What purpose is the shroud on an Impact?

I can tell for sure that air does go in the shroud.

When i had my impact i bout a new barrel kit (used) have a bad oring on the closest to the breach. When i would shoot a big piff of air would come out.

I cant remember but when you unscrew the threaded end for a ldc its actually a stripper also

It may seem like the shroud is not doing anything but like Deadeyedill said it does draw back a lot of air. On the .25 and .30 there's an air stripper about 1 inch long inside. Enough to strip some air back into the shroud and what's left goes into the LDC. If you had a shroud + LDC, you can get by with a smaller LDC but if you are going directly from barrel to LDC, I would suggest an LDC a little bit longer because it will be taking the full force of the air.

Azycray, please forgive me if I'm sidetracking this post, but your talk of shrouds, LDC's and _harmonics_, got me to wondering if LDC's had any positive/negative effects on accuracy. It all has to do with consistency. Beyond harmonics, and I am absolutely sure that harmonics do play a role in AG accuracy. (You can prove that by shooting a group from a rest in your usual fashion. It will probably be with a bipod or with the forearm on a bag. Shoot your target in the same way, and then with a 5 pound weight suspended/taped from/to the end of the barrel. Your point of impact will likely be different, of course, but more importantly one group may be much better than the other. (This is a crude example, but you get the idea).

Anyways... beyond "harmonics" I'm wondering if LDC's affect accuracy in a positive or negative way. In theory, a clean exit from a perfect crown with a pellet with a perfect base/skirt is good for accuracy. My question is, for those that have experimented with AG's with and without LDC's... is there any difference? Doest the pellet get buffeted by the air turbulence likely to occur in the LDC? After all... HPA is quicker than a hunk of lead traveling through a baffled tube. I have a Gemtech suppressor I sometimes use on an AR-15, it's quieter, and does not expand the group size, although it does lower the POI and inch or so at 100 yards which is not a big deal. 

Well guys I half to say the answer to the question was answered by The Godfather of LDC and shrouds the one and only Donny fl I would say he knows his stuff and as always Donny a pleasure to see you on this form and answering questions love your products. John Day 

What is the LDC? It's probably obvious. I hate abbreviations, especially when the first time used, it is not spelled out. It used to be a common courtesy that is unfortunately not so common today..



I have a new Crown in.25. It is not back yard friendly. I ordered an adapter from Donnyfl and was very impressed with its fast shipment......thank you Danny. I would have bought a moderator as well, but Danny does not ship to Germany. Other than cost, it is no problem for me though as it is always less expensive to buy a part that is already in production than to make a one off. I have a machine shop, but I am a bit concerned with the adapter's alignment with the bore, as it appears to mount to the shroud. So my question to Danny is what bore to baffle clearance should I be using?

The LDCs from DonnyFL don't negatively impact accuracy.

My Wildcat 25 shot a 1" group at 100 yds with the KOI attached.....8 shots.

Steve-I 

In your post you say Danny a few times do you mean Donny? As in Donny fl the maker of moderators adapters etc. if so you can go on Donny's fl website and ask any questions he will gladly help he is a great guy very helpful. John Day

Thanks Bob_O, glad to hear that!

Regarding a .22 Impact, if the LDC attaches to the shroud (and I'm betting a DonnyFL shroud would be better set up for a LDC than the FX one, correct me if I'm wrong) what keeps the barrel centered in the shroud? Do you still retain that "telescoping" centering piece, even though it does not extend? AND... does that shroud assist the LDC since there must be some kind of "gap" between the muzzle and the LDC? Hopefully not too many questions here!

Steve-I 

In your post you say Danny a few times do you mean Donny? As in Donny fl the maker of moderators adapters etc. if so you can go on Donny's fl website and ask any questions he will gladly help he is a great guy very helpful. John Day

Click to expand...

