kilotanker22
New member
WARNING, although I will not be sharing any specific load data in this post, I will be discussing loading above maximum published data. Neither myself or TFL can be held responsible for what you do with the information that comes to light through the course of this thread. I strongly recommend that you do not try what I will be attempting. This thread is about an issue that I have experienced and my theory surrounding details on SAAMI maximum pressure ratings across different rifle platforms.
Not too long ago I picked up a Ruger American rifle in 450 Bushmaster. I can see that SAAMI maximum pressure is 38.5K PSI. I also know that the 460 S&W has a SAAMI max pressure of 65K PSI. I am assuming that the lower max pressure of the 450 Bushmaster is due to the cartridges common use in AR platform firearms.
I thought to myself that the 5.56x45 Nato round has a max pressure of 55K PSI so why does the 450 have a max pressure rating 16.K PSI lower than the 5.56? The only sensible conclusion I can draw is that it must have to do with the amount of thrust applied to the bolt during firing. The increased cross sectional area of the bore would create significantly higher rearward thrust on the bolt. Also this cartridge has a rebated rim. The rim of the case being smaller than the body would induce a greater stress on the smaller diameter cartridge base.
Now, we all know that modern bolt action rifles have a significantly higher strength in their lock up than an AR 15 bolt. My question is, in a modern bolt action rifle is it reasonable to assume that the max 38.5K PSI pressure rating given to this cartridge could be safely exceeded, but by how much?
This question stems from a recent trip to the range where I tested two powder charges of both CFE BLK and Lil Gun. What I found was a little surprising to me with the CFE BLK, but that is not the cause of this discussion.
With LIL Gun I started with the max listed load from the Hornady tenth edition book. The reason that I started at max load was because I was concerned by the amount of case volume that was empty with all of the charges of this powder. This cartridge uses small primers so naturally when lighting that much ball powder I went with magnum primers. I must admit that I use Wolf small rifle magnum primers, because I wanted to save my CCI 450 for my Creedmoor. I have used the Wolf primers in both the Creedmoor and my 5.56 with no trouble other than a larger than normal ES, however I did not expect to have the amount trouble that I had with the 450. I figured that igniting a dose of faster burning [shotgun powder like LIL Gun would be easier than igniting, say, H4350 that burns much slower.
I loaded at two different lengths, one right at the lands and one to the cannelure. The bullets seated to the cannelure were jumping .130" until they made contact with the lands. Here is the fun part.
With LIl Gun powder and the bullet seated to the lands Every single round went off, but they were hang firing just a little bit. Velocity was about 150 fps lower than I was expecting after seeing the results I got with the CFE BLK powder, which was a compressed load. However, the velocity spread was pretty good with an ES of only 30 fps across a 5 shot string. So I decided to go ahead and fire the rounds with the bullets seated deeper in hopes that the reduction of free space inside the case would allow for more powder to be ignited by the primer, boy was I wrong...
With the Lil Gun powder charge and the bullets that were seated to the cannelure, I had a 100% failure to fire and the fifth one that I tried lodged the bullet into the rifling. Luckily it was not stuck too far into the lands and I was able to hammer the bullet out with a wooden dowel. At first I thought that the primers were DOA. After coming home I saw that all primers had fired, although to what degree they actually performed as designed I can not confirm.
Now I plan to test the same load using the CCI 450 to see if my problem was the primer or the powder, although at this point, I intend to increase my powder charge by .5 Grains increments until I can hopefully achieve reliable ignition while maintaining a safe pressure. This brings me to my concern with bolt thrust.
At this point there is no sign of excessive pressure on the case head, bolt lift, primers at all. The primers are not even cratering around the dimple left by the firing pin. Case head diameter is the same as the standard cartridges and using small primers so I am not concerned with gas leakage past the primer at this point. I personally don't see a reason that this cartridge should be limited to the same 38.5K pressure rating that it is limited to in the AR platform rifle. In an AR rifle I would be concerned with sheering bolt lugs under higher pressure due to the increased bolt thrust. This is a documented issue with 6.5 Grendel bolts loaded to full power in AR rifles. Hornady also provides different data for bolt guns and gas guns in their 6mm ARC cartridge. Again I presume that this is due to the increased bolt thrust shearing bolt lugs when loaded to higher pressures. That cartridge has a max SAAMI pressure of 52,000K PSI if memory serves me correctly.
In my Ruger American rifle, all three lugs make contact within the lug recesses in the receiver on about 85% of the bearing surface. It is my theory that in a modern bolt action rifle, there is no reason that this cartridge can not be loaded to pressures higher than SAAMI maximum pressure of 38.5K I will update you all with my progress.
