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Should I safely be able to use Weatherby loads
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Member Posts: 168,427 ✭
in a standard chamber that doesn't have the freebore jump? The reason I ask is b/c my Ackley books say to use the 300 Weatherby load Data for the .300 Mag AI.
Baring any other pressure signs, what should I watch for with the Chronograph? Am I safe to just watch for Weatherby velocities?
Without that freebore jump, am I going to have a pressure spike?
Baring any other pressure signs, what should I watch for with the Chronograph? Am I safe to just watch for Weatherby velocities?
Without that freebore jump, am I going to have a pressure spike?
Comments
Some barrels will run higher or lower velocity's than others so thats not a good way to check..
The biggest reason for the long freebore was to reduce pressue, so with out it you just may get into territory you don't want to be in.
Best to start low and work it up to be safe...
Measure the capacity of the parent and the fire formed final cases. For each 4% increase in capacity, you will see a 1% increase in velocity (at the same pressure). IOW if "book" for the parent is 3000fps, than 3100fps with your improved round would be pushing the limit on pressure.
When loading into the lands, reduce the starting and maximum load level by 10%
Normally you would start your load development with mid range loads for the parent case and work up, but with your "jammed in the lands" OAL, I wouldn't go but a gr or 2 over the 300 WM starting loads.
Parker tended to run load levels that today would be referred to simply as "proof loads". Use his data at your own risk.
Measure the capacity of the parent and the fire formed final cases. For each 4% increase in capacity, you will see a 1% increase in velocity (at the same pressure). IOW if "book" for the parent is 3000fps, than 3100fps with your improved round would be pushing the limit on pressure.
When loading into the lands, reduce the starting and maximum load level by 10%
Normally you would start your load development with mid range loads for the parent case and work up, but with your "jammed in the lands" OAL, I wouldn't go but a gr or 2 over the 300 WM starting loads.
Thanks for the info. I started getting more accurate loads the hotter they got. I went up to 74.5 grains with the parent case and 180 grain pills (I'm using 190's now) with no noticeable pressure signs. The hotter loads were more accurate. This will be the first time I've used the fire formed Ackley cases.
If I understand you correctly, I'm going to experience greater pressures with the same amount of powder b/c the case capacity is larger.?.? Will this formula hold true considering the fact that I fired the same loads in an ackley chamber with the parent case, while fire forming the brass? I know you should use light loads when fire forming, but I was still waiting on my dies and I was trying to find my best loads.
That is not what I said.
Same powder charge in larger case = lower pressure.
I'm saying that at the same pressure, the ratio of case capacity increase to velocity increase is 4:1. It will take more powder to get there. BUT, you also tossed in the "seating into the lands" issue, and that normally dictates a lower powder charge to keep pressures at the same level.
The rule of thumb for a starting charge is 10% less than max.
The rule of thumb for a "in the lands" OAL is to lower the "standard" charge by 10%.
I'm simply combining those 2 rules, and taking into account your "improved" case, when I say to not go more than a gr or 2 over the books starting load for the standard round.
quote:If I understand you correctly, I'm going to experience greater pressures with the same amount of powder b/c the case capacity is larger.?
That is not what I said.
Same powder charge in larger case = lower pressure.
I'm saying that at the same pressure, the ratio of case capacity increase to velocity increase is 4:1. It will take more powder to get there. BUT, you also tossed in the "seating into the lands" issue, and that normally dictates a lower powder charge to keep pressures at the same level.
The rule of thumb for a starting charge is 10% less than max.
The rule of thumb for a "in the lands" OAL is to lower the "standard" charge by 10%.
I'm simply combining those 2 rules, and taking into account your "improved" case, when I say to not go more than a gr or 2 over the books starting load for the standard round.
Gottcha...That explains why the 300 Weatherby takes 4 more grains of powder to achieve a slightly higher velocity than the 300 Mag...something like 50 fps.
a chronograph is a very helpfull tool in these areas. Knowing when too much velocity is present, will let you know that too much pressure is present.
So, should I be looking for a spike in velocity...or will it plateau out with an incomplete burn? The reason I ask is b/c the Win Mag achieves almost what the Weatherby achieves with 4 grains less powder (RL-22). I guess case design and freebore has a lot to do with it, but I was kind of thinking that the Weatherby might not be getting as thorough of a burn as the Mag.?.?
Is there a magic number I should be watching for with the velocity? I'm using 190 grain VLD's out of a 27.5" barrel. Thanks again!
EX: each 1/2gr of powder has been giving you 25fps increase in velocity. If the next 1/2 gr goes up by 50fps OR if it shows no increase in velocity (it may even show a decrease) than you have gone past the efficiency peak for that combo/powder
Watch your powder increase / velocity increase. When it goes off the "ramp" your at the max for that powder (note: this may be above safe pressures).
EX: each 1/2gr of powder has been giving you 25fps increase in velocity. If the next 1/2 gr goes up by 50fps OR if it shows no increase in velocity (it may even show a decrease) than you have gone past the efficiency peak for that combo/powder
Thanks again!