GTA
Airguns by Make and Model => Benjamin Airguns => Topic started by: PCPhack on April 17, 2019, 06:15:51 PM
-
I will now revisit my 257 prototype build from over a year ago, as I received some long awaited custom machined parts a few weeks ago.
Thanks to JSAR for making the parts and to Bob for the idea in the vented barrel tensioner.
First up...let's see what we have here.
-
;D
Belleville tensioned barrel, with venting into carbon fiber shroud!
-
Longer than standard sidelever breech.
I am not sure if I will be satisfied with the power level using this piece as the flow through bolt is not full bore. If not, then this breech will go to my .25 brod build, and I will use my Marauder one modified with a retractable bolt.
-
More to come after the holiday weekend when I have time to build.
-
I like that breech. Finally one with enough area to actually support a barrel. 8)
-
Those Bellevilles on the barrel tensioner look pretty thin, what is the maximum tension that can be applied before they go flat?....
Does the shroud go inside the breech, or butt up against it?....
Bob
-
Those Bellevilles on the barrel tensioner look pretty thin, what is the maximum tension that can be applied before they go flat?....
Does the shroud go inside the breech, or butt up against it?....
Bob
I haven't measured the tension yet, but as I mentioned in my email to you, I don't think it is enough. It was not what I expected. The good news is that I could go up in size although it would require a larger outer nut. I should have sent them the washers that I bought last year that you suggested. Another aspect of this for my .257 is that the barrel is 32 inches and tensioning at that length may be questionable anyway. I may need to sleeve the barrel as well. We will see. This is still a bit of an experiment.
The shroud goes a short distance into that shroud trim piece, which is bonded to the breech. I wanted it to go much further but that was not possible because they put those window cutouts on the breech. Again, not what I wanted, but it is how they made this one, and there was no telling how long it would take to get one without them. I am willing try it though and we will see how accurate it can shoot. As said, it may go to my .25 build anyway due to the porting restriction.
With regard to the breech, a key here for anyone reading to remember about custom orders (from JSAR in this case) is that there is not necessarily parity between what is promised on the forum and what is produced at the end with such new products. Here online we asked for no windows and thought it would be so. In the end they still came with the windows, but just not fully cutout. The reason I was voting for no windows was thinking ahead about this tensioning and I ordered an extra long breech with the idea to deeply seat a shroud. So imagine my surprise when it arrived with windows. So we reworked it with the collar as a compromise to not wait for whenever they might make another production run of the parts. The collar setup should retain the shroud well enough, although I would have preferred it deeper into the breech.
-
What is the ID and OD of the Bellevilles?.... There may be thicker ones available....
Bob
-
I was thinking the same thing on the breach. It looks racey, but would prefer thicker breach for my purposes as well.
I would think about leaving that long barrel. It hugly helped my 100+fpe Rainstorm in both .257 and .25 cal. Shrank groups by quite a bit better than 50% and is much more consistent. Fliers went totally away with bullets.
Using the term bullets here because Mr. Bob doesn't like the term slugs. LOL! (Yes my "Up North Friend, I'm picking on ya)! ;D
I grew up watching old westerns. They may have shot bullets, but seemed t always dig out a slug when some one got shot. LOL! And my bullets are intended for vermin. But I do dig the slugs out if no pass thru to check performance. ;) ;D
Knife/Mike
-
What is the ID and OD of the Bellevilles?.... There may be thicker ones available....
Bob
They are these:
https://www.asraymond.com/catalog/B0862014?unit=english (https://www.asraymond.com/catalog/B0862014?unit=english)
-
That is a REALLY oddball size of Belleville.... and they are VERY thin, hence the low load capability.... They will go flat with hardly any tension on the nut, may as well not bother with them.... Here are some from McMaster Carr….
https://www.mcmaster.com/belleville-disc-springs (https://www.mcmaster.com/belleville-disc-springs)
0.531" ID x 1" OD are available in 0.062" thick (1090 lbs. flat load) or 0.089" thick (1542 lbs. flat load)…. The ones I used in my build were #9712K77, which were 0.50" ID x 1" OD x 0.073" thick, which are 1335 lbs. flat load.... a 12 pack is $9.62....
