Tale of THREE BRods - .25, .30 and .357 Completed, Page 19 !

[PakProtector]

Yes you have to remove the check valve inside the bonnet of the regulator.... It's nice that Travis made the passages through the drop down so large so that if you use it unregulated the bottle can flow fully into the plenum.... that adds a touch of volume to the plenum, too....

Bob

You're welcome Bob...recall if you will that the porting on that drop down came from the CAD I licensed to those two.

I just got a .25 LW polygon that is going to go onto the second Brod ever made... The .22 Brod I have running an other LW polygon is superbly accurate. Whilst sorting the LW site, they have choked and un-choked polygon barrels, but no .294/.300 barrels yet. Would love a polygon for the big JSB's. Given that the .25's are a .254 groove for .250 head pellets, I could see a .296/.302 working very well.
cheers,
Douglas
cheers,
Douglas

[rsterne]

The LW .30 cal barrel is pretty big at 0.298/0.306".... Tim @ Mac1 Airguns tried it and found it an epic fail with the JSB pellets.... WAY too big....

Bob

[PakProtector]

All three of the TJ's that have come into my hands have .3015 groove diameters. They shoot quite well... Maybe it is time to get after LW for a custom. It is possible; a few small BR manufacturers have gotten .177 polygon tubes with custom twist rates. Just a matter of $$ I suspect, and a really sweet 30 cal pellet barrel would be worth a bit to me. Time to call LW I guess... and then perhaps a new thread...
cheers,
Douglas

[T3PRanch]

Last time I inquired (a year and a half ago) the minimum run of custom barrels at LW was 10. There might have been a set up fee as well.

[oldpro]

I have a manufacturer making us custom barrels in different twist rates I’ll be doing some testing soon

[rsterne]

I have more information that would apply to someone building a 6 mm or .257 cal BRod, based on the results from this winter's PCP projects....

https://www.gatewaytoairguns.org/GTA/index.php?topic=128036.300

The 6 mm with a 29" barrel, regulated at 2800 psi, is getting in the mid 900s with the 64 gr. bullet.... Since the Lyman 257420 is the same Sectional Density (0.155), this means that the idea I talked about above, using the SS valve in a regulated .257 BRod with a similar barrel length can be considered a proven concept using a 500 cc CF 4500 psi bottle.... Starting with a 1/2" OD TJ's barrel with a 14" twist, and sleeving it up to 5/8" with a CF tube inserted into the front of the receiver just shy of the 4-40 screws is completely feasible, although you would have to single load bullets of that length (maybe)....

This brings up a new idea I am working on for longer magazines to fit the MRod receiver, for up to .357 cal.... There are several ways to do this, and here is the first prototype I am working on....



The magazine is shown mounted in a 5C collet in a hex block to enable indexing to drill the holes for the pellet/bullets.... You can see a JSB .35 cal pellet on the right, and a 154 gr. .357 cal bullet on the left (they are sitting on a couple of pieces of dowel to raise them up for the photo).... The material is a piece of 1.25" OD 2024-T3 aluminum bar stock, and it is long enough to make 2 mags.... I am not sure yet how I will mount the mag. and it will likely have to be indexed manually, but one way it could be mounted is on a retractable pin set into the MRod receiver, similar to the way a Hatsan mag. is located.... I checked the width of the mag. slot in a .25 cal MRod receiver, and it is long enough to accommodate that 154 gr. bullet if there is nothing else in the slot, and the barrel is not protruding.... This isn't my plan, I would never want to shoot anything that heavy.... and likely I will make the mag. wheel thinner to help mount and index it.... but it does shown some possibilities....

The other way to make a mag. for a .357 cal. is to copy the MRod .25 cal mag. but with a larger wheel in a similar housing, possibly made by a 3D Printer.... I have drawn one up and sent it to Travis for him to look at.... It would be the same inside length (0.45") as the .25 and .30 cal mags, but that would fit the JSB 81 gr. pellets, the EPP-UGs, and my 109 gr. BBT.... so likely all the length you would need for most .357s based on an MRod.... The advantage to this method is that it would be self-indexing....

