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

Originally Posted by Tentman

You need to get to grips with how bolt thrust works, there is a reason the mini action is smaller than a std 1500 ,. . . I also think the 6 GT would be a great cartridge for NZ, I currently run a 6.8 SPC (pretty much the same as the 6.5 Grendal) and something with a bit more snot but without the barrel burning habits of the 243 and 6 CM would be nice. I doubt you'll fine a gunsmith brave enough to do it in any of the mini actions, and if you do you'll find yourself in mag feeding hell, there is a big difference between the x39 based cartridges and the ex 308 ones.

I am not sure the bolt thrust has much to do here. F(bolt)=P(max)xA(internal or external), so long the pressure is same and the case head is same then the bolt thrust is the same. So really it is the pressure we are talking about here. the 5.56 (nato version if 223) has sammi pressure of 62366 psi, and your 6.8 is not far behind. Both are used in AR, a platform known weaker than a bolt action. the mini certainly will be weaker than a standard action but by how much is anyone's guess. Again you have very good point there. As for magazine, if it can deal with 450 bushmaster then it should work on GT. I have a 3d printed mini magazine so it is not end of the world if the factory one doesn't work.

Originally Posted by hey

I am not sure the bolt thrust has much to do here. F(bolt)=P(max)xA(internal or external), so long the pressure is same and the case head is same then the bolt thrust is the same. So really it is the pressure we are talking about here. the 5.56 (nato version if 223) has sammi pressure of 62366 psi, and your 6.8 is not far behind. Both are used in AR, a platform known weaker than a bolt action. the mini certainly will be weaker than a standard action but by how much is anyone's guess. Again you have very good point there. As for magazine, if it can deal with 450 bushmaster then it should work on GT. I have a 3d printed mini magazine so it is not end of the world if the factory one doesn't work.

Nice i have been trying to find the STL for those for a while.

Originally Posted by hey

Very good point there Pommy. the sammi pressure for 6mmGT is 62000PSI. However, I think howa mini can handle it fine. The custom rifle the guy built used BAT bumblebee action, which is aluminium. I am pretty sure mini is stronger than that. I didn't know there is mini for 450bushmaster, looks the mini family are expending

Originally Posted by hey

I am not sure the bolt thrust has much to do here. F(bolt)=P(max)xA(internal or external), so long the pressure is same and the case head is same then the bolt thrust is the same. So really it is the pressure we are talking about here. the 5.56 (nato version if 223) has sammi pressure of 62366 psi, and your 6.8 is not far behind. Both are used in AR, a platform known weaker than a bolt action. the mini certainly will be weaker than a standard action but by how much is anyone's guess. Again you have very good point there. As for magazine, if it can deal with 450 bushmaster then it should work on GT. I have a 3d printed mini magazine so it is not end of the world if the factory one doesn't work.

Originally Posted by hey

Don't think GT can be compared to 308 or creedmoor, 43gr VS 54gr water capacity. I agree the Bumblebee could be strong but doubt will be as strong as howa mini. steel is roughly 2.5 times stronger than AL, and I don't think bumblebee is twice as big.
good discussion though guys. have a good weekend

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.

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.