Reattaching suppressor and POI change

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elh0102

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Jul 31, 2018
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I have several rifles on which I use silencers. On most, if I remove the silencer after sighting in, I can reattach it later with no POI change (or negligible). I recently bought a Brocock Bantam Sniper HR .22, mainly for squirrel hunting. With this rifle, when reattaching the silencer after sighting in, the POI changes enough that I need to make a scope adjustment. It's not really a problem, as I intend to hunt without the suppressor. If I want to use it, I can always just keep it on the rifle after sighting in, being sure that both the shroud and silencer are good and snug, so no real problem either way. I just find it interesting that the Bantam behaves differently than my other rifles. Just wondering if other folks have experienced the same? Maybe my other rifles are the exceptions. 
 
So take this for what it is worth, which is to say the ramblings of a crazy dude on the internet, but that suggests to me that something inside the moderator is interfering with the pellet. Not clipping necessarily, but some sort of un-repeatable turbulence such as the pellet passing too close to a baffle or surface or something. Thus the lack of repeatability of the mount changes that every time, and your POI wanders around. Probably a concentricity issue, if that is the case. 



The way to diagnose that would be to try a different, or larger bore, silencer. If the problem goes away, you probably have your answer. 

Just my thoughts, I could be completely wrong. 
 
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pretty normal considering floating barrel (or semi) the bantam has, more weight in the tip.
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Did u read his post ?

he sighted in with moderator on, removed it, put it on again and has to re-zero.



do you have to re zero when you give your barrel/shround a minimal bump ?

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I did and IME you have (at least check for it) it happens with several floating "type" of barrels, usually is more accurate but a small bump can change the POI due several reasons

It happens with the impact that has a SEMI floating barrel, for sure it will happen in the BK Bantam that looks a full floating barrel (try the search tool and you might find some treads about it)
 
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So take this for what it is worth, which is to say the ramblings of a crazy dude on the internet, but that suggests to me that something inside the moderator is interfering with the pellet. Not clipping necessarily, but some sort of un-repeatable turbulence such as the pellet passing too close to a baffle or surface or something. Thus the lack of repeatability of the mount changes that every time, and your POI wanders around. Probably a concentricity issue, if that is the case. 



The way to diagnose that would be to try a different, or larger bore, silencer. If the problem goes away, you probably have your answer. 

Just my thoughts, I could be completely wrong.
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I believe if that were occurring, I would see an effect on accuracy, in terms of grouping, which seems constant. But, I'll compare the internal diameter with my other suppressor. If the other is larger, I'll try it. Thanks for the suggestion.
 
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If you are sighting in then putting the suppressor on after then this is common. Best thing to do is sight with the suppressor on. If you need to take it off for whatever reason like it will not fit into storage/case then do so but you will need to put it back on when you want to shoot. There is a pressure difference that can effect the pellet when it leaves the barrel or shrouded barrel. Best thing is to sight it in with it or without it and shoot it that way. With that said some of the mentioned above can be an issue as well. A floating barrel or semi-floating with the added weight can cause this also. Now if you are sighting in with the suppressor and taking it off then simply to store it and only having the issue when putting it back on then the act of simply tightening it down can cause an issue. Though not usually to much of an issue but it happens. Your best bet is to just leave it on if you continue to have the issue if you can.
 
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Yes, I know that adding the suppressor will change POI on any rifle, some of mine as much as 4 MOA. But this issue is the latter, sighting in with the suppressor, then removing for transport or storage, and re-attaching. But, as I said, not a big deal, I'll either sight in with it and leave it, or, hunt without it, don't really need it for hunting, just back yard use. 
 
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Long story short, YES, floating or semi floating barrels can change the POI (specially in MOA or SubMOA accurate airguns) even with just a touch of the barrel (so moderator on and off for sure will), is not uncommon, is not much, but it can change ... hope that help!
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That's pretty much my conclusion at this point. I'm probably just luck that neither my Crown nor Red Wolf seem effected to anything more than a negligible amount by re-attaching the silencer. My Steyr accepts the silencer directly to an adapter on a plain barrel, very sturdy, so I didn't expect an issue with it, and I was right. Good thing, because it is very loud!
 
