POI drop

[Vernal]

Practicing in the garden with my LGV when my wife complained that it is a very noisy gun. I had a spare Weihrauch moderator from a HW95 lying about, so I fitted that and it transformed it into the quietest gun I have. BUT although it groups almost as tightly as before, the POI dropped a full .75". The mod just looks like an empty tube, so I really don't see why the POI should drop, it is obviously not clipping or it wouldn't be grouping so tightly. Could someone kindly enlighten me?

The other problem is that it is too long to fit in my gun cupboard with the mod on. Could anyone recommend a mod that is light, effective, preferably better looking than the HW lump, and less than 5" overall length.

[thumbhole]

Most guns will drop POI with a mod fitted, if you intend to use it with the mod, just re zero it back up to where it was job done.

[Phil Russell]

Yes ... can happen. I believe it is something to do with the extra weight of the moderator and the change in barrel harmonics related to pellet exit point.
Cheers, Phil

[GB2017]

i put a swift stumpy modular on mine, just using the top and bottom parts, did the job for me

[Vernal]

Yes ... can happen. I believe it is something to do with the extra weight of the moderator and the change in barrel harmonics related to pellet exit point.
Cheers, Phil

I knew it would be something I couldn't understand!

Thanks for replies

[eyebull]

I have a stumpy square-ended delrin Matt W moderator on mine, looks the business and is effective too. About 5", they come up second hand from time to time. As you say it makes it very quiet.

[Scubashot]

I knew it would be something I couldn't understand!

Thanks for replies

I think that the barrel harmonics is rather like a hosepipe that flicks about if left free, as the water is turned on.
We are after consistency, so that all pellets go in the same place, so we need the barrel to have always flicked into exactly the same place as the pellet leaves the muzzle.
If you screw a moderator onto the end of the muzzle it will inevitably have a small but significant effect on the way that the barrel moves and therefore the position of the muzzle as the pellet exits.

[Shed tuner]

Yes ... can happen. I believe it is something to do with the extra weight of the moderator and the change in barrel harmonics related to pellet exit point.
Cheers, Phil

Well that might be some of the affect, but the rather larger affect is that a big weight on the front reduces muzzle flip, threfore the muzzle is a bit lower at the time the pellet exits, therefore the shot goes lower. If anything it will increase accuracy / reduce hold sensitivity.

The delrin "soundbiter" is a compact 1/2" UNF silencer that is great on springers. Also those little "manders" silencers. I think neither are in current production, but not too hard to find secondhand.

[Vernal]

The delrin "soundbiter" is a compact 1/2" UNF silencer that is great on springers. Also those little "manders" silencers. I think neither are in current production, but not too hard to find secondhand.

Thanks, I will look out for this, or something like it, on second hand pages. I see quite a few new "shorties" say "suitable for gas powered rifles". Do springers have different mod specs?

[Steyr]

Putting a mod onto a barrel will typically shift the poi down due to weight and changes in the harmonics of the firing cycle.

HOWEVER... it can also send the POI up or left or right or ANY combination of these.

You rezero to allow for this shift and remember the POI will again shift if you take it off.

I also generally find the group may tighten a little but as the bore of the mod and the barrel may not coincide...there is no guarantee it wont open up either. The other possibility is clipping but this is usually pretty obvious due to not being able to hit a barn door and shaving in the mod etc.

[baldinio]

I've just put a huggett belita on my ultra, a tiny mod which performs as well as a full size one in my opinion

[Vernal]

I've just put a huggett belita on my ultra, a tiny mod which performs as well as a full size one in my opinion

I like the look of it (but not so much the price), but back to my earlier remark, is this designed specifically for a pcp?

[baldinio]

I like the look of it (but not so much the price), but back to my earlier remark, is this designed specifically for a pcp?

I know what you mean about the price mate, bought mine second-hand from another member on here for a princely 45 quid. I've seen a few second-hand in the sales section. As far as I am aware these should work on a springer

[Mjoh]

I had the same thing happen simply putting a sunshade on my scope. I shoot FT with a TX200 and Big Nikko and p.o.i. dropped about 10mm at 55 yds. I assume the (very) slight increase in weight caused this.