FX Not convinced an FX Crown bottle clamp is a good idea

[steve-l]

My gut feeling told me that if it was safe or recommended then FX would have endorsed it and probably marketed a bottle clamp. I do not feel like it is safe for me.

FX is avoiding this subject because it makes very public a serious design fault. It is no safety issue using a bottle clamp. There is no stress on the bottle. The design fault is the weakness and flex of the thin wall barrel design, but the real cause of the POI shift is the loose coupling of the barrel to the receiver.Some rifles are tighter than others. It is called manufacturing tolerances. Some rifles exhibit this POI shift and others do not. For those deniers here, just remove and replace the barrel back into the receiver and note the inevitable change in POI. The fit between the barrel and receiver is a slip fit clamped by a set screw. There should be a tapered surface in the receiver that mates with a matching male taper on the barrel and clamped in place with a nut. If that simple design was keyed, no POI shift would occur. You will note that this issue is present across most of the whole FX product line, not just the Crown.

Don't get me wrong here. The Crown is a beautiful and very accurate rifle. I really love my Crown and I will never sell it. Although a barrel clamp is an obvious Band-Aid, it really helps. I still must be careful not to bump the barrel or lift the gun via the barrel, but otherwise, the gun will now hold its zero session to session. I must caution the readers here, that all barrel clamps are not equal. All the clamps available appear to be 3D printed and most of the plastic used in this process is crap. It stretches' and deforms under pressure over time. Those that use a fiber reinforced plastic fairs better, but all will slip when bumped. They should be metal, but none appear to be available.

 

[Airgun Al]

FX is avoiding this subject because it makes very public a serious design fault. It is no safety issue using a bottle clamp. There is no stress on the bottle. The design fault is the weakness and flex of the thin wall barrel design, but the real cause of the POI shift is the loose coupling of the barrel to the receiver.Some rifles are tighter than others. It is called manufacturing tolerances. Some rifles exhibit this POI shift and others do not. For those deniers here, just remove and replace the barrel back into the receiver and note the inevitable change in POI. The fit between the barrel and receiver is a slip fit clamped by a set screw. There should be a tapered surface in the receiver that mates with a matching male taper on the barrel and clamped in place with a nut. If that simple design was keyed, no POI shift would occur. You will note that this issue is present across most of the whole FX product line, not just the Crown.

Don't get me wrong here. The Crown is a beautiful and very accurate rifle. I really love my Crown and I will never sell it. Although a barrel clamp is an obvious Band-Aid, it really helps. I still must be careful not to bump the barrel or lift the gun via the barrel, but otherwise, the gun will now hold its zero session to session. I must caution the readers here, that all barrel clamps are not equal. All the clamps available appear to be 3D printed and most of the plastic used in this process is crap. It stretches' and deforms under pressure over time. Those that use a fiber reinforced plastic fairs better, but all will slip when bumped. They should be metal, but none appear to be available.

 

[steve-l]

View attachment 466784

What's your point? That photo is not a barrel clamp.

 

[Kola]

What's your point? That photo is not a barrel clamp.

The thread topic is not barrel clamps...

 

[HogKiller]

FX is avoiding this subject because it makes very public a serious design fault. It is no safety issue using a bottle clamp. There is no stress on the bottle. The design fault is the weakness and flex of the thin wall barrel design, but the real cause of the POI shift is the loose coupling of the barrel to the receiver.Some rifles are tighter than others. It is called manufacturing tolerances. Some rifles exhibit this POI shift and others do not. For those deniers here, just remove and replace the barrel back into the receiver and note the inevitable change in POI. The fit between the barrel and receiver is a slip fit clamped by a set screw. There should be a tapered surface in the receiver that mates with a matching male taper on the barrel and clamped in place with a nut. If that simple design was keyed, no POI shift would occur. You will note that this issue is present across most of the whole FX product line, not just the Crown.

Don't get me wrong here. The Crown is a beautiful and very accurate rifle. I really love my Crown and I will never sell it. Although a barrel clamp is an obvious Band-Aid, it really helps. I still must be careful not to bump the barrel or lift the gun via the barrel, but otherwise, the gun will now hold its zero session to session. I must caution the readers here, that all barrel clamps are not equal. All the clamps available appear to be 3D printed and most of the plastic used in this process is crap. It stretches' and deforms under pressure over time. Those that use a fiber reinforced plastic fairs better, but all will slip when bumped. They should be metal, but none appear to be available.

I'm going to agree with you on the taper, if you absolutely positively want something to be dead repeatable a taper is the way to go. The only issue is getting them apart again. A shallow taper is a B to get apart. I'm almost inclined to say two tapers, one at the receiver end of the pellet port and one at the barrel end instead of one long one. On the fitting repeatability of a FX barrel assy, I'm lucky mine are pretty darn close, not zero but close enough at 30 yards when tested.

 

[Airgun Al]

I think that for some rifles, its the best option for mounting certain accessories like a bipod.

 

[steve-l]

I'm going to agree with you on the taper, if you absolutely positively want something to be dead repeatable a taper is the way to go. The only issue is getting them apart again. A shallow taper is a B to get apart. I'm almost inclined to say two tapers, one at the receiver end of the pellet port and one at the barrel end instead of one long one. On the fitting repeatability of a FX barrel assy, I'm lucky mine are pretty darn close, not zero but close enough at 30 yards when tested.

You are correct, a long taper would not be appropriate. A short , keyed taper and a clamping nut is the correct answer.

 

[Long_Gun_Dallas]

Yes, but air pressure isn't really the issue. With a bottle clamp mounted up front, you are creating maximum leverage against the bottle/action connection. Under normal use, it shouldn't be a problem, and many folks use it, but, using the stock as the mounting platform is strong, and creates no potential pressure on the bottle connection. And it's a very simple job, no stock mutilation required. It's just a matter of opinion and preference.

