Help with 8208xbr & Amax

[outlaw45]

I've built my Grendel with a Lija 20" barrel, Giesselle SSA-E, and Vortex 6-20. I've been shooting 123 A-maxes with 8208xbr and looking to get 1/2 moa. Shooting the factory Hornady 123 A-max I can get about 1" or a little bigger. (bottom right group) On this target I've loaded 28.3gr, 28.5gr, and 28.7gr. 28.5gr seems to be the better of the three loads. C.O.L. was the same as factory Hornady, 2.245 and Win small primers were used.

I shot 4 groups of 28.5gr yesterday and all groups were 2 inch or better. Today, one group of 28.5gr seemed to group somewhat consistent to the Hornady load.

Velocity for 28.5gr averages 2473 fps, on this target it was shot last and velocity averaged 2503 fps. The factory Hornady's load averages 2485 fps.

Sounds like everyone has good luck with 28.5gr except me, can anyone help?

[Drifter]

28.5gr of 8208 with 123gr A-max has been rather hot in most barrels that I've tried, resulting in vertical dispersion as a couple of your groups show.

I usually have better luck around 27.8gr of 8208, and with COL of ~2.250 with the 123gr A-max. Trying different primers can sometimes help also.

If you haven't already done so, try an OCW and / or ladder test to determine your optimum load. Check your brass and watch your chrono for irregularities as you approach max charge weights.

[NugginFutz]

^^^ This.

Virtually all the 8208 loads for 123 Amax or SST cap out at 28.5.

Mine shoots quite well at 28.0, seated at 2.260".

Cases are Hornady, primers are CCI 450's.

Mild crimp, using the Lee Collet crimping die (1/4 turn after initial contact).

I also wipe each case down with Liquid Aim, prior to dropping the charge.

This is a snap of my OCW from a while back. This was a secondary OCW, where I was confirming the node @ .1 gr increments. You might say it was an "OCDW".

[outlaw45]

Did you do your OCW test at 200 yards? Pretty good groups for 200 yards.

I went up to 28.7gr just to match the Hornady load velocity, wondered if groups shrink. I'll work up some lower charges.

What velocity are you getting with 27.8 and 28.0?

[outlaw45]

Also on a side note,

with OCW test, are you looking for the smallest group or groups with the smallest vertical spread?

[NugginFutz]

Yes, that OCW was done at 200 yards. That would be what I consider a minimum distance, as vertical dispersion is more apparent at longer distances. 300 yards is considered ideal by many.

For long range considerations, I am always looking at smaller vertical dispersion when performing an OCW workup, with an eye on horizontal group sizes that are reasonable for wind conditions.

MV @ 27.3gr was ~2560 fps, and for 28.0gr is ~2615 fps, through a 22" BHW tube. SD is 8.7 fps.

[Drifter]

Velocity from an 18" runs ~2450 IIRC. This can vary by barrel, and with primer choice.

I look for small balanced groups, and also groups that don't change POI with slightly higher or lower charges. I usually do OCW tests at 200, and ladder tests at 300 or more.

I'm not looking for a load that occasionally produces a great group, but rather a load that consistently produces good groups. In a small sample, it's easy to get distracted by one magic group.

If you vary the charges by ~0.3gr, the resulting groups often show an area of potential.

If you want to match or exceed speeds of Hornady factory ammo, I suggest CFE-223 and / or LeveRevolution.

Experiment with COL based on your particular chamber (and magazines).

Some barrels apparently handle 28.5gr of 8208 just fine, but not the 15 or so that I've tried. Watch the chronograph closely when working with max loads, as it will usually tell you when things are getting dicey.

[tackdriver]

I have owned 6 -6.5 or .264 LBC barrels and all seemed to get pretty "hot" around 28.0 but I think there is a small difference in most all peoples scales. I use a rcbs 505 (old school), it is not fancy but repeatable it is. If you go to LVR or CFE then you should find a sweet spot around 31g+/-.

[jose]

Lever evolution

I shot some lever to fire form some lapua AK brass the other day. 28 grains with nosler cc 123 blems 24" AA at 200 yea and was about 1/2 MOA. Truly shocked.
Would post target be suck at computers.

[outlaw45]

I loaded up 27.5, 27.6, 27.8, 28.0, 28.2, and 28.3. I'll see how they do. They are loaded to a C.O.L. of 2.245, after this round I'll push them out longer to 2.250 or so and see if that changes anything.

[LR1955]

I loaded up 27.5, 27.6, 27.8, 28.0, 28.2, and 28.3. I'll see how they do. They are loaded to a C.O.L. of 2.245, after this round I'll push them out longer to 2.250 or so and see if that changes anything.

Outlaw:

What type of scale do you have that lets you measure down to .1 grain? I bet if you re-measured some of these that they wouldn't be what you think. May be higher or lower. That's why we normally do changes in .3 grains.

And, if your barrel is so sensitive to a change of .1 grain of powder that your groups go from a minute to two minutes, your barrel does not like the bullet, the powder, or more likely something is wrong with your rifle somewhere.

When you hit 28 grains of 8208 with a Grendel and a bullet in the 120 grain range, you are messing with dangerous conditions.

LR55

[waveslayer]

I did a quick run through QL and according to it you may want to try 27.8 grains of XBR which should give you around 2500 FPS. Your COL is a little short compared to others and their loads. if you push it out to 2.26 COL watch for pressure signs but you might find a node around 28-28.3 grains.

[mtn_shooter]

My rifle digs 27.6gr. I would check to see where your bullets hit the lands before seating longer. In my chamber it's right around 2.250" COAL. Once I hit the lands in mine, pressure spiked hard.

[outlaw45]

Outlaw:

What type of scale do you have that lets you measure down to .1 grain? I bet if you re-measured some of these that they wouldn't be what you think. May be higher or lower. That's why we normally do changes in .3 grains.

And, if your barrel is so sensitive to a change of .1 grain of powder that your groups go from a minute to two minutes, your barrel does not like the bullet, the powder, or more likely something is wrong with your rifle somewhere.

When you hit 28 grains of 8208 with a Grendel and a bullet in the 120 grain range, you are messing with dangerous conditions.

LR55

I loaded these on a RCBS ChargeMaster.

Then why do a lot of people claim that 28.5 grains of 8208xbr is the magic load that seems to work in every Grendel?

http://www.65grendel.com/forum/showthread.php?3861-6.5-Grendel-Preferred-Loads

[outlaw45]

I cleaned the rifle and even took off the A2 flash hider and cleaned the crown and end of barrel. Not sure if the flash hider would have any impact on accuracy but I took it off and used a thread protector instead.

The first 3 shots of the gun were factory Hornady 123 A-max. Here's that target on a 1" orange dot.


Then I shot my test loads. First 27.5gr, 27.6gr, 27.8gr, 28.0gr, 28.2gr, and 27.3gr. Groups were 4 rounds per group. Looks like around 28.0gr might be promising.


After shooting my test loads I shot 3 more factory Hornady loads. They opened up quite a bit.


So maybe a hot barrel is to blame? Temp was 87 degrees and I waited about 3-5 minutes between groups.