Moderator effect

[jon]

Opened a new powder lot and loaded for a sighting in of re-mounted scope (@ 100)... only change to the whole process was the powder lot' (so usual 'low check loads' etc )

New load added 150fps (ES below 20) over previous powder batch with same charge and patterned like a flock of pigs on sennapods - usually get around 10 - 20mm.

Oh well ..a what now moment! so decided to see how POI shifted with the Mod - normally just 30mm down/ 20 left with similar grouping. This time just 50mm down .. but the 3 shots shrank from A6 to 5mm.

Removed mod - back to splatter: mod on again & 2 more 3 shot, 6mm groups: so its repeatable.

Whilst I'm happy with the result ... but slightly surprised too.

Why / how should a mod make the difference? I don't really want to work up 'with/without loads.!

[Chris-NZ]

 

Why / how should a mod make the difference?

 

 

A mod adds mass so changes the harmonic vibration pattern of the barrel as the bullet travels down it. In this case, it's put a useful antinode right at the muzzle and shrunk the group. The opposite could have happened but in general, a mod should be helpful by providing more damping to the system

 

Chris-NZ

[jon]

In this case, it's put a useful antinode right at the muzzle and shrunk the group.

 

Chris-NZ

 

Ok .. that seems logical ... so 1 anti-node just trumped all my other nodes?

Hopefully its a velocity thing so at least it will last more than a can of powder:

Thanks Chris-nz

[Jon2]

Ok .. that seems logical ... so 1 anti-node just trumped all my other nodes?

Hopefully its a velocity thing so at least it will last more than a can of powder:

Thanks Chris-nz

 

Not wanting to hi jack your thread Jon but I noticed for the first time, the other week, that a different type of mod can change completely the performance of a rifle from an accuracy perspective.

 

I have a Jet Z compact on my Sako 75 .22-250 and also a Reflex T8 for the same.

 

I put the T8 on and shot a 5 shot group which measured just over 1.5 MOA (shot at 100 yards).

 

I then shot the same with the Jet Z and group size was in the 4's!

 

I suppose when thinking about it, the fact the mods are different in design would mean the results should not have come as a surprise but to be honest it did surprise me. I just assumed that group size would be the same or similar with either but the contrast was dramatic.

[Chris-NZ]

Changing either mass (weight) or stiffness will directly affect the natural vibration pattern of the whole barrel system. You can't expect to have no change in accuracy and certainly POI when you significantly change the weight of mod hanging on the end

 

Chris-NZ

[Jon2]

Changing either mass (weight) or stiffness will directly affect the natural vibration pattern of the whole barrel system. You can't expect to have no change in accuracy and certainly POI when you significantly change the weight of mod hanging on the end

 

Chris-NZ

 

Yes I agree Chris it makes total logic but any T8 I have used in the past enhanced accuracy and I was surprised at the amount of difference between the 2 group sizes bit as I say and you too it makes total sense in terms of harmonics being changed by the different designs. It was a v interesting exercise.

[jon]

Welcome to the discussion Jon2..

Chris-NZ ... the lump on the end does things ... as you say.: so I'm off to the range to see if I can use it to best advantage, with a sort of OCW ladder downwards to see how wide a window I have and because the new powder batch has warmed things up more that I really want.

Also I want to see if there's a with/without mod sweet spot.

Because the mod doesn't alter speed its use is the variable.

(Anyway I'm told a x55 is only a slow olde thinge and can't possibly get 120-130s over 3000 !!)

[lancslad]

Welcome to the discussion Jon2..

Chris-NZ ... the lump on the end does things ... as you say.: so I'm off to the range to see if I can use it to best advantage, with a sort of OCW ladder downwards to see how wide a window I have and because the new powder batch has warmed things up more that I really want.

Also I want to see if there's a with/without mod sweet spot.

Because the mod doesn't alter speed its use is the variable.

(Anyway I'm told a x55 is only a slow olde thinge and can't possibly get 120-130s over 3000 !!)

Any addition to the barrel is going to effect harmonics, various weights of mods will effect the harmonics and therefore effect grouping.

[jon]

Back to Mods 101 ... at the range the mod mass effect was consistent across a spread of loads/ fps and Cols... poi just shifted .. without mod middle aged spread arrived across the board. ho hum .. ... so a result: but not yet sure at what yet.

thanks for the input.

NB .. having looked at the figures and group, it seems to have a wider 'sweet spot (band?)' and tolerance of speed, load and COL doing a ladder with the mod than without. but it looks as tho' the non- mod load is more prissy. Just to confirm it at 300 and settle on an 'ideal point' with some latitude for the nut on the back.