Hi there,
I have recently made some modifications to a Relum 322 which I would like to post so that others can possibly do the same if they wish.
My Relum was originally my fathers gun which he bought new in the early 60's, and as a young teenager i learned to shoot with it - The internet suggests these guns are Hungarian donkeys and useful for nothing more than hammering fence posts in but for some bizarre reason i quite like it and I've spent significant time making it "good".
The rifle has a 26mm chamber with a stroke of ~80mm delivering a swept volume of 42474 cubic millimeters, the transfer port to the loading tap is on the diagonal and 5mm in diameter with a length of 28mm giving a transfer port volume of 550 cubic millimeters. The static compression ratio is 77:1 which is probably responsible for some of the guns poor performance especially with synthetic seals.
This is the exit of the 5mm transfer port into the loading tap:
My cylinder was slightly out of round and somewhat scared from decades of use, i honed this (if honed is appropriate for such a crude process) with a tightly bound roll of scotchbrite on a rod attached to a drill. The results were better than expected and restored the finish a great deal.
After experimenting with a parachute seal from a HW77 i decided that my out of round cylinder was not going to work, hereafter i used O-ring seals
I machined several brass piston heads to mount on the standard carriage. My final dimensions for the head is 25.5mm OD head, 8mm deep with a single 20mm ID x 3mm cross section nitrile O-ring. The O-ring sits in a slot which is 3.05mm wide and has a 20.75mm centre.
This is a similar piston head i experimented with, the final is the same bar the above dimensional changes:
The carriage has a 7mm hole where the rivet previously fastened, the brass piston head is bolted though using a slotted head bolt i machined and secured with a nyloc nut
At the other end, the spring has been replaced with a mainspring from a Meteor, I machined a new back stop to have 13mm of extra preload and an integrated spring guide.
The full inside assembly:
This resulted in a velocity of 428ft/s (426, 427, 428, 428, 428) with Superdomes giving 5.9 ft lbs - however it also gave horrendous noise, vibration and wear to the end of the piston head. This was the massive transfer port causing insufficient back pressure to stop the head to slamming into the end stop.
To prevent this i needed to increase the compression ratio, this was done via sleeving the transfer port. As stated the transfer port is 28mm x 5mm, i machined a sleeve with a 2.5mm ID x 25mm long 4.95mm on one side and 5.05mm on the other. The sleeve has a 60 degree entrance and exit.
Fitting this pin on a diagonal from inside the chamber was a challenge!!! I used a long rod, a dead centre attached to a metal rod, soft blow hammer and a lot of patience.
Sleeve half fitted:
Sleeve fully inserted and seated:
The exit of the sleeve is visible behind the tap loader through the barrel:
The fitting of the sleeve has had a dramatic effect, not only does the gun not try to dismantle itself on firing the power output has risen substantially. I don't have a chronograph with me but whereas at 5.9ft lbs i was burying pellets tail deep into a piece of pine i am now putting the tail between 5 and 8mm below the surface. I suspect in the region of 10ft lbs but i will report back when i have had it tested with a chronometer.
Don't get me wrong, it is still a very agricultural gun and the cocking effort with 13mm preload is heavy but i am very happy with the result.
Last to do is to re blue the barrel and sand & oil the stock.
I must say thanks to a member on this forum called T20, whilst he did not help me directly his thread on improving the B2 rifle gave me a good nudge in the right direction with regards to sleeving the transfer port to increase compression ratio.
Regards,
Tom