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making the blow-forward breech work

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Unread postAuthor: jackssmirkingrevenge » Sat Mar 08, 2008 11:56 pm

VH_man wrote:...are you sure you will fill the chamber up fast enough with that?


That size of chamber fills up almost instatly gtrom a schrader, and this has better flow thant hat, so it shoukld be fine. Anwyay, I'm absolutely arseoled and should be heading to bed, so give it a few hours and we'll see if the much vaunted theotry works :)

if that isn't PUI i tdon't know what is :D
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Unread postAuthor: Novacastrian » Sun Mar 09, 2008 12:00 am

jackssmirkingrevenge wrote:
VH_man wrote:...are you sure you will fill the chamber up fast enough with that?


That size of chamber fills up almost instatly gtrom a schrader, and this has better flow thant hat, so it shoukld be fine. Anwyay, I'm absolutely arseoled and should be heading to bed, so give it a few hours and we'll see if the much vaunted theotry works :)

if that isn't PUI i tdon't know what is :D


Woot! That's the best effort of PUI you have made i think JSR, well done! :D :lol:

Edit: Don't forget the aspirin :)
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 09, 2008 12:03 am

already taken :"D along with 1 litrew of water. I', m booked at the range tiomorrow morning but i dont think i'll be able to tresist giving this baby a go. before i leave :)

seriouly,m i'm going to bed,.
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 09, 2008 12:04 am

did i say tomorrow morning? it's bloody six in the morning, I meant in 2 hours time! lol./
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Unread postAuthor: LikimysCrotchus5 » Sun Mar 09, 2008 12:04 am

I sense a hangover....... :D (yes im gifted)

Im surprised you answered the question.... lol

"Welll..... i think its about time i hit the old dusty trail" (family guy quote)
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 09, 2008 1:13 am

I *really* should go straight to bed when I arrive home, apologies.

No hangover is imminent as due to aggravated circumstances I haven't managed to sleep yet, keeping myself hydrated in the meantime et voila. As soon as it's socially acceptable to fire up my compressor on a Sunday morning I'm giving this thing a go :)
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Unread postAuthor: MrCrowley » Sun Mar 09, 2008 1:21 am

jackssmirkingrevenge wrote:I *really* should go straight to bed when I arrive home, apologies.

No hangover is imminent as due to aggravated circumstances I haven't managed to sleep yet, keeping myself hydrated in the meantime et voila. As soon as it's socially acceptable to fire up my compressor on a Sunday morning I'm giving this thing a go :)

You might be lucky and get some guy mowing his lawns :)

That's if there are any lawns to mow around your area...
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Unread postAuthor: jackssmirkingrevenge » Sun Mar 09, 2008 7:26 am

The results are in, and not at all encouraging I'm afraid.

I tried first with my stiffest stiff spring, popped off nicely past 100 psi, but on the return stroke (just as judgement arms had predicted) it hung open and reset very slowly. Weaker springs were even more prone to this effect as there was less force to reset them. I can't fit a stronger spring, because that means it won't pop off at all.

My next solution was to reduce the diameter of the bolt piston slightly to reduce friction and increase blow-by, this improved the hanging issue but unfortunately now the bolt wasn't moving forward enough to seal the barrel.

So, in a nutshell, one cannot prove this, but it "is" in the same sense that Mount Everest "is"... this would make a great semi-auto design if you removed the check valve and stem and simply hooked it up to a blowgun, it opens very fast and would be good for airsoft or similar. However, my aim was full-auto and as such this design was a failure.

Preloaded cartridges are looking like an even more attractive solution to achieve my objectives. I got some experience with fiddly little valves in this project however, which has got me thinking that perhaps this design deserves to be built. The question is, will it suffer from the same "hanging" issues that the blow-forward breech does?
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Unread postAuthor: Antonio » Sun Mar 09, 2008 7:57 am

Ah that kinda sucks then! I have this model to find the exact spring tensions etc for auto fire but its kinda complex. What about making the hammer valve auto but then only with the bottom cylinder tube. If this works then u can add the top barrel etc. Btw I have made airguns thinking they were crap but later came to realize they were very good. Like my poppet valve guns, I made that one half a year after I starting building these things. It didnt work as I didnt have a hammer but I opened the valve with my hands. I think your problem is the spring tension. > There is only a small margin for autofire< I will try yo refine the excel doc I am workin on now so that other ppl can use it as well. I though about buying a spyder paintball gun to compare my calculations with real life. But yeah I dont think my parents will allow me to buy one.
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Unread postAuthor: Skywalker » Sun Mar 09, 2008 8:36 am

Shucks! That's too bad. So you're saying that it doesn't let all the air out of the firing chamber? I guess that means it doesn't have enough momentum compared to the spring strength to blast way open. Could you add some mass to the bolt/hammer? Or maybe put a hole or a valve to vent the thing when the piston is returning?
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 10, 2008 1:31 am

What about making the hammer valve auto but then only with the bottom cylinder tube. If this works then u can add the top barrel etc.


I was thinking this would be a good next move. I could try and add some mass to the bolt by packing it with lead as Skywalker suggested, but I doubt this will solve the problem. Still, worth giving it a go I suppose.

Or maybe put a hole or a valve to vent the thing when the piston is returning?


Given the relatively small size of the chamber, you would think that it would be enough to dump in one go when the bolt moves forward (as of course the chamber air supply is blocked off as soon as the bolt starts moving, but clearly this isn't the case. I'll go with the heavy bolt, and in the meantime get started on the hammer valve.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 10, 2008 9:09 pm

Here's the new heavyweight (around 450% of the original) bolt in its syringe tube mould as I wait for the epoxy to cure. You can see the steel washer i included in the casting for extra strength and weight, as well as the extra foam ring half way around the bolt temporarily added to to keep it centred in the tube. Maybe I should write up a bolt casting how-to? :roll: :D
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Unread postAuthor: Sticky_Tape » Mon Mar 10, 2008 9:34 pm

Maybe I should write up a bolt casting how-to?


I don't think there is any need to just keep everything centered btw thats a good looking bolt so far.
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 10, 2008 9:43 pm

spudchucker wrote:I don't think there is any need to


I know, hence the :roll: :D

Should be ready for testing some time today, let's hope it works - or at least, gives an indication that it's close to working, then I can make an even heavier bolt.
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Unread postAuthor: Sticky_Tape » Mon Mar 10, 2008 10:12 pm

I'm off to bed I guess it will probably be done when I get up right in about 9h I guess can't wait to see it work cant wait to see it work.
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