Shortening a choked barrel (Artemis CR600W)

[elmury]

Hi all,

I wish to shorten the length of my Artemis CR600W .177 CO2 air rifle barrel.

After pushing pellets manually through the bore I notice;
- a narrow part in the beginning
- a wider part in the middle
- and a narrow part at the end of the bore.

So, in contradiction to many other CR600W owners/reports here on GTA, it seems my barrel is choked.
(perhaps European models come with choked barrels?)

Anyway, as I have understood, manufacturers choke their barrels to make them less pellet fuzzy.
Does all this mean that I can go on and cut my barrel, loosing the choke, re-crown it and end up having a nicely shooting un-choked barrel?

Lex.

[Ribbonstone]

Throw the dice….see if it comes up odd or even? No one can tell if it will shoot as good, worse, or better (just that its most likely to shoot slower).

 With a tight spot at the breech and a tight spot at the muzzle...the muzzle end could be intentional or by accident.  Pretty sure the breech end tight spot is by accident.


Couple of questions:

Sure it’s a tight spot at the breech..not the o-ring in the barrel, the start of rifling engraving the pellet, or a burr?

SUSPECT that the Gen 2 barrels (Storm-rider barrels are the same as the 600W barrels) might show a slight muzzle choke, likely due to the way they are threaded for the new style LDC.

--------

Usually think about “worst case” ( in case the dice toss came up “craps”) and look on-line before I reach for the hack saw.    Really hesitate to cut a good shooting $200 barrel in the hopes of turning it into a great shooting barrel. 

Thinking the replacement barrel cost for that rifle would be more like $35.

[elmury]

@Ribbonstone
I think you are correct. I have the Gen 2 barrels on my CR600W and CP2 pistol/rifle.
The ones with the screw on LDCs.

About the narrow spot at the breech side;
Could it be that it only feels tight and narrow but actually is the rifling that is being cut into the pellet?

[Ribbonstone]

'Likely' is my best answer...there is a larger/non rifled short smooth bore section (if it were a firearm, would call it the "chamber") leading up to the rifling, so it always feels like a restriction when the rifling starts to engrave the pellet.

Took me like 5 weeks of thinking about it to get me to cut off a .177 QB79 barrel to carbine....just to match a previously done .22 QB 79 carbine.  Shot so good uncut, was really hesitant to cut it just to make a set of "twins".

Same kind of care getting a good crown as any other barrel.

Grouped just as well as before....just shot a different pellet best and was a bit slower.

[elmury]

'Likely' is my best answer...there is a larger/non rifled short smooth bore section (if it were a firearm, would call it the "chamber") leading up to the rifling,

I think that section is called "leade" with airguns?

so it always feels like a restriction when the rifling starts to engrave the pellet.

Ok. Must be it then. So no tight area at the breech side. Just at the muzzle. Makes sense.

Took me like 5 weeks of thinking about it to get me to cut off a .177 QB79 barrel to carbine....just to match a previously done .22 QB 79 carbine.  Shot so good uncut, was really hesitant to cut it just to make a set of "twins".

I can imagine that took some real hard thinking!
But the QB79 barrel just looks so awfully long. Especially with a LDC attached.

Grouped just as well as before....just shot a different pellet best and was a bit slower.

Good to hear that It all worked out fine.
I'm getting all confident now:)

[elmury]

@Ribbonstone
Btw, did you re-crown those QB79 barrels yourself?
If so, how did you do it?

[nervoustrigger]

Make a square cut, then use a brass screw with an abrasive compound to establish a burr-free bevel.   

My CR600W had rifling damage at the muzzle so I chopped and recrowned it with this method.  The result:



A more detailed writeup on the CR600W:
https://www.gatewaytoairguns.org/GTA/index.php?topic=143793

And a barrel troubleshooting and accurizing how-to:
https://www.gatewaytoairguns.org/GTA/index.php?topic=130555

[elmury]

@nervoustrigger
Yes, I had read your posts about the CR600W.
Very nice result. Also nice grouping at 25/43 yards!