I have no idea how strong the barrel mounting is, as that will determine the maximum tension you can place on it.... but I run at least 800 lbs. of tension in mine, up to about 1200....
Bob
-
Yes, I know about the tested range you use and Tom had also suggested from earlier threads. I think that JSAR is just not familiar with the load requirment for proper tensioning, and they used these thin ones. I should not have assumed they would know. I did buy some of the Mcmaster ones last year, 9712K77, but the OD is too much for the nut they provided, so I will have to have a new one machined if I want to use them.
What I can do in the meantime, is just use the 9712K77 ones with a regular nut for testing. This won't be nearly as nice looking as the washers will be visible, but I can at least experiment.
-
Good plan....
Bob
-
Something like this, except I need to stop by the hardware store for a hex nut in 1/2-20 thead that I can tighten with a wrench.
Now I can also see that the threaded area is probably not long enough for a moderator after it, which was one of my other requirements. Sigh...
Here is also a McMaster-Carr 9712K77 next to the JSAR shipped washer.
-
I looked up those bellevilles on that website you linked.... they are for retaining a ball bearing in a housing.... hence the weird size.... ::)
Bob
-
I am 0 for 3 with custom parts coming back as wished. At first I was too detailed, so specifications were skipped. Now it seems I did not specify enough. Maybe a new machine shop...
Hopefully we can shave down the shoulder further past the threading to free up more threading area for the larger washers, a nut, and still leaving enough for a moderator.
Another idea on the washers is to try to find some in the right pound range that still fit inside the nut JSAR made.
-
I don't think you will find a Belleville that is roughly 7/8" OD with a 1/2" hole, they are usually 7/16" ID.... Why not just use the Moderator as the nut to compress the Bellevilles?.... You don't really need the fancy cover, it's only cosmetics....
Bob
-
I don't think you will find a Belleville that is roughly 7/8" OD with a 1/2" hole, they are usually 7/16" ID.... Why not just use the Moderator as the nut to compress the Bellevilles?.... You don't really need the fancy cover, it's only cosmetics....
Bob
I might do that if I can torque the moderator enough. In the end, eventually, I would like the pretty one also. :D
-
Ok, I had a closer look and I have plenty of threads, but may just need to trim the carbon fiber shroud down. There are many more turns available.
-
New test setup. I can cut down the shroud more later. I don't need the moderator on just to test.
-
I built my rifle how bob described the moderator tightens up against the washers hand tight this did not tighten my groups but made the poi consistent. Before temperature and storing the rifle would drastically shift poi. the biggest accuracy enhancement was from sleeving the barrel and resonator placement. Picture is 100 yards 10mph+ wind not holding for wind or waiting for condition 257420 at 920. my breach has a leak I cant nail down so she is with JSA getting that ironed out before I can progress . I look forward to seeing your build progress.
(https://oi1113.photobucket.com/albums/k520/kabona50/20190329_162822.jpg) (https://s1113.photobucket.com/user/kabona50/media/20190329_162822.jpg.html) (https://oi1113.photobucket.com/albums/k520/kabona50/20190329_144802.jpg) (http://s1113.photobucket.com/user/kabona50/media/20190329_144802.jpg.html)
-
Nice to see another Brod platform based 257! Thanks for posting the picture. I am surprised to hear you are only hand tightening. Is yours not tensioned?
I tested tonight tightening down mine, putting up around 1000 pounds of tension on the barrel with the Bellvilles inline to check that the barrel would not slip. It did not.
-
Something is surly amiss here. That simply is not .257420 .257 accuracy. Has the bbl. been laped yet?
Perhaps using too much air and getting a shift with the different pressure?
Knife
-
I have only put about 100 bullets threw the rifle before sending it off to JSA. I plan on experimenting with more tension and lapping the barrel when I get it back. Thank you knife for all your contributions I have been following your threads and learning a lot!! Ill start my own thread once I get a chance to put a little more lead down range (https://oi1113.photobucket.com/albums/k520/kabona50/20190329_150527.jpg) (http://s1113.photobucket.com/user/kabona50/media/20190329_150527.jpg.html) This was the best group of the day it was in the morning before the winds picked up and at 75 yards I put a 22 shell in for size reference
-
Oh Yeah, nice! Looking forward to the progress with this good looking shooter!
Mike/Knife