Author Topic: Barrel problem  (Read 483 times)

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Offline Baggawind

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Barrel problem
« on: February 06, 2018, 11:35:02 AM »
I went to the zeroing barn the other day, I wanted to test the Blue Meanie prior to taking it to the HFT club. It now has an Air Arms S200/CZ barrel fitted. First four shots at 45 yards = cloverleaf. Great , I thought. Then things went pear shaped. The groups started to open up , even at 30 yards. I was using AA field and JSB Exact so, to my mind, didn,t think it could be the pellets. So I gave up and drove home to check the barrel. Now the barrel was fitted with a blast diffuser and covered with a Carbon Fibre shroud. Maybe that,s upsetting the harmonics, I thought. So off came the shroud and on went a silencer in its place. While I had the barrel off I check for tight/loose spots. What surprised me was how tight the choke was , it took a lot of effort to push a pellet passed it. So then I checked it for accuracy in my back garden. Only 21 yards but it gives me an idea of how it should perform. JSB and AA,s , not that good. Then I remembered the Mapid, it has a choked BSA barrel and it loves H&N Sniper Mediums , so gave them a try. Result, same holing. Now I have to try it out at longer ranges . Bloody airguns ,Eh ?

Offline IceBlerk

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Re: Barrel problem
« Reply #1 on: February 06, 2018, 01:20:22 PM »
Why do you think the groups were so tight on the first three shots before opening up so much?

Did you put the shroud back on and still get decent groups with the H&Ns?
..........so I packed up and went to the pub.

Offline seagate

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Re: Barrel problem
« Reply #2 on: February 06, 2018, 09:33:54 PM »
Both my neighbour and myself have owned a few  177 cz barrelled rifles , all but 1 favoured a jsb ammo. The pig in the poke was a well used example that thrived on hn ftt.
I plink , therefore I am.

Offline Baggawind

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Re: Barrel problem
« Reply #3 on: February 07, 2018, 03:05:45 PM »
Well, that,s got me completely baffled. I took the rifle back to the zeroing barn this morning. Using Sniper Mediums at 32yards = one hole. 45 yards = 10mm edge to edge. Great, I thought then as before , things went tits up. The groups started to open up dramatically then dropping. Bollocks, back home I go. First thing I checked was the pressure left and the velocity. 120bar and 10.4fpe. ??? Somethings wrong. The last time I did a shot string test I got 60  VERY consistent shots at 11.4fpe from a 170bar fill. So I decided to fill the rifle to 200bar and test again. Result? 12.0fpe and 55shots down to 145bar. Can,t make it out as I haven,t altered anything inside the rifle. Bloody air rifles  >:(   

Offline seagate

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Re: Barrel problem
« Reply #4 on: February 07, 2018, 10:13:14 PM »
Have you got any grease/lube on any of the internals , I'm thinking viscosity/low temperature type of thing.
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Offline Baggawind

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Re: Barrel problem
« Reply #5 on: February 08, 2018, 12:06:54 PM »
No, no lubricants. The hammer is fitted with Delrin bearings. The only thing I can think of is valve extrusion , a common fault on Air Arms rifles. That is when the valve material starts to creep into the valve throat, upsetting the airflow. It only takes 0.2mm to do it. It drops the power resulting in a higher pressure needed to maintain the same performance. Thing is though, my valves are based on the BSA/Falcon design and are made from Delrin , unlike the AA valves so should be more resistant to creep. Oh well, i,ll pull it apart when I feel like doing so, just to check. But for now it,s back to re-zeroing , i,ve got an HFT shoot at the weekend.

Offline IceBlerk

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Re: Barrel problem
« Reply #6 on: February 08, 2018, 12:14:18 PM »
Good luck with the Blue Meanie, Baggy.

............... i,ve got an HFT shoot at the weekend.

And good luck with that HFT! Don't forget to let us know how you get on.
..........so I packed up and went to the pub.

Offline seagate

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Re: Barrel problem
« Reply #7 on: February 08, 2018, 06:22:56 PM »
    It must be frustrating gggrrr.

  Good luck with the comp. :)
   

 
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Offline Baggawind

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Re: Barrel problem
« Reply #8 on: February 09, 2018, 10:34:13 AM »
It must be frustrating gggrrr.

You got that right. trouble is, this was the rifle into which i fitted a gauge and it was a bas?@8d to stop leaking  ??? >:(
« Last Edit: February 09, 2018, 03:48:56 PM by Gambo »

Online Gambo

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Re: Barrel problem
« Reply #9 on: February 09, 2018, 03:47:37 PM »
Errrr broken quote in the above post........please let me help you with that Mel. ;)