used, none have shown any sign of overpressure using either primer. In "most" instances, 50,000 psi is not in the magnum category and would not necessitate the use of 450 primers in the 6.5 Grendel. One other clue is the primers look identical. Both have an identical yellow cup. This would tell me that there is no liability issue if you were to mistake one for the other. Apparently, Bill Alexander used CCI450 primers in the development and it just stuck. All of the Alexander Arms reloading information I have found always lists the primer as CCI450. Other manufacturers use different primers such as WSR. Just my thoughts!
A Reply :
No you did not read that. Nowhere has this forum said that "you must use cci450 primers" for this cartridge." Let's get that settled right now.
There is a lot of advice/opinions on which primers are better, or worse, for not only AR but also for a bolt action. You pays your money and you makes your own choices. With powders, brass, primers, bullet, rifle model, even reloading protocols. It is ALL under your own direction. And I believe if you are honest that is the tenor of the advice on here.
As to primers: The brisance of the 2 versions, 400 v 450, is different, as are the physical dimensions (several posts on this). That is the heat or flame ability. Each of the different primer versions, Mfr X vs Mfr Y, regulars and magnums, has a different brisance. Read about the tests online. CCI, Federal, Remmy, Winchester, Wolf, Mil-std, they are all different in their specific heat/flame.
No one, that I recall, is saying that you "must" use one primer or not, all of these are simply recommendations and you are in control of your own loading.
The 400 has a thinner cup and is more liable to a pierced primer or possible slam fire than the magnum, or than the #41 (for small rifle primers).
If you simply substitute a different primer for your "normal" primer/load combo, then for sure the MV will differ, and may or may not be more accurate, or even more or less scattered- SD-wise for MV. Same is true for substituting one brass for another. Or one lot of powder for another. Raw substitutions without proper workup - any bad impacts are on you because you did not start low and work up.
Now I personally have not had any slamfires nor any pierced primers from AR shooting but then again I do not shoot 1000's of rounds a year.
Others whom I respect have had the same.
You get to make your own choices.
another Reply :
Thanks for the post - always good to get more info as I try to learn as much as I can about this cartridge. You mention that the velocity is lower in comparison, but may I ask, were these side-by-side comparisons fired on the same day? Or is this in comparison to prior records? I ask, because most people don't really account for barrels slowing down as they age. I suspect it's the lengthening throat letting more gas leaks by, or the bore gets more loose. But in any event, it is known that barrels slow down as they age. Other possible factors include powder aging, if this is the very same jugs, and they are getting older. It won't really go bad or weaker with age, so much as it can accumulate humidity over time, even through the plastic. Not sure your situation, storage practices, etc, but gunpowder mass can change up into the full digit percentage point, depending on their humidity exposure over time. Someone who scientifically tested this, found as much as 3-digit velocity change, just based on the humidity of his powder exposure. Also, in my experience, the Chorny being used can matter as well, and I tend to find the precision of a chronograph can be good on any given day, but it's actually accuracy can move around by well over 10 fps, (or so I suspect).
Just trying to point out some items to ponder, as 10 fps isn't that much of a velocity difference.
As to primer impact on round performance - to be honest, with 6.5Grendel, I don't think it matters that much. Over the years, I did test and find with a really slow blue-dot powder in 9mm, magnum primers gave a measurable change in velocity. But that was a really slow pistol powder that's difficult to ignite and leaves lots of unburned powder when used; primer hotness mattered. Rifle is another matter. I personally haven't noticed much difference when switching primers at all in Grendel, to be honest, aside from a couple learning experiences I'll note below.
As to primer choice, I like CCI450 in the 5.56 AR15 as a general purpose primer, but have run pretty much everything under the sun. The only time I had issue was running surplus H335 at below-minimum load in 5.56 (trying to be "safer" doing a test on something), using weak CCI400 primers. With that much void space with a difficult to ignite ball powder - those rounds would hang-fire. That's where I learned void space matters. I repeated that experience running faster 4064 in 6.5CM in small primer brass. This had a decent amount of void space. CCI450 would 1/4 second hangfire almost every single shot - cost me a deer-neck shot ending up being a gut-shot - that sucked (yea yea, "it wasn't my fault"; but I made the ammo, so still my fault). CCI41 would fire per normal. There are Johnny's youtube video's on this very topic (that I discovered AFTER). Void space in a casing matters a lot, and frankly, I consider that a factor on my primer selection first - as only use your hottest primer, if it has a lot of void.
But 6.5 Grendel does not have hardly any void. It's a small case, and in the end, it's the gun-powder that makes it go. Point being, no, I personally don't have issue with CCI400 in 6.5 Grendel, and would run it if I had it. It's a low pressure round, with low void-space, and usually fed with faster powders that are happy to ignite, like 8208. I've never had a slam fire with a CCI400, or know anyone who has.
As to your slower velocity difference, my own suspicion is it's either a more worn barrel when tested, or other system experimental error (such as the calibration scale being .1 gr off, or sizing neck tension of this brass was different, or the chrony was mounted just a time bit different), than actually due to the 450 sending a weaker shot than a 400.
One More reply :
My experiment with .223 Rem
CCI #400
2861
2871
2872
2875
2873
Average 2870
SD 5
ES 14
CCI #450
2947
2925
2925
2933
2936
Average 2933
SD 8
ES 22