However, I didn't quite get the squaring up part using the drill press + emery wheel?
So the barrel spins in the drill press and the emery wheel spins as well in a dremel??

Anyway, I'm thinking of using a sander to square up the muzzle face.
(see attachment)

[Ribbonstone]

Same basic plan...although as the crown was always going to be covered by an LDC, didn't bother to mirror polish it or bee as deeply recessed.

Just eyeball work to get it to flat....machinist square, files, time...once it is really squared, then the brass lap and polishing.


Good luck with the cut-job.  it's a bit of a random thing, the spot you pick for the cut can be less nice than the parts you cut off.

[nervoustrigger]

I didn't quite get the squaring up part using the drill press + emery wheel?
So the barrel spins in the drill press and the emery wheel spins as well in a dremel??

Right, you got it.  Barrel spinning in the drill press, emery wheel spinning in the Dremel.  Slowly bring in the edge of the emery wheel until it just kisses the muzzle.  Don't push the wheel into the muzzle, do your best to hold it so the abrasive only wears down the high spots as the barrel goes round and round.  Eventually the skipping you feel and hear will become continuous and you'll know the end is square.

Your sander idea can work well also.  I would advise rotating the barrel on a near continuous basis as it approaches being finished, that way any potential lack of squareness will simply become a slightly convex face concentric to the OD, provided the bore isn't badly out of center.  If it looks centered, you should be well poised to achieve a better result than the factory.

[elmury]

@nervoustrigger and @Ribbonstone:
Thanks guys for all the tips.

So both you guys own the CR600W (= mrodair SPA plinkster) as well.
I have seen both your target scores at https://www.gatewaytoairguns.org/GTA/index.php?topic=143793.20
at 25+ yards. Very nice!

I am shooting at 12 meters (~40 feet on my AO scope) indoor bench rested and have a really hard time getting it to group well.
At that distance and conditions it should be literally hole in hole.
Instead the groups are 12 to 15 mm center to center at best!

Been through the usual;
- barrel cleaning
- pellet choice
- manual single shot loading
- LDC on/off, clipping check
- chrony testing (no weird fps changes detected)
- scope swap
- leade and TP hole burr smoothing
- barrel band tight/loose, on/off, change position

So 2 suspects remain:
- bad crowning
- barrel harmonics (very thin long barrel)

(sorry for the metrics)

[Ribbonstone]

It’s an old one (Gen I) as sold by MrodAir as the “Plinkster”.  Tried it with two bands (one borrowed from the PCP version), one band, loose band, and no band.   

Two bands didn’t make any difference, one tight band worked just as well, loose band or no band shot worse.  Did exchange the horrible Gen I LDC for a better LDC, adjusted the trigger, got the safety working with the adjusted trigger, but still running the factory crown.

Might be realistic expectations.  Would NOT be happy with the 25 yard groups with a rifle I had hopes for being a 1” at 100 yard rifle.  Am pleased with it as a co2 rifle that won’t get used past 30-35 yards.

Bought it about 2016...so 5 years of being used.  Changed the o-rings, changed the 12gr. seal, and broke the bolt handle (which seems to happen to both the PCP and Co2 versions on occasion).

Look at it this way.  IF you cut the barrel, you’re going to have to recrown.  If you recrown it full length, you may now want to cut it.  Worst case, you get practice at re crowning.

As a practical matter, if you've not recrowned barrels before, once you cut off the barrel...use the cut off length as practice.

[elmury]

Might be realistic expectations.  Would NOT be happy with the 25 yard groups with a rifle I had hopes for being a 1” at 100 yard rifle.  Am pleased with it as a co2 rifle that won’t get used past 30-35 yards.

Of course, I too would be happy with your results at 25 yards, but I am talking/shooting 13 yards (12 meters)!
At such short distance, indoor, bench rested, with scope, .177 at ~590fps it should be literally hole in hole or at least under 10mm (~0.4") groupings.
Am I not Right?

