GTA
All Springer/NP/PCP Air Gun Discussion General => European/Asian Air Gun Gates => China/Asian AirGun Gate => Topic started by: tracker1955 on November 05, 2014, 05:51:43 PM
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Hey guys, am having difficulty getting groups to tighten up on my new 177 cal B-50, how many tins do you think before barrel starts to come in. So far have tried some winchesters that were on hand, some rws superdomes, some jsb exact heavies, and some cpd magnum's. Best so far has been the jsb's, but still to big a group. Have played with fps but not much change in group sizes. Looking to keep fps in low 900's. Still gotta get some h&n barracuda's to try. So far have put +/- 600 pellets through the rifle trying to get it to break in and tighten up.
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If barrel is somewhat rough from manufacturing it may never really tighten up on its own.
What I would do is remove it and receiver taking out the cocking bolt so a cleaning ROD can be used threw the breech end.
Using a Jag and patches using some JB bore paste / Automotive paint rubbing compound or like fairly aggressive cleaner scubb the bore down with 50-75 passes.
Make sure crown has no burrs etc ...
Clean up and try again ;)
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Thanks, I'll try the bore paste and see what happens. Did run some patches through and they came out pretty clean but did not try the bore paste route.
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On my .22 the first thing I did was check and redress the crown, then I checked for transfer port damaging the pellets and I found a burr so I removed it with emery cloth stuck to the tip of my cleaning rod and finally did some lapping to polish inside the barrel and with each problem I addressed accuracy improved and I am satisfied with the results.
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Payday today so was able to spend a little money. Could not find JB bore paste anywhere today after checking with several gun shops. Academy guys suggested valve seating compound from an auto parts store. Ended up with some permatex brand and a new jag with a mop, and went to town on the barrel. Removed the breach and bolt assy. and made at least 75 passes through polishing the barrel and also the crown, although the crown looked good before I started, I just wanted that smooth polished look to dispel any doubts. Had run a pellet over the chrony before starting and was still a little high at 970 fps so backed it down a little more before re-assembling. Will find out fps tomorrow when sun is up again, and test if accuracy has improved. Also ordered some more jsb heavies and some H&N barracudas from pyramyd air. Forgot to mention that I also checked the transfer port for any burrs, and all looked clean and smooth. Will test with the CPD magnums tomorrow until the others come in on Tuesday, also have 50-75 jsb's left which I'll try again also. Wish me luck, I really want this to shoot as well as others I've read about, and at least close to what my marauder does. I got lucky on the Crosman marauder barrel lottery and got a good one first time out. Just thought I'd also mention that I had tried the pellets before both lubed and without lube. My marauder likes them dry, but my old disco only liked them lubed. Now only time will tell.
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Follow up to last nights report. Ran the Crosmans across the chrony this morning, still a bit fast but will wait until H&N's are delivered and tested before making another adjustment. The good news is that that group size shrunk by about half, down to around 3/4 inch at 30 yards. Seems to do good for a few shots and then loosen up again. At one point I thought it had really come in when I put six rounds through the same ragged hole, (JSB's) then went off by almost a half inch again. At least things are headed in the right direction. Will determine if more work needs done to the barrel after testing the new batch of pellets when they get here. Thanks for the help, and I'll post again when I know more.
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Have not had time before now to post again what has transpired since receiving my new batch of pellets. Was able to run a few through the gun before dark on Thursday to see how they would group. I had high hopes for the H&N Barracudas but was sorely disappointed. The crummy CP magnums grouped better than the H&N's did. Took the barrel off one more time and lapped the barrel with more of the pematex and my electric drill. Also inspected the crown again in case I had missed something. (Old eyes) but all looked good. JSB's didn't group to bad, but still not what was hoped for. With the sun at my back I could actually watch as the pellets would veer off their course, missing the point of aim. I began to be convinced that the JSB's were going to be the best choice, but wondered if the accuracy would improve if I could bring the velocity down. I tried contacting BIGED"S airgun supplies, but got no response, was wanting to but a new transfer port with a smaller diameter hole. Finally decided to try and make a new one myself, or somehow modify the one that came with the rifle. Went out to the garage yesterday after work and crafted a new port with a 1/16 diameter hole. Went out this morning to test the results across the crony, and see what accuracy would be like. First test with a 2000 psi charge had an average of 789 fps and 14 fp. Accuracy had improved a bunch but there was room for improvement. Ran the pressure down to 1000psi and noticed about 1/3 of the way through my string that the group began to cut one hole. This got me excited so wanted to see if I could repeat the results. Next group I only charged to 1500 psi, and checked to see how many usable /accurate shots I could get before POI dropped, or group opened up. I found I had 20 good shots that stayed within 1/2 inch at 20 yards. Before I put the chrony away I checked one more shot string. I still need to re-adjust the striker so I can get a more consistent plateau before the velocity drops, and maybe increase my shot count. At least things are moving in the right direction.
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Trial .. Success, Trial ... Failure is the path in learning & hopefully in the journey the losses with learning when you have gone to far along the way become manageable.
Valve lapping compound is VERY aggressive, tho have done so myself. No criticism to be said on that subject ;)
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I hope the electric drill was for the crown.
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Yes the drill was used in reverse on the crown in direction of barrel twist with just the mop and permatex. I was really surprised that the JSB's wouldn't group well above the 750 fps mark. You all maybe right about the crown although I really can't see a problem with it. Haven't talked to mike again since receiving the rifle, not sure if he checks the crown on them when he goes through them and makes some of the modifications he does. Outside of trying to get the pellets to group well, I really like the rifle. It's not the end of the world if I have to keep the fps in the low 700's, as this gun wasn't intended as a hunting rifle, but one to plink with when grand daughter or company comes. Even at that it's still putting out 12 fp's. I kinda like the 1500 psi charge, as I can do a whole lot of shooting on my 80 cu ft tank before having to get it filled again. My 22 cal. Marauder is my hunting gun at 900+ fps and 33 fp with 18.13 JSB's, and it will punch the numbers out on a shoot-n-see target at 30 yds. Very happy with it. Picked it up to shoot after holding the Bam for awhile, made my marauder feel lite. One more change I want to make to the B-50 is the addition of and off set mount so I can bring my scope back further and shorten the eye relief. I have the rings and the scope as far back as possible, but the way I shoot off sticks, it really needs to come back some more. Maybe next payday.
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Maybe you should consider shortening the stock, 15-1/2" LOP is too long for a lot of people. I replaced the butt pad with thinner material and then I cut an inch off the stock, made a difference in how the gun handled.
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I'm 6ft 1 with a 34 sleeve so the length is ok for my frame, it may also be partially due to the scope choice, I just need to be able to move it back a bit. Am looking at the picatiny to dove tail extension that will clamp to the rear portion of the breach and allow easy access to the loading try. I did consider your suggestion but the rifle fits well, it's just heavy.