New moderator fitted and now I can't hit a barn door


Evening all,

I've recently had a Hardy (over barrel) moderator professionally fitted to my trusty CZ American .308 and it's scattering rounds all over. Without it I can still shoot two inch groups on the range but with it fitted I'm not even on target. I've been told it could be the 'harmonics'. Has anyone any idea why this is happening? Would a different moderator work?


Well-Known Member
try a piece of paper from the end of the forend to the action and see if it is touching with the mod on


Well-Known Member
Not being on target doesn't necessarily equate to scattering bullets all over. On one of my rifles, the POI changes 6" down and 2" right with the mod on - but the group was still good.
Are the bullets definitely going all over the place rather than all in the same place, but not where you're expecting them?


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Check the moderator exit hole, to see if there are any witness marks of the bullet touching it. I've had this.

Also worth removing the mod', cleaning the threads and internal shoulder, and the shoulder on the barrel, and try again.


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Harmonics wont make it scatter. As Dalua says above, you need to use a bigger bit of paper, see if its printing groups elsewhere. If it's scattering with Hardy mod, but not without, there's an issue with either the mod or the muzzle threading job. If it groups fine with another moderator, albeit elsewhere on a large bit of paper, then its the Hardy mod at fault.


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You don’t say but I’m guessing your rifle has been threaded to take the Hardy? Was the thread cut up to the shoulder or into an undercut (best practice is into an undercut with a sharp, neat shoulder for the mod to tighten up to). Very much doubt it is the Hardy as these are CNC machined and have a chamfer lead in to the female thread.

If not the above then as mentioned before, your POI may well have shifted so go back to 50 and increase paper size.

Good luck and let us know how you get on - solved problems are always good to pass on :thumb:


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My first rifle, many years ago, a Sako, was fitted with a mod by a very reputable gun shop. I took it to the range and couldn't even get a shot on the board - it was a big board. Mod off and it was shooting nice little groups. Took it back to the shop and they found the thread wasn't cut square and the bullet was just touching the side of the mod on exit, deflecting it to who knows where.

A mod might change the POI by and inch or so but it really shouldn't move it more than that. I have Hardy mods on all my rifles and they all behave very predictably. The "harmonics" thing is a red herring.


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You will much of the time get a different point of impact with and without a moderator on your rifle barrel, only occasionally will you get absolutely NO change of point of impact. Just adjust your scope zero for the new point of impact.

Alternatively if your rounds fired through the mod' do REALLY give you groups to be embarrassed by whereas before the mod' is connected the POI of rounds fired is giving lovely groups, then the answer most likely is that you are getting what is called "Baffle Strike" where the rounds are literally touching the moderator's baffles on the way twixt end of barrel and end of moderator during the firing cycle!!..

Hope you get that sorted, like QUICKLY"!!

ATB ..... and shoot safely

Sent from my iPad using Tapatalk


Well-Known Member
Evening all,

I've recently had a Hardy (over barrel) moderator professionally fitted to my trusty CZ American .308 and it's scattering rounds all over. Without it I can still shoot two inch groups on the range but with it fitted I'm not even on target. I've been told it could be the 'harmonics'. Has anyone any idea why this is happening? Would a different moderator work?
Mauserman, Hardy moderators have a very good record/reviews.
If it was me who professionally machined your rifle and fitted it and the groups were not better now, than without it. I would want to examin what is causing the problem. My advice is take it back to your gunsmith. john


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As for you having your mod'. "Professionally" installed I will tell you a horror story that happened to me that might give you an idea that your scattered(?) shot-fall is likely a product of Baffle Strike i.e. POOR end of barrel threading...

About 20 years ago I gave my .223 HBVS Remington 700 in to a very reputable and much visited and liked RFD to have the muzzle screw-cut to allow fitment of a moderator of my choice... in this case one of the early but brilliantly alterable 'Wildcat' variety that I collected personally from their shop in the Midlands somewhere.

My much respected RFD passed this simple(?) job onto a friend of his who at the time was doing all manner of dodgy things to circumvent firearms rules and regulations on semi-auto rifles. He was and I think still is a well known geezer.. Anyway, he did the screw cutting.

