Thread: Ultimate compact rifle & catrige - 6mmGT/22GT in howa mini action

Originally Posted by Stocky

I agree with tentman your in dangerous territory making engineering assumptions especially as you clearly dont grasp even half the concepts.

The BAT action uses a 4140 chromoly steel (around 655Mpa yield) portion at the front for the bolt lug recesses and the barrel threads. This is the area that takes almost all the load and is further supported by the 7075 heat treated aluminum sleeve (around 450Mpa yield). It is larger than the howa mini (made of some sort of stainless probably a 416r(around 650Mpa) by a significant portion and far stronger and takes magnum cartridges. You can see the aluminium is not much weaker and the 4140 yield i gave is as supplied it can be much stronger whereas the 416 has issues with impacts if hardened further. Also the lugs on the mini are tiny, a kimbers are noticeably larger to take 308 cases. The lugs of the remington 700s or BAT action are larger again.

Everything behind the ejection point can be almost any material i.e. how ar15s can be made with plastic upper receivers and the majority are aluminum as all the chamber forces are maintained with steel up front and the only serves assistive functions and only needs to cope with recoil forces. there are lots of aluminium actions nowadays, seekins, sauer, gunwerks, blaser to name a few

Bolt thrust increases significantly as bolt face cartridge diameter does. A 62kpsi case the diameter of a 223 and one the diameter of a 308 is not even close to the same when talking bolt thrust its 56% higher. Also case diameter is the main determining factor is bolt thrust not powder capacity. This can be seen in the 84M and 84L kimber action which share the same action design from the ejection port forward as the bolt face remains the same even though i can run a 280AI in one that holds equivalent powder to most short magnums.
Its even hypothesized that with minimal taper cases that the longer cases actually work better as they gain more grip with the sides of the case to help the brass hold some of the force reducing bolt thrust.

After all that I know Guys have built 6mmBR Howa minis and their wildcats but all are playing on the fine edge of things where an oily chamber cause cause a failure whereas normally it would just cause a sticky bolt as damaged brass. Most smiths wont do it in NZ.

Lastly why build a 6.5GT on a Howa action when its performance gains in short short barrels is minimal then its no longer compact and for less weight a 16 inch 6.5 creed in a kimber will outperform it easily without going custom.

Good explanation about the bat action, Stocky. I believe the counter force for the bolt thrust is called "friction effect", where the case direct the force to the chamber wall, as much as half of the total force? A long straight case has better friction force than short & tapered one. That is one reason the nickels plated case is no good.
For you all firearm experts here. Here is something I am always unclear. For a bolt gun, is the chamber pressure more important than bolt thrust, or other way around? Cause usually I only hear people talking about bolt thrust in none bolt action rifle, like contender, but in a bolt gun I hear more about chamber pressure? hence people will attach a strain gauge to measure it and determine if the load is safe. I am an engineer and I do believe in math and numbers. So if you think you are right it is best to provide some solid science.