GTA
All Springer/NP/PCP Air Gun Discussion General => Vintage Air Gun Gate => Topic started by: beerbrewer on August 02, 2017, 02:01:36 PM
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I'm new to the forum as I stumbled onto the site looking for info on how to repair my old 1972 or 1973 Crosman 760 air rifle. I found my old gun in the basement and I decided that I'd like to put it back into working condition. So I started reading and watching how to videos on disassembly and modifying it. Some people have done some crazy mods to the 760!
At this point I have the gun all apart and now know why the gun doesn't work. Well, at least "ONE" major reason why it doesn't work...there may be more. My piston pump has completely fallen apart. Now I've found two possible solutions (both the same price) and I don't know which is better. I can buy a replacement pump piston from JG Airguns, but I have to send the old one to them and they will swap it out with a repaired one OR I can new type of Head Piston Rebuild kit from Mac1 (mac1airgunshop.com). The latter replaces the piston head with grey plastic head that uses an O-ring and doesn't require me to mail anything back to them.
Has anyone tried either?
Also, I read a lot of discussion about rifling while doing my research. I had always thought that my gun had a smooth barrel, but the original box (yes I still have the original box) says that the barrel is "solid steel, 19 inch (483 mm), button rifled". What does button rifled mean?
Thanks
Bob
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My vote goes to the Mac1 setup. Durable and easily replaced O-ring for a future reseal.
Button rifling describes the method used to impart rifling into the barrel ID. I think it's become the most common way to rifle a mass produced barrel because it's fast and generally leaves a smooth finish.
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Cobalt327....does that mean that my 760 actually has a"riffled" barrel or is it just marketing hype? Will this button rifling actually spin the BB or pellet enough to matter? If so, I wonder what the twist rate was used? I own two 54 caliber black powder rifles, a Lyman that has a 1 in 60" twist and shoots round balls best, the other has a Traditions with a 1 in 32" twist that shoots sabots best. Truthfully either gun can shoot sabots or round balls but as well as the other. If I shoot round balls out of the Traditions rifle the balls tend to spin out of control and sabots out of the Lyman tend to get like knuckle balls. So if it was in fact rifled, I wonder if it was rifled for bbs or pellets".
I'm leaning heavily towards the Mac1 setup. I just had never heard of them, but I like the concept.
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Contact Rick at Precision Pellet... you'll be a happy guy.
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The riffling is to spin the pellets. The riffling will not spin bbs in any helpfull way. The bbs are steel and too small to engage the riffling. They just float down the barrel. I have two old 760s .I replaced both the pump cups with a o ring type pump head. Made like you are looking at from Mac's. Mine work great and I consider this to be a improvement. With both of my guns I had the most trouble with the white plastic valve with the cone taper. A replacement is helpfull here.
n.h.schmidt
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Cobalt327....does that mean that my 760 actually has a"riffled" barrel or is it just marketing hype? Will this button rifling actually spin the BB or pellet enough to matter? If so, I wonder what the twist rate was used? I own two 54 caliber black powder rifles, a Lyman that has a 1 in 60" twist and shoots round balls best, the other has a Traditions with a 1 in 32" twist that shoots sabots best. Truthfully either gun can shoot sabots or round balls but as well as the other. If I shoot round balls out of the Traditions rifle the balls tend to spin out of control and sabots out of the Lyman tend to get like knuckle balls. So if it was in fact rifled, I wonder if it was rifled for bbs or pellets".
I'm leaning heavily towards the Mac1 setup. I just had never heard of them, but I like the concept.
Button rifling is "real" rifling, not a marketing ploy. It is now used for most guns you will buy, along with "hammer forged" barrels. You can do a search for the minutia on them.
The twist rate used on airguns varies but is usually around 1:16. Some info on rifling (there are many other sources) is from the blog at PA https://www.pyramydair.com/blog/tag/twist-rate/ (https://www.pyramydair.com/blog/tag/twist-rate/)). Rifling can benefit pellets, even though modern pellets don't necessarily have to have rifling to stabilize them (their design makes them self-stabilizing). You may hear rifling used for pellets and BBs as being a "compromise" type of rifling. Steel BBs don't gain anything from rifling and even Crosman warns shooting them from a rifled barrel can eventually wear the rifling (http://www.crosman.com/discover/airguns/airgun-ammunition?source=pepperjam&publisherId=21181&clickId=1177137551 (http://www.crosman.com/discover/airguns/airgun-ammunition?source=pepperjam&publisherId=21181&clickId=1177137551)).
So the best bet is to shoot lead pellets from your 760's rifled barrel.
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I would definitely go with the mac1 kit, that's what I used on my '71-'74 powermaster 760 and its a great kit. You also get more stuff li new lock washers, a new pivot pin , new rubber for the transfer port, and a 2of bottle of his excellent secret sauce oil for pump airguns.
You are very lucky to have a rifled barrel because mine is a smooth bore and of the same 1971-1974 2nd variant as yours. ( FYI the date code in the serial number only applies after some time in the mid to late 70's )
BTW when you put the stock back on put a little piece of bike tube rubber above and below the screw hole, this will help keep the stock from shifting without you having to over tighten the screw.
You'll also want to adjust the piston head by loosening the nut and turning the piston head out a little bit then tighten the nut back down. You want the pump to take a little force to fully close so it stays closed without having pressure in it.
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I went with the MAC piston kit for my 1972 1400 rebuild. Got excellent results. As to the piston cam over thing. The crosman factory service manual states this, Adjust for piston to just touch. No cam over pre-load. I found a copy of crosman service manual on the web. It looks official too. A lot of miss info around the web.
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I went with the MAC piston kit for my 1972 1400 rebuild. Got excellent results. As to the piston cam over thing. The crosman factory service manual states this, Adjust for piston to just touch. No cam over pre-load. I found a copy of crosman service manual on the web. It looks official too. A lot of miss info around the web.
I'm pretty sure this changes when you have the mac1 flat top piston installed.