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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
.375/416 Barret?
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<blockquote data-quote="Fiftydriver" data-source="post: 359093" data-attributes="member: 10"><p>Wish I would have seen this sooner but will offer my opinion on it now just for the heck of it. When I was researching my wildcats on the 408 CT case, before that I played with designing them on the 50 Spotter case, basically the parent case to the 416 Barrett. </p><p> </p><p>Having shot the 50 BMG ALOT over the past 15 years or so, I have learned a thing or two about these very large cases and learned even more when working with the 408 CT cases and my AM wildcats.</p><p> </p><p>First off and a very important rule of thumb. As the case head diameter increases, the amount of stress applied to the bolt is dramatically increased. This is why you can blow the primer pocket out of a 223 Rem and have very little if any sign of high pressure. You can put 20,000 psi less pressure in a 408 CT case and still blow the primer pocket out!!! Why, the large case diameter is harder for the brass to contain the higher chamber pressure and it also exerts dramatically more bolt thrust onto the receiver.</p><p> </p><p>Another issue, case baring surface. In my testing, you can have as little as 7 to 8 thou per inch of case taper in a RUM class case before extraction becomes an issues at comfortable top end pressures, being 65,000 to 68,000 psi.</p><p> </p><p>The Lapua needs to have at least 8 to 9 thou per inch to get good extraction with same pressure loads.</p><p> </p><p>When I started testing my 338 AM, I had only 7 thou taper per inch on the reamer and cases were sticking severely even at moderate pressures, why? Such a huge increase in baring surface compared to the smaller chamberings. You would think a properly polished chamber would make this irrelevent, that simply is not the case. In fact, I had to increase case body taper to 11 thou per inch to get good extraction which is where it stands today, roughly.</p><p> </p><p>The 50 BMG case, VASTLY larger case body baring surface compared to the Chey Tac case, for this size case my tests show you should have at least 13 to 14 thou per inch of case body taper if you want good easy extraction at working pressures.</p><p> </p><p>Now back to the case head diameter thing. The large the case head, all other things the same, the less amount of pressure that the cases can handle without sticky extraction. For example, the 50 BMG is standardly loaded to around 50 to 55,000 psi in pressure, a bit more then a 30-30 round!!!</p><p> </p><p>Believe me, I have pushed the 50 BMG to higher chamber pressures and extraction becomes a huge issue in a hurry as does bolt lift. Primer pockets also open up with relative ease compared to the smaller cases. Because of this, smaller cases, with modern powders can match or exceed the big BMG case. </p><p> </p><p>One clear example. The standard load for the 50 BMG is a 647 gr FMJBT loaded to 2700 fps but thats in a 45" M2 barrel length. In a 28 to 32" barrel length it will be more like 2575 or 2600 fps.</p><p> </p><p>My 50 AT based on the 408 CT case will get just shy of 2500 fps with a 750 gr A-Max and 2600 fps with a 647 gr FMJ in a 33" barrel length and using 145 grains of RL22 to get it compared to 245 grains of H-50BMG in the 50 BMG.</p><p> </p><p>Now lets look at the Barrett case. Its performance has been a bit hyped over the years as far as velocity and bullets BC. I have never owned a 416 Barret but I have shot a few of them using both handloaded ammo and factory loaded ammo. In both cases, none of these rifles came anywhere near 3250 fps with a 400 gr Solid like advertised and BC values looked to be much closer to .85 then their advertised +.9 numbers.</p><p> </p><p>I am no fan of the 408 CT either but in its factory form, it is rather watered down. They list the 419 gr solid with a muzzle velocity of 3000 fps, most factory loads will clock around 2900 fps. The 305 gr. High Velocity load is rated at 3260 fps. Case in point, my 338 AM will drive this same weight bullet well over 3300 fps as you well know so obviously the CT case is underloaded.</p><p> </p><p>Put the same caliber on both cases, that being the 375 cal and you get a couple things. The 338 AM becomes VASTLY more effienct when necked up to 375 cal. You go from powder burn rates of H-50BMG down to Retumbo so thats a pretty significant expansion ratio shift.