GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Tack Driver 10 on February 11, 2021, 12:40:46 PM
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The 760 is the Rodney Dangerfield of airguns.
It just don't get no respect!
Some of the reputation is rightfully deserved.
The time has come to change this perception.
Going to convert a late 70s version into a bottle rocket.
Acquired ten 760s in a lot from EBay for $15 a copy shipped before the maddness.
All are the 77-81 version 5 with the brass bolt.
Here's the game plan:
Add a drop block to attach an HPA bottle.
22 cal big bore barrel. (big is a relative term here)
Recently modded a 13xx gun in a similar manner and it made over 30 FPE.
Here it is mocked up:
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Tuning into this one. I think I passed on that lot I was looking for old 760 at the time.
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I like the barrel band/ support built into the drop block 8)
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following
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Got quite a bit done despite the cold weather.
Been in the mid teens for a high temp with sub zero coming next week.
I think I'll take a vacation to Alaska to warm up....LOL
The valve is similar to the 13xx gun.
The stem is bored up close to the TP at .187".
Pinned with 2 8-32 screws counterbored into the valve.
Turned the barrel at the breech end to 5/16".
Cut off the nipple on the tiny breech and counterbored it 1/4".
Will get a Delrin TP.
Machined the receiver halves where the probe slides.
Opened it to .234" for 22 cal.
Just have a few small items left and the gun should be ready to go.
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very cool , nice to have the old school cast parts and not have to ream out the flimsy plastic rear barrel Tp they make now.
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Following
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Made the probe.
Since the original is 17 cal turned it down and threaded it 8-32.
The 22 cal probe screws on.
The hammer is 12 grams made of Delrin with a metal core and poly bumper.
Finished the remaining minor parts and assembled the gun.
Pumped it to 1200 psi, has a very slow leak at the gauge.
No problem dry fired it inside this morning, 90 dB on the sound meter.
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Was hoping to chrony the gun today but a major catastrophe befell me.
I shot the gun and the bolt would no longer cock the gun.
Took the gun apart and discovered the valve stem has been beheaded.
Funny thing is the gun still sealed with the stem disconnected from the head.
When I drilled the holes to pin the valve I nicked the stem.
Probably pulled it a bit and shooting it finished it off.
Made a shiny new valve stem, same diameter but taller with more insertion.
That should take care of it.
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The gun held 1200 psi rock solid overnight.
Has a sealed 90 gram CO2 bottle installed so running off the plenum.
Makes it easy to pump and fix any leaks etc.
Got to chrony the gun this morning, 03 degrees (-16 wind chill), between snow storms.
Pumped the gun to 1600 psi, 22 cal 24" barrel, 12 gram hammer/2300 spring.
14.3 CPHP
806 FPS 20.62 FPE
818 FPS 21.25 FPE
820 FPS 21.35 FPE
820 FPS 21.35 FPE
Pumped the gun to 2000 psi
775 FPS 19.07 FPE
Pretty "respectable" considering the light 12 gram hammer.
With a stock 30 gram hammer and an SSG the gun should really perk up.
The 13xx gun made 926 FPS 27.22 FPE with a heavier hammer so this gun should be close to that.
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8)
Right up there with Maximus power, Interested to see shot counts...
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Put a stock 30 gram 760 hammer and 2100 spring in the gun.
2000 psi
14.3 CPHP
1004 FPS 32.00 FPE
25.4 JSB Monster
812 FPS 37.18 FPE
33.95 JSB Beast
700 FPS 36.93 FPE
Without an SSG uses a lot of air but had to try it.
Now I'm thinking a 17 cal Plastic Fantastic 760 that breaks the sound barrier.
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awesome, probably the only 37 fpe 760 on the planet.
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Weather cooperated today, a balmy 26 degrees....LOL
Removed the 2100 hammer spring and used a 2400 spring with a .360" spacer.
The 2400 spring is lighter and shorter so should detune the gun some.
Ran 2 test shots yesterday at 1800 psi, 884 and 888 FPS.
Used an empty 90 gm CO2 bottle pumped to 1800 psi.
Going to run a shot string until power falls off.
14.3 CPHP
01. 797 FPS 20.17 FPE--1800 psi
02. 882 FPS 24.70 FPE
03. 888 FPS
04. 890 FPS
05. 890 FPS 25.15 FPE
06. 893 FPS--------------1600 psi
07. 891 FPS
08. 897 FPS
09. 899 FPS
10. 898 FPS 25.60 FPE
11. 892 FPS--------------1400 psi
12. 888 FPS
13. 889 FPS
14. 885 FPS
15. 878 FPS 24.47 FPE
16. 870 FPS
17. 865 FPS--------------1200 psi
18. 858 FPS
19. 850 FPS
20. 835 FPS 22.13 FPE--1000 psi
First shot was low for some reason but then settled down.
Might not have closed the bolt fully???
Has a good amount of hammer bounce without an SSG.
I think a 9 ci bottle regulated at around 1250 psi might be a good fit.
Should also bump up the shot count substantially.
Guesstimate 60+ shots from 3K to 1250 psi.
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Made an SSG and test hammer.
The SSG uses a light 2300 spring and the hammer weighs 19 grams.
Gone is the 3 shot burst sound replaced with one tight punchy note.
Last night pumped the gun to 1800 psi and dry fired it to 1000 psi.
Got 26 shots vs 20 without the SSG.
