Canadian Airgun Forum

The #1 Community for Airguns in Canada!
It is currently Fri Nov 22, 2019 5:30 pm

All times are UTC - 5 hours


The Canadian Airgun Forums are a place for people to discuss and learn about airguns and the airgunning sport in Canada. There are lots of discussions about airguns, airgun accessories, reviews, modification and repair information, airgun events, field target and free classifieds!

 

You need to register before you can post: click the register link to proceed. Before you register, please read the forum rules. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload your own pictures, and access many other special features. Registration is fast, simple, and absolutely free! To start viewing messages, select the forum that you want to visit from the selection below.








Post new topic Reply to topic  [ 18 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: Fri Nov 02, 2012 2:37 pm 
Offline
User avatar

Joined: Thu Oct 04, 2012 10:27 am
Posts: 1108
Location: Thunder Bay,On.
Here's something interesting: Taken from an article on air flow through a reduced opening:

"Again, at the exit end of the gun, a nozzle reduces the diameter of the exit, increasing the speed of the air and abrasive."

So I guess if someone drills out the restricted transfer port on 1377's,etc. the air speed to the pellet is REDUCED.

_________________
The cave you fear to enter....holds the treasure you seek


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 4:01 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
Except that past the transfer port the passageway expands again, slowing the air.... In most cases, having all the ports matching (ie constant in area) works the best.... With a bottom port like on a Crosman, that limits you to about 3/4 the bore size or the pellet may be damaged on loading.... For a .177 that is 0.0134", which is the size of a stock Crosman barrel port.... 22XX and 13XX transfer ports are usually 0.140" unless restricted to detune the gun.... Therefore in most cases, there is no benefit to going larger than that in .177.... In a .22 cal, however, you can often go up to about 0.162" and get worthwhile gains....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 4:46 pm 
Offline
User avatar

Joined: Thu Oct 04, 2012 10:27 am
Posts: 1108
Location: Thunder Bay,On.
If there is no point in drilling out the Canadian transfer port ,then why does the U.S. 1377's have a BIGGER transfer port?Why reduce the Canadian one if it has no effect in pellet fps? There's a vid on you tube and this guy is machining 1377 valve ports and boring them out to 3.95mm from what he says start out at 1.9mm.It supposed to give you 50fps from an otherwise stock gun.I think we need a physicist. I'm confused.

_________________
The cave you fear to enter....holds the treasure you seek


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 5:46 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
Quote:
22XX and 13XX transfer ports are usually 0.140" unless restricted to detune the gun....

Read that again.... Canadian 1377s use a transfer port that is about 0.078" IIRC.... You are the one that starting this thread by stating you would lose velocity by drilling out the port.... That is incorrect, providing you don't go too far.... No Physicist required, just practical experience....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 6:06 pm 
Offline
User avatar

Joined: Thu Oct 04, 2012 10:27 am
Posts: 1108
Location: Thunder Bay,On.
Well this science journal says air flow increases as its pushed through a smaller orifice.So HOW would anyone else consider it a restriction of air velocity? Obviously I don't see the whole picture.Anyway,I am new here. Lots of conflicting ideas on this site.Guess I'll have to do trial and error and find out for myself.I want to start modding.

_________________
The cave you fear to enter....holds the treasure you seek


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 6:11 pm 
Offline
Supporting Members
User avatar

Joined: Mon Jan 01, 2007 10:54 pm
Posts: 4924
Location: Saint John NB
I agree with Bob.....no need for any edumacated :lol: xperts.......we have many people(myself included) that have many hours(years) of tooling time into our Crosman platform guns. There are people on here that know Crosmans guns better than Crosman themselves, so I wouldnt call out the cavalry just yet :mrgreen:

_________________
Jonathan

Im addicted to brake fluid..........but I can stop anytime....


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 6:38 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
Quote:
Well this science journal says air flow increases as its pushed through a smaller orifice

I'll bet it doesn't.... It says the VELOCITY of the air flow AT the restriction increases (and incidently the pressure reduces as well).... The FLOW will very likely actually decrease from the added resistance.... In addition, as soon as the airflow passes the restriction and enters the barrel, the VELOCITY of the airflow will slow down again.... Since airguns are driven by the MASS of air moving through them, we want lots of FLOW.... That means, generally, no restrictions in the ports....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 6:42 pm 
Offline
Supporting Member 2009
User avatar

Joined: Sun Dec 24, 2006 12:37 am
Posts: 3468
Location: Out There
Bob is correct- Velocity increases, not volume. Whomever used the term "airflow" in whatever article obviously equates "flow" with "velocity" which is misleading.

