.22 QB/PCP wont group well, any ideas from the experienced builders ?

[Gertrude]

First,
 this thread IS NOT meant as a complaint, flame, bash, or ANYTHING to be even remotely interpreted as a negative context.
 We are ONLY asking for help, from knowledgeable experienced builders, to try to figure out what is causing it to perform below reasonable expectations.
 So with that being said, here's what we've got.

This rifle has been Professionally built/tuned by one of our finest builders, including all the bells and whistles.
It is pushing 14.3 CPHP's at 920,... 21gr Barracuda Match at 845.
and yes, with several popular, proven, pellets/weights/styles tested in between.
 (and No, we have not run any JSB 18.13's through it yet, only because we are out of them right now).

 ES no greater than 5 FPS, (no matter what pellets are fed down the pipe).
 This tells me the Regulator's output pressure, is VERY consistent,... as well as the TP, Bolt seal, Barrel seal, Poppet, Hammer spring, and all internals, are functioning properly and consistently.

So what's the problem you ask ?
Well,... no matter what ammo we have fed it so far, (probably 7 or 8 various brands, weights, styles),
 It simply Will NOT group any better than 1 1/2" to 2" at only 30 yards ! (completely unacceptable).

Especially when we consider my other QB/PCP (with practically identical build), is known as the 50yd "Aspirin Assassin"  and regularly takes 100+ yd headshots on GS, Rabbits, Hosp's, etc.

So here's what we checked so far, (leaving us now pretty perplexed) :
LDC is NOT clipping, (but we removed it anyway) just to take it out of the equation... still no change in groupings.
Crown is perfect and passes the Q-tip test no problem.
Barrel band is tight.
Barrel/Breech screws are tight.
No leaks at barrel/breech, bolt probe, TP, or anywhere else. (remember, it has an ES of no greater than 5 FPS)
Scope and rings are tight. (even tested with a second scope,... and no change in grouping)
Stock is tight. (ALL screws are tight throughout entire gun).
Both the cocking action and firing cycles are clean and smooth.
Trigger breaks sharp, clean and predictable.

We have shot from both a shooting rest, a bipod, as well as sandbags, all on a solid non-shaky bench.
 Still no improvement in groupings.
We have tried dry, as well as lightly lubed pellets. we've cleaned the barrel, we've "dirtied" (leaded) the barrel,
Again, no significant improvements.

So basically, we are down to trying some tried and true JSB 18's as soon as we can get some, but to be honest, I don't think that is going to be the magic pill... considering that EVERYTHING else we have put through it, is doing about the same, with no significant or noticeable performance variations between any of them.
 and remember,.. this is ALL at ONLY 30 yds !
 
Heck,
 this gun should At LEAST be doing nickel sized groups with just about ANYTHING at that short range.

Any idea's from the experienced QB building Guru's ?

Thanks in advance

[Gippeto]

What did the builder have to say? If there is a problem, reputable folks will deal with it. I assume you did the decent thing and gave them a chance before posting about it on an open forum?

Personally don't put much stock in the "Q-tip" test. A look with a loop gives more information. Would take the barrel off and push some pellets through the bore to get an accurate idea of what's going on in there.

Pay attention to increases or decreases in bore friction and their location in the bore as you push the pellet through.

Al

[Gertrude]

What did the builder have to say? If there is a problem, reputable folks will deal with it. I assume you did the decent thing and gave them a chance before posting about it on an open forum?

Personally don't put much stock in the "Q-tip" test. A look with a loop gives more information. Would take the barrel off and push some pellets through the bore to get an accurate idea of what's going on in there.

Pay attention to increases or decreases in bore friction and their location in the bore as you push the pellet through.

Al

Hi Al,
Thanks for the reply.
Yes I spoke with the builder and he is certainly both reputable and more than willing to help.
 No problem there at all.
He is quite confident in our diagnosis abilities and he confirmed we have pretty much covered everything the same as he would. This is not at all, an issue of him not supporting us.

The gun shot fine for him, as well as me too in the beginning. I have no complaints with him, or his build, what-so-ever.
 We ALL just want to figure it out. That is why I am posting it up in hopes that if there IS something we are overlooking,... that one of the fine members here may be able to make suggestions we might not be thinking about.
 As you well know, that's what makes this forum and it's members as great as it is.

I agree with you that the loop as well as slugging the barrel will be the next step to take, and had already made that suggestion in our conversation.

Thanks for your interest, help, and concern... and please keep the suggestions coming.
Cheers,
Ron

[TheBman]

The gun shot fine for him, as well as me too in the beginning./u]

So you HAD acceptable accuracy initially?? How good was it?

[Bentong]

1+ on Al suggestion on pushing pellet through the barrel and check rifling and any mark that can throw it off when shot. TP hole most time gouge the head or skirt.

[anti-squirrel]

I'm not a builder or tuner by any stretch (I only work on my own stuff)... The main thing that stood out is you said your barrel band is tight.

Loosen it (or take it off) and fire a couple shots.  Could be a resonance thing.  All the other details look just fine.  My QB has the repeater breech, so it is not an apples-to-apples comparison, but if everything normal looks normal, and it went from peachy accuracy to pooh, something is having a negative impact external to the firing operation, especially with such a tight ES.

[nervoustrigger]

The only thing I have not seen mentioned is the scope.  The owner said he does not have another one available to try at the moment.  Seems like a bit of a long shot but since the rifle was shooting well previously (with two different scopes) and all the other factors seem to be in check, I think it needs to be tried.

