375-408

[jrivera1]

Tag

 

[royinidaho]

Tag

J,

Click on "Thread Tools" in the tool bar in the "View This Thread" tool bar and select "Subscribe to this thread".

Saves time on booth ends.

 

[jrivera1]

Thank you

Will do going forward...

 

[Fiftydriver]

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.

I have good and bad news. And sorry for missing this question. The old Jamison brass, for some reason seems to be softer and a bit stickier to the chamber and as such when it gets older, there are some issues with extraction getting a bit sticky. The new Bertram brass solves a lot of this problem.

I have seen this comparing the 338 Lapua cases as well used in my 7mm AM, 300 AX, 338 AX and 375 AX. If I use Lapua brand brass, no problems at all. If I use Norma, HSM or Hornady, as the brass gets a bit long in the tooth, the cases get sticky but that is not the case with the Lapua brand brass. I am sure this has to do with the alloy used more then anything.

It is critical on my wildcats that you FL size the cases JUST enough so that they chamber easily with no resistance as a sized empty case. If there is any resistance when you close the bolt on a sized case, you WILL have slightly sticky extraction.

I have been testing this issue a lot lately and have come to two positive decisions.

1. I have reordered my 338 AM and 375 AM chambering reamers to be made with the base 0.003" larger in diameter then the original design while leaving the shoulder diameter the same as original. This will SLIGHTLY add to the case body taper and will help with this matter. This small amount of increase will not be enough to require any new dies to be made as the standard dies work just fine with the new chamber design.

2. I have decided that for cut rifled barrels, I will be using nothing smaller then 1.400" shank diameter and for button pulled rifled barrels, there will be nothing smaller then 1.400" shank diameter used. This has proven to offer more support to the chamber, especially around the case shoulder area to prevent any chamber swelling under pressure.

What this does is all chambers swell under pressure and then they contract. This is why barrel work and do not blow up when firing a round, they stretch but do not break!!! Well, if the barrel shank if small enough, it allows more of this swelling under pressure. The brass swells to fill this swollen chamber. When the chamber pressure drops on new brass, the brass contracts back down dramatically and releases the chamber walls and can be extracted easily.

As the brass gets older, it looses much of its elastic properties and as such, the barrel and brass expand under pressure, they when the pressure drops, the barrel contracts back down to original dimensions but the older brass does not have the ability to contract back down as it could when it was new. As such, you get a tight fit in the chamber and sticky extraction.

All new XHS rifles I build will use this new chamber design and will also use 1.450" shank diameter for button pulled barrels and 1.400" shank diameters for cut rifled barrels to pretty much eliminate this issue. This will also pertain to any rebarreling down the road but again remember that my original dies still work just fine for the new chamber.

That combined with the stronger, more slippery Bertram brass will give another boost to these already hyper performance chamberings.

 

[LR3]

Great thanks very much for the insight and explanation Kirby! Fascinating. Look forward to seeing how the Bertrams holds up. Stay warm.