My Rapid-70 Bullpup Thread

[mackeral5]

A quick update.  A lot of back and forth Prod/1720/Fortitude hybrid testing has occurred in the past month or so.  I have settled on a regulated 1720 tune, somewhere in the neighborhood of 45 shots around 740-750fps of Crosman 10.5gr.  I haven't settled on which final versions but I am leaning towards the Rapid-70 kit being a .177 vs. .22. 

After a bit of waffling back and forth about a magazine fed 1720, I decided to give it a go. This was after testing my drill press/cross slide vise's ability to run an end mill.  I used an old QB78 repeater breech to test with, these were sold by Archer several years back and used Marauder magazines with oring on probe breech sealing.  I opened up the magazine well to fit a .25 magazine for a possible future project.  This won't be new ground as I have already built magazine fed QB78 repeaters in both .25 and .30.  Anyway, QB's are not the subject here. 

While we are at it here is a pic of the QB breech in the process of being opened up to fit a .25/.30 marauder magazine.  This at least shows what cruelty was in store for the 1720. 



While not perfect and it was a very nerve wracking exercise, I became confident enough to put the 1720 breech in my cross slide vise and have a go at it with an end mill....  Here is the end result.





Magazines are Mrod, with the bottom sanded down a bit to fit.  I also run a modified Mrod single shot tray.  There just isn't enough meat in a Prod/1720 breech to cut the mag slot deep enough to accept unmolested Mrod magazines/trays, IMO.  The probe had to be turned down just a bit to clear the magazines, that is the final bit of modification required. 

I still need to finish some file work to clean up the chatter marks....

I now have the 1720 upper mounted on my QB stocked Prod action for fine tuning prior to putting it all back in the Rapid-70 bullpup kit.  For now the magazine seems to stay in place with no problems even with the gap.  If that becomes a problem I can make a spacer.... 

[Rallyshark]

That's some nice work!  I'd say you did pretty darn well with it  

[mackeral5]

That's some nice work!  I'd say you did pretty darn well with it

Thanks Donny.  Not perfect by any means, but it is good enough for me and it functions as it should.  No loss of accuracy in shooting from the mag vs. single shot tray, which for me isn't the case with every gun....

I finally put the 1720M  back together.  The more I shoot the Rapid -70 Bullpup kit the more the novelty seems to fade.  I may work on an extended/dropped buttplate to see if that helps with the ergonomics.  Also need to look at possibly sliding the grip back a bit as the trigger is super close to the grip, worse than my Taurus G2C's....



If someone had a Mrod Gen 1 .25 breech, barrel, and trigger they were willing to put up for trade I may consider parting ways with the Rapid-70 kit itself.....not interested in putting up for sale though. 

[mackeral5]

While digging through my junk bin I found a couple of old Mossberg 500 stocks that will never get used.  So I borrowed the recoil pad off of one of them.  This made all of the difference in the world .  It shoulders much better and the soft, slightly tacky recoil pad grabs your shoulder very well with little effort required.



I also added a short piece of pic rail just forward of the trigger.  Here is another pic with a bipod attached.

[PG in San Diego]

While digging through my junk bin I found a couple of old Mossberg 500 stocks that will never get used.  So I borrowed the recoil pad off of one of them.  This made all of the difference in the world .  It shoulders much better and the soft, slightly tacky recoil pad grabs your shoulder very well with little effort required.



I also added a short piece of pic rail just forward of the trigger.  Here is another pic with a bipod attached.

Great Job Mike! That is awesome!

Can you explain how you added the pic rail?

Thanks,

Philip

[bear air]

Sweet looking BP Mike.

[mackeral5]

Thanks...   It is growing on me now that I added the butt pad.  In OEM form the butt plate is just too minimalistic for my uses.  Adding the pic rail to allow for accessories helped as well. 

The pic rail is just bolted in place with a couple 10/32 SHCS.  The rail was actually a shorted Marlin lever action scope base.  Note the space between the sideplates is actually too narrow for a pic rail to fit between.  This required a slight narrowing of that section of rail, I made short work of it with a file.




The Rapid-70 kit is neat, and a very practical design.  However it has one major design flaw.  The core chassis part that houses the trigger sear is made of fairly soft aluminum, IMO it should have been made of steel.  I am the second owner of this one and one of the tiny threaded holes that is used to retain a spacer/shim during assembly, this spacer/shim contains the trigger linkage/sear pins, one of the screws was already stripped.  Very small, M3 screws threaded into 2mm thick aluminum makes for very fragile threads.  Extreme care must be taken when assembling and one must rely on blue Loctite to keep all fasteners in place. 

