Author Topic: My Rapid-70 Bullpup Thread (Read 2775 times))

mackeral5 · « **on:** April 12, 2021, 08:51:11 PM »

As always, I was late to the Crosman/Benjamin party, but I'm finally here... I picked up Dillon's 1720T Rapid-70 Bullpup, it arrived today along with a 1/2-20 adapter. I pulled an older Tanto out of inventory and was pleasantly surprised that fitting a Tanto with cone style end allows for fills without requiring LDC removal. I found a set of medium rings and an old Bugbuster scope to start out with--this will likely be short-lived as the Bugbuster's very fine reticle isn't a good fit for my contacts prescription.

Anyway, here is a quick pic after shooting a bit and growing aggravated with a loose pistol grip which required close to full disassembly. I added back up washers and loctite to the 2 grip boss/adapter screws. As a sidenote, I don't see why a determined individual could not make a grip adapter to accept AR grips... The Rapid-70 grip appears to be something adapted from perhaps a CO2 pistol of sorts? it has an out of place mechanism in the trap door and is strangely, overly complex for a grip.

A few quick shots over the chrony with Crosman heavy domes showed velocities in the 690fps range.

More to come. It is going to have to have a magazine, eventually.

YEMX · « **Reply #1 on:** April 12, 2021, 09:54:03 PM »

Very nice!! I like it!

ranchibi · « **Reply #2 on:** April 12, 2021, 10:21:08 PM »

Congratulations! That is one sweet looking pup! You and Dillon have great taste in PCP’s 😉. Enjoy shooting it.

null · « **Reply #3 on:** April 12, 2021, 10:31:52 PM »

I don't like that design... but that's me...

bear air · « **Reply #4 on:** April 13, 2021, 07:11:32 AM »

Congrats on the new pup Mike. I'll be interested in how you source a mag for it.

mackeral5 · « **Reply #5 on:** April 13, 2021, 07:16:53 AM »

Thanks for the responses.

Quote from: manualf150 on April 12, 2021, 10:31:52 PM

I don't like that design... but that's me...

It is definitely ugly....and fairly complex, yet simple in many ways. For example, once I am ready to tackle a tuning process I will likely convert back to the OEM configuration. For now I am really enjoying shooting a gun that sips air and can stack pellets at 40 yards. This design does not lend itself to quick/simple disassembly/reassembly. But, such is the case most of the time when guns, etc are altered so drastically different from their original form.

With that said...Rapid-70 did an awesome job of designing this kit. The trigger system works perfectly and does not modify the factory parts in any way.
Guns do not get much lighter and more compact than this.

Plans include a magazine breech, a regulator and I will likely modify a valve to include a peek poppet and Cobra Chamber. Will likely become a dual caliber gun as well.

But again for now I am really enjoying it as-is.

Rallyshark · « **Reply #6 on:** April 13, 2021, 07:28:08 AM »

I kinda like it!

Tonycalves · « **Reply #7 on:** April 13, 2021, 09:18:33 AM »

In my experience after I put my cheek to the rest all I see is a cross hair. So I don't care a whole lot about looks. I had his OG bullpup and loved it, best backpack gun. If you gas it to 25+FPE it becomes a very capable little gun. Mike it looks great you'll love it!

FuzzyGrub · « **Reply #8 on:** April 13, 2021, 10:29:42 AM »

Welcome to the "small" tube crosman lego gun world!

Those Rapid-70 BP's are tiny!

Even if it didn't need a LDC, I would, just to prevent shooting my left hand.

mackeral5 · « **Reply #9 on:** April 13, 2021, 05:40:11 PM »

Quote from: FuzzyGrub on April 13, 2021, 10:29:42 AM

Welcome to the "small" tube crosman lego gun world!

Those Rapid-70 BP's are tiny!

Even if it didn't need a LDC, I would, just to prevent shooting my left hand.

