Removed the brass firing pot.

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RichieRich612
Posts: 104
Joined: Fri Apr 19, 2019 2:02 pm

Removed the brass firing pot.

Tue Jul 09, 2019 10:31 pm

I removed the tube from the pot which extends into the air cylinder and found my Mpr is more consistent.
There is a tiny bit more of a twang when firing a pellet but it's made a big difference to velocity consistency.
Has anyone here tried this?
Richard

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TenMetrePeter
Posts: 1024
Joined: Wed Jun 29, 2016 5:40 pm
Location: Luton Beds UK

Re: Removed the brass firing pot.

Wed Jul 10, 2019 9:59 am

What did you do with the valve spring S306?
If there wasn't one and you have no reg fitted then that may have been the problem.
The tube adjusts in and out to tension the valve spring. Quite interesting it is consistent at all.

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RichieRich612
Posts: 104
Joined: Fri Apr 19, 2019 2:02 pm

Re: Removed the brass firing pot.

Wed Jul 10, 2019 11:55 am

TenMetrePeter wrote:
Wed Jul 10, 2019 9:59 am
What did you do with the valve spring S306?
If there wasn't one and you have no reg fitted then that may have been the problem.
The tube adjusts in and out to tension the valve spring. Quite interesting it is consistent at all.
The screw in section which houses the valve stem and spring is still there.
Only removed the elongated section which protrudes into the air cylinder.
Richard

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TenMetrePeter
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Joined: Wed Jun 29, 2016 5:40 pm
Location: Luton Beds UK

Re: Removed the brass firing pot.

Wed Jul 10, 2019 12:57 pm

OK thought it was one piece in those.

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RichieRich612
Posts: 104
Joined: Fri Apr 19, 2019 2:02 pm

Re: Removed the brass firing pot.

Wed Jul 10, 2019 1:11 pm

TenMetrePeter wrote:
Wed Jul 10, 2019 12:57 pm
OK thought it was one piece in those.
So did I!
No they are 2 pieces held together with loctite.
There's a faint line roughly 5mm above the threads, just slips off with some heat.
Lot better now.
Richard

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TenMetrePeter
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Joined: Wed Jun 29, 2016 5:40 pm
Location: Luton Beds UK

Re: Removed the brass firing pot.

Wed Jul 10, 2019 2:29 pm

My 6ftlb MPR doesn't have the extension . I’ve never got to dismantle it and they’re so rare there’s no images online either.

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tonyc
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Joined: Mon May 29, 2017 10:55 am

Re: Removed the brass firing pot.

Sat Jul 13, 2019 11:16 pm

I suggest you chrono a full string from 190 bar to 90 bar with and without the pot then you will see how it functions. It's possible if you chrono just a few shots (say 10) you will see more consistency but that will be coincidental depending on the cylinder pressure. Removing the pot shifts the peak of the power curve to a lower cylinder pressure but makes the curve more pronounced by causing the valve to close more quickly at higher cylinder pressures. For example, if you chrono a S400 with and without pot at 120-110 bar, with the pot the velocity is coming out of the sweet spot and falling, without the pot it's still in the sweet spot and relatively flat.

The other effect is the peak power will increase, so anyone removing the pot (or the pot falling off as mine did) from a gun that was running at 11.5ft lbs will probably find it running at 12+. I've no experience with the MPR, just the S400, but the principle is the same. I chronoed several full strings trying to figure out what was going wrong. I had a series of power variations on the S400 which I finally found was caused by the two sections of the pot coming loose and the volume changing before the end section eventually became completely separated.

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RichieRich612
Posts: 104
Joined: Fri Apr 19, 2019 2:02 pm

Re: Removed the brass firing pot.

Sun Jul 14, 2019 6:04 am

tonyc wrote:
Sat Jul 13, 2019 11:16 pm
I suggest you chrono a full string from 190 bar to 90 bar with and without the pot then you will see how it functions. It's possible if you chrono just a few shots (say 10) you will see more consistency but that will be coincidental depending on the cylinder pressure. Removing the pot shifts the peak of the power curve to a lower cylinder pressure but makes the curve more pronounced by causing the valve to close more quickly at higher cylinder pressures. For example, if you chrono a S400 with and without pot at 120-110 bar, with the pot the velocity is coming out of the sweet spot and falling, without the pot it's still in the sweet spot and relatively flat.

The other effect is the peak power will increase, so anyone removing the pot (or the pot falling off as mine did) from a gun that was running at 11.5ft lbs will probably find it running at 12+. I've no experience with the MPR, just the S400, but the principle is the same. I chronoed several full strings trying to figure out what was going wrong. I had a series of power variations on the S400 which I finally found was caused by the two sections of the pot coming loose and the volume changing before the end section eventually became completely separated.
Yes that's exactly what I did.
Full chrono string of 100 shots and found my sweet spot.
Power did slightly rise but easy to tune back to legal limits.
It's my h.f.t rifle now after tuning myself to be more consistent than air arms shipped them out!

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