375-408

So I am getting some conflicting information. I called and talked to Montana Rifle Company and their Gunsmith said if I wanted to I could safely and easily use that action for a 375-408 I would just have to shoot it single shot because of the mag box length. They also mentioned if pressure was an issue with a round higher than the 505 Gibbs what is rated for 39,160 PSI how could they use the action for the 338 Lapua which runs at 60,916 PSI as pressure is pressure according to him. The 408 runs a max PSI of 63,800 so yes it is more than the Lapua but a 378 Weatherby runs a max PSI at 63,817 and I was told that a 378 Weatherby case would not have an issue either and I believe it this action has about twice the iron of the Weatherby action. So my question is what are you guys seeing with this action that it will not handle the 408 case but it can handle the 338 laupa or the 378 Weatherby? The action was a gift from a friend of mine and he is also the one that will be building the rifle so I am in a tough spot here. I really cannot say nope the action is not good enough but I do not want to build something that would not be safe either. So basically I am trying to figure out who is right here?
 
dakor said:
They also mentioned if pressure was an issue with a round higher than the 505 Gibbs what is rated for 39,160 PSI how could they use the action for the 338 Lapua which runs at 60,916 PSI as pressure is pressure according to him. The 408 runs a max PSI of 63,800 so yes it is more than the Lapua but a 378 Weatherby runs a max PSI at 63,817 and I was told that a 378 Weatherby case would not have an issue either and I believe it this action has about twice the iron of the Weatherby action.
Click to expand...

WOW, that speaks volumes to the knowledge of their smiths.......

Its not a simple PSI issue. You can take a 223 Rem and load it to 80,000 psi in a strong rifle with zero headspace brass and often times have no sign of pressure problems unless the primer lets loose. Bolt lift will be wasy, extraction will also generally be effortless.

If that smith does not understand that as the case head diameter increases, bolt thrust expodentially increases, then he needs to find another job. If you have two rounds that produce the same chamber pressure, lets say 65,000 psi, one has a 0.585" head diameter and the other has a 0.640" diameter head which one do you think will produce the most bolt thrust.

Remember this is 65,000 pounds of pressure PER SQUARE INCH!!!! The larger the head diameter, the more bolt thrust will be produced that the receiver has to support.

ANother good example of this is the 50 BMG. The receivers for the 50 BMG are MASSIVE things, several times bigger then even those for the 408 CT, still, if you load the 50 BMG even close to 60,000 psi, you will get extraction issues because the bolt thrust generated by that huge case head is just unreal. The test to see if your loads for the 50 BMG are excessive in pressure is to take a JUST fired case and rechamber it back into the rifle, if it chambers easily, your pressures are fine, if there is resistance on the bolt to close it on the fired case, your pressures are to high!!! Cartridge brass will permanently deform at 50 to 55,000 psi depending on the brass used. THis means that if your pushing the 50 BMG much over 55,000 psi, your loading it to hot, even for those massive chamberings. It all has to do with case head diameter and bolt thrust. PSI is a small part of the equation.

This simply amazes me that he would give you information like this. DO what you like, YOU HAVE BEEN WARNED!!! I am not saying it will blow up on the first firing or maybe even the first 100 firings but if your going to do this, DO IT RIGHT and with the Montana Rifle Company receiver, you are NOT doing it correctly.

One example is my Raptor receivers. They are easily stronger then any 338 Lapua class receiver on the market, that includes BAT, Nesika, Surgeon, McMillan, any of them. This is because I intentially wanted to design it so that it could, in the future be used as a platform for the 408 CT based wildcats as well.

All that said, as strong as it is with its MASSIVE bolt and MASSIVE bolt lugs and HUGE AMOUNTS of steel supporting the bolt lugs in the receiver. It STILL failed to offer safety margins high enough to support the 338 Allen Magnum because its shear strength was boaderline and I guarantee that the Raptor is DRAMATICALLY stronger then that MRC receiver.

Again, do what you want but you have been warned by two guys that are not trying to sell you a thing, Joel and I just want you to do this right the first time so you are safe and get the best investment for your money, we have both recommended what receivers that WILL work properly and none of those receiver companies have any connections to use at all. We are just giving you good advice from our real world experience.

The Smith at MRC just gave you an opinion saying it SHOULD be fine. That is not enough, especially when his knowledge base is obviously limited in the effects of case head diameter in relationship to bolt thrust........

You have been warned, your choice. Go half *** or do it right, your call. Not trying to insult you in any way, just being blunt so you get the seriousness of your decision and the poor recommendation you got from that smith at MRC.
 
I think I will just go with either a 338 Lapua or a 378 Weatherby on this action and be done with it. I will decide which one when I order the barrel. When I go to the bigger 408 case I will buy a barker or stiller action that I know will work. Thanks for the info.
 
