Shot about 10 rounds of .260 through my Tikka T3x CTR (20") barrel chronoed with the radar type chrono graph from an RO at the range.  Sorry I didn't write down the actual data.

Average 2690
SD.  28

I was a little surprised with the velocity spread.  Best accuracy I've achieved (and I could be to blame) was .75" 5 shot group at 100.

Not terrible but it doesn't fit with the internet hype surrounding the Prime ammo.

Which hype are you commenting about, accuracy or velocity?  I've been shooting a lot of Prime though a LaRue .260 gasser with a 22" barrel.  I'm getting 2880fps with SDs in the low teens.

Both.

Maybe your rifle just doesn't prefer the Prime.  FWIW, I'm getting very consistent MVs and took the LaRue to 1000y using the Prime.  The Prime is loaded to the top end for a gasser and I'm actually getting better groups from the Hornady 130 ELD-M which is clocking about 100fps slower.

.75 and an ES of under 30 is about as much as you can ask for in factory ammo.  

ETA I was thinking ES of 28.  Your barrel may not like it and you'll ave to try something else.  

Not .260, but bought 200 rounds of the Prime Ammo 6.5 Creedmoor to run in my Savage + Shillen 24" 1:8".

10-shot with Labradar:
Average 2877.52 fps
Highest 2897.46 fps
Lowest 2850.45 fps
Ext. Spread 47.01
Std. Dev 14.42

The groups were not good at all. Just over an inch at 100. I ended up selling the rest of the ammo after I couldn't even get the brass to shoot well in reloads.

It really does shoot good enough I think, for now.  good enough that I just ordered some more to use until I get the reloading gear set up.

Hopefully the brass works for me.  I'll have several hundred pieces, I was kinda banking on it.

I'll leave as a reference some Prime 130gr data from my 22" Krieger gas gun in 6.5CM.

10 Average shot, shot during break in. Directly  after this group was shot I shot ELD-X and the SD was 10.1 for a 10 shot group which was representative of a very good lot of ammo as Hornady loads tend to have SD's in the teens far more commonly but I don't think the barrel breaking in was the issue.

Max 2861
Avg 2829
Min 2787
SD 23.8

NEXT group was after break in the velocities come up a bit due to the break in but the sd's are still high. 19 rounds

Max 2909
Avg 2869
Min 2825
SD 22.2

Both of strings Prime were from the same order so probably the same lot. I haven't shot it without the bayo on for accuracy yet because once I saw the SD I was unmotivated. All in all Prime ammo tested for the highest SD's of any factory match ammo I've tested in both my 6.5 and 300WM. I don't know if I just hooked into a bad lot but if it happened again I'd steer clear for good. I want to see SD's in the mid to low teens for factory match ammo and I've velocity tested enough loads to know that it's very doable. Hornady varies highly and SD's have ranged from 10-20 in both my calibers, but seems to more often be around 15. FGMM was 9.6 SD for the 300wm btw.

I'm curious if the OP has tested FGMM in the 260?

For all the hype Prime advertises with single digit SD in a wide array of rifles, I'd be contacting them for an explanation. High 20s for SD is unacceptable when compared to what they've been stating they're ammo is capable of. Heck cheap $20/box Hornady 6.5 CM 140 BTHP is only an SD of 8-9 fps in three rifles I have.

Granted I know each rifle is different, but still...give them a call and see what they'll do. Their customer service is very good and I know one person who ordered some 9mm match ammo that they helped when their glocks just would not accurately shoot it.

I haven't shot any Prime 260, but I have shot a ton of the 6.5 creedmoor that utilizes the same projectile and powder and it has been very consistent and accurate in several bolt guns and AR's.  I also have several friends that absolute love the Prime 260, so I'm guessing you are one of the unfortunate ones who has a rifle that just doesn't like it, which sucks.

No I haven't tried the FGMM.  The rifle is new with only 63 rounds down the tube.  I did email Prime.  They said the SD was higher than they are used to seeing.

From what I've been told they are using Norma brass, which I've always thought was really good brass.  Any idea as to why the brass would be an issue with your reloads?

Norma is a Ruag company and IIRC the 260 uses Norma brass and the Norma 130gr Golden Target bullet.

You were told correctly it is norma brass, and I do find it very odd that he isn't having good results with the brass for reloads, a close friend of mine has 800 pieces of their 6.5 creedmoor brass with 4 reloads on it with great results.

Have you tried other ammo yet?

My results, Prime .260 130g
Savage LRP 26"

Avg. fps 2879 @ 76 deg F

ES: 76
SD: 25

Groups not great, just over 1 MOA, but keep in mind I don't shoot this rifle as well as I do some others.

Other commercial loads do better for me.

Yeah I definitely recommend getting a box or two of several different brands and seeing what your gun likes.

I have no idea. Granted, Hornady once-fired didn't shoot well for me either. I wonder if it is my reloading process, or even the CCI BR2 primers.

I have some data and photos comparing Lapua and Prime brass here: https://www.ocabj.net/precision-rifle-project-series-savage-10fp-part-4/

I tried some Prime 260 in my 24" 1/8 lightweight Remington.

It didn't really group well at all.  1.5-1.75MOA.  It was consistent out to 1K..  Didn't do anything that any cheap (relatively) off the shelf loading wouldn't.  

I case of the 77SMK in 223.  We'll see how it does from a 1/8 Pac-Nor.

I used my Chrony on a new lot of Prime.  I don't have many rounds left.  What I noticed was that I could feel a difference in recoil and those higher recoil rounds had higher velocity.

Data

cold bore

2728
2696
2694
2717
2738 More recoil
2720
2721

warm bore

2718
2708
2737 more recoil
2743 more recoil
2747 even more recoil
2737 more recoil
2737 more recoil
2711
2701
2743 more recoil