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PostPosted: Wed Dec 26, 2018 6:15 pm 
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Location: Bowmanville, Ontario
So, the Benjamin trail .22 with the nitro pistoney is supposed to top out at 950fps with a lead pellet, I assume a crosman 14 grain. I have the Canadian Benjamin fully tuned, with a nitro piston. Fires great, but tops out around 630fps also with 14 grain (about 580fps with jsb 18.1 domes)

Out of the box, how fast is that American stock Trail ACTUALLY shooting?
I'd like to get my Benjamin a bit faster. I have the BT9M22-00-5A gas spring from Gravel. I can't remember if it was the strongest or down a few levels...

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PostPosted: Wed Dec 26, 2018 8:39 pm 
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I’m reading on the crosman website the 950fps is with alloy and 800fps is with lead but i’d expect between 700-750fps.


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PostPosted: Wed Dec 26, 2018 9:53 pm 
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Ronan_357 wrote:
I’m reading on the crosman website the 950fps is with alloy and 800fps is with lead but i’d expect between 700-750fps.



Link? Cause the trail page I read was over 1000 for alloy and 950 for lead.

https://www.crosman.com/airguns/air-rif ... xl-1100-22

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PostPosted: Thu Dec 27, 2018 5:47 am 
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The link you posted is for the Trail XL, which is a magnum version of the Trail. They also sell a Trail NP2 to add to the confusion.
That spring is the full power for the B18 Trail, which normally spits out a std 14.3gr pell at ~700-750, sometimes a little more, often a lot less. It just depends on the guns flaws. So if it's 630 I'd first suspect the spring, and being new means nothing because they can leak at any time or maybe has been leaking slowly since it was made. Other flaws are the main seal which are usually cut up from the factory. The breech seal leaks but we try to keep it to a minimum, some leak a lot so check it. Barrel flaws can cause significant leakage/blow by.
It could also be your gun was a std 500fps model with a weak BT5 spring and long piston, but you only changed the spring? If so it would give you the power you're seeing. If that's the case you need to cut your piston down or buy one (~$36CA).
Either way I'd replace the main seal, and if you want peak performance I'd mod the seal too.
I have details on cutting the piston dwn, modding the seal and lots more mods for it if you want. chevota at hotmail and I'll send it


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PostPosted: Thu Dec 27, 2018 7:52 am 
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Hi Chevota.

This is that Benjamin .22 with the totally remachined hinge, and many many other tuning jobs done I posted about over the past year.
As far as tuning goes, I really don’t think there is much else I can do. The rifle fires amazingly well, and extremely consistently. It’s just not as fast as I was aiming for. The gas spring that’s in it now was recommended by yourself. And I believe you had mentioned it was the most powerful gas spring at the time.

What I’m asking now is, IS it the most powerful gas spring available for this rifle? Or was this BT9M22-00-5A a slightly lower power gas spring?

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PostPosted: Thu Dec 27, 2018 10:05 am 
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Yeah that part # you gave is for the Benjamin Trail NP which is 800 FPS with lead. Realistically should be 720ish.

I had a aftermarket gas spring in a phantom 22 and was like 780.


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PostPosted: Thu Dec 27, 2018 3:30 pm 
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Sorry, so many people email me I get confused as to who's who and what they have.
Well, I'd still suspect the gas spring as the issue since all of mine have leaked to some degree. I can tell by feel when cocking but you can put a luggage scale on it to be sure. Using a std (US) 18.5" barrel and parachute cord tied 1" back from the end I get a peak reading of 28lbs. That's for a gun I've tinkered with so friction is minimal, a new oem is more like 32. Using a bathroom scale is usually a fail at low wt like that. The digi scale was ~$5 on ebay. A fishing scale should work too.
Yes it's the full power spring. The NP2 spring is a little stronger, and the NPSS spring is a lot stronger, but both are imo too strong. I think the BT9 is a bit too strong as well so as long as it hasn't leaked it's plenty. My most powerful B18 is 20.4ftlbs using the BT9 and all the normal oem dimensions, no extra stroke to anything outside the norm. So clearly the spring can deliver, anything less is the guns fault. Altitude hurts power too, I think I was losing 10fps in 177 per 1000'. So it hurts power just like it does a car.
If none of that is the issue then I guess I'd look at the crony?


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PostPosted: Thu Dec 27, 2018 4:53 pm 
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No worries. I know a lot of people contact you. You're very generous with your time.

I guess I have some testing to do.
I never did change the piston seal, I just tuned it. I did also notice the breech seal is wearing flat on the top. Maybe I'll shim it with a .005" shim and make sure everything's snug and oiled and run some tests if I find some time home alone.

I still have leadslingers chrony. I'll do one more test before send it back this week.

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PostPosted: Thu Dec 27, 2018 5:09 pm 
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The only test i could do immediately was the cocking pressure. My quick dirty test was on a digital scale that fluctuates real time. with the rubber butt on the scale I cocked the rifle. With the rifle half cocked pushing down on the muzzle end on the barrel against the push of the gas ram, with the rifle still balancing on the scale, I read the scale. 47-51 lbs. Repeatable.
No idea what that means... maybe a bad test. It is a difficult rifle to cock. And it's all spring pressure. No binding.

