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Thread: Geometric puzzlement

  1. #31
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    drop relative to bore

    Quote Originally Posted by Baldie View Post
    What CF is this?
    - what I meant to ask was:

    "Is the amount of elevation adjustment on a 12 ft/lb .177" air rifle at 55 yards about the same as a centre-fire rifle at 200 yards?"

    Chairgun tells me that pellet drop (relative to bore) at 55 yards is about 12" (lots of variables).

    If I remember right (which is doubtful), the old .303" bullets used to drop about 12 - 13" by 200yards, and I presumed .308" was roughly the same. As I haven't fired a centre-fire rifle for two decades, I could be talking complete prematurely senile b*ll*cks, though
    B.S.A. Airsporter Mark 4 .22" , Webley Osprey .22", Feinwerkbau 300 S .177", Webley Senior .177"

    Sign here: http://petitions.pm.gov.uk/TargetPistols/

  2. #32
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    Quote Originally Posted by sarf View Post
    - what I meant to ask was:

    "Is the amount of elevation adjustment on a 12 ft/lb .177" air rifle at 55 yards about the same as a centre-fire rifle at 200 yards?"

    Chairgun tells me that pellet drop (relative to bore) at 55 yards is about 12" (lots of variables).

    If I remember right (which is doubtful), the old .303" bullets used to drop about 12 - 13" by 200yards, and I presumed .308" was roughly the same. As I haven't fired a centre-fire rifle for two decades, I could be talking complete prematurely senile b*ll*cks, though

    You is definitely a Londoner, or doing a good impression of one.

    .303 and (less so) .308 use quite heavy bullets, both travel fairly slowly in the great scheme of things. If you are really interested I'll go dig out some figures, but a .224 bullet out of moderm CF rifle or 6mm/.243 out of one, will be travelling a bit quicker than the stuff you are used to, and the drop would be measured in 'one hand of fingers' type measurements.

    The -20 MOA Picatinny rails I mentioned earlier, might be found on .308 rifles shooting 1000 yards.
    ...
    To be good, one must do good.

  3. #33
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    Pellet lobbers

    Quote Originally Posted by Baldie View Post
    a .224 bullet out of moderm CF rifle or 6mm/.243 out of one, will be travelling a bit quicker than the stuff you are used to, and the drop would be measured in 'one hand of fingers' type measurements.
    Hmm, my information is pretty out of date then. I was just trying to get a rough comparison. What you say about modern high velocity CF re-inforces Gary C's point that airguns are mortars by comparison.

    I have to remind myself that Pellet/bullet drop is only half the story . .

    Seems to me that whether the scope rails need to be inclined depends not only on the pellet/bullet drop at the zero point, but also how far away that zero point is.

    The nearer the zero point, the more sharply downward the scope needs to be angled.

    Extreme case: 12" drop zeroed at 50 yards is like 20 *FEET* drop at 1000 yards!

    Comparing to the old .308", the airgun would have to be dropping only 2" at 50 yards to have the same scope angle as the .308" zeroed at 300 yards. In practice a legal airgun will be dropping 2" by 25 yards, I reckon.

    So, if you zero your FT airgun at 55 yards, a fairer comparison is a .308" at 600+ yards or probably somewhat more (the ballistics of the supersonic bullet will be far better than an airgun pellet), or perhaps a more modern CF at 1000+ yards, as you say?

    (corrections welcome!)
    B.S.A. Airsporter Mark 4 .22" , Webley Osprey .22", Feinwerkbau 300 S .177", Webley Senior .177"

    Sign here: http://petitions.pm.gov.uk/TargetPistols/

  4. #34
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    Quote Originally Posted by xbow View Post
    "you won't get far trying to lap aluminium with a steel bar, the grinding paste sticks to the softer material and laps the harder one"!
    He's got a point. I've only used abrasive paper so far. I'd like steel mounts but haven't been able to find any for airgun 'scope rails.
    Agreed. Does anyone import BKL? I see they offer drop-compensated mounts:

    Available Bullet Drop Compensation::
    .004" per inch-typical for Rimfire applications
    .007" per inch-typical for Airguns applications
    - and 7/1000 is about what we've discussed as a suitable slope!
    B.S.A. Airsporter Mark 4 .22" , Webley Osprey .22", Feinwerkbau 300 S .177", Webley Senior .177"

    Sign here: http://petitions.pm.gov.uk/TargetPistols/

  5. #35
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    Quote Originally Posted by sarf View Post
    Agreed. Does anyone import BKL?

