UK Crosman 1377 now restricted to 495 FPS - like Canada

[Zeroexpo1]

Hi Guys,

I've just bought a brand new Crosman 1377 and noticed it's restricted to 495 FPS like the Canadian version. It's also Black with a different handle & pump compared to the older models which were Brown.

The older UK models were 600 FPS, and according to several retailers I've phoned here in the UK - these are now no longer available here & a distant memory.

Only the 495 FPS models are now available here as per the image below.

Does anyone know what Crosman have done to restrict these, and is there a workaround to bring it up to 600FPS which is still below the UK limit?

As it stands, out of the box, this pistol will achieve only about 3.5 ft/ib at best, but I remember my older one doing around 5ft/ib in stock form.



https://i.ibb.co/gmLV4Vk/20191110-124344.jpg
upload

[Modski66]

The valve has a small hole on the underside; when the hammer knocks open the valve, most of the released air goes up, through the port and propels the pellet, the rest of the air vents down into the frame.

The 'wasted' air is what limits the pellet fps. What anyone chooses to do with this information is up to them, I am just explaining how it works...

[harvey_s]

The valve has a small hole on the underside; when the hammer knocks open the valve, most of the released air goes up, through the port and propels the pellet, the rest of the air vents down into the frame.

The 'wasted' air is what limits the pellet fps. What anyone chooses to do with this information is up to them, I am just explaining how it works...

Actually it's on the end with the valve stem...

[Modski66]

Mine was quite old, so it has obviously been re-positioned, easier to get at?.

[TonyL]

The fix has been posted on here in the past. I'm hopeless at links and stuff, but a search should reveal the results. Seem to remember it involving tapping and fitting a screw in there with some thread lock.

Another fix might be the flat top piston conversion available from G-Mac. Guessing that this wouldn't have the bleed hole. Apparently, with the extra volume gained on the pump stroke, 7 pumps with the flat top conversion equates to ten with the standard set-up (without the bleed hole).

Hope this helps.

By the way, I love the looks of the later black models with the chunkier forend.

[TonyL]

@ Zeroexpo1. I've revived that old thread which you should find useful.

And a very warm welcome to the forum.

[--ped--]

the bleed hole on early 1377's was underneath with the .22 having flats on the stem
a flat top works because it is more rigid so doesn't deflect as much under load but mainly because it's adjustable and head space can be eliminated
shimming a std cup and shaving the valve nose will give similar results to a ftp up to 1500psi

[Zeroexpo1]

Great info' so many thanks guys.

I keep seeing a lot of aftermarket transfer ports available for the 1377; do these entail drilling the barrels, drilling the actual component, or are they plug n play?

Are they generally a worthwhile investment, or am I better just keeping the transfer port stock?

I've read a few things about an ideal size for TP, then going bigger makes things worse. Is this true?

[TonyL]

Great info' so many thanks guys.

I keep seeing a lot of aftermarket transfer ports available for the 1377; do these entail drilling the barrels, drilling the actual component, or are they plug n play?

Are they generally a worthwhile investment, or am I better just keeping the transfer port stock?

I've read a few things about an ideal size for TP, then going bigger makes things worse. Is this true?

It's not something I've played with. Some of our other friendly chaps will be in the know. And details given on other threads. I think they're pretty much fit and done. And, yes, like just about any gun, once you've found the largest ideal size, returns will then drop off once you go larger.

[harvey_s]

Great info' so many thanks guys.

I keep seeing a lot of aftermarket transfer ports available for the 1377; do these entail drilling the barrels, drilling the actual component, or are they plug n play?

Are they generally a worthwhile investment, or am I better just keeping the transfer port stock?

I've read a few things about an ideal size for TP, then going bigger makes things worse. Is this true?

Yes, and proved by testing.
2.9 - 3.0mm is the optimum size, going larger will just lose power.

But, you're wasting your time unless you plug the vent hole first

[--ped--]

about .132" is the ideal port size for them

[Zeroexpo1]

So, when people say the transfer port is smaller in the restricted Canadian/UK models - are they only referring to the exhaust hole being smaller, IE the internal diameter.

In other words, the physical dimensions of the actual component are the same between the Canadian & American transfer port and it's only the exhaust hole that's smaller?

I don't want to be drilling holes in barrels because the physical dimensions are different, hence my question.

Hope I'm making sense.

[harvey_s]

about .132" is the ideal port size for them

You'll be on the downward side of the curve at that point.
Not by much, but a noticeable amount.
And even if it was the ideal size - I'd like to see you drill it I've never seen a 17/128" drill bit!

[--ped--]

to drill it that size you'd sharpen a drill so it cuts off centre or stone a larger drill bit till it was the right size
the data I have came from a gunsmith in Canada and is direct from crosman and relates to air not co2 guns they produce and shows port sizes to fpe
granted the chart is more for pcp use but the principles of air flow and ratio's is the same it's just your only getting one bite of the cherry with a pump up
I'm not saying your results are wrong just that maybe that they were correct to your gun only what was the set up pistol rifle -flat top std piston
crosman put a lot of development into port sizes and whilst they have gone for a one size fits all in the co2 and pump guns(UK/Can pistols use smaller)due to cost

[harvey_s]

to drill it that size you'd sharpen a drill so it cuts off centre or stone a larger drill bit till it was the right size
the data I have came from a gunsmith in Canada and is direct from crosman and relates to air not co2 guns they produce and shows port sizes to fpe
granted the chart is more for pcp use but the principles of air flow and ratio's is the same it's just your only getting one bite of the cherry with a pump up
I'm not saying your results are wrong just that maybe that they were correct to your gun only what was the set up pistol rifle -flat top std piston
crosman put a lot of development into port sizes and whilst they have gone for a one size fits all in the co2 and pump guns(UK/Can pistols use smaller)due to cost

Mmmm.... I'd like to see you grind an off-centre drill to cut .132" in less than a dozen tries
My figures relate directly to trail and measurement on precisely the gun questioned, not generic results for PCP's at much higher pressures, which was pretty much what the OP was asking .
The piston pump head used was the standard one.
If Crosman put in any development to port sizes on their pump-ups then they did not use the data they had to maximise the efficiency.
However, if the OP wants to use generic data and trial and error to get the TP hole to .132" - I'd certainly be very interested to see what figure he gets - It would be interesting.