Different Primer Produced Unexpected Change

[3deers]

After a bullet failure from a competitive brand premium bullet last year, I decided to get back to my roots, and load only Nosler Partitions, which have never let me down.

My load for my 308Win was always as follows:
- Single-lot, R P Brass, partially-sized, and trimmed to 2.010
- CCI 250 Magnum LR Primers
- 47.0gr of WIN748
- #16330 - 165 gr Partition Spitzer

This load averaged 2,698 FPS with very little variation, and shot 1" groups, .900 on a good day.

Unable to find the magnum CCI's anywhere, I did a textbook No-No, and changed a component without reducing the load and building back up at 1/2 grain intervals. I replaced the CCI 250 magnum primers with CCI 200 regular Large Rifle primers. Although some primers were flatter than I usually accept, there were no other adverse indications of pressure. However, accuracy was a completely different story! The load sprayed 4 inch groups at 100 yards. (I did not have access to chronograph that day.)

This is so far removed from my expectations that it prompted me to write. Can this be? Should I be looking for another problem with my reloading, or does this actually make some sense to anybody? Variations in the "flatness" of the fired primers suggests to me that the regular primers are not providing the consistency of ignition of the powder that the magnum primers of the same manufacturer provide.

I tried a few factory loads afterwards just to make sure that there wasn't a malfunction in my erector tube, or some other mechanical failure.

Any expert opinion is appreciated.

 

[DrMike]

Primers can affect pressure by a significant degree. I've witnessed velocities changing by as much as 150 fps by a change from a magnum primer to a large rifle primer. Pressures were altered accordingly. Change the pressure curve and the nodes change. Change the nodes, and accuracy is altered. Makes perfect sense both from theoretical and practical observations. Consequently, welcome aboard. Glad to have you joining in the conversations. This was a great question that addresses an issue often ignored. I doubt that you did anything wrong other than change the primer, which altered the brisance in a major fashion.

 

[MAinAR]

Would not have seen near the change if had stayed with Mag Primer like load was developed with, would have been some change but not to the degree you witnessed had you used Fed 215 or WLRM instead of going with "cooler" / lower brisance primer when you switched from CCI250 to using CCI200. Considerable difference there.

Backing down and coming back to known speed with another quality "Magnum" primer and accuracy will return. Not to mention that most of the time any "Ball" powder needs the Magnum Primer.

 

[sask boy]

3deers welcome to the site !! I am sure that you are going to enjoy the posts here as the guys & gals are very knowledgeable & a lot of fun as well.
I have changed primers on many of loads with very little change in accuracy but I do not use magnum primers unless it is a magnum cartridge and I do not use ball powders. I am not saying there is anything wrong with that it is just my own loading practices.

Blessings,
Dan

 

[Kodiak]

Its to be assumed that you've looked for loose screws, etc. as a go-over on the rifle. Some times even changing lots of the same powder can result in group sizes and pressure changes. And inserting a pistol-primer for a LR primer does wonders for groups.

Just guessin' ya know,

 

[OU812]

DrMike gave a spot on explanation as to what you observed. My 06 with 165 BT shot 3-4 inch groups with WLR primers and shot less than an inch with Fed210 primers with all else being equal.

 

[3deers]

Primers are probably what I know least about as it pertains to hand-loading.
Can someone offer where I can learn more about "Brisance" and "nodes" ?

 

[1Shot]

As to your primers being more flattened when you went from the mag to the standard. It probably was not caused by MORE pressure it was just the effect that the already high pressure had on the thinner primer cup on the standard primer. According to some of my load data you are only 1/2 gr from a max load of 748. Different primers do make a lot of difference in accuracy. Changing from one bullet to another of the same weight can also cause pressures to go wild. Like you already know but did not follow, if you change anything in a load BACK OFF AND WORK UP.

 

[3deers]

Thank you, 1shot. I appreciate the input.

 

[HomerOz]

G'Day Fella's,

3 Deer, it is generally recommended that when using Ball or Spherical powders (like Win 748, which FYI is a great choice for the .308 Win), that it's best to use Magnum primers for best results.

FYI, the only rifles I reload ammo for that I use Standard LR primers in, is a .22-250AI and a 6.5x47 Lapua. In all other rifles (with either Ball or Extruded powder), I use CCI-250 or Rem 9 1/2 Magnum primers, and obtain great accuracy with most!

Hope that helps

Doh!
Homer

 

[PJGunner]

Homer. I'm inclined to disagree on the use of magnum primers with ball powders. Until I got my RCBS Chargemaster I almost totally quit using extruded powders of any kind with the exception of 4895. One of my favorite powders is Winchester's long discontinued WMR (Winchester Magnum Rifle) that I use in the .270 Win. and .300 Win. Mag. I get good velocity and tight groups whether it's 100* outside or a few degrees below zero. I get basically the same results with W760 and all I use is the Winchester standard WLR primer.
I use the data from the little Winchester #15 loading booklet and they say to NOT USE magnum primers with their ball powders. Loads worked up in the summer and used in December and January on my elk hunts have worked just fine with no change in point of impact. I do use magnum primers when I load the .404 Jeffery and .416 Rigby as they literally take a dump truck load of powder. :wink: :lol:
Paul B.