Nice morning at the range; mod POI change ?

MauserM03

Well-Known Member
Surrey Heath-20130720-00155.jpg Surrey Heath-20130720-00153.jpg Surrey Heath-20130720-00156.jpg

Had a pleasant and educational morning experimenting with my new mod down at the range this morning.

Was interested to find out that the difference in POI for mod off / mod on is a full 6cm at 100yards; so using the mod means the bullet strikes 6cm higher than it would without for the same zero. No change in the horizontal plane so I'm guessing this is down to a reduction in recoil. This is in 6.5x55.

It seemed to me to be quite a large change in POI and more than I was expecting; is this a typical shift ?
 

charadam

Well-Known Member
All the mods I have used have shifted the POI downwards, but that's only 6 mods on 3 rifles.

The shift with a T8 was 6" and with a Spartan, 3".

It made sense to me as the Spartan weighs less than the T8.

But your POI shifts upwards, well as they say across the pond, go figure!
 

MauserM03

Well-Known Member
I agree, it surprised me. Instinct told me that the POI should go down.

Extremely consistent results though over about 40 rounds with the mod coming on and off regularly.
 

MauserM03

Well-Known Member
Aluminium. It is an Atec CMM4; pretty light at about 220g if I recall correctly.

​Wish I'd paid more attention in physics...can't figure out the logic.
 

csl

Administrator
Site Staff
More likely its the weight of the mod changing the barrel harmonics that causes the majority of the change in POI (which could be in any direction) but it's also not uncommon for a mod to increase velocity slightly by acting like a barrel extension so that could have a tiny bearing on it too.
 
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RickoShay

Well-Known Member
More likely its the weight of the mod changing the barrel harmonics that causes the majority of the change in POI (which could be in any direction) but it's also not uncommon for a mod to increase velocity slightly by acting like a barrel extension so that could have a tiny bearing on it too.

+1, on harmonics. Barrel compensation can be upward as well as downward.
Adding the mod will have adjusted the 'harmonics wave' (energies released on the shot) barrel 'up' as the shot leaves the moderator muzzle.
There is a lot written about this viz a viz WW2 Mauser vs. Enfield - and we all know you've got a Gerry rifle!
I'd stiil have come to spot for you ;)

PS Glad that mod has worked out for you, I'm very happy with mine
 
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MauserM03

Well-Known Member
Ah, got it, makes sense now. Knowing 'why' will give me more confidence in the kit.

RS - you're welcome to spot anytime ! By the way, best group was 4 touching for under 1cm. That was the (unmoderated) 30.06 though; the old 6.5x55 has a deadly rival !
 

RickoShay

Well-Known Member
Excellent shootin' J, be good to see that 30'06 in action. Do you take the case with you in the field? :D Tis very smart..
 

j0e_bl0ggs

Well-Known Member
More likely its the weight of the mod changing the barrel harmonics that causes the majority of the change in POI (which could be in any direction) but it's also not uncommon for a mod to increase velocity slightly by acting like a barrel extension so that could have a tiny bearing on it too.

How does that work then?
 

j0e_bl0ggs

Well-Known Member
Nothing really concrete there at the end of the day.
No scientific analysis present at either link, just unfounded WAG & hypothesis.
 

j0e_bl0ggs

Well-Known Member
What would your explanation for the increase in velocity be?


I asked 'how does that work then?'

It is not for me to answer that question.

I can see that there is much 'clutching at straws' and no real evidence being provided so far.

Now if there is some real research to cite...


"onus probandi incumbit ei qui dicit, non ei qui negat"
 
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MauserM03

Well-Known Member
CSL - thanks for the links; make for interesting reading.

ROS - thanks, the case is great as it allows the rifle to pack down to a much more manageable size, which is great when travelling by car in particular with a lot of other gear. I usually keep my main stalking steed (the 6.5x55) ready assembled in a drag bag though.
 

bills

Well-Known Member


I was reading how a handful of arabs who couldn't fly a Cessna managed to carry out the WTC attacks without any inside help.

I also read how Hitler started the Second World War by invading Poland.

I also read that there were definitely WMD in Iraq.