</p><p> </p><p>When you take the Barrett case which calles for use of H-US869 which is in the same burn rate class as H-50BMG and neck it down to 375 caliber, you really drop the expansion ratio which means you need to take several steps slower in burn rate to get much that will work well. There really is not alot out there much slower burning then US869. WC872 is slower in some lots, VV 20N29 is also slower but MUCH more bulky. Barrett uses US869 because its a ball powder and he can get 195 grains of powder in his case.</p><p> </p><p>The problem lies in the fact that the Barrett can not be loaded hot enough in pressure to make this powder burn cleanly. This is a serious problem with any ball powder. If they are loaded to pressures under around 65,000 psi, they leave alot of carbon fouling.</p><p> </p><p>It was because of all of this that I simply went with the Chey Tac parent case. Yes the Barrett based wildcat may get you another 50-75 fps with very top loads but to get that you will need another 50 grains of powder, a huge receiver, heavy rifle, and new loading equipment for the ammo, not to mention very expensive loading dies.</p><p> </p><p>Certainly not saying to not go for it, very interested in your results and as you know full well, I am never one to call overbore a bad thing!!! But when the velocity gains drop to this small amount, I tend to question if its really worth it.</p><p> </p><p>I am in a similiar place right now. I have a 458 Allen Magnum reamer sitting here waiting to be used. Its my 510 Allen Magnum(BMG) necked down to 458 caliber to use the heavy Lehigh solid bullets. I ordered the reamer when I started with all my other AM projects but from what I have learned I am leary to proceed, simply because I fear I know what I can expect to see. The 458 AM would be very similiar in expansion ratio to the 375 Barrett Improved if not a bit milder in expansion ratio.</p><p> </p><p>Let me know how things turn out for you. If I could offer one more bit of a comment. If ever a round begged for a forward ignition system, this is it. You may want to play with that concept a bit and see where it gets you, you may be amazed with the results. It would be much easier to convert the Barrett case for forward ignition then any of the smaller calibers because the case head is so heavy between the powder chamber and primer pocket. May well offer significant ballistic improvments as well as MUCH longer barrel life. </p><p> </p><p>Keep us posted, I sure it will be fun and hope its what you are looking for. Just remember that the 375 AM will get you 3300 fps with the 350 gr SMK, if you beat that by 100 fps and do so with good primer pocket life and case extraction, I will be VERY impressed. Good luck, have fun, to much is never enough!!!</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 359093, member: 10"] Wish I would have seen this sooner but will offer my opinion on it now just for the heck of it. When I was researching my wildcats on the 408 CT case, before that I played with designing them on the 50 Spotter case, basically the parent case to the 416 Barrett. Having shot the 50 BMG ALOT over the past 15 years or so, I have learned a thing or two about these very large cases and learned even more when working with the 408 CT cases and my AM wildcats. First off and a very important rule of thumb. As the case head diameter increases, the amount of stress applied to the bolt is dramatically increased. This is why you can blow the primer pocket out of a 223 Rem and have very little if any sign of high pressure. You can put 20,000 psi less pressure in a 408 CT case and still blow the primer pocket out!!! Why, the large case diameter is harder for the brass to contain the higher chamber pressure and it also exerts dramatically more bolt thrust onto the receiver. Another issue, case baring surface. In my testing, you can have as little as 7 to 8 thou per inch of case taper in a RUM class case before extraction becomes an issues at comfortable top end pressures, being 65,000 to 68,000 psi. The Lapua needs to have at least 8 to 9 thou per inch to get good extraction with same pressure loads. When I started testing my 338 AM, I had only 7 thou taper per inch on the reamer and cases were sticking severely even at moderate pressures, why? Such a huge increase in baring surface compared to the smaller chamberings. You would think a properly polished chamber would make this irrelevent, that simply is not the case. In fact, I had to increase case body taper to 11 thou per inch to get good extraction which is where it stands today, roughly. The 50 BMG case, VASTLY larger case body baring surface compared to the Chey Tac case, for this size case my tests show you should have at least 13 to 14 thou per inch of case body taper if you want good easy extraction at working pressures. Now back to the case head diameter thing. The large the case head, all other things