Author Topic: Improving the accuracy from a Crosman 1077  (Read 1442 times)

Offline Mintie

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Improving the accuracy from a Crosman 1077
« on: October 18, 2017, 05:37:56 PM »
Hi Guys,

I didn't really take pics while I was doing all this work im afraid, and I wasn't the one to come up with most of these ideas either - I just googled "1077 mods" for a while wanting to improve what is to be honest a really crappy rifle from the factory.

To start I will explain myself. I bought a 1077 a few years ago, I shot a couple of hundred pellets through it and gave up without opening it up. It wouldn't group (like A4 sized at 25y), the velocity was unbelievably inconsistent and the trigger pull was horrific. So I got rid of it and forgot about them for a while. When the Benjamin Wildfire came out I thought it looked familiar and started watching videos about it and the 1077 again which stirred a bit of interest again. A cheap deal came up second hand so I grabbed it hoping maybe this one would be better than the last. Nope. Even at 7m the grouping was about 40mm and the velocity went from 480 fps to 351 fps over 6 shots (not super rapid fire but faster than a single shot loaded rifle). I guess I already knew this would be the case as I wasn't really surprised, so I got on with stripping it down for a closer look at why!

Somewhere during the years of manufacture Crosman made a few small changes to this model. The later ones often don't have all the screws holding the two halves of the receiver together, is missing an oring on a part referred to as the "magazine detent" and I believe there are some other small changes as I have seen some bulk fill kits as advertised to only suit some variants. The one I picked up was the later model.

The mods I performed and where I heard about them:

Detent oring replacement - Apparently helps to make the rifle more efficient and adds a few FPS. Fairly easy to do and these instructions are good, how much difference it made I don't know as I did a few other bits while I was at it.

Valve gauze removal - This was done while I had the receiver open for the detent mod. Very simple mod and just helps the Co2 to flow a little easier which helps keep it a little bit more consistent when shooting rapidly. All you need to do is separate the tube from the plastic receiver, remove the brass valve and unscrew the face that holds the seal in place, remove the seal and the gauze screen and then reverse these steps.

Added hammer weight - I read that this can help increase power a little so while the receiver was open I glued a bit of extra lead weight to the hammer to help it hit the valve a little harder, hard to know if it helped and I didn't weight how much extra I added sorry.

Trigger spring weight reduction - I managed to find a spring that was the right outside diameter and was a much lighter weight than the stock spring, this did help the trigger pull a bit but to be fair its still pretty bad. Worth noting that there is also a spring on the magazine that you are working against when pulling the trigger, I will replace that at some point.

Barrel stabilization - As part of the design there are two tabs at the receiver end that help to push the inner barrel forward to allow you to clear any pellet jams, this means the "inner" barrel on this rifle flops around inside a false "outer" and has nothing really putting any tension on it or even keeping it in one place vs the scope rail etc. The recommended fix for this is pretty simple really, knock the front sight off and push some thin foam down inside between the outer and inner barrels to stop it from floating around and then push the front sight back on. From all the mods I did I think this probably increased the accuracy the most.

Barrel outer bedding - This one is a little harder to explain but you will see what I am talking about when you have it all apart. The way the outer barrel is held to the large plastic molding (spacer between the stock and the barrel), the receiver and the bottom tube is pretty poor and it tends to wobble around quite a bit. I fixed this by "bedding" it with a hot glue gun which I feel has given the rifle a much more solid and stable feeling in the hand, before this it really used to wobble around a bit and all felt loose. Between this and the above inner barrel stabilization the rifle is now shooting good groups that clover 3 shots into around 8mm ctc.

I haven't really done these with the aim to increase power, more just to actually get it shooting the way it should have out of the box. It is shooting a bit hotter than standard now with the Geco Diablos shooting at 610-630 fps for around 6fpe but the main thing is that it is grouping well now and is much more consistent.

Future mods? Im not sure if I will bother taking this any further but if I did find the time it would probably get a wooden stock, a bulk full kit (maybe hpa?) and a Carbon fiber shroud.

Some before and after grouping pics, and a couple of the rifle.
Lots of airguns

Offline Akzle

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Re: Improving the accuracy from a Crosman 1077
« Reply #1 on: November 11, 2017, 08:52:08 AM »
Nice job man.
if these are the ones i'm thinking of they share the double action from crosmans 357.
co2 benefits from long barrels and expansion chambers, you can open and mod the valve for increased volume which will give higher velo's and potentially give accuracy at longer ranges.