My Artemis CP2 (which is practically the same gun as the CR600W) in pistol mode does exactly that; hole in hole.
As does my unregulated BSA Buccaneer .22 PCP (ok maybe different league gun).

So there's something really funky going on with my CR600W rifle/barrel.
I'll try to post a picture of the muzzle crown.

[nervoustrigger]

Both of my SPA-made long guns had damaged rifling at the muzzle.  They were purchased 2 years apart from different vendors so it seems to be a systemic quality problem rather than an isolated issue.

Meanwhile, none of the 3 pistol-length barrels had the problem.

https://www.gatewaytoairguns.org/GTA/index.php?topic=166821

[Ribbonstone]

1. Could be worrying about the wrong end.

The barrel is held to the action by little set screws.  On my old one,  both the set screws were kind of rounded looking and stripped.

Didn’t shoot well because the breech end of the barrel wasn’t tight.  Wouldn’t tighten because the screws were stripped (or just made crappy).

Actually think the screws were bad rather than the threaded holes...swapped screws with the ones on the old LDC, which seemed to cure it..started shooting well because the butt-end wasn’t “wiggling”.

The PCP version was ordered at the same time...didn’t have that problem...so it’s not a universal problem

2. Go ahead and play with the barrel band. If tight band vs. loose band shows a BIG difference in point of impact, pretty good indication that the band is stressing the barrel in some way.

3. Every barrel maker screws-ups now and again….generally, the expensive barrels are QC better and the turds are likely to get rejected.  it’s much more common with “cheap” barrels.

Does seem that for about $35 you could replace it (I’d go with a GEN 2 barrel...which would fit, and give you a threaded end to attach a different LDC.

Same inexpensive replacement cost would make experimenting with crowns/lengths much more attractive...worse case, are out $35 to start over and you’ll learn a whole lot along the way.

[elmury]

Both of my SPA-made long guns had damaged rifling at the muzzle.  They were purchased 2 years apart from different vendors so it seems to be a systemic quality problem rather than an isolated issue.

Meanwhile, none of the 3 pistol-length barrels had the problem.

https://www.gatewaytoairguns.org/GTA/index.php?topic=166821

Aha, now we're getting somewhere.
Same here; the CP2 pistol barrel shoots great, the longer rifle barrels not!
Have tried them both. Same inconsistent groupings.
Note that these are all GEN 2 barrels. The ones with the threaded muzzles.

After visual inspection it seems the pistol crown looks smoother then the rifle crowns.
I did not see any rifling damage like in your photos.

I think I'll try a re-crown first whilst keeping the threaded muzzle section.
Don't know if enough thread length remains since the sunken crown part is quite deep:)

[elmury]

1. Could be worrying about the wrong end.

The barrel is held to the action by little set screws.  On my old one,  both the set screws were kind of rounded looking and stripped.

Didn’t shoot well because the breech end of the barrel wasn’t tight.  Wouldn’t tighten because the screws were stripped (or just made crappy).

Actually think the screws were bad rather than the threaded holes...swapped screws with the ones on the old LDC, which seemed to cure it..started shooting well because the butt-end wasn’t “wiggling”.

The PCP version was ordered at the same time...didn’t have that problem...so it’s not a universal problem

2. Go ahead and play with the barrel band. If tight band vs. loose band shows a BIG difference in point of impact, pretty good indication that the band is stressing the barrel in some way.

3. Every barrel maker screws-ups now and again….generally, the expensive barrels are QC better and the turds are likely to get rejected.  it’s much more common with “cheap” barrels.

Does seem that for about $35 you could replace it (I’d go with a GEN 2 barrel...which would fit, and give you a threaded end to attach a different LDC.

Same inexpensive replacement cost would make experimenting with crowns/lengths much more attractive...worse case, are out $35 to start over and you’ll learn a whole lot along the way.

