Weird barrel/accuracy issues - Brocock Concept Lite

[Arzrover]

I agree with you Rj but yes, I've actually had more that were uneven than even in bore diameter.... mostly LWs. It was explained to me many years ago that some of the Brit makers had spec'd it that way .... higher velocity was the justification , iirc. Many of the test barrels in 25 for the ART project were that way and I even asked Frank Walther himself why.... but he always sidestepped the question. I've purchased a good number of blanks for myself and never had a single one that was like that so it HAS to be spec'd or the result of some particular step in the fitting prep. Frank guaranteed a manufacturing tolerance of only .2% iirc which is so far beyond the pellet tolerances it isn't worth considering so it isn't in the bore and rifling process. The testing we did was about rifling profiles, bore size and choke. The barrels we felt were best and ended being one of the production models had even medium bore and soft choke. The choice by others of the team was a tight bore, tight-loose-tight , and heavy choke. Both shot well w the 25.4s at 100 but our choice also would shoot the 33.4s and Baracudas and several slugs.... all very well.

Back to the OP, since it appears to be a tight-loose-tight barrel, I would do some work to soften the leade and port edges and see what that accomplished. If you don't feel inclined to do that, a call to your dealer or AOA might prove beneficial. Seems like you've at least found 1 pellet that's respectable .

 

[bad_lighting]

Quick update:

Did some testing today. A little windy, hence my groups have 1-2 that are left/right by a half inch or so. I learned a few things.

1. Bare barrel w/ no shroud or suppressor is L O U D.

2. Bare barrel with no shroud/suppressor is TWICE AS ACCURATE AS WITH SHROUD.

I tested with/without suppressor. No change in accuracy. I tested with/without shroud and groups were cut in half. I had a hunch it would do that, so I tested it. Sure enough, much improved performance.

AOA sent me a different barrel to try out. It appears to be some used barrel off of another gun or something, not factory new. Didn't improve accuracy any and actually shot a little worse.

Top left/ middle right groups are with shroud, no suppressor. Bottom left/right/center are bare barrel. Fliers are either due to wind or in the middle group's case two errant rounds from different ammo who's aiming point was top right diamond. WAAAYY off with that ammo. Grid is 1". Basically, without changing anything other than removing the shroud the gun went from 2.5-3 MOA to sub 1 MOA at 50 yards. This to me says one of two things: somehow my shroud is defective/causing problems or all shrouds are a bad idea and reduce accuracy no matter what implementation they have. I'm leaning towards #2. I've been researching barrels and wouldn't you know it, all the Field Target guys aren't using shrouds and they're all using air strippers/brakes of some sort.

Some detail shots:

 

[Arzrover]

I had the opportunity to shoot a Brocock XR on Wednesday and we were discussing various things about it and others. It shot extremely well but it was pointed out that SOMETIMES they shoot better without the shroud. Got me thinking ... if the barrel, shroud, and mount base aren't all perfectly straight, you end up with bending stresses on the barrel which can affect consistency. What if you put an oring at the base to screw the shroud down against ? It might help alleviate those bending stresses if you don't over tighten. 

Just a thought on something to try.

Bob

 

[bad_lighting]

I had the opportunity to shoot a Brocock XR on Wednesday and we were discussing various things about it and others. It shot extremely well but it was pointed out that SOMETIMES they shoot better without the shroud. Got me thinking ... if the barrel, shroud, and mount base aren't all perfectly straight, you end up with bending stresses on the barrel which can affect consistency. What if you put an oring at the base to screw the shroud down against ? It might help alleviate those bending stresses if you don't over tighten. 

Just a thought on something to try.

Bob

It has an O-ring at the base of the threads at the receiver end, as well as at the muzzle end. The shroud (on my Concept Lite that is, haven't seen the XR setup) isn't what I would call a "stressed member" in the assembly and doesn't contribute to barrel rigidity. It floats at a micro level. That said, my rifle's groups drop to dime size or less without the shroud. With the shroud they're 1.5"+ at 50 yards. Terrible.

 

[Arzrover]

It should not be stressed but so I was just trying to think of a simple way to relieve stress that should not be there. If you shine a light in the breech end and look at the muzzle , does the bore appear centered in the shroud?

Bob