Air Arms Owners Club

So after seeing the HFT 500 and wanting one (but not having the cash to buy one at the moment)

I decided that I would go about converting my MPR

I was able to purchase the longer (HFT 500) 480mm cylinder tube and the spacer to replace the barrel band from Julian,
The spacer also has a little rubber grommet which supports the barrel a little, so the barrel is now semi floating I guess
Cylinder Tube (JT335FT) was just over £50
Spacer (to replace barrel band) (JT486) was about £10
Grommet (sits in spacer an supports barrel) (E870)
The grub screw from your existing barrel band can be used to fit the spacer.

Now the tube is longer than the barrel and the standard AA MPR muzzle break dosent fit, but it is easily modified by elongating the flat section on the bottom of the muzzle break by about 2-3 inches, I just took it to a local engineers who did it there and then with a milling machine in about 2 minutes , they only wanted a couple of quid for it but I gladly have them £10 as it would have been tricky and time consuming to do it with a file or something. Now the barrel with the muzzle break on it about 3inches longer than the tube and is nicely balanced too.

While I was adding the cylinder I chose to alter the firing pot settings, I have set the firing pot to 52mm (which is as far as it will screw in) and I have wound the Venturi screw ,almost, all the way out, it was just over 12ft lbs with it all the way out so just needed a little tweak to bring it down to 780 FPS with AA 8.4 grain pellets .

Not had a chance to do a full shot string yet, but I reckon that the increased air capacity and the different firing pot settings will improve the consistency and lengthen the sweet spot, so rather than filling to 160 and getting 40 good shots,

I may be able to fill to 150 and get 50 very consistent shots.

I recon that this is probably the easiest and relitively cost effective (£60-70) way to get more consistency out of you rifle without regulating it. The proof will be in the shot string hopefully! What I should have done was to shoot a full shot string before I made the changes so I could compare them but hopefully some of you on here may be able to compare it to "standard" settings.

Will add pictures later and will be sure to show the shot string results as soon as I get round to it.

More pics

got your mail mate but above is showing just fine now, not sure if the fault mas me (on my tablet) but no need to re-post!

looks good but personally i would have tried to get the muzzle brake ending flush with the cylinder.

avfc1982 wrote:looks good but personally i would have tried to get the muzzle brake ending flush with the cylinder.

Yeah, I was going to get UK Neil to make me a custom barrel extension but I read on here somewhere that he has recently retired and sold all his equipment. So this is just a diy job for now, but may get something made up in the future.

It looks ok for now and am more concerned with getting a little more consistency out of it.

If it stops raining for more than 5 minutes I will do a full shot string later.

I bought an mpr of a friend who fitted the fac cylinder to his mpr
And had a custom.muzzle break made so it finish flush with the barrel .
It's not the best picture but it's all I had on the phone

Stoohundred wrote:
While I was adding the cylinder I chose to alter the firing pot settings, I have set the firing pot to 52mm (which is as far as it will screw in) and I have wound the Venturi screw ,almost, all the way out, it was just over 12ft lbs with it all the way out so just needed a little tweak to bring it down to 780 FPS with AA 8.4 grain pellets .

Not had a chance to do a full shot string yet, but I reckon that the increased air capacity and the different firing pot settings will improve the consistency and lengthen the sweet spot, so rather than filling to 160 and getting 40 good shots,

I may be able to fill to 150 and get 50 very consistent shots.

I recon that this is probably the easiest and relitively cost effective (£60-70) way to get more consistency out of you rifle without regulating it. The proof will be in the shot string hopefully! What I should have done was to shoot a full shot string before I made the changes so I could compare them but hopefully some of you on here may be able to compare it to "standard" settings.

With the pot set at 52mm I'd be amazed if you had a useable sweet spot at all.

I'm guessing that you'll just have a massive inconsistent power curve....... But let us know!