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  #1  
Old 11-18-2019, 10:49 AM
USGuy
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Being thinking about spare magazine for BB 7-2 I did my homework and found many topics on subject, but most of them does not contain simple and affordable solution I would like to implement. Most practical are to use 3-D printer or solder 3 shims to compensate wall thickness between original magazine and suitable Marlin 22lr which is widely available and very inexpensive. Not everybody has a 3-D printer including myself, so it is not an EAZY option to have UNLIMITED and UNEXPENCIVE supply for a BB 7-2 magazines.
Long story short: here is my idea for this long rolling problema:

Marlin 22LR rifle magazine 7 shot capacity:



Plastic water bottle (suitable wall thickness).

Heat gun.

Final product:








Total expences:
Marlin magazine: 12-15 USD on eBay
Water bottle: FREE
Heat gun: 14.99 USD (free if you have it)


Pictured version might not manufactured perfectly, but it is working solution and functioned as expected. Water bottle plastic is very durable and holds well against friction. I found this plastic to be THE BEST for this job and always available for quick and easy replacement.

Also, I was thinking about Kydex wrap around case, but it would require 0.5mm wall thickness for Kydex sheet which is I was not able to find.
Ideally if someone will be able to create a snap on plastic case for that Marlin magazine, that will be a professional solution for this problema.

Last edited by USGuy; 11-18-2019 at 11:42 AM.
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  #2  
Old 11-18-2019, 08:10 PM
Gobber
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Now thatís a cool hack

My question is if the feed ramp and lips are in the right position to align the top round to chamber properly.

Another possibility is heat shrink wrap. Hobby store LiPo battery wrap is too thin and would need too many layers but there is much thicker heat shrink out there for high voltage cable that might do the trick.

Kydex is available in pretty thin sheets and is really easy to work with. Problem is joining it at the seam- has to be a mechanical lock. Glue wonít stick to it.

My thought was to tape up the mag and apply a build-up of resin with either carbon fiber or fiberglass. Trim off the top & bottom excess flash and sand down the wall thickness to fit. If you scuff the metal beforehand, it ainít coming off. Then cut the release notch where needed. Touch it up with a thin layer of resin for a smooth finish.
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  #3  
Old 11-18-2019, 10:34 PM
USGuy
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Quote:
Originally Posted by Gobber View Post
My question is if the feed ramp and lips are in the right position to align the top round to chamber properly.
As it is now every and each round was feed in and extracted without issue.

Quote:
Originally Posted by Gobber View Post
Another possibility is heat shrink wrap.
Water bottle heat shrinkable and that is how this prototype was created


Quote:
Originally Posted by Gobber View Post
Hobby store LiPo battery wrap is too thin and would need too many layers but there is much thicker heat shrink out there for high voltage cable that might do the trick.
I tried this solution with this. It was not stand well against friction.

Quote:
Originally Posted by Gobber View Post
Kydex is available in pretty thin sheets and is really easy to work with. Problem is joining it at the seam- has to be a mechanical lock. Glue won’t stick to it.
I was thinking about kind of hot welding

Quote:
Originally Posted by Gobber View Post
My thought was to tape up the mag and apply a build-up of resin with either carbon fiber or fiberglass. Trim off the top & bottom excess flash and sand down the wall thickness to fit. If you scuff the metal beforehand, it ain’t coming off. Then cut the release notch where needed. Touch it up with a thin layer of resin for a smooth finish.
My idea was to make it easy and less technology advanced, so most simple guys, like me, could repeat this on the bench. I need more experiments to find better geometry for that plastic wrap. Thanks for your notes - something to think about.

Last edited by USGuy; 11-18-2019 at 10:37 PM.
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  #4  
Old 11-19-2019, 08:23 AM
Triggershoe
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Quote:
Originally Posted by Gobber View Post
Now thatís a cool hack

My question is if the feed ramp and lips are in the right position to align the top round to chamber properly.

Another possibility is heat shrink wrap. Hobby store LiPo battery wrap is too thin and would need too many layers but there is much thicker heat shrink out there for high voltage cable that might do the trick.

Kydex is available in pretty thin sheets and is really easy to work with. Problem is joining it at the seam- has to be a mechanical lock. Glue wonít stick to it.

