FX Impact Inconsistent Velocities

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jking

jking

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May 12, 2015
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Hobbs NM, United States
Hey all, ran into an issue today while punching paper and setting up my turret markers. Everything was going great but then I notice some of the shots suddenly were impacting lower and off center. I decided I needed to shoot a few through the chrony and found that it was shooting 948ish then dropping down to 925 then back up to a higher velocity once again. First thing I checked was my delrin C3 and it looked fine. After putting it back together I shot a few more over the chrony and here is the string. JSB Re-designed 22's. Cleaned and very lightly lube with FP-10

937 935 937 937 936 955 933 932 (added air) 939 937 934 940 961 931 941

Forgot to mention to that the regulator is holding steady at 149-150 and I had previously (quite a while back) installed a larger VS and hammer weight. I also pulled the barrel to check the inlet inner and both outer orings and they appeared to be fine. I bet it's happened before but my search didn't turn up anything. Any thoughts would be appreciated. I'm kind of leaning toward something going on with the hammer strike.

Jimmy




 
Jimmy, assuming you still have the micrometer with rubber ball, you could try to turn in the end stop a bit until the speed drops, and see if it gets more consistent.

Another thing to try is to see if it happens at lower power wheel settings as well. Like others already said, it indeed looks like the hammer strike is the culprit, and not the reg.

I replaced the C3 with a Delrin washer I made, not a fan of any soft parts between the hammer and valve rod. It needs something more solid for the best consistency.

With the Power Plenum installed, I am currently trying out some custom springs for the valve adjuster, as I found out the rather weak valve spring did not bring me the adjustment range I was looking for. It is fun to form springs with the auto feed on the lathe :)


 
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When you changed out the Hammer weight did you lube it? That could be the cause. It should be dry. Lube in the hammer area can collect grit and give inconsistent hammer strikes. I doubt it’s the reg...
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I wonder if design differences call for different maintenance of the hammer? The reason I ask, couple of years back I began getting poor accuracy and inconsistent chrono measurements from my HM 1000 RAW. I talked to the maker about it, and he recommended that I disassemble, clean and lightly lube the hammer assembly, using Mobile 1 oil. The hammer was dirty and dry, and the cleaning and lube corrected the issue, and it has been fine since. He said it should not dripping with oil, but that it should be lubricated.
 
Upvote 0
When you changed out the Hammer weight did you lube it? That could be the cause. It should be dry. Lube in the hammer area can collect grit and give inconsistent hammer strikes. I doubt it’s the reg...
Click to expand...


I wonder if design differences call for different maintenance of the hammer? The reason I ask, couple of years back I began getting poor accuracy and inconsistent chrono measurements from my HM 1000 RAW. I talked to the maker about it, and he recommended that I disassemble, clean and lightly lube the hammer assembly, using Mobile 1 oil. The hammer was dirty and dry, and the cleaning and lube corrected the issue, and it has been fine since. He said it should not dripping with oil, but that it should be lubricated.
Click to expand...

I agree that lube should not be an issue as long as it isn't overdone and it is a lubricant that does not get too thick in cold weather. Mobile One is probably fine as long as it doesn't migrate to the seals but why not stick with an established gun lubricant that is seal safe like FP10?

It is much better to use a lubricant and clean once in a while than not use one. The friction and wear will be less. The only places you absolutely don't want lube is in the regulator internals or plastic bushings. Lube in the regulator can effect it's function and lube in plastic bushings can attract dirt causing premature wear because they are soft surfaces.
 
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Thanks for the replies guys.

Redick, fortunately I haven't had any problems with my regulator unless I go crazy and experiment around 170. At 150 and a tad lower it is very stable and I was checking it between shots yesterday to ensure it was recharging correctly. That was one of my first thoughts as wells.

Mike, when I added the hammer weight I reassembled dry, not to say that it might not need some attention now. If the problem persist I'm definitely going to pull it and check it for wear or rough spots.Might even take the hammer weight out at that time.

Gijs, I'll definitely try changing up the HS setting and valve setting and see if that makes any difference. I have it tuned to run on the third line most of the time. My C3 is a delrin I made, I checked it for a cracking after another member said his cracked and caused the same problem I'm experiencing. It had a wear groove on it when I pulled it yesterday but that was all. I'll replace it just to make sure. Seriously, making springs on a lathe, I've made some nice curly cues but never knew springs were possible lol. 

MtnGhost, I feel pretty confident in my chronograph since it was reflecting what I was seeing on the range (changes in elevation). I set my gun in a tripod just to make sure its in the same position as well on each shot.

Sonny your correct, yesterday I was trying to set up some markers on my turret after I knew the gun was steady around 945 to 950. Thought I had them all dialed in shooting off a cement bench only to go back through the yardages to confirm the settings then all of a sudden most were lower POI's. That's when I shot it through the chrony and found some of the shots were now dropping down to 925 then back up. After I degassed the high side by removing the bottle I opened up the regulator a tad to bleed the plenum off. After I checked the C3 and put it back together the string was what I posted above but it had the random higher increases. Odd I know, but just my luck..