Sorry John, you are correct. My error, I meant Donny. I asked the question about baffle clearance here because he has already responded to this thread. My question is the same as what has been asked by Leadfoot. The silencer attaches to an adapter on both the Crown and the Impact and in both cases the adapter fits to the shroud not the barrel. In that light maintaining concentricity with the barrel bore seems a bit dubious because the fit of the shroud to the barrel is a bit loose. I'm not questioning the functioning of Donny's silencers. They clearly work well. I would like to know the clearance I should be using between the baffles and the center of the bore that adaptor requires. For instance, the center hole in the adaptor is .375" and the original FX shroud cap has a .312" hole, so there is plenty of clearance there. I was under the impression that a minimum clearance is more effective.

Minimum clearance certainly IS more effective. Even the old 16mm Beeman M/B's were cal. specific. All the original volumetric are cal. related & naturally everything over sees seems to come with different cal. inserts. The Marauder even had different baffles at first just too many people double loading & thinking it should be a warranty issue.

And the difference may not be all that large.

But what you seem to be talking about involves a lot of stack(ed) tolerances. A threaded barrel ( threads cut to the bore center ) with direct attachment is really the only way to keep your baffles tight which does work best.



John

Well, I'm no specialist but I'm using a 25 Caliber model Sumo and Tanto on my Streamline 22 and I can't tell a difference from my 22 Caliber Sumo (presently on loan to a fellow air gunner).

Maybe there is more clearance with the larger calibers where some rifles aren't as accurate right out of the muzzle, so as to avoid problems such as clipping. I don't know.

ADDED:

My FX Wildcat 25 has Donny's suppressors and adapter attached directly to a shroud as well.

Well, I'm no specialist but I'm using a 25 Caliber model Sumo and Tanto on my Streamline 22 and I can't tell a difference from my 22 Caliber Sumo (presently on loan to a fellow air gunner).

Maybe there is more clearance with the larger calibers where some rifles aren't as accurate right out of the muzzle, so as to avoid problems such as clipping. I don't know.

ADDED:

My FX Wildcat 25 has Donny's suppressors and adapter attached directly to a shroud as well.

Click to expand...

Well, you could measure the outlet hole on those suppressors and answer the question as well as Donny I guess. As I stated, my machine shop is not a commercial endeavor I have 3 lathes, four milling machines, shapers presses and saws and a complete welding facility. I will make a moderator because I can't buy one. In the end, I will measure any misalignment that may exist between the barrel bore and the shroud and report back here with the number.



Your observation may be spot on as well. That clearance may not matter very much on a PCP. On a powder burner, it certainly does. Consider that on a powder burner chamber temperature starts around 2000C and drops as the bullet progresses down the barrel to around 600C at muzzle exit, more or less depending on the propellant and its burn rate. On a PCP the propellant air temp will drop.as well, but it will drop to a temperature much lower than ambient. As the charge air temp drops, so does its volume. Perhaps this difference is the reason for your observation. I guess, I'll see soon enough.

I just went to DonnyFL's website and clicked on the "FX Impact Fixed Shroud" link and see where there's a long slotted "cage" maybe 5 inches long that centers the barrel in the shroud and also has the threaded section the end. So it seems there is a gap between the barrel and the LDC which would provide for even more volume to help increase the the function of the LDC. This is for the .177 and .22 cal only. For the .25 there is an air stripper which probably also centers the barrel and has the threaded section on it. I'll be giving him a call when it's time for me to order!

I just had the 25 Cal Crown apart to measure everything. Here's the deal. The air stripper does locate the 9mm OD barrel to the shroud via the stripper O-ring. The barrel is choked. It measured .241" go .242" no-go. I measured this with precision hole gauges. The ID of the shroud is slightly over 1" . Fully extended the distance between the air stripper and back side of the shroud cap is 9.395 cm from the factory. This equates to 47.6 cc volume of that expansion chamber (LDC?).The factory shroud end cap is bored .312" (5/16"). I will make a barrel extension alignment gauge to measure the shroud to barrel parallelism and any misalignment there is to determine the real moderator internal bore clearance required for the moderator. Stay tuned.