Help me figure out why I'm blowing primers

[smithjasona1978]

So first I'm a noob. Not new to shooting just to reloading. I need help understanding my cartridge max overall length and the impact it has on pressure. I have a new Weatherby vanguard in. 300WBY mag. I have been shooting factory ammo in it until recently. Now I'm ready to start reloading. And my question is what should my oal be? I have a huge amount of length to play with. I can go from factory oal all the way up to 4.0 inches. 4.0 is my rifle using Hornady 208 grain eld-x touching the lands. Remember Weatherby freebore. Max I can load and have caliber diameter in the case neck is 3.85. So that still leaves me roughly a quarter inch of length to play with. And I am Also a speed freak. I want as much velocity as I can get. So should I just find the most accurate load that I can starting at the 3.85 and work incrementally shorter until I find the most accurate load? I need a starting point. I did my first round of load development at 3.75. But my manual has the length at 3.56. And the differnce in length has caused me to blow 2 primers.

 

[birdiemc]

That's a good starting point. If you have a chronograph, Lots of folks start with all seated at the same depth which they choose based on experience. Then shoot for the most consistent velocity, that settles what charge weight to use. The go back to seating depth in start as far out as you can and work back in increments of .002 or .005 .020 whatever you want to fine tune your group size.

 

[smithjasona1978]

That's a good starting point. If you have a chronograph, Lots of folks start with all seated at the same depth which they choose based on experience. Then shoot for the most consistent velocity, that settles what charge weight to use. The go back to seating depth in start as far out as you can and work back in increments of .002 or .005 .020 whatever you want to fine tune your group size.

Thanks. I'm having some trouble working up a load. I have blown 2 primers. I loaded a 75 rounds. 3 different powders. 5 different charge weighs of each powder. I examined each spent case with a magnifying glass checking for signs of pressure. Before I saw any visible signs of pressure I blew 2 primers. Now I'm scared. So I took some time off. The pressure changes caused by different oal has me spooked.

 

[birdiemc]

How are you seating your primers? Are they flush or a bit recessed of the case base?
If you cant even reach the lands and stay in the case, then that shouldn't be where the pressure is coming from.
When you press the bullet in do you feel the powder crunching ? That could cause higher pressure.
Any oil in your chamber that can cause high pressure. (Excessive case lubes perhaps)
Just a few quick things to check

 

[smithjasona1978]

I seat the primers flush.
Only crunches I heard was with 89 grains of R33. But its to slow. Velocity was unimpressive. Chamber and all rounds are clean clean clean. I blew primers with 81 grains of 7828. And 88 grains of Magnum. Good velocity 3075 and 3102. I'm backing way off to 77 and 84 and starting over.

 

[RT2506]

You need to understand the Weatherby chambering. The reason it has that long free bore is to reduce pressure. Remember 70+ years ago when the 300WM was designed there were not any powders slower than around the 4350s and H4831 which was a surplus military powder. With these you can get more velocity with safe pressure at the standard factory ammo COAL with the long free bore. Jump forward 70ish years and there are all these new sloooooow powders and fancy sleek long heavy bullets and the thoughts that you need to have the bullet close to the lands to shoot it's best but want screaming velocity and you now have your primer popping condition. You need to know the limitations of the round and work within it's limits. If you can't live with the limitations of the 300 WM then you will need a larger capacity case.

 

[smithjasona1978]

You need to understand the Weatherby chambering. The reason it has that long free bore is to reduce pressure. Remember 70+ years ago when the 300WM was designed there were not any powders slower than around the 4350s and H4831 which was a surplus military powder. With these you can get more velocity with safe pressure at the standard factory ammo COAL with the long free bore. Jump forward 70ish years and there are all these new sloooooow powders and fancy sleek long heavy bullets and the thoughts that you need to have the bullet close to the lands to shoot it's best but want screaming velocity and you now have your primer popping condition. You need to know the limitations of the round and work within it's limits. If you can't live with the limitations of the 300 WM then you will need a larger capacity case.

I'm fine with the limits of the cartridge. I just don't have any load data for it at coal anything other than factory spec. And for whatever reason the cases and primers weren't showing any signs of pressure before the primers blew. I examined each one with a magnifying glass.