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I have read several issues regarding POI and barrel (and experienced myself). Sometimes it just do not happend, but when it does it can be fixed usually easy with a few touches, others with mods, others just no ... in my case a re zero every week (just in case) and if I hit the barrel, even a light branch touch, I check it. Nice Guns you have! Happy shooting
 
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I never see this when running a .30 LDC on my .25's. I "always" see it if running a .25 LDC on my .25's with the current batches of tight tolerance CNC produced LDC's.

It never occurred on the older hand produced LDC's I have in .25. 

I believe the issue as stated in a post above is turbulence caused by the acceleration of air through the smaller baffle holes in the newer units.
 
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For me, if an LDC affects my POI, I don't use it. Normally boring it up one size fixes the problem. My reasoning is that if the POI is affected from no LDC to with an LDC, then the LDC is doing SOMETHING to the pellet... Good, bad, or indifferent, I don't want that happening in my guns. Case in point is my .25 Vulcan Tactic gen4. I have/had a DonnyFL Sumo on it, and it shot pretty good, perhaps quarter sized groups at 50 yards. I shot it that way for months, until just last weekend I was just experimenting and took it off. The groups went about 1" high, and 1/2" right as with the LDC. There has been no clipping or odd flyer, anything like that. But surprisingly, the groups went from quarter sized to penny sized, consistently. I can only surmise that the LDC was somehow affecting the airflow around the pellet in some way. So now my plan is to bore out the Sumo to the same diameter as the .30 Ronin I use on my .30 FX Bobcat.
 
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HI I read everything and if it shoots good groups then just rezero gun when you remove it , if you have clippings in moderator then enlarge it ,

I bet it is 1 of 2 things , put moderator on like 1/2 turn from fully tightening , the can you wiggle play in threads??? I bet you can , sometimes play in threads can make it impossible to be in exact place each time , if you understand , if you hold up while final tightening each time it will have same poi , remember we live in an imperfect world a bit of play in a thread can shift moderator a few thousands ,and cause huge poi shifts ,

I know in say a real gun with a timable moderator if it isnt on exact can cause poi shifts many feet in long range .

I do not think it is harmonics like some said floating barrel , but any little thing on gun makes huge difference down range .

LOU ,
 
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LOU,

While I suppose several of the other suggestions could be variables, 
what you just brought up about thread-precision is a definite factor.. 

I have 6 PCP guns [5 rifles and 1 pistol] and use DonnyFL setups on all of them..
5 out of 6 guns use adapters, and all of them use the same 2 suppressors..

5 guns are .22 cal, and 1 gun is set up as a .25 cal.
All adapters and both suppressors have a max dia for .25 cal.

If I shoot each gun 'naked' - no adapter, no suppressor, I'll see a certain POI.
If the adapters are threaded on, I don't think I've ever noticed a POI difference..

But, when the suppressors are added - and Yes, the male/female threads are Very Nice, 
however, they're a course thread, not a fine thread, so, there will be room for 'error'..

While installing / threading the suppressors on, there is a noticeable amount of play 
until' the very end when the suppressors' back caps bottom out on the end of the adapter..

That is when and only when there is absolutely no play..

Repeating this doesn't guarantee that the suppressor and adapter meet 100% the same every time though..
And I think that part is what some people don't always take into consideration.. 

So in the case of thread-play Only, I've tried using Yellow 'Teflon' / Thread tape on the adapter threads, 
and the tape does exactly what it's supposed to do - it takes up the gaps between threads, 
and tightens things up a bit more.. When screwing things together after that, there's a big difference.
[Threading things on/off anyways] After doing that, I didn't notice having to adjust as many 'clicks' as before..

🙂👍 

Sam - 

PS: On my direct to barrel setup, [Kral Puncher Breaker] I did notice a little bit of 'barrel droop' 
from the added weight of the suppressor and that is normal..
To help with that, I added a few rubber grommets to the front shroud clamp/ring where the bbl passes through..
It is not too loose, or too tight, but just enough to keep the bbl 'free floating', but not droop.. Cheap / Effective. 

