Grouping MOD on/off


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If it is any help, I thought I was being smug by using the purple (.22) diffuser in my Wildcat Evo on my .243, after all there did seem to be adequate clearance, and yes it certainly worked and did seem to help to reduce the report substantially, then all of a sudden I completely missed a Fox at 70ish yards. The following paper test at 50yds produced a 6" scattergun group, change to green diffuser and back to single hole groups.
Moral of the story, eat humble pie and follow manufactures recommendations.


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any mod that alters accuracy (negatively) rather than just point of impact is not fit for purpose
unless it is a stock issue exacerbated by the addition of a mod eg ProHunter

There are too many variables to diagnose properly online. But, if it was me I would try eliminating some variables:

Lets suspect the mod first -

Look for baffle strikes in the mod.
Try the mod on somebody else's rifle.
Try someone else's mod on the rifle.

Lets suspect the stock second-

If using a bipod, take it off and shoot off bags.
If that works put the mod back on, preload the bipod to hell and shoot a group.

Humour me here, third suspect a combination of ammo and mod -

Get a factory ammo with a different 150gr bullet and shoot it. If that solves it I would suspect the barrel/mod is incorrectly threaded, just not quite bad enough to get strikes

That process will give you some more information hopefully pointing towards the likely culprit

If none of that isolates the problem, find the best 'smith you can and get him to check the build of the mod for a misalignment between the centreline of the mod thread and the bore, and/or lop the end off the barrel and rethread/crown it. Not hugely expensive.


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how odd, sometimes a mod can actually tighten up a group. sounds like a pita,, keep eliminating possible causes and you must find the cause eventually.


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You don't say whether you have actually checked the free float clearance, or have I missed it?

I doubt that the moderator weight would have much effect on a heavy barrel profile...but if the stock is particularly flimsy the mod weight may be sufficient to flex the fore-end into contact with the is the quickest and easiest thing to check which could cause your symptoms.

Check the clearance by sliding a £20 note along between the barrel and fore-end. Resting the rifle on the bipod/fore-end with the moderator on and off both cold and warm and see what the clearance is...The £20 note thickness is minimum there is no particular maximum.

If the clearance is close, your shooting hold might also be increasing the effect if you bear down on the stock, so try a light downward pressure on the scope and make sure the £20 note is still not trapped.

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If you screw the mid on and pinch it up firmly, then look down the barrel with the bolt removed and the barrel held over an A4 sheet in bright light, can you tell if the mod is central or pulled off centre as it pinches up?

If it's even slightly off axis, there may be your problem.

If not and it looks concentric, it could be as ActiveVIII says...harmonics and nothing to worry about. Groups scattering like that can also be an indication that the barrel whip is contacting the stock so increasing free float gap should sort things out. Adding the mod can alter and may increase harmonic amplitude. If you home load you could try different load combos until you tighten up the group again but if not, try different ready-mades. Some will shoot better than others. If you can't get factory to shoot with it, and you don't want to pare away some material from the stock then I'd look at replacing the mod for something lighter/shorter/both.