Recently purchased my first chronograph and am interested in comments/suggestions on how to use it most effectively.
Up to now, I have used tables in reloading manuals, tables downloaded from bullet or powder manufacturer's websites as my guide when developing charges in the different calibers I reload. As I walk up my ladder developing the charges for each combo of bullet+powder I closely watch for pressure signs:
I've known all along that ALL charge tables come with muzzle velocity (MV) numbers that go with the suggested charges. Most boxed ammo also come with MV numbers as a measure of the expectation for the round.
I've been looking for references on using chronographs to develop reloads and there are a few that seem conflicting. I understand that MVs are not a "measure" of pressure, but it seems clear that MV is an "indicator" of whether a certain pressure has been reached, or close to it.
For example: Hornady 9th Edition shows for .223 Rem, a 24.9gr charge of CFE223 behind a 75gr BTHP bullet set at 2.250" COAL will result in a MV of 2700fps in a 20" bbl Colt AR with 1:9 twist. This is the listed max charge. In the past I work up my load and reach 24.9gr of CFE223 and see the earliest pressure signs (flat primers). Without a chrono all I know is pressure signs have just started.
Now that I have a chrono, I test the load and find the average muzzle velocity for the max load is 2600fps. Lower than expected. What does that mean?
What if the reading is 2800fps? Higher than expected. My assumption would be to lower the charge until I see 2700fps and make that my new max charge?
Note that for every bullet+powder I have previously worked up EITHER of these situations could be the case where I have reached the max listed charge (90% of the time).
Do I use my chrono readings as an "indicator" that I have reached the max charge when the MV readings match those provided in the tables (adjusting for differences like barrel length when needed)? Not all load data provides the make/specs for the rifle used so there are often assumptions that have to be made. But this is the same as boxed ammo which just give MV specs but no gun specs.
Here's a second similar question... I have load data for a powder I have previously worked up (eg. CFE223). I empty my canister and must buy a new 1lb or 8lb keg. Since it has been a while the new canister has a different lot#. Also I can no longer find the same primer brand locally so I switch to a different make but same size (sm rifle) primer. Being a safe reloader I restart my load ladder and safely reach the same max charge. My chrono tells me this new combo of powder+primer results in a different average muzzle velocity than previously. If it is a higher MV I will diligently reduce the load. But what if the MV is lower? Do I increase the charge until I replicate the previous MV. The only variable here is the powder and the primer. Unlike the comparison with a manufacturer's pressure barrel I am more confident with the suggested max load since I have already worked it up using the previous lot#.
Any comments would be appreciated.
Up to now, I have used tables in reloading manuals, tables downloaded from bullet or powder manufacturer's websites as my guide when developing charges in the different calibers I reload. As I walk up my ladder developing the charges for each combo of bullet+powder I closely watch for pressure signs:
- flat primers
- ejector marks on the head of the case
- craters in the primer indentation
- blown/missing primers
- difficulty extracting
I've known all along that ALL charge tables come with muzzle velocity (MV) numbers that go with the suggested charges. Most boxed ammo also come with MV numbers as a measure of the expectation for the round.
I've been looking for references on using chronographs to develop reloads and there are a few that seem conflicting. I understand that MVs are not a "measure" of pressure, but it seems clear that MV is an "indicator" of whether a certain pressure has been reached, or close to it.
For example: Hornady 9th Edition shows for .223 Rem, a 24.9gr charge of CFE223 behind a 75gr BTHP bullet set at 2.250" COAL will result in a MV of 2700fps in a 20" bbl Colt AR with 1:9 twist. This is the listed max charge. In the past I work up my load and reach 24.9gr of CFE223 and see the earliest pressure signs (flat primers). Without a chrono all I know is pressure signs have just started.
Now that I have a chrono, I test the load and find the average muzzle velocity for the max load is 2600fps. Lower than expected. What does that mean?
What if the reading is 2800fps? Higher than expected. My assumption would be to lower the charge until I see 2700fps and make that my new max charge?
Note that for every bullet+powder I have previously worked up EITHER of these situations could be the case where I have reached the max listed charge (90% of the time).
Do I use my chrono readings as an "indicator" that I have reached the max charge when the MV readings match those provided in the tables (adjusting for differences like barrel length when needed)? Not all load data provides the make/specs for the rifle used so there are often assumptions that have to be made. But this is the same as boxed ammo which just give MV specs but no gun specs.
Here's a second similar question... I have load data for a powder I have previously worked up (eg. CFE223). I empty my canister and must buy a new 1lb or 8lb keg. Since it has been a while the new canister has a different lot#. Also I can no longer find the same primer brand locally so I switch to a different make but same size (sm rifle) primer. Being a safe reloader I restart my load ladder and safely reach the same max charge. My chrono tells me this new combo of powder+primer results in a different average muzzle velocity than previously. If it is a higher MV I will diligently reduce the load. But what if the MV is lower? Do I increase the charge until I replicate the previous MV. The only variable here is the powder and the primer. Unlike the comparison with a manufacturer's pressure barrel I am more confident with the suggested max load since I have already worked it up using the previous lot#.
Any comments would be appreciated.