Bob

[rsterne]

Well I got sidetracked on the long .357 aluminum mag project.... I had another look at the .25 cal MRod mag. and came up with a different way to modify it for .35 cal and still use the original housing, albeit modified somewhat.... The first step was to make a .35 cal wheel that would fit inside the .25 cal mag. and the only way to do that was to reduce the radius that the holes are on that hold the pellets from 0.50" to 0.45".... This would normally raise the center of the pellet 0.050" above the boreline, but I realized that if I inserted the magazine further to the left, while keeping the feed hole at the same height (which it must be to align the pellet with the bore), I could just rotate the wheel a bit more counter-clockwise (when viewed from the back) to get the height to work out.... here are some photos of the work so far....



The wheel was machined from a piece of MDS, with seven positions, one of which uses a glued in blanking plug that prevents you from closing the bolt when the mag. is in the empty position.... Drilling 7 holes was a challenge with a manual milling setup, the key was to use an online calculator to convert from Polar coordinates (radius and angle) to Cartesian (x and y) coordinates, and then just position the vertical and crossfeeds on the milling attachment on my lathe to drill the 7 holes around the 0.9" diameter circle.... It worked out great, although there was a lot of hand finishing to do, removing the milling flash where the holes broke through the outer diameter of the wheel.... You will notice that the recess in the back of the wheel for the torsion spring is smaller in diameter, so I will need to find or make a smaller OD spring to force the necessary rotation of the wheel to make the mag. self-index....



Here is a photo with the wheel in place, but I have not yet moved the feed hole over in the outer casing, or milled away part of the bump stop to make it stop in the correct place.... In the photo below I have machined a larger hole in the clear cover in the correct location.... You can see that it is shifted about 0.090" to the right of the original location.... and you will notice that part of the bump stop will have to be machined away when I mill the hole in the outer housing in the correct location to allow the mag. to slide to the left....



There are lots of things that will remain to be done to make the mag. functional.... the spring as I mentioned, and a new location for the small brass pin that rotates the wheel to allow loading pellets when you rotate the cover.... I will also have to figure out a way to hold the mag. in place, because the slot in the front for the barrel will lose the little bumps that allow the mag. to "snap" into place on the barrel stub.... First I have to get the mag. to function and line up.... then I will worry about the details....

Bob

[rsterne]

I took me many hours and lots of hand work, but I now have a fully functional 6-shot .35 cal MRod magazine, made from a .25 cal.... Here are the photos....



The spring is a mess, cosmetically, but it works.... I made it by winding the stock spring around a 9/32" drill bit to tighten the coil enough to fit inside the 1/2" hole in the wheel.... Of course it came out a mess, so I spent a lot of time with two needle-nose pliers tweaking it to get it to work....  .... I had to hand carve the groove for the pin in the cover that rotates the wheel with a tiny burr on a Dremel, and again it may not be pretty but it is functional....



The housing was milled out with a 3/8" end mill to move the hole over and increase it in size.... There is a 1/32" hole drilled through the filler plug in the wheel for the tail of the spring, which is installed in the photo....



The position of the feed hole, and it's associated recess that clips over the end of the barrel were the key to this project.... They are the same height as in the stock .25 cal magazine, but are moved 0.084" towards the centerline of the mag..... That was necessary for the hole to line up with the smaller radius of the wheel, which was necessary so that the pellets fit inside the housing.... I was concerned about how to retain the magazine in the slot, but as it turns out, that was a non-issue.... When I plunged the 1/2" mill into the front of the housing to create the recess, it left two tiny bumps that slide past the barrel when you insert it, exactly the same as on a stock mag.... The difference is that as you slide the mag. into place, you feel it "click" twice as it slides past the OD of the barrel, once for the stock bumps, and then for the new ones, which are actually tighter than original.... Once in place, the mag. protrudes that 0.084" past the left hand side of the receiver because it sits that much further to the left to line up....



