I've had some batches of safety ladders worked up using CFE to get an idea of where my carbine stands with regard to velocity and consistency with Hodgdon's CFE223.

123gr A-MAX First
I had a suspicion that Hornady's data in the 9th Edition for 120-123gr pills could be based on the least common denominator of the projectile with the most drag in bore and start pressure sensitivity, which is the 120gr GMX solid copper unit.

Two things that steered me in that direction were the data meticulously recorded by Bwild97 here, and Hornady's CFE data for the 129gr SST, which is .5gr higher for the max load compared to the 120-123gr pills.

I already know that my Grendel handles 31.0gr of CFE well behind the 123gr A-MAX, so I wanted to run more extensive testing to see where the charge weight starts to spike.

I loaded 10 incremental charges, with 2 batches of each 10-round sequence. I used the longest COL I could get away with in my chamber and mags, which was

* 2.272"-2.277"
* once-fired Lapua brass
* Remington 7.5 primers
* 123gr A-MAX
* CFE223

Here's where you need to check yourself when viewing this data, because I literally expected to hit bad pressure signs much earlier. Thoroughly examine your experience with hand-loading before considering using any of the below data, especially since I set out to depart from published max loads.

A Chrony Beta Master was used for velocity readings as a potential indicator of pressure spikes, erratic deviations from a trend, or consistent charge weight to velocity increase.  The Chronograph was at least 15ft from the muzzle. Temperature was 60 F measured on-site with a thermometer out of the sunlight, next to the shooting position.

Brass was measured before and after shooting, at the case web just above the extractor groove, using dial calipers in order to inspect for case web expansion (serious pressure sign). Before, measurements were consistently .441"-.442" at this location. After each round was fired, the chronograph reading was observed, recorded, and brass inspected visually and with the calipers.

31.1gr 2489 fps case web .441" dia., no ejector swipes, no primer abnormalities
31.4gr 2520 fps same, velocity increase was 31fps
31.7gr 2532 fps same, 12fps increase
32.0gr 2553 fps same, 21fps
32.3gr 2572 fps same, 19fps



At this point, I stopped and double-checked everything, since I was into some unusually fast velocities for a 16" Grendel with a 123gr A-MAX. I had not seen any significant jumps in velocity outside of 31fps at this point, which is consistent with .3gr increments in this case and other powder/projo combos.

I decided to seek the point of departure by pressing forward cautiously.

32.6gr 2598 fps no dimensional change in the web, primer GTG, 26fps increase
32.9gr 2612 fps same, 14fps
33.2gr 2640 fps primer starting to crater, 28fps increase
33.5gr 2698 fps slight cratering again, 58fps spike

At this point, I had found what I was looking for, which was a clear departure from the trend, confirmed with slightly cratered primers. I had to have been well above Grendel SAAMI Maximum Average Operating Pressure by then for certain. The question is, when did I exceed that point, and what is a safe load for me?

2698 fps from a 16" Grendel carbine pushing a 123gr A-MAX is some bad ju-ju, and you won't find any industry-tested data from a 24" gun to-date over 2650fps that I'm aware of.

Either way, CFE appears to be some very forgiving powder as to building pressure ideally in the Grendel. I chose not to fire the last round of 33.8gr, because I knew I would have even more of a cratered primer or worse, and I had already exceeded MAOP much earlier.

107gr SMK
I then moved on to my 107gr loads with CFE.

107gr SMK
CFE223
Lapua 1 x fired brass
Rem 7.5 Primer
2.275" COL

Everything went haywire at this point. I could not correlate one charge weight with a sensible velocity at all. I don't know if the Chrony went to lunch, the sun angle made readings skewed, or what. First time I have seen it with this chronograph.

31.5gr 2708 fps no pressure signs on brass or primers, velocity reading WTH?
31.8gr 2522 fps
32.3gr 2526 fps
32.7gr 2658 fps
33.0gr 2750 fps
33.3gr 2575
33.6gr 2672
33.8gr 2668
34.0gr 2757

I don't know if the cartridges were rearranged in my case, or got somehow out of sequence, but the brass was all fine, no cratered primers, nothing other than a mystery with the numbers, especially since the first and last loads were so close, as well as the middle????

Questions
I started wondering if my digital scale had been subjected to RF interference during the loading session at my bench, and other sanity checks, as this is the first time I have seen this type of behavior with the Grendel. I was definitely scratching my head.

It could also be that my COL is so long, that I'm spiking the pressure from the start with the ogive jammed into the lands. Dimensional variation in the projectiles can account for different jump and jam depths, even with the same raw COLs, so I think I need to consider reducing the COL.

Experiences in the past with TAC and the 100gr NBT showed pressure signs right where one would expect them when I exceeded published velocities for max loads with that combination, to include blatant ejector extrusion, cratered primers, and velocity excursions from the safe trendline.  Today, I didn't see one single instance of ejector extrusion or even a hint of ejector shadow on either of the load batches.

