.375/416 Barret?

[eddybo]

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.

 

[Fiftydriver]

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!!!

 

[eddybo]

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.

 

[Chas1]

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

 

[Fiftydriver]

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.

 

[slwatson]

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.

 

[Black Diamond 408]

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

 

[eddybo]

I am going to read up on frontal ignition. These cases are so big that it may be doable. I have sort of come up with an idea of how it could work, but am not sure wheter my idea is feasible. Would plug threaded into the case head be safe? I was planning on threading it into the case head from the inside of the case and having a shoulder on the plug larger than the threads. How strong is a 50bmg primer? Would it blow the plug out and down the barrel?

 

[Extremist458]

Fiftydriver, eddybo, Dave,

I'm glad to see you guys posting on the subject, and this thread is a great read. It appears many of us are on the same quest right now, as Dave knows. We (GS Custom Bullets) were just recently asked to design an ultra long range .375 bullet for two guys doing this very thing. One is using a 375 Snipe-Tac and the other a special 375/50 conversion. As you all know, the powder is the limiting factor.

In the case of the 50 conversion, we ran into two configurations that worked well, so far, and the guys in Australia can confirm this. One is limited around 150 grains real case capacity and was designed by the SMc crew, Superior Ballistics Inc. Those guys know what they are doing when it comes to powder burn efficiency. Thing is, their case design actually promotes a faster burn, which is not really what we are after here. They did however reach 3100fps with that case using H50BMG and ADI 2218, with the prior being 102% case fill! The other discovery they made is that if you use the US869 at higher pressures, around 70,000psi+, it burns better (and in a shorter barrel), then either of the two prior powders. It was actually the best performer for our specific use, but we declined because of the pressures...yes, we like to be safe, and the spent brass to extract...

They are however offering the case design to the market, if anyone cares to buy it from them. No real agreement was reached, so it's fair game.

The other design was very basic, much like your work, with it being a 416Barrett necked down and improved, while setting the shoulder back a little to get a .8"+ neck. This proved to be the ticket, so far. It's 177 grain useable capacity was just about right (I believe that was actually higher, but they might have rated that based off real powder charge cap, not sure). And the longer case neck worked great for this longer bullet and it looks like (statistical date reported from SBI) the longer case neck will greatly improve throat life, as well as the GS Custom bullet design does, so this is a great combination for the long haul (pun intended).

The dark side of this story is that it is being loaded by a private company that uses custom powders I have no access to. The reported maximum is said to be 3,400fps with the design bullet, 415 grains, and a 34" barrel. And, to thicken the plot, I have heard VV is coming out with N570...

The bullet is finished and the first small order is on it's way here for me to see this thing work first hand. The gentleman with this 375/50 should have it all lined up for us to load up and shoot to 3000m...to see the true potential of this bullet first hand. Interesting thing is it's basically the same design as the 338 295 grain bullet that has been shipped all over the world since 2004. It's stable through transonic and accurate at these ranges, so I am dying to see how this turnes out. On Quickload at least, it shows the 415SP outrunning the 350LRBT (Jamison) bullet supersonic by 500 meters, worst case. So I cannot wait.

In my small and realistic opinion, I think what Dave is doing with the .688 case is a fantastic idea. It might end up being the best option for a so-called standard sized action (non-BMG). The case is also the base for the 577 T-Rex from A-Square. They are making their own cases, and I am hoping they have improved their quality in this area to make the case feasible for use at 65,000psi., and consistent. Expensive to say the least though.

I must add though that I have magnum-itus as much as any guy here does. And I cannot get enough of the stuff we are doing here. Eddybo, rock on man! Just let me know if I can help with anything as it is my passion as well, aside from work. I've been toying with this for over 2 years now.

Forward ignition is the right idea, I believe. You would be best off making a small reamer to open up the primer pocket and allow a SS or brass tube with a T-flare. The tubes can be rather simple and cheap, and VariFlame might be able to help you out with that (spoke to them a few years ago). Looks like they will outlast your brass many times over.

