450 Corvette

[LlindeX]

I hesitate to publish the load, because you wouldn't believe it anyway or think it irresponsible. But I was trying out some 230gr FMJ 296 loads I had, on the rifle length gas system and saw speeds of well over 2800fps, with only .0005" to .001" of case head expansion, measured where the fl die lets off or about .200" north of the rim and very little flattening of the primer (normal), and no swipes.

Suffice to say these ARE NOT loads you can shoot in your Standard Factory Weapon, you'd need a 450 Corvette Conversion to even start to think you can do this..

..t

Wildcatter,
Your Corvette mod to the 450BM looks to bring an awfully interesting improvement to performance. I understand that the design of the factory FTX bullets were a limiting factor for the max. factory ammo velocity. However, with your knowledge of the situation: What was Bushmaster's original reasoning for making the 20" barrels with the carbine length gas system in the first place? They had to have some reason for doing so. Couldn't they get the factory loads to cycle in a 20" barrel? For the life of me, I can't figure out why they went with the carbine gas system in both barrels.

[Texas Sheepdawg]

He's at the Shot Show so you may not get an answer until this weekend.

[Epaphroditus]

I have been ask quite a bit now, as to what is involved in the conversion. We have gone over this allot in the other Thread, so I won't rehash all of that, unless asked.

What other thread? I have money and I want to spend it!

Is there a consensus or preferred upper to start with as a base for the 450 Corvette mod?

I have no clue or experience but this topic has got my brain juices flowing. I wonder if adding some loops into the gas tube would buy some extra time so the bolt stays shut a bit longer. Isn't that the point (one of them anyway) of the rifle length versus carbine length business anyway? A bit more time with the bolt in battery to reach even higher velocities?

If not loops then other games with the gas tube geometry to slow down the gas just a bit (like a bubble/expansion chamber, etc)? As long as there is sufficient dwell time past the gas block why not? If such tricks work then they could also work in carbines as well (maybe).

[jerdebson]

Tim is at the Shot Show I believe. I am not up to fully explaining why the loop tube doesn't quite fill the bill but... The rifle length tube gets its gas further from the chamber thus slowing the timing with relationship to the bullet not only the tube length and smoothing the pulse. The relationship to the end of the barrel also comes into play if I remember right. There are other things to consider but I'm not an expert on the subject to cover them. Hopefully someone will clear up the water I may have muddied up here.

[Texas Sheepdawg]

Tim is, indeed at the Shot Show. I communicated with him this morning. He is going to try and get us some information on reloading component outlooks, ie Powders, primers, bullets, Hornady, Hogdon, etc. I also asked him to check out a few personal interests regarding a few different firearms MFGrs. Hopefully, he will find some time to check in later.

[Epaphroditus]

Tim is at the Shot Show I believe. I am not up to fully explaining why the loop tube doesn't quite fill the bill but... The rifle length tube gets its gas further from the chamber thus slowing the timing with relationship to the bullet not only the tube length and smoothing the pulse. The relationship to the end of the barrel also comes into play if I remember right.

As I said I really don't know or have experience on this ....

The idea of loops or chambers in the gas tube is to further increase the effective length of the tube or at least increase the amount of time it takes for the pressure to propagate from gas port to gas key. Looking at the timing on the diagram in this post(http://www.450bushmaster.net/viewtopic. ... =60#p43120) one could imagine another mark out past "rifle" which would mean an even longer time in lock-up.

The relationship to the end of the barrel also comes into play if I remember right.

If I'm understanding correctly the time that bullet passes the gas port until it exits the barrel is the only time there is actually gas pressure in the gas system. So long as there is sufficient time and pressure to get the bolt carrier assembly moving then things function properly. For a nominal 2000 fps bullet and 16" barrel with rifle length gas that gives 0.17 milliseconds of "gas time" - amazing anything works at all!

It seems interesting to ponder getting "rifle length timing" into a carbine length system using tricks like expansion chambers to control the speed of the pressure wave as it moves from gas port to gas key. Mostly me just a case of having little knowledge and too much time on my hands! I bet this kind of stuff has been tried and discarded several times in the past.

[jerdebson]

Well its obvious that you know more than I do about the gas system of the AR so I didn't need to try to baffle you with my lack of knowledge.

I have a 450C because it sounded like something I would like to try. As of yet it is unfired but not for long, I hope. How does life get so complicated? Tim changed mine over to rifle gas and other assorted "Fairy Dust" and TSD threw in some Voodoo and it was done. Timing the gas system is above my understanding past what I already posted, come to think of it I'm not sure I understand all I know.

[Epaphroditus]

"Loops" evidently are a 'known' thing http://www.brownells.com/rifle-parts/ga ... d1591.aspx

Reinventing the wheel I suppose is what I'm doing .... at least it is not completely whacko! I like my idea of expansion chambers better than loops anyway. Maybe even an adjustable sized chamber so one can dial in the timing they want kind of like how a adjustable gas port works kind of thing.

Anytime I see "adjustable" and "50,000 PSI" I see parts flying all over the place (that would be bad). One must tread carefully in such a context.

[MarkCO]

There are numerous safe methods to control/regulate/utilize high pressure flows in other industries. Most of the "great" inventions (sans miniaturization of CPUs) of the last 40 years have just been technology transfer. When you think inside the box, you tend to not be able to see out of the box.

[jerdebson]

Just keep in mind if it was as simple as an extended "loop" gas tube we all could have a 450C for the price of a gas tube. Boy would I feel stupid having spent $250.00 to get WC to convert my 450B. Thankfully I don't have to know how to design an AR to shoot one. My engineering experience is in another totally unrelated field.