Warnberg wrote:

Here was my thought and I could be all wet... but I have "heard" in the 204 partially compressed loads preform better with a magnum primer and that the 204 seems to just like partially compressed loads. So I specifically started working with a load that once worked up to max (as long as no over pressure signs where present) would end in a 100% plus fill ratio. My current test loads are with the standard CCI 400 primer. With that in mind I was thinking that a magnum primer would work better to fully ignite all the powder, thus giving better performance... Am I on the right track? FYI, I will also be testing the 35gr Berger and the 32gr Hornady V-max Thanks Dave

Hi Dave, you are on the right track for sure. My .204 was by far most accurate with slightly compressed loads. The Sierra bullets, especially the 39gr Blitz King had a very slight edge over the Hornady bullets. I did not experiment with standard primers, but used only magnum primers as this is what was recommended in all the reloading manuals (CCI450 and Rem 7 1/2). I tried Varget (not so good results) and several IMR powders. The best results for accuracy were with IMR 3031 powder. IMR 4895 also worked quite well. Interestingly, IMR 4064 gave the most consistent chrono results (least deviation) but not the best accuracy. The only signs I ever had of pressure issues was with 8208XBR powder - cratered primers well below the max listed loads.
The loads my rifle especially liked were both with IMR 3031 powder in Nosler Custom brass (Rem bulk brass also ok):
25.6gr powder with the Sierra 39gr bullet
26.5gr powder with the 32gr bullet
Rem 7 1/2 and CCI 450 primers gave identical accuracy and chrono results.

inthedark wrote:

Hey MacD I use magum primers in both my 22-250 and 308 loads WHEN I am hunting in 0 degree F or below weather. I have found that using the magum primers in warm weather throws my accuracy right out the window. And as I am in brisk old Saskatchewan, I have had plenty of experience with the benefits of mag primers.

My Brother in-law used to have a .17 rem center fire and I used to load ammo for him. We where out coyote hunting one cold winter day (Southern Sask.) and he was getting a misfire about every other round. A couple days later I worked up a new load for him, using magnum primers, and he never had another misfire. Accuracy was the same.

I use mag primers in my 25-06 but standard primers in all the rest.

Oh, forgot to mention this, but 1895's post reminded me. I tried comparing chrono results between rounds frozen (-4* F for three days in the freezer) and rounds at 75* F, using several powders. All were .204 rounds with magnum primers. NO misfires (40 rounds total). There was absolutely no difference at all between frozen and warm rounds using 8208XBR and IMR 4895 powders, and only about 60 to 150 fps difference using IMR 6064 and IMR 3031 powders. Velocity range over all the different loadings was 3650 to 3900 fps, so this was a very small percentage. The 3031 and 4895 loads were slightly compressed, the 6064 had a little room left, and the 8208XBR left lots of airspace.

Edit: The 3031 had the widest spread on the chrono, but still the best results for accuracy.

Unless the manual specifies magnum primers use the standard primer. If you want to switch to magnum primers then reduce the load and start working the load up from there.
NOTE: magnum primers and light loads are not necessarily safe. Magnum primers can cause detonation with light loads if too much powder is ignited at once. Powder is supposed to ignite and burn from a single end (or side) to the other end (or side). If it starts burning in more than one place the flame and shock fronts meet causing a rapid rise in pressure that can be well over what a normal burn would produce. This is more likely to happen with slow burning powders and double base powders but it is not limited to those powders.
Please be careful.

While I strongly agree that magnum primers should not normally be used in non-magnum cartridges, as with most things there are a few exceptions. One of these is when using ball or spherical powders. These powders usually have a heavier protective coating than "stick" or "short-cut" powders and often give inconsistent ignition, particularly in cold weather. It should be up to the individual to conduct "due diligence" and research the powders with which they are working to see if this is a fit for their application.

And, as always, if making a change to magnum primers, be sure to reduce the load and carefully work up.

SingleShotLover wrote:

While I strongly agree that magnum primers should not normally be used in non-magnum cartridges, as with most things there are a few exceptions. One of these is when using ball or spherical powders. These powders usually have a heavier protective coating than "stick" or "short-cut" powders and often give inconsistent ignition, particularly in cold weather. It should be up to the individual to conduct "due diligence" and research the powders with which they are working to see if this is a fit for their application. And, as always, if making a change to magnum primers, be sure to reduce the load and carefully work up.

Thanks for this. I like to hunt in cold weather and was avoiding those powders as they show temperature sensitivity.

would it be safe to assume that the start load would be safe with a magnum primer?

i.e. this is according to berger's load chart for thier bullet

40gr Berger BT (bullet) ruger 204
H414 powder
start load 26.0 gr (safe to use magnum primer starting here)?
Max load 28.8 gr

Warnberg:

If you use a mag primer and start with min recommended load, you'll be ok.

Warnberg wrote:

would it be safe to assume that the start load would be safe with a magnum primer? i.e. this is according to berger's load chart for thier bullet 40gr Berger BT (bullet) ruger 204 H414 powder start load 26.0 gr (safe to use magnum primer starting here)? Max load 28.8 gr

Again, Warnberg, you are talking about the .204 - Magnum primers are recommended for the .204 in all the loading manuals I have ever seen (six different manufacturers' manuals). I would hesitate to try standard (non-magnum) primers in .204 cartridges.

Marty -

My Lyman and Hornady manuals say Rem 7 1/2 (not really 'magnum' primers). No mention of magnum primers being recommended for the .204 Ruger. Not to say they can't be used, but I've never found them necessary for accuracy or reliable ignition.
H4895 or IMR8208XBR with Rem 7 1/2 primers produce excellent accuracy and velocity.

On the subject of primers for the .204; don't use CCI 400s. Way too soft a cup for the pressures the .204 develops, except at very light loads.

44marty wrote:

Magnum primers are recommended for the .204 in all the loading manuals I have ever seen (six different manufacturers' manuals)

Are you calling the Federal 205M a magnum primer by chance ???
I see it listed more than any others in the .204
The "M" stands for "Match" not magnum. Federal has confused a lot of re-loaders with this one !!!

The Rem 7 1/2 and Fed 205M are both "match" or "benchrest" primers - Hotter than standard primers. Hornady's manual lists them as magnum primers in their primer comparison table. The Rem 7 1/2 is approximately equivalent to CCI small rifle magnum primers (CCI 450).
I was getting no difference in either velocity or accuracy using Rem 7 1/2 and CCI 450 in my .204 given the same brass, bullets and powder charges.

I knew that some time ago Federal revamped the rather weak 205M to a hotter primer.......... just didn't know they turned it into a magnum.

Marty -

found the chart you were talking about. Yup, they call the Rem 7 1/2 'magnum'. Kinda surprised me, as disagree with that.
Then, I saw the caveat at the bottom which says:

"This chart is not intended as a substitution chart. It does not indicate primer intensity, merely a primer's physical dimensions."

The major physical difference between the standard SR primer and what they call magnum is cup wall thickness. The standard primers run about .020"
where the others run about .025" thick. The purpose being to withstand the higher pressures run by the match and BR loads. This, also follows for use by us shooters who load high pressure varmint cartridges like the .204 Ruger.

If you load to pressures in the 40,000 psi range and above, it's best to leave the standard primers behind.

HayCreek wrote:

If you load to pressures in the 40,000 psi range and above, it's best to leave the standard primers behind.

HayCreek: it's best to leave the standard primers behind.

You may want to re-think this, I re-load a 340 wby mag with no problems at all using a large rifle primer (not magnum) behind 4831 with no problems. My rifle is a mark v 340wby, higher pressures it is but never had a failure in 18 years.