 

[243winxb]

Your definition of "blowing primers"? Primer pocket expanded, Primer fell out?
An expanded pocket is high pressure. It may take up to 5 loadings till the primer fall out. When this happens reduce the load.
Hole in primer? Could be gas leaking between the case and primer, loose pockets.
Winchester did have a problem with some defects in the large rifle primers.

As said above- "You need to understand the Weatherby chambering. The reason it has that long free bore is to reduce pressure."

Bullets that jump to the rifling can be very accurate. A COL that is to long can cause powders not to burn correctly. A secondary pressure spike can be a problem when bullets move to soon.

Use a magnum primer.

Maximum COL 3.560"


​

 

[fiftybmg]

You should use a chronograph. If you're looking to push the envelope, a very useful tool is a 1/10000 micrometer to measure case expansion on new brass just north of the belt. It should be half of 1/10000 when you've hit maximum velocity for the powder / primer / bullet / AOL combination in your rifle. This is a useful method to load for max and still be in the pressure limit.

It is not a good idea to rely on signs of pressure with your eyes, because you can't see it till it's too late. If you don't have the micrometer, start low and don't exceed what the book says is max velocity.

Don't ever load to what other people say they loaded. Use the manual as a guide. Always work up and verify for yourself.

IMO, speed just wears everything out faster, there is no point in chasing it.

 

[smithjasona1978]

Your definition of "blowing primers"? Primer pocket expanded, Primer fell out?
An expanded pocket is high pressure. It may take up to 5 loadings till the primer fall out. When this happens reduce the load.
Hole in primer? Could be gas leaking between the case and primer, loose pockets.
Winchester did have a problem with some defects in the large rifle primers.

As said above- "You need to understand the Weatherby chambering. The reason it has that long free bore is to reduce pressure."

Bullets that jump to the rifling can be very accurate. A COL that is to long can cause powders not to burn correctly. A secondary pressure spike can be a problem when bullets move to soon.

Use a magnum primer.View attachment 165220 View attachment 165221

Maximum COL 3.560"


​

Primer fell out. Was in the bottom of the mag. Was new Hornady brass.

 

[smithjasona1978]

You should use a chronograph. If you're looking to push the envelope, a very useful tool is a 1/10000 micrometer to measure case expansion on new brass just north of the belt. It should be half of 1/10000 when you've hit maximum velocity for the powder / primer / bullet / AOL combination in your rifle. This is a useful method to load for max and still be in the pressure limit.

It is not a good idea to rely on signs of pressure with your eyes, because you can't see it till it's too late. If you don't have the micrometer, start low and don't exceed what the book says is max velocity.

Don't ever load to what other people say they loaded. Use the manual as a guide. Always work up and verify for yourself.

IMO, speed just wears everything out faster, there is no point in chasing it.

I was using a chrono. Velocity was higher than my book max, but my length was a quarter inch longer and I was using about 2 extra grains of powder because of that extra space. Isn't that the point of these new short fat cartridges? To be able to use a long bullet and not have it reduce case capacity? I have a digital mic. Ill definitely be doing a before and after measurement next time I'm at the range. Thanks for the advice.

 

[fiftybmg]

Velocity was higher than my book max, but my length was a quarter inch longer and I was using about 2 extra grains of powder because of that extra space.

That's the logical thought process there, but if we extend the argument to space enough for four extra grains of powder, or five, where do you end up.

Mostly, the velocity from the powder manual can't be achieved in hunting rifles, because they use proof barrels and those are usually longer than a hunting rifle barrel.

As a general rule, if you have the extra case capacity and a barrel to burn it in, use a slightly slower powder for load development and you could get more velocity without exceeding pressure limits.

 

[243winxb]

was using about 2 extra grains of powder because of that extra space

Bad idea. Follow loading manuals. Even the published maximum load may produce high pressure.

Change any component in the data & pressure will change.

 

[smithjasona1978]

Bad idea. Follow loading manuals. Even the published maximum load may produce high pressure.

Change any component in the data & pressure will change.

So how does everyone on here shoot rounds loaded longer than max coal?