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PostPosted: Thu Dec 27, 2018 11:28 pm 
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To do a bath scale test you need to put the muzzle on the center of the scale with the barrel almost horizontal, basically as horiz as you can so only the muzzle is touching. Or put something down like a folded up paper towel to act as a spacer. Then rotate the gun to cock it while keeping the barrel horiz. Again bath scales are usually off at low pressure like that, and usually off period, but some are ok. The digital ones read best, old school mech ones are often just pathetic. To test it you can measure a known wt like a gal or more of water and see what it says. Also, that's with an 18.5" US barrel, many 500fps guns have 16" or so, if that's the case you'll have to do the math. Measure from the pivot point, not overall. the pivot is like 1.5" back??? So subtract that, lets say 14.5 compared to my 17, but I also measure 1" back so really 16". Then you have to compare to where you measured, so if you put a PT down then use the center of that. Make sense?
The oem breech seal is rather lame imo, but if it's flush with the breech I think odds are it's leaking. Ideally I'd use a rubber O-ring. Also note that the guns with the cross bar for a barrel catch will likely stop on that bar and prevent good seal contact. So oem or O-ring you want the barrel block to rest on that bar for consistency, but no more than needed so most of the pressure is on the seal. This is one reason rubber Orings work better b/c there is more room for error. The hard oem seal has virtually no room for error. The older guns with a chisel catch put all the pressure on the seal until the seal compresses so far the barrel block hits the receiver side, then you end up with the same issue. That metal to metal contact up top and visible is a reminder that you need to shim or replace the seal. With the cross bar it's not so easy to tell which is why imo many people are leaking and don't know it.
The main seals can often be saved by sanding the face so the seal is thinner. I do this no matter what b/c it bumps compression and gets more air into the xfer port, plus the air cushions the piston impact better. It still hits and you still need to leave some seal sticking out above the dovetail or it'll hit metal to metal. Usually I push it to ~.008-.010" seal height over the dove, which I do by putting a flat metal bar over half the seal, pushing down to somewhat c to compress the seal, then measure w/ a feeler gauge. How much you push down is the question but I guess maybe 10-15lbs? The idea is basically to ensure any air gap under the seal is gone, or maybe I should say firmly seated down so any more compression is sheer piston impact force. So .008 is borderline depending on the gun and how you measure, so I suggest more like .015 to be safe. If I want to check for contact then I sand the dove smooth with a Dremel, like shiny smooth so if the breech touches it'll leave a mark. Then shoot the lightest lead pellet you'd ever use a few times, take it apart for a look-c. Then if all good and you want sand more, repeat until you see contact. Then decide if you want to sand a new seal to be a couple thou thicker than the contact height, or shave a couple thou off the dove.
Optionally you could fill in the dove recess with silicone or Goop, but I doubt it'll stay. I believe My Crosman experimented with that but I can't recall if it lasted. Sanding the seal thinner also nets that much more stroke, which isn't much at all but it's better than nothing. Going from memory the seals are ~.200 to .215 thick and I sand them to ~.185". But that is dependent on the doves height and being made in china you really have to do each by hand. So up to a mm is stroke which is worth ~1% power, but the real power is from getting it so the seal, under impact, is forcing the most air into the port. So I guess eyeball your seal and if the damage can be removed by sanding to say .190" thick then I'd give it a try. If not it'll still be way better than it was. Also; that sanding removes any safety margin for dry firing, which is no doubt why the seal is so thick in the first place, so be extra wary not to dry fire it b/c it'll no doubt hit metal to metal which can be really bad, waaaay worse than a dry fire w/ an unmodded seal.


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PostPosted: Thu Dec 27, 2018 11:47 pm 
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Mine is the cross bar latch. I did considerable playing here, re-shaped the rubbing face of the pin, and installed a much heavier spring. This was all part of trying to reduce any play and wiggle in the hinge. Side to side, but also stop the barrel from bouncing up and down From compressing the breech seal. So, it’s a tight fit. Which is likely why the crap oem seal is wearing flat. A rubber seal may stand up to more friction, but I’d have to get the stick out amount just right. I want the metal on metal contact of the barrel and receiver, so the firing harmonic travels evenly through the gun. But I also need/want just the right amount of seal to give the least amount of leakage with the least amount of seal compression so as to not shim the barrel off the receiver possibly creating that barrel bounce.

All that work was what was able to get me 1/2” - 3/4” groups at 30 yards with zero fliers, ever. With a cheap Chinese detuned Benjamin that started life with a 3” spread.

What I wasn’t able to do was test the speed once I finished all the mods. I did not have a chrony at the time.

So, it seems I have to revisit that breech seal possibly and retest speed.

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PostPosted: Fri Dec 28, 2018 12:01 am 
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Location: Klowntown BC
holy too much to know batman!!
i didn't know i didn't know so much about airguns since climbing on board this forum.

(i just tighten up my groups by moving closer to the target.)

:oops:

happy 'nother year all.


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PostPosted: Fri Dec 28, 2018 7:27 am 
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Leon Yrag wrote:

(i just tighten up my groups by moving closer to the target


Hahaha... and I keep trying to move further away.


I had many “ah ha” moments about the mechanics of a springer when I was rebuilding this gun. Something I would not have learned had I just bought a higher quality rifle... so it begs the question, which direction is better?

This way... this way was better. I like tinkering.

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PostPosted: Fri Dec 28, 2018 8:21 am 
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Yep, great work! I'm sure you'll get this latest challenge figured out. =)

Sent from my EML-L09 using Tapatalk

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