The above described material choice and the pistol grip are my major complaints.  The pistol grip should have been designed to accept AR grips.  It is very similar, but much too wide for an AR grip.  It is almost as if the grip adapter was designed around an existing grip from a CO2 gun.  There is an odd, out of place mechanism in the grip that looks like a CO2 cartridge securing system. 





Some have reported to use this hollow pistol grip to store items such as a spare magazine.  I find it too awkward to open, whatever you store here shouldn't be something that you will need quick, easy access to....

Now I just need to find a way to securely carry 3-4 magazines and this one will be complete. 

[mackeral5]

Another quick note on .177 Mrod and Gauntlet mags. 

I learned that the 12 shot magazines from the Umarex Synergis can be used in anything that accepts .177 Mrod mags. 

Currently they are rather inexpensive at 2 for $15 on Amazon.



These do not block open the bolt on the last shot and have a slight difference in fitment, but they seem to work just fine. 

Note the use of Mrod mags in a Prod and this 1720T conversion requires slight clearancing of the magazine's bottom side.  This is due to the relatively tight barrel to tube relationship---there isn't enough meat in the Prod nor the 1720T breech to fit unmolested Mrod magazines....





This is how they sit in the breech of my 1720T magazine conversion.

[mackeral5]

After mulling over various options to make the Rapid-70 more friendly towards swapping grips, I remembered some info from my AK/Saiga conversion days....  Most any gun with a flat, sheet metal style receiver/stock can be easily adapted to use AK grips.  And there are adapters that allow AR grips on AK platforms.  So, all that was required was to cut a square hole in the Rapid-70 kit to allow for the AK style grip nut and we were in business.   The AK grip nut had to be narrowed slightly to fit in the piece of channel that makes up that portion of the stock. 

Now most any AK or AR grip can be used on the Rapid-70 1720M

I had a Hogue grip in my junk box, so that is what she is wearing for now.  With this setup I was able to lengthen the distance between trigger and backstrap of the grip, which is a big help for my medium/large hands. 



I used an inexpensive composite AR grip adapter and a steel AK grip nut.  Total cost including shipping was less than $20 from Carolina Shooters.  Then just add you preferred grip.

This is the AK/AR grip adapter I used.  One can choose to purchase higher grades of this unit that are CNC machined/anodized, etc.  I went cheap on this one....



There are also AK grip nuts that are flange mounted and can be screwed to the stock, not requiring the square nut cutout. 

[bear air]

Looks awesome Mike.

[mackeral5]

Looks awesome Mike.

Thanks Chris. 

The lengthened trigger reach, the butt pad, accessory rail, and 12 shot magazines have resolved most of the things I didn't like about this one.  I think it has graduated to "keeper" status.

[rapid-70]

After mulling over various options to make the Rapid-70 more friendly towards swapping grips, I remembered some info from my AK/Saiga conversion days....  Most any gun with a flat, sheet metal style receiver/stock can be easily adapted to use AK grips.  And there are adapters that allow AR grips on AK platforms.  So, all that was required was to cut a square hole in the Rapid-70 kit to allow for the AK style grip nut and we were in business.   The AK grip nut had to be narrowed slightly to fit in the piece of channel that makes up that portion of the stock. 

Now most any AK or AR grip can be used on the Rapid-70 1720M

I had a Hogue grip in my junk box, so that is what she is wearing for now.  With this setup I was able to lengthen the distance between trigger and backstrap of the grip, which is a big help for my medium/large hands. 



I used an inexpensive composite AR grip adapter and a steel AK grip nut.  Total cost including shipping was less than $20 from Carolina Shooters.  Then just add you preferred grip.

This is the AK/AR grip adapter I used.  One can choose to purchase higher grades of this unit that are CNC machined/anodized, etc.  I went cheap on this one....



There are also AK grip nuts that are flange mounted and can be screwed to the stock, not requiring the square nut cutout.

Excellent work. Our most sincere congratulations.

[rapid-70]

Although in principle, the design of the bullpup kit did not include a lower bipod rail for "visual aesthetics".
And like many clients, seeing that you incorporated a lower rail, they have asked us if we could include it.
We have decided to incorporate said rail to be able to place a bipod or a flashlight.
Wishing you like it, a cordial greeting.