Can I get a math check?

[VoidSuicide]

Alright, so I'm going to drill vents in a cylinder I have to reduce the pressure pop when my gun fires a bb.

the barrel is a total of 220mm with a radius of 3mm (I wasn't counting the extra .3-4), totaling 6222.857142857137 cu. mm.

The cylinder is 88mm with a radius of 10mm, totaling 27657.142857142833 cu. mm.

If these calculations are correct, then I would be fine dropping 20000 cu. mm from the cylinder and still have enough volume to actually give the BB velocity.

So if I drill the air escape 35mm from the nozzle, I should have 10999.999999999989 cu. mm. of air left in the cylinder, which is plenty to launch BBs.

And note that I didn't include the nozzle, which would add somewhere around 2000 cu. mm. (estimate)

[D.Smitty]

Fluid mechanics are (is?) some the hardest physics I ever came across. The equations go crazy with just a little turbulence. Even with a simple bb flying through an air nozzle, you have to keep second and third order approximations...

Anyway, you don't need all the numbers to know that you are going to get a noise reduction, and you are going to get a FPS reduction from this hole. Really, if you have the cylinder to spare (they aren't all that expensive), give it a shot. Any roughness around the hold will probably have a bigger impact on things than seeing whether it's 35 mm or 40 mm away from the nozzle.

To answer your question, you did apply the formula for the volume of a cylinder properly (if that's the math you wanted checked). You have to remember, though, that "air vents" don't automatically negate the cylinder volume behind them.

A tire with a hole in it will still stay inflated for a while...by that same token, a cylinder that is 80 mm long with a couple small holes around 35 mm is not the same as a 35 mm cylinder. The piston will still build pressure during those first 45 mm, and not all of that excess pressure has enough time to escape before the piston passes those holes.

Just do it and see how you like it.

[VoidSuicide]

I have, and if if fails/screws up, then I will be getting new internals sooner than I planned.

[severed]

Have you measured how far down the ports go on a ported cylinder? Also you can use a silenced piston head and a sorbothane cylinder head pad.

Unless you polish the inside where the new ports you're talking about are you're going to chew the piston o-ring up like woah.

[Star_folder]

Alright, math time. Let's look at those numbers again.

Your barrel length is 220mm long, and the radius is 3mm. We both get 6220 cubic mm for the size of the barrel.

Now the cylinder, you measured 88mm with a 10mm radius, that's 27646 cubic mm on my math, just a little off of of yours? That's a little strange. but, it's not far, and won't be important unless you want your gun to be silent.

So, the barrel has 6220 cubic mm, and the cylinder has 27646 cubic mm, that's a 4.44 air volume ratio and is incredibly outrageous. You mentioned putting the hole at 35mm, effectively making the volume 35mm with a 10mm radius. That's 10996, again, right (just a little off something must be up with our calculators, Did you use 3.14 as pi? or pi as pi?). And that would make the ratio 1.77, which is just about spot on. Looks like you've done your math fairly solidly.

NOW WAIT, before you go cutting into your cylinder, I have some questions. When you measured your cylinder, did you take into account the cylinder head and piston head that will be sitting in the cylinder? Because, cutting 35mm from the end of the cylinder is about 15mm difference from the end of the cylinder. And that's the difference between a crappy gun and a quiet gun. Again, the piston head also takes up space, you should take that into account.

Once you make your hole, be sure that the closest point of the hole is where you cut, not the center. If you put a 2mm diameter hole at the 35mm mark, you've effectively made a hole at the 34mm mark.

Also, be sure the hole is large enough to ensure air flows properly. And as Severed brought up, be sure and deburr the hole, you don't want those metal shavings ripping up your o-ring.

Lastly, I suggest you be sure you have 100% air seal after doing this, and before for that matter. The lower the quality of your air seal, the lower the barrel/cylinder ratio becomes. 1.7 is good for most applications, but you really don't want it dropping below 1.5.

[VoidSuicide]

Alright, math time. Let's look at those numbers again.

Your barrel length is 220mm long, and the radius is 3mm. We both get 6220 cubic mm for the size of the barrel.

Now the cylinder, you measured 88mm with a 10mm radius, that's 27646 cubic mm on my math, just a little off of of yours? That's a little strange. but, it's not far, and won't be important unless you want your gun to be silent.

So, the barrel has 6220 cubic mm, and the cylinder has 27646 cubic mm, that's a 4.44 air volume ratio and is incredibly outrageous. You mentioned putting the hole at 35mm, effectively making the volume 35mm with a 10mm radius. That's 10996, again, right (just a little off something must be up with our calculators, Did you use 3.14 as pi? or pi as pi?). And that would make the ratio 1.77, which is just about spot on. Looks like you've done your math fairly solidly.

NOW WAIT, before you go cutting into your cylinder, I have some questions. When you measured your cylinder, did you take into account the cylinder head and piston head that will be sitting in the cylinder? Because, cutting 35mm from the end of the cylinder is about 15mm difference from the end of the cylinder. And that's the difference between a crappy gun and a quiet gun. Again, the piston head also takes up space, you should take that into account.

Once you make your hole, be sure that the closest point of the hole is where you cut, not the center. If you put a 2mm diameter hole at the 35mm mark, you've effectively made a hole at the 34mm mark.

Also, be sure the hole is large enough to ensure air flows properly. And as Severed brought up, be sure and deburr the hole, you don't want those metal shavings ripping up your o-ring.

Lastly, I suggest you be sure you have 100% air seal after doing this, and before for that matter. The lower the quality of your air seal, the lower the barrel/cylinder ratio becomes. 1.7 is good for most applications, but you really don't want it dropping below 1.5.

I used an online calculator for my math, so idk about the difference. But this is for my ASR that I cut all that barrel off of.

I had previously sorbo'd both the piston head and the cylinder head.

I took into account the cylinder head for all measurements.

And I did my best to clean and ensure the seal on everything before reassembly. I'm very OCD about things like this, between not wanting to screw up and being a perfectionist.

[Star_folder]

Alright well it sounds like you've done your work then. Remember, you can always remove more material, but it's hard to put anything back. It'd be better to have too much air than not enough. If anything, it might be a good idea to cut it a little long, and then slowly decrease the volume.

[Cannon Fodder]

I think all of this math made my childish mind explode

[Avenger]

I think all of this math made my childish mind explode

I KNOW it made my brains blow out my ears. It made pretty colors on the wall.

[VoidSuicide]

The good news, It made it quieter.

The bad news, the range really sucked, so I put in the stock spring, which made it loud again.

the really bad news, the actual reason for suddenly crappy range is that the adjustment arm and another small (seems unimportant) piece of the hop up unit broke. It seems I need to find a bucking and adjustment arm asap.