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Thread: Looking for advice on ballistics

  1. #1

    Looking for advice on ballistics

    In order to get accurate figures on load software regarding velocity and energy, how important is it to get accurate muzzle velocities? How accurate are the book figures, which just go on powder type/weight and bullet type and weight?

    Would i find large differences between book figures and actual figures if i used a chrono? Im no where near the stage where i am worrying about velocities and bullet drop yet as i havent sorted my .308 loads out yet.

    On that note, if im going to buy some good quality brass for my .308, what would you go for?

    Some of you have read my thread regarding my PRVI saga and may recall that i have replaced the non expanding bullets with hornady SST 150gn. I re used the powder which was in the PRVI ammo, and just did an average, ie 1640gn of powder divided by 40 rounds, give 41gn of powder per round. These are shooting OK, but i would like to play around with them. If i were to load the rounds with more than 41gn of the powder, is there a danger? Or is it if i load with less than 41gn when it becomes more dangerous?

    Im sure a lot of you are cringing right now thinking about this numpty (me) and what im doing. Im just trying to do some load development without wasting the PRVI components. By doing this, am i wasting my time?

  2. #2
    Ok lets go through this. Each and every barrel is different so the velocities in the loading manuals are guides only. That's what they managed in the particular barrel they were using during the testing and development. With computer data the old saying:-

    garbage in = garbage out

    Is very true. So yes you need accurate velocity reading to get accurate data out of one of those programmes likewise tell it your sight is 1 1/2" above the bore and it's 1 3/4" above it the graphs will be out.

    Folks say that Lapua is the best however according to the Norma catalogue they claim to make the Lapua brass but what is wrong with the Privi brass?

    I ask becasue I have used some old Privi brass in 6.5x55 marked NNY for a long time without any problems. As for wasting your time swopping bullets ............................... that depends. Have you learnt anything by doing so?

    If you have then it cannot have been a waste of time regardless if the ammunition was more effective or accurate.

    If i were to load the rounds with more than 41gn of the powder, is there a danger
    Not knowing the powder or it's burning rate then yes they could feasibly be some danger. Also not being able to examine the fired casesIi am loathe to say " no problem load em up higher " that would be highly irrisponsible of me to do so. Caution in reloading is a must not an option .

  3. #3
    Brithunter- Thanks for the reply, Ive used some PRVI brass for some load development, using my own powder and primers. I am going to invest in a neck sizing only die also as i think this may help a little.

    The height of the sight above the bore- is there any way of measuring accurately?

    Im not going to put any figures into the programme until i have settled on a certain load. I will also need to buy a chrono (or borrow one?!) Also, do you think that there is any way to find out what powder PRVI use? Is it likely to be from a known brand or more likely (considering the price) to be some eastern block gash stuff? If i do find a load which is vastly more accurate than the ones with PRVI powder, i will pull the Hornady heads out and replace powder and primers with my own.

    Ive learned a fair bit through the whole fiasco ive had with PRVI ammo so i guess its not been a waster of my time and the PRVI ammo was thrown in with the rifle so its not cost me anything really so far.

    So regarding powder in the case, as i understand it, the less powder in a case, the faster the burn due to more oxygen? So potentially putting less than minimum powder in the case could also be dangerous? In general terms?

  4. #4
    If you are using scope mounts that are split horizontally, a simple measurement from the joint to the blow off safety aperture, normally situated at 90 degrees to the face of the bolt head would be good enough, or anything similar to this method, for sight height, without a chronograph there is no exercise. some bullets in place of a particular load menu of components, will give very different results, just any old bullet shape / type will not be good enough. less than the required minimum charge, would at the very least invite a visit to a gunsmith, to remove a stuck bullet from someway up the bore. burn rate of powder is governed by the manufacturer's mix of "stuff", ammunition powders will burn if initiated without an outside supply of oxygen, this is contained / produced on firing the powder.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  5. #5
    Thanks Finnbear. The loads i did last night, with H4895 and Hornady 150gn SST, ive done 4 of each at 43gn, 43.5gn, 44gn, 44.5gn, 45gn with a MAX at 45.5gn. By the looks of it, you couldnt overcharge it if you tried due to the case being full.

    Ive heard that the case being pretty full is better as it gives a more uniform burn? Good idea regarding measuring the scope height also, that makes a lot of sense. I will post the results of the loads up on here. Im going to wait til i get the moderator on it first and also give the rifle a good clean out. Ive found a use for my PRVI match rounds, to foul the bore after cleaning..

  6. #6
    Just make sure that the scope rings are split at the centre point ............................ not all are!

    As for Privi Partisen one must remember that it is an old established firm but has suffered some problems in recent years. I think it has also been involved it the struggles/war call it what you will. They make Sniper grade 8mm Mauser ammo and it wa sused in the Bosnian trouble I believe. People used to look down on Meopta because it was eastern Block .

  7. #7
    Good Point Brithunter, Im going to have a bash with the PRVI brass, see what i get from it. I was reading on A.N Other forum regarding PRVI brass and it seems that they make/made brass for the likes of Lapua and the rest of those 'top end' manufacturers. What i did notice last night when loading was that over 20 rounds, there was a split of about 6gn between the lightest case and the heaviest. Also, when putting them into the lee autoprime, some slid into the shellholder as normal and others were bl**dy tight! I checked the caseholder for debris but think its the cases.

  8. #8
    The most likely reason for tight fit on shell holders is an extractor claw mark on the rim, you can usually nip those off with a craft knife & then buff with a "borrowed" nail file pad, overcharging can also be achieved by using the "compressed load " method, a correct procedure in some loads but not all.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  9. #9

    As I understand it, and I am sure somebody will put me right if I am wrong the real theoretical problem with using reduced loads occur when you fill the case to less than half full of powder. With the case in the chamber and the rifle held in the horizontal position the powder lies in the case with the primer flash hole not covered with powder. When the primer detonates it sends a flash of flame over the entire surface area of the powder lying in the case, this cause almost all of the powder to ignite in an instance, this cause a massive spike in pressure. Normally the primer will ignite some of the powder this starts off a chain reaction with the rest of the powder burning; this control burn provides a progressive expansion that leads to no pressure spikes.

    Hope that makes sense.

    In a nut shell never load a case less than half full; another advantage is if you fill your cases more than half full of powder you cannot double charge one when reloading as the powder pours over the neck.



  10. #10
    One or two from Muir now & you should have all the gaps filled in!
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

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