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Crosman 760
15 June 2018, 18:48,
#1
Crosman 760
About 10 years ago I decided to set up a shooting range in the belly button of suburbia. No kidding, it was a place like I see in your newspapers where the houses are smack together without even a driveway between them.

I still had a back garden about 25 yards wide and 35 yards deep with a good fence all around and a place to hide my shooting position between the back deck and the shed, so I decided to go for it with the quietest, cheapest air rifle I could find.

It turned out to be one if these, a Crossman 760.

https://www.crosman.com/pumpmaster-760-rifle-177

These devices and been around since the early 1960s in one form or another and they also serve as the foundation for the 1377/1322, the rat catcher, the back pacer and the host of CO2 and PCP converted models sold word wide.
The power plant is basically the same for the entire series.

6-8 pumps offers 650-700 fps with BB ammo. That is well below your 12 pound limit and even if one "overcharges" the gun to 10-15 pumps it is unlikely that one could send a BB along at the +1000 fps needed to break UK law!

If you try to put too much air into them they will "pressure lock" since the hammer can not release the valve. Keep going and you can blow the pressure chamber O-ring or ruin the chamber itself. It is just made from aluminum with a plastic valve, so it has its limits.

And one does not particularly need full power for each and every shot! Unlike a springer or single stroke air gun the 760 can be pumped one time or ten times and the BB will exit the barrel with whatever level of power the user desires. Two pumps makes a fine inside the house gun for shooting into a cardboard box filled with crumpled newspaper.

These guns were devised to be one step up from the Daisy Red Ryder BB gun and they fill that niche well. They are double the power of the Daisy and accurate for a few more yards due to the increased velocity.

Over here they are "cheap as chips" as you would say, with a retail price of about half what the manufacturer lists. I got mine new for $20 U.S.

The joy of these little guns is that in the base model they are a smooth bore, best suited to shooting BB ammo, but 4.5mm pellets will also work. That means short range, but in crowded conditions the range will always be short.

They are also quiet, with the sound of the pump handle working usually making more noise than the shot. One of my neighbors told me they could hear me pump the gun, and the "ding" when the BB struck the steel knock down target, but never heard the discharge.

I rediscovered my little 760 the other day and decided to investigate it more closely than before. I did some research and made a few modifications. There are all sorts of strange instructions on the internet about how to force more power out of this little gun, but after watching all of them I came to the conclusion that these people were not doing anything to increase performance more than putting a couple of extra pumps into the gun would do, and in its current design there is no way to increase the performance beyond what UK law allows, so why risk breaking the law and/or messing up a good BB gun?

But being the piddler that I am I could not help but modify the rifle a bit. I did open up the air transfer port just a hair so the air would flow better when the little gun farted. I also lopped the last 6" off the barrel, crowned it on my hobby lathe, and moved the front sight back against the end of the pressure tube.

No real reason for that, I just wanted too do it.

I also installed a cheap "red dot sight". After spending a few minutes getting the little dot positioned where the BB ammo was landing when I stood 10 yards from my target backstop I called the job finished.

Also be advised that one should not use a solid backstop or pellet trap when shooting BB ammo. The steel shot can bounce back with force equal to what it left the barrel. Use something soft like a carpet scrap or a block of duct seal. If you make the trap correctly you can reuse the BB ammo.

All my shots were landing inside the space the dot covered and I was hitting my 2" steel danglers with each shot. You do not want to mess with someone that can hit your danglers from 10 yards!

Rats and pidgins would be in danger also.

No, it is not the best choice of rifle, but not everyone needs the "perfect air gun" along with its limitations of use and added expense for only occasional use. The 760 is cheap, accurate, has adjustable power with ability to shoot inside a small room or enough power for eliminating small pests, and it is easy to shoot.

