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 Post subject: Build from scratch?
PostPosted: Tue Dec 31, 2013 10:21 pm 
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I was wondering what the issues are around building airguns from scratch, from a rules and regulations standpoint? Or more specifically, using generic DOM steel tube instead of a tube from an existing gun, which seems to be the part that has the serial number.

Any thoughts?


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 Post subject: Re: Build from scratch?
PostPosted: Wed Jan 01, 2014 12:07 am 
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Location: Victoria, BC and Clarkston, WA
I'd like answers for that too! Want to build a better 2240!

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3 Custom Crosman 2260
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 Post subject: Re: Build from scratch?
PostPosted: Wed Jan 01, 2014 7:49 am 
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id forget all that and just build it :)


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 Post subject: Re: Build from scratch?
PostPosted: Wed Jan 01, 2014 8:06 am 
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Location: Fredericton, NB
i thought about that too at one point, interesting question indeed

i would think that if you build an airgun that shoots lower then 500 fps, it would probably fall under the same category of those you have on the market now, so not requiring any sort of licence, and if above 500 fps, same restrictions under the law.

so the questions may be;

1-would you need a special firearm licence to build it, like a gunsmith licence
2-once you build the gun, would you have to submit it to the canadian firearm center for certification, would they ask to brand the gun with some sort of serial number supplied by them, of make up your own


would be interesting to submit that question to the firearm registrar

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 Post subject: Re: Build from scratch?
PostPosted: Wed Jan 01, 2014 9:56 am 
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Location: Nova Scotia
Unless you build a handgun of high power and obviously a restricted type and since we no longer have a long gun registry, the government should not need to be involved. If you build a long gun for yourself even if you were to include a serial number, the government does not have any place for you to register the number.


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 Post subject: Re: Build from scratch?
PostPosted: Fri Jan 03, 2014 4:22 pm 
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Posts: 231
Location: England.
Cant help with your regulations but have made 21 one offs all different down to the last screw from raw materials and not copies of anything.
Over here you can still make your own if legal but cant sell. Anything other than that we need an RFD equivalent to your gunsmith licence.

DOM would be better than whats used on 90% of rifles made. More of a concern is not only the wall thickness which should withstand 1 1/2 times operating pressure, most guns wont. Also if tube ok at 1 1/2 times pressure, its the end plugs that's usually the weakest link.
If using a fine thread though ultimately very strong, if the tube expands too much over them whats going to happen! ala Ginb
Early ones used hydraulic tube steel and stainless, tungum alloy in 96 and a variation of grade 6082 aluminium from 97 to 98.

Remember theres no warning when an aluminium tube is about to go, at least you might see a bulge appear with steel tubing and dubiously a titanium lower grade.


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 Post subject: Re: Build from scratch?
PostPosted: Fri Jan 03, 2014 7:17 pm 
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Location: Coalmont BC
I didn't understand half of what you said Jon, and my reading comprehension is pretty good (eg. tungum?).... I do have one question, however, on what planet is it OK to engineer a pressure vessel for only 1.5 times working pressure?.... They are hydrotested (when required) to 5/3 MSWP, and typical safety margins run at least 3:1 to yield and 4:1 to burst ratings on the tubing and similar on the fasteners and end plugs.... I wouldn't even want to be in the same room with a gun with only a 1.5:1 safety margin.... You must be the only gunsmith in the last century to make his own screws....