My thought was to tape up the mag and apply a build-up of resin with either carbon fiber or fiberglass. Trim off the top & bottom excess flash and sand down the wall thickness to fit. If you scuff the metal beforehand, it ainít coming off. Then cut the release notch where needed. Touch it up with a thin layer of resin for a smooth finish.
Gobber-- my thoughts (on the chamber alignment) exactly. A friend of mine has made these Marlin mags (shimmed with sheet steel) work well with his 7-2, but initially experienced some bullet damage (shaving lead) when fed from the Marlin mag. His solution was to modify the follower to present the round at a more favorable angle, along with a slight "tweaking" of the feed lips. I seem to recall he made a small add-on piece that was glued or otherwise mechanically fastened to the follower, and that fixed the problem. He made up two Marlin mags for his 7-2 in this fashion, and I have seen him use these in our last CMP style "Rimfire Sporter" match without any problems. It sounds as though the OP did not experience this issue, so not exactly sure what is in play here. It could be that folks that have converted these Marlin mags have slight differences in the location of the "filed in" mag catch notch, or differences in how the mag is shimmed to fit the mag well. The good news for those of us that need a few spare 7-2 mags, is that the Marlin mags CAN be made to work. It just may require some individualized tweaking to get them to work properly.
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  #5  
Old 11-19-2019, 02:00 PM
Gobber
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Triggershoe - I see you list northeast Ohio as your location. How far from Pittsburgh are you?

Now on to the fun stuff.
Picked up a few of the Marlin 10rnd mags a while ago, but been too busy with other projects to pursue.
What initially put me off was the way the rounds presented themselves in the Marlin vs Izhmash mags.
The Marlin mag has the tip of the round riding higher than the Izhmash.


But you guys got me thinking, that really doesn't matter.
It's how the round 'ramps out' of the mag, engages the bolt and approaches the chamber. That's where things looked up.
As the round moves forward, things start looking good.


So I did a quick duct tape mock up to snug it up into the mag well.


And a few strokes of a mill file for the release notch.


It all locks in nice and pretty.


However, the proof is in the pudding... And I like it
Even running the bolt at half speed, it still engages well.
Video Link:
https://photos.smugmug.com/photos/i-...4hw4hL-640.mp4

Cycled several mags of ten rounds without issue unless I was running the bolt too slow, but this is identical to the original Izhmash mags.
If the extractor and keeper do not grab the round, it gets fumbled in the ejection port.

After mic'ing the dimensions of both mags, the slightly smaller Marlin size looks like a really good candidate for a fiber wrap to fill the space in the mag well.
I am thinking two approaches here.
1- Rough up the mag body, fill the interior with clay, give it a carbon fiber wrap and shape it to fit the mag well. Should hold up well and might look cool in the process.
2- Fill the mag with clay to make a molding plug with no mechanical locks, treat it with wax & releasing agent, give it a CF wrap, then pull it off as a spacer.
Trim and shape to fit the mag well.
It just might work...

More to follow...

Last edited by Gobber; 11-19-2019 at 02:25 PM.
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  #6  
Old 11-20-2019, 07:54 AM
Triggershoe
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Quote:
Originally Posted by Gobber View Post
Triggershoe - I see you list northeast Ohio as your location. How far from Pittsburgh are you?

Now on to the fun stuff.
Picked up a few of the Marlin 10rnd mags a while ago, but been too busy with other projects to pursue.
What initially put me off was the way the rounds presented themselves in the Marlin vs Izhmash mags.

The Marlin mag has the tip of the round riding higher than the Izhmash.
But you guys got me thinking, that really doesn't matter.
It's how the round 'ramps out' of the mag, engages the bolt and approaches the chamber. That's where things looked up.
As the round moves forward, things start looking good.
So I did a quick duct tape mock up to snug it up into the mag well.

It all locks in nice and pretty.
However, the proof is in the pudding... And I like it
Even running the bolt at half speed, it still engages well.

Cycled several mags of ten rounds without issue unless I was running the bolt too slow, but this is identical to the original Izhmash mags.
If the extractor and keeper do not grab the round, it gets fumbled in the ejection port.

After mic'ing the dimensions of both mags, the slightly smaller Marlin size looks like a really good candidate for a fiber wrap to fill the space in the mag well.
I am thinking two approaches here.
1- Rough up the mag body, fill the interior with clay, give it a carbon fiber wrap and shape it to fit the mag well. Should hold up well and might look cool in the process.
2- Fill the mag with clay to make a molding plug with no mechanical locks, treat it with wax & releasing agent, give it a CF wrap, then pull it off as a spacer.
Trim and shape to fit the mag well.
It just might work...

