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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
High Velocity Throat Erosion
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<blockquote data-quote="Fiftydriver" data-source="post: 2587399" data-attributes="member: 10"><p>Coming late to the party. Have a bit of experience with extreme rounds and have learned a little bit about throat life. Many factors effect throat life. In my testing, velocity has very little to do with it. I have done extensive ballistic testing with my wildcats using a very wide range of velocity loads. For example, My 26 Stalker will do 4100 with a 100 gr TTSX bullet. Top loads with the 156 gr berger will top 3450 fps out of the same rifle. And most of my wildcats have similar velocity potential spreads.</p><p></p><p>keys to long barrel life no matter the velocity i would rank in this order:</p><p></p><p>1. simple bore temp control</p><p></p><p>2. throat dimensions </p><p></p><p>3. positioning of bullet in throat</p><p></p><p>4. powder used</p><p></p><p>5. expansion ratio of chambering</p><p></p><p>lets review each.</p><p>1. Bore temp eats more throats then anything. Keep a barrel cool and they will last a very long time, get them hot and keep shooting and it really does not matter how fast your velocity is, you will damage your throat. A very non exact example i tell my customers. shots 1-3 out of a cold bore will do X amount of bore damage, a fourth shot will do as much damage as the first three and a fifth shot will do twice the damage as the first three……. Point being, bore wear increases exponentially the more rounds you shoot in a string which is why those that demand a minimum of 5 shot groups to mean anything is a joke. Does not matter if your running 4100 fps or 3200 fps, if you keep your bore temps low, your bore will last a very long time.</p><p></p><p>2. throat dimensions</p><p>there is a reason factory barrels often erode faster then a properly machined custom throat. It is largely because throat diameter is much looser then most custom throats. When a throat is over sized, the hot gases from the powder will blow by the bullet body and have a blow torch effect on the throat because it will be hyper accelerated as it passes through this small space between the bullet body and throat. Its not uncommon to see factory throats be 0.001 to 0.002" larger in diameter then nominal bore diameter. In contrast, every reamer i have made has a throat diameter that are 0.0003-0.0005" over nominal bullet diameter. Not only does this very tight fit limit the flame jetting action but also greatly improves a rifles accuracy, consistency and also makes the rifle much less dependent on bullet seating depth for accuracy and consistency. Loose throats burn throats faster, tight throats slower.</p><p></p><p>3. related to this, if you seat a bullet within 10 thou of the lands it will also limit the blow torch effect of hot gas blowing by the bullet before the bullet seals in the bore. If you have a 0.300" long freebore, alot of hot gas will blow by your bullet before it seals in the bore. A properly dimensioned throat diameter as mentioned above helps limit this no matter the seating depth but longest throat life is generally had with the bullet seater close to the lands.</p><p></p><p>4. some powders simply produce more heat then other powder. Some feel ball powders are less abrasive to the throat the. Stick powders and i am sure there is some degree of truth to this. However flame temp is much more critical to bore life. most recent manufactured powders have chemicals that help keep temps down as much as possible. One comparision i often share is how VV570 and RL33 will produce nearly identical performance and results but RL33 will have a measurably lower bore temp with same number of rounds down the bore because of its lower flame temp.</p><p></p><p>5.expansion ratio is a huge factor in bore life. Much more then velocity has. For example, a 22-250 loaded with a 40 gr bullet to 4100 fps will have a dramatically longer bore life then my 26 Stalker with 100 gr loaded to the same 4100 fps. Why is that. Well, the expansion ratio of the 22-250 is quite high. Meaning the powder charge in the 22-250 will convert to gas and expand several times over as it fills the volume of the bore. The 26 Stalker has a much lower expansion ratio. Case powder capacity volume will expand very little. this means fast burning powder can be used in the 22-250 compared to the 26 Stalker. Fast burning powder generally produces lower bore temps the slow burning powder simply because the slow burning powder releases more energy over a longer period of time, subjecting the bore to more heat.</p><p></p><p>tips i give my customers customers have nothing to do with limiting velocity. I tell them to limit shot strings to only 3 shots and let barrel cool. Seat your bullets close to lands if bullet design permits it. keep the bore clean.</p><p></p><p>i also do tell customers not to red line their pressures but this has more to do with the increased blow torch effect as pressures increase, not because of velocity being hard on barrels. Plus, they just eat up brass life for an extra 50-75 fps.