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.375/416 Barret?

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  #15  
Unread 02-06-2010, 03:20 PM
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Re: .375/416 Barret?

Little bit of an update. Got my brass, looks good anyway. My donor rifle should be on the way. PTG is sending me a reamer print for approval. I have not ordered a barrel yet because I am still unconvinced as to twist. How does 13 T sound? I am really still leaning toward the rocky mountain 375s right now but am worried about blowing those guys up. I have heard the jackets were pretty thick, we will see.

For perspective on the size of this case, from right to left 223, 308, 280AI, 7RUM, 338AM, 416 Barrett. I cant wait to see the shoulder blown forward and the taper lessened.



Here is the rifle I bought to build on.

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Last edited by eddybo; 02-06-2010 at 03:24 PM.
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  •   #16  
    Unread 02-06-2010, 05:10 PM
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    Re: .375/416 Barret?

    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!!!
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      #17  
    Unread 02-06-2010, 07:35 PM
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    Re: .375/416 Barret?

    Kirby,

    I very much appreciate your input, because I have the greatest respect for your work and you. The 338AM and the 270AM put me in awe everytime I pull the trigger. I really wish you had jumped in a little earlier I may have changed course. I am going to give it a try at this late date. Experimenting is fun, and that is the only reason I play with these things anyway. I really really appreciate the tip on case taper, and any other tips you can give.

    I will make sure to leave a long shank on the barrel. If it does not work out I will try something else.
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      #18  
    Unread 02-06-2010, 10:06 PM
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    Re: .375/416 Barret?

    416 case that's a big one. Best of luck, keep us posted on how it goes. BTW safety first...get a wallplate for that electrical outlet...Only kidding
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      #19  
    Unread 02-07-2010, 10:45 AM
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    Re: .375/416 Barret?

    Experimenting is ALWAYS fun!!! Even if it does not work out as you expected.

    Worst case senerio, it does not work out as you expected, you still have a great receiver and stock to build on and the 50 BMG action is a great one for many things.

    I remember reading that the AR-50 receiver was originally designed for the 50 Russian round which is significantly longer and more powerful then the 50 BMG. That made me decide to get my first AR-50. My plan was to design my 510 AM off the longer 50 Russian case and I would have had it not been for the fact that getting Russian brass was nearly impossible at an affordable price, thats why I stepped back down to the BMG case.

    Point being there are always twist and turns on the road to development, have fun and keep us posted. In my opinion, the 416 Barrett, necked up to 458 and with an improved shoulder design would be most impressive. That is another one I have on my list of "someday" fun projects. It would easily drive a 600 gr VLD to the same velocity as the 50 BMG would drive an 800 gr VLD but do so with much less powder and with very similiar BC values.

    There are endless possibilities you can play with on that receiver, again, have fun and keep us posted.
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    Kirby Allen(50)

    Allen Precision Shooting
    Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

    Farther, Faster and Flatter then ever before.

    Web Page: www.apsrifles.com

    allenmagnum@gmail.com
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      #20  
    Unread 02-07-2010, 10:28 PM
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    Re: .375/416 Barret?

    I've also been contemplating building either one of these or a 408/416 Barrett. What would the expansion ratio look like on a 408/416? How does the expansion ratio and overbore compare to very fast cartridges like a 22-250 or a 220 swift? I know they are barrel killers but they are very fast. Is there anyway you could "supersize" a 220 swift or 223 wssm using the same ratio of case capacity and bore diameter sort of like the 50 BMG is a "supersized" 30-06?

    Another question is that if I built a 375 based off the BMG case would it be better to shorten the 416 Barrett case some but with less body taper so it looks like a WSSM cartridge. Does this burn the powder more efficiently? My mind goes crazy just thinking about a cartridge that has the same proportionate dimensions of a 223 WSSM but with a 375 cal bullet. Wouldn't that be something, a "short action" 375/.50 BMG rifle lol.
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      #21  
    Unread 02-08-2010, 10:47 PM
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    Re: .375/416 Barret?

    Its allways fun to mess around with wildcats but i am afraid you will be disapointed with the 375 on that big case, like Kirby said, there is too much case capacity for that bore size/bullet weight. It has allready been done by several guys in Australia and New Zealand with poor results. They have found the 460 Steyr is a much better fit, the larger bore helps the case breath better.

    The 408 case wildcatted to 375 is about the best fit for powder capacity and bore size. There is one other case out there that i have been working with some, the 585 African, Not Nyati. It is the next step up from the 408 case, same basic length only larger in dia. .688 base. I have the 416 reamer for it, results are similar to the 416 barrett only with standard primers and powders. Last time i talked to the guys in New Zealand they were going to neck it to 375cal. I expect that would be similar to the 338-408 wildcats for overbore results but only with the larger bullets. Velocity is unknown at this time for this chamber but the 416 version will push the
    400gn bullets 3200+ I also have the reamers for the same case necked to 50cal, one rifle is in the works if the action ever gets finished. I expect that chamber to duplicate most 50cal loads in a standard rifle.

    Dave
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