substituting magnum primers

[mrappe]

I have been shooting 38-40 (38 WCF) in my 73 Winchester for years with CCI LP primers and 5.3 grns of Hodgdon Clays for Cowboy Action Shooting. I ran out of LP primers and I have a brick (1000) of LP magnum primers that i bought several years ago that I no longer need so I am going to use them instead. I need to know about how much powder to back off in my loading to compensate for the difference if any to be in the same ballpark.

Thanks

[JSnover]

the rule of thumb is to reduce the charge by 10%

[bangerjim]

Agree........I use 10-12% less.

banger

[Elkins45]

Agree........I use 10-12% less.

banger

This begs the question: why not always use magnum primers and save powder?

[BK7saum]

As a rule, it is best to back off 10% and work back up. I would chrono the original load, back off 10%,and work back up to my original velocity.

In strong actions, I have substituted magnum primers on mild loads without backing off. If running near Max pressure, backing off and working up is the smart thing to do.

Brad

[dragon813gt]

This begs the question: why not always use magnum primers and save powder?

Cost difference in powder is most likely negligible. Cost difference in primer types can be substantial. Primer type can and will effect accuracy and SD.

[Outpost75]

+1 on the 10% reduction. I gave used this as a general rule, double-checking against a chronograph, and it has worked well for me in both rifles and revolvers, .38 Special, .44-40 and. 44 Mag. With recent primer shortages I have had to use what primers I could get. With standard pressure Cowboy loads of Bullseye powder I actually got better accuracy and more uniform velocities with the magnum primers using 3.2 grains with 155 grain bullet in .38 Special, 6 grains in . 44-40 with 200-grain, .45 Colt with 230-grain and 7 grains in .44 Mag. with 215 grain,

[bangerjim]

This begs the question: why not always use magnum primers and save powder?

Because most peopel hate math!!!!!!! HA.......ha.

banger

[w5pv]

I have used magnum primers with no problems.I never backed off the load but I always load on the lower end of the tables,no hot rodding.

[Love Life]

Magnum primers are usually the last to go out of stock during the component runs.

I have loads worked up for my guns with both magnum and standard primers. I just swap and change loads as needed.

[youngmman]

I have always used magnum primers in rifle or pistol since I started loading. If you actually develop loads rather than simply use the tables in the manuals then it doesn't make any difference because you are (or should be) very sensitive to pressure signs.

I only use magnums for the extra boost in ignition but frankly never had an issue with standard primers.