HW77 .177 transfer port size

[magnummike]

Hi chap's in 1993 I bought a 77k in .177 with a 25mm piston . Back then most people were fitting OX kits including me Anyway a year later I sold it to a mate and he has had it since then . The other week I managed to buy it back after 19 years and I stripped it . The ox was still in there so degreased etc and plan to fit a standard spring when I get 1 . But all them years ago I cant remember if i opened up the transfer port when I fitted the OX kit , just wondering if anyone knows the standard size so I can check it ATB Mike

[brucegill]

I think it's 2.8mm or something like that. If yours is bigger than 3mm you opened it up

[magnummike]

I think it's 2.8mm or something like that. If yours is bigger than 3mm you opened it up

Cheer's Bruce I'll get the caliper out , fingers crossed E'h

[MattyBoy]

I run all my 77s and 97s with a 3.2mm TP

I have a special "Gold" drill bit just for that job.

3.6mm is still perfectly fine but if it's over 4.0mm then it's sleeve-down time.

JB swore by 4mm so it seems the TP diameter is variable but different sizes will obviously affect the shot cycle considerably.

I like 3.2mm myself

Matty

[Phil Russell]

Could optimal tp size depend on the spring as well?
The mention of the 'Maximiser' reminded me of my own, new in about 1984, HW77k.
The Maximiser tuning kit was all the rage then and I bought one as all the adverts promised me it would transform the feel of the standard rifle. It was my first attempt at any form of tuning so I leapt at the chance. I sweated all morning to get it fitted. I remember the square section spring (Ox??) took a lot of preload and I did not have a compressor of any sort. But I did it ..... all fitted with the minimum of spilt blood.
What a transformation. From a pretty docile but bit twangy rifle I now had a rifle that bucked and jerked around in my grasp. I had no chrono so did not know what it was doing; but assumed it was still within spec. But I hated the firing cycle. Late afternoon I took it apart again and refitted the original spring. All became nice again ... the piston liner and 'debur' carried out as per Maximiser instructions had helped. No more twang and a good sweet firing cycle.
The rifle stayed like that for about 20 years when a chrono check showed power was declining so I put a new standard UK power spring in. A chrono check revealed power ott so spring reduction was needed. No problem.
I have never touched the transfer port.

Cheers, Phil

[Bulsaye]

or .118" if you want the decimal size.

[TonyL]

Could optimal tp size depend on the spring as well?
The mention of the 'Maximiser' reminded me of my own, new in about 1984, HW77k.
The Maximiser tuning kit was all the rage then and I bought one as all the adverts promised me it would transform the feel of the standard rifle. It was my first attempt at any form of tuning so I leapt at the chance. I sweated all morning to get it fitted. I remember the square section spring (Ox??) took a lot of preload and I did not have a compressor of any sort. But I did it ..... all fitted with the minimum of spilt blood.
What a transformation. From a pretty docile but bit twangy rifle I now had a rifle that bucked and jerked around in my grasp. I had no chrono so did not know what it was doing; but assumed it was still within spec. But I hated the firing cycle. Late afternoon I took it apart again and refitted the original spring. All became nice again ... the piston liner and 'debur' carried out as per Maximiser instructions had helped. No more twang and a good sweet firing cycle.
The rifle stayed like that for about 20 years when a chrono check showed power was declining so I put a new standard UK power spring in. A chrono check revealed power ott so spring reduction was needed. No problem.
I have never touched the transfer port.

Cheers, Phil

Hi Phil,
Nice little write up. I'm sure many fell for these kits/springs back then, resulting in harsh firing cycles, probably OTT power and maybe the square edges of the square section springs nibbling away at the precious internals. I just thank my lucky stars that I never fell for them....I stripped and serviced a few rifles belonging to friends, all containing Ox springs. At least two HW35s and a Mercury to two, and all became much nicer once fitted with nice, sensible, round springs.

I know some have posted on here that some of the square section springs, such as the ones HW fitted to the 97 as standard for a while, were actually fine, as they didn't exhibit those nasty, sharp edges.

And, yes, big time. Any tune, on any gun, will be down to balance. So a certain TP size will suit a certain set-up better than another. There will be cases, however, where the standard size is too small or large for any ideal set-up, I bet. And, as Matty Boy says, yes, by the sounds of it, with the 77 you can go right out to 4mm, depending on personal preference. A TP this wide would be a bad move on many guns with longer TPs, due to more lost volume, certainly at our power level.

[brucegill]

I run all my 77s and 97s with a 3.2mm TP

I have a special "Gold" drill bit just for that job.

3.6mm is still perfectly fine but if it's over 4.0mm then it's sleeve-down time.

JB swore by 4mm so it seems the TP diameter is variable but different sizes will obviously affect the shot cycle considerably.

I like 3.2mm myself

Matty

Hi Matty

Do you just drill yours out, or do you ream them as well?

Cheers for the info
Bruce

[greenwayjames]

When asked JB said he used to use a 5/32" drill on FWBs, HW77s etc but advised against doing it unless the rest of the conversion that he did was carried out. He used a 5mm drill for HW80s