1. I wish that was the problem. Alas, the 3 barrel screws are ok on the gun.

2. I played with the barrel band a lot and it's impact on POI is huge.
As with most of these cheap "receiver/barrel over tube" constructions the barrel points a bit upward and is bend down by the band towards the tube.

3.  I don't think these barrels are sold separately (as a replacement part) here in Europe.
That's why I'm a bit reluctant to mess it up.
btw, these are gen 2 barrels that I have.

[nced]

Hi all,

I wish to shorten the length of my Artemis CR600W .177 CO2 air rifle barrel.

After pushing pellets manually through the bore I notice;
- a narrow part in the beginning
- a wider part in the middle
- and a narrow part at the end of the bore.

So, in contradiction to many other CR600W owners/reports here on GTA, it seems my barrel is choked.
(perhaps European models come with choked barrels?)

Anyway, as I have understood, manufacturers choke their barrels to make them less pellet fuzzy.
Does all this mean that I can go on and cut my barrel, loosing the choke, re-crown it and end up having a nicely shooting un-choked barrel?

Lex.

Not PCP related but that is what I did when I bought a .177 R1 barrel, then did a home "chop and choke" and the results were good.

The first choke job was using a large pipe cutter where I turned rollers 01 tool steel rollers to replace the existing "cutting rollers". This worked, however it also damaged the muzzle finish..........


My next scheme was to make a "choke clamp" from the head of a 1" grade 8 hex head bolt. The head of the bolt was bored with a hole .005 larger than the muzzle OD, then hack sawed across the "corners" so the kerf of the hack saw blade would form the relief for compressing the muzzle using a heavy 5" bench vise............
   

The choking was done by pushing a new pellet through the bore after the "swage" and gaging the amount of choke "by feel". This needed to be done several times pushing a new pellet through the bore till the greatest restriction during the trip through the bore was at the choke. This took a lot of "vise pressure" requiring a long "cheater bar" on the vise handle. When the choke was finished the tightness was only about 3/4 that of a HW factory choke but the resulting accuracy was excellent. After shooting the first group at 50 yards (sitting on a bucket resting the gun on cross sticks "hunter class field target style") I was impressed so I took a few more shots to zero the poi on the 50 yard bull and shot the second 5 shot group instead of using holdover. Funny thing is that the chopped R1 barrel on my R9 was the only barrel I've had that shot Beeman FTS pellets well.........


Anywhoo, I don't know how relevant but home choking can be done, however a lot of hassle.

[nervoustrigger]

Yeah if the crown looks gnarly, a first attempt at dressing it sounds like a good plan.  Let the abrasive do the work.  Don’t apply pressure more than roughly a pound or so…meaning less than the weight of the drill itself when working with the muzzle pointed up.  And keep the drill moving in a random orbit to avoid developing a lopsided bevel.
 
However I’m a little alarmed by your comment about the thread length and depth of the crown.  Sounds pretty sketchy if it’s so deep that removing it would remove nearly all the threads.  For example when I had to shorten mine to get rid of the damaged rifling, there was still adequate threading remaining.  The OEM crown should be nowhere near that deep.

[Ribbonstone]

Just going to mention something about depth of the crown recess.

Have a couple of very good shooting BSA .177 springers.

The muzzle looks like an 8mm air gun.

They didn’t do it by hand...they backed bored the rifle from the muzzle for about 1.2”….and formed the .177 crown way down in the  back-bored hole.

Taking a look with a light.,..down in that 1.2” recess is a nice even flat crown with a good smooth radius at the rifling.

The other extreme is the dead flat crown put on Colt cap-n-ball barrels (and good reproductions).  Nice even smooth tiny radius for the rifling…..but they “ding” easy (almost defy you to find an original that’s not AFU).

The dept of radius is for ding-protection...smooth and even is for accuracy.  If it’s hidden under an LDC or inside a shroud, ding protection is already a given.