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Question on temp and FPS?

N8Will
What effect does temp have on FPS? I cant get close to book speeds with my 280 AI. Ive been shooting in 30 degree weather and Im 100 to 150 FPS slower than the book. Im shooting a 24 inch barrel, 168 berger VLD, 2650 fps with H4831sc and 2750 with IMR4350.The elevation is about 4200 and not much humidity. Is it just the Temp?
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9 comments

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  • nononsense
    N8Will,

    Unfortunately there are a number of variables which can have an affect on velocity, temperature being only one. Most modern powders are being produced with less sensitivity to temperature variations than ever before but that doesn't mean that it still can't occur.

    Which book are you using for your loads?

    Does it mention primers?

    Does it list a barrel length?

    Thoughts about velocity loss:

    Any barrel in particular can be faster or slower that any other barrel with similar bore/groove dimensions, chamber and material construction. Barrels manufactured one after the other on the same equipment can show variations in velocity. Go figure.

    The powder itself can show variations depending on the lot number and manufacturing controls used.

    No matter the powder and its formulation, a change of primer can yield a substantial change in velocity. Check and change your primer selection.

    Chronographs are notoriously inconsistent given atmospheric conditions. This applies to most chronographs used outdoors but has even more impact on the cheap chronographs which covers the vast majority found in this country today.

    I would start by checking your scale first. Be sure it's calibrated and correct. The check and change each of the other variables one at a time. Keep good records and review after each change.

    Best.
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  • N8Will
    Im shooting a custom rem 700 with a 24 inch Brux barrel. Im duplicating the loads out of the Nosler book and still cant get with in 100 FPS of what they are claimimg. In there older book they use a 24 inch test barrel. Same result with Seirra and Hodgdon. I guess Im just wanting to get close so I can order turrets from Leupold. Im not looking for max speed but it seems like they should go a little faster than Im getting.
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  • N8Will
    Also I use a RCBS chargematser combo and Im real careful in my loads. My SD is down to 15 so I dont think its my scale. Does anyone use mag primers with a 280 AI?
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  • nononsense
    N8Will,

    Magnum primers are a possibility as are primers from other manufacturers. This is a simple switch for a reloader.

    I'd also suggest trying another lot number of the same powder. Or...

    I had good results in my 280 AIs with heavy bullets over Re-22, Re-25 and V V N560. The honor of highest velocity went to the N560 in all tests. My favorite though was the Re-22.

    Consistency and accuracy will always outweigh the highest velocity. The double base powders add a little to the velocity yet allow for accuracy also.

    Best.
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  • N8Will
    I totally agree, Im getting great groups best so far is .4 and that is with Imr4350 but everyone was telling how great the 4831sc was in this cal so I tyed it and the groups grew a little and the FPS feel a hundred so I think Ill keep on trying. Im thinking I should not have bought this chronograph, Is making rethink alot of my loads. I will try some RE-22. Thanks for the advice
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  • 11b6r
    In addition to possibly affecting the burn rate of powder (only if the cartridges are chilled) remember that colder air is denser than warm air- and that DRY air is denser than humid. Greater density of air means bullet works harder to push it out of the way. Whether it would have a significant effect over the short distance to the chrono screen, I dunno- but used to shoot military rifles in Alaska at -40 to -60 air temps, and it REALLY makes a difference.
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  • tsr1965
    Something else you want to remember, is a lot of the "book" data is accumulated in controlled labratory type conditions. In some labratories, the ambient conditions are so controlable, that they can change ambient conditions for best results. Most normal or average shooters, and even a lot of above average shooters, do not have access to anything but real world type conditions. Then throw in some tweaking from the marketing group, and you can have something else.

    For what it is worth, stick with consistancy in your SD, and accuracy. If you have top end speed, then that is a bonus. If you have speed that is between mid loads and top end, then it is still a bonus, as you have above average consistancy. Your custom turret can be made with the trajectory curve you send Leupold, and should be...not the one you would like it to be.

    Best
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  • sandwarrior
    Something is wrong there if all you are showing on your chrono is 2650 with a 168 Berger. That is pretty much 7mm-08/7x57 velocities with that bullet. 2750 is closer but still not where it should be at.

    First thing is to check the average drops of the bullets. Shoot short range, like 100, then long like 300-400-500. Check the drops against a reasonably accurate computer ballistics program and see what they give for velocities.

    You also need to run a ladder and see where your barrel is shooting best vs. getting pressure signs. You may see for that caliber that Nosler is pretty low when in fact you can go 2-3 grains higher. But only if accuracy stays tight. Load up some ladders, and test them.
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  • N8Will
    Sand , Do you have a favorite pwoder for the 280AI? SO far with my tests I havent gone over max loads in any book but I do know that with my rifle like the max end it dosent group with light or mid rangr loads. I also have the PO reloading book and his loads are a littl stiffer than the other books, but I havent tryed them yet. what power brand did he use all it says is the #?
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