Am I over pressure?
- Thread starter GcG166
- Start date
Slighly flattend primer is really not a good indicater of high preasure. Soft primers like Federals will somtimes show slight flattening near starting loads. You prob should not be using mixed head stamped brass if you are getting close to max loads because what might be safe in one brand of brass may be over preasure in another brand.
hometownhero
CGN Ultra frequent flyer
- Location
- Toon Town, Sk
Winchester typically has the highest case capacity.
If it shoots good use it. It is no where near max load. I was loading 53gr vmax (they are a long bullet for weight) at 25.7gr and accuracy was stellar. Shot many thousand of those rounds in a few guns. It is actually the load I have recommended to a few nutters and they have had good success as well but some went up a bit higher as their gun shot a bit more powder better.
It is varget we are talking about. I have burnt up probably 10+ pounds of the stuff and the same load winter or summer shot the same. Even with a full case of powder -35 to +35
Look for primer cratering (although this could also be caused by an overly large firing pin hole), extractor marks on the case base, sticky bolt lift.
I think you are ok. 25.5 grains of Varget behind a 55 grain fmj is my standard AR plinking load and I've gone through thousands of these, in the summer and the winter.
As stated above a primer can be a very poor indicator of chamber pressure and give a false indication of high pressure. As an example if you full length resize your cases per the dies instructions you may be pushing the shoulder back too far. When the cartridge is fired the ejector and firing pin have pushed the case forward until the shoulder of the case contacts the shoulder of the chamber. This creates head clearance or a air space between the rear of the case and the bolt face and the primer backs out of the primer pocket until it contacts the bolt face. As the pressure increases the rear of the case is pushed back over the primer until it contacts the bolt face.
Watch the animation below as the cartridge is fired and the primer is forced backwards. Look at the edges of the primer and how the rounded edge decreases and flattens. The more head clearance or air space between the rear of the case and the bolt face the more the edge radius decreases. And if your head clearance is excessive the primer will even looked mushroomed and become larger in diameter than the primer pocket.
Below is a workup load and the degrees of primer flattening, "BUT" primer cup thickness and hardness "AND" your head clearance will govern how flat the primer will be after firing. Meaning reading fired primers is only a ballpark idea of chamber pressure.
At the link below is a better method of measuring chamber pressure at the base of the case just above the extractor groove. "BUT" remember the brass hardness effects how much it expands after firing. Below is the Rockwell hardness of the .223/5.56 cases listed, so remember a Remington case at 49 Rockwell will expand more in the base with the same load fired in a Lake City case at 96 Rockwell.
LC 2008 = 96
Lapua 223 Match = 86
Norma = 76
Winchester 223 = 69
Remington "R-P" = 49
Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-trick-monitoring-pressure-your-rifle-reloads
At AccurateShooter.com one of the long range shooters stated he kept increasing the load until he had brass flow into the extractor and then backed off one or two grains of powder. This is a visual indication of what you are measuring the base of the case for, and again varies with brass hardness.
In another reloading forum a poster worked up a load using Lake City brass and then used the same load in Remington cases and had brass flow into the ejector. The poster was asking about internal case capacity thinking the Remington cases had less capacity increasing chamber pressure and the actual problem was softer brass.
Bottom line, without actual chamber pressure measuring equipment looking at fired primers and measuring base expansion are just ballpark ideas of chamber pressure.
Watch the animation below as the cartridge is fired and the primer is forced backwards. Look at the edges of the primer and how the rounded edge decreases and flattens. The more head clearance or air space between the rear of the case and the bolt face the more the edge radius decreases. And if your head clearance is excessive the primer will even looked mushroomed and become larger in diameter than the primer pocket.
Below is a workup load and the degrees of primer flattening, "BUT" primer cup thickness and hardness "AND" your head clearance will govern how flat the primer will be after firing. Meaning reading fired primers is only a ballpark idea of chamber pressure.
At the link below is a better method of measuring chamber pressure at the base of the case just above the extractor groove. "BUT" remember the brass hardness effects how much it expands after firing. Below is the Rockwell hardness of the .223/5.56 cases listed, so remember a Remington case at 49 Rockwell will expand more in the base with the same load fired in a Lake City case at 96 Rockwell.
LC 2008 = 96
Lapua 223 Match = 86
Norma = 76
Winchester 223 = 69
Remington "R-P" = 49
Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-trick-monitoring-pressure-your-rifle-reloads
At AccurateShooter.com one of the long range shooters stated he kept increasing the load until he had brass flow into the extractor and then backed off one or two grains of powder. This is a visual indication of what you are measuring the base of the case for, and again varies with brass hardness.
In another reloading forum a poster worked up a load using Lake City brass and then used the same load in Remington cases and had brass flow into the ejector. The poster was asking about internal case capacity thinking the Remington cases had less capacity increasing chamber pressure and the actual problem was softer brass.
Bottom line, without actual chamber pressure measuring equipment looking at fired primers and measuring base expansion are just ballpark ideas of chamber pressure.
If you are at all concerned about pressure, just back off your load a bit, even if it is for peace of mind. I got my best accuracy with 24.6 grains of Varget using that bullet in a Remington 700 VSSF II (1:12 twist). Another thing that, I think, could increase pressure is the twist rate. It would seem to me that a faster twist rate would tend to bring up the pressure as well. Another thing you have to consider is your seating depth. If your bullet is jammed into the lands, there would be a significant pressure spike. I generally am off the lands by 0.010" in the .223. More or less in some of the rifles I have.
hometownhero
CGN Ultra frequent flyer
- Location
- Toon Town, Sk
Twist doesn't have anything to do with pressure. At the seating depth he is using it will not be jamming the lands with a factory chamber.
I suggest everyone that doesn't know what to watch for get a reloading manual and READ IT
Hmmmm... I tend to disagree reagrding the twist rate.
A 1-in-9 inch twist will not have the same pressure curve as a 1-in-12 inch twist with all other variables held equal. Pressures increase as the twist tightens. There is a lag time with tighter twists because more work is required to move the bullet down the barrel because of the increase rotational kinetic energy as the bullet follows the rifling, therefore, the pressure from the burning powder has more time to build up behind the bullet as it propelled down the barrel.
