Tuning New 7-spoke with thinner o-ring dampener design for Crown MKII CF sleeve spacer

[bd2021]

Edit: I am back to the thicker o-rings. See https://www.airgunnation.com/topic/new-7-spoke-with-thinner-o-ring-dampener-design-for-crown-mkii-cf-sleeve-spacer/#post-1251339

I may go with some intermediate thickness o-rings eventually.

I designed a 5-spoke CF Barrel sleeve / shroud spacer with a thicker o-ring, as is on the right below. On the left is a new 7-spoke spacer with a thinner o-ring design.

For comparison of the new 7-spoke to the OEM spacer (that works with the barrel without the FX CF barrel sleeve):

For a size comparison to a dime:

In the following photo, an intermediate 5 spoke design with thin o-ring is on the front, and the last two spacers are the new 7-spoke design. This is just to illustrate installation:

I'm too lazy to go back and take a photo with the 7-spoke design on the front, as I already put the shroud back on.

In any event, I am not as confident in these new spacers because they take more care to install as the o-ring can walk off if care more easily if the shroud is forced over the spacers too quickly or forcefully.

We have two takers already: Consequently, if anybody wants to try these new 7-spoke spacers, let me know. You pay only for shipping ($4.80 for first class shipping with tracking). I have two sets available for trial in exchange for your feedback after you try them.

Personally, I like the older 5-spoke spacers with thicker o-rings, but I ordered the wrong o-rings and am waiting on the correct ones to get here. The older thick o-rings are supposed to be here Monday. The hardware store charges too much for them. The reason I like the thicker ones is the o-ring function is not a seal, but to dampen...at least that is my intent. Both the thin and thick o-ring versions install easier with a little silicon grease and a clean shroud. 

I could even do a 5, 7, 9 or even 15-spoke set if desired, which is cool, but I am still trying to figure out the trade-offs.

The following shows the installation of the longer 5-spoke with thicker o-rings.

which looks like this rendered without o-ring:

 

[jdh2550]

I have the carbon fiber sleeve for my .22 Crown MKI. I would be willing to try a set.

I have not tried the cf sleeve since I don’t have spacers. 

 

[ChRiSiS]

I too have a Crown MK2 with a 700mm barrel that i would be happy to try the spacer on. I have both a .22 barrel and a .30 barrel with CF sleeves that i have not yet installed (because of the very problem that these spacers solve). Happy to try either one if you still have it.

Chris

 

[bd2021]

Great. 

 

[bd2021]

Hi @ChRiSis and @jdh2550,



I tested the 7 spoke version with the thinner o-ring and it worked okay. However, when I removed the shroud today to clean the barrel after yesterday's shooting session, the o-rings got mangled and one of the spacers slid up the CF sleeve. This is not a suitable design as it would require electrical tape in front and behind the spacers, and would also require o-ring changes every time you want to clean if my experience with this new 7-poke design is indicative. 

So back to the drawing board. 

If you two can send me a PM I'll let you know when I get a design that won't waste your time, and same deal, just shipping if you test and evaluate. By test I mean clean your gun, take a string of 5 shots at some distance, then use the CF sleeve and spacers and shoot again, and see if the group shifts, contracts, and/or expands.

I already epoxied my CF sleeve to my crown barrel so I cannot do this test.

The testing I'm doing is just for fit during shroud installation and removal. 

 

[jdh2550]

PM sent. Thanks!

 

[ChRiSiS]

PM sent. Thanks again.

 

[bd2021]

So I have a new design back to the thicker o-rings for better dampening.

Since the spacer allows airflow, the purpose of the o-ring is to center and dampen, not seal. The 7-spookes provides additional centering radial support.

What I hope to do this summer is test some ideas I have and their effect on accuracy. I hypothesize that the location of each spacer can be made optimal to reduce barrel harmonics. However, CF tubing is pretty stiff, so in reality, these are first and formost centering spacers to keep the barrel aligned with the shroud exit hole.

 

[Jlowe]

I have the original one I bought from you and that thing is rock solid on my 25cal 500mm barrel. You could put any mod on you want and that thing wouldn't move. 

 

[bd2021]

I am with you @jasmlowe. The original with thicker o-rings is working for me, too. I am testing another design with 7 spokes and thick o-ring now though the additional spokes are not necessary from what I can tell.

 

[Scotty1]

So far, so good with my originals as well, have pretty tight o-rings on it, and don’t plan on disassembling for any reason. If I do disassemble, I have no problem putting new o-rings on if necessary. Nice and solid on my 500mm .22 cal. 

