Fake Gas Block on the 20" 450 B Upper?

[Texas Sheepdawg]

This deserves it's own thread, so here we go...
What is the deal with the Fake gas block on the 20" 450B?
What was the reasoning? Is there actually a hole in the
Barrel at this Gas Block? Why add the extra weight?
Is it there purely to add an accessory front iron site?
Was it done like this to change the timing?
Why, Bushmaster? Why? Inquiring minds want to know.

[greggs]

I took mine off and have killed three deer with it since. just extra weight.

[artalon]

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Re: Bettering the board...

Postby wildcatter » Wed Dec 01, 2010 10:15 pm
I'd like to comment about the fake block and maybe some of this might get incorporated in to the FAQ.

The fake gas block was just for looks, mainly. But I for one use much slower powders for much higher speeds than we are used to. The problem with the carbine block is that it starts the bolt opening far too soon with many of the the loads, we might be playing with. As an aside, this to-soon-opening, is a blessing of sorts, as when this is happening you'll see either the rims start to be ripped off or the action will start to short-stroke, and all this because the case is still sealed in the chamber, when the action starts to open. The blessing is, Usually, this problem arises a long time before you over pressure the weapon, of course I say Usually, because you could come up with some kind of load combination that makes all this un-true, but using our "Usual" techniques, this can be your best sign to back off on your loads.

Now, what I do to the fake gas block is to activate it. I turn our carbine gas block 180° and use the set screw to block the gas port, of course I've removed that carbine gas tube. I then pass a new rifle gas tube over the upside-down carbine gas block, to the now reactivated rifle length gas block. Why? It's a timing thing for me, I am experimenting and need the chamber to open far later than what we deal with in our standard rig. Several days ago I just did one for Barnes, for a 650lb +- pig hunt. They wanted ammo that outperformed the 45-70 hands down. Part of their theory was that a charging pig, starting out at say 50yds, there wasn't enough time to jack another round into the chamber, for another shot, before the animal was on you. I did the the flip thing and put on the rifle length tube and am using their 325gr Barnes Busters at 2100fps, whereas the 45-70 was only getting 1700fps with the same bullet at SAAMI specs. Keep in mind this is lab stuff, but is a great example of what can be done. As they say, your results can and will be different and what I've just described is dangerous. However, if you do, do this, i.e., use the rifle length gas tube and block, the factory ammunition will short stroke, but the conversion back is easy and fast. You can see this is the reason why I love the fake block, it allows me to experiment.

Now that I've properly hy-jacked the thread, we can get back to FAQ's. I just wanted to insert something I thought useful, sorry guys..t
Safety First..t

[Hoot]

Just in case you do not know this, there is no hole from the bore to the outside of the barrel under the unused gas block. If you want to experiment with it, or a gas block mounted in a different location, you will have to drill a hole through the barrel underneath where you place it. For most of us, money doesn't grow on trees and we don't want to have to buy a separate barrel. If you don't have that hole drilled with an EDM, chances are you are going to introduce a non-conformity point into the bore, AKA rough spot. Repeated shooting will over time clean up the hole, but along the way, it will be shaving every bullet. The point being, don't just do this because you can.

If you get deep enough into R&D with this caliber that you need to change the timing to continue, there is an alternative to a second hole that uses a gas delay-line block available to introduce what is in effect a longer gas tube, folded back on itself before continuing to the receiver. I don't know who makes it, but I saw an image of one in a thread somewhere. Achieving delay is not as simple as adding a restricting valve to the carbine length block. You need an unrestricted longer path for the gas to travel.

The down side to this approach is when the gas flow is diverted, either through a series of right angle turns or even a loop-back, there is a tendency for residue to accumulate at the point where it is diverted from it's original direction. Whether you'll shoot enough rounds for that to be an ongoing maintenance issue remains to be seen.

Hoot

[wildcatter]

Just in case you do not know this, there is no hole from the bore to the outside of the barrel under the unused gas block. If you want to experiment with it, or a gas block mounted in a different location, you will have to drill a hole through the barrel underneath where you place it. For most of us, money doesn't grow on trees and we don't want to have to buy a separate barrel. If you don't have that hole drilled with an EDM, chances are you are going to introduce a non-conformity point into the bore, AKA rough spot. Repeated shooting will over time clean up the hole, but along the way, it will be shaving every bullet. The point being, don't just do this because you can.