Fifty, If you are ever interested in trying the GSC 458 566SP bullet against the Lehigh/Predator bullets, give me a call. It has been extensively tested from a 460 Steyr with great results! GS CUSTOM USA - Contact

-AP

 

[Chas1]

Extremist, what is forward ignition?

 

[eddybo]

VV570 is available right now....I have 8 lbs ready to burn but have been busy building smaller rifles for buddies. I have a couple of bigger guns in line so I should get to burning a little over the next week or so.

I am waiting on my reamer very similar to what you described. I am glad for any info you can share, and will give you a call. Right now I am thinking a primer pocket reducer that has a tube for forward ignition would be the ticket. I am thinking it could seat in the BMG primer pocket and the tube will extend through the flash hole....have not figured out how I would deprime the cases if I do that. Still just in the thinking stages on forward ignition. I need to take a look at variflame, never heard of them.

If I had a reamer and a barrel I would be playing with this thing.

 

[kellyzier]

I have been pondering a .375 Cheytac or .375 Am as a big brother to my .338AM, but got side tracked a little. I do not know a thing in the world about the 416 Barret. It is bascically a .50BMG shortened and necked down to .416 from what I read on wickpedia, but with about 40 grs more capacity than the 408 based cases. It has me really wondering what a .416 case with minimal body taper and a sharper shoulder would do when necked to .375.
Here are my questions?

1. Downfalls of the .416 brass problems etc.?

2. Rocky Mountain RBBT bullets ? I have used a few in a buddy's 375 CT, seem to shoot okay any idea on performance on big game?

3. Reloading stuff? I have never dealt with .50 BMG sized cases. What am I going to need for trimming cases, priming them etc? What primers do they use?

4. I am thinking about a McMillan big .50 repeater action, any experiance?

5. Probably a Lawton 10 Twist .375 would get used since I do not plan on shooting solids. That sound about right as far as twist?

6. I know I will not make weight in some states as far as legal for hunting. How many states have weight restrictions?

7. Is this just a bad idea?

8. I know I will have to have a finish reamer ground and a reamer for a sizing die, anything else that I would need to get on order?

Any input is appreciated, especially contact info for anyone who has tried this.

Eddybo,,,

I just posted my opinon on here tonight about using the edge or Lapua for an all around shooting and training gun and then the snipe tac or allan mag for an interim gun, but I didn't allude to my third gun the 416.

Backing up a bit, why not take your 338 AM and simply kick it up to the 375 AM or 375 snipe tac. I will refrain from my opinion on which 375 because of fall out on this web site, but either way, you have an easy and fairly cheap upgrade with your AM

On another note, Dessert Tactical Arms is on the verge of something really awesome with the 416-375...This caliber with the ZA or GS solids could very well be the cats meow in long range shooting to 3,000 yards.

I intend to build this rifle that will convert from a medium weight gun to a heavy weight for target shooting. Call Mike from Carbonbarrels.com and he can give you some ideas or talk to the guys from DessertTacticalArms. It sounds like once they develop this cartridge, we will have readily available brass for the 416-375

In summary, I have spent tons of time calling folks,, emailing folks and reading up on the 375. Several gun builders (dave viers n kirby allan alike) are leaning towards the 375. It has a lot of promise in my eyes and the parent case (408 chey tac) is an awesome middle of the road big cartridge.

The end of the road in my eyes is the 416-375.....Im currently building the 375 snipe tac...And waiting on dessert tactical arms...If they accomplish what Im hearing, my next step will be the 416-375......

This is just my opinion, and you know what they say....
kz

 

[Extremist458]

Eddybo,

How's the N570 working out? You got to let us all know! Hope it's as good as I think it will be!

 

[Black Diamond 408]

Extremist,

I necked down one of my 416 Viersco Mag cases to 375 and ran a few capacity tests with
various powders. US869 180.gns, BMG-50 170 gns. This was measured from filling the case to the bottom of the neck. I made up a set of loading dies, bushing FL sizer and Sliding bushing seater die with Micrometer stem. Looks like the neck will end up just shy of .400 long.

I will have a set of reamers done for this in the following weeks. I will need to get a test barrel
ordered in 8 twist, 34" should be plenty long enough. I am thinking Brux for this one.

Dave