Username:

Password:

Author Topic: Crosman 1377 full mods  (Read 317 times)

Offline Mintie

  • Hero Member
  • *****
  • Posts: 1319
  • Age: 34
  • Location: Auckland/Hawkes Bay
  • Mana 30
    • View Profile
Crosman 1377 full mods
« on: August 31, 2018, 11:26:52 AM »
I have been sitting on a 1377 project for someone for a while and decided to get onto it yesterday. The build is a basically brand new Crosman 1377 pistol with the following parts that he had imported direct to me.

18" Crosman .177 barrel
Crosman Steel breech
Hawke Medium height match rings
Leapers 3-12x32 Bugbuster scope - The new model with side focus
Alliance Hobby - Stainless screw and pin kit
Alliance Hobby - HST adjuster
Alliance Hobby - High flow transfer port
Alliance Hobby - Flat top piston
Alliance Hobby - 2 stage trigger kit
Alliance Hobby - Barrel band (to allow a longer barrel)
Alliance Hobby - Hammer to suit the 2 stage trigger

First I did a run over the chrony at 1 - 15 pumps to see how it performed in a factory state. These tests were run using the Geco 6.94 gr pellets.

1- 178 fps
2- 288 fps
3- 358 fps
4- 408 fps
5 - 446 fps
6 - 477 fps
7 - 497 fps
8 - 520 fps
9 - 547 fps
10 - 564 fps
11 - 566 fps
12 - 591 fps
13 - 591 fps
14 - 602 fps
15 - 610 fps

The strip down was fairly simple, I have resealed a few of these before so I knew the process well. A few tricks for anyone else wanting to do this, The valve has to be pushed from the rear of the tube to come out the front of the tube (the barrel works well for this), The roll pin can be a pain but comes out easily if you use a vice or have a proper sized punch, use a T5 torx screw driver on the hidden breech screw - it gives a much better grip than the allen key.

The only parts we were keeping from the original organ donor was the empty tube, the grips and the pump arm and linkage.  The tubes on these ALWAYS needs a bit of a debur along the lever opening and around the holes for the pivot pin, if you don't do this you will destroy the seals as you reassemble it all.

The reassembly was fairly basically in the reverse of disassembly but with the new parts, the Alliance flat top vale and piston are not adjustable which makes it easy to install but I do wonder how close the tolerances are as this match generally needs very fine tuning to get right. The screw and pin kits comes with a solid roll pin to replace the pivot roll pin which is a much better design and will wear much less, it wasn't quite a perfect fit and needed some slight adjustment of the holes to get it to fit but its now a solid fit with cir-clips holding it in place. The newer style pump arm the donor has seemed to interfere with both the new pivot pin and the new barrel band so it needed a few mm removed in a couple of spots to get it right.

The 2 stage trigger kit is a massive improvement over a standard trigger! It is a proper 2 stage trigger with adjustable 1st and 2nd stage and adjustable weight. make sure you follow the instructions from Alliance when fitting this as there are a few quirks to getting it right.

Once it was all together it was time for a few photos for the owner and a test over the chrony. It was a little disappointing to find the increase in velocity wasn't as much as I was hoping for but it does seem to be building pressure quicker than without the FTP and FTV with it getting more velocity at 10 pumps than it used to get at 15 pumps in stock form.

1- 38 fps (may have been a bad read)
2- 322 fps
3- 412 fps
4- 464 fps
5 - 509 fps
6 - 545 fps
7 - 573 fps
8 - 580 fps
9 - 596 fps
10 - 627 fps
11 - 644 fps
12 - 648 fps
13 - 677 fps
14 - 682 fps
15 - 687 fps

It seems to be holding a bit of air after each shot above 13 pumps so I will open it back up and change the valve spring out for something a bit lighter and after a bit of reading I might swap the TP back to the slightly more restrictive standard one to help keep the pulse of pressure a bit higher. The HST adjuster seems to be a bit of a waste with it only adjusting from 0 to "wont cock" in 1/4 of a turn, more HST seemed to lower velocity slightly as well. It did come with another spring in the HST adjuster kit but it looked like a heavier weight and longer spring - might try that as well but from playing with the adjuster a little so far I don't think it will help.

Heavier pellets do seem to increase the energy a bit, at 15 pumps JSB Heavies used to get 493 fps for 5.58fpe where they now get 600 fps for 8.27 fpe. The success I have read from other people show that this setup should be up in the 11fpe range so more tuning to come...
Lots of airguns

Offline irwanz

  • Newbie
  • *
  • Posts: 10
  • Mana 1
    • View Profile
Re: Crosman 1377 full mods
« Reply #1 on: August 31, 2018, 02:26:48 PM »
Aaahh Mintie you did it again mate  :) never get bored with Crosman aye..!! Apart of what you do mate just wondering all the components you had from Alliance hobby....is it hard to bring it all in here ?

Offline Mintie

  • Hero Member
  • *****
  • Posts: 1319
  • Age: 34
  • Location: Auckland/Hawkes Bay
  • Mana 30
    • View Profile
Re: Crosman 1377 full mods
« Reply #2 on: August 31, 2018, 05:32:22 PM »
Aaahh Mintie you did it again mate  :) never get bored with Crosman aye..!! Apart of what you do mate just wondering all the components you had from Alliance hobby....is it hard to bring it all in here ?

Just cant get myself away from them eh!   The parts were ordered by the owner himself and addressed to me, Didn't seem to have any issues with them getting into the country!
Lots of airguns

Offline Dvlnme

  • Sr. Member
  • ****
  • Posts: 395
  • Mana 4
    • View Profile
Re: Crosman 1377 full mods
« Reply #3 on: September 01, 2018, 07:56:16 AM »
thats guna be one expensive 1377 going on what its owner told me he spent on parts eh!but should end up
 being a real nice gun eh!sorting it out will keep you outa the pub anyway mate.
 cheers mike

Offline Mintie

  • Hero Member
  • *****
  • Posts: 1319
  • Age: 34
  • Location: Auckland/Hawkes Bay
  • Mana 30
    • View Profile
Re: Crosman 1377 full mods
« Reply #4 on: September 05, 2018, 10:09:48 AM »
Yeh some money has gone into this build alright. Starting to get somewhere now managing 810fps on 20 pumps and 855fps on 30 pumps with 7.3gr. To get there I had to use half of the Alliance flat top valve and half of the Crosman valve, theory behind taking that route was that the Alliance valve is opened up for max flow with a larger and angled tp opening which is probably best suited for .22, in .177 this is counter productive as you want the least amount of volume between the valve seat and the pellet so the blast of air remains as high in pressure as possible.

I was also starting to retain air at around 13 pumps so decided to swap the valve spring out for something lighter, as suggested on one of the threads I read the factory spring from the trigger sear works well once set. Now it needs the hammer tension taken off the valve by cocking it before pumping it up otherwise it dumps the air from each pump, I might play with a softer hammer spring to see if it can reduce the need for that and still hit the valve hard enough to get this power.

On an 18" barrel I think this is probably around as good as its going to get, with 30 pumps on JSB heavies its getting around 13.3fpe. 20 pumps on the same pellets was getting 11.6 fpe so I would probably shoot it at around that.
Lots of airguns