FX MKIII BT randomly inconsistent

[aznmistborn]

Hi y'all I'm having accuracy issues with my new MKIII. I got it a couple of months ago and have it tuned for 960fps with Javelin 22 slugs (23grs .218 head).
Then today while I was shooting I started getting pretty bad groups. Prior I was easily putting 5 or more pellets in one ragged hole at 50yards and within an inch at 100.
Today I'd get a couple slugs touch in a separate groups. Two left, three right, one left, 2 right etc. I also noticed that the holes in the target at time were more ragged instead of a nice hole punch in the paper. I'd also have some shots there were just very low, but a few inches at least.
Is there something I should be looking at or checking? I don't know my way around an air rifle yet so please be patient if I ask something dumb.
Thanks

 

[hawkeye69]

I'd suggest that first thing you need to do is check the speed.

 

[Gerry52]

Being that you're shooting slugs, I'd bet you're getting some fouling in the barrel too, among other things.

 

[douger]

maybe you getting some wbble with the slug

 

[Revoman]

Sounds like a barrel/liner cleaning is what might be needed. Most times (not necessarily every time) when accuracy falls off, it needs cleaning. Slugs tend to foul a barrel sooner than pellets. Of course once it's cleaned, it will then take a few shoots to 'dirty it up' enough to continue with the good groups again.
mike

 

[aznmistborn]

Hey y'all so I just went to chrono and test.
It was
834
748
830
893
831
768
814
1009
1005
1008
1000
999

When it was in that 750-850 range the gun wasn't cocking properly. Sometimes it would and sometimes it wouldn't. There was also a small mechanical grinding sound when I went to cock it. Then it just stopped and I got those 1000fps strings.

 

[aznmistborn]

Another 20 shots I got

• 999
• 997
• 999
• 998
• 998
• 1000
• 988
• 993
• 994
• 996
• 996
• 989
• 986
• 987
• 994
• 989
• 991
• 991
• 989
• 993

 

[EDventure]

Hey y'all so I just went to chrono and test.
It was
834
748
830
893
831
768
814
1009
1005
1008
1000
999

When it was in that 750-850 range the gun wasn't cocking properly. Sometimes it would and sometimes it wouldn't. There was also a small mechanical grinding sound when I went to cock it. Then it just stopped and I got those 1000fps strings.

I wonder if IHS is maxed out causing cocking issues and inconsistencies.

 

[aznmistborn]

I wonder if IHS is maxed out causing cocking issues and inconsistencies.

IHS?
So this morning after 53 shots. (sorry for the odd number)
1st String (12 shots) A.FPS - 902.9 / SD-102.49 / E.S 261
2nd String (20 Shots) A.FPS - 993.35 / SD - 4.42 / E.S 14
3rd String (20 Shots A.FPS - 998.2 / SD - 3.99 / E.S 16

 

[madeintheuk]

I’m no expert on the mk3, but I had a similar issue with my mk2 when the hammer weight got stuck inside the hammer. If you’re having inconsistencies THAT bad, and your reg is staying constant, I’d look for mechanical issues with the hammer/cocking assembly. There’s been issues with the rear adjusters getting gouged up and hammer damage occurring. If you’re rear block is getting gouged or the hammer is damaged in any way (could be possibly with the grinding you’re hearing while cocking) the. It would certainly cause the issues you’re seeing.
id remove the power wheel, and pull the hammer and weight out to see if there’s scoring or damage.

 

[aznmistborn]

I’m no expert on the mk3, but I had a similar issue with my mk2 when the hammer weight got stuck inside the hammer. If you’re having inconsistencies THAT bad, and your reg is staying constant, I’d look for mechanical issues with the hammer/cocking assembly. There’s been issues with the rear adjusters getting gouged up and hammer damage occurring. If you’re rear block is getting gouged or the hammer is damaged in any way (could be possibly with the grinding you’re hearing while cocking) the. It would certainly cause the issues you’re seeing.
id remove the power wheel, and pull the hammer and weight out to see if there’s scoring or damage.

Gotcha. Can you point me to a good resource on disassembling this thing?
The sounds also completely stopped after shot 7 this morning.

 

[madeintheuk]

This is a good place to start

 

[aznmistborn]

So kept going. Got some more awesome shots then it dropped it again. I looked at the wheel and this is what I see.
I'm not sure how to degass this gun? Its the BT model

 

[madeintheuk]

You don’t need to degas to remove the power wheel

 

[madeintheuk]

But if you insist, the easiest way is to remove bottle, and loosen The rear gauge until air starts to escape. Then wait until the hissing stops. At that point if the gauge can be removed by hand, you’re empty. If there’s any resistance, their is still air in the system.

 

[aznmistborn]

Oh okay wasn't sure. What size allen do I need for this the power wheel? I can't seem to find one that fits.

 

[aznmistborn]

Nvm. I got it. But where does this screw go??

 

[IndyDurtdigger]

If you check out the FX YouTube channel they have a series of videos on MkIII rifles that cover tear down, reassembly, and tuning.
Don't get hung up on the bottle aspect. Also while you have it off the stock I would mark and drill the stock so you can access the front regulator for future tuning without taking it off the stock.

 

[DonaAna1]

There are plenty of videos on youtube to help you.

 

[Nosbigshot]

Hi y'all I'm having accuracy issues with my new MKIII. I got it a couple of months ago and have it tuned for 960fps with Javelin 22 slugs (23grs .218 head).
Then today while I was shooting I started getting pretty bad groups. Prior I was easily putting 5 or more pellets in one ragged hole at 50yards and within an inch at 100.
Today I'd get a couple slugs touch in a separate groups. Two left, three right, one left, 2 right etc. I also noticed that the holes in the target at time were more ragged instead of a nice hole punch in the paper. I'd also have some shots there were just very low, but a few inches at least.
Is there something I should be looking at or checking? I don't know my way around an air rifle yet so please be patient if I ask something dumb.
Thanks

I have the same gun with exact same problems minus the grinding. Did you figure out what was wrong I'm ready to use mine for a boat anchore