    They do, but you wouldn't buy them if you had a choice. BKL won't export direct though. The UK distributor has to make a profit, but the price difference between US and UK prices, must mean they are hand couriered.

    Can't respond to the .308 at 600 yards vs airgun at 55 yards.

















    But I may know a man who can.

    Will PM "The Cavalry".
    ...
    To be good, one must do good.

  6. #36
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    Nice find - that is exactly what I want - 0.007" per inch is spot on with my calcs too.

    Only 50 bucks too, but it's probably nearer 100 quid by the time it reaches these shores

    [I'd prefer another inch in length, but wouldn't we all ]
    “We are too much accustomed to attribute to a single cause that which is the product of several, and the majority of our controversies come from that.” - Marcus Aurelius

  7. #37
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    to avoid packing i've used b-squares, and now have them on all my rigs...

    if your careful to make sure the windage is the same on each and have a wind free range to check and eliminate any cross over, they only take 20 mins or so to get close to zero just using the mounts. When I mean close I mean less than 10 clicks on a 1/4 moa scope.

    getting the windage sorted seems to be the trick with them, so taking time to make sure they are central before mounting them is a good start...the walther and hw rails they sit on are pretty damn straight so i've found they've needed little or no adjustment in the windage dept.

    they sit on a gimble, so although it does leave the head worrying that it might come loose, once you've realised that even with a little tightness they cant shift, locking them up and leaving them, with a bit of shooting brings back the confidence. I've had them on for almost a year on one rig without any problems.

    The 2 piece ones are easier to setup than the one piece ones...because you can simply undo the rear dovetail section and spin it to adjust elevation (with the other screws loose to allow both gimbles to move).

    The only downside i've found with them is that they are built to very tight tolerances...the clamps arent 180 degree split, which means they need carefull effort not to scratch the scope when placed on...and the threads need to line up precisely because the threads wont allow any give on the angle before tightening...they need to be bang on or there is a danger of cross threading...a little bit of countersinking on the threads would go a long way to help.

    This tolerance problem revealed itself on the one piece mount which needed to have the rail clamp exactly parallel to the block in order to be tightened...and on a dipped scope which after dipping meant the tube was a little over 30mm, which meant that the scope clamp bolts needed careful alignment. It also happend on a big nikko...which wasnt dipped, but 5 mins with a swiss file on the clamp holes saw that solved.

    So, to sum up...can be a bit of work, but they completely solve the need and problems of shimming...and in my book are rock solid in performance.

    I'd like to see a set of the sportsmatch mounts to see how they work as well though.

  8. #38
    Beer Hunter Guest
    Quote Originally Posted by sarf View Post
    "Is the amount of elevation adjustment on a 12 ft/lb .177" air rifle at 55 yards about the same as a centre-fire rifle at 200 yards?"

    Chairgun tells me that pellet drop (relative to bore) at 55 yards is about 12" (lots of variables).

    If I remember right (which is doubtful), the old .303" bullets used to drop about 12 - 13" by 200yards, and I presumed .308" was roughly the same. As I haven't fired a centre-fire rifle for two decades, I could be talking complete prematurely senile b*ll*cks, though
    Is this what you were looking for?
    If so, then a .177 air rifle, zeroed at 35 yards is going to need about 18 clicks for 50 yards and a .303 on a 100 yard zero will need 10 clicks at 200 yards.
    Any modern centerfire is obviously going to need far less.

    Kev.

  9. #39
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    Quote Originally Posted by Baldie View Post
    Unless I'm very much mistaken ( ) Sportsmatch do 30mm adjustables, and these come highly recommended. If you have a problem getting the product number, let me know and I will ring them.

    Funny you should mention the HW100.

