CROWN POI CHANGE

[2D1C]

I'm sure you guys have noticed a POI change when shroud is in versus out. I am talking with an individual who can make a CF shroud baffled that could be fixed.
What got me thinking about this was the other day at the range a guy wanted to shoot my gun. The shroud was extended, I standing behind him was really surprised how much vibration there was! So I retracted it had him shoot some more and no vibration. I remembered a video Matt dubber made on LDC's and the difference in the POI especially of free floating barrels. I have had the shroud and barrel off numerous times but haven't paid attention to how that adapter works that allows the shroud to extend, I'm thinking it could be moved all the way back and tightened to stay there.
I think a 3" longer CF baffled shroud would not only look great but also be functional. Thoughts???

Dennis

 

[Widget23]

I'd be interested to know if there is something loose in your barrel/shroud assembly. 
Your idea sounds like a good plan though.

 

[2D1C]

No not that I am aware of. I extend and lock it.

 

[Oregun]

*

 

[SocalTrail]

When I had my Crown, I noticed definite POI changes between shroud extended, collapsed and collapsed with a Donny FL sumo attached. This is to be expected swing as how your changing the harmonics of the barrel and changing the weight distribution. That said, the rifle was consistent with each change. My concern with this was the amount of variation in POI change with the different variations. With my Taipan Mutant and WAR Flex, I have little to no variance in POI when adding / removing the mod or extending the shroud in the FLEX. I will probably catch poop from the FX fans but I think the Smooth twist x barrel system is inheritantly less “solid” and and more prone to have a POI change compared to something with a nice heavy steel barrel attached firmly to the receiver. Part of the reason I sold my Crown after 2 months.... but that’s a whole story in itself.

 

[GriffyGriff]

"SocalTrail".... I think the Smooth twist x barrel system is inheritantly less “solid” and and more prone to have a POI change compared to something with a nice heavy steel barrel attached firmly to the receiver...

Now that’s an interesting assumption. Is the Smooth Twist X barrel far more harmonically sensitive than the original Smooth Twist and steel rifled barrel counterparts? I feel a comparison coming along soon.

 

[broekzwans]

I don't think it has that much to do with the harmonics of the barrel but more with the weight distribution that's changing. The X barrel system is very thin (barrel liner is only 10mm and outer tube wall thickness is around 1 mm if I recall correctly) which makes it very dependent on the attached weight and the weight distribution. I have a LW barrel of 600mm long and the .30 STX barrel of 600mm long. If I attach a weight of about 100 grams (magnetospeed bayonet) to the end of the barrel the POI change is completely different for both. The LW barrel drops about 5cm/2 inches at 100 meters and the STX barrel drops about 6 to 8 inches at 100 meters dependent on whether the shroud is retracted or extended.

I'm now thinking about adding a carbon fibre tube over the STX barrel system for extra ridgidity... I'm only shooting competition with my crown so probably the shroud will be removed because sound isn't a problem.

 

[AirSupply]

In Australia the fixed shroud comes as standard. It doesn’t reduce sound. I changed mine to Carbon Fibre. I used the fx parts and just replace the aluminium with CF. 
broekzwans I like your idea. I did here that FX had a proto type smooth X barrel that did have CF outer barrel instead of the steel. 

 

[wolfie]

Hi guys
Haven't tinkered too much with mine. 25 laminate.
Gun comes with shroud in nearly touching the end and fully out about 4 inches I would guess. All this I know you know but for others reading this.
No poi change in or out noticed.
About 200 shots only so far. 
Barrel fully cleaned after a 100 shots.
See a lot of people having the shroud fully closed but adjusted to about 4 inches or so further away. Might this be the reason.
May be worth trying with Chrono set up shooting at target , both closed and open shroud.
I guess it is what individuals are looking for but think noise level is acceptable, more noise from pellet impact. Certainly at a range quiet shooting guns IMO are unnecessary, what with high powered PB's going off. I use a Howard Leight impact ear protection, so not fussed at noise.

You know FX put a huge amount of research time into their products and then we make non standard changes which may change all the parameters. 
Not forgetting that makers of after market products are always looking to enhance their sales, rightly so but be aware. I wonder how much research those same companies can do what with access to special testing gear across many different makes of gun.
Is it worth the effort for a couple of decibels. Each to their own though.

safe shooting

 

[SocalTrail]

"GriffyGriff"

"SocalTrail".... I think the Smooth twist x barrel system is inheritantly less “solid” and and more prone to have a POI change compared to something with a nice heavy steel barrel attached firmly to the receiver...

Now that’s an interesting assumption. Is the Smooth Twist X barrel far more harmonically sensitive than the original Smooth Twist and steel rifled barrel counterparts? I feel a comparison coming along soon.

