Very new to PCP! Have new synrod need help.

[Budracer1]

Hello folks former competition bench rest shooter here but first time PCP owner, my name is Jason and I'm from western North Carolina.
So I took the plunge and bought a new synrod, have probably put close to 500 shots through it in my basement which is about 15 yards. Shoots 1 ragged hole at 15 with 3 different pellets but seems to like the crosman premier domes the best. Haven't got to shoot outside any because of schedule and the weather here in NC.

So...while it shoots very good at 15 yards, I decided to shoot it over the chrony today. This is with factory tune as I have adjusted anything yet, except I did take receiver off to check the screw in the bolt because of hard cocking issues but I seen no problems there, as both the screw in the bolt as well as the one in the hammer were tight and the detent screw in the top was not overly tight....anyway here are my numbers and I was hoping someone could point me in the right direction for an accuracy/efficiency tune.

Shot with crosman premier domes, starting psi 2700 ending 1950. I have jsb exact Kings 18.1s and H&N barracuda match 21s but so far at 15 the crosman has been better for stacking.

1. Error
2. Error
3. 918
4. 914.9
5. 910.9
6. 909.7
7. 916.1
8. 905.3
9. 903.9
10. 901.4
11. 900.6
12. 903.7
13. 903.8
14. 892.5
15. 890.9
16. 891.7
17. 886.6
18. 895.4
19. 878.2
20. 871.8

So where do I go from here and as an fyi the hard cocking is still there but not on every shot, just kinds randomly shows up

Thanks in advance.

[Budracer1]

Fixed the hard cocking, I decided to go in and gave another look, this time I tried cocking the gun with a wrench and found that it was in the hammer, so I removed the hammer and spring to find scarring in the bottom of the tube where it looks like the hammer has dug in, anyway, rounded edges and polished hammer as well as smoothed out the dug in place, put moly graphite ep grease on the hammer then wiped with a paper towel, put same grease on screw head in bolt and reassembled everything and now it smooth as glass.

So that part is done, now to get it tuned...


Thanks JB

[AlanMcD]

What you see is that you are shooting all on the downside of the power curve. This means one of two things: you are not filling the gun to a high enoguhg pressure for the hammer energy you have, or you have too much hammer energy for the fill pressure you are using.

That means that you either need to fill higher, or reduce the hammer energy to get to the upside of your curve.

The first thing I would try, if you can, is to fill to 3000 (or maybe even up to 3200 psi for this one test, if you can get there) and shoot a full curve from there down to 2000 psi or so, noting the pressure every five shots or so. First, this will give you a full curve like you want, and then you can use that data to decide what you want to do next - either run at the higher pressure or tune it work with the lower fill pressure.

If you can't do that, you could reduce the hammer spring preload and shoot again to see what you get. There is lots of good info on tuning that you can refer to, but the easiest quick answer might be to shift your fill pressure range from 2700 - 1950 psi to 3000 - 2250 psi. Testing will show the answer.

[Bob La Londe]

Alan is right on with needing to KNOW where your gun is in the curve. Then you can use this information to try and decide to decide on where to start.

http://www.crosman.com/connect/benjamin ... -may-vary/

None of those tunes are guaranteed to be dead on. They are just a good place to start. Every gun is a little different.

[Budracer1]

The reason for the low fill pressure to start was because my scuba had dropped pressure and that's as high as it would go, I probably also need to replace the gauge with a more accurate one as well as more graduations so I can better identify pressure, my scuba tank is filled to 3400 psi by my fire dept and I would imagine that there 20,000 dollar system is pretty accurate, so until I get a new gauge would it be safe for me to fill the gun to that once just to see how far gauge is off??

Thanks JB

[Bob La Londe]

I do not think anybody is going to guarantee its safe to overfill your gun.

That being said I start tuning runs for high power on my .25 at 3200 PSI. Usually I peak around 2900 and hit the bottom of my curve around 2200. MIne hasn't blown up yet, but I won't promise you its safe.

[AlanMcD]

You need to make your own decisions on going over the manufacturer's recommended fill pressure - you alone are respnsible for the consequences, no matter what anyone says here . . . .

That said, I ran mine with a 3200 PSI tune for at least 18 months, and all that time it was refilled and stored at that level waiting for the next use. Several times (maybe 5 or so) I filled to 3400 as part of testing the top end of a tune. It is not something I would want to do on an ongoing basis (liek the 3200 storage), but I was very confortable with having the gun be at that level for about 5 minutes at a time, as I was immediately shooting it down from there. I have since moved on to a regulated set up, and have had the gun apart many times with no signs of ill effects (but also no metalurgical checks either - just visual checks on the tube and valve screws and fill assembly threads).

If you do decide to fill it that high, do be sure to go slow at the top end - no point in adding to the pressure stress with thermal stress too . . . . I would let it stabilize and cool down at around 3000 psi or so, and then take about 20 seconds or more to fill the last 400 psi.

[Budracer1]

Thanks for the input guys, I had some lighting issues yesterday and couldn't use chrony, but did today, started the gun at 3250 per the stock gauge, still factory settings except for I've polished the hammer. Here are the results. They seem inconsistent, especially at the end, I had to pause to reload after each 10 and paused between each shot to right down numbers as my chrony will only store strings of 10. I also was not on a bench shooting, I was just holding rifle just behind and over top of chrony.

Starting PSI 3250. Ending PSI 2250. 30 shots

861.3
869.5
871.2
871.8
873.9
877.5
884.8
869.9
880.8
880.2
886.2
879.3
885.1
881.0
895.2
892.3
894.2
881.5
894.2
883.3
875.1
873.0
877.2
889.2
888.5
890.5
892.3
874.9
877.2
876.3

Also is there a program for iPhone/iPad where I can plug these numbers in and it give me avg, sd, es, etc???

Thanks in advance
JB

[AlanMcD]

Great! You now have a full curve. Interesting that you lost some speed with the hammer polishing. Did you lube it, and if so with what? Excessive lube can sure lead to jumpy numbers. You may need to adjust things depending on that, but in general it might just need a while to settle down, so you can always just shoot it some more and try again.

But the important thing is that you now know where you stand - throw out the first two shots, and if you ignore the jumps for now you can see that have a pretty good tight curve there (think big picture and ignore the spikes since those may go away on their own - if not, we will help track it down).

It looks like your gun wants to be filled to close to 3200 psi for a good shot string - we have seen a lot of the Gen 2s coming from the factory this way. I'm guessing that you don't want to fill that high, so you will probably want to tune for a lower fill pressure. It is time to read the tuning guide - here is a link to a re-write that Ray did on it and it so much better to read than the original: viewtopic.php?f=14&t=2577

Once you read it and get to the point you want to dive in, we can help more. In the mean time, nothing wrong with shooting shorter strings from a lower fill pressure.

[Budracer1]

Thanks Alan, I'll get to reading. And for the record on the hammer, I polished and applied moly graphite ep grease all over the surfaces that would contact the cylinder and then wiped it off with clean cotton t shirt.

And as far as filling to 3200, my gauge could be off and what's reading 3200 could actually be 3000. I do know that the gauge on my scuba fill station reads exactly the same but then again there both cheap gauges, maybe I can find a really accurate gauge with 1/8 pipe thread to put in the fill station and not worry about the one on the gun. Any suggestions?

Thanks again

JB