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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Internal ballistics frustration.
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<blockquote data-quote="Fiftydriver" data-source="post: 132675" data-attributes="member: 10"><p>Meichele,</p><p></p><p>Several things come to mine. </p><p></p><p>First off, is this a standard spec 300 RUM chamber meaning is it consistant with the standard 300 RUM case dimensions. I realize it may be tighter but has there been any modifications to shoulder diameter in any way, even slight?</p><p></p><p>Second, This is in no way a shot at maker of the rifle, just something else to check out. Take a fired case and hold it up to a light and look down the body of the case. Is it perfectly straight or can you see any expansion bands around the body of the case.</p><p></p><p>Anytime you chamber a barrel to a min taper design you run the risk if turning a chip and ringing the chamber. This can vary from extremely mild rings that are generally polished out in the final chamber polish to more siginificant rings that can be seen of you hold the case up and look down the line of the case body.</p><p></p><p>This happens from time to time even if you do your best to prevent this it can happen with a min taper chamber design. The 300 RUM has a bit of taper but not alot.</p><p></p><p>So your probably wondering why this would cause this. If you have a ring in the chamber it would do have sticky extraction from the very first shot and with all shots right, not nessecarily.</p><p></p><p>The reason is because on the first shot, the brass is very elastic, it stretches under the chamber pressure but as soon as the pressure is released the case will contract back down a significant amount allowing the case to eject easily.</p><p></p><p>That said, the heat from that first firing has begun to temper the brass case and it is now not as elastic as it was on the first firing. On the next loading, the case expands again under pressure but this time does not contract down as much as the first firing, bolt lift can get a bit stiffer and extraction can get a bit sticker.</p><p></p><p>THe case now has become even more tempered and has lost more of its elastic properties because of the heat from firing and work hardening from FL sizing.</p><p></p><p>You load it again and shoot and this time it expands but does not contract back down and the case is basically stuck in the chamber and needs to be tapped out.</p><p></p><p>Another situation that can cause this is if the bore is not polished properly. Again this is due to the same reasons as the above example. The case gets harder and does not contract as easily and with a rough chamber it gets tight to extract.</p><p></p><p>One more area to look at is the diameter of the brass head in comparision to your chamber. In a min spec chamber, many times you will find a lot of brass that is a couple thou larger in diameter at the head then the average and when you chamber those rounds, the first couple may work alright but as the case head expands slightly under pressure, it gets larger in diameter and can wedge in the chamber if the fit is to tight.</p><p></p><p>I have encounters your problem with my Allen Magnums when building the first few test rifles. Several things were the problem, main one was to little taper in case design which resulted in modifying the reamer to correct the problem. Also, a ring in the chamber, Yes I did this until I learned that I really needed to take alot of time and take very shallow reamer cuts between cleaning to prevent this.</p><p></p><p>Some will polish a chamber with 400 grit paper. I do not feel this is enough for a large diameter, long case such as the 300 RUM. I go to at least 600 grit polish. The larger surface area of the case and chamber require a finer finish for easy extraction, especially with a min taper case design.</p><p></p><p>Just some more things to look at.</p><p></p><p>It does seem odd that you need to set the shoulder back that much to chamber easily with a sized case. Do you have even bolt lug contact and has your receiver been accurized and trued?</p><p></p><p>Let us know, what you come up with, very intersting.</p><p></p><p>Kirby Allen(50)</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 132675, member: 10"] Meichele, Several things come to mine. First off, is this a standard spec 300 RUM chamber meaning is it consistant with the standard 300 RUM case dimensions. I realize it may be tighter but has there been any modifications to shoulder diameter in any way, even slight? Second, This is in no way a shot at maker of the rifle, just something else to check out. Take a fired case and hold it up to a light and look down the body of the case. Is it perfectly straight or can you see any expansion bands around the body of the case. Anytime you chamber a barrel to a min taper design you run the risk if turning a chip and ringing the chamber. This can vary from extremely mild rings that are generally polished out in the final chamber polish to more siginificant rings that can be seen of you hold the case up and look down the line of the case body. This happens from time to time even if you do your best to prevent this it can happen with a min taper chamber design. The 300 RUM has a bit of taper but not alot. So your probably wondering why this would cause this. If you have a ring in the chamber it would do have sticky extraction from the very first shot and with all shots right, not nessecarily. The reason is because on the first shot, the brass is very elastic, it stretches under the chamber pressure but as soon as the pressure is released the case will contract back down a significant amount allowing the case to eject easily. That said, the heat from that first firing has begun to temper the brass case and it is now not as elastic as it was on the first firing. On the next loading, the case expands again under pressure but this time does not contract down as much as the first firing, bolt lift can get a bit stiffer and extraction can get a bit sticker. THe case now has become even more tempered and has lost more of its elastic properties because of the heat from firing and work hardening from FL sizing. You load it again and shoot and this time it expands but does not contract back down and the case is basically stuck in the chamber and needs to be tapped out. Another situation that can cause this is if the bore is not polished properly. Again this is due to the same reasons as the above example. The case gets harder and does not contract as easily and with a rough chamber it gets tight to extract. One more area to look at is the diameter of the brass head in comparision to your chamber. In a min spec chamber, many times you will find a lot of brass that is a couple thou larger in diameter at the head then the average and when you chamber those rounds, the first couple may work alright but as the case head expands slightly under pressure, it gets larger in diameter and can wedge in the chamber if the fit is to tight. I have encounters your problem with my Allen Magnums when building the first few test rifles. Several things were the problem, main one was to little taper in case design which resulted in modifying the reamer to correct the problem. Also, a ring in the chamber, Yes I did this until I learned that I really needed to take alot of time and take very shallow reamer cuts between cleaning to prevent this. Some will polish a chamber with 400 grit paper. I do not feel this is enough for a large diameter, long case such as the 300 RUM. I go to at least 600 grit polish. The larger surface area of the case and chamber require a finer finish for easy extraction, especially with a min taper case design. Just some more things to look at. It does seem odd that you need to set the shoulder back that much to chamber easily with a sized case. Do you have even bolt lug contact and has your receiver been accurized and trued? Let us know, what you come up with, very intersting. Kirby Allen(50) [/QUOTE]
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