Not too long ago I picked up a Ruger American rifle in 450 Bushmaster. I can see that SAAMI maximum pressure is 38.5K PSI. I also know that the 460 S&W has a SAAMI max pressure of 65K PSI. I am assuming that the lower max pressure of the 450 Bushmaster is due to the cartridges common use in AR platform firearms.
I thought to myself that the 5.56x45 Nato round has a max pressure of 55K PSI so why does the 450 have a max pressure rating 16.K PSI lower than the 5.56? The only sensible conclusion I can draw is that it must have to do with the amount of thrust applied to the bolt during firing. The increased cross sectional area of the bore would create significantly higher rearward thrust on the bolt. Also this cartridge has a rebated rim. The rim of the case being smaller than the body would induce a greater stress on the smaller diameter cartridge base.
Now, we all know that modern bolt action rifles have a significantly higher strength in their lock up than an AR 15 bolt. My question is, in a modern bolt action rifle is it reasonable to assume that the max 38.5K PSI pressure rating given to this cartridge could be safely exceeded, but by how much?
This question stems from a recent trip to the range where I tested two powder charges of both CFE BLK and Lil Gun. What I found was a little surprising to me with the CFE BLK, but that is not the cause of this discussion.
With LIL Gun I started with the max listed load from the Hornady tenth edition book. The reason that I started at max load was because I was concerned by the amount of case volume that was empty with all of the charges of this powder. This cartridge uses small primers so naturally when lighting that much ball powder I went with magnum primers. I must admit that I use Wolf small rifle magnum primers, because I wanted to save my CCI 450 for my Creedmoor. I have used the Wolf primers in both the Creedmoor and my 5.56 with no trouble other than a larger than normal ES, however I did not expect to have the amount trouble that I had with the 450. I figured that igniting a dose of faster burning [shotgun powder like LIL Gun would be easier than igniting, say, H4350 that burns much slower.
I loaded at two different lengths, one right at the lands and one to the cannelure. The bullets seated to the cannelure were jumping .130" until they made contact with the lands. Here is the fun part.
With LIl Gun powder and the bullet seated to the lands Every single round went off, but they were hang firing just a little bit. Velocity was about 150 fps lower than I was expecting after seeing the results I got with the CFE BLK powder, which was a compressed load. However, the velocity spread was pretty good with an ES of only 30 fps across a 5 shot string. So I decided to go ahead and fire the rounds with the bullets seated deeper in hopes that the reduction of free space inside the case would allow for more powder to be ignited by the primer, boy was I wrong...
With the Lil Gun powder charge and the bullets that were seated to the cannelure, I had a 100% failure to fire and the fifth one that I tried lodged the bullet into the rifling. Luckily it was not stuck too far into the lands and I was able to hammer the bullet out with a wooden dowel. At first I thought that the primers were DOA. After coming home I saw that all primers had fired, although to what degree they actually performed as designed I can not confirm.
Now I plan to test the same load using the CCI 450 to see if my problem was the primer or the powder, although at this point, I intend to increase my powder charge by .5 Grains increments until I can hopefully achieve reliable ignition while maintaining a safe pressure. This brings me to my concern with bolt thrust.
At this point there is no sign of excessive pressure on the case head, bolt lift, primers at all. The primers are not even cratering around the dimple left by the firing pin. Case head diameter is the same as the standard cartridges and using small primers so I am not concerned with gas leakage past the primer at this point. I personally don't see a reason that this cartridge should be limited to the same 38.5K pressure rating that it is limited to in the AR platform rifle. In an AR rifle I would be concerned with sheering bolt lugs under higher pressure due to the increased bolt thrust. This is a documented issue with 6.5 Grendel bolts loaded to full power in AR rifles. Hornady also provides different data for bolt guns and gas guns in their 6mm ARC cartridge. Again I presume that this is due to the increased bolt thrust shearing bolt lugs when loaded to higher pressures. That cartridge has a max SAAMI pressure of 52,000K PSI if memory serves me correctly.
In my Ruger American rifle, all three lugs make contact within the lug recesses in the receiver on about 85% of the bearing surface. It is my theory that in a modern bolt action rifle, there is no reason that this cartridge can not be loaded to pressures higher than SAAMI maximum pressure of 38.5K I will update you all with my progress.
). Maybe low powder fill vs case capacity and inadequate primer ignition contributed to your problems. Thank God you weren't using a semi-auto and squeezed off another shot behind your squib!