Here is a photo of the loaded magazine.... You can see the brass rotating pin, which I had to relocate, and the enlarged, kidney-shaped loading slot in the clear cover.... It functions perfectly, indexing to the next pellet each time you push one out.... I even tried it sitting on the end of my .357 barrel, and the pellet just slides right into the bore, exactly as it should.... Now that I have figured out how to do this, I will order another .25 cal MRod receiver and bolt, and a PRod trigger group and AR stock so that I can complete a third BRod in .357 cal.... I already have the bottle, tank block, and a spare FLEX tube, and most of the parts to make a valve.... so it looks like a regulated .357 BRod repeater shooting pellets is the next project.... although it likely won't get done until next winter, I am quickly running out of time as spring is here and the Motel will soon be busy....

Bob

[lloyd-ss]

Ya know Bob, if you had asked me a month ago, I would have said you couldn't fit .357 pellets inside the M-rod .25 cal magazine.  Glad I was wrong, LOL.
Pretty slick, despite the prototype "appearance". Decreasing the hole diameter for the spring (along with all the other tedious modifications) seems to have done the trick.
Very good.
Lloyd

[rsterne]

That was one of the keys.... The other was to move the hole in the body and cover plate to the right, closer to the centerline of the mag.... so that the vertical height of that hole (which you can't change) lines up with the smaller radius of the wheel required so that the outer edge of the pellets fit inside the body of the magazine.... THAT was actually the key to making it work.... The smaller spring was an obvious requirement, moving the hole over, not so much.... 

So when is AirGunLab going to start producing .35 cal MRod mags?....  .... I'll take two, please.... 

The only production change I would make is that the clear cover plate is quite thin at the top left of the much larger ammo slot.... Making the edge of the cover a straight line, tangent from the top of the "bump" to the outside of the radius, instead of following the profile of the body, would greatly increase the strength at that point by nearly doubling the width there....

Bob

[rsterne]

I cast up the new NOE pellets today.... The mould comes with 4 sets of RG base pins, and they produce 3 skirted pellets and one solid with a flat base.... They look like this....



The weights in 40:1 lead/tin alloy are 35.0, 37.0, 38.5 and 42.6 gr.... They all chamber perfectly in my .25 cal LW Polygonal barrel, but that is not surprising as I cut the chamber to allow for bullets as well as pellets.... I have my BRod set up with a Cothran valve and the WAR adjustable regulated tank block, set at 1900 psi.... I checked the velocity of all 5 pellets (including the JSBs) and got the following averages for one 8-shot magazine of each....

34.1 gr. JSB = 947 fps (67.9 FPE)
35.0 gr. NOE = 937 fps (68.3 FPE)
37.0 gr. NOE = 919 fps (69.4 FPE)
38.5 gr. NOE = 906 fps (70.2 FPE)
42.6 gr. NOE = 871 fps (71.8 FPE)

I was only shooting inside my shop, with the backstop 20 feet away, and all groups were one ragged hole, with no real difference between any of the pellets.... That is encouraging, because some pellets or bullets can't do that when shooting through the Chrony at that distance.... and those that do usually shoot pretty good at least out to 50 yards....

My summer is taken up with sitting at the Motel reception desk waiting for guests, and we are entering our busiest season now, so it is unlikely I will get to try these at distance any time soon.... but the velocity and energy is right where I want it for testing.... I can't wait....

Bob

[YEMX]

Goodness Bob, that mag is AWESOME!!!

[rsterne]

I'll tell ya'.... you only want to make ONE !!!! ….

Bob

[YEMX]

Honestly, after reading all the work that went into it, I thought the same thing!  I'm completely okay with single loading!!   

[rsterne]

Perfect project for a 3D Printer, I would think....

Bob

[YEMX]

Perfect project for a 3D Printer, I would think....

Bob

Absolutely!  Plus a little water jet cutting for the clear lids...  I would think the only real hard part would be to find a supplier for the spring.

[rsterne]

My parts came in today from Joe at DiscosRUs, and I didn't waste any time whacking the front off the Gen2 MRod stock and grinding it out to fit over the WAR tank block.... Here is what it looks like with the Gen2 trigger installed also, plus a 500 cc 3000 psi aluminum bottle....



