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Discussion Starter · #1 ·
As I fine tune everything with my chamber I realized something interesting. Under perfect circumstances the blue nozzle( standard vsr ) will put the bb about 20~30% down the length of the patch of a non bridged(open) barrel and bucking combo( ML / X-R ). With a bridged barrel this placement would be near the bridge and about as good as you can get. With the unbridged barrels I feel like there is room for improvement and why we don't see much of a difference between the two systems. If I move the bucking/nub/barrel forward away from the nozzle I would lose the proper air seal around the first step of the nozzle.

The other option is to shorten the length of the nozzle by .100( 2.5mm ) which is what I did with the yellow nozzle below. This would put the bb right at the start of the contact patch and with the flex at the nozzle side of the bucking it would hold the bb in place. The bucking pressure or the contact patch from the nub isn't shown in these models.

OK so why is this an issue? It's not exactly an issue but more like trying to squeeze the last bit of performance out of the unbridged barrels. HOWEVER, with the regular blue nozzle if you do not have the nozzle/bolt all the way forward, you risk putting the bb further back on the patch which results in more patch distance and over hop or flyers. Vice versa if you are forceful with the loading, you risk pushing it further down which is less hop. We're talking about microns here but that will make or break you at 300 feet.

With the yellow nozzle you gain that additional 20~30% contact area which allows for less pressure needed for heavier bb's, also allowing for heavier weights at weaker FPS/joules. This also means a longer patch guide which arguably means a more stable hop. I also believe less pressure on the bucking will give you better results compared to more force applied for the same trajectory. Just a theory. With the shorter nozzle you would also run less of a risk of loading the bb in different spots of the contact patch since the neutral position is just before the patch.

I will be testing a shorter nozzle like the yellow one and try to be as scientific as possible. The goal is to see a more stable hop with less vertical variation at distance. I'm open to your ideas and love to hear opinions on the topic.
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Ideally the bb would be held just at the start of the bucking contact patch with zero movement possible. That way the bb is always starting its movement in the same place, increasing shot to shot consistency. It’s difficult to pick what axial position that correlates to when factoring in different bucking designs though. You can also widen the ID of the nozzle so the bb sits farther inside it instead of reducing the length of the overall nozzle.

Unfortunately all of this tuning goes out the window when every cylinder is a slightly different length and every receiver/barrel manufacturer uses a slightly different length as well. Additionally most bolt handles don’t fit in the receiver cutout with zero play either, so nozzle placement will depend on how consistent you close the bolt, and then not touch it while you run around. All this just means that you are going to get different bb placement with conventional cylinder and nozzle designs.

The way I solved all this was with a self-adjusting cylinder head. Basically just indexes off the face of the hop up chamber so the nozzle is always in the same spot.
 

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Discussion Starter · #3 ·
The yellow puts it where you described. I think drilling would bring it in some but maybe only about halfway. You’re absolutely correct with the variation where the bolt and cylinder sits. I made these models assuming that the nozzle flange sits flush with the chamber every time, which is not always the case. I do testing using an E-Bolt and a return spring on the nozzle so it pushes all the way up to the chamber no matter what.

Dealing with spring there’s all those factors like you described. That’s a whole other topic to try and get that as consistent as possible like the self adjusting head. For now I’m just assuming it’s in the forward most position every time. Maybe a telescoping nozzle would solve these loading inconsistencies or something like you did.
 

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Yeah, there's this Japanese guy who seems to have "discovered" this a good while ago, and I tried it myself with good results.

Watched ALL of his airsoft related videos, probably 300, and sorted out the useful ones into this playlist.
If you sort it old to new and then read the titles as well as look at the thumbnails, you'll get a good idea of where it's at.
Also, check it out on a computer of some sort as they almost always have a translate function for normal text, and the browser version of YouTube has an auto translate function if you turn on CC and go to the settings icon.


As for my stuff, I seem to have lost the best picture but I'll take a new one soon and leave it here.
Here are two pictures of my stuff from this winter though, with a 2021 70° Autobot to allow you to see the BB a little more clearly than anything else.
You want the center of the BB about 1mm onto the patch, as at the edge seems to sometimes pull the edge of the bucking and it will catch.
Any more and your accuracy seems to get a little worse.
This seems to get you the optimal length without deforming the patch, and seems to grip the BB pretty well.
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One thing that was mentioned is bolt handle lock up and cylinder head stability.
These two are VERY VERY important, like really important.
You want to add epoxy to the back of your cylinder handle slot in your stock to keep the handle locked and pushed as far forward as possible.
This is sort of useless if your cylinder or nozzle is too short, as the face of your cylinder head should be making full solid contact with your chamber.
If you aren't getting that, you should screw your outer barrel in a bit, or file the end of it so you can screw it in even further.
 

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I think a while ago masada mentioned on his rifle he had the bolt handle fit the receiver cut out perfectly so the nozzle was held in the exact place firmly each shot.

edit I see Masada touched on that in this thread.

Plus how Mr. Sword described it. Due to learning all of that, I made a bolt stop for my lefty rifle since most of the left handed designs don’t lock in place. I hate the idea of being able to pull the bolt back without lifting the handle.
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That is one reason that I quit using a straight pull BOLT when I used a VSR, as I feel like you need a heavy spring to make it work properly, which to me was a bigger cost than having to lift up a handle.
When making my VSR-SS I had this in mind, as I made my bolt handle lock very securely into my modified AirsoftPro receiver.
 

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Discussion Starter · #8 ·
Here's that pic of the patch to help others understand this a little better.
I couldn't get a good angle on my half bucking, so I drew this instead.
Obviously not 100% accurate, but it's basically there.
View attachment 20524
Yeah I think having it start at least a little on the patch like this would be better than the edge of it. Either way there is still some patch distance to gain from drop in parts.
 

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Yeah, I think that no matter what, people will have issues, but I think it would be cool if you and Masada could somehow sell his style of cylinder head to lessen these problems.
HPA with the BOLT is very versatile though, and I feel like the serious users of this chamber will own a BOLT.
 
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