SOLVED: bad barrel - work on it or replace it?

[K.O.]

point is even cheap and mickey moussed these things work...

I hope like heck the limb saver works ...

I do think that even the bad barrel(over size could be fixed with the right ammo) as long as rifling/harmonics/end psi  works

can usually be fixed... but man I am on this .177 one...

[K.O.]

I stubbornly want 800 fps .22 using only modded Crosman parts... and Jason wants to learn from this Barrel.

any reasonable barrel would have given in by now...

So is this barrel just the wrong  MOE for its length  or what...?

just a slightly different hardness and POW clover leafs...   

[K.O.]

Hey this 1 in 14  .257 looks to have both the plunger and a stripper I wonder how much it helped; he is using 70-100gr ammo though

http://tofazfou.blogspot.com/2013/03/long-range-airgun-shooting-18th-and-14.html

[nervoustrigger]

Kirby, I wish I had a friend who could temper it because that would be an interesting thing to try.  Just too cost prohibitive if I have to pay for it when that money would probably cover a new barrel.

Right now I'm in a lull with testing the .177 since I don't have a spare HPA bottle at the moment.  Andy's bottle is on the .22 and it's shooting great so I don't want to tempt fate by robbing it.  I have a spare regulator and ordered a couple of 17ci bottles earlier this week thanks to a pointer from Andy so I'll be back on it when those arrive. 

Also, the Limbsaver deresonator arrived.  It is not as big and obtrusive as I imagined and I am not expecting it to be a magical fix but it will be interesting to see if it makes a proveable improvement in the groups.

[K.O.]

Nah even if it is hardening steel , from pulling the button thru  it would twist in quench I am pretty sure. I do not think anyone knows what steel they are using.

[nervoustrigger]

Good news, the 17ci bottles arrived today.

Bad news, I was running the .22 cal over the chrony and the extreme spread was as much as 40fps.  Perhaps partly because of the regulator not being broken in yet but I'm also suspicious that my O-ring fix to the leaking valve stem is contributing.  So this evening after work I took the other valve out to the shop and prepared it, doing a few additional things to see if I can squeeze a little more performance out of the rifle:

• enlarged the valve throat
• tapered the poppet
• enlarged the brass body around the poppet
• turned down the valve stem in the region of the exhaust port

and the other usual stuff...

• milled slots in the valve body
• polished the stem
• radiused the exhaust port inside the throat
• ground a seat on the poppet for the return spring
• lapped the valve seat with polishing compound (using the valve stem to ensure a good seal)

So I'll be working on rebuilding the .22 before I move back to the .177.  With any luck I'll have an update before the weekend is out.

[nervoustrigger]

Well, I got ants in my pants last night and went ahead and drained the rifle and stripped it down and swapped the valve assembly.  Even managed to get it pumped back up to 2000psi before I turned in for few hours of sleep.  This morning I went outside and put some shots over the chronograph. 

Velocity did not improve, at least not compared to the very initial chrony readings I took.  However I think the regulator was already setting in because before I tore it down I noticed the peak velocity with the RVA screwed in had fallen about 30fps but I didn't know if it was because of the regulator or the blowby at the valve stem due to the sloppy tolerances.  Recall I had installed a modified O-ring on the stem to prevent it but I had my doubts that it would be 100% repeatable on a shot-by-shot basis.   And it occurs to me that maybe it wasn't a weak burst disk that blew out on me the evening I first assembled it after adjusting the belleville stack in the regulator.  Oh well, I don't think the ground squirrels are going to care about that too much as Andy zips a JSB 18.1gr through their noggins at 50+ yards.

The good news is that the new valve appears to have remedied the wildly varying velocity, taking the extreme spread from 40fps down to 19fps (2.4% of 800fps). 

Oh and on a totally unrelated note, cycling the bolt is smooth as freakin' butter.  The one on my 78 is stiff by comparison so that's something I'll have to look into if and when I take it down again.

[vigilandy]

I didn't know that you could do so much work to an airgun!  Its a learning experience for me. 

Question: What kind of tools are you using to radius the exhaust port in the barrel?  This is to prevent the pellet from scraping on a sharp edge correct?

Another question: I understand that the QB79 power is limited by the short tube.  Would a regulator extender help create more "on deck" air? Or is the tank block too constricted to matter.  The extender basically adds a little bit of space between the tank block and regulator.  The side bonus is that some come tapped and would be easy to add a gauge to show regulated pressure. 

[nervoustrigger]

Andy, yes after enlarging the barrel port, I deburr it with a small diamond ball grinder and then smooth it with 400 then 600 grit wet/dry paper on a dowel.  That is to prevent the pellet from being damaged as it is chambered.