</p><p></p><p>if you really want to increase bore life, lets talk about forward ignition systems. That will blow your mind as far as how performance will dramatically increase as will bore life!! If you want to discuss those tests we can on a different post.</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 2587399, member: 10"] Coming late to the party. Have a bit of experience with extreme rounds and have learned a little bit about throat life. Many factors effect throat life. In my testing, velocity has very little to do with it. I have done extensive ballistic testing with my wildcats using a very wide range of velocity loads. For example, My 26 Stalker will do 4100 with a 100 gr TTSX bullet. Top loads with the 156 gr berger will top 3450 fps out of the same rifle. And most of my wildcats have similar velocity potential spreads. keys to long barrel life no matter the velocity i would rank in this order: 1. simple bore temp control 2. throat dimensions 3. positioning of bullet in throat 4. powder used 5. expansion ratio of chambering lets review each. 1. Bore temp eats more throats then anything. Keep a barrel cool and they will last a very long time, get them hot and keep shooting and it really does not matter how fast your velocity is, you will damage your throat. A very non exact example i tell my customers. shots 1-3 out of a cold bore will do X amount of bore damage, a fourth shot will do as much damage as the first three and a fifth shot will do twice the damage as the first three……. Point being, bore wear increases exponentially the more rounds you shoot in a string which is why those that demand a minimum of 5 shot groups to mean anything is a joke. Does not matter if your running 4100 fps or 3200 fps, if you keep your bore temps low, your bore will last a very long time. 2. throat dimensions there is a reason factory barrels often erode faster then a properly machined custom throat. It is largely because throat diameter is much looser then most custom throats. When a throat is over sized, the hot gases from the powder will blow by the bullet body and have a blow torch effect on the throat because it will be hyper accelerated as it passes through this small space between the bullet body and throat. Its not uncommon to see factory throats be 0.001 to 0.002” larger in diameter then nominal bore diameter. In contrast, every reamer i have made has a throat diameter that are 0.0003-0.0005” over nominal bullet diameter. Not only does this very tight fit limit the flame jetting action but also greatly improves a rifles accuracy, consistency and also makes the rifle much less dependent on bullet seating depth for accuracy and consistency. Loose throats burn throats faster, tight throats slower. 3. related to this, if you seat a bullet within 10 thou of the lands it will also limit the blow torch effect of hot gas blowing by the bullet before the bullet seals in the bore. If you have a 0.300” long freebore, alot of hot gas will blow by your bullet before it seals in the bore. A properly dimensioned throat diameter as mentioned above helps limit this no matter the seating depth but longest throat life is generally had with the bullet seater close to the lands. 4. some powders simply produce more heat then other powder. Some feel ball powders are less abrasive to the throat the. Stick powders and i am sure there is some degree of truth to this. However flame temp is much more critical to bore life. most recent manufactured powders have chemicals that help keep temps down as much as possible. One comparision i often share is how VV570 and RL33 will produce nearly identical performance and results but RL33 will have a measurably lower bore temp with same number of rounds down the bore because of its lower flame temp. 5.expansion ratio is a huge factor in bore life. Much more then velocity has. For example, a 22-250 loaded with a 40 gr bullet to 4100 fps will have a dramatically longer bore life then my 26 Stalker with 100 gr loaded to the same 4100 fps. Why is that. Well, the expansion ratio of the 22-250 is quite high. Meaning the powder charge in the 22-250 will convert to gas and expand several times over as it fills the volume of the bore. The 26 Stalker has a much lower expansion ratio. Case powder capacity volume will expand very little. this means fast burning powder can be used in the 22-250 compared to the 26 Stalker. Fast burning powder generally produces lower bore temps the slow burning powder simply because the slow burning powder releases more energy over a longer period of time, subjecting the bore to more heat. tips i give my customers customers have nothing to do with limiting velocity. I tell them to limit shot strings to only 3 shots and let barrel cool. Seat your bullets close to lands if bullet design permits it. keep the bore clean. i also do tell customers not to red line their pressures but this has more to do with the increased blow torch effect as pressures increase, not because of velocity being hard on barrels. Plus, they just eat up brass life for an extra 50-75 fps. if you really want to increase bore life, lets talk about forward ignition systems. That will blow your mind as far as how performance will dramatically increase as will bore life!! If you want to discuss those tests we can on a different post. [/QUOTE]
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