3000 psi tube QB78

[SeanMP]

Haha okay here is some more practical bling

Instead of a muzzle brake how about a choke band.

A 2" long tube that has the ID cut on a taper of 0.005" over it's length. The widest part of the taper is the OD of the barrel and the narrow end is obviously .005" tighter. The tube is installed with the narrow ID at the muzzle.

The tube is heated to light blue on the iridescent oxide scale and the slide into place and allowed to cool. It will shrink the muzzle and give an effective choke.

Take it one step farther and thread the tube so you can install an air stripper as well

[rsterne]

I would think that 0.005" taper might be too much.... but not having tried it don't know one way or the other.... Dr. Frankengun did this to a QB barrel a few years ago.... He made a steel sleeve in which he used a #1 Morse tapered reamer.... He then machined a matching Morse taper on the muzzle.... He heated the sleeve and slid it onto the barrel a bit further than where it normally stopped.... IIRC, maybe 1/10"???.... I think he achieved a total choke of about 0.0008" and drastically improved the groups from what was previously a mediocre barrel....

Bob

[SeanMP]

Ooooo a morse taper. Nice!

I have heard Dr Frankengun has done some amazing stuff but I've never been able to get on his site. For some reason his sight and my Linux don't get along.

Yes .005 might be a little tight but I wouldn't try less than .0035 and if you happened to get more than 0.001" choke you can trim back a little.

[remtom1200]

so im curious what type of material is used in such an application?

[SeanMP]

It needs to be steel because of the negative tolerances. You can dress it up to look like a muzzle brake and the air stripper on the end can be brass.

Spending some time playing with barrel weights to see what gives you the best groups would give you an idea of how much material you need to accomplish both tasks.

[remtom1200]

There must be some formula or somethin to determine how thick the wall of the choke band must be to squeeze the 15mm barrel to desired tightness? I have no idea but trial and error to find this out.

[SeanMP]

Ya I bet there is. The first place I would look is "The machinists handbook" or "machinery's handbook" I personally like the former but it hasn't been produced in 50 yrs and they are worth a fortune.

But I think you could could sneak by with a thumb rule. Calculate the cross section of material in % of the barrel OD. If you match it with an equal % cross section of material on the choke you should achieve something close to equal squish and stretch.

However I would figure out what weight gives the best barrel harmonic. Then you can tailor the interference fit to give you the desired .001 squish

[ARSIE]

The process that Dr. Frankengun used to choke a Pel that wouldn't group worth a damn

http://www.getphpbb.com/phpbb/viewto...d&mforum=drfaf


The results speak for themselves after the choke


http://www.getphpbb.com/phpbb/viewto...d&mforum=drfaf

[remtom1200]

Some quality time with the crown brought me dime sized clover leafs without using a bench so I am thinking my barrel is gonna be just fine for now. Maybe sometime soon I will have a day off work that is windless, above -5, and not raining or snowing....I know that is impossible here in NS.

[SeanMP]

Thats great news Remtom.

From personal experience it took a couple thousand rds to really see what the QB barrel was capable of.

I'll be doing the same thing myself as I'm getting a new .177 barrel from Eric today