Conclusions
CFE is a very forgiving powder in my Grendel at 60 F with the above loads. I need to reevaluate my bench, look at COLs again, and double-up Chronographs next trip. I'm still at a loss on the 107gr SMK's. I suspect a mistake somewhere on my part. Either way, many of the velocities were above max book value for 24" Grendels, which is a major red flag I think, but I also suspect that CFE will safely deliver noticeably higher velocities than any of the other powders I have worked with, and not spike. It also might be that CFE does weird things with 100gr pills. The guy who brought CFE up and did a ton of testing with it on the Grendel Forum said he had the same type of experiences with 100gr Hornady's...very erratic velocities.

Even at ~ max listed book data of 31.1gr under the 123gr A-MAX, I'm within 11fps of Hornady's 18" Grendel published max loads. What this day did for me was establish a set of known parameters where I can look for accuracy nodes in the future with my set-up.

BTW, every one of these loads was shot at 500yds on a large rock formation, with nice impacts. We video'd it through a spotting scope when I shot on IPSC steel as well.

I called Hodgdon's today to speak with a tech about CFE since my 107gr SMK velocities were so erratic, while the 123gr followed a textbook predictable pattern.

The conclusion was that CFE needs a certain amount of pressure in the case to burn consistently, so 123g or 120gr are probably where the bottom end is for bullet weights, and those pills should have long bearing surfaces as well.

I will do some ladders with it using 129gr SST's in the future, as I think I can get much higher velocities than I originally expected from a 16" gun. I just need to find nodes now with the 123gr A-MAX, and pressure-test the 129gr SST.

I'm thinking the 2532fps will be an accuracy node, since there was minimal velocity jump to it and from it.  I have about 100fps to play with from 2450fps on up, so there will be some nodes.

Very impressive speeds.  You are close to my 24"BHW barrel but I am coasting on mine.  I love velocity in tandem with accuracy but I would be concerned about case longevity when I started going for the stratosphere numbers.

Greg

To be honest, I'd be happy staying in the mid-high 2400's.  2500fps is 18" velocity, and I found several loads that were that and higher with no signs. From a 16" barrel, I'm already getting more than I ever expected.

Comprehensive Report. Certainly makes the case for the short, fat 6.5x39mm Grendel cartridge, in a 16" barreled rifle.

Since this was all done at 60 degrees F, it will be interesting to see what happens when the temps jump up to 80, 90, and 100 F. We don't have to worry about that for a while, but we had a ton of 100 F + days this past summer.

Good info, OP.

Just wanted to toss in that the factory 123 A-max is 2546 avg. in my 20" Grendel.
And that the 123 gr. SST set the new standard for accuracy among the ten or so factory rounds I've tried in that gun.
Right now I'm working up some Sierra 120 gr. Pro-Hunters over IMR 8208 XBR, but will be loading some of the 123 gr. SST's shortly.





 

How do the Sierra 107's do accuracy wise? I got a 1K box of them for the someday 6.5 build.

Just don't go over 28.5gr of 8208, and work up to it. It's a rather fast powder, but people like it for the temp stability.




Bwaites has gotten impressive accuracy with the 107gr SMK in at least one of his Grendel's. I think the 107's are better for longer barreled guns where the velocity can make up for the lower BC just a bit, but I personally prefer the 123gr pills.

Have you done this with 8208?  I am getting  2550 ish with an under max load in my 24" and mid 2450 ish with my buddies 20"

I've done some ladders with 8208 and the 100gr Nosler Ballistic Tip.

Brass: Lapua
Primer: Rem 7.5
Powder: IMR 8208 XBR
Bullet: 100gr Nosler Ballistic Tip
Barrel: 16"

29.0 gr 2523 fps
29.2 gr 2540 fps
29.4 gr ?
29.6 gr 2568 fps
29.8 gr 2629 fps
30.0 gr 2584 fps
30.2 gr 2641 fps
30.4 gr 2675 fps  

Nosler has published data for that bullet and powder. Their max published load for 8208 with the 100gr NBT and Partition is 29.0 gr, which gave them 2745 fps from a 24" Pac Nor barrel. My ladder appears to have gone 1.4gr higher than max.

Nosler Grendel Data

I just pulled my records for my testing on the CFE. 24" Black Hole 264 LBC. 123 AMAX  Lapua new cases with Remington 7 1/2's.

31.2       2655
31.5       2692
31.8       2710

Primers were looking good and accurcy was decent for intial testing.

Greg

Isn't 31 gr of 8208 up into the neck?

Just went and checked. Yes, it is for me, just barely staring to hit the neck. With the 100gr NBT's, I'm sure it was a compressed load, even at 30.4gr.

Here's a cool video made by one of the Grendel Forum members, blasting steel in Las Cruces New Mexico:

That's cool, but I do that with my 18" BCM 5.56 and Privi 75's over TAC.
Off a bi-pod and a rear bag on the ground

I do not think he was implying you couldnt

A 120 or 123gr hitting steel at 300-500yds is a different ball game than a 75gr HPBT.

I watch a lot of 5.56 on steel throughout the year. The Grendel makes a much nicer silhouette shooter, with solid impact on steel.