Think the of the transfer port like a venturi (i.e. like on a carburetor)- same thing.


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 7:14 pm 
Offline
User avatar

Joined: Thu Oct 04, 2012 10:27 am
Posts: 1108
Location: Thunder Bay,On.
Here it is here.maybe I just misunderstand the physics of it I guess.
http://www.ehow.com/about_6535612_sandb ... ation.html

_________________
The cave you fear to enter....holds the treasure you seek


Top
 Profile  
 
PostPosted: Fri Nov 02, 2012 9:52 pm 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
No, you understand it perfectly, and that article is correct.... The nozzle in the case of a sandblaster is the LAST part in the system before the abrasive is expelled.... The air accelerates (velocity, not flow), and the abrasive with it.... The air then expands and slows down, but the abrasive, being much denser, carries on at the now higher velocity....

An airgun is different.... The transfer port is NOT the last piece in the system, the barrel is.... The transfer port is smaller than the barrel (in the case of a restricted one, a LOT smaller).... The air accelerates through the (restricted) transfer port, then slows down again before getting to the pellet.... which so far is AT REST.... The air reaching the pellet then has to accelerate it down the barrel.... It is not the velocity of the air at any given point in the system before it gets to the pellet that matters, but the MASS of the air available to accelerate the pellet down the bore.... More MASS (and a longer barrel to accelerate in) results in a higher velocity....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Sat Nov 03, 2012 5:10 am 
Offline
User avatar

Joined: Thu Oct 04, 2012 10:27 am
Posts: 1108
Location: Thunder Bay,On.
Ok.then I will assume it is safe to drill out the transfer port a little and I should expect close to 500fps without any other power mods.Thats what I'm looking for. thanks.

_________________
The cave you fear to enter....holds the treasure you seek


Top
 Profile  
 
PostPosted: Sat Nov 03, 2012 10:54 am 
Offline
User avatar

Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8979
Location: Coalmont BC
If you don't have a Chrony, I would strongly suggest you don't mod a Canadian non-PAL pistol....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Top
 Profile  
 
PostPosted: Sat Nov 03, 2012 1:55 pm 
Offline
User avatar

Joined: Thu Oct 04, 2012 10:27 am
Posts: 1108
Location: Thunder Bay,On.
Oh..I didn't realize one could go over the limit so easily.I DO have a chrony on the way. thanks for the heads up.

_________________
The cave you fear to enter....holds the treasure you seek


Top
 Profile  
 
PostPosted: Tue Nov 13, 2012 7:13 pm 
Offline

Joined: Thu Sep 13, 2012 2:29 pm
Posts: 35
MyCrosman wrote:
Oh..I didn't realize one could go over the limit so easily.I DO have a chrony on the way. thanks for the heads up.


Get a # drill index. #1 to #60 any man who does not have a set of # drills should turn in his man card (jokes). Did you ever price a letter drill index? :shock:


Top
 Profile  
 
PostPosted: Sun Nov 18, 2012 4:13 pm 
Offline
User avatar

Joined: Thu Feb 02, 2012 8:39 pm
Posts: 207
Location: Waterdown, Ontario
I have modified my co2 gun, 2240 and increasing the air transfer port definitely increased the fps. However I have a BSA meteor springer, which is a .177. THe transfer port was .125 and it shot at 650fps. So I thought by increasing the air transfer port to .170, close the the barrel size of .177 it should yield an increase in fps. It actually decreased it to 510 fps. I was shocked :shock: and very unhappy. Tested it on a chrony 10 more shots and it was around 510fps. a decrease of 140fps. Luckily I was able to tap the transfer port, put in a threaded brass insert, with a hole set to .125, inserted it in with loctite and the fps increased back up to 650 fps all with the same 9.6g pellet.
Still trying to figure it out.

_________________
"If it can be built, it can be taken apart, re-assembling is another story...."
2240
2240 bulked CO2
2260
XT15
Sig Sauer SP2022
BSA Meteor MK5 .177
Webley Alecto .177
P17
HW45 Blackstar .177


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 18 posts ]  Go to page 1, 2  Next

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
News News Site map Site map SitemapIndex SitemapIndex RSS Feed RSS Feed Channel list Channel list

Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group

phpBB SEO