When I eventually got the rifle back at the initial RFD's shop I went there, new Wildcat mod. in my hands and screwed said onto the muzzle of my freshly returned and turned rifle barrel. As soon as I had screwed the over-barrel mod. just a few turns onto my rifle's muzzle it was PAINFULLY OBVIOUS that there was something WILDLY AMISS... The moderator was so very obviously NOT on straight, even to the untrained eye!!..

I held my rifle up to the light so I could look down the bore and on into the bore of the silencer and all I could see was but a thin crescent of light coming down the bore passed the baffles whereas I SHOULD have seen effectively NOTHING if the mod. had been fitted accurately so that IT'S bore centerline was shared with the rifle's bore centerline....

Following some quite heated discussions between me, the RFD and coincidentally that fella (whom was visiting my RFD at the time) whom he had commissioned to do the simple(??) task of screw cutting, I eventually got a new barrel fitted by that guy... But only after another long wait. I had him screw cut it too, and THIS time it was all done as it should have been done in the first instance!!

So you see, having a moderator "Professionally" installed on your rifle barrel by having the end of the muzzle screw cut by a qualified machinist might NOT necessarily be the perfect done deal one should expect. Occasionally it can be that the screw cutting does NOT perfectly line up with the bore of the mod with the bore of the rifle's barrel, and in this situation even a slightly poor installation will likely give you occasional baffle strikes!..

So look down your rifle bore from the chamber end (with the bolt out) with the moderator firmly screwed into place and check very closely that you CANNOT see anything that looks like it may be even very slightly obscuring the path of sight and therefore the path of your fired projectiles.. If there is ANY doubt whatsoever, take your rifle back to the one you gave it in to to have the screw cutting carried out and discuss the situation with him, and be firm but not rude, OK.!?

ATB ....... and shoot safely

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Well-Known Member
Professional means only someone who is paid.......
I have always gone to recommended gunsmiths for rebarreling/ threading, Even if it does cost a little extra.


Distinguished Member
You say scattering rounds off target

But are the rounds grouping elsewhere (as in point of impact has shifted and a re set of sights is required )


Scattering - as in group opened up to over what the rifle “groups” without mod


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Many years ago I had my m77 screw cut for a mod and off a bipod it shot great. Then one night I thought I would just check zero before a wander by leaning on a wall with bipod folded up. It still shot a good group but about 9in high it turned out that the bipod was lifting the barrel causing it to shoot high out came the knife and a bit off the belt was inserted under the bipod fitting and good to go Hopefully your's will be as simple to rectify


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Barrels need to be indexed off the bore for threading and not all people threading do this.
I've done quite a few rimfires, where I've shortened the barrel down before threading. And surprising how many times you find the bore going off axis when only taking a few inches off. Suggesting that that last bit of the boor was significantly off axit to the outer barrel.
So that always gives the possability that even a well fitted moderator, may still have alignamnt issues.
Also where the threads between the mod and rifle are tight, and the mod does not fully seat against the barrel step, when nipped up tight.
On low power rimfires, the barrel harmonics doesn't really seem to be an issue. So it reduces the variables.

On my 308, which came to me as a second hand outfit, including mod. I started loading for it and testing initially with the mod off. As I increased the charge, I noticed that the group opened up significantly. But with the mod on and the same loads, the groups stayed tight. And the velocity didn't change over the chrono. So for this I concluded that it was most probably barrel harmonics.

In my case, I've not done any more development as what I have works.
But if the extra weight of the mod can bring the harmonics into a sweet spot and bring in a group. I can't see why adding a mod could not upset it.


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I have had a PES mod that was built on the skew so don't discount the sound mod, dave wylde threaded the rifle in front of my eyes and showed me the setting up process with absolute precision. Wasn't until I went to the range and test fired it with the mod fitted, it shot all over the place and on close examination, you could see where the bullets had been striking the exit hole of the mod. Taking it off and looking through it, you could see that the threaded section (spider?) wasn't in line with the bore of the moderator. I should say in the defence of PES, it was bought second-hand and the multiple other models of theirs that I've had have been fine.