To your question about tube extensions, putting more volume between the regulator and the valve will indeed improve the energy potential of a 79.  I am not familiar with the one you are referring to although it sounds similar in concept to a hipac.  If you wanted to go that route, I expect that buying a 78 air tube would cost less, look cleaner, and eliminate a joint where it could potentially leak.

[vigilandy]

So is the ball grinder small enough that it fits into the barrel port so you can deburr the interior?  Where do you get something like that?

Here's the link to a regulator extender:
 http://www.ansgear.com/Custom_Products_Inline_Regulator_Gauge_Port_Adapte_p/cpreggaugeportadapterdred.htm

I was looking at these as a way of measuring regulated output by adding a downstream gauge.  Seems like it might also help increase the volume of air at the same time.  How else can you check the regulator settings?

[nervoustrigger]

Yeah, the ball grinder is from a set of 1/8" shank grinding bits.  You can get a set off Amazon or Harbor Freight for $10 or $15 for casual hobbiest work.  You can get by with just the sandpaper for a one-off job but the paper tends to wear out and tear very quickly when working down a freshly-drilled sharp edge.  The grinding bits make it much quicker, and even the cheap ones will last a long time if you apply some oil each time you use them and keep the bit moving so it doesn't heat up excessively.  I wouldn't be without them.

Regarding the regulator extender, I'll have a look at it when I get back to my PC this evening but I will make some general comments for now.  If it appreciably increases the regulated air plenum and the price is reasonable, it may be worth it.  However, I really do not see the need to monitor the regulator.  That is something that gets set once...in this case, it's something I adjusted and tested.  You just need to know the pressure in the bottle and as long as it is equal to or higher than the regulator's setpoint, you know you are in good shape.

Another way to look at it is, how many regulated rifles do you know of that have two gauges?  A regulator is very reliable but in the rare event it goes bad, you'll know it pretty quickly based on trajectory and/or the report...or by a ruptured burst disc.  I say trust the regulator unless it gives you reason to think it can't be trusted

[nervoustrigger]

Okay boys and girls, another progress report.  I got the .177 rifle assembled this weekend with the 17ci bottle and 850psi Ninja regulator.  I went ahead and gave all the internals the full treatment.  Shot some groups with and without the Limbsaver deresonator installed and the results were not good.

So this evening I went ahead and took a hacksaw to the barrel and removed 1.5" and then went to the drill press to crown it.  I wish I could have gotten a better picture of the rifling but here's the best of several photos:



It was late when I finished buttoning it all up but I was anxious to try it out so I hung a target at 25 yards and trained a flashlight on it.  BTW, these groups were all shot with the deresonator and without a LDC.

Tried 5 different pellets so far and the first to group well were the Air Arms 10.3gr:



Strangely, while the H&N Field Target (4.50mm) had previously grouped horribly, they turned in a decent group this time around:



To see if it was a fluke, I dialed a few clicks and shot another group:



I haven't been so excited to see 1/2" groups in a long time   I'm not quite ready to celebrate yet but this looks encouraging.

[K.O.]

 

[vigilandy]

Hey, that's good progress! The groups are tighter and pretty consistent now.  Do you think it was just bad harmonics or something wrong with that last 1.5" of barrel?

Another way to look at it is, how many regulated rifles do you know of that have two gauges?  A regulator is very reliable but in the rare event it goes bad, you'll know it pretty quickly based on trajectory and/or the report...or by a ruptured burst disc.  I say trust the regulator unless it gives you reason to think it can't be trusted

I'm the naturally paranoid type.   

I've read somewhere that all regulators leak down eventually.  Was thinking it might be a good way to keep an eye on it if the rifle is being stored pressurized. 

[nervoustrigger]

Hey, that's good progress! The groups are tighter and pretty consistent now.  Do you think it was just bad harmonics or something wrong with that last 1.5" of barrel?

Well, I wish I knew.   I have no reason to think the last 1.5" of the barrel was defective.  The rifling looked clean and uniform, and pushing pellets from breech to muzzle did not reveal varying tightness and looseness.

The way it tended to shift groups around on the target at different RVA settings led me to come back around to suspecting harmonics but I really expected that at least one of the myriad of settings I tried would have resulted in a vibration node at the muzzle.  Also, it's not like I removed a significant portion of its length...it amounts to having 15.5" beyond the barrel band now as opposed to 17" previously.  I don't see how that would have dramatically shifted the resonant frequency. 

A third plausible scenario is that, although I identified a burr at the crown early on and did a complete recrown, maybe I had a defect that I could not detect.

I've read somewhere that all regulators leak down eventually.  Was thinking it might be a good way to keep an eye on it if the rifle is being stored pressurized.