Very well put Kirby, you beat me to the punch. **** you..:)

Dakor~ Kirby and I have a vast amount of experience with the chamberings on the .408 case, and we are just trying to pass on our "real world experience" to you. Neither one of us wants to see anyone get hurt based on the "opinions" of someone without the knowledge of those willing to offer it.

Good call on using the Lapua or Wby case with that action. Give Kirby a jingle when you decide to step up to the .408 case, he's a wealth of knowledge...
 
One more thing to consider on any build that will be using the 408 CT for a parent case. You should have a MINIMUM thread diameter of 1.185" and a barrel shank diameter no smaller then 1.350" diameter to at least 1" past the end of the throat of the chamber.

This is MINIMUM.

In fact if your using a button pulled rifled barrel, this can be CRITICAL and your chambering reamer had better be designed properly. Why...... Well, let me explain, if you use a button pulled rifled barrel, it will be relatively soft in comparision to say a cut rifled barrel. If you use an improved chamber that has to little body taper, you will have extraction issues, especially when the brass gets a bit older.

NEVER go smaller then 1.185" thread diameter for a Chey Tac based chambering just to be on the safe side. Remember, along with the bolt thrust issue, the chamber pressure also pushes on all sides of the case. The 408 CT has DRAMATICALLY more case baring surface to the chamber so that 65,000 psi is applied to a much larger area, harder for the barrel to contain.

The main reason you need at least 1.185" of steel around the chamber at the threads and the shank needs to be a minimum of 1.350".

Trust me, I have played with many chambering reamers and barrels to find out these are the minimums you need to use. Now ovbiously, even larger diameter threads are better and there is nothing wrong with a barrel shank larger then 1.350.....

I am pretty sure that the MRC does not have a thread diameter that large.
 
Kirby and Joel. Given the above discussion I would appreciate some advice. My problem is I love shooting my 375 Allen Magnum and now I ve put about 500 rounds through it it and shooting out to 2400 yards it does great. If anything its getting more accurate but that may be I m shooting it better. But, Kirby the fire formed rounds I bought from you for it are now getting a little tight and difficult sometimes to extract. My first question is when should I give up using them and should I order some more fire formed ones from you? Should I cycle them through the chamber as empty cases to check them before reloading? Secondly, I have a Gibbs 505 loaded with 144gr reloader25 with barnes tsx 525 at 2270 fps. As you know one reason the 505 is liked in Africa is because of the low pressures particularly in the heat. But it is stiff and needs a good pull to extract. Do you think the pressures may be to high? Looking forward to comparing the 338 am you are building for me with the 375am. Interesting Joel you find the 338 is more accurate and that both of you dont find solids after multiple shots not that accurate. Very interestin discussion. Thanks.
 
LR3 said:
My problem is I love shooting my 375 Allen Magnum and now I ve put about 500 rounds through it it and shooting out to 2400 yards it does great. .
Click to expand...

I'm smiling really big here. This is where I was with my 270 AM. My 375 AM is, as my wife would say, being savored. It's by far the most fun shooting gun I have (only have 4). Only 25 shots thru her and we are dialed in like we've been dancin' for decades.
 
Roy. Be careful - Soon your wife may say it s me or the gun!! :) Mine just bought me a new blue tooth Kesterel and Nomad so I cannot complain.
 
Fiftydriver said:
One more thing to consider on any build that will be using the 408 CT for a parent case. You should have a MINIMUM thread diameter of 1.185" and a barrel shank diameter no smaller then 1.350" diameter to at least 1" past the end of the throat of the chamber.

This is MINIMUM.

In fact if your using a button pulled rifled barrel, this can be CRITICAL and your chambering reamer had better be designed properly. Why...... Well, let me explain, if you use a button pulled rifled barrel, it will be relatively soft in comparision to say a cut rifled barrel. If you use an improved chamber that has to little body taper, you will have extraction issues, especially when the brass gets a bit older.

NEVER go smaller then 1.185" thread diameter for a Chey Tac based chambering just to be on the safe side. Remember, along with the bolt thrust issue, the chamber pressure also pushes on all sides of the case. The 408 CT has DRAMATICALLY more case baring surface to the chamber so that 65,000 psi is applied to a much larger area, harder for the barrel to contain.

The main reason you need at least 1.185" of steel around the chamber at the threads and the shank needs to be a minimum of 1.350".

Trust me, I have played with many chambering reamers and barrels to find out these are the minimums you need to use. Now ovbiously, even larger diameter threads are better and there is nothing wrong with a barrel shank larger then 1.350.....

I am pretty sure that the MRC does not have a thread diameter that large.
Click to expand...

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