Changing primer improved accuracy by 1.5MOA is that even possible?

[Toydy]

I finally got a new lot of RL26 and I wanted to try WLRM primers in my 280AI. I wanted to change over to them because the barrel is short and I often hunt in the cold- sometimes extreme cold. So I first loaded up a ladder with the new batch all with the WLRM. Went to the range and fired them and when I got to 2905FPS I shot the next 1/2 grain up, light ejector marks, so I came home and pulled the higher charges.

I reloaded 4 with BR2 primers and 4 with WLRM, same charge, same seating depth. HUGE jump, which I have been reading has been successful for some people.

Went back to the range and shot all over the chrono. The crazy thing is my AVG MV was exactly the same over both strings at 2886. My SD and ES were a bit better with the WLRM, BUT my group size shrank from nearly 2MOA with the BR2 to just over .5MOA with the WLRM.

I'm like, whoa, is this even possible? I'm still kind of in disbelief and wondering if there is something wrong with my mount, or my action screw. How can group size shrink that much when MV stays the same, the only difference being primer?

I had nearly given up on my 270wsm as I couldn't get it under 1.5 inch at 100 with federal 215m primers. Same load with cci br2 primers now shoots 3/4 inch at 200.
Blew my mind

 

[Chase723]

The PRB did a test looking at ES/SD w/ different primers and found that there was definitely a difference with different primers. Personally, the only ones I've ever used are Federal and Winchester, and I've had excellent results with both across several rifles. That being said, the thought of even buying and trying several different types of primers for load development doesn't cross my mind at all. Get a match grade barrel and free float it. It'll solve the vast majority of "problems" and reloading for one is easy. To the point that when I buy a barrel in the caliber/cartridge that I want I typically decide what bullet I want to shoot out of it first and then spec the barrel so that I expect that it'll shoot it. I.e. with the correct twist and enough barre length to generate the velocity to guarantee it'll stabilize it, and will perform at the distance I intend to shoot it at. At that point there's no reason it shouldn't.

For perspective, I just re-did some load development for a 6.5 Creed that had a little throat erosion and stopped consistently shooting 1/3 MOA. The bullets I was previously using couldn't be seated long enough anymore to stay in the case to chase the lands. So I bought 500 130gr Berger hybrids on the premise that 1) They are jump tolerant 2) They should stabilize in a 1:8 twist and 3) They should be long enough to get me 20-30 thousandths off the lands and still fit in my magazine. That all materialized and in less than 20 rounds I had a load that shoots 1/3 MOA at 300. The wind was constantly shifting and gusting 35mph so I haven't used it at 500 yet but my expectation is that it's going to pretty decent.

 

[pslater]

I finally got a new lot of RL26 and I wanted to try WLRM primers in my 280AI. I wanted to change over to them because the barrel is short and I often hunt in the cold- sometimes extreme cold. So I first loaded up a ladder with the new batch all with the WLRM. Went to the range and fired them and when I got to 2905FPS I shot the next 1/2 grain up, light ejector marks, so I came home and pulled the higher charges.

I reloaded 4 with BR2 primers and 4 with WLRM, same charge, same seating depth. HUGE jump, which I have been reading has been successful for some people.

Went back to the range and shot all over the chrono. The crazy thing is my AVG MV was exactly the same over both strings at 2886. My SD and ES were a bit better with the WLRM, BUT my group size shrank from nearly 2MOA with the BR2 to just over .5MOA with the WLRM.

I'm like, whoa, is this even possible? I'm still kind of in disbelief and wondering if there is something wrong with my mount, or my action screw. How can group size shrink that much when MV stays the same, the only difference being primer?

I too am doing what you are in my 28" barreled 284 Win - trying RL26 with magnum primers. Did you back your loads down for the magnum primers? If so, how much.

 

[crkckr]

My first thought was, go out and shoot 4 more groups with the same load and then you can call it a .5 moa load. I've "missed" the shots into a small group before and was never able to duplicate it again! And the following groups were not very good, either. Very disappointing, to say the least.

Assuming you can duplicate the load & accuracy again, I would venture a guess that the combo of the new lot of powder and the primer change is what did. I've had changes in accuracy with primer changes but never that dramatic. If you can duplicate the load at least a couple of times more, I'd run (ok, drive fast!) back to where you got them and buy as much of both lots as you can afford!
Cheers,
crkckr

 

[Troutslayer2]

I did back down, but MV remained pretty much the same.

I checked my load at 300 yds- same size group just over .5MOA and it was a little breezy. This was eye opening for me. My theory- taller powder column in 280 paired with short 22" barrel = give it more fire to make sure all powder is ignited before the bullet exits the barrel.

 

[Mikecr]

You won't get all the powder burned in 22". Some of it will turn to fireball(high muzzle pressure) igniting against the backside of released bullets. If you set up paper ~6' from the muzzle you'll see it peppered with burning & unburned powder.

 

[crkckr]

I'll have to agree with Mikecr, with anything short of 15 gr. of Bullseye, it's pretty unlikely you'll get everything to burn in a .280 with any rifle powder. That said, you certainly may have improved the burn with a different primer, which may have given you that jump in accuracy. I'd say in this case, don't try to science the stuff out of it, just go get some more of that same lot of powder and primers and enjoy your new-found luck! Personally, I'd be happy as a clam with luck like that, it's not the kind of luck I usually have, that's for sure. Last night the wife's battery died and I spent most of this afternoon getting a new one at just over a hundred bucks. That's a lot of powder & primers!
Cheers,
crkckr

 

[Dirtrax]

It is all in the way the primers are seated and of course barrel timing.

Please explain.