modding a crosman 1377

[riverboats]

I have a crosman custom shop 1377 carbine showing up soon. I'm guessing the only difference on these guns and a Walmart one is the steel breech and the lw barrel.

Question is what can be done to a pumper? I plan on the adjustable trigger spring and those smalls washers to shim the trigger\sear area if it's sloppy.

What other mods can be done to pumpers,  I've only messed co2 and PCP guns. I know I don't care a bit about power mods if it means pumping 18 times. 10 pumps is enough, 8 is better.

As I said never dismantled a pumper very far, if I dig into it, am I going to need a spring compressor device?

[happymecanic]

A lot can be done to a pumper, particularly the 13xx platform. Here are some suggestions for you to start with:

Flat top piston and valve: will improve the pumping efficiency, you may need to pump only 8 or 9 times to get the same fps as before the mod. I've even seen more fps at 8 pump than 10 before the mod. The valve itself can be extensively modded to gain even more power. Do a little search here on the forum, lotsa good stuff!
Steel breech kit / metal barrel band: will stabilize the barrel (thus helping to improve accuracy), and give you a good mounting point for a scope or other optics.
Extended / flow through bolt probe: will make the pellet seat past the transfer port, allowing better flow and probably help to gain some fps
Lothar Walter 10.1'' barrel: will greatly improve accuracy.
De-burring / polishing of the pump tube: will help to insert the piston and valve without damaging the O-rings / seals.
Polishing of the hammer and trigger contact points: will facilitate the cocking and firing of your gun.

Those are some common mods, but there's more that can be done.

And no you don't need a spring compressor, the hammer spring is very easy to tame by hands. Just keep your thumb on the rear cap when you remove the screws. HTH

[Gipper]

There is a thing or 2 that can be done to them that is for sure.  Here is mine.

Brian

[WyoMan]

Hi Christopher,

Some ideas to give you some ideas...

http://www.gatewaytoairguns.org/GTA/index.php?topic=123428.0
https://www.gatewaytoairguns.org/GTA/index.php?topic=128347.0
https://www.gatewaytoairguns.org/GTA/index.php?topic=129229.0
http://www.gatewaytoairguns.org/GTA/index.php?topic=124905.0

You can go as far as you want. And, you don't have to do everything right away. I'm six years into now, LOL 

Wyo

[PBguns]

Let your imagination go wild. Build something you haven't seen done before. Have fun with it!

[Mosin Marine]

There is a thing or 2 that can be done to them that is for sure.  Here is mine.

Brian

That is downright beautiful!

[B-Roc]

Let your imagination go wild. Build something you haven't seen done before. Have fun with it!

Wow.  That is a cool build 

[kj]

if you want the best possible trigger install a p-rod trigger group

[JMJ in NC]

Short list:
- flat top adjustable piston and matching valve
- extended probe bolt
- 1701P 2-stage trigger
- 2289 forearm

Plenty of things to do on these guns.

Uploaded at Snapagogo.com

Uploaded at Snapagogo.com

JMJ

[Tack Driver 10]

Some of mine
More fun than a barrel of monkeys

[Mosin Marine]

Some of mine
More fun than a barrel of monkeys

What is the average investment of those? So i can save up lol

[Tack Driver 10]

Some of mine
More fun than a barrel of monkeys

What is the average investment of those? So i can save up lol

Not sure how much my gun addiction costs but I do a lot of my own work so I can keep the cost down and get custom quality.
Most of my guns have LW barrels and just the barrel costs around $100+ but to me are well worth it.

[Mosin Marine]

Some of mine
More fun than a barrel of monkeys

What is the average investment of those? So i can save up lol

Not sure how much my gun addiction costs but I do a lot of my own work so I can keep the cost down and get custom quality.
Most of my guns have LW barrels and just the barrel costs around $100+ but to me are well worth it.

I really like the second on from the bottom with the AR style butt stock! Looks like it would be a treat to take out best shooting!

[anti-squirrel]

Arguably, the best starting point on the 13xx pumpers is cleaning up the trigger and then adding something to quiet the clack-clack of pumping.  An LDC is a fine addition as well.  But there's a reason they are considered "Lego" guns.  A carbine stock makes for a functional compact rifle, and with your steel breech and LW barrel, you have a potent little pesting tool.  I do recommend reinforcing the pump arm and replacing the roll pins just because it does increase the durability.


There are things you can do down the road for more power, but if I were in your shoes, I'd just shoot and see how you like it as-is first, then figure out what you want to do.

[Tack Driver 10]

Arguably, the best starting point on the 13xx pumpers is cleaning up the trigger and then adding something to quiet the clack-clack of pumping.  An LDC is a fine addition as well.  But there's a reason they are considered "Lego" guns.  A carbine stock makes for a functional compact rifle, and with your steel breech and LW barrel, you have a potent little pesting tool.  I do recommend reinforcing the pump arm and replacing the roll pins just because it does increase the durability.


There are things you can do down the road for more power, but if I were in your shoes, I'd just shoot and see how you like it as-is first, then figure out what you want to do.

Lego guns for sure. I don't modify guns because I don't use most of the parts.
I order a trigger, pump tube and steel breech from Crosman. I have several NOS 766 pump arms that are super sturdy that I use.
The rest of the parts I can make from scratch or modify from existing parts.

All the guns above use different pump tubes.
From top to bottom:
MK tube (3/4" x 4" stroke) 766 pump arm
66 tube (5/8" x 4" stroke) 2100 pump arm
2100 tube (5/8 x 4 3/4" stroke) 766 pump arm
13xx tube (5/8" x 3 1/2" stroke) NOS 760 pump arm
Disco tube (3/4" x 7" stroke) 140 pump arm, reinforced

Some brass barrel bands: