shrink fitting does not "choke" a gun barrel.....

[Bhawanna]

i know some of you out there are going to blast me on this but that is ok.  i have read several post on "shrink" fitting brakes to choke a barrel and that is impossible to do to a 15mm or 16mm barrel.  just in case you question my credentials, bsme with a minor in metallurgy.  it will take a 20 ton press to "hammer" a choke on cylinderical steel with .250" cross-section on a .22 cal. 16mm barrel. even the "faux" choking on the rws diana barrels where the dovetails are pressed-in doesn't choke the barrel.  heat shrinking does not have the "force" needed to compress the compositional make-up of steel (one component being carbon) to change the inside diameter even 2%  which would be .0044".   granted air rifle barrels are not hardened steel but still maintain a rockwell hardness greater than Rc38.  test it and see....measure the inside barrel diameter then heat shrink a "collar" on the end of the barrel and then measure the inside diameter again....prove me wrong.

[Jaymo]

How about on a thin barreled .22, like the Baikal MP512M?

[Bhawanna]

what is the thickness of the cross-section between the bore and the o.d. of the barrel?  i am not familiar with that gun but if the cross section is more than .100" it wil be a waste of time and effort.

http://www.airgunforum.ca/forum/viewtopic.php?t=22948

http://www.getphpbb.com/phpbb/viewtopic.php?t=2195&highlight=choke&mforum=drfaf

Seems to work for Dr. Frankengun  :emoticon:

[Timmyj1959@yahoo.com]

Im with you Roger,, sorry Folks,, I think Roger is right on this one. I talked to my "People" about it,, they agree,,not gonna happen. Just my 2 cents.  Tim.

[gunsup0331]

A bold post indeed. I have zero cedentials but i would have to say the tool the Dr.F used in that link to measure didnt look too precise....Results may have been optimistic?

 I have searched this topic on various forums and have not seen much in the way of  "definitive results"  Just my very uninformed opinion.  

 Question: What would be a optimal, functional "degree of choke"
 IE: Lands measure .177 uniformly down the barrel till the end, which would taper down to .17XX<--?? in an "optimally choked" barrel?

im not a naysayer, just in search of whats what!

[melloroadman]

I will constrain my thoughts to the tools . Inside telescoping gauges are very accurate with the combined use of a out side micrometer . It is the general combination of machinist and mechanics world wide . Marvin

gunsup0331 - 8/14/2008  9:10 PM

A bold post indeed. I have zero cedentials but i would have to say the tool the Dr.F used in that link to measure didnt look too precise....Results may have been optimistic?  

The numbers may not be exact (different tools will give slightly different results by different users) but I'm pretty confident that the before and after are what he is claiming. From scatter gun to one holer... actions speak louder than doubtfull words IMO.

[gunsup0331]

I misread the post about the grouping  results, i was under the impression the end user had not found an accurate pellet yet...oh, and the pics helped, too..Nice RWS group, wow!

[jeep98]

Well, until you lads prove Bhawanna wrong, I'll have to go along with what he says. Using Jethro Bodine tactics I figured threading the end of the barrel with 5/8-18 die would give me the specs (within .001 to ,020, LOL) bore reduction. Pellet moved thru barrel as freely as before undertaking. The Plus is the barrel didn't expand either. The best choke should be just noticable, and consistant when pushing a pellet thru the end of the barrel, otherwise you have too much drag. Jeep 98

[Bhawanna]

Wrong!!!!...maybe a mis-interpretation of data.  what i think has happened to frankengun, if you notice his brake has a small diameter bore.  what i think is happening is the air flow exiting the barrel changed because of the brake's extension past the crown of the barrel thus resulting in a change in poi and exiting pressure.  the "choking" was not a result of shrinking the brake on.  i'll bet you could take the same brake and fit "normally" on the barrel have very similar results.

[Bhawanna]

I am not doubting that people are getting better groupings with muzzles but the "choke" is not a result of shrink-wrapping the barrel.  the groupings are the result of air flow between the crown of the barrel and the exit port of the muzzle brake.  i quickly made a crude diagram to explain this.  the diameter of exit hole in the muzzle brake plays an important factor in this as well as the distance between the barrel and the muzzle brake exit port. one needs to remember these are "AIR"guns.  they have no propulsion other than AIR.  the direction and dispersement of the air at the point of exiting the barrel/muzzle brake will determine the poi of the projectile.  that is why it is so crucial to have a "polished" and "concentric" crown on the barrel.  i will post again with some SCIENTIFIC metallurgical data backed-up by the laws of physics on the "compression" of tubular steel.

[melloroadman]

N/T

[Bhawanna]

I knew someone would try and make this PERSONAL but it is not an ATTACK on anyone's integrity or character.  This post was intended to keep "beginners" from buying a propane torch at home depot and going home and heating up a muzzle brake and trying to shrink it on a barrel because they heard it would "choke" a barrel.  DON'T MAKE THIS PERSONAL!!!!!!!  Fix, Paul and whoever else should not take this as a slam or personal attack.....it wasn't meant that way and YOU PEOPLE SHOULDN'T MAKE IT INTO THAT!!!!!!!!!

[howie1a]

Fire arms bore rifling is measured bu slugging a barrel basicly you take a lead slug and force it through the bore forming it to the rifling when it somes out you can mike the groves very easy, Also I have a nicro press tool it is used to swage fittings on marine schrouds ( the steel lines that hold up a mast)  I have tried useing it for chokeing a barrel it semes to work when you push a pellet throught the barrel you can feel the restance where the chock is , I am useing a tork wrench to control how mush pressure is applied this way I can get the same squeeze all around. what do you think do I have something here? howie