Moral of the story... Don't believe everything you read!
Sorry, but I can't see how on earth a moderator can ever "act" like a barrel extentsion. A barrel is rifled, a mod is not only un-rifled, it isn't even a solid tube. Once pressure are released which is exactly what a mod begins to allow to happen, the barrel has ended and the mod has started, the two can never be unified. It's just a physical impossibility. I admit I haven't read the links, the same as I wouldn't if you posted a link about how water was "definitely drier than sand". There is a view and a "proven" point for any point you can think of somewhere online, but some things just can't happen. Hell there are books about some bloke called God, a lot more books about it than you will have on Moderators being part of the barrel. Are we all in Church every Sunday? Well I ain't!

If that theory is true and proven, my FLO won't mind me cutting another 6 inches off my rifles, as the mod is actually a barrel extension and I could weld them on :)

If there are instances of higher velocity, IF, then there simply must be another explanation, as a moderator can't possibly contain the same pressure as the barrel, else it wouldn't be a mod, it would be a barrel.

Just my tuppence worth.
 

csl

Administrator
Site Staff
It seems to be a fairly frequently documented phenomenon that moderators can increase observed velocity. I mentioned it only as a point of interest and didn't really expect people would jump down my throat over it.

It happens on mine (slight increase in velocity) and the "extended barrel" theory is as good as any as to the reason why. In fact it seems to be the only theory 'out there' that I can find?!

I wouldn't have put that in the '911 conspiracy theory' league either but there we go....
 

User00003

Well-Known Member
I was reading how a handful of arabs who couldn't fly a Cessna managed to carry out the WTC attacks without any inside help.

I also read how Hitler started the Second World War by invading Poland.

I also read that there were definitely WMD in Iraq.


Moral of the story... Don't believe everything you read!
Sorry, but I can't see how on earth a moderator can ever "act" like a barrel extentsion. A barrel is rifled, a mod is not only un-rifled, it isn't even a solid tube. Once pressure are released which is exactly what a mod begins to allow to happen, the barrel has ended and the mod has started, the two can never be unified. It's just a physical impossibility. I admit I haven't read the links, the same as I wouldn't if you posted a link about how water was "definitely drier than sand". There is a view and a "proven" point for any point you can think of somewhere online, but some things just can't happen. Hell there are books about some bloke called God, a lot more books about it than you will have on Moderators being part of the barrel. Are we all in Church every Sunday? Well I ain't!

If that theory is true and proven, my FLO won't mind me cutting another 6 inches off my rifles, as the mod is actually a barrel extension and I could weld them on :)

If there are instances of higher velocity, IF, then there simply must be another explanation, as a moderator can't possibly contain the same pressure as the barrel, else it wouldn't be a mod, it would be a barrel.

Just my tuppence worth.


increasing freebore allows you to seat the bullet further out, increasing effective case capacity, which of course, in turn can increase velocity.

as for moderator, I have not tested and measured, but I did read that a moderator could offset around 1" of barrel shortening...I suppose perhaps it's that when the bullet leaves the crown of the rifle, inside of the moderator, there is an environment which is less negatively impacting on the bullet than other 'normal' environmental circumstances would.
 

bills

Well-Known Member
It seems to be a fairly frequently documented phenomenon that moderators can increase observed velocity. I mentioned it only as a point of interest and didn't really expect people would jump down my throat over it.

It happens on mine (slight increase in velocity) and the "extended barrel" theory is as good as any as to the reason why. In fact it seems to be the only theory 'out there' that I can find?!

I wouldn't have put that in the '911 conspiracy theory' league either but there we go....


Certainly wasn't jumping down your throat. If you were the fool who invented the theory I might have, but you didn't, you just quoted it.

I don't know of a 911 conspiracy theory, all I have seen is 911 conspiracy fact.
2 planes, 2 impacts, 3 massive buildings, er ok, I am a theorist.
4000 degrees centigrade, enough to melt steel within the building core (not possible btw), but not hot enough to burn the Koran and the plastic ID card of the pilot, which just landed in the dust without so much as a scorch or melt to make it illegible, yeah, I am still just a theorist. :D

I will drop my FLO a letter about it and quote the links you mentioned. Be interesting to see if they approve my "permission to include mod in barrel length limits please" request :D. Of course that wouldn't prove anything either, as they are about the least knowledgeable people I have met when it comes to firearms, but will be interesting at least to see how they view the "information".

I don't think the barrel length theory is "as good as any". I do however think PKLs comments are definitely as good as any, re the increase case capacity or offset. Of course I don't know the answer, just stating my view that a moderator is a moderator, and a barrel is a barrel, I can't see any physical possibility of the mod adding to barrel effects.
 
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