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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Severely Overbore Chartidges and short barrel life myths...
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<blockquote data-quote="Fiftydriver" data-source="post: 427717" data-attributes="member: 10"><p>Pyroducksx3,</p><p> </p><p>Are you ready for this.... My load development will be scorned by most but her goes.</p><p> </p><p>Start at a know safe starting point, in the case of my 7mm AM with 160 gr AB I started at 92.0 gr of retumbo and worked up to 97.0 gr. One round each, adding one grain to each load on the way up. I shot these over a chrono graph behind the shop into my bullet trap, no paper, no groups, nothing, shoot and write down velocity and most importantly watch for any increase in effort needed to open the bolt on firing.</p><p> </p><p>There were no pressure signs at 97.0 gr so I increased one more grain to 98.0 gr Retumbo which clocked 3507 fps and there was a noticable increase in the bolt lift so 97.0 gr was then considered my max working load in that rifle with this componant combo.</p><p> </p><p>Then I look at the velocity numbers and see if anything stands out. In this case it did. I gained good velocity until I hit 95.0 gr of powder which had an actual chrono velocity of 3411 fps for that one shot. After that, the velocity increases flatlined even though there were no pressure signs until I reached 98.0 gr. THis tells me that with this powder, in this bore diameter and behind this bullet, 95.0 gr is the max that I can burn relatively effectively in this barrel length.</p><p> </p><p>So, I take the 95.0 gr load, load 5 rounds and shoot them over the chrono and record the velocities. If they show less then 40 fps spread for all five shots fired, I am at that point done with load development and onto long range testing. At this point I have 12 rounds down the barrel!!!</p><p> </p><p>If this was a totally unproven load combo, I would then load up 12 test loads with this exact load and head out to my long range shooting area. I would find a very small(sub 1/4 moa in size) target rock which there are hundreds of them where I shoot, set up at a range that I consider at least the max I would use this specific rifle for in the field. </p><p> </p><p>It generally takes 3 shots or so to get point of impact very close to point of aim. At this point, I let the barrel cool and if alone, set up my video camera with its 72x optical zoom. I am not looking to hit the target rock. I only want a very small aiming point for a quality hold and then I use the camera to record where each shot lands. I will shoot a shot every 4-5 minutes, recording each shots impact. That way I can get back home, and review the tape. Watching impacts on video tells you 10 times what you see through the scope. What often appears as a solid center hit through the scope is seldom that when you see it through a high powered video camera.</p><p> </p><p>I now have roughly 25 shots down the barrel and when I watch the video I am looking for two things. Group consistancy and size and also making sure there is no vertical stringing. If shooting in good conditions, you will rarely see much more then 1 moa of horizontal stringing, even in a lightweight rifle as long as its mechanically sound. The vertical stringing tells you what your velocity consistancy is.</p><p> </p><p>Books have been written on the topic of Low extreme spreads but I doubt many that read about this and try to get ES numbers into the single digits have ever tried to tell the difference between a 40 fps ES and an 8 fps ES at 1/2 mile shooting from field positions. If you can tell the difference your a MUCH better shot then I am and there are many that are. For me however, it means nothing. As long as I see consistant shot impacts I am satisfied.</p><p> </p><p>At that point, my total load development is done.</p><p> </p><p>Developing a drop chart can also be done very quickly. Generally in less then 5 shots, at least to get it close. Once you have a rifle zeroed at your desired range. Mine is 250 yard zero because I do not dial up for each shot, I use a ballistic reticle for hold over and I do not want to have to use up my reticals MOA with a 100 yard zero. Plus, anything from 0 to 400 yards is just point and shoot with most of my wildcats.</p><p> </p><p>With your known zero, then you need to pick out and test at at least three other ranges. For an 880 yard max range I would test at 400, 600 and 880 yards. Take one or two shots at each range, record your drops and if they impact off point of aim, record by how much in moas. Generally, if your BC is close, are your off, you will be consistantly off. For example, if your on at 250, 1 moa low at 400 you will generally continue to be low at 600 and 800.</p><p> </p><p>Once you get this data and correct for the drop adjustment with either a tweak of your ballistic data or a scope adjustment, you will be pretty **** well set with your drop.</p><p> </p><p>All you need now is to continue to test it at various ranges to confirm drop at all the different ranges. You will also learn that things will vary slightly from day to day. If you hunt in the same general area and conditions, it will generally not be enough to even notice big game hunting but because of this, you want your drop chart to be as accurate as possible for the majority of shooting conditons you will be hunting in and that is just done by testing the drop chart at various ranges.</p><p> </p><p>That does not mean you need to take alot of shots. You could take your rifle out with you every time you shoot, set up each session at a different range, take one shot, record the data and be done and over the summer you will have a wealth of ballistic drop data and probably only have 15-20 rounds down the barrel.</p><p> </p><p>Like I said, extremely simple.</p><p> </p><p>I do not use the ladder test. I have never been lacking with the loads I have developed using this method and I have yet to have a load not produce at least 3/4 moa which is what this rifle does. Most of my heavier rifles are WELL under 1/2 moa using this method.</p><p> </p><p>Now if your shooting a factory rifle, ladder tests can be more valuable because their vibration patterns can be pretty wild. In a properly machined and assembled custom rifle, you will not see as dramatic of vibration patterns as you would in a factory rifle for the most part.