I'll keep the updates posted.

Jimmy
 
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I agree that lube should not be an issue as long as it isn't overdone and it is a lubricant that does not get too thick in cold weather. Mobile One is probably fine as long as it doesn't migrate to the seals but why not stick with an established gun lubricant that is seal safe like FP10?
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Well, Martin has been building the RAW/Theoben rifles a long time, so I figure, who better to advise on maintenance? And synthetic Mobile One, I think, is as friendly to O rings as any "gun" lubricant. In fact, I've using it, and the fully synthetic Mobile One grease a lot, and both work very well on all firearm and air rifle applications I have tried. 
 
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I worked on the Impact today. The plan was to remove the hammer weight and go back to factory to eliminate any issues there. I was surprised to find that I had taken it out sometime back and had just forgot. Anyway I did clean the hammer, spring, guide and shaft up along with putting a new C3 delrin washer on it. The problem didn't go away, I also tried lighter HS, less valve adjustment and even weighed a few pellets to make sure their wasn't some weird thing going on there. Back off the regulator to about 145 as a test as well. Took the gun back down and pulled the valve stem and seat out to inspect them. Every thing looked good to me, back together and still getting bad chrony fluctuations. I then broke out my old Shooting chrony hoping mtnGhost might be right, no such luck. That's where I left if for the day.

Tomorrow I'll stick my 25cal system on it and see how it acts that way.

Jimmy
 
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I have been struggling a little getting my extreme spread and s.d. to tighten up, so far for 56 shots the best standard deviation is 5.6! Valve bumper all the way out! I’ve adjusted the valve bumper/stop etc. to no avail, Started at 890fps went down to 870’s still no better e.s. But one thing I did notice was my group’s at 65yds were no better or worse whatsoever! Actually my best groups of the day “today” had the largest e.s. of 20fps? I know many variables to this equation.., but still leaves me scratching my head? I hear about everyone’s impact With a sd of 4 or less! if not “something is way wrong!”
 
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Here’s another example, after adjusting & scratching my head all afternoon with the impact , I decided to get out the RW and shoot the same pellets approximately same speed 880fps “factory setting” for 56 shots extreme spread of 11fps SD of 3.1 with groups about the same? Not really sure what all this proves if anything? But I hear what your saying cc! to be honest I’ve never really worried about it before just how the groups looked like on paper
 
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Here’s another example, after adjusting & scratching my head all afternoon with the impact , I decided to get out the RW and shoot the same pellets approximately same speed 880fps “factory setting” for 56 shots extreme spread of 11fps SD of 3.1 with groups about the same? Not really sure what all this proves if anything? I’ve never really worried about it before just how the groups looked like on paper
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In a way you’re correct. At short distances like 25 to 50 yards a 20 to 25 FPS variance doesn’t really reflect on the POI much. But as you go further it does make a difference. You start to see it at 100 yards and further. It can mean up to an inch difference at 100 yards. It would be very difficult to shoot MOA at 100 yards with an ES of 25 FPS. Just another reason why 3 shot “groups” are a farce... ;)
 
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Aside from the one or two inconsistent speeding pellets, the rest of the shot string is pretty tight. I would like to see you weight sort those pellets as a test. If you have one pellet that is light and with a smaller head and skirt to is going to be zipping down the barrel considerably faster. I know when I started weight sorting my pellets and slugs the spread tightened up and I quit getting those odd high numbers across the chrony.
 
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How much documented croine work did you before your problem? This problem may have been a round quite a while or creeping up on you for some time. With the high regulator setting of 145b and lighter hammer. IMHA, I dont think your opening the valve consistent. If was going to guess your valve adjustment is around the 3-4th line out and your hammer is maxed out. I fill at you need to add hammer weight or spring pressure. Either one, just more strike force. You need to to be able to take your hammer adjustment to the point that the speed of the pellet isn't building any speed. Then back off the hammer strike. It maybe a case your hammer spring has began to settle. Adding a shim under the spring, tightening the grub screw adjustment or replacing the spring may help. If your bring your VA in slowly can your get the speed to stabilize around 920fps. yep, your not hitting the valve as hard as before. I like to creep my VA adjustment in slowly 1/8 if a turn per 3-4 shots over the cronie. Looking for FPS constancy.

There is one other thing that may have been over looked. Is the pellet probe loose or move to the point it not center over the transfer port. Ive seen where that will cause the speed to get a little weird. Be sure your barrel is seated back tight in the receiver.

Cheers
 
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Aside from the one or two inconsistent speeding pellets, the rest of the shot string is pretty tight. I would like to see you weight sort those pellets as a test. If you have one pellet that is light and with a smaller head and skirt to is going to be zipping down the barrel considerably faster. I know when I started weight sorting my pellets and slugs the spread tightened up and I quit getting those odd high numbers across the chrony.
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This +1.. Weight and head / skirt size could be the variable. IF everything is sorted and identical, then the hammer / valve system is where I would be focussing my attention.

And my bad, I somehow missed the part of you saying that POI was affected.
 
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