I left the stock long enough to cover the tank block and the bonnet section of the regulator.... There is a bulkhead in the stock JUST in front of the front of the tank block when it is mounted in a WAR tube, so about 3/4" ahead of that is where I made the initial cut, and then ground it to fit with my Dremel....

I also purchased a .25 cal MRod receiver and bolt, which I will be modifying as before to fit the .357 cal TJ's 26" twist barrel I have, with a high-modulas CF sleeve glued over it to stiffen it, like I did with the .30 cal barrel.... I already have a modified .25 cal MRod magazine which will give me a 6-shot .357 cal repeater when it is all together.... I probably won't get much done before the winter, but at least I now have all the parts, other than the valve and hammer which I have to make....

Bob

[YEMX]

Beauty!!  I went with the Armada chassis, but I do like the look of the synthetic Gen2 stock!  Excellent work as always Bob!!

[rsterne]

The SynRod stock comes with a rubber block that is designed to put some upwards pressure on the tube.... It fits over the boss for the sling swivel.... I moved it back 3 bays so that it is behind the tank block.... At that point, the stock is two different depths inside, because it dips down to create the swell for the back of the foregrip.... The rubber block is the correct height at the back of that bay, but too shallow at the front, so I simply pushed a snug fitting piece of wooden dowel into the moulded in hole that fits around the sling boss, and then ground it down so that it holds the rubber block the same height all the way along.... That way it fits snug against the bottom of the main tube, preventing the stock from moving around forward of the trigger, which it can do without it in place....



I have been looking at what is required for porting for the .357 barrel, and I have decided that I won't be bothering with making an oblong barrel port, since I am building a pellet shooter…. In addition, I plan to try using a short transfer port that only seals against the receiver instead of against the barrel.... The reason for that is that the barrel wall is so thin there is not enough room to create a 3/8" diameter flat on it for the end of the transfer port to seal against, as the flat would break through into the bore.... Travis uses the steel barrel sitting directly on the aluminum receiver (held down by the setscrew above it) to seal, and assures me it works great, so I am going to try it.... The plan is to drill the exhaust port, transfer port, and barrel port all to 9/32" (0.281"), which is 79% of the bore.... That way I should not have any issues loading pellets.... We know that 7mm (0.276") porting is a great mod. on the Korean 9mm's, so 9/32" ports should produce lots of power, especially when heavy bullets are not the goal....

The port is larger than anything I have used on a .357 conversion before (I have never gone bigger than 7/32" on a Disco valve)…. In order to have enough flow in the throat in the SS Valve I plan to build, and not have to use a poppet larger than the 3/8" OD PEEK I made for my recent 6 mm and .257 builds.... I plan to use a piece of 3/32" music wire for the stem, instead of the 1/8" stem which is usual for an MRod valve.... Using a the same 5/16" throat I have used before, this will make the throat area of the valve the equivalent of a 0.298" hole, or about 12% more area than the porting.... which should be enough to compensate for the turbulence around the stem.... I will be using a 1/8" bolt probe, which just fits into the base of a JSB 78 gr. pellet.... In the .357" chamber that leaves an area equal to a 0.334" hole, so the smallest porting will be the 9/32" exhaust, transfer and barrel ports....

Part of the reason for not trying to increase the ports any larger than 9/32" is the restriction inside an MRod valve caused by the small diameter required between the two 4-40 receiver screws.... You can get a bit more area at that point without going wider than the 1/2" maximum ID to leave enough material around the screw holes by using an end mill to make the inside of the valve at that point taller than it is wide.... Here is a photo of an MRod valve I machined out inside to prototype this idea....



With an SS style valve, there is a sleeve around the outside of the poppet, and with a 3/8" poppet the sleeve is about 7/16" OD.... That doesn't leave a lot of room for flow around that inside a 1/2" hole.... hence the reason to mill out that hole larger in height for more flow area past the sleeve.... As you can see, trying to find enough room inside an MRod valve to flow lots of air for a .357 is a bit challenging....

Bob

[YEMX]

Can the Cothran valve's exhaust port be opened to .281" safely?