I’m not sure I would necessarily call if more “harmonically” sensitive but it based on my experience with the crown and other rifles, I observed the crown to be more sensitive to any changes imparted in the barrel or shroud which is a direct result of its design. Not saying it’s bad but the thin little barre liner covered by another thin tube will never be as stable and environmentally consistent as a heavy barrel. Airguns and firearms have similarity in the fact that after you pull the trigger, an explosion essentially happens - ie. Gasses expanding which makes the projectile go down the barrel. As a result of this we get harmonic waves that travel down the length of the barrel. In firearms, this element is actually exploited in reloading processes to essentially time the bullets exit of the barrel with a flat spot on the harmonic oscillation. They do this by load development and even further with weighted barrel tuners. The tuners move a weight fore and aft on the muzzle of the barrel in an attempt to manipulate the oscillations. With the crowns barrel, the design seems to me that due to its lack of rigidity, it would be very sensitive to any changes - muzzle devices, shroud movement, etc. and this is exactly what I found when I had mine. If I left my crown in a gun rack and there was any pressure on the barrel, my poi would slightly change also. Adding or subtracting anything from the shroud also changes the poi. By adding a mod or extending the shroud it is actually physically weighting the end of the barre down to change the POI but it is also changing the harmonics in the system.

Someone above mentioned attaching a magneto speed to the end of a barrel. I have long range centerfire rifles with heavy barrel contours (M24 and MTU for those who know) and can attach the magneto speed to those with very little to no change in POI or harmonics. The rifle will still put up solid groups without a change in impact. On the other hand I have a lightweight 7mm hunting rifle with a pencil barrel profile. You attach the magneto speed to that and the point of impact changes almost 2 inches and the groups open up double the normal size. This all goes back to the original point. A little long winded but I wanted to give my observations a little backbone. I play with this stuff A LOT on a professional and recreational level.

 

[broekzwans]

"AirSupply"In Australia the fixed shroud comes as standard. It doesn’t reduce sound. I changed mine to Carbon Fibre. I used the fx parts and just replace the aluminium with CF. 
broekzwans I like your idea. I did here that FX had a proto type smooth X barrel that did have CF outer barrel instead of the steel. 

Nice shroud @AirSupply !

I haven't heard that FX was testing with CF outer tubes for the X barrels but maybe they are?! The advantage of CF is that it is a good vibrations damper which might help dampen the amplitude of the harmonic oscillation of the barrel. For the X system this probably won't hold since the liner is "floating" in the outer tubes via orings and held in to place inbetween the barrel end nut and the breech end of the outer tube.

 

[Springrrrr]

Leverage is working against you with the extended shroud. You want to see a POI change, look at the Gauntlet after the barrel has been bumped.

My Daystate Wolverine seems to be very stable. Even when I put the Huggett moderator on it there was no POI change to speak of and it holds POI because the shroud is locked in pretty tight to a thicker barrel than that of the FX.

 

[SocalTrail]

"Springrrrr"Leverage is working against you with the extended shroud. You want to see a POI change, look at the Gauntlet after the barrel has been bumped.
My Daystate Wolverine seems to be very stable. Even when I put the Huggett moderator on it there was no POI change to speak of and it holds POI because the shroud is locked in pretty tight to a thicker barrel than that of the FX.

You hit the nail on the head with that example. Daystates, RAW, WAR, and the old theoben rifles use nice thick barrels and substantial barrel / receiver interfaces. There are others out there that do the same, those mentioned above are the ones I’ve had personal experience with. 

 

[2D1C]

@AS can you share where you found that shroud?

 

[nomojo65]

I do love the look of carbon fiber!, I thought of just wrapping mine?, Rather have the real thing., I to have seen some POI changes with shroud at various lengths, but I expected it..., I shoot with the shroud retracted Noise isn’t really a concern where I shoot,also about the barrel stiffness or lack of! It’s designed, engineered this way and I believe as long as it’s repeatable and constant in nature I’m happy! I mean they had to come up with a system that was cost effective to produce plus give the customers want they wanted ( multiple calibers in one platform.), I didn’t buy mine to be the ultimate target rifle!, there are better choices for that application! All guns will change POI for various reasons( to many to list!) Personally I like mine, does what I expected plus Gives me reason to experiment and learn.

 

[2D1C]

I didn't mean to imply I was not happy with the Crown. It's great! More than happy I bought it.

 

[nomojo65]

Sorry, I didn’t mean to imply that!

 

[agnthooziast]

I just found out where I prefer the shroud adjustment and leave it there (fully extended with a Donny FL tatsu). I'm gettin' 3/8" to 5/8" groups at 50yds that stay on poi which trips my trigger. It is vewy vewy quiet when hunting wabbits too!

 

[AirSupply]

broekzwans thanks. It was over a year ago I heard they had a CF barrel. When they announced the Crown. Nothing came of it. May have cost to much. 
Dennis in Oz there is no sound moderation allowed. The shroud we get looks the same but doesn’t telescope it’s fixed. The piece at the breach end I’d guess is the same as yours the other end looks like this. 

Its really just an air stripper without the hole. I had to cut the aluminium tube to get the 2 ends off. Then a bought a CF tube in the same size as the original aluminium and cut it to fit. Bit of fiddling but not difficult. AussieGav mentioned Airfective are doing a CF shroud for the Crown. He makes great stuff. 
Michael

 

[2D1C]

Cool! Thank you Michael, I'll google them.
It's great fun figuring all this out. The Crown is accurate extended or not. Now I'll experiment with that as well. My thought process is...Shooting subsonic? The further the quarry the greater the chance of it dodging the pellet. So silence is golden in hunting. Also a loud gun is going to possibly attract unneeded attention.
Appreciate all the responses.


Dennis