Original mod 50

[junglie]

Can anyone help me with my mod 50?? bought recently & after replacing the mainspring & piston seal noticed that the transfer port size is larger than the bore?(it's a 1980 .22) the rifle shoots harshly & won't make more than 7.5ft/lbs . I suspect some previous owner has drilled the port out too big, does anyone know the correct size for the port? I was thinking of siver soldering an insert the correct size in or welding up the hole with mig & re boring it. Either way it's not going to be an easy fix.

[pennineway.fswo]

Can anyone help me with my mod 50?? bought recently & after replacing the mainspring & piston seal noticed that the transfer port size is larger than the bore?(it's a 1980 .22) the rifle shoots harshly & won't make more than 7.5ft/lbs . I suspect some previous owner has drilled the port out too big, does anyone know the correct size for the port? I was thinking of siver soldering an insert the correct size in or welding up the hole with mig & re boring it. Either way it's not going to be an easy fix.

Hi Junglie
Opening up the port on the 50 must have been a very tricky job performed with a very long drill or reamer down through the cylinder.
It may not be a parallel hole and it will be difficult to silver solder a bush into but not impossible

Early .22 Model 50's were good for about 9.5 ft lbs and the latest one (with extended cocking lever)gave around 10.5 ft lbs in .22, so yours is certainly underpowered. The fact that it is harsh to shoot would point to too large a transfer port but I am unsure what it would normally be. I suspect 3 to 4mm would be pretty close to the factory size
John

[1984]

hi there,
if your thinking of closing up the port a little with a mig, why not un sweat the cylinder off,and attack it that way, but if your bluing is good then it will ruin the blue and have to be reblued afterwards

[junglie]

Thanks john & 1984 for the feedback. I guessed the standard port size should be about 4mm & the blueing on this one is 99% perfect too. I am going to strip it again & measure the actual size with plastigauge. I would have been happy with 10ft/lbs so wasn't expecting miracles. The gun is still very accurate & I'm going to re-fit a new leather piston washer too to slow down the piston first before more drastic solutions are tried, as it's running a ptfe one now, i suspect the barrel may have been removed to drill it out from that end if that's what has been done.

[keith66]

I had a similar problem with a BSA Standard a few years ago, it was very low powered & upon stripping it down it could be seen that the transfer port had been enlarged from the piston end to nearly half its depth to a diameter of approx 5/16". After much head scratching i got the size from a long piece of dowel rod knocked into the hole from the rear & turned a tranfer port bush from a piece of brass. After checking it was dead level with the cylinder end this was set in loctite engineering adhesive. The rifle now shoots much better!

[gingernut]

I had one like this and I could never get it to shoot well despite its good looks so sold it.
Mind you I cant fix things so good luck as you seem to be on it.
And would people stop drilling out transfer ports please!

[coburn]

Before stripping I'd suggest dry firing with the PTFE washer, then re chrono.

I've often found that PTFE washers need this before performing properly.

[Hsing-ee]

It is definitely the PTFE washer that is causing the problem. Had the same experience when I fitted one to my HW35. No-one in their right mind would open up the transfer port on a Original 50, far too much work.

Best fit a leather washer and see what happens.

[coburn]

Whilst I agree that it may be the PTFE washer to blame and returning to the leather previously fitted may be a good idea.

I fitted a TR Robb one to my HW55 to replace the leather washer that was in it.

I find the ptfe washers easier to size to the cylinder than leather washers and not so prone to dieselling. I chronoed the 55 at the weekend over five shots the spread was from 797 to 811fps with an average of 804fps with Hobbies for an energy of 10ftlbs, slightly up on the previous leather washer and more consistant.

[Hsing-ee]

Whilst I agree that it may be the PTFE washer to blame and returning to the leather previously fitted may be a good idea.

I fitted a TR Robb one to my HW55 to replace the leather washer that was in it.

I find the ptfe washers easier to size to the cylinder than leather washers and not so prone to dieselling. I chronoed the 55 at the weekend over five shots the spread was from 797 to 811fps with an average of 804fps with Hobbies for an energy of 10ftlbs, slightly up on the previous leather washer and more consistant.

Thats excellent consistency, perhaps the Original 50 has a slightly bell-shaped cylinder which won't work with the PTFE?

[junglie]

Thanks for all the advice, I re-fitted the leather piston washer turned inside out & soaked in silicone oil to swell it over a couple of weeks as i haven't found some suitable thickness leather to make a new one yet . I left the thin ptfe washer in place too to shorten the stroke. This has made it much nicer to shoot & raised the power to 8.5ft/lbs, but the port is about 6.5mm so will have to be sorted to get it running as I want it, just going to shoot it for a while first & decide what option to reduce the port size ,on the plus side I'm getting pretty quick at stripping & rebuilding mod 50's ;-) I wish people would'nt drill them out too!! Going to persevere with this one though as it shoots very accurate.