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Thread: SR25 bullets/ballistics

  1. #1
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    SR25 bullets/ballistics

    Using a 16" APC Carbine, 1 in 10 twist, trying to determine the maximum weight/bullet size that will stabilize reliably. I know there are other factors in terms of the barrel length, grooves, etc.. Looking for a rule of thumb type input here. Also, what is the lightest weight round that can be run with that much twist? Can you drop to 149/150gr without issues?

    Also not sure what the limitations are in terms of the overall size of the round, chambering safely in the weapon and the maximum size that fits in the LR118 PMAG.

    There are some amazing results with the new aluminum tipped .308 rounds, but it looks like the overall length is going to be too much for the mag, probably too much for the chamber.

    Have the following to test next week:

    Black Hills 168gr BTHP
    Black Hills gold 178gr ELD-X
    Asym 168gr SMK
    Asym 175gr SMK
    Berger 185gr Juggernaut OTM

  2. #2
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    The 130 SOST class profile is probably the lightest/longest you can go in 1:10, but the pick up in velocity kinda helps that out.
    I've shot it to 800 with decent result, but the ammo itself is right around 1.5 MOA in my experience.
    There are lots of good 150 class hunting options that tend to shoot fairly adequately.
    I've shot 110gr (about 2900 MV from a 16"), which is super good inside 300, but really falls apart past 600. Again, dispersion was in the 1.5 area.
    The Palma 155s are pretty good, but I've never put real legs on them.
    When it comes to 7.62, it's a rare projectile indeed that does very well through the trans-sonic range, tending to pick up about 1/4-1/2 of the average dispersion present inside the trans-sonic range. Even the venerable 175 SMK falls victim to it. The good news is that that range is out at 800 meters or so, even in 0ft DA air.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

    Director of Training

    FB@ Facebook.com/F2SConsultingLLC
    As accurate as needed, as fast as possible, as many times as it takes.

  3. #3
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    Although my 308 AR's are not an SR25, I also do run PMAG's exclusively. Longest I have run OAL out to is 2.820... and the loaded rounds are JUST kissing the front of the mag. No reliability issues to speak of though. No chambering or pressure issues were encountered in my Criterion or FN chrome-lined barrels using all bullet weight loaded out the max length like this.

    In terms of bullet weight - I have shot bullet weights between 110 to 190 grains. Overall the most consistent and forgiving loads have between in the 150-155 gr range. They are easy on the gun and brass, and have been sufficient for consistent hits in moderate wind out to 720 yds. Recoil is also a little lower than heavies.

    I have not had the best results with the 185-190 gr class projectiles. They benefit most from being loaded longer than mag length which is gas gun shooters cannot do. Recoil is higher and when loaded to an useful velocity brass starts showing ejector swipes despite being near minimum loads.

    Now many 165-175 gr class loads are excellent as well, but like all of this advice, there is a trial and error element to trying then in your gun. These are probably the best for trying to break into the 1000 yd club, as 155's need to be running very fast to stay supersonic this far. It is pretty much impossible to get them going fast enough in a 16" gas gun. A friend of mine has had outstanding results shooting the 168 Berger hybrid over a stiff load of Varget at 1000 yards. It has the BC of the heavier bullets but can be pushed faster.

  4. #4
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    Thank you for the info! I'm really loving the SR25, but its a whole new school for me on the ballistics front. The alco rounds that mirror .300 win mag out of a .308 look amazing, but the bullets are very long. Seating them under 2.820 overall length looks like it would be a no-go. (The BC on the 168gr Aluminum tip is .678!!!)

    https://www.alcobullets.com/30-Caliber-308_c_13.html

    The Berger OTM juggernauts are supposed to be optimized for use in semi-auto weapons. Not having the 20" barrel, I'm curious how that will turn out.
    http://www.bergerbullets.com/product...uggernaut-otm/
    Assuming muzzle velocity of 2400fps (2600fps out of a 24" barrel subtracting 200fps for loss of 8" of barrel), looks like it will be transonic at around 700 yards. Supposedly, it transitions well and remains stable through the threshold. 45ACP muzzle velocity at 1000 yards, still pushing a sizeable round. I'm really curious as to the bullet drop at the range.

    I've been hoarding some SOST that I'll have to try out, I mainly have a boat load of DAG and M80 ball that I want to eat for training purposes. Still looking to punch small groups, but also be able to run the rifle as a heavy carbine when I feel the need without the high cost per round.

    Not intending to make this a thousand yard gun, the majority of its life will in the 300-600 range where I think it will perform very well. I just didn't realize what was possible with .308 in today's world.

    Jack, off-topic but the KAC bipod is awesome! That thing needs some more press, I didn't really know what I bought until I used it.
    Last edited by ryanm; 11-09-18 at 11:34.

  5. #5
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    Just finished reading Bryan Litzís Modern Advancements in Long Range Shooting while flying home today. Really good material, I definitely learned more than anticipated.

    Now I understand the why better than when I woke up this morning.

    It sounds like there are a few ballistic sweet spots that are reachable with the SR25 platform, especially in 6.5CR.

    The section on determining true barrel twist was also a real eye opener. The impact the unique yaw characteristics of every barrel was something I hadnít previously considered. Also, how elevation/density changes those values was a whole new thought process for me.

    Going to do some shooting next week but Iím going to start out with some math to figure out what my goals are and if I can match the anticipated results.

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