As for POI shifts due to using suppressors - Centercut brought up some good info, points, and improvement 
Since the expelled air is obviously going to be different w/ vs. w/o the use of suppressors, 
I've also noticed that going with one dia size up from the round being fired has always worked like a charm..
*That's why I use the .25 cal suppressors on all of my .22's and not a 22 dia on them..
Tighter space when the pellets exit, so more apt to effect them 

Some people argue against doing that - when it comes to sound lowering efficiency, 
but IMO, I'm much more concerned about accuracy / precision in the end..
 
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Yes loose threads can get you every time . LOL I have used Teflon too , or I have tightened threads with , epoxy , the play causes some to change poi on PCP guns , on a Mag powder burner , you must have perfect threads on both as you have extreme pressures , remember , real silencers use a much harder material then the aluminum we use on our Pcp guns because we do not have extreme pressures that say a .338 Laupa or a 50 BMG , in that case u need precision on your locking mechanism meaning every angle of male and female threads must have 0 play or it can be catastrophic .

If gun shoots accurate then it is fine , so what if it shifts , If you tighten threads it wont shift so you have exact play each time .

If you mount you gun in a gun vist and loosten moderator and measure bottom of moderator say from bench to bottom of moderator and push threads up and sideways you will see your moderator moves alot more then you think . Tighten threads and retry . if you get it same each time you wont have a shift



Hey Dirtydov I spent alot of time to figure out this was happening with one of my guns now I know if I have similar issue look at this first if no clipping ., and as far as hole , yes I also go bigger to prevent alot of things which may happen . Donny FL also told me This as well . But if everything is precise and square you can go smaller but Why the DB savings is not huge so I ream if needed or get 1 size bigger like 30 cal for 25 or 25 cal for 22 .

Centercut , has a point as well too as turbulence changes and creates different flight patters slightly , any little thing changes drastically down range
 
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I appreciate everyone's response, the reading has been interesting, if not especially productive. Not that a lot of valid comments were not offered, the problem is on my end, and I can't figure it out. I've checked and rechecked everything on the rifle, scope, and Donny Silencer, and all appears well. But if I remove and reattach the silencer, the POI changes enough to make it a problem in a hunting situation. Just for the heck of it, I pulled the FX Crown out of the case, which is the rifle that the silencer was on when I bought the Bantam. The Crown hasn't been shot in about a month. I screwed on the silencer, didn't even dry fire it or look at the reg reading. There was a 1" square piece of orange peel stuck on a tree at 30-35 yards from my deck. Put the Crown cross hairs on it and drilled it dead center first shot. And I have had the same experience with the Hogan silencer on my Red Wolf; some rifles you can just trust. Anyway, back to the Bantam. It is a short, handy rifle, and I still plan on hunting with it next season. My solution to the silencer issue, don't use it! I don't need to anyway, just thought I would use it here in the yard. I guess the next thing I will check is the rifles resistance to POI changes from dings on the barrel. I treat my rifles with care, and I would not expect any of them to withstand a major hit with no effect. But minor brushes with trees and branches are unavoidable, so guess I need to test it a little. Given the silencer thing, I'm keeping my fingers crossed.
 
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Gents,

Based on years of shadetree gunsmithing on powder burners, I'm not convinced that a tight barrel/moderator thread fit is the answer to accuracy or clipping problems. Threads should self-center, absent any outside influence. Picture screwing a LDC on the end of a barrel. If everything is dead-nuts, the flat or shoulder of the LDC will mate perfectly with the shoulder of the barrel and the threads will be centered regardless of thread fit (within reason). If something is crooked, all of this goes out the window regardless of thread fit. Something in the chain has got to give. In the powder burner (PB) gunsmith accuracy world, we don't cut tight barrel tenon threads for just this reason. We want the trued face of the action, which is running dead nuts perpendicular with the centerline of the action, to mate up with barrel tenon shoulder, which is dead nuts perpendicular to the centerline of the bore, to center-up the barrel in the action. Trying to accomplish this centered-up fit by using a tight thread fit is difficult for myriad reasons that I won't get into.

