Lobbed off 4" or barrel and got no FPS change!
This is the second time this week that i’ve read about this anomoly.
STORY: When i got my Disco .22, i turned it into a CROSMODS DISCO .22. I kept the stock 24″ barrel on it. I tuned the CM.22 to shoot 18 gr JSB’s at 880 FPS. Then, once i field tested it, i found it liked the 15.9 gr JSB’s a little more. So then i tuned the gun to shoot the EXACTS at the same 880 FPS. Now, after numerous folks have talked me into adding the BAFFLES (LOL), i decided to chop off 4″ of the 24″ barrel to fit the baffles into the shroud. After lobbing off 4″ of barrel and putting the gun back together, i’ve found that the gun still shoots the same 880 FPS as before i chopped off the 4″.
So what gives? Can any of you make sense of this as i thought adding or removing 1″ of barrel equated to 15 FPS. So 4″ should have resulted in my gun shooting the Exacts at 820’ish FPS not the same 880 FPS. But believe me……..I’M NOT DISAPPOINTED AT ALL…LOL. Just curious. I also checked the gun with the 18 gr JSB’s and they were also traveling roughly the same as before the “SNIP”.
10-shot string in FPS:
1) 878.5
2) 877.2
3) 872.3
4) 881.3
5) 881.4
6) 876.0
7) 866.9
8) err2
9) err2
10) 868.3
All Replies
80.
I never tested it with and without the shroud. I never would have even tried it that way.
So what are your thoughts on the “with the shroud on….with the shroud off”?
I’m just curious: is the fps the same when the shroud is not in place?
Way to go out on a limb AFTER he cut the barrel! 😆
Sounds like you cut off 4″ of extra weight.
Barrels will have an idea length and actually slow down if more length is added.
Apparently 20″ is just fine. If you kept cutting back it will drop but I would think 18-20″ is probably best range to make out your gun.
Yep, you guys are right. During the INITIAL build, i was pushing the 18 gr JSB’s at about 910’ish. Then i turned it down to 880’ish. Then went with the even lighter 16 gr JSB’s at 880’ish.
Building this gun has been a fun learning experience. Woohoooo
Longer barrels need additional air to keep increasing the speed of the pellet as it travels. Cutting that much off, you should have seen a drop of at least 50 fps, if the air passage was optimized for the barrel length. Obviously it wasn’t.
There is a lot of merit to that and is a component of the full tuning of an airgun that is sometimes overlooked. We all talk about hammer weight, hammer spring, valve stem spring, pressure and volume, but barrel length does play a part in the equation as well. Ideally, when tuning a gun, you want to minimize air blast after the pellet has left the barrel, which is why a well tuned gun will be substantially quieter than a non tuned gun…all things considered.
What that tells me is you weren’t getting enough air to use the longer barrel.
Longer barrels need additional air to keep increasing the speed of the pellet as it travels. Cutting that much off, you should have seen a drop of at least 50 fps, if the air passage was optimized for the barrel length. Obviously it wasn’t.
ROB, thanx man. I should asked you first. Seriously. This is my 2nd barrel crowning job and its seriously fun believe it or not.
Cant wait to get this thing into the field again. She has lost a LOT of her BARK….lol
I’ve noticed the same with Crosman and QB barrels… chop off some and they are just as or more accurate and no decrease in velocity…and in some cases, a slight increase.
As for Condorbob’s 34… yes, they are choked, but if you are getting good accuracy, then great. Typically with a springer if you lob off some barrel, you will change the firing behavior of the gun, but as for accuracy… hit or miss (pun intended) I sent mine off to get chopped so had a choke put back on.
Tofaz… as always… great work and great pics to accompany.
Exactly Packrat. I’m simply glad that its shooting the same as before….lol
PHEWWWW, good thing croman barrels are super cheap…lol
I don’t think the disco barrels are choked 🙁 🙁 🙁 As far as it being as accurate as it was before…that’s no surpise at all…just means you did a good job on it…a shorther length wouldn’t affect the accuracy at all ..
I chopped my rws 34 and it seems to shoot harder but its loud as all get out. Does anyone know if rws barrels are choked?
Riffraff.
To be honest with you, i’m simply not sure because, i’ve really never heard of anyone talking about choked benjamin/crosman barrels. Everybody who owns a Crosman of some sort has cut and recrowned the barrel and claimed to get FANTASTIC accuracy. Just not sure if CROSMAN barrels are choked or not. I know LW barrels are.
So far, the gun is just as accurate as before i chopped off the barrel. Go figure man.
Nice crown work!!! Interesting find also.
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Just curious as poi has been known to vary on some rifles with/without shroud…I wonder if their is any variation in fps. Also, I wonder if the shroud helps minimize the “wasted air” detriment that can occur on shorter barrels with hopped up valves… ❓