If there is anything wrong with the barrel, it isn't the usual factory roughness or burrs because it has been thoroughly worked over.  It would have to be some sort of subsequent damage.  The crown would be the thing most susceptible in most cases but it has been protected by an LDC, and the owner is an accomplished gunsmith and does not find anything concerning with it.  But yes, at some point it would be prudent to pull the barrel and give it a good inspection, but I think I would try a new scope and some JSBs first. 

[Gippeto]

Ron,

VERY happy to hear you spoke to the builder first, this seems to be an increasingly rare courtesy. Also very happy he is a reputable bloke and trying to help you.

Might have been prudent to include this fact and that the rifle did shoot well initially in your original post though.

You've been pretty thorough going through it from your list, but something had to change between "shooting good" and "not". Did it start shooting poorly after being apart, or just started "out of the blue" as it were?

Al

[10gaOkie]

From my own experience with air rifles, I have had the same good to bad accuracy with the cause in these areas...
1. barrel crown
2. scope
3. scope mounts
4. air power adjustment knob backing out ( I now use blue loctite when tuned)
5. LDC

Chris

[nervoustrigger]

Oops, I just re-read Ron's summary and he mentioned they tried a second scope.  They didn't have one to try last night when we talked so I still had that in my mind.
 
Another thing I will mention is I've seen bent or damaged bolt probes cause a degradation in groupings because the pellet is not chambered evenly.  In this case the owner inspected the hollow probe and confirmed it has a neat and clean cylindrical profile so we ruled that out.

[RDB]

Just a thought. Is it something that got progressively worse or went to pot all of a sudden?  How many crosmans down the barrel?

My qb's have kind of loose bores compared to other rifles I've slugged. Still shoot great. The alloy of the crosmans will smear a bore at those velocities. A patch with goo gone or wd would pull clean...but hoppes #9 and a bronze brush would produce quite a bit of lead.

Something worth a look when you get the barrel off.

Good luck and hope it's something simple.

Rod

[Gerard]

I'm leaning towards agreeing with anti-squirrel about the barrel band and barrel harmonics. At the higher velocity your QB is pushing, barrel vibration becomes a fair bit more significant than at lower energies. Even a very slight change in barrel band location can make a big difference, as the nodes and anti-nodes are shifted by such a move. If you've also changed band tightness that just takes it further from where it was when shooting well. Or if it's in the same location as previously, but now tightened more, that's still a change which could affect vibration. Testing ten shot groups with the band in different locations can tell you whether this is the culprit.

[nervoustrigger]

That's a good point.  Leading could develop relatively quickly.  Ron said they've experimented both clean and after its had an opportunity to lead up, but I can't speak for "how clean is clean".  I will say however that I have never needed to use anything but tight patches (T-shirt material) and Kroil on a pull-through.  Guys like Tim McMurray and Mike Niksch swear by good old WD-40 doing an excellent job releasing lead, which is what Ron described.  So that's something to consider for sure but I personally do not recommend a rod and brush.

[Gertrude]

If there is anything wrong with the barrel, it isn't the usual factory roughness or burrs because it has been thoroughly worked over.    But yes, at some point it would be prudent to pull the barrel and give it a good inspection, but I think I would try some JSBs first.

Thanks Jason,
Agreed.
I believe some JSB's will be on the way to Steve before the day is over. That will be the next thing we try before removing the barrel.

The strange thing is, just a week before sending it to Steve, I was hitting chicken eggs with it at 75 and soda cans at 100 yds with relative ease. Sure, I missed a few shots, but it was nothing to cause me any alarm.
 It did not seem to be pellet picky, and shot CPHP's, Polymag's, H&N's, JSB's all with pretty acceptable accuracy.

so yes, the most "major event" that happened between me shooting it, and Steve shooting it, was it getting shipped 350 miles, ... BUT ,... (before anyone asks),...
 NO, there was no damage during shipping. It was triple bubble wrapped inside the box, then any/all extra space was stuffed with Styrofoam and newspaper, it was taped, then double boxed and taped again. I was quite intentionally going overboard with the packing and protecting before sending it out... as this is a "precious" and highly prized member in my AG stable.
 You could have dropped it from a plane and run over it with a train, and it would have survived LOL.
 I took photos of it before shipping it out, and when it arrived, there was literally zero damage to the box. no crunches, no creases, no folds, impacts, punctures,... nothing.
 So it is pretty safe to say that nothing physically happened during shipping.

Obviously, something is causing it to group poorly, and I am confident we will eventually figure it out, but I'll be darned if I'm not a bit baffled, that we have not yet figured it out, with all that we have already checked.

maybe I should remind Steve that the rounded end goes into the barrel, and the skirted end is to the rear ?     
 LOL !     
Just Kidding Steve !... we'll get this figggerrrddeded owt   

[Gertrude]

I suppose I should mention here, that after checking and trying all the normal possible issues,... when we did decide to clean the barrel, we did run a couple of pases with a brass brush, followed with a couple of wet patches, then several dry patches.
 After that, we only shot it maybe 20-25 times before calling it a night.
 So yeah,... it very well could be that it needs to see some more shots before it starts to settle back down. I know my Mrod sometimes acts like that after a barrel cleaning.

on the other hand, maybe the rifle just does not like Steve, and it wants to test him to see who is "boss", hahaha.
 or maybe it does not like Arizona air ? LOL !

We WILL get it figured out, and it has become kind of an oddly interesting phenomenon now for both Steve and myself.

Maybe when he gets off of work later today, he can post up some shot strings and groupings.

(note to Steve)- you've got to get your post count up to 20 before you can post a pic on the forum,... so jump in here, and lets make that happen.

Thanks to all who have helped so far, and keep the suggestions coming.
 We will not let this silly rifle win this little battle.
 We WILL PREVAIL ! ! !