Well, I’m almost out of large rifle primers. If I want to keep shooting I’ll have to start using my stash of Federal 215 to use with my 180 ELDMs and 56 grains of RL 26 in my 7 Shehane. The usual answer is “reduce by 10%” but that seems like overkill to me. Is it really necessary to reduce this load by 5.6 grains just due to the different primers?
Switching to magnum primers
- Thread starter Gunracer
- Start date
For what its worth, I changed from Fed 215s to std large rife Federals in my 30.06 and 300WW, 30.06 there was just about no difference with VV N550 and I think I upped the charged in my 300WM maybe 0.2gr if I remember correctly with N560 to get to my original speed again
Not necessary IMO/IME. I would test in .2gr increments starting at .6gr below current charge and test up through your current charge by .2gr. Basically you are looking for the optimum charge for that primer not necessarily dropping for overpressure concerns. I've never had a magnum primer test cause overpressure compared to my standard primer load. For the record, I do not shoot loads on the border of overpressure to begin with so there is plenty of margin for my magnum testing.
searcher
Gold $$ Contributor
I'd drop 5% and work up. I have done a lot of velocity comparisons regarding small rifle standard versus magnum primers and found that a number of loads actually had lower velocity with the magnum primers - all being equal. I've not run such experimentation on large rifle primers - but I'd think 10% would be "excessively safe" - if there is such a thing.
If true this means you have to be careful if switching from magnums to standard in high pressure cartridges, but probably gonna be fine when switching the other way.
Ned Ludd
Silver $$ Contributor
I tried some CCI 450 and Russian 5.56 magnum primers in a .223 Rem load with 90 VLDs that had been worked up using Fed 205 primers. Both magnum primers gave an almost identical 30 fps increase in velocity for that particular load as compared to the exact same load with Fed 205s. With that particular load, it was a definite problem because the load with Fed 205s was already pretty stout, and it pretty much killed the primer pockets on the test cases with the magnum primers. I was in no way expecting that much of an increase in velocity/pressure, or I would have dialed back the charge weight by a few tenths grains with the magnum primer load. Fortunately, I only used 10 pieces of brass for the test.
So any difference you might experience going from standard to magnum primers depends on a least a couple critical factors. The first is how much greater (if any) is the brisance of the magnum primers you intend to use as compared to the standard primer you already have been using. This might be a consistent general overall increase in brisance between the two primers, but there is also likely to Lot-to-Lot variance involved as well. In other words, there can be Lot-to-Lot variance in brisance even between different Lots of the same magnum primer. One Lot might be a bit hotter than another, or vice versa.
The second factor would be how hot is the load with the standard primer? If it is a mild load and there is a lot of headroom before approaching MAX, then you can probably afford to back off the load by a smaller amount when switching to the magnum primer. The bottom line is that there is no good way to predict exactly what will happen. So the wisest thing to do is simply back off the load by some safe amount with the magnum primer, then determine average velocity with a few rounds. Comparison of this value to the velocity obtained with the old primer generally makes it pretty straightforward to to dial the load (i.e. charge weight) with the new primer back to approximately the same velocity as with the old primer, especially if you use a reloading program like QuickLoad. Even if you back off the load a bit more than you might have intended, that's always better than not reducing it enough.
So any difference you might experience going from standard to magnum primers depends on a least a couple critical factors. The first is how much greater (if any) is the brisance of the magnum primers you intend to use as compared to the standard primer you already have been using. This might be a consistent general overall increase in brisance between the two primers, but there is also likely to Lot-to-Lot variance involved as well. In other words, there can be Lot-to-Lot variance in brisance even between different Lots of the same magnum primer. One Lot might be a bit hotter than another, or vice versa.
The second factor would be how hot is the load with the standard primer? If it is a mild load and there is a lot of headroom before approaching MAX, then you can probably afford to back off the load by a smaller amount when switching to the magnum primer. The bottom line is that there is no good way to predict exactly what will happen. So the wisest thing to do is simply back off the load by some safe amount with the magnum primer, then determine average velocity with a few rounds. Comparison of this value to the velocity obtained with the old primer generally makes it pretty straightforward to to dial the load (i.e. charge weight) with the new primer back to approximately the same velocity as with the old primer, especially if you use a reloading program like QuickLoad. Even if you back off the load a bit more than you might have intended, that's always better than not reducing it enough.
MGYSGT
Silver $$ Contributor
I only use Mag Primers. Just easier to keep track of. During the last primer shortage that is all I could get. Didn't see much difference. Of course I tend to load middle of the tables. I can say when I loaded 25 gr of Varget with an 80 VLD they got pretty flat but didn't blank. I don't shoot 1,000 any longer so I don't go that high any more.
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