Hmm, I would interested in reading about that if you have a link.  I don't know what that's about.  To my way of thinking, the only way a regulator can leak is to allow the high pressure side to get through to the low pressure side, in which case a properly selected burst disc would rupture.  The only other type of leak I can think of is not really the regulator leaking, rather that seals on the regulated side are leaking.  In that case, the regulator would open to maintain the downstream pressure until the tank eventually leaks down to the point where it can't any more.  In either of these situations, the symptom is pretty obvious and by no means a normal condition that all regulators experience.  So I'm wondering if what you read was about some other condition I am not thinking of.

[nervoustrigger]

More encouraging news, tried 4 additional pellets types and 3 of them produced groups under 3/4", the smallest of which was 0.42".  Combined with the few pellets I tested yesterday, these results suggest strongly that the rifle is much less pellet picky than before. 

But the most encouraging part to me is not so much the size of the groups as it is consistency of where they grouped.   Previously, what I had resorted to doing was shoot at the dead center of a target printed on an 8.5" x 11" sheet of paper and there was about an equal chance that a given pellet type would group in quadrant A, B, C, or D.   For example, CPUMs might group down in the lower right corner of the paper and AA 10.3gr might group in the upper left 6" or more from each other.   I don't recall ever before seeing such a dramatic difference between pellets.  Now it looks like most pellets want to group in the same general vicinity to the point of aim.   

[vigilandy]

Well, I wish I knew.   I have no reason to think the last 1.5" of the barrel was defective.  The rifling looked clean and uniform, and pushing pellets from breech to muzzle did not reveal varying tightness and looseness.

Crazy that last 1.5" was causing the pellets to scatter so much without any visually obvious defects.  Some mysteries can't be solved I guess! 

It sure was an improvement though.  Looks like Those Falcon 7.33gr perform surprisingly well!  I always thought lighter pellets would be less accurate, but they also do pretty well in BZ's QB79.  Not the first choice, but not far behind either.

Re: Regulators - I think I was using the wrong term.  I meant "regulator creep."  Here's an example:  http://www.network54.com/Forum/275684/thread/1174423503/converting+a+900+psi+paintball+regulator+into+1500-1800+psi+output

But as you said, this is why there's a downstream burst disc!

[K.O.]

" Well, I wish I knew.   I have no reason to think the last 1.5" of the barrel was defective.  The rifling looked clean and uniform, and pushing pellets from breech to muzzle did not reveal varying tightness and looseness.

The way it tended to shift groups around on the target at different RVA settings led me to come back around to suspecting harmonics but I really expected that at least one of the myriad of settings I tried would have resulted in a vibration node at the muzzle.  Also, it's not like I removed a significant portion of its length...it amounts to having 15.5" beyond the barrel band now as opposed to 17" previously.  I don't see how that would have dramatically shifted the resonant frequency. 

A third plausible scenario is that, although I identified a burr at the crown early on and did a complete recrown, maybe I had a defect that I could not detect. "




I still think it was most likely harmonics especially since the looser pellets are shooting pretty good now and it is not moving around as much with different pellets...

that 1.5" you cut off raised the resonant frequency by about 9% or so and the pellet is in the barrel for a little less time; which can move the

point at which the pellet leaves the barrel from a point at which the barrel is at  greatest excursion, towards when it is at the point of least excursion.

plus it may have moved the resonant freq of the barrel from one that the barrel is harmonically active at to one where it is less reactive.

The M.O.E. of steel is such that sound travels about 20,000 fps (stainless steel is about 19,000) and the pellet is at about  800-850 fps so it

does not take a lot to change poi or cause things to be less active. Think about the 40 fps valve problem and the overly large amount vertical

stringing with the bandless shots...

A forty fps variance was magnified by the harmonics... 8/15 edit*  I meant 15 fps

[K.O.]

I put more thought into heat treating and if it were a hardening steel,  then with a very quick heat, just enough to get the outside and bore walls to temp to achieve just a slight bit of case hardening might work...

[nervoustrigger]

It was a rough day at work today so when I finally made it home and ate some dinner, I had to get out into the yard and shoot a few groups.  Tried some different pellets that had performed poorly before and wasn't happy with how things were going so I went and grabbed the tin of Falcon 7.3gr that had grouped well yesterday.  First group:



Then I went and installed an LDC and shot two more groups:





Hmm, I had never even heard of Falcon pellets before but I guess I need to try them in my son's QB.  Looking at those groups, the shocking thing is some of the skirts are noticeably out-of-round and I was making no attempt to cull them...just picking one from the tin and dropping it into the rifle, giving attention only to its orientation so I didn't chamber one backwards.  The tin is marked Czech Republic and they appear very similar to JSB 7.3gr but have slightly different features inside the skirt, akin to what I've seen between JSB and Air Arms pellets.