Originally Posted by Fiftydriver
Not to ruffle your feathers but the Nesika Model M does not have a thread diameter large enough to be safe with the 408 CT and its wildcat offspring.
Have you done this or seen it done? IF so, I would HIGHLY Recommend it not be done. Not a question of receiver strength, its a question of barrel thread shank diameter, not enough for this size of chambering.
All the 408 CT receivers I know if have at least a 1.125" thread diameter and most are larger then this. 1.0625" is not large enough for the CT or its wildcat siblings.
It may work for a while but your really stessing those barrels and if you use one of the softer barrels, you could be in serious trouble.
Just my opinion.
Just talked to Richard yesterday at Nesika, he said again they have no receiver that will work with the 408 CT and have no plans on making one.
My Raptor receiver is far stronger then the Nesika Model M receiver and there is no way I would ever consider chambering it in the 408 CT simply because of the barrel thread diameter issues mentioned.
Not meaning to offend you but I can not agree with your recommendations and feel there are HUGE liability issues at hand converting a Nesika M receiver for the 408 CT.
But for sake of discussion, lets do some math for fun.
Not having one in front of me, I'm going off what I can pull off the "internetz".
According to Wikipedia the .408CT has a major diameter of .647".
The Minor thread diameter on a 1.0625X18 thread is .998" if I'm not mistaken.
So, were looking at a wall thickness of .1755".
Comparing this to a 338 Lapua shows there is .014" more wall thickness with the 338 than the 408.
While I am anything but an engineer, I do have to wonder:
The 338 LM is a high pressure cartridge. Over 60,000 CUP. If its only .014" wall thickness material that differentiates between safe operation and catastrophe, then I'd have to conclude that Nesika and most any other manufacturer using a 1.0625 diameter thread is playing with fire and dancing with the devil when it comes to any of the 30-375 caliber high pressure, high performance magnum cartridges.
Experience shows us though that this thread pitch runs fine with these kinds of cartridges. (300-378 WBY, 338 LM, 300 RUM, etc. . .)
So, that being said, is it really so reckless?
We'll take the assumption that it is. Here is the parachute that saves my hide and keeps me from looking like a fool: (Ok, not really)
If you notice in my post I did state it would require some work to do this. I think I even mentioned that Nesika does not offer an action specific to this cartridge.
(From my initial post)
I'd suggest a Nesika Model M. They won't do it for you, so you'll have to take to to someone who will. You need the M cause its long enough (with a little port elongating mind you ) and has the bigger bolt diameter which is what you REALLY need here. This case is a boomer for sure. (end quote)
Personally, if it were my gun, I'd of left the threads alone and ran it without fear, but since its been brought up.
I'd order a Nesika Model M. I choose an M because it has a .750 Bolt body diameter. The other Nesika products run at .700". I'd have the bolt face cut for a 338 Lapua Magnum because, as stated, Nesika does not offer an action specific to the CheyTac. I'd order it without an extractor. It would either be 1.470" OD or 1.700" OD. (Nesika is offered in three diameters. 1.35, 1.47, and 1.700)
I'd have to elongate the loading port to load the cartridge. I'd probably try to modify an AR-10 extractor and use it for the bolt to avoid having to make something from scratch.
Now for receiver threads:
Taking your advise:
I'd open the threads up on the action. My personal preference would be to fixture the receiver in a vertical CNC mill capable of thread milling. I'd establish my datums, find center, pick up the existing thread, and begin opening the receiver up to an arbitrary thread diameter. Probably take it out to 1.093 or maybe even 1.125". The limiting factor would potentially be the two dowel pin registers drilled into the receiver face that clocks the recoil lug.
In this case I'd more than likely start my thread behind the holes. Using a CNC makes this a simple programming change when modifiying. Just a canned circular pocket cycle is required. Since I want all my thread tension at the end of the barrel tennon anyways, this is probably a better way to go from an accuracy standpoint.
I still get to thread the barrel all the way to the shoulder if I choose so that I have the option of setting the barrel back later without an interruption of thread on the barrel.
These threads don't exist per say in the machinery hand book and they don't have to. Just fit the barrel to the action and its of no consequence.
Is this a lot of work? Certainly. I'm jaded. I worked for Nesika for three years as the rifle department manager. I have a genuine affection for the product.
Anyways, an interesting discussion regardless.