As pictured 5lb 5oz, with those heavy UTG quick detach rings I'm sure a more appropriate set of rings could shave a couple of ounces. 25" long with the Tanto, 20.5" without.

Yes, risk of shooting one's hand/finger is real with this one. The 1720 is fairly quiet, but adding the Tanto makes it even more so. I definitely feel more safe with the Tanto vs without.

i hope this is my only foray into the small tube crosman world---I have more than my share of 7/8 tube stuff albeit in QB form vs. Crosman. I have already come up with a few different Lego configurations to put together, some for only a brief period just to test/demonstrate platform flexibility.

screwwork · « **Reply #10 on:** April 13, 2021, 05:58:18 PM »

The Rapid BP stock makes for a great truck & carry gun for sure. The looks are not for everyone, but I sure like it, super small & lightweight. I agree with finger protectors on this BP with factory shroud. Rocker1 sells some factory shroud diameter LDC that is about 3ish long which would be good for lower-powered BP's.

Nice looking shooter Mike.

oldpro · « **Reply #11 on:** April 13, 2021, 06:07:05 PM »

Quote from: screwwork on April 13, 2021, 05:58:18 PM

The Rapid BP stock makes for a great truck & carry gun for sure. The looks are not for everyone, but I sure like it, super small & lightweight. I agree with finger protectors on this BP with factory shroud. Rocker1 sells some factory shroud diameter LDC that is about 3ish long which would be good for lower-powered BP's.

Nice looking shooter Mike.

exactly my thoughts

mackeral5 · « **Reply #12 on:** April 13, 2021, 06:08:08 PM »

Quote from: screwwork on April 13, 2021, 05:58:18 PM

The Rapid BP stock makes for a great truck & carry gun for sure. The looks are not for everyone, but I sure like it, super small & lightweight. I agree with finger protectors on this BP with factory shroud. Rocker1 sells some factory shroud diameter LDC that is about 3ish long which would be good for lower-powered BP's.

Nice looking shooter Mike.

Thanks Randy. I have enjoyed it so far. I like the looks/length with the Tanto. I am considering a shroud-length barrel to make it a little easier to get pellets up to speed. Probably sleeved in cf and breech counter bored so the sleeve is inserted. Then setscrews between the barrel band and barrel. Everything i've experienced with bullpups tells me to make the barrel/pic rail a solid connection to prevent wandering POI due to barrel bumps, etc. The free floating barrel seems a bit unstable, though the barrel band is in place and prevents significant movement.

Lani52 · « **Reply #13 on:** April 13, 2021, 07:51:32 PM »

I have read that you can grind the bottom of a Mrod 177 mag to fit.

My prod takes Mrod 10 shot 22 mags, I do have a new prod magazine in the card package I ordered by mistake but those holes are too big to help you Mike.

Regards,

Roachcreek

screwwork · « **Reply #14 on:** April 13, 2021, 08:58:52 PM »

Mike,
On my Mrod barrels for the Prod I use a barrel to barrel band adapter that takes up the room so the barrel is non floating and it works very well in .22 & .25 cal Prods. One is secured with an oring that fits tight and the other for the .25 barrel is held in by 3 set screws in the barrel band. LDC are slip on units from a good friend of mine. My stock or shorter length barrels haven’t had any issues but I’m cautious about bumping the barrels on it. They get beat up in the Jeep on back country and fire access roads and I have never had a zero issues. I almost always check zero anyways before hunting but after I don’t worry about again until the next outing

mackeral5 · « **Reply #15 on:** April 14, 2021, 07:32:35 AM »

Quote from: screwwork on April 13, 2021, 08:58:52 PM

Mike,
On my Mrod barrels for the Prod I use a barrel to barrel band adapter that takes up the room so the barrel is non floating and it works very well in .22 & .25 cal Prods. One is secured with an oring that fits tight and the other for the .25 barrel is held in by 3 set screws in the barrel band. LDC are slip on units from a good friend of mine. My stock or shorter length barrels haven’t had any issues but I’m cautious about bumping the barrels on it. They get beat up in the Jeep on back country and fire access roads and I have never had a zero issues. I almost always check zero anyways before hunting but after I don’t worry about again until the next outing