More to follow...
Gobber-- I'm about an hour or so NW of Pittsburgh. I have to say your (and others, of course) work adapting the Marlin mags to the Izhmash is encouraging! USGuy has presented some good ideas on modifications as well. This could be THE solution to the basically unobtanium and very pricey Izhmash mag issue. I have two NIB Marlin mags I recently picked up just for this purpose, but have not played around with them as yet. However, after viewing your video cycling the rounds through your rifle, it looks like the rounds actually present very nicely to the chamber, maybe even nicer (straight in) than the originals! It looks like the key to this is that the extractor/case holder controls the round as it exits the feed lips of the Marlin mag, and feeds into the chamber.

In your video, is that at "actual" speed when you are cycling the rounds? Are you seeing any damage to the bullets on the ejected rounds? How does it cycle when working the toggle very quickly, as one would in a rapid fire segment of a CMP style "Rimfire Sporter" match? That CMP style RF "Sporter" match is one of my main usage venues for my 7-2.

Your idea of the carbon fiber "wrap" sounds great, please keep us informed on any further work with this idea.
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  #7  
Old 11-26-2019, 03:44 PM
Gobber
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Was able to get a carbon fiber wrap on a Marlin Mag that seems to work fairly well.
As with everything, itís a two step forward one step back process.
Disassembled, scuffed, plugged and taped of the mag housing to add two layers of 6K CF around the main body.
Cut out a small wood insert to fill the interior voids and give it something to grab onto.


Did a wet layup of the CF with some scrap off the work bench.


Tossed it in the vacuum bag with another project and pulled it down tight.


Debagged it the next day- never pretty with it first comes out.


Here it is trimmed up next to its mates.


Proof is in the pudding.
Cycling it a bit quicker with the last round slow to show the line up.
Works well.
https://photos.smugmug.com/photos/i-...Z7hbM-1280.mp4
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  #8  
Old 11-26-2019, 04:37 PM
Gobber
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Hereís the Warning of the One Step Back- Beware that the Marlin Mags can ride higher into the mag well while you are shaping them to fit.
Their steel feed lips can easily push against the ejector pin and bend it up a bit to block the bolt from cycling forward.
Then when you go to gently tap the ejector tab back into place, it can snap off.


Not a big deal as the ejector pin is made from a small section of 4mm rod.
Got a section of 4mm stainless rod coming in from Amazon tomorrow and will fabricate a replacement.
This is where I really love the simplicity of the 7-2 design.
Bit of a pain, but should be a straightforward repair. I plan to make the replacement a bit more robust if possible.

Also to ensure the steel feed lips donít contact the ejector pin, I trimmed off a small notch on the Marlin Mag to keep it from bending the pin if the mag get jammed in hard.
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  #9  
Old 11-26-2019, 05:39 PM
Triggershoe
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Gobber--great work on that carbon fiber wrap. Looks nice (and unique!) as well. Thanks to your (and others') work on adapting the Marlin mags to the 7-2, we certainly now have a viable alternative to the pricey and virtually non-existent factory Izhmash mags.

I noted that broken ejector in your subsequent post---OUCH! As you mentioned, though, pretty simple repair. Hopefully the 4mm rod will be large enough to end up with a light press fit in the receiver. If not, red locktite or JB to the rescue.

I'll eventually get around to fiddling with the two Marlin mags I picked up, hopefully sooner than later
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  #10  
Old 11-27-2019, 05:29 AM
Gobber
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Quote:
Originally Posted by Triggershoe View Post
Gobber--great work on that carbon fiber wrap. Looks nice (and unique!) as well. Thanks to your (and others') work on adapting the Marlin mags to the 7-2, we certainly now have a viable alternative to the pricey and virtually non-existent factory Izhmash mags.

I noted that broken ejector in your subsequent post---OUCH! As you mentioned, though, pretty simple repair. Hopefully the 4mm rod will be large enough to end up with a light press fit in the receiver. If not, red locktite or JB to the rescue.

I'll eventually get around to fiddling with the two Marlin mags I picked up, hopefully sooner than later
TS- the CF wrap is pretty cool and doesnít add much weight.

After adding it and then sanding / shaping to fit, it ends up being a really thin layer. I plan to try a removable sleeve version, but have some doubts on how it would hold up being that thin. I do have some pretty thin 3k CF material that may do the trick if I can get it to the right thickness. Good thing is that it takes only a small piece and final trimming/shaping is pretty easy with a cheap diamond file set.

As for the ejector pin, got a set of rod stock coming that has 2.5-8mm sections.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

If 4mm isnít enough, can always sand down the 5mm. Looking forward to using the new Proxxon Press with X-Y table to see how good of a grind I can get. It has a bit of play, but typically works well enough. A real improvement over free handing


Will advise on how the replacement works out.
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