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Thread: how much recoil is reduced by mod weight

  1. #1

    how much recoil is reduced by mod weight

    good evening

    im hopeing to get a 308 and am looking at moderators. it either between the heavy north star or a cmm4 al. i had a t8 on my 243 and found it very front end heavy. im only 5 foot 5 so really notice when the rifle is slung over my shoulder.

    how much recoil is reduced by a heavy mod compared to a light mod or is it the fact that the gasses are slowed that makes the diffrance.

    i probably wil only get through 60 rounds a year which also may make a differance for peoples recomendations

    regards pj1

  2. #2
    The mod reduces recoil by reducing the amount of gas that goes flyiing out the front along with the bullet. While the mass of the mod will add to the mass that is displaced by recoil and so this will have a small impact upon the felt recoil it is the reduction in the mass of gas flying directly away from the shooter out the front that is where a mod makes a real difference to recoil.

    My 308 is shooting a 150 grain bullet with 49 grains of powder behind it. I'm told that the gas may exit the barrel at up to 6,000fps. Allowing for the mod not being totally efficient and just counting the weight of powder as approximating to the mass of the expelled gas then you are probably looking at a reducion in recoil of about a third.

    However, I would say that if you don't like the recoil then it might be best not to rely on a mod to reduce it but rather to look into a rifle with slightly less recoil. That way you will be happy with the rifle with mod on or off.

  3. #3
    thanks caorach

    im not worried about the recoil and if i stalked in the middle of no where i would not use a mod at all. but i need a mod so im just trying to decide which would be best for me. and in doing so am trying to work out the pros and cons of heavy and light mods. if the heavy mod really helps with accuracy by reducing recoil then maybe thats the one for me. if a light mod reduces recoil efficently then maybe thats the way to go

    cheers pj1

  4. #4

    I have a tikka t3 .308 with a north star mod on it. The recoil and noise has been reduced significantly. Well worth doing.


  5. #5

    If you have ever shot a rifle with a muzzle brake you will aspirate how much they cut recoil without adding hardly any weight to the rifle. A bipod weighs a similar amount of weight as a moddy, nobody comments on how that cuts down on felt recoil.

    If I was going to have a guess I would say 75% of the recoil is reduced because of the way a moderator works, redirecting the gases back, less than 25% is because of the extra weight.

    I hope that assists you making up your mind which way to go.



  6. #6
    thanks tahr

    thats very useful. the only experience i have of muzzle brakes is at a bisley open day. dont know what the rifle was but standing to the side and slightly behind it felt like my trousers were going to be made into shorts. the more i think about it the more im heading towards the lighter mod. i havnt had a bipod on any of my rifles as i didnt want the extra weight either.



  7. #7
    A good discussion on recoil at

    You can do the maths - a heavier mod will reduce recoil more than a lighter one, just as any additional weight will reduce recoil. Bear in mind there is also the nature of the kick - some calibres with high velocity have a jabby kick, whereas others - big bores tend to have more of a shove.

    A mod is also out at the end of the barrel so it's weight will slow down any muzzle flip upwards. A straight shove feels a lot less than a rifle kicking upwards and slapping you in the face.

    I am sure in a moderator there is also an effect of the gases hitting the barrels which push the moderator forward thus reducing felt recoil in the same way as a muzzle break and different designs will have a different effect.

  8. #8
    Done the maths. Assume rifle weighs 3000g, bullet is 10g at a velocity of 850 m/s (much easier in si units).

    Recoil energy is 24,083 joules

    Add a 500g moderator

    Recoil energy drops to 20,642 joules or about 20percent.

    If the mod is only 200g recoil energy is 22,578joules.

    So in conclusion, given that users of mods claim a very big reduction in recoil, a big effect must be the muzzle break effect.
    Last edited by Heym SR20; 08-03-2011 at 14:58.

  9. #9
    thanks heym sr20

    glad you did the maths. i had to read your workings out several times to get it in my head. guess it was a given really wasnt it. have probably got another couple of weeks before my fac comes back with the variation so will eventually make up my mind. im sure i read somewhere once that if you block out all the noise from a gun being fired if you have a flinch with recoil then it pretty much goes when you cant hear a thing. anyway thats beside the point. was just curious about weight differance to try and make my mind up

    thanks again

  10. #10
    Hi pj1

    I don't think so much as weight difference but more a balance issue with mods. I have a 308 sako with a northstar. I don't find this an issue from any shooting position but it drives me crackers when trying to use my binos with both hands as the rifle slips backwards. I am looking ay the cmm4 now to help counteract this.

    Atb Steve

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