Upgrade of barrel attachment

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Upgrade of barrel attachment

Postby Scotchmo » Wed Mar 18, 2015 4:40 am

I never really liked the pair of tiny set screws typically used to attach a barrel. I always worry about small changes in alignment.

I recently re-barreled my Marauder pistol and went with a threaded attachment. I had used a similar method (minus the o-ring and thimble) when I re-barreled my QB58 a few years ago.

I'm an amateur machinist so it is a slow process. Turned threads cause me fret. And I ended up doing it twice. First trial on the full length barrel. After being satisfied with the results, I chopped the barrel, and machined it again to give me just under 15". Not perfect but serviceable and secure. The thimble is not for indexing. Cutting the tiny internal o-ring groove was another ???? test for my machining abilities. The barrel threads into the receiver and the step at the end abuts the o-ring and recess in the thimble. I went with a .120 port in the thimble. I believe that the smaller hole prevents scarring of the pellet as it is pushed past the opening. I may need to enlarge the port a little more as I'm only using a 1200psi setpoint on the regulator and getting just under 11fpe.

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The 9 shot group under the #4 bullseye was shot with the full length barrel at 35 yards, in a slight wind, sitting with an unattached bipod supporting the pistol. Much better than the Crosman barrel that it was replacing. The Crosman barrel on my first rifle was great. The one that this gun originally had was not so great. The new barrel is a Weihrauch barrel that was last used on a USFT. I got the barrel from Vince Pacheco as part of a trade.
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Re: Upgrade of barrel attachment

Postby JimW » Thu Mar 19, 2015 12:00 am

Nice work Scott!

Was that HW barrel blued already? Those are great barrels with the right pellet.

I still need to pop my threading cherry on my lathe. I like the idea of doing the mini barrel first. ;)
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Re: Upgrade of barrel attachment

Postby Scotchmo » Thu Mar 19, 2015 1:38 am

The HW barrel came blued and a little rusty. I removed the old blue and redid it after I cut the short piece off and remachined the 15" portion.
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Re: Upgrade of barrel attachment

Postby JimW » Mon Mar 23, 2015 11:27 pm

Ah.

Thanks again to you and Allan for all the hard work and dedication to the sport. Looking forward to the April match and of course the Westerns!
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Re: Upgrade of barrel attachment

Postby RickinAZ » Tue Apr 07, 2015 4:11 am

Scott
I always enjoy your posts and learn something too. I have a couple questions if you don't mind.
- How did you cut the internal threads in the receiver? Tap or on the lathe?
- I like the thought of threads being a stronger way of attaching the barrel but why use a thimble? Is it easier to try different transfer port sizes? Now that I think about it I guess it is the only way you can index the thimble (transfer port).
- How is the thimble secured? With a set screw like the origional barrel?
- What type of cutter did you use to cut the internal o-ring groove for the probe in the barrel?
- On the MROD pistol what kind of lathe set up did you use to cut the internal threads for the fill port on the shortened air tube? I have a small hobby lathe with 1" bore in the headstock so that won't work.

I have been wanting to cut down one of my Marauders to about 36" for a handy carbine. I need to practice up my threading skills. I usually end up with rough threads so I need to experiment with other lathe speeds. I am a total rookie when it comes to machine work. But I'm having fun.

Thanks for any info
Rick in AZ
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Re: Upgrade of barrel attachment

Postby Scotchmo » Tue Apr 07, 2015 8:27 pm

RickinAZ wrote:Scott
I always enjoy your posts and learn something too. I have a couple questions if you don't mind.
- How did you cut the internal threads in the receiver? Tap or on the lathe?
- I like the thought of threads being a stronger way of attaching the barrel but why use a thimble? Is it easier to try different transfer port sizes? Now that I think about it I guess it is the only way you can index the thimble (transfer port).
- How is the thimble secured? With a set screw like the origional barrel?
- What type of cutter did you use to cut the internal o-ring groove for the probe in the barrel?
- On the MROD pistol what kind of lathe set up did you use to cut the internal threads for the fill port on the shortened air tube? I have a small hobby lathe with 1" bore in the headstock so that won't work.

I have been wanting to cut down one of my Marauders to about 36" for a handy carbine. I need to practice up my threading skills. I usually end up with rough threads so I need to experiment with other lathe speeds. I am a total rookie when it comes to machine work. But I'm having fun.

Thanks for any info
Rick in AZ

I cut the internal thread on the breech with a tap. On a previous rifle, I used a 9/16-18 UNF taper tap. I decided that I wanted it even a little finer this time. eBay has just about any size/pitch available (from China). While looking on eBay, I was lucky enough to find an old USA made set in 9/16-20 (taper, plug, and bottoming).

A thimble was used in order to keep the transfer port lined up regardless of how much the barrel had to be tightened. Also - if you mess up on the T-port in the barrel, that's it! If mess up the thimble, it will be easier and cheaper to correct. Also makes barrel swaps easier.

The thimble has a small flat on top, and is secured with the original rear set screw. I could have cut off the end of the scrapped Crosman barrel and made a thimble out of that.

The o-ring tool - I made a miniature o-ring grooving tool. Simply a piece of HSS with a hooked end ground on it. Crude, but it worked OK.
Like this but smaller:
http://internaltool.com/products/lathe/ ... oove-tools

I have an 11"x48" lathe but it only has a 7/8" spindle bore. A while back, I needed to thread a long 1-1/4" tube but was leery of doing it on the lathe, so I made a large tap. It worked but it took a huge amount of torque to cut the threads, even in aluminum. Almost impossible to hold the tube from turning. It would not have worked for me on the steel Marauder tube.
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I ended up using a steady rest setup. I was using the full length of the lathe to do that operation.:
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My pistol had a shorter tube so it was easier.

Rather than threads, it is also possible to use the shear force on cap screw heads to retain a fill port adapter. You might be able to machine the threads off the Marauder port adapter (if there is enough wall thickness). Or make you own. That is doable on a small lathe. The cap screw holes and recesses can be done on a drill press. You'll want to insure adequate shear area for the pressures involved.

My lathe cut threads are very rough. I'm definitely not a pro-machinist. I don't usually cut threads under power. I turn the spindle manually as the threads are cut. I finish it up with a 60 degree file and carbide paper while spinning it on the lathe.
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Re: Upgrade of barrel attachment

Postby RickinAZ » Wed Apr 08, 2015 1:09 am

Thanks for taking the time to reply. And pictures are always appreciated. Who knew you could make your own tap.
See .......I learned something again.
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