I sent the remaining 32 gr Vmax's back to Hornady and the 3 casings with the popped primers. Here's an email I got this morning. Excellent customer service.
"I just want to run you through what I tested on the 204 Ruger 32 grain ammunition you sent in, share the data with you and explain the conclusion that it led me to.
The first guess of most people in looking at these rounds is some high pressure events happening. It is important to note that the powders we use in the 204 Ruger allow us to perfectly fill the case to capacity while staying under pressure specification. What this means is that it is literally impossible to put too much powder into one of these rounds or the bullet will not seat. However, just to be sure I took the ammunition down to our ballistics laboratory where I shot it for pressure and velocity. Hornady specification for MAP (maximum average pressure) is 55,500 psi. The 6 rounds I shot (1 fouler) averaged in at 53,100 psi with no singular round exceeding 54,000 psi. Therefore I ruled out high pressures being the issue in this case.
My next suspicion was that maybe the cartridge case headspace was too short on these cases. Headspace is a measurement from the base of the case (case head) to a point roughly halfway up the shoulder. This determines how the ammunition will index in your chamber. Your chamber has a headspace specification to that you can think of as simply a negative copy of the cartridge case with slightly bigger dimensions so the case has room to expand. In this instance if the cartridge case headspace is too short then there will be excessive slop between the case and your chamber walls/breach face. This can cause the case to not quite stretch far enough fast enough when ignition occurs. With the bottom of the shell head (where the primer is) not pressed against the breach face the primer is subject to 50,000+ psi with nothing to hold it in place and will most certainly "pop." SAAMI specification for 204 Ruger headspace is 1.558" - 1.565". I measured 5 cartridge cases pulled randomly from the boxes. They measured at 1.560", 1.561", 1.560", 1.562" and 1.560". These cases are clearly within headspace specification and so I ruled this out as an issue.
The next thing I checked was the headspace of the fired cases you sent in. When you fire a round in the chamber of a gun the cartridge expands and essentially makes a near perfect mold of the chamber. Therefore by measuring fired cases I can tell if someone has a chamber headspace problem. This works in the exact opposite way that case headspace does, so what I was looking for was a chamber that is too deep. When the chamber is too deep the exact same thing happens as explained above, the case must stretch too far too fast and the primer pops. SAAMI specification for 204 Ruger chamber headspace is 1.561" - 1.571". I measured 3 of the fired cases you sent in, they measured at 1.564", 1.564" and 1.564". This is nicely in spec and so I ruled out your chamber as a problem.
This leaves us with one thing left that can be causing this problem...the gas system in your gun. In an AR style rifle there is a gas port down towards the end of the barrel this port takes the hot gas that the powder is turning itself into as it burns and redirects back into the receiver. The energy from this gas is used to open the bolt and eject the fired case in the process feeding another case into the chamber. However, I believe this problem is being caused by (most likely) too big of a gas port in your barrel. This lets too large of a volume of gas into the system essentially overwhelming it. When this happens the bolt is opened too early while the case still has a significant amount of pressure in it. Again without the breach face there to press in on the primer and case head the primer simply pops out.
I know this seems like me just sitting here blaming your gun and while I do think this is a gas system issue I have a possible solution. The 32 grain VMAX load uses more powder with a lighter bullet that requires less force to move it down the bore. What this means is that a bunch of the powder is still burning while it passes the gas port. This makes the 32 grain much less likely to work in finicky guns.
I would like to replace your 32 grain boxes with some 40 grains. The 40 grain load has a couple advantages in your case. First it uses about 2 grains less powder. Second the 40 grain bullet requires more force to drive down the bore this makes the powder burn much more efficiently. So when the 40 grain bullet passes your gas port a much larger portion of the powder has been completely rendered into gas. Essentially your gas system will not be receiving as much gas that has just transformed from powder and that is very hot and traveling at a high velocity. This ought to make the 40 grain load not interact so violently with the gas system in your gun.
If this is an acceptable solution please let me know and we will get the new ammunition on its way to you ASAP. You can reach me at my contact information below. Also if you have any further questions or comments please do not hesitate to give me a call I am more than willing to clarify or try to explain things in a different way."
