Short stroking 4 teeth on 200mm barrel

[steverebo]

Can I short stroke 4 teeth (2 pickup 2 release) on a 200mm barrel I've done it with all my 270 - 300mm barrels without issue and it makes a lovely sound very snappy semi AEG but at 200mm length I'm a bit concerned about air volume 

[Terry_Rist]

The general consensus is that for shorter barrels you need less volume so I don't understand why you think it would be worse on a shorter barrel when you are happy with the same set up on longer barrels? 

[Adolf Hamster]

The main issue with short stroking is voluming, if you've got the gun volumed correctly then as long as the piston is clearing the front of the port then you're not gonna mess up the voluming from short stroking.

 

If you're happy with that level on a longer barrel then you aint gonna have issues with shorter.

 

As for pickup/release, i've always tend to go predominantly from pickup. The following paragraph is me trying (and probably failing) to explain my thinking:

 

When its being released the tappet plate is under spring tension and takes time to close, and its not ideal for accuracy to be releasing the piston before then.

 

If you only take from the pickup side then the tappet plate will be retracting earlier (relative to the piston) but releasing at the same time (as an un-modified sector) whereas if you take from the release side then the tappet plate will be closing later relative to the piston (ie less time between tappet closing and piston closing) and could mean it doesnt have time to close fully before the air starts coming. Needless to say for a snappier build this isn't ideal.

 

Ofc main issue with taking from just the pickup is the sector might pick up the tappet before the piston, meaning there's no braking effect from the piston to slow the sector a tad before it engages the tappet. Although with a decently pokey motor odds are it wont be slowing that much on pickup anyway.

[steverebo]

38 minutes ago, Adolf Hamster said:

The main issue with short stroking is voluming, if you've got the gun volumed correctly then as long as the piston is clearing the front of the port then you're not gonna mess up the voluming from short stroking.

 

If you're happy with that level on a longer barrel then you aint gonna have issues with shorter.

 

As for pickup/release, i've always tend to go predominantly from pickup. The following paragraph is me trying (and probably failing) to explain my thinking:

 

When its being released the tappet plate is under spring tension and takes time to close, and its not ideal for accuracy to be releasing the piston before then.

 

If you only take from the pickup side then the tappet plate will be retracting earlier (relative to the piston) but releasing at the same time (as an un-modified sector) whereas if you take from the release side then the tappet plate will be closing later relative to the piston (ie less time between tappet closing and piston closing) and could mean it doesnt have time to close fully before the air starts coming. Needless to say for a snappier build this isn't ideal.

 

Ofc main issue with taking from just the pickup is the sector might pick up the tappet before the piston, meaning there's no braking effect from the piston to slow the sector a tad before it engages the tappet. Although with a decently pokey motor odds are it wont be slowing that much on pickup anyway.

I have tried just pickup previously and ran into timing issues with the tappet plate but when I took a  equal amount from both ends those issues disappeared and I've had some really nice results with accuracy and and a nice snappy semi auto and 3 round burst

[Adolf Hamster]

34 minutes ago, steverebo said:

I have tried just pickup previously and ran into timing issues with the tappet plate but when I took a  equal amount from both ends those issues disappeared and I've had some really nice results with accuracy and and a nice snappy semi auto and 3 round burst

 

hmm, as i explained not sure how it'd get timing issues from a full release side (as it's basically the stock release time) but tbh unless you're going full brrt then i doubt it's gonna be that sensitive.

 

whichever teeth you're removing though, if it's fine on a 300mm, then it'll not hurt a 200.

[Rogerborg]

4 hours ago, Adolf Hamster said:

not sure how it'd get timing issues from a full release side (as it's basically the stock release time)

 

That is making my brain hurt too.  However, it is airsoft, so weird things happening is not only possible, but inevitable.

[Adolf Hamster]

39 minutes ago, Rogerborg said:

 

That is making my brain hurt too.  However, it is airsoft, so weird things happening is not only possible, but inevitable.

 

i can see breaking tappet plates if they're being engaged at full speed by a motor that's not been braked by a mainspring, but can't see the closing side having issues. if anything the reverse, as it gives the tappet plate the most time to return to battery after release before the mainspring is unleashed.

 

but as you say weird things happening is inevitable, stuff that should shoot fine is all over the place and stuff that's nothing to write home about can punch well above its weight.

[SSPKali]

Some good advice here, I am looking at losing 3 (maybe 4?) from my build and was going with 2 from release, 1 from pickup but after reading @Adolf Hamster great explanation I think I will lose two pick up, one release to avoid timing issues with the tappet plate.

This contradicts what Luke at Negative Airsoft suggests but I guess I can always even it up to 2 / 2 if needed? Ported cylinder and 240mm barrel doesn’t need the piston back that far so would just be wasted energy. I am after a snappy response but not W*nker Gun territory as this is a back up / loaner!

[Leo Greer]

On 01/03/2023 at 12:45, SSPKali said:

This contradicts what Luke at Negative Airsoft suggests but I guess I can always even it up to 2 / 2 if needed? Ported cylinder and 240mm barrel doesn’t need the piston back that far so would just be wasted energy. I am after a snappy response but not W*nker Gun territory as this is a back up / loaner!

 

Luke is a troller. Some of the stuff in his videos can be downright nonsense... much of it intentionally so.

[Rogerborg]

16 hours ago, Leo Greer said:

Luke is a troller. Some of the stuff in his videos can be downright nonsense... much of it intentionally so.

 

I thought he kept it to one lie per video. That's still a lot of lying, but at least it's deliberate, unlike Skylar on Reddit.

[Leo Greer]

21 hours ago, Rogerborg said:

 

I thought he kept it to one lie per video. That's still a lot of lying, but at least it's deliberate, unlike Skylar on Reddit.

 

I'm not a definitive expert on anything to do with his "lies", but I do know that in his video on porting he literally says to place the port so the piston head is never pulled past it based on how many teeth you short-stroke... which is extremely silly.

[SSPKali]

On 10/05/2023 at 15:41, Leo Greer said:

 

I'm not a definitive expert on anything to do with his "lies", but I do know that in his video on porting he literally says to place the port so the piston head is never pulled past it based on how many teeth you short-stroke... which is extremely silly.

If it is the same video I am thinking of he said that any travel past the start of the slot was wasted energy.

 

Also, the piston doesn’t have to clear the cylinder slots to allow air in-front of the piston. It can be pulled in through the nozzle and round the piston o-ring just fine.

[Leo Greer]

2 hours ago, SSPKali said:

If it is the same video I am thinking of he said that any travel past the start of the slot was wasted energy.

 

Also, the piston doesn’t have to clear the cylinder slots to allow air in-front of the piston. It can be pulled in through the nozzle and round the piston o-ring just fine.

 

Of course--that's why ported piston heads are a thing. In fact at low RPS you can get away with a non-ported piston head, like the original TM design, as the piston is able to pull air in through the nozzle with no issue. At higher RPS non-ported causes extra drag.

 

Part of the advantage of porting is that when the piston has room to accelerate before achieving airseal with the cylinder, which increases efficiency a lot. This is similar to using higher pressure in HPA rather than a larger air volume.

 

It's silly because there's no point to it--why not just have a full cylinder, or whatever cylinder is correct for the BB weight and barrel length?

 

For example, on an MP5K or G&G ARP9 with a 150mm barrel, a 50% cylinder is about right for even heavy BBs (.32g+), and using a larger cylinder would just make it louder, have PME earlier, and require a change of a part. Luke's logic dictates that the port should instead sit behind the piston head at all times... which is the same as a full cylinder.