A tight, higher class thread fit is necessary for applications where strength in the joint is an issue (more thread contact = more thread strength).

What I think we should be more concerned with, and I think is more likely to blame for the clipping problem, is the barrels threaded tenon for the LDC not being machined dead-nuts to the bore, and/or a shoddy crown. Àn LDC that sits cocked in relationship to the centerline of the bore is likely to exhibit clipping, as will a crown that is not perpendicular to the centerline of the bore. I highly doubt that the airgun factories, whilst fitting-up barrels to their guns, are dialing in the bores at both ends to .0001-.0002 in the lathe prior to any maching operations. If they did, and put the same care into their moderators, I would be willing to bet some folding money that clipping issues would be few and far between. Further, how are these threads being cut? Are they being single-pointed in the lathe, or done with a die of some sort? No matter how accurate the barrel is set-up, I would not trust a die to cut a straight thread.

I wouldn't be surprised if the POI shifts some are experiencing after removing their LDC's is caused by these alignment issues and the LDC's "locking up" differently when being screwed back on, and this in turn playing hell with the barrel harmonics.

Having been inside numerous factory PB's, and being less than impressed with the workmanship, I can say with confidence that DonnyFL's are built to a FAR higher tolerance than what the airgun manufacturers hold on their barrels. I'm sure Donny's name has been taken in vain numerous times after one of his LDC's exhibits clipping. Well...it ain't Donny's fault.

Fortunately, a quick fix to clipping is going with the next size up caliber wise, at the expense of LDC efficiency. Unfortunately, this akin to treating a symptom, as opposed to getting after the disease. The real fix is somebody who understands the problem, has a lathe, and knows how to use it.

Justin
 
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Justin, you obviously have an understanding of the machine work involved in gunsmithing. I am neither a gunsmith nor machinist, just a worn out old banker. But, I have been the user of the products of such craftsmen for a long time. I have also been occasionally successful, and frequently a dismal failure, at my own gunsmithing projects. 

Before my involvement with air rifles, I was mostly active with heavy varmint and bench rest rifles. Let's briefly compare. Metallic cartridge rifles of the type I mentioned involve a heavy barrel, screwed into a heavy action, end of story. "Precision" air rifles, of the Bantam type compare very differently. We have a light barrel, attached to a light action with a couple of grub screws, centered by O rings (I mean, really). But it gets much worse. We have a shroud, which is attached at the breech end to a separate base, which in turn is attached to the barrel with a couple of small grub screws. Then, up front, we have an air stripper that screws onto a threaded muzzle (which itself is a problem). Both of those pieces contact a shroud that fits over both and, again, is centered by the good old O rings. Inside the muzzle end of the shroud, extends a plastic piece that sits just forward of the air stripper, through which the pellet passes, not even sure of its purpose, but I assume it is designed to work in conjunction with the air flow directed by the stripper. Now, we add the silencer and its associated pieces. I've lost count of the pieces involved in all this, but someone better educated in statistics would, I think, calculate a probability of accuracy-degrading error in the air rifle at a far greater likelihood than the cartridge rifle. I guess all this gets back to the air rifle history, focused on indoor and short range target shooting, where robust reliability is not an issue. The number and type of parts involved in air rifle design simply don't transport very well to the woods. O rings certainly have their place in containing highly compressed air. But, why use them everywhere as a crutch for imprecise machine work? 

Bottom line, I'll give the air rifle a season in the woods. If it doesn't work, i have a gun case full of great shooting rimfire rifles that are not much louder (sub-sonic ammo), carry much greater killing power, and have a much greater range. And as a bonus, I can drop them, beat them on a tree, about anything short of running over them, and the POI will not shift. Something else of great reliability, good Kentucky bourbon, and it's that time. Thanks to all for your responses. 
 
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