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Mouse
01-12-2004, 06:19 PM
I am posting here, hoping to gain from the knowledge some of you have from already doing the type of upgrade i am attempting to do.

I am going to install a Systema M16 Tightbore barrel in my SR25. I know that because the barrel is very long and wraps tightly around the bb, the FPS will lower considerably, and the gun will require some internal adjustments to keep the weapon at 400 fps.

I am wondering, what type of spring or cylinder (of combination of both) do i require to make my weapon shoot at 400 fps, with an M16 tightbore barrel?

I know some of you may have used different parts and part brands. Listing them, as well as what you know might work, would be most helpful.

Thanks in advance,
William

Dark
01-12-2004, 08:07 PM
I may be wrong, but I think, if anything, a tight bore barrel would increase FPS by a very small amount, since less air escapes around the bb.

AustinWolv
01-12-2004, 08:25 PM
I know that because the barrel is very long and wraps tightly around the bb, the FPS will lower considerably, and the gun will require some internal adjustments to keep the weapon at 400 fps.
Untrue regarding the smaller diameter of the tightbore causing a drop in muzzle velocity. While a long barrel *may* decrease your muzzle velocity, it is because of the cylinder having holes cut in it, thus decreasing the volume of air in the cylinder and that volume being smaller than the air volume in the barrel. Was your SR25 based off a M16 or a M4 variant?


I am wondering, what type of spring or cylinder (of combination of both) do i require to make my weapon shoot at 400 fps, with an M16 tightbore barrel? M120 or PDI170% spring. To maximize air volume in the cylinder, you would get a regular Type0 cylinder, like this: http://www.wargameclub.com/pcart/shopper.php?itm=SYS-ZS-04-16_cat_Systema Cylinders&PHPSESSID=4f11d24ceb23c96592aef8089d832a5c

You would only get a bore-up cylinder if running a M140 spring or higher, in case you are wondering.

Paladin
01-12-2004, 11:11 PM
If the base gun of your SR25 was an M16 you will already have a Type-O Cylinder (as wolv was alluding to)

Agrovale
01-12-2004, 11:19 PM
Originally posted by AustinWolv
You would only get a bore-up cylinder if running a M140 spring or higher, in case you are wondering.

Hmm, I run a bore up in all of my guns with M120 springs. Even my M4 with the stock barrel! :o

AustinWolv
01-12-2004, 11:29 PM
Well, I didn't say it was impossible. It just isn't a necessary item.
I'm guessing you are maintaining ~400fps? I guess the very small increase in cylinder air volume isn't enough to slow up the piston assembly too much, eh?

Mouse
01-12-2004, 11:53 PM
Originally posted by AustinWolv
Was your SR25 based off a M16 or a M4 variant?

Yes, it was based off a TM SR16.

Before i respond further let me get my terms correct. A "bore up" cylinder is one with out the hole right? And according to Wolv (not according to Agro) You would only use one in a run with an M140 spring?

If i just completely butchered that response let me know :p .

AustinWolv
01-13-2004, 08:29 AM
No, a bore-up cylinder has a slightly larger inner diameter.

The "types", such as Type0 or Type1, define if a hole is present and where it is located.

Since you had a SR16, you would want to pick up a Type0 cylinder.

Agrovale
01-13-2004, 09:07 AM
Originally posted by AustinWolv
Well, I didn't say it was impossible. It just isn't a necessary item.
I'm guessing you are maintaining ~400fps? I guess the very small increase in cylinder air volume isn't enough to slow up the piston assembly too much, eh?

Where did our Bernoulli effect post go? :) Whether you have a bore up or not should not affect FPS since spring tension is a constant, and should create the same PSI in a cylinder no matter what the volume is. Theoretically anyway ;) I have never seen FPS drop just from installing a bore up kit... YMMV

AustinWolv
01-13-2004, 12:05 PM
Theoretically anyway Supposedly. Our Airsoft cylinders are quite small, so the frictional losses and inlet losses (from the square inlet path through the cylinder head) are likely quite small.

Using the Bernoulli effect equation restricts you to incompressible, steady, frictionless flow, correct? I don't believe you can treat it as an incompressible flow because the fluid in question is moving faster than 100m/s.

Assuming you can treat it as incompressible, I ran the calculations and if I did them correctly, the difference is neglible, as the exit pressure from the nozzle only varied by a couple thousandths of a PSI. Obviously not enough to make a difference. :)

Mouse
01-13-2004, 09:24 PM
Thanks for the help guys! Type - O Cylinder it is. Does anybody have one available here for purchase? I don't really care what type, just as long as it works. :)

joeyphoshowey
04-07-2009, 02:13 AM
Wow. I cant believe I understood wolv's last post.

Ohhhhh, good ol' Thermodynamics:
Piston-Cylinder system. It's just funny how relevant it is to Airsoft, who would have thought?


Correct me if I'm wrong, but I thought bore up cylinder kits were supposed to be used in conjunction with longer barrels, so that the bb can have more time to stabilize its trajectory while spinning down the barrel.
With the bore up kit it has more force to do so, but in a shorter barrel, say M4 (363mm); wouldn't it be more turbulent while exiting the barrel - thus countering the purpose of the hop-up?

I read this info somewhere and it seems to be conflicting with some of the things posted above.