Bob

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 Post subject: Re: Build from scratch?
PostPosted: Fri Jan 03, 2014 7:53 pm 
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Location: Victoria, BC and Clarkston, WA
I have used 4140N and 4340 For ages and never had pressure problems(powderburners). Hell sometimes I exceed 65,000psi(300 Win mag Ackley improved) for Chrome Moly barrels without any incident except a sore shoulder from Recoil! :D
4140N is rated to 180,000PSI

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Pardini K10
Brocock Concept .22
3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
Mrodair CP-1M .22 and .177


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 Post subject: Re: Build from scratch?
PostPosted: Fri Jan 03, 2014 8:46 pm 
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Quote:
4140N is rated to 180,000PSI

All that means is that the tensile strength is 180,000 psi, not that it will stand that much pressure.... It means is you had a 1" square piece and tried stretching it, it would fail at 180,000 lbs. of load.... The MSWP depends on the thickness/diameter ratio just as much as the tensile strength.... Larger diameters or thinner walls reduce the safe working pressure....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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 Post subject: Re: Build from scratch?
PostPosted: Sat Jan 04, 2014 3:00 am 
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Location: Victoria, BC and Clarkston, WA
rsterne wrote:
Quote:
4140N is rated to 180,000PSI

All that means is that the tensile strength is 180,000 psi, not that it will stand that much pressure.... It means is you had a 1" square piece and tried stretching it, it would fail at 180,000 lbs. of load.... The MSWP depends on the thickness/diameter ratio just as much as the tensile strength.... Larger diameters or thinner walls reduce the safe working pressure....

Bob



Just saying Bob, that I would feel better with a steel air tube then an aluminum one.

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-Rick
Pardini K10
Brocock Concept .22
3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
Mrodair CP-1M .22 and .177


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 Post subject: Re: Build from scratch?
PostPosted: Sat Jan 04, 2014 7:06 am 
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rsterne wrote:
You must be the only gunsmith in the last century to make his own screws....
Bob


Grant still makes his own screws...

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 Post subject: Re: Build from scratch?
PostPosted: Sat Jan 04, 2014 7:35 am 
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Time to show my ignorance again - MSWP?


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 Post subject: Re: Build from scratch?
PostPosted: Sat Jan 04, 2014 8:44 am 
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Location: Edmonton
EverHopeful wrote:
Time to show my ignorance again - MSWP?


Maximum Safe Working Pressure

J


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 Post subject: Re: Build from scratch?
PostPosted: Sat Jan 04, 2014 1:14 pm 
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Thanks JSP.

Let's see if I'm following the conversation. I have a hopefully modest project in mind - a stretched 1377 with the valve separated into two halves to form an air reservoir between them and an increased pump stroke to make pumping more efficient. I purchased .75" OD .065 wall steel tube which the vendor says comforms to ASTM A513 which I found online at http://www.industrialtube.com/client/images/A513.pdf

TABLE S5.1 Hardness Limits and Tensile Properties for Round Tubing gives the yield strength for the various grades. The tube vendor doesn't specify exactly which grade it is, but gives a range: 1020 - 1026. Looking in the table and picking the lowest value to be conservative gives 60 ksi for 1020 DOM. Engineers Edge has a handy calculator for getting pressures from material strength and tube dimensions at
http://www.engineersedge.com/calculator ... t_calc.htm

So feeding in the tube dimensions, 60k yield strength and Bob's recommended 3x safety factor gives a working pressure of 4200 psi against a calculated deformation pressure of 12600 psi (and checking with the ultimate strength value from the materials table suggests the burst pressure would be 14600 psi), all assuming that any fittings could be made stronger than the pipe itself.

Did I get that right?

Now, of course the next point of concern is that I have no idea what the typical operating pressure of a 1377 is, but it seems unlikely that the simple, low tolerance pump mechanism can get anywhere near 4000 psi, so it looks like everything is good on paper. Whether I can make it without proper tooling is another question entirely.

Jim


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 Post subject: Re: Build from scratch?
PostPosted: Sat Jan 04, 2014 2:28 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8974
Location: Coalmont BC
Your tube is overkill for a 1377 conversion.... Just realize that if you can fire the gun one-handed and it's over 500 fps you will need an RPAL and have to register it....

I built several rifles from scratch / parts when the long gun registration was still in effect and had no problem registering them, whether they were from Commercial parts or not.... Since the registration is gone and I have my PAL I no longer concern myself with my rifle creations, I just build and shoot....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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