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Thread: ammo v BT V ppu problem - possibly?

  1. #1

    ammo v BT V ppu problem - possibly?

    The situation, 2 shooters, 2 rifles, a T3 and Prohunter in 243. Both with 5x30x50 Z6i BT newly installed on top. Our local supplier had run out of our usual reloading bullet supplies so rather than messing about we bought cheap ammo to zero on and try the BT, before working up a new load with the only bullets our local supplier had in stock. All should be simple, as the swarovski has the PPU ammo in the programme so the BT should be bang on. However we knew the PPU flew slower than the published figures due to the shorter barrels in our rifles, however we had the speed from the chrono from a few weeks before, 2810 - 2830 fps.

    We zeroed both rifles at 100 yards, and achieved 10p sized groups, in both rifles, so happy. I ran the swaro app on my phone and we needed 6 clicks up at 200 yards, all very easy. so we did this in both rifles and did a test at 200 meters, expecting a group at about bull, but double size, so say 2 inch ish? Cold and windy, 10 - 15mph so a bit of drift would not worry us, and it would be checked again before stalking, we just wanted to get the new toys almost there and ready.

    The problem, the group was open and 5 inches low, despite both rifles having 6 clicks added to the BT as directed by the app. Everything tested and correct.The app was adjusted for the slower expected speed, but to achieve this crap group and drop it would have had to drop from 2820 ish to 2300 ish FPS, in 2 rifles in a week. Typically the chrono we had with us had a flat battery, but it was only there as part of the zeroing box.

    The question. Why in 2 rifles was there an unexpected 5 inch drop in POI and a far larger grouping over an additional 100 yards, from the expected one. The only possible change is batch of ammo, but as factory bought i would not expect this to loose 500fps?

    We are out tomorrow again, with fresh batteries in the chrono, but the wisdom of SD would be appreciated.


  2. #2
    Hi Dave
    Temperature difference when shooting? - Hot on first day & cold on the second? Did you get sooty cases on second day?


  3. #3
    Hi Ian
    Thanks for answering. The cases were the same each time, clean and as expected, certainly nothing noted. The first day was bitter and cold, the second was just cold! I would say 3-5 degrees both days, just Aberdeen last week really, but an interesting question, temperature could have been an issue, but to have made for these variations we either had a dodgy crono, and it was producing expected figures, a BT issue, we could have set them wrongly, but we already have 2 and they are fine, or ammo way slower then expected. Could the cold have done this much, or made for so much change?


  4. #4
    Both rifles performed the same so i would pin it on the ammo velocities. As to the grouping not being linear: A 10-15 mph wind not a consideration??~Muir

  5. #5
    Another possibility (not sure how much it would affect it at 200m) is that the BC is velocity dependant so the stated BC for the bullets would be lower if the velocity is lower too.

  6. #6
    Hi Muir

    What i meant was the wind would not blow them down by 4-6 inches. i knew it would move them sideways, but i was not concerned about this as it was to be expected.

    Nun_hunter, i really dont know about that, it is certainly possible, though could this make for such a large drop?

    Anyway, out again today with the chrono and a large choice of ammo inc my home loads so willsee exactly what the issue is.


  7. #7
    I know a lot of people get on well with PPU, but that's where I'd lay the blame.
    Nearly failed my DSC1 shooting test due to duff ammo. I had zeroed with it a week before no problem. Not the best group, but good enough. Day before the test we went on the range to do a run through, walked it.
    Then test day, first shot was about 6" low, second was just on the line of the 'kill zone'.
    I had to re-zero and then carry on. Luckily it worked out ok.
    Trying a few more rounds at home I had the same happen again. Once bitten......

  8. #8
    SD Regular
    Join Date
    Nov 2010
    Herefordshire, Hampshire or Essex
    This probably doesn't help - but I had the same issue with Prvi 22.250 ammo at 200m. I put it down to velocity/BC not as expected, but didn't investigate further. I keep a box of Prvi for emergencies, and shooting at 100 where it seems to do OK, but nothing more.
    Nooooooooooooobody expects the Spanish Inquisition!! Our main weapon is.........

  9. #9
    seems a big drop over 100m for a 243, same batch of ammo? usually when something goes way wrong, there's something fundamental . temp shouldn't make that much difference . Try different ammo, or you possibly haven't quite worked out your new scope, or you have wound it the wrong way even.( unlikely but Ive done it ) check the chrono again and see whats happening would be a guess. very odd all the same .

  10. #10
    After reading all the above, I reckon it is a problem between two batches of ammo. -- Could be very wrong though!
    The only thing to do is try it all again & get a second chrono (with good batteries) to cross check the results. Fire all shots over both chronos in line & you should soon see what really is wrong.
    Do the same with some "decent" ammo too - maybe RWS or Norma.

    Fill yer waders Dave!


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