"I just want to run you through what I tested on the 204 Ruger 32 grain ammunition you sent in, share the data with you and explain the conclusion that it led me to.
The first guess of most people in looking at these rounds is some high pressure events happening. It is important to note that the powders we use in the 204 Ruger allow us to perfectly fill the case to capacity while staying under pressure specification. What this means is that it is literally impossible to put too much powder into one of these rounds or the bullet will not seat. However, just to be sure I took the ammunition down to our ballistics laboratory where I shot it for pressure and velocity. Hornady specification for MAP (maximum average pressure) is 55,500 psi. The 6 rounds I shot (1 fouler) averaged in at 53,100 psi with no singular round exceeding 54,000 psi. Therefore I ruled out high pressures being the issue in this case.
My next suspicion was that maybe the cartridge case headspace was too short on these cases. Headspace is a measurement from the base of the case (case head) to a point roughly halfway up the shoulder. This determines how the ammunition will index in your chamber. Your chamber has a headspace specification to that you can think of as simply a negative copy of the cartridge case with slightly bigger dimensions so the case has room to expand. In this instance if the cartridge case headspace is too short then there will be excessive slop between the case and your chamber walls/breach face. This can cause the case to not quite stretch far enough fast enough when ignition occurs. With the bottom of the shell head (where the primer is) not pressed against the breach face the primer is subject to 50,000+ psi with nothing to hold it in place and will most certainly "pop." SAAMI specification for 204 Ruger headspace is 1.558" - 1.565". I measured 5 cartridge cases pulled randomly from the boxes. They measured at 1.560", 1.561", 1.560", 1.562" and 1.560". These cases are clearly within headspace specification and so I ruled this out as an issue.
The next thing I checked was the headspace of the fired cases you sent in. When you fire a round in the chamber of a gun the cartridge expands and essentially makes a near perfect mold of the chamber. Therefore by measuring fired cases I can tell if someone has a chamber headspace problem. This works in the exact opposite way that case headspace does, so what I was looking for was a chamber that is too deep. When the chamber is too deep the exact same thing happens as explained above, the case must stretch too far too fast and the primer pops. SAAMI specification for 204 Ruger chamber headspace is 1.561" - 1.571". I measured 3 of the fired cases you sent in, they measured at 1.564", 1.564" and 1.564". This is nicely in spec and so I ruled out your chamber as a problem.
This leaves us with one thing left that can be causing this problem...the gas system in your gun. In an AR style rifle there is a gas port down towards the end of the barrel this port takes the hot gas that the powder is turning itself into as it burns and redirects back into the receiver. The energy from this gas is used to open the bolt and eject the fired case in the process feeding another case into the chamber. However, I believe this problem is being caused by (most likely) too big of a gas port in your barrel. This lets too large of a volume of gas into the system essentially overwhelming it. When this happens the bolt is opened too early while the case still has a significant amount of pressure in it. Again without the breach face there to press in on the primer and case head the primer simply pops out.
I know this seems like me just sitting here blaming your gun and while I do think this is a gas system issue I have a possible solution. The 32 grain VMAX load uses more powder with a lighter bullet that requires less force to move it down the bore. What this means is that a bunch of the powder is still burning while it passes the gas port. This makes the 32 grain much less likely to work in finicky guns.
I would like to replace your 32 grain boxes with some 40 grains. The 40 grain load has a couple advantages in your case. First it uses about 2 grains less powder. Second the 40 grain bullet requires more force to drive down the bore this makes the powder burn much more efficiently. So when the 40 grain bullet passes your gas port a much larger portion of the powder has been completely rendered into gas. Essentially your gas system will not be receiving as much gas that has just transformed from powder and that is very hot and traveling at a high velocity. This ought to make the 40 grain load not interact so violently with the gas system in your gun.
If this is an acceptable solution please let me know and we will get the new ammunition on its way to you ASAP. You can reach me at my contact information below. Also if you have any further questions or comments please do not hesitate to give me a call I am more than willing to clarify or try to explain things in a different way."
