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Air Gun Home Forum Index » Airgun Smithing » Adding choke Goto page 1, 2, 3  Next    View previous topic :: View next topic  Adding choke   Posted: Tue Apr 10, 2012 7:59 pm garththomas Veteran Member Joined: 12 Jan 2012 Posts: 165 Location: Ontario, Canada I would really like to try to put a little choke in the barrell of my QB57, I was hoping that I could get some ideas on how to go about it. I am planning to shorten the barrell to 12" so I have some room to practice before I get there. I have access to some machine tools but no experience running them and the people I know who do are limited. I saw yourdaddyjoes steady rest bearing job but that looks beyond my capabilities, any other ideas. _________________ QB57 Backyard Sweeper   Posted: Tue Apr 10, 2012 8:57 pm garththomas Veteran Member Joined: 12 Jan 2012 Posts: 165 Location: Ontario, Canada Well I just finished reading up on the yellow and I've got something to try. _________________ QB57 Backyard Sweeper   Posted: Wed Apr 11, 2012 10:56 am yourdaddyjoe Supporting Member Joined: 26 May 2008 Posts: 4027 Location: Tatorville, USA you would defo. need heavier bearings to do the job. I've replaced all 3 once just doing my regular stuff... _________________ Say "NO" to BB Gun Wars... Quid Pro Quo Rule: An eye for an eye... www.HPASports.com www.Facebook.com/hpasports   Posted: Wed Apr 11, 2012 11:54 am Slavia Moderator Joined: 31 Mar 2008 Posts: 4382 Location: Waseca, Minnesota, USA SMP recently wrote about using a pipe cutter with a bearing instead of the cutting blade. I cold forged the choke on my G1 with a hammer and a split metal sleeve made from steel pipe. I have read about hand lapping the bore to open up the span behind the choke. One tuner on the net uses a precisely fitted steel muzzle brake, installed with heat. When it cools it supposedly constricts the area around the muzzle. _________________ ¡Listo! ¡Apunte! ¡Fuego!   Posted: Wed Apr 11, 2012 1:17 pm garththomas Veteran Member Joined: 12 Jan 2012 Posts: 165 Location: Ontario, Canada In the article I read the fellow milled a hole .005 larger than the dia. of the barrel into the head of a large bolt and then he cut it off and in half and squeezed it in a large vice. He figured it worked, and I think I will try that for my first attempt. _________________ QB57 Backyard Sweeper   Posted: Wed Apr 11, 2012 4:35 pm SMP Silver Status Member Joined: 04 Feb 2011 Posts: 1183 Location: Just south of "Out There"- Land O Lakes Ontario I think thats a bit risky. If you've got the gear to mill that hole I would use the shrink on sleeve method them lathe it off afterwards _________________ Sean   Posted: Wed Apr 11, 2012 8:19 pm garththomas Veteran Member Joined: 12 Jan 2012 Posts: 165 Location: Ontario, Canada I wouldn't know how to begin to calculate the dimensions and the expected amount of shrinkage to achieve .002 reduction of the bore. Maybe if the first attempt fails I'll try that. I'm cutting the already reduced area that accomodates the muzzle break tonight. Hopefully I'll be able to have it back together tomorrow night for some test shots. _________________ QB57 Backyard Sweeper   Posted: Thu Apr 12, 2012 9:48 am SMP Silver Status Member Joined: 04 Feb 2011 Posts: 1183 Location: Just south of "Out There"- Land O Lakes Ontario .005-.007 has been pretty good in my experience _________________ Sean   Posted: Thu Apr 12, 2012 11:23 am garththomas Veteran Member Joined: 12 Jan 2012 Posts: 165 Location: Ontario, Canada Also I don't have the means to measure the bore so I'm just going by feel when I push a pellet down the barrel. I've just swedged the barrel now so I'm going to redo the crown and reassemble after work. I've kind of decided to make a new stock as well using baltic birch ply and it's in the clamps right now. I hope I can find all the parts as it was an impulsive frenzy kind of decision last night. _________________ QB57 Backyard Sweeper   Posted: Thu Apr 12, 2012 5:55 pm SMP Silver Status Member Joined: 04 Feb 2011 Posts: 1183 Location: Just south of "Out There"- Land O Lakes Ontario Oooh nice I like working with Baltic Birch. Very nice and consistent. _________________ Sean   Posted: Thu Apr 12, 2012 7:30 pm garththomas Veteran Member Joined: 12 Jan 2012 Posts: 165 Location: Ontario, Canada Wow, I was on the right track when I decided to try a little choke. I just tried out my nemisis CPHPs and they got their best group to date. Before this the only pellets I was getting good groups with were Daisy precision max wadcutters. I figured since the CPHPs were harder alloy they weren't catching the grooves. Now so far I've tried CPHPs. Daisys and RWS super point extras and they are all giving 3/4" groups which may not sound like much but untill now not possible with crossmans. So tomorrow I cut the barrel to 12" and do the choke again or maybe because I wanted to thread the end of the barrel, I may thread what I have to see if that changes the choke. I'm going to have to think about what style I want for the new stock. When I first thought of changing it I was thinking cool lets make an Steyr Aug look but now I want comfort for accuracy. I must be maturing _________________ QB57 Backyard Sweeper   Posted: Thu Apr 12, 2012 9:15 pm garththomas Veteran Member Joined: 12 Jan 2012 Posts: 165 Location: Ontario, Canada A further update, I just put 5 CPHPs in a dime. I can't believe the difference, I hope I don't screw it up tomorrow. _________________ QB57 Backyard Sweeper   Posted: Thu Apr 12, 2012 9:52 pm SMP Silver Status Member Joined: 04 Feb 2011 Posts: 1183 Location: Just south of "Out There"- Land O Lakes Ontario Not to worry..Barrels are relatively inexpensive but knowledge is priceless _________________ Sean   Posted: Fri Apr 13, 2012 5:42 am Alstone Moderator & Site Supporter Joined: 01 Mar 2007 Posts: 4139 Location: Linconshire, ENGLAND garththomas wrote: In the article I read the fellow milled a hole .005 larger than the dia. of the barrel into the head of a large bolt and then he cut it off and in half and squeezed it in a large vice. He figured it worked, and I think I will try that for my first attempt. If you do this you will finish up with an oval shaped bore and ruin the barrel. SMP has the best idea using a large converted pipe cutter. Al _________________   Posted: Fri Apr 13, 2012 10:03 am rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Quote: .005-.007 has been pretty good in my experience Really?!?.... I thought it was 0.0005"-0.0007".... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count! 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