Air Gun Home :: View topic

montanatim · New Member

My questions for the Guru's here;
I have a Crosman/Benjamin Titan. When I fired it initially I went through 198 rounds before really studying what I had. Crosman recommended 100 or so rounds for break in. They also talked of the thing dieseling for awhile during this break in period.

Velocities were below what were claimed on the box, what a shock Wink

I called Crosman to ask what's up. The nice lady said my velocities were indeed about 50fps lower then they should be. (CPHP-avg. 706.1 fps @ 14.6gr) (Beeman Silver Bear HP-avg. 692 fps @ 12.7gr)

I started reading on this forum and decided to check my piston seal. It was ugly, big gouge down the side with pieces of seal lip broken off and metal flakes. I ordered 3 new ones from Crosman. I also ordered the Crosman RMC oil as they specified that it was proper to prevent seal damage and dieseling.

Now finally for the questions after the back ground, Can anyone tell me why the thing would diesel if the proper lube was used during assembly?

The new seal does not seem to fit as tightly as the old one (I only deburred to protect entry of the new one) do they very that much in size? Did they perhaps use a petroleum based lube at assembly that swelled the old seal and caused the initial dieseling?

My velocities seem to be unchanged. I did have a rough crown but have polished that out with a 5/16 ball bearing and valve compound.

What else could keep velocities down? I replaced the breech seal and polished the chamber surface it mates to on lock up. I tried shimming under the breech seal, I don't know how much I took off during the polishing so I started with .020 it was definitely overkill and I may still try a .005, But the point to this is, even with the too thick shim I fired it with really good seal at the breech with no change in the velocities.

The old seals both are yellow/brown looking as if they absorbed some cheap Chinese oil. The new ones are nice whitish material, this lead me to the swelling theory. The old ones are both softer then the new ones.

I searched these forums and did not find the answers yet I sure hope you guys can help.

AirGunEric · Site Admin

I can't speak for the Titan as it's a big box (Walmart) product, but if it's a .22- 690fps using 14.3gr pellets is about right.

There is no "proper lube" in the gun from the factory- every bit of oil and grease in/on it is there only to prevent corrosion. Your gritted up internals only underline this.

Clean it up/out, lube things properly and replace the piston seal- you will be glad you did.

montanatim · New Member

It is a .22 I did replace the seals after a complete cleaning and lubed everything with the RMC before re-assembly. So far no difference, hence the questions.

AirGunEric · Site Admin

RMC is for lubing the piston seal through the transfer port- not lubing the piston walls or spring.

You will not see a power difference- as I stated- 690fps in .22 is to be expected- anyone telling you any different is BS-ing you- the Crosman Customer Service person too (think they really know anything about the guns they sell?). The "800fps" number they advertise is with lightweight alloy pellets- not standard-weight lead.

The "difference" should be in how it cocks- ie. no more scraping or grinding.

lampy · Veteran Member

You mentioned finding metal flakes in your first post, are there scratches in the compression tube where the seal rides?
I have to agree the advertised FPS for air guns is almost always with light weight ammo.

montanatim · New Member

I couldn't understand where the flakes came from either, the part of the tube the seal rides on looked polished.

The advertised velocity on the box says:
"Up to 950 fps with alloy pellets"
"Up to 800 fps with 14.3 grain lead pellets"

Now I realize that Up to... could mean anything (they) want it to but come on 692 fps with a 12.7 gr pellet? Really?

That is why I called Crosman to ask questions, and am now here to talk to folks who really know.

AirGunEric · Site Admin

If you look at those numbers you posted- you actually stated you had 706fps with 14.3gr pellets (not sure where the CPHP got 14.6gr on them- this is new), the lighter pellets dropped your velocity- which is telling me they are either too loose or too tight in the barrel- i.e. something is either not sealing or is jamming. Unless those Silver Bears are shooting extremely accurately, perhaps they are not the best pellet for this rifle. The rifle certainly seems to be within specs ("specs" as experienced in the real world, not the BS advertising numbers).

If you had no scoring in the chamber, great. The grit may have been from rough edges on the piston or just crap in the "lube"- either way if you cleaned things up that issue is not something to be worried about now.

montanatim · New Member

How big a part in the velocity game does the hole in the air chamber play? (the one air rushes out to drive the pellet)

Is there an optimal size for .22? Smaller then the pellet of course. /or not?

Is there another break in period required for things to settle down with the seal replacements?

lampy · Veteran Member

It's going to take some shooting to get everything settled back into place and lube redistributed after a tear down. Not 100's of shots but it will take some shooting.
Personally I wouldn't mess with the transfer port it's easy to make it bigger, hard as hell to make it smaller if you go to big.
How is this rifle grouping? For me being able to hit what I'm aiming at is much more important than trying to gain 100 fps...

robert w · Senior Member

yoyr fps is on par as the 1 i had was in that range . it will quit dieseling after a while. they just print numbers that sound good for sales . it should be illegal to print wrong numbers but they state up to ... just shoot it a bunch and crony again after 4-500 shots