Home Forums Hunting & Shooting Ask The Gunwriters Switching primers

John or whoever, I've been loading 10mm auto with 220 grn. Hard cast over 8.3 grains of Blue Dot with CCI 300 primers. My question is I've run out of CCI 300 but have plenty of CCI 350. How much should I reduce the powder charge to compensate for the hotter primer. This is a pretty heavy load but I ran it up 9.0 grains with no apparent problem but backed off to a interpolated charge figuring different between 180 and 200 grain book loads.
Thanks much --- Mel

Nobody?

Mel I use 8 gr max most accurate in my 10MM with standard primers. Same 220 gr bullets you use. If I was you would drop it to 7.5 grains and work up for accuracy and reliability. Not much data on the 220 gr cast bullet in the 10 MM and it runs pretty close to the edge.

Thanks Kurt. I was thinking of dropping back 8.0 with the magnum primers
My 8.3 load was worked up to and past and seems to work well with good accuracy and function. No signs of excess pressure and was arrived at by comparing book loads different between 180 and 200grain loads. Started out at 7.5 and worked up. Went all the way to 9.0 grains of Blue dot and still showed no pressure signs other than recoil was getting a little strong. Backed off to what I had figured as a max load and all worked well. I pretty much figured how much to back off , just hoping for a little discussion. And you're right about no info with 220 gain cast.
Looks like if you ,(I) run out of blue dot. You can work up to around 8.0 of 2400 and get good results --- Mel

I'm in the same position primer wise. I bought the last online issue for Handloader Magazine because the front cover had a line about substituting primers.... Turns out it was one letter asking Brian Peirce about one specific powder and load. Brian broke out his chronograph and found no real difference in fps. His reply was a careful "with this load you are probably OK but start low..". I was hoping for more detail.

If you do a search, you’ll find a couple of recent threads here about substituting primers. Despite all our concern over the years, the current situation seems to have moved us in the direction of “primers are primers.”

Rule of thumb was reduce load by 10%.

In the past, I have seen significant differences in accuracy when switching among large rifle primers.

The standard of 10% reduction has always seemed a bit extreme to me, particularly when it would take the load that I am shooting below the suggested starting load.

Velocity could be the same but what about the pressure curve? I have no qualms about substituting mag primers for regular primers but I reduce and work up to be safe especially when near or at max.

How are you determining this pressure curve?

I leave the pros do that and I use their published data.

There is no way I could know how a particular powder will react with a particular primer. That's the problem and that's why I stay with published data especially when dealing with fast burning or handgun powders.

Without published data I work up gradually.

I seem to recall several years ago I was loading .44 mag pretty close to Elmer's load, 250 hard cast Keith over I forget exactly around 20 - 21 grains (Elmer's was 22 grain) of 2400 with CCI 300 ,Elmer's load was too hot for modern cases)for some reason loaded some with CCI 350 and the cases were pretty sticky on extraction, backed off 1 grain and all was well again. Gun was a 4 screw 4" Mod 29 Smith. Think I've answered my own question. --- Mel

I experienced the same thing with my 29. I started out with Norma brass and Elmer's load of 22 grains of 2400. I had the cases sticking. Dropped down to 20 grains and everything was OK. I always attributed it to Norma brass being soft but stuck with 20 grains for any case just to be safe.

I believe Elmer stressed regular, not magnum primers. I seem to recall, also, that today's 2400 is a bit faster than 2400 in Elmer's day. I too have loaded and shot a lot of "Elmer's load", but reduced it to 20 grains of 2400. As a matter of fact, I was looking for my RCBS 44-250K mold at my son's house recently, still looking. I'd like to make up a batch of them.