Indeed. One of my crown stocks broke like this. The bottle connection and block on the other hand, I'm fairly certain I could not break if I wanted to. Dropping the gun would easily induce exponentially more force on this area. Not that any of us do this, but it would have to be accounted for. Large safety margins exist well above the capability of a bipod or slings ability to produce. But, I agree it is largely opinion and preference.

If bottle clamps are good why then at big matches are the pro’s not using them so much anymore. Maybe that says something. Something else is look how many rails are out now!

Even if there is a minute concern and money is no issue, a rail system would be preferable. As we've demonstrated plenty of people have concerns and share them, which can create even the tiniest bit of doubt or hesitation in another's mind. Which is enough... Also, people could be tired of having this exact conversation with their friends and simply not want to be hassled about it at matches

I have only tube guns. I would love to know if and how much carbon tanks grow from empty to fully charged? May be a stupid question but 4500 psi is a lot. Are they wrapped aluminum tanks or truly carbon fiber?

I'd use a clamp on a tube gun as well, but due to length I'd want a barrel band on it, and use one of the Sabre clamps with rubber pads.

 

[alejo]

The POI shift on my Crown was truly terrible. Just the lightest jar of the barrel would knock the POI all over the place. Just session to session everything would change. Just putting the rifle in the case would cause POI shift. I started using bottle to barrel clamps and my POI shift just went away. They work very well and add little to no stress to the bottle. One point of caution........not all clamps are good. Most all I have seen are printed plastic and the material stretches and the grip relaxes. be careful choosing which the one you use.

Hello quick question, what kind of clamp are you using? I’ve been having POI issues on my crown too at 50 yards.
I’m trying to see my options, thanks be safe.

 

[steve-l]

Hello quick question, what kind of clamp are you using? I’ve been having POI issues on my crown too at 50 yards.
I’m trying to see my options, thanks be safe.

Saber Tactical. You will note the clamp is made using a fiber reinforced plastic The fit around the shroud uses a rubber like cushion. The gap between the the shroud bore and bottle bore is perfect and places no lateral stress on the bottle. The clamping screws fit into brass fittings molded into the plastic. I have been using this clamp for 18 months without issue The plastic has not stretched and relaxed its grip on the bottle like the three other clamps I have used. It works really well. It is however a Band-Aid that helps an engineering fault by FX, but does not correct it. I also use a CF sleeve over the barrel without glue.

 

[alejo]

Saber Tactical. You will note the clamp is made using a fiber reinforced plastic The fit around the shroud uses a rubber like cushion. The gap between the the shroud bore and bottle bore is perfect and places no lateral stress on the bottle. The clamping screws fit into brass fittings molded into the plastic. I have been using this clamp for 18 months without issue The plastic has not stretched and relaxed its grip on the bottle like the three other clamps I have used. It works really well. It is however a Band-Aid that helps an engineering fault by FX, but does not correct it. I also use a CF sleeve over the barrel without glue.

Thank you very much I really appreciate it, be safe.

 

[MEC17670]

Before I made wood stocks for my 3 P35s I attached a bipod using a 34mm scope picatinny adapter. The air tube of the P35 is about 33mm so I put some tape in the adapter to take up the clearance. It worked well but you had to get the rotation right, of course, or you were building in cant. Now I have metal picatinny rails bolted to the stocks.

The air tube is an aluminum pressure vessel which I believe there is more reason for concern than there is for carbon fiber bottles. I believe that because of destructive tests on aluminum and carbon fiber tanks documented on video and included here by another member. The aluminum tank failed at a much lower ration of failure pressure to working pressure. In addition, the carbon fiber tank had a chunk machined out of it greatly increasing the stress in that area. And it still failed at a much higher pressure. But without any data or design information it is hard to know how the margin built into the tanks tested compares to the margin built into the guns and tanks we use. Still, I believe carbon fiber tanks in general have more margin against mechanical failure than aluminum pressure vessels. The carbon fiber is not uniform, it is woven and impregnated with resin and it would be irresponsible to assume it is homogeneous when designing the thickness. So the only real choice is to make it plenty thick which in the real world means higher margin.

The twisting force on the bottle from load being applied to the bottle through does stress the reduced diameter near the attachment point. I am confident the clamp squeezing the bottle is not harmful because that stress is in the wrong direction (compressive versus tensile) to be harmful. But the neck down area would have compressive loading on the top and tensile on the bottom. It would take a real calculation to know the significance but I believe it is not important because of the margin in the tank design. If I buy a bottle gun I would consider a bottle clamp for picatinny attachment. I don't think it's a risky thing to go. I don't think any of the manufacturers recommend against it but if they did, that could change my mind. They have the design data and could easily do a calculation to have a much better informed opinion. But since they apparently are not, I think that is another sign it's not risky.

How about the torque applied due to using the bottle clamp as a sling connection?

 

[Peashooter]

I have both a tube and a bottle clamp, but i dont use either CUZ i dont like them, also i feel rifle makers should really make proper rails and not just a attachment spot for a bipod right in front of the trigger.

Dunno about you guys, but i feel a bipod belong in the front of the barrel not at the very back of it.

 

[MEC17670]

I have two bottle clamps now, 1 on my Crown mk2 and 1 on on my HW100 buddy bottle set up.
The HW100 has had it on now for 3 years showing no poi change and is capable of a sling support.
Crown mk2 bottle clamp is new and a much better clamp than my HW100 clamp. I need a sling point further out than my stock mounted sling support to allow to " hang" my gun in a more comfortable way. So far no problems. Only time will tell.