Made 3 test shots this morning at 1600 psi
14.3 CPHP average 870 FPS 24.03 FPE
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nice.. wonder if you could mod that reciever to take the 5 shot stripper clips.. I converted a m417 to co2 a while back and the stripper clip was a nice feature for once.
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Would be difficult but have two M4s and a black/gold 66 that have the clip receiver.
Both are plastic fantastic guns.
How did you mod your M417 for CO2?
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machined a drop down on the main tube and pinned the valve..( i used a 9oz tank and an asa adapter ) Ive done quite a few pcp and co2 conversions over the years ( probably dozens ) the m417 was a way better gun on co2 , the stripper clip with some practice was pretty fast for follow up shots. Problem with the m417 is remounting the forearm , no matter the config , You need serious clearance internally on that big forearm.
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Made a new block and swapped the 90 gram CO2 tank for a 9ci regulated bottle.
Set the reg at 1400 psi.
I like the form factor of the CO2 bottle on this gun so.....
Might put the CO2 block and tank on a 760 plastic fantastic.
Won't that be fun.
14.3 CPHP, SSG with 2300 spring and 19 gram hammer.
Ran 5 shots over the crony
915 FPS 26.58 FPE
918 FPS
916 FPS
914 FPS
915 FPS
Should cut the reg down some and settle in at around 800+ FPS
I'll have to put a scope on it and see how it shoots first.
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Put a scope on the gun and after sighting it in benched at 20 yards with a 15 mph cross wind.
Tried different pellets:
CPHP, hated them
H&N Barracuda Hunter Extreme, nope extremely inaccurate
RWS Superpoint Extra, I've had better
H&N Barracuda Match, getting warmer
H&N Field Target Trophy, 10 shots dime size, you get the Trophy
Not going to win any FTT competitions but did OK fresh out of mod, trigger needs improvement.
The BMs were 5.52 and the FTTs were 5.55 so I think the fatter pellet did good in the loose Crosman barrel.
Might have to get some BMs in triple nickel and stretch it out to 30 yards.
I would feel comfortable pesting with this gun as is though.
No USPS mail boxes were harmed in this experiment, this one was recycled.
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The trigger has a lot of creep and quite frankly, It was.....creeping me out....LOL
Previously I cut the bar on the trigger back to .100" so the gun can be decocked.
To reduce the creep made a 5/32" bushing that fits over the bar and pulls the sear off the hammer.
Should cut the creep down to an acceptable level while still being safe.
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Didn't get a chance to shoot the 760 BYOB gun today.
So to keep myself entertained converted my 760 Plastic Fantastic to HPA.
I've had this gun since the mid 80s and it was OK at the time.
The bolt would fly back when pumped for high power.
Used a bolt body from a V5 760 and notched the receiver, problem solved.
Also swapped the plastic breech for the cast metal type, drilled and tapped it for 6-32 screws.
The valve is similar to the BYOB gun with an external spring on a Delrin stem.
Pumped it to 1600 psi, should get a chance to chrony test it this weekend.
Weighs in at a feathery 3.5 pounds.
Here it is along with the BYOB gun for comparison.
This bad boy is too cool for school....LOL
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Time to road test the 760 Plastic Fantastic PCP.
Charged the 90 gram spent CO2 bottle to 2000 psi.
With a stock 30 gram hammer, 2100 spring, 18" smooth bore barrel:
7.9 CPHPs
1003 FPS 17.64 FPE
10.65 Barracuda Match
933 FPS 20.58 FPE
The 30 gram hammer and 2100 spring was too much so......
Installed a 12 gram hammer with a lighter 2400 spring.
7.9 CPHPs
853 FPS 12.76 FPE
846 FPS
852 FPS
844 FPS
840 FPS 12.38 FPE
850 FPS
10.65 Barracuda Match
742 FPS
745 FPS 13.12 FPE
Looks like a great config for this gun.
Using about 20 psi per shot and making good power.
Gun has iron sights and a smooth bore barrel.
Took a few shots at a can at 20 yards, seems pretty accurate.
More testing to follow.
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When I assembled the 760 Plastic Fantastic PCP I cut a few corners.
I used a metal breech but left it stock in order to "get er done".
I modified the breech by drilling it 1/4" and used a Delrin TP at .157" vs the stock .140".
Also made a new probe since the one I was using wasn't sealing good.
Velocity increased 60 FPS about the same as a hot 2100 pumped 15 times.
Bottle pressure 1900 psi
07.9 CPHPs
918 FPS 14.78 FPE
911 FPS
10.65 Barracuda Match
795 FPS 14.94 FPE
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Some cool stuff here; following along. 8)
Jesse
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Continuing on with the 760 Plastic Fantastic:
Put a scope on the gun to test accuracy.
The original barrel was a smooth bore, not going there.
The barrel I put on the gun is a 760 rifled barrel from another gun.
It has the 3 sight screws drilled into and through the rifling.
The rifling was almost non existing probably had a lot of BBs through it....LOL
Wasn't accurate (no surprise) so prepped a 1760 barrel and installed it.
Shots taken benched at 13 yards.
The upper LH orange target is sight in.
The upper RH orange target is 5 shots with 7.9 CPHPs.
The center orange target is 10 shots with H&N FTT, 4.52 head
The lower LH orange target is H&N Barracuda Match, 4.50 head
Looks like the H&N pellets did best.
Need to stretch out the distance but very pleased with the accuracy at this point.
An LW barrel on this gun would really improve the accuracy.