Recent Posts

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Correct. Please read the rules, although you could still qualify as the giveaway is not over.
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Hajimoto's Airgun Annex / Benjamin Marauder GEN2 Weight Loss
« Last post by Hajimoto on February 19, 2018, 08:39:58 PM »
Well New Years Resolutions are always made to lose weight and here is my MROD GEN2 .22 keeping its promise to lose a few pounds. I upgrade the heavy steel air tube with a Jefferson State Aluminum Cylinder and man does it lighten up the rifle!

The rifle will be torn down and reassembled with a JSAR Aluminum Air Cylinder, JSAR SS Balanced Valve, JSAR Super Hammer, JSAR TSS GEN2 and Huma regulator. The rifle will weigh almost 2 pounds less when this is all said and done. The MROD had most of these modifications already installed but I never documented the installation but have been promising you guys that I would, well here it is!

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Ask Bob / Re: Tank sizes
« Last post by rsterne on February 19, 2018, 07:21:36 PM »
I made an error with the Helium, it is corrected in blue in the post above....

One other thing that the VanDerWaals effect causes that I mentioned briefly above.... For each 500 psi increase in pressure above about 2500 psi, you put less air in the tank.... This means that if you are using a regulator to tether to a high pressure tank, and shooting at, say, 2000 psi.... as the tank pressure drops by 500 psi, you will get fewer shots at high pressure than at low.... Let's say that you get 100 shots from 2500 psi down to 2000 on an SCBA tank....  If the same tank is filled to 4500 psi, from 4500 down to 4000 you will only get about 80 shots.... If you are tethered to a 6000 psi tank of the same internal volume, from 6000 psi down to 5500 you will only get about 60 shots... The higher the pressure, the fewer the shots you will get from a 500 psi drop.... This also means that you won't get as many fills from a 6000 psi welding tank as you thought, particularly when the tank is full.... the pressure will drop very fast at the beginning compared to when it is at only "half full" at 3000 psi....

Bob
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PCP, C02, and Helium Powered Airguns / Re: Any Interest in 6mm ? - Build Thread
« Last post by rsterne on February 19, 2018, 04:56:47 PM »
I made the 6mm reamer this afternoon.... still not hardened and tempered but it turned out dimensionally accurate....



It is made from O1 Drill Rod.... The next step is to heat it to cherry red and quench it in oil to harden it.... Then I will polish it, hone the cutting edge again, and then temper it in the oven.... tomorrow's jobs....

Bob
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Contests, Give aways and more. / Re: Benjamin Fortitude Contest / Giveaway!
« Last post by Crosman999 on February 19, 2018, 04:47:10 PM »
$13.13

Thanks
Don't believe a 1st post qualifies?
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Ask Bob / Re: Tank sizes
« Last post by bnowlin on February 19, 2018, 02:17:42 PM »
Thanks Bob,
> Carelton says they make a 100 cu ft carbon tank for the military etc but not for public.  I think he told me they make larger with like 6000 psi also but not for public.  Tote them around if you will.  Thanks for all the info I needed that.
> Bob
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PCP, C02, and Helium Powered Airguns / Re: Any Interest in 6mm ? - Build Thread
« Last post by rsterne on February 19, 2018, 12:46:39 PM »
I cut the chamber in the .257 barrel today, using the reamer I made for my Monocoque....



Here are all the bullets that will fit.... They were all chambered to a depth of 0.60" from the end of the barrel, which will put the base just ahead of the front of the barrel port.... All bullets were sized to 0.257" before testing how they chambered.... When the chamber is too short, you sure know it, as you have to push hard enough to mark up the base, and it's pretty obvious when you get the length right....



I enhanced the contrast as much as possible so that you can see the rifling marks, but they are still hard to see on all except the longest two BBTs (112 gr. FN and 98 gr. HP), where they are clear on the back of the head.... The shortest bullet is the Lyman 257420 73 gr. and it barely touches the leade.... If you push it in by hand, you can only feel resistance for about the last 1/16", and basically cannot see any marks, even with a loupe, unless you push it in another 1/16", where you feel significant resistance.... I don't expect the two longest bullets to work in the 10" twist in this barrel.... but since I can chamber them I will be able to test that and prove or disprove the validity of the Kolbe Twist Calculator numbers for them.... Many of my BBTs seem to be stable in a slower twist than it gives, so there is a chance that the 98 gr. HP may work.... providing I have enough power to push it....

The other four bullets all slid in between 0.50-0.54" and then took a bit of a push (not much, mind you) to seat them to 0.60".... If you look carefully you can see shallow marks from the tapered leade, which they are sitting firmly against when chambered.... Those 4 bullets, from L to R, are the 91 gr. Noble, the 85 gr. NSA BTHP, the 88 gr. RCBS 82301, and the 82 gr. NOE 260-80 FN.... If I find one particular bullet shoots the best and want to play with different seating depths, I can do that by changing the length of the bolt nose....

Next step is to make the bolt, cut the O-ring groove and polish the chamber behind the barrel port.... then cut the CF sleeve to final length and glue it on.... and then machine the barrel port.... I was very pleased with the way the 3-flute reamer worked, so I am going to copy that design when I make the one for the 6mm barrel.... just smaller diameters for the pilot and chamber of course....

Bob
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Ask Bob / Re: Tank sizes
« Last post by rsterne on February 19, 2018, 08:37:54 AM »
Absolutely correct, Bob.... ALL the 1 hour size SCBA tanks hold 88 CF of air, not 98 (or 100) as advertised by some companies.... Likewise, the 45 min. tanks are 66 CF and the 30 min. are 44 CF.... The best way, if you are unsure, is to go by the internal volume (water capacity) of the tanks to compare them....

Incidently, this is why the pressure in your 4500 psi tank drops faster from 4500 to 3000 than from 3000 to 1500 psi.... and why a 6000 psi welding tank does not hold twice the air it would at 3000 psi.... Incidently, you can't put as many CF of Helium in a tank at the same pressure as you can with air (and the loss is linear).... Here is a graph showing how air, Nitrogen and Helium compare to an ideal gas....



Note that if you filled a 1 hour SCBA tank with Helium to 4500 psi it would only contain about 84 CF of Helium.... and Nitrogen would be about 86 CF....

Bob
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Airgun Hunting / Information on jacks
« Last post by Alan on February 19, 2018, 04:26:51 AM »
www.thejump.net/small-game/jack-rabbit.htm

I was looking for more information on the sub species of jacks, when I found this specific page. If you hunt jacks, it makes for an interesting read. They cover other game too.
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Ask Bob / Re: Tank sizes
« Last post by bnowlin on February 18, 2018, 08:22:56 PM »
Thanks Bob,
That means to me that some of the sellers are over advertising on some of their big tanks and smaller also just to sell them especially if they are the same size like 88 and 98.  The fire and diving, etc  people do it by minutes. for safety reasons and leave 15 minutes or so in them.
Appreciate ya. 
BoBn
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