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

[Bhawanna]

howie,
yes because you are using a PRESS!!!...key word.  airgun barrels are not heat treated like powder burners.  i don't have access to a metallurgical lab anymore but from performing a spark test on the metal i am guessing it is like a 1020 or 1040 carbon steel.  this type of steel is being "worked" hardened during its manufacturing process.  Work hardening is best demonstrated by taking a paper clip and start bending it back and forth....the more you bend it back and forth the more difficult is gets to bend until it "snaps".  the barrel rifleling is actually doing this in the airgun barrel.  that is why people want the "hammer-forged" barrels for guns.  anyway, "controlled" compression from a press/vice, etc (not heat shrinking)...can in fact compress a barrel.  check the o.d. of the barrel where you pressed it and see if there is a diameter change.  also, how many ft/lbs of torgue are you using to compress it?...that only substanciates my post.

[howie1a]

the od is smaller than the rest of the barrel after it is choked at the point where the chokkeing was applied also you can mike the barrel at this point my thinking is if it is one or two thousands at this point on the od it should be about the same on the id and when using a tork wrench I found that 400 inch lbs works fine we are looking at about a 1/2 inch id barrel approx I am not hone so I can't mike the barrel now, I do have to do the press in two steaps since the nicro press tool does only top and bottom sides and then turn it 90 deg. to do the orthes sides this way it is nessayr to use a tork wrench so you get the same finished job. also i was reading about pope barrels when i got into this chokeing thing my thinking is he had to make the tapered barrels ( his barrels had a choke the full length of the rifle ) using a hammer forged system else how could you drill a tapered barrel and rifle it? From what I understand hammer forging is to make a mamdrel of the inside of the barrel and form the barrel to it by hammering it to the shape of the mandrel. howie

[gunsup0331]

Bhawanna - 8/15/2008  6:28 AM

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.

 LoL you are my hero.  Im not gonna lie: My dumb a$$ was about to do this, too(on a test barrel first, however.)

 BTW  Bhwanna if im not mistaken the Frankengun brake was cut clean after attachment leaving no gap between the rifled bore and the end of the brake. It is discussed further if you follow the bottom link in  BCSteels post.

[Bhawanna]

howie,
that is roughly 33-1/2 ft/lbs of torgue on the barrel.  just for calculation purposes what is the o.d. of the barrel and caliber?...i would like to know the cross-section thickness of the steel.

[howie1a]

it's 177 cal I'm not sure of the barrel dia since I am out of state right now but it's is on my TF78 maybe that is a help howie about 1/2 to 5/8 inch dia howie  PS the surface area pressed is approx 1/2 inch

[Bhawanna]

i feel like a CSI Miami character with this post...ha!  everyone keeps referring to Dr. Frankengun's post so i went out and read it and reviewed the pics.  i don't think we are getting the WHOLE story here.  first of all, i need everyone here to do me a favor.  if you have a muzzle brake on your gun, look at the end of it and see if you can see the "definite" appearance between the end of the barrel and where the muzzle brake touch. there always will be some sort of "gap" between the two.  look at the pic of frankengun's muzzle brake below.  i see no barrel.  also, there is no CROWN!!....look at the marks in the muzzle brake bore that the red area points to.  those are not tooling marks from a drill or reamer.  Now, i suspect the bore of the muzzle brake is .001" to .003" smaller than the bore of the barrel.  NOW THAT WOULD CHOKE THE BARREL!!!!.  I believe those marks are from pellets!.  so....if the muzzle brake's bore was machined a few thousands smaller in diameter than the barrel diameter and then heat shrunk onto barrel it would indeed choke the barrel.  also, for a lead pellet to make those kind of grooves, the muzzle brake must be made of very low carbon steel or even aluminum.  constant shooting will eventually wear out this muzzle brake to the same diameter of the barrel and will no longer be a useful choke.  in order for him to replace the "choke", he will have to re-heat it and this time it will ALSO HEAT THE BARREL and possibly damage the barrel.  this is only my opinion based on the picture enlarged 300x.  and once again this is not a bang against dr. frankengun but i think the picture shows more than the story tells.

[Bhawanna]

did try pushing a pellet through the barrel BEFORE the muzzles were put on?

[Bhawanna]

the machining process for rifleing the barrels may have "taper" which would be a factory choke.

[3n00n]

When 'fix' first used this method I thought the same thing, but after thinking about it for a while I thought temperature itself might have some annealing affect. For lead pellets, annealed steel would be no big deal, just use care that itis not damaged as it is possibly softer than the rest of the barrel.

What do you think Rodger? I don't have near as much hands on as you do, so I'd be interested in your observations ontemperature transmission to the barrelduring the 'fix' choke process.

[Bhawanna]

your case involves the usage of marine bronze.  is that nickel aluminum bronze or manganese bronze?  the two have different properties.
Mechanical Properties (Normal Range)the bottom numbers being manganese bronze.

Yield
 35 – 43,000 psi
 27 – 33,000 psi
 
Tensile  80 - 95,000 psi  60 - 72,000 psi  % Elong in 2 in
 15 – 30
 20 – 35
 
Proof stress
 28,000 psi
 14 – 16,000 psi
 
Brinell hardness
 152 – 190
 112 – 130
 
Fatigue – air
 21 – 25,000 psi
 9 – 14,000 psi
 
Fatigue – salt water
 18 – 22,000 psi
 9 – 12,500 psi
 
Density – lb/cu in
 0.273
 0.297
 
since you like play in your shop try this.....take a 10lb piece of steel and raise it 30 inches above the bronze and drop it.  measure the indention's depth and diameter.  now do this to a 1020 (low carbon steel)....which is greater? also when your bronze was heated up, what was the temperture it was heated to?  how long did the heated bronze stay on the barrel before it was cooled?  was it air cooled, oil quenched or water quenched?.  could it have stayed on the barrel long enough to heat the barrel also?  there are alot of variables here. did the barrel heat up during the process and then rapidly cooled and perhaps put a small "warp" in the rifleing?...just a thought.

[Bhawanna]

i said a 20 ton press....not 20 tons of force.  a 20 ton press would be adequate for this type of compression.  the force will be distributed across the contact area in pounds per square inch depending on the thickness of material and material composition and hardness.  not all barrels are made equally!  a bam barrel is not manufactured to the same standards an air arms, weihrauch, or theoben are therefore different pressure amounts would be used for different barrel materials and processes.  a 20 ton press was used as a "standard" piece of equipment that could handle the range of extremes.

[Bhawanna]

annealing will begin around 1600 f. on low carbon steel.  so here is ANOTHER kink in the chain....the bronze needed to be heated to over 1000f.  if in fact the steel barrel was annealed during the process, now you have a "soft" spot in the barrel that will wear more rapidly than the rest of the barrel.  if there is a choke on the barrel will it wear out?......things that make you go "hhmmmmmmm".

[Bhawanna]

Fix,
how hot did you heat the bronze up to?

[Bhawanna]

that is hot enough to turn the steel dullish red but not anneal it..Once again Fix, this is not a bashing or attack on anyone or their character.  it is an OPEN discussion on choking.  Please don't take it to heart because it was NOT aimed at you! anyone on this forum that knows me will tell you that i don't discredit people.   It was actually meant to keep someone from going to the hospital trying to duplicate it in their backyard.  i already had one post where i "saved" someone from being injured.

[melloroadman]

Fix the method you are using has been used for over a 100 years . Keep up the good work and please keep giving us your trade secrets . I might need them some day . When I took metal shop in high school ever so may years ago this method was taught to us . Marvin