</p><p> </p><p>Hope this helps some. For those that are already biting their lip on this post, I apologize but it works and works well.</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 427717, member: 10"] Pyroducksx3, Are you ready for this.... My load development will be scorned by most but her goes. Start at a know safe starting point, in the case of my 7mm AM with 160 gr AB I started at 92.0 gr of retumbo and worked up to 97.0 gr. One round each, adding one grain to each load on the way up. I shot these over a chrono graph behind the shop into my bullet trap, no paper, no groups, nothing, shoot and write down velocity and most importantly watch for any increase in effort needed to open the bolt on firing. There were no pressure signs at 97.0 gr so I increased one more grain to 98.0 gr Retumbo which clocked 3507 fps and there was a noticable increase in the bolt lift so 97.0 gr was then considered my max working load in that rifle with this componant combo. Then I look at the velocity numbers and see if anything stands out. In this case it did. I gained good velocity until I hit 95.0 gr of powder which had an actual chrono velocity of 3411 fps for that one shot. After that, the velocity increases flatlined even though there were no pressure signs until I reached 98.0 gr. THis tells me that with this powder, in this bore diameter and behind this bullet, 95.0 gr is the max that I can burn relatively effectively in this barrel length. So, I take the 95.0 gr load, load 5 rounds and shoot them over the chrono and record the velocities. If they show less then 40 fps spread for all five shots fired, I am at that point done with load development and onto long range testing. At this point I have 12 rounds down the barrel!!! If this was a totally unproven load combo, I would then load up 12 test loads with this exact load and head out to my long range shooting area. I would find a very small(sub 1/4 moa in size) target rock which there are hundreds of them where I shoot, set up at a range that I consider at least the max I would use this specific rifle for in the field. It generally takes 3 shots or so to get point of impact very close to point of aim. At this point, I let the barrel cool and if alone, set up my video camera with its 72x optical zoom. I am not looking to hit the target rock. I only want a very small aiming point for a quality hold and then I use the camera to record where each shot lands. I will shoot a shot every 4-5 minutes, recording each shots impact. That way I can get back home, and review the tape. Watching impacts on video tells you 10 times what you see through the scope. What often appears as a solid center hit through the scope is seldom that when you see it through a high powered video camera. I now have roughly 25 shots down the barrel and when I watch the video I am looking for two things. Group consistancy and size and also making sure there is no vertical stringing. If shooting in good conditions, you will rarely see much more then 1 moa of horizontal stringing, even in a lightweight rifle as long as its mechanically sound. The vertical stringing tells you what your velocity consistancy is. Books have been written on the topic of Low extreme spreads but I doubt many that read about this and try to get ES numbers into the single digits have ever tried to tell the difference between a 40 fps ES and an 8 fps ES at 1/2 mile shooting from field positions. If you can tell the difference your a MUCH better shot then I am and there are many that are. For me however, it means nothing. As long as I see consistant shot impacts I am satisfied. At that point, my total load development is done. Developing a drop chart can also be done very quickly. Generally in less then 5 shots, at least to get it close. Once you have a rifle zeroed at your desired range. Mine is 250 yard zero because I do not dial up for each shot, I use a ballistic reticle for hold over and I do not want to have to use up my reticals MOA with a 100 yard zero. Plus, anything from 0 to 400 yards is just point and shoot with most of my wildcats. With your known zero, then you need to pick out and test at at least three other ranges. For an 880 yard max range I would test at 400, 600 and 880 yards. Take one or two shots at each range, record your drops and if they impact off point of aim, record by how much in moas. Generally, if your BC is close, are your off, you will be consistantly off. For example, if your on at 250, 1 moa low at 400 you will generally continue to be low at 600 and 800. Once you get this data and correct for the drop adjustment with either a tweak of your ballistic data or a scope adjustment, you will be pretty **** well set with your drop. All you need now is to continue to test it at various ranges to confirm drop at all the different ranges. You will also learn that things will vary slightly from day to day. If you hunt in the same general area and conditions, it will generally not be enough to even notice big game hunting but because of this, you want your drop chart to be as accurate as possible for the majority of shooting conditons you will be hunting in and that is just done by testing the drop chart at various ranges. That does not mean you need to take alot of shots. You could take your rifle out with you every time you shoot, set up each session at a different range, take one shot, record the data and be done and over the summer you will have a wealth of ballistic drop data and probably only have 15-20 rounds down the barrel. Like I said, extremely simple. I do not use the ladder test. I have never been lacking with the loads I have developed using this method and I have yet to have a load not produce at least 3/4 moa which is what this rifle does. Most of my heavier rifles are WELL under 1/2 moa using this method. Now if your shooting a factory rifle, ladder tests can be more valuable because their vibration patterns can be pretty wild. In a properly machined and assembled custom rifle, you will not see as dramatic of vibration patterns as you would in a factory rifle for the most part. Hope this helps some. For those that are already biting their lip on this post, I apologize but it works and works well. [/QUOTE]
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