Randy- thanks for sharing this experience. I recall following your Prod builds over the years. I have noticed a slight wandering POI between shooting sessions. It groups tight, but at 40 yards POi moves around a little bit--like in a 1.5" circle. Groups hold to .5-1" but the groups' relationships to the POA move around When removing the dust cap to fill I believe I am slightly tweaking the barrel as it is all but impossible to do without putting some degree of pressure on the barrel/shroud assembly.

Lani52 · « **Reply #16 on:** April 14, 2021, 02:49:08 PM »

I think occasionally of repurposing my LW poly choked barrel from my dead Skyhawk. I would get serious about it if I did not shoot only low power and it has a MM on it now.

Roachcreek

mackeral5 · « **Reply #17 on:** April 14, 2021, 09:30:10 PM »

Huma ships FAST....ordered over the weekend, it arrived today. I will be using a longer plenum (IIRC this is for a Disco.) The valve has been modified with a .240" OD peek poppet with a 2mm stem and a Cobra chamber. While not needed for .177, I went ahead and reduced stem diameter for a couple of reasons--1) I already had a peek poppet left over from previous P15 tuning and 2) I plan to have a .22 caliber change kit to go along with the .177. Going to a 2mm stem made throat area equal to approximately .160 porting, which is more than sufficient for whatever I would want out of .22.

The .240" OD peek poppet seals on the inside taper of the OEM valve seat. This should result in very minimal hammer strike being required. Which is good, as my ultralight peek hammer only weighs 9 grams, lol...

Hopefully it all works out. The biggest concern is hammer strike. I can make up some brass hammer weights if needed. Hopefully I won't have to though...

mackeral5 · « **Reply #18 on:** April 15, 2021, 07:56:03 AM »

Hammer strike did not end up being a concern. Being I had no idea where this extreme set of changes would end up, I made the hammer to accept a larger than stock spring in both length and OD. When I first put it together it was wasting air and shooting in the 760's. I had to clip coils and put the hammer in free flight to stop wasting air.... Right now it is stable at 750-755fps with Crosman 10.5. Reg is set just under 90bar. Cocking effort is similar to stock. The shot cycle is quick and crisp. A nice "POP" out of the muzzle with the shroud removed. No hammer noise, no ping.

I plan to put a few hundred shots through it in OEM form to ensure everything is stable prior to putting it back in the bullpup stock.

mackeral5 · « **Reply #19 on:** April 15, 2021, 09:40:02 PM »

So far so good. I am planning a tear down for tomorrow afternoon to make the final set of tweaks prior to putting it back in the Rapid-70 bullpup kit.

In pistol form the 1720 is HUGE.

After a tin of pellets I have to say this is the most accurate .177 I've ever owned. I am not a good shot with a pistol and wasn't taking the greatest care in shooting these groups, but the 1720 consistently does its job. Wherever the crosshairs are aimed, that's where it puts a .177 pellet This target was shot with groups of 10 or 20, and the bottom left bull was a group of 30 shots. The center bull was the first group of 10, then a series of scope adjustments and groups. Distance of 30 yards.

Current state of tune is approximately 45 shots of Crosman 10.5gr @725fps. Tomorrow I will do a final (hopefully) disassembly and this set of tweaks:

Reduce stem protrusion to .200
Increase regulator set point by 3-5 bar.
Through drill/tap the end cap 3/8-24
Clean up the Cobra chamber carrier a bit to ensure adequate airflow to the valve seat.
Possible slight increase of the Cobra jet

I know I am late to the party here, but if anyone wants an accurate, quiet, compact .177 backyard plinker, look no further than the 1720T!!!!

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My Rapid-70 Bullpup Thread

Author Topic: My Rapid-70 Bullpup Thread (Read 2775 times))