I had a brain fart the other day and thought I should share the results with all of you. This incident was dangerous and could have ended with serious injury and much worse damage to the rifle. I was very lucky.
Was testing some loads for a new custom rifle chambered for the .300 Imperial Magnum. First three rounds fired were uneventful with all shots landing within .75” @ 100 yards. The 1st round from the second batch of three test loads was much different. The recoil from this shot was felt only slightly more from this muzzle braked rifle but the bolt was frozen shut. It could not be opened by hand. The pressures from this round was obviously very high even though my load records said it should be within the acceptable limits of approx. 58,000 psi.
Went back to the shop, tapped open the bolt with a mallet. The bolt opened but the extractor ripped a piece off the case rim leaving the case stuck in the chamber. A cleaning rod was used with some force to tap the case from the chamber. The primer had been blown out of its pocket and serious pressure signs were all over the head of the case. This is the photo of the blown case.
I disassembled the other two rounds from this test batch and found both the bullet and powder weights were as they should be. WTF??? I should mention that the body of the blown case did not show any obvious signs of excessive pressure although later measurements would reveal the problem.
Went back to the range and fired one round from the 1st test batch that had performed well only one hour before. The bolt is now jammed shut for the second time – what the hell??? Back to the shop for some more work with the mallet. More surprises this time. The case was stuck in the chamber as before and required the rod and mallet to bang it out but this time there were no pressure signs on the primer or case head. This is the photo of the second jammed case head;
BUT this time there were pressure signs on the case body. As you can see in the next photo the body has an expanded section approximately 0.90” in length that starts about 0.40” from the case head, which is why the case would not extract. The center portion of the chamber is approx. .010” larger than the rear of the case. Don’t know why the bulge is not obvious on the case that caused the problem but it is certainly obvious on the second case – you can both see and feel it.
At this point I’m not sure what to think and then, there it was. I look over at the loading bench and a canister of Varget is looking at me when it should be H1000. Yes, after 50 years of reloading I finally did what I always feared I might do. I used the wrong powder. Varget is a faster burning powder than H1000 and it peaks the pressure much sooner than it should for these large cases. Varget is an excellent powder for small to medium sized cartridge cases but 91.5 grains of it pushing a 165 Nosler Partition was way more than even the large .300 Imperial chamber could handle. I am sure the rifle was very close to coming apart in many ugly pieces.
The obvious has been said many times before however it can’t be said too often. Reloading is a very safe pastime but always double-check your loading procedures. I only wrecked a good barrel – it could have been very much worse.
Regards
Aubrey
Was testing some loads for a new custom rifle chambered for the .300 Imperial Magnum. First three rounds fired were uneventful with all shots landing within .75” @ 100 yards. The 1st round from the second batch of three test loads was much different. The recoil from this shot was felt only slightly more from this muzzle braked rifle but the bolt was frozen shut. It could not be opened by hand. The pressures from this round was obviously very high even though my load records said it should be within the acceptable limits of approx. 58,000 psi.
Went back to the shop, tapped open the bolt with a mallet. The bolt opened but the extractor ripped a piece off the case rim leaving the case stuck in the chamber. A cleaning rod was used with some force to tap the case from the chamber. The primer had been blown out of its pocket and serious pressure signs were all over the head of the case. This is the photo of the blown case.
I disassembled the other two rounds from this test batch and found both the bullet and powder weights were as they should be. WTF??? I should mention that the body of the blown case did not show any obvious signs of excessive pressure although later measurements would reveal the problem.
Went back to the range and fired one round from the 1st test batch that had performed well only one hour before. The bolt is now jammed shut for the second time – what the hell??? Back to the shop for some more work with the mallet. More surprises this time. The case was stuck in the chamber as before and required the rod and mallet to bang it out but this time there were no pressure signs on the primer or case head. This is the photo of the second jammed case head;
BUT this time there were pressure signs on the case body. As you can see in the next photo the body has an expanded section approximately 0.90” in length that starts about 0.40” from the case head, which is why the case would not extract. The center portion of the chamber is approx. .010” larger than the rear of the case. Don’t know why the bulge is not obvious on the case that caused the problem but it is certainly obvious on the second case – you can both see and feel it.
At this point I’m not sure what to think and then, there it was. I look over at the loading bench and a canister of Varget is looking at me when it should be H1000. Yes, after 50 years of reloading I finally did what I always feared I might do. I used the wrong powder. Varget is a faster burning powder than H1000 and it peaks the pressure much sooner than it should for these large cases. Varget is an excellent powder for small to medium sized cartridge cases but 91.5 grains of it pushing a 165 Nosler Partition was way more than even the large .300 Imperial chamber could handle. I am sure the rifle was very close to coming apart in many ugly pieces.
The obvious has been said many times before however it can’t be said too often. Reloading is a very safe pastime but always double-check your loading procedures. I only wrecked a good barrel – it could have been very much worse.
Regards
Aubrey
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