the same, the less amount of pressure that the cases can handle without sticky extraction. For example, the 50 BMG is standardly loaded to around 50 to 55,000 psi in pressure, a bit more then a 30-30 round!!! Believe me, I have pushed the 50 BMG to higher chamber pressures and extraction becomes a huge issue in a hurry as does bolt lift. Primer pockets also open up with relative ease compared to the smaller cases. Because of this, smaller cases, with modern powders can match or exceed the big BMG case. One clear example. The standard load for the 50 BMG is a 647 gr FMJBT loaded to 2700 fps but thats in a 45" M2 barrel length. In a 28 to 32" barrel length it will be more like 2575 or 2600 fps. My 50 AT based on the 408 CT case will get just shy of 2500 fps with a 750 gr A-Max and 2600 fps with a 647 gr FMJ in a 33" barrel length and using 145 grains of RL22 to get it compared to 245 grains of H-50BMG in the 50 BMG. Now lets look at the Barrett case. Its performance has been a bit hyped over the years as far as velocity and bullets BC. I have never owned a 416 Barret but I have shot a few of them using both handloaded ammo and factory loaded ammo. In both cases, none of these rifles came anywhere near 3250 fps with a 400 gr Solid like advertised and BC values looked to be much closer to .85 then their advertised +.9 numbers. I am no fan of the 408 CT either but in its factory form, it is rather watered down. They list the 419 gr solid with a muzzle velocity of 3000 fps, most factory loads will clock around 2900 fps. The 305 gr. High Velocity load is rated at 3260 fps. Case in point, my 338 AM will drive this same weight bullet well over 3300 fps as you well know so obviously the CT case is underloaded. Put the same caliber on both cases, that being the 375 cal and you get a couple things. The 338 AM becomes VASTLY more effienct when necked up to 375 cal. You go from powder burn rates of H-50BMG down to Retumbo so thats a pretty significant expansion ratio shift. When you take the Barrett case which calles for use of H-US869 which is in the same burn rate class as H-50BMG and neck it down to 375 caliber, you really drop the expansion ratio which means you need to take several steps slower in burn rate to get much that will work well. There really is not alot out there much slower burning then US869. WC872 is slower in some lots, VV 20N29 is also slower but MUCH more bulky. Barrett uses US869 because its a ball powder and he can get 195 grains of powder in his case. The problem lies in the fact that the Barrett can not be loaded hot enough in pressure to make this powder burn cleanly. This is a serious problem with any ball powder. If they are loaded to pressures under around 65,000 psi, they leave alot of carbon fouling. It was because of all of this that I simply went with the Chey Tac parent case. Yes the Barrett based wildcat may get you another 50-75 fps with very top loads but to get that you will need another 50 grains of powder, a huge receiver, heavy rifle, and new loading equipment for the ammo, not to mention very expensive loading dies. Certainly not saying to not go for it, very interested in your results and as you know full well, I am never one to call overbore a bad thing!!! But when the velocity gains drop to this small amount, I tend to question if its really worth it. I am in a similiar place right now. I have a 458 Allen Magnum reamer sitting here waiting to be used. Its my 510 Allen Magnum(BMG) necked down to 458 caliber to use the heavy Lehigh solid bullets. I ordered the reamer when I started with all my other AM projects but from what I have learned I am leary to proceed, simply because I fear I know what I can expect to see. The 458 AM would be very similiar in expansion ratio to the 375 Barrett Improved if not a bit milder in expansion ratio. Let me know how things turn out for you. If I could offer one more bit of a comment. If ever a round begged for a forward ignition system, this is it. You may want to play with that concept a bit and see where it gets you, you may be amazed with the results. It would be much easier to convert the Barrett case for forward ignition then any of the smaller calibers because the case head is so heavy between the powder chamber and primer pocket. May well offer significant ballistic improvments as well as MUCH longer barrel life. Keep us posted, I sure it will be fun and hope its what you are looking for. Just remember that the 375 AM will get you 3300 fps with the 350 gr SMK, if you beat that by 100 fps and do so with good primer pocket life and case extraction, I will be VERY impressed. Good luck, have fun, to much is never enough!!! [/QUOTE]
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