    Do not lap your ring mounts. Great idea, but ... No, thinking about it, useless idea. This procedure will allow you to line up the scope tube through the rings if they are misaligned, but a one piece adustable from Sportsmatch won't need this. IIRC they released a two piece version 3-4 months ago. But a HW100 should have a one piece.

    Lapping a 25 or 30mm ring will make it larger. Lapping a mis-aligned ring will make it eccentric (oval). Use Burris Signature rings if you have to, but don't lap your air gun mounts.

    Remember:

    If the gods wanted you to lap your rings, They would have supplied a 1" or 30mm ground bar with every set of rings, and a side order of grinding paste.



    Sportsmatch are the best ring/mount manufacturer (for airgun) bar none. I doubt they would design anything that didn't work. Don't worry about adjustables not working. You've nothing to lose by trying. If they lose zero on your rifle, you get your money back. Simple, eh?

    I cant find any one piece adjustables for a 30mm tube Baldie, Sportsmatch do just what I want for an inch tube, but only that. I also agree, my gun should have a one piece, i will fit, it will work and I want it but can I find one?

    Unless of course you know something I dont (most of you here do )

    Cheers
    Barry

  10. #40
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    Quote Originally Posted by Barry View Post
    I cant find any one piece adjustables for a 30mm tube
    To sum up this thread . . doesn't seem to be such a thing on the market. Best solutions:

    1) that BKL canted rail with a couple of standard 30mm mounts on top. Not adjustable, but will almost certainly put you "in the ball park", as the Yanks say (if you can find anywhere to buy it).

    2) the Sportsmatch 2-piece 30mms, which as they *BOTH* tilt, it should be possible to retain perfect alignment between front and rear ring.
    Last edited by sarf; 14-03-2007 at 11:00 PM.
    B.S.A. Airsporter Mark 4 .22" , Webley Osprey .22", Feinwerkbau 300 S .177", Webley Senior .177"

    Sign here: http://petitions.pm.gov.uk/TargetPistols/

  11. #41
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    Quote Originally Posted by Beer Hunter View Post
    If so, then a .177 air rifle, zeroed at 35 yards is going to need about 18 clicks for 50 yards and a .303 on a 100 yard zero will need 10 clicks at 200 yards.
    Interesting Kev. What ballistics software did you use?
    B.S.A. Airsporter Mark 4 .22" , Webley Osprey .22", Feinwerkbau 300 S .177", Webley Senior .177"

    Sign here: http://petitions.pm.gov.uk/TargetPistols/

  12. #42
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    b-square do one piece 30mm adjustables...have a set on a springer.

    http://airgunbuyer.com/Showproducts....quare%20Mounts

  13. #43
    Beer Hunter Guest
    Quote Originally Posted by sarf View Post
    Interesting Kev. What ballistics software did you use?
    The values came from Sierra Infinity.

    Kev.

  14. #44
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    Aluminium Oxide

    Quote Originally Posted by xbow View Post
    I checked with "The font of all (engineering) knowledge", (Tim!) at work and he offered the following: "you won't get far trying to lap aluminium with a steel bar, the grinding paste sticks to the softer material and laps the harder one"!
    Slightly off-topic . . I'm familiar with the effect that Tim is describing. However, I've always presumed that the cause is the fact that all aluminium will have a very thin surface coat (once exposed to air) of aluminium oxide, which is of course extremely hard and often used as abrasive. Unless this surface layer is broken through, the aluminium oxide will resist the grinding paste better than the steel. Well that's my theory anyway.
    B.S.A. Airsporter Mark 4 .22" , Webley Osprey .22", Feinwerkbau 300 S .177", Webley Senior .177"

    Sign here: http://petitions.pm.gov.uk/TargetPistols/

  15. #45
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    Quote Originally Posted by Beer Hunter View Post
    Is this what you were looking for?
    If so, then a .177 air rifle, zeroed at 35 yards is going to need about 18 clicks for 50 yards and a .303 on a 100 yard zero will need 10 clicks at 200 yards.
    Any modern centerfire is obviously going to need far less.

    Kev.
    Ah, The Cavalry has arrived!!

    Nice one Kevin. Demonstrates Gary's remark "we pretty much use the rifle as a mortar bomb compared to a C/F" rather well.
    ...
    To be good, one must do good.

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