If you get deep enough into R&D with this caliber that you need to change the timing to continue, there is an alternative to a second hole that uses a gas delay-line block available to introduce what is in effect a longer gas tube, folded back on itself before continuing to the receiver. I don't know who makes it, but I saw an image of one in a thread somewhere. Achieving delay is not as simple as adding a restricting valve to the carbine length block. You need an unrestricted longer path for the gas to travel.

The down side to this approach is when the gas flow is diverted, either through a series of right angle turns or even a loop-back, there is a tendency for residue to accumulate at the point where it is diverted from it's original direction. Whether you'll shoot enough rounds for that to be an ongoing maintenance issue remains to be seen.

Hoot

I'm editing my follow-up quote for better clarity..t

[Texas Sheepdawg]

So, from what I am taking from this, the fake block on the 20"
is most likely installed so the average "Joe" could theoretically
utilize the secure block to mount a front iron sight or other
accessory. There is NO hole under the fake gas block. So
it COULD be removed to reduce weight if iron sights are
not an issue.
As for timing.... I will just be sure my loads work for my
Rifle.
Am I wrong?

[Hoot]

So, from what I am taking from this, the fake block on the 20"
is most likely installed so the average "Joe" could theoretically
utilize the secure block to mount a front iron sight or other
accessory. There is NO hole under the fake gas block. So
it COULD be removed to reduce weight if iron sights are
not an issue.
As for timing.... I will just be sure my loads work for my
Rifle.
Am I wrong?

That is correct. As soon as I go my 450b, I disassembled it to give it a good cleaning in the wash tank. The fake block came off easily and unlike some other bargain basement ARs, I was pleased to see that Bushmaster had phosphated the barrel before putting the block on. Seriously, A fellow at work asked me to do some work on his Blackthorne AR. When I took the gas block off, the part of the barrel it covered up was bare metal. They phosphated it with the block on. The rest of the rifle's quality was on par with DPMS, but the bare spot on the barrel diminished my opinion of them.

Wildcatter educate me. Why wouldn't a delay line work the same way as delaying when the gas is sampled by virtue of the port being further down the barrel? Seems to me it's 6 of one and half a dozen of the other.

Thanks,

Hoot

[artalon]

Wildcatter educate me. Why wouldn't a delay line work the same way as delaying when the gas is sampled by virtue of the port being further down the barrel? Seems to me it's 6 of one and half a dozen of the other.

Thanks,

Hoot[/quote]


Im with Hoot, what are we missing?

[wildcatter]

Wildcatter educate me. Why wouldn't a delay line (the simple answer is that, your so-called Delay Line, doesn't delay anything important to us, more below) work the same way as delaying when the gas is sampled by virtue of the port being further down the barrel? Seems to me it's 6 of one and half a dozen of the other.

Thanks,

Hoot

Im with Hoot, what are we missing?[/quote]


So here's one that will wrap around the barrel, giving lots of Delay, or so you'd think.

To take a stab at answering the question, I hope my Prose is up to the task..

Think of it like this.. Assuming you had a completely full garden hose and it's 100' long. Also assume, no water could come out until you blew on one end of the hose. Now suppose you had a mouth full of water and blew that into the hose and then and only then, could the water come out the other end. I know, I know, I'm making allot of assumptions, but hang with me a moment and give me some Artistic License. Ok, Back to our Fantastic Voyage. Anyway, the water coming out the other end is not be the same water you blew into the hose and more importantly, as the water you blow into the hose is under pressure the water coming out the other end comes out under the Exact same pressure and at the Exact same moment, you are putting your water into the hose.

So, we could have ten miles of gas tube and when the gas first goes onto the tube, gas comes out the other end at the same moment as when the gas first goes in. In other words, no length of gas tube or shape or length can change the timing. Does any of this make sense?

If you are having a Timing problem you must adjust/change the Timing. If you are having a gas problem, then adjusting/changing i.e. controlling the gas, is what is needed. Lengthening the gas tube does nothing to solve a timing problem, but might be an aid in a gas problem, depends on the problem.

Hope this doesn't further confuse the issue..t

[artalon]

i see what your saying and i dont want to be the thorn in your side but the pipe is not full of hot compressed gas where as the garden hose is already full of water, this is exactly how electrons pass along through wire, sorry had to throw that in there.
if you take that same garden hose and dump all of the water out and blow on one end its going to take some time to compress the air enough to move it out the other end, right?
it is not my intent to get any one peeved or up set in any manner so if i did so i am truly sorry and please accept my apologies