Air Arms S400 Mrp-Ft

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RichieRich612
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Air Arms S400 Mrp-Ft

Tue May 21, 2019 10:07 pm

Hello chaps, I did a shot string of 100 pellets weighing 7.8 grain using the Mrp-ft and got this. Is there any way in improving the sweet spot as from the data it's only good from 160-140 bar.
Tried to attach the file but even 69kb is too large I'm afraid 🙄

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Roger5
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Re: Air Arms S400 Mrp-Ft

Wed May 22, 2019 11:40 am

Hi Rich, I don't have an MPR, but I do have an S400 pretty much same rifle, I use AADF 8. 4 gn and sweet spot is about 160/165 down to about 100bar with not to much variation, I would be looking for 50/60 shots before topping up, and think that's reasonable for this rifle, my S400 is a carbine and as the MPR has a classic cylinder, I would be expecting a few more, the MPR has been out of production for a while, maybe a strip and polish would help, Rog

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RichieRich612
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Re: Air Arms S400 Mrp-Ft

Thu May 23, 2019 3:06 pm

Roger5 wrote:
Wed May 22, 2019 11:40 am
Hi Rich, I don't have an MPR, but I do have an S400 pretty much same rifle, I use AADF 8. 4 gn and sweet spot is about 160/165 down to about 100bar with not to much variation, I would be looking for 50/60 shots before topping up, and think that's reasonable for this rifle, my S400 is a carbine and as the MPR has a classic cylinder, I would be expecting a few more, the MPR has been out of production for a while, maybe a strip and polish would help, Rog
Thanks Roger yes basically it's a s400 .177 with a fancy stock.
I don't bother filling to 190 bar anymore, fill to 165 and shoot to 140, that gives me about 30 shots with little spread.
I'm really considering getting it regulated so I can use the full 190 down to 140.
Rich

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Roger5
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Re: Air Arms S400 Mrp-Ft

Thu May 23, 2019 4:39 pm

You will get a lot of devided opinions on whether to reg or not, I've fitted a couple (Altaros) and to be honest they have been fine, I like the Altaros, as there is no drilling of the cylinder, so if your not happy with the result, you've not done anything that's not sortable, Tony might be able to tell you a bit more, as he had one off me that I'd fitted an Altaros too, have you first stripped it and given the hammer rail a good polish, it might be all you need. Rog

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tonyc
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Re: Air Arms S400 Mrp-Ft

Fri May 24, 2019 5:48 pm

Hi Rich. My S400 peaks at around 130bar, 780fps with 8.44gr pellets. The curve up to peak is flatter than the curve down, so velocity at 160 bar is about the same as at 110bar.

Here are some notes fro my original testing:

125 shots from 190-90bar, 135 shots 190-80bar (min 700fps/9.5ft lbs)
Useful pressure range 185-105 bar - approx 90 shots (760-780fps/10.8-11.4ft lbs, av.772fps/11.1ft lbs)
AA claim up to 80 "full power shots" 80 shots
80 shots fall within a 2% velocity range
Reasonably consistent 50 shots between 160-110bar (av.775fps, +/-0.5% equiv. to one pellet dia at 50yds)
Best performance around 130bar
Approx 30 shots over 11.2ft lbs and within 0.6% velocity range
Approx 70 shots over 11ft lbs (within 3% power range)
Most powerful 25 consecutive shots: average 776.5fps (std.dev 1.53fps), 11.250ft lbs (std.dev 0.044ft lbs)
Most consistent 25 consecutive shots: average 776.4fps (std.dev 1.44fps), 11.246ft lbs (std.dev 0.042ft lbs)
Maximum velocity measured: 780fps
Maximum power measured: 11.35ft lbs

The Altaros reg won't give any more shots over a given pressure range as it uses the original firing valve, hammer and springing. But it will give consistent power/velocity at the optimum air efficiency of the original set-up. Mine is set at 125bar which gives me 70 shots between 11.2 and 11.3ft lb from the S510US carbine. Typical variation is no more than +/-2fps in a 10-shot string. I'd expect 90 shots with similar consistency from the S400.

I don't have full-string data for 7.87gr pellets but I'd expect the number of shots to be the same but at lower power - down 0.2-0.3ft lb.

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RichieRich612
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Re: Air Arms S400 Mrp-Ft

Fri May 24, 2019 8:14 pm

Thank you for your comments chaps, I've decided to buy a Lane Regulator as they have a lot of good reviews.
Yes I will have to drill a breath hole in the cylinder and a few other mods which maybe enlarging the transfer port.
I haven't measured the port diameter just yet on the Mpr so may not have to do anything to it.
Looking at a few videos the transfer port diameter would have to be approximately 3mm for the regulator to work It's best on a low bar setting.
Higher the bar lower the port diameter.
A lower bar will mean the regulator will work for longer which is better.

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TenMetrePeter
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Re: Air Arms S400 Mrp-Ft

Sat May 25, 2019 8:42 am

Yes, you need to use somewhere like photobucket to post photos on here.
Just two caveats.
First you need to minimise the burr inside the hole by not leaning on the drill, and smooth it to perfection with very fine wet n dry. Secondly you may be unlucky and have a tube with swageing marks (grooves) inside. AA don't manufacture these to have internal bores that are perfect - they spend all the time on the outside finish, so be prepared to buy another tube if the inside will not form a good seal round the two O-rings.

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RichieRich612
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Re: Air Arms S400 Mrp-Ft

Sat May 25, 2019 1:20 pm

TenMetrePeter wrote:
Sat May 25, 2019 8:42 am
Yes, you need to use somewhere like photobucket to post photos on here.
Just two caveats.
First you need to minimise the burr inside the hole by not leaning on the drill, and smooth it to perfection with very fine wet n dry. Secondly you may be unlucky and have a tube with swageing marks (grooves) inside. AA don't manufacture these to have internal bores that are perfect - they spend all the time on the outside finish, so be prepared to buy another tube if the inside will not form a good seal round the two O-rings.
I'm fully prepared to do the work on installing the reg correctly. I'm a firm believer that the work you put in the better you get out.
Do you have any experience with the Lane Regulators?
Rich.

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Roger5
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Re: Air Arms S400 Mrp-Ft

Sat May 25, 2019 6:26 pm

As Peter said, the A/A cylinders aren't perfect, I usually give them a hone, I've been caught out before,with air leaking past a seal. Rog

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tonyc
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Re: Air Arms S400 Mrp-Ft

Sat May 25, 2019 9:48 pm

I've no experience of the Lane regs. I understand you will get more shots than with Altaros. All I can tell you is Rog fitted my Altaros over 4 years ago and I've had the gun for about 15 months. When I got it the reg pressure was close to 140 bar and was giving 50 regged shots. I've taken the end cap off the cylinder to adjust the reg pressure to 125bar and taken the cylinder off to tweak the firing valve pre-load, which together gave me an extra 20 consistent shots. Apart from that I've not touched it. Altaros say if the reg pressure creeps up the reg inlet valve needs cleaning, something I haven't needed to do. It may not be as efficient as the Lane but it's consistent and does the job for me. I reckon they are good value.

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