I am using an Odin Works 18" DMR profile, adjustable gas block, and a suppressor.  I am shooting factory 123 Amax, 123 ELD-M, and 123 ELD-M handloads with 29 gr of CFE223.

At 100 meters I got around .4 MOA.  A little worse with the factory stuff.  No problem, but at 200 meters, I couldn't hardly hit anything.  I did finally find that zeroed at 100 meters was giving me around 8 inches of drop.  Why would that be?  Also, my groups really opened up, like 2 MOA or more, this was with factory ELD and AMAX.  Not sure why.

On my handloads using 29 grains of CFE, No. 41 Primers, once fired Hornady brass originally fired in my weapon, and 123 ELD-M bullets, I was starting to get some flattening of the primers, not excessive, but more so than I would have thought.  This was with both suppressed and unsuppressed, did not adjust the gas block, left it at my suppressor setting for both (doesn't eject the brass on that setting, just buffers them some).  OK or back off some?  Tried using the club chronograph but it was not working, need to buy my own.

Thoughts?  Thanks.

That does seem strange.  Ran some numbers and it looks like if you are truly zeroed at 100 you should be close to 4" low at 200.  8" low seems a bit extreme.  A chronograph would help figure things out a bit.  Sorry, I know that's not much help.  Was this just on a single range trip?  If so maybe try to repeat the results you saw...?

29.0gr of CFE is a very mild load under a 123gr cup and core bullet.

I'm guessing somewhere in the high 30ksi region for pressure, provided you aren't jamming the lands.

What are your fired case neck measurements for diameter?

How long are your cases before and after firing?

What is your bolt face depth?

What is the gas system length?  Is it Intermediate (between MLGS and RLGS)?

If your case necks are .267" outer diameter, something is way off.  That would be for a 6mm wildcat, not Grendel.  (.267 - .243 = .024, .024 / 2 = .012" neck thickness )

Fired necks should be at least .295" for the tighter chamber variants, and .300" for SAAMI.

That was internal diameter.  I will check out diameter when I get home.

Outer diameter was .299 to .300

Do cartridges fit snugly in your chamber, or do they rattle around?

Checked that too, cartridges seem good in the chamber.  Maybe I am just being a little paranoid since these were my first handloads. Gonna order the chronograph tonight.

Since I had posted this originally here, I thought I would add the below, which is a cross-post of mine from the Reloading forum.

Okay, I got Caldwell Chronograph and took it out today, really like it and the app to use on your phone. I tested 556 and 6.5 Grendel, my own loads and then looked at some factory loads and the stated fps on the boxes. I want to see how accurate the advertised fps is compared to my loads and the accuracy of the chronograph.

Are factory fps specs on the ammo boxes usually very accurate? I shot a 5 round group of factory AE 223 55gr FMJ that on the box shows 3240 fps and I got 2949 avg. I also shot a 5 round group of factory Hornady 123gr ELDM that on the box shows 2590 fps and I got 2472 avg. (and the Hornday manual shows a speed of 2590 fps exceeding the max fps for all powders listed.

I was using the IR option on the chronograph, instructions said it is more accurate. It was sunny out. Temp was 79. BP was 30.01 inHG.

556 loads: 25.5 =/- .01-02 grains of CFE223 shooting Hornady 75gr HPBT out of a 16" barrel, shot five sets:
- Set 1: Avg of 2619 fps with a range of 2553 to 2716 fps (5 shots total, one did not register)
- Set 2: Avg of 2652 fps with a range of 2613 to 2696 fps (5 shot group)
- Set 3: Avg of 2711 fps with a range of 2631 to 2774 fps (4 shot group)
- Set 4: Avg of 2676 fps with a range of 2614 to 2730 fps (5 shot group)
- Set 5: Avg of 2695 fps with a range of 2669 to 2712 fps (5 shot group)

The Hornady 10th edt manual for 556 for this load is around 2800 fps.

6.5 Grendel loads: 29 gr =/- .01-02 grains of CFE223 shooting Hornady 123 gr ELDM and SST out of a 18" barrel, shot two sets:
- Set 1: Avg of 2291 fps with a range of 2215 to 2322 fps (5 shots total)
- Set 2: Avg of 2254 fps with a range of 2191 to 2299 fps (8 shot group)

The Hornady 10th edt manual for 6.5 Grendel for this load is a little over 2300 fps. I previously shot a three shot group and got a little over .3MOA with it.

I am not sure why the factory stated FPS are so far off or why the 556 and 6.5 Grendel loads are so much less than the manual.

Sometimes in the manual they will test the load using a 24" barrel.  I think the published FPS for ammo is a lot like MPG or Horsepower on a car.  Real life is always lower.  You are getting great groups, I wouldn't sweat it.  

By the way, My Grendel shoots plain old Nosler 120gr. Hunting bullets better than the fancy schmancy Hornady A-Max.  Go figure.
There's nothing like popping a Coyote in the noggin at 3 or 4 hundred yards.  

The Hornady manual says the test loads were shot from an 18" Alexander Arms barrel with WSR primers.  I would imagine various factors would contribute to differences and this is my first foray into reloading.  I inspected the factory Hornady brass I shot and compared them to my loads, does not appear to be much of a difference.  I might load them up a little more and try again.

Hornady shows 2300fps from an AA 18" Grendel with a collection of 120-123gr bullets, including the 120gr GMX, which really needs its own data separate from the cup and core bullets.

They show 28.7gr of CFE223 at 2300fps, which is what I would expect from the 120gr GMX.

That's a really low pressure load for Grendel, probably lower than 9mm working pressure.

With a 123gr Hornady cup and core bullet, 31.9gr of CFE223 is where a pressure test SAAMI chamber/breech averaged 50ksi.

Notice how Hornady's data goes up for 129gr cup and core bullets to 31.7gr, because there is no GMX in that weight class.

An 18" Grendel will easily do over 2500fps with not even a max load of CFE223, so there is no need to stress the system to get performance.

The 2590fps figure you see on box ammo or on Hornady's site is for 24" Grendel.

Their 2350fps numbers are for a 14.5" AA Grendel, and that's slow for a 14.5", more like 12.5" Grendel speeds.

A general guideline that seems to play out well is that 12.5" Grendels are in the low-mid 2300fps region with 123gr, 14.5" are in the mid 2300-low 2400fps, 16" are in the low 2400-mid 2400fps, and 18" are in the mid 2400-low 2500fps range.  20" are in the low to mid/high 2500fps.

Temperature is the biggest variable I've noticed, which is normal.

Thanks, sounds like I can safely up the velocity some then to around 29.5 to 30.  Mostly going to do ELDs but some SST for hunting.

31.2gr of CFE223 under a 120-123gr cup and core bullet (not a solid for those that are just getting into reloading), is a mild load in a SAAMI chamber.

We're looking at 46,235psi average with that load for me at 2.245" COL.

30.0gr of CFE223 under a 123gr Hornady bullet is still very mild chamber pressure, all things equal.

Hornady's max listed load under a 129gr cup and core bullet is 31.7gr in the 9th Edition.

For comparison's sake I was getting ~2480 fps with 31.2g of CFE223 behind the 123 AMAX's out of my 18" Lilja barrel.