And it's fun! That is the basic reason this little gun was designed back in the '60s. It was made to promote the FUN of shooting! Inside, outside, by young or old, everyone/anyone can operate this little gun.
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15 June 2018, 21:40,
#2
RE: Crosman 760
Did you chrono the gun before cutting 6"" from the barrel Mort?. Not that I've ever cut a pneumatic, I've only shortened and recrowned Spring air rifles . From what I understand though a precharged or pump up benefits from a longer barrel compared to a spring gun . The pump up or pcp having a larger amount of air pushing the pellet compared to the limited amount a spring rifle can compress in the cylinder . Like a steady push of air compared to the short sharp compression a spring rifle generates.I did once tune a career 707 in .22. The results were dramatic to say the least .
I quickly brought it back to 12ftlb's and sold it .
I'm curious if you saw any noticeable drop after the barrel cut.
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16 June 2018, 06:47,
#3
RE: Crosman 760
I have not clocked the BBs since I did the barrel cut but I will in the next few days. I need to get the chrono out and check the speed of the heavy JSB pellets out of the 2 PCP rifles.

I clocked them with 11 and 14 grain pellets when I first got them both but I have not checked the speed on the heavy 18.1 grain pellets and they are the most accurate I have found for either of those rifles.

With 14 grain pellets the Stormrider produces 27ft/lbs and the Gauntlet produces 21. The Gauntlet is a regulated system and it only varies 14fps across the entire 40 shot string.

The Stormrider is not regulated so it has a pressure curve and changes POI slightly as power goes up and down. You have to catch it on the flat part of the curve. I usually only pump it to 17 bar and stop shooting around 12 bar for best accuracy, which limits me to about 15 shots.

Even with a power curve the little Stormrider will put the JSB pellets into 1/2" @25 yards. The Gauntlet is a bit better.

I will probably not see much change in velocity from the barrel cut. This is the same power plant that is used in the 1377 pistol and this barrel is about the same length as that, I just have a rifle stock on it instead of the pistol grip. Coleman seems to use the same internals on almost all their multi-pump guns.

I will check speeds for both BBs and pellets when I run the test.

"Tuning" springers is easier than most folks would imagine. Polish the inside of the tube, apply some silicone grease to the spring, make some PVC washers and preload the spring as much as possible and still have it cock and you are about there. If you were just below 12 lb before you will be very close to 12 after.

My own problem, if you would believe such, is that my good rifles have too much power to allow me to compete in field target! We have a top limit of 20 ft/lb and both my rifles are above that.

That is why I bought the Umarex Gauntlet. I can work with the regulator and reduce the power enough to get below the limit and still retain the uniform velocity and accuracy.
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18 June 2018, 00:14,
#4
RE: Crosman 760
I have numbers!

The 5 grain steel Daisy BB shot is going 580 fps 5 feet from the muzzle for 3.74 ft/lb energy.

The Crosman .177 wad-cutter pellets of 7.9 grains are going 520 for 4.75 ft/lb energy.

Now we should compare to other well known guns.

The Daisy Red Ryder BB gun and all the lever cocking BB guns from Daisy use the same power plant and it gives 275 fps average speed for .84 ft/lbs energy. I know that I have killed hundreds of starlings and black birds with those shooters.

My favorite old style BB gun was the Daisy M25 which gave 350 fps and was probably the strongest Daisy power plant made. It gave 1.65 ft/lbs energy.

That is stepping down so probably step up one notch. The old favorite Weihrech HW30/Beeman R7 pushes a standard 8 grain .177 pellet at 620 fps from the add copy and some tests say it is actually 650. That is either 6.83 or 7.5 ft/lb depending on the number you use.

But the HW30/R7 costs $300US !!

All the other selections I can find here in the US are either weaker in performance or jump directly to the "magnum" power levels.

For $100US I can buy Crossman, Ruger, Umerax, Gamo 1000 fps gun. Those same guns would be available to you at 12 pound limits for less cost than the "better brands", some of which are owned by the less respected cousins.

With Gamo owning BSA and Umarex owning Walther, Diana and RWS ad building the Ruger air guns, and Beeman and Weihrech being partners one never knows what to expect.

Plus they all have Chinese production outfits
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