HFT 500 air blast

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Archer50
Posts: 174
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Location: Perth

HFT 500 air blast

Mon Aug 08, 2016 10:08 am

I’m new to Air Arms guns and I’m looking for some advice please. When shooting my HFT 500 I suddenly got a really strong blast of air in my face. I checked, and as I expected the breech o-ring was gone, so I replaced it. There was still a lot of air so I checked the transfer port o-ring and that was split, so I replaced that as well. There is still quite a noticeable blast of air going forwards from where the barrel leaves the bolt housing, but not back from the breech. I double checked the o-rings and they seem fine.

Is this a blast of air forwards from the barrel mounting acceptable? I’ve read somewhere that Air Arms say that a small amount of air escaping is normal. If not, does anyone know what might be causing it, and how I might fix it?

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Roger5
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Re: HFT 500 air blast

Mon Aug 08, 2016 10:51 am

You seem to know what your doing, have you had the barrel out? I would check to see if transfer port lines up with it, look up hole in bolt housing. Rog

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Archer50
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Joined: Mon Jun 20, 2016 5:06 pm
Location: Perth

Re: HFT 500 air blast

Mon Aug 08, 2016 4:49 pm

Thanks Rog. I haven't taken the barrel off yet - I hope to have time to do that in the next few days. I've just read on another forum that the the barrel has through-holes where the three upper grub screws locate :o . Anyone know if this is true? I hope not - I assumed the grub screws located into depressions, not holes. If they really are holes right through to the bore, I think I might have just found the problem (not to mention a crazy piece of bad design).

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Roger5
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Re: HFT 500 air blast

Mon Aug 08, 2016 5:42 pm

Doubt very much that holes go through into bore, depressions more likely, but as said have a look from under bolt housing, you might find it dsnt line up, then just tweak until it does, must admit I have only taken anti tamper out of Hft for a mate, you will probably find that there is a grub screw under bolt housing holding barrel as well as the ones on top. Rog

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Mark112
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Re: HFT 500 air blast

Tue Aug 09, 2016 10:29 am

Hi,

As above. The two grub screws on top should push the barrel down tight against the transfer port hole thus sealing it. Not sure what the bottom grub screw is for as it is only on anti-tamper models (earlier S4*0 without a/t don't have it fitted) and to me it would seem to open a gap up so personally I would only nip this one up lightly if at all. As it sounds like A/T has gone I would fit the barrel to the bolt housing as a separate sub assembly prior to fitting to the rest of the action that way you can ensure the transfer port hole fully align.

Mark
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Archer50
Posts: 174
Joined: Mon Jun 20, 2016 5:06 pm
Location: Perth

Re: HFT 500 air blast

Tue Aug 09, 2016 11:38 am

Thanks guys. I’ve just spent a happy couple of hours with the gun in the workshop (ok, the kitchen) and I think I've found the problem. As Mark said, the grub screws (three in an HFT 500) push the barrel down onto the transfer port hole. I may be wrong, but I think the S400/500 transfer port is part of a separate brass piece that can be rotated but the port of the HFT 500 is directly drilled into the steel barrel and its alignment can’t be adjusted, as far as I can tell. Fortunately, mine seems to be correctly aligned, but even with the grub screws tightened as far as they could safely go, it’s impossible to form an air tight seal – and with the hard steel barrel, I don’t see how it ever could be without help of some sort.

I did consider Hermetite-style sealant (and I might have to come back to that idea), but in the end I used good old PTFE plumbers tape, and at the moment, it seems to be working perfectly, with no detectable air blasts anywhere. If anyone else wants to try it, I found that the best way was to wrap a single, unbroken piece of tape from the breech to about where the barrel leaves the housing, lubricate it very lightly with o-ring grease, and pick the tape out the transfer port very carefully with a wooden cocktail stick after you have 'screwed' the barrel in place.

I’m still not sure whether this is a manufacturing fault on my particular gun, or a design flaw and I’d be interested to know if anyone else has found this problem, and how they solved it. I’d also be interested to know if I’ve done anything silly or missed anything obvious – like I say, I’m a newcomer to Air Arms.

Alan

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TenMetrePeter
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Re: HFT 500 air blast

Tue Aug 09, 2016 11:59 am

The metal to metal design seems to have passed the test of time but if you gan get plumbers tape in the clearance between barrel and housing and it doesnt all get squished out it sounds like the tolerances are too wide.
But if it works, its ok. I might have used bearing fit loctite. We used that to fix keyless sprockets to shafts in the car factory (conveyors not cars!) That would be permanent!

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Archer50
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Location: Perth

Re: HFT 500 air blast

Tue Aug 09, 2016 12:49 pm

TenMetrePeter wrote: if you gan get plumbers tape in the clearance between barrel and housing and it doesnt all get squished out


You can get about three full wraps in the gap and, provided you use a smear of grease, the barrel still goes in and out without too much trouble.

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TenMetrePeter
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Re: HFT 500 air blast

Tue Aug 09, 2016 9:48 pm

I'll bow to the experts but that doesnt sound like an engineering sliding fit to me. Is it the original barrel?

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Mark112
Posts: 210
Joined: Mon Feb 16, 2015 5:25 pm

Re: HFT 500 air blast

Wed Aug 10, 2016 10:58 am

Glad you got it sorted and thanks for feeding back your solution.
S410C .177 Regged - MTC Viper 4-16 x 50
S410K .177 Regged - Hawke Nite-Eye 4-16 x 50 AO IR
S410K .22 - Hawke Sport HD 3-9 x 50 AO IR
Logun Mk1 .22 - AGS 3-9 x 40
Theoben Taunus .22 - Simmons 4-12 x 40 AO
BW1911R2
Walther CP99
Webley Premier .22

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