Canadian Airgun Forum

Although not impossible, it is rare for a PCP to diesel, unless you introduce a highly flammable lube on the pellet... For the most part the air cools as it expands down the barrel, although there is a very brief, transient heating in the transfer port.... You would have to have a fuel with a low flash point to ever see dieseling.... the temperatures are much lower than that reached in a springer.... I have personally never experienced it....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Another bit of good info, Bob. Thanks.
Come to think of it my only experience with dieseling was a springer pistol (Cometa Indian). I first wondered where the smell was coming from...

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Thanks all for your input. All the shooting was outdoors. It was sunny, but myself and the chronograph were in the shade. I will give the gun another good cleaning just in case.

Brian

Update: I'm pretty sure it's the chrono. Tried 30 more shots (2 runs of 15 from 2000-1200psi). Results were the same. So I tried 10 rounds with my Savage .22lr with 1070fps loads.
Velocities ranged from 110-1750fps!!! Sometimes doesn't pay to buy "previously enjoyed"

After a long decision making process, then a longer wait for stock @ Amazon.ca, I finally got my Chronograph. I had made the mods suggested by Bob in the meantime (.166 ports, 7/32 valve throat and gauge block, material off the poppet and bolt probe). After trying many pellets over the summer, the 2 most accurate out of my gun are the H&N Baracuda Power 21.14gr (copper coated) and Predator GTO 11.75gr!! How's that for opposites. Unfortunately because of my earlier malfunctioning Chrony, I have no pre-modded data to share. Once I figure out why I can't upload my Excel worksheets here, I'll share the data. Anyways, using the H&N 21.14's with 3 turns out from max preload, she averages 795 Fps and 29.7 FT-Lbs over 10 shots from 1900-1400 psi. I'm sure as seen in Bob's mod, if I could get a poppet equivalent to the one he made, the results would be significantly better. Since my goal was 900 Fps average with Jsb 18.3 Heavies (waiting for more from AGS), I think it must be close. I will update when they arrive.

Brian

Congrats on the chrony and successful mods =).
I actually thought it'd be a little faster with all that work but still quite a bit faster than stock. I'll have to shoot a few 21 gr h&n to compare, since mine is still stock setup.

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Thanks Wes,

I was hoping for a little more power, but as seen from Bobs mod, a good percentage of his gain was from the new poppet. I will try and source one like his, since I don't have the resources to make my own. JSB Heavies to arrive Monday, so will report on how they perform.

Brian

29ft/lbs is a lot of power anyways! I think mine is putting out only 23 or so. I still need to open a tin of Barracuda and report my velocity here.
If you find a source for that poppet please share!


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I finally shot my Chief tonight over the chrony with the 21gr Barracuda match, and they were averaging around 742fps. My Qb78D is shooting them around 765-783fps, mostly on the 770's. A lot louder though so I'm thinking I'm wasting air and need to do some adjustments.
So compared to my Chief yours is shooting in a much more useable velocity for hunting at longer range with heavy pellets.

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Wes,

Still not too bad for stock. Should put down most pests out to 40-50yds. Where did you have the preload adjuster set? If your QB78 is louder, maybe your Chiefs preload is backed out a fair bit. Did you shot at a target? If you did, how accurate?

Brian

I've shot it out to 100 yards at my dads farm. It was windy so didn't do great at that distance, but it shot well at 50 yards and really good at 40 or less.
Today I finally got my infrared lights in the mail and those numbers I posted yesterday are wrong. I had finally bought the hockey puck lights at Canadian Tire (my 3rd set of led lol) that Leadslinger had recommended and thought wow these work good, but today with the infrared I see that it was still making the velocity higher than it should.
My Chief is now shooting at around 700-710fps with the h&n Barracuda where it was set. I couldn't seem to adjust the hammer spring, so took it all apart and found out the spring was jammed in the back plug and the washer that was in there to push against the spring was bent, perhaps from me reefing on the hammer adjustment =(.
Anyway I got the spring unjammed. Saw it was cut and sticking out, not flattened off. Bent it flat and turned the spring around, left the washer out and stuck it back in. Now I actually could adjust velocity, from 200fps all the way to 783fps with the h&n Barracuda. That's more like it! The highest velocity was at 2000psi and dropped from there with the hammer adjustment maxed. Without the washer I'm able to turn it all the way without coil bind. Now I'm wondering if I forgot and cut this spring myself and did a crappy job of flattening it or what, or if it came from the factory like this.
Anyway much better now!


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I flatten spring ends with a diamond wheel on the dremel after cutting them. Very fast and easy.
I may put the RVA back on my A/R to get the string a little flatter. We'll see what happens with the latest t/p idea first.

-D.S.

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Wes,

Bob had that same issue with the cut off hammer spring, mentioned in this very post (such a long time ago lol) I have seen several more tear-down reviews of the chief on Youtube that showed the same cut off hammer spring, so I'm sure it wasn't something you did. Now the bent washer At least you found the issue and have your power adjustment back. I haven't had to use the infrared led's with the Caldwell yet, as everything has been outdoors so far. If you're just going to have a target session, I really recommend the Predator GTO's. You can back the hammer adjustment out 6 or 7 turns and get 20 or more shots between 950 - 900Fps, with great accuracy out to 50 yards, and a bonus of a much quieter gun adjusted like that.

Brian

Thanks! I'll have to get some of those in. =)


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Hi all,

After a break to tackle a health issue, I'm up to speed enough to participate in our hobby once again. Finally have some number to share from my tune on my QB Chief. I finished up using Bob's recommendations almost to the letter. Ports all enlarged to 11/64". Valve throat and gauge block passage 7/32". I also countersunk both ends of the gauge block passage to 3/8" diameter to a depth approx. 3mm either side of the gauge port. As much material was removed from the bolt probe and poppet as I felt was safe. The results were a little short of what I was hoping for, which was an average of 900Fps using JSB 18.13 Heavies. I believe if I could have produced an upgraded poppet as Bob did, I would have met my goals. As it is, the hammer spring setting which I will stick with, 4 1/4 turns CCW out from full preload, yields a fairly consistent 15 shot string averaging 850 Fps & 30 Ft-Lbs. I am trying to source a regulator to fit the Chiefs tube, but no success as of yet. A screen shot of 4 shot strings through my Caldwell chronograph, using Jsb 18.13gr Heavies is attached. The 3 best pellets through my gun
for accuracy are Jsb 18.13 Heavies, Predator GTO 11.75 and H&N Baracuda Power 21.14. The Heavies and GTO's are basically 1 hole @ 25M, while the Baracuda's are a ragged hole. Happy Holidays everyone.



Brian

Great job! looks like you've tuned it for a really nice shot string.
Does a marauder have the same inside diameter as the chief? Maybe one of the marauder regs would work?

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