 

[ChRiSiS]

I received the 7-spoke design from Mike a few days ago and finally got out to try it on my FX Crown MK2 today. The Crown is a .30 with a 700mm barrel. I typically shoot FX 44.8 grain pellets out of this gun, and it has been typically very accurate. It had a Superior liner, but no CF liner tube (unlike my Impacts) primarily because I couldn’t figure out how to use it with the SuperLight barrel. Obviously the design above would deal with that problem.

Now, because it has always been a very accurate gun I wondered if I would see any material difference, especially at the 50 yard distance that I have in my yard and that I typically shoot from the bench. I shot a 5 shot group with it in the original state, then put on the CF liner and installed the spacers before replacing the shroud and shooting two more 5 shot groups.

Here’s a photo of the gun at my 25 yard range.

First of all, the installation was pretty painless. Everything worked just as it should. I did lube the o rings with some silicone oil before I put the shroud on, and I did have to hold it in place to ensure that the threads on the shroud didn’t push the spacers out of place, but that was the only complication, and that happens with the normal spacers anyway.

So, did I feel a difference? Absolutely not. The gun felt the same, just as I expected it would. Did it shoot any different? Well, hard to say for sure. You can judge for yourself from the groups I show below, but I can definitely say that it wasn’t worse, and may have been a little more consistent with the CF sleeve/spacer combo.

Here is the “Before” group.

And here are the two “After” groups.

Note that I have my gun shooting above the POA so that i don’t blow my aiming point away, thereby making it difficult to shoot a good group. Also, I shoot multiple rifles at this target, so there are holes all over it.

The two groups with the CF/spacer combo are technically “better”, at least in terms of group size according to Ballistic-X. However it is obviously very close. Perhaps at 100 yards i would see more of a difference. What I can say is that i have no intention of removing them, since there is absolutely no downside and there may be some upside.

Chris

 

[jdh2550]

Nice review! I’m so anxious to try the set I received. Hopefully this weekend. 

 

[bd2021]

Wow @ChRiSiS thanks for the feedback. A lot of effort on that post. I originally started looking for this spacer after installing a CF sleeve and receiving bad advice that from a vendor that no spacers were necessary with the CF sleave on the crown. Long story short I ended up destroying a moderator without spacers. Since I ended up using expoxy on the CF sleeve to barrel interface, and because I wasn't thinking ahead, I have no before / after comparison. However when I get some time I do want to experiment with number of spacers and spacer placement to see if it has any effect. If it does not it might turn out that only one spacer is necessary. I have three now because that was the OEM number before the sleeve. 



Good luck @jdh2550, especially on finding time. I have a long honey do list right now that is keeping me from my hobbies.

 

[jdh2550]

Had the opportunity to get to the range today. @chrisis did a fantastic review. I’ll try my best. 


My .22 FX Crown MKI was purchased used a few months ago here in the classified section. It has a 600mm smooth twist X superior barrel. I purchased a CF sleeve and messed up. It was longer than the barrel. I cut the sleeve down to leave approx 1.5 inches of exposed barrel once installed.


@bd2021 was generous with this offer and I took him up on it. They arrived quickly and well packaged. They seem sturdier than factory spacers. 


I went to the range and shot several 5 shot groups at 50 and 100 yards with the gun in the factory condition, using JSB 18 gr. pellets (they shoot the best in this gun).


Then I installed the sleeve and spacers. Placed some electrical tape in front and behind each spacer to prevent them from moving, and installed the shroud. I shot several 5 shot groups at 50 and 100 yards with the shroud and spacers installed. 


The results are obvious. The CF sleeve with these spacers drastically increase accuracy at both distances. 


i shot slugs after and had no problem keeping 5 shots within a dime at 100 yards. 


The air temp was in the low 80’s. There was next to no wind. I was shooting from a bench. CF sleeve was not epoxied. The gun feels slightly different with the CF sleeve and spacers during the shot (maybe it’s in my head). Feels slightly tighter, is the best I can describe it. 


I’d like to thank @bd2021 for his generosity and creativity! Without a doubt this gun will always have the sleeve and spacers installed as long as I own it. 


1/2 inch reduction in group size at 50 yards. Over 1 1/4 inch reduction in group size at 100 yards. Pictures of groups were typical of groups shot all day, not cherry picked.

 

[bd2021]

Pretty cool!