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  1. #1
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    Question for the operators fluent in ballistics and precision

    Jim (JuKk0o) and I got together today at MRC for some shooting fun but also with a mission to sight in my new scope. Here are some of the details with a question at the end of this post.

    The Scope: Vortex Viper PST 4-16x50 FFP ERB-1

    The Evil Blackness: Mega Maten with .308 Mega 18" Midlength 1:10 Barrel

    Distance: 100 Meters

    Ammunition 1: Started out with American Eagle 7.62x51mm 168 Grain OTM (Open Tip Match) for M1A



    Ammunition 2: Ended up with PPU .308 WIN 150 Grain SP (Soft Point)



    I started out with lady luck on my side. The Viper was putting the AE ammo on paper right out of the gates. I was pleased with this but my elation soon turned to frustration. I was able to achieve a decent zero fairly quick but for some reason I could not for the life of me achieve what I would consider an acceptable shot group. I employed all the marksmanship skills I've learned and practiced but despite my best efforts I just couldn't pull a good shot group together. I figured that today just wasn't going to be my day. Feeling a bit dejected, I finally gave up and took a break to show off and shoot my newly blued Browning Hi-Power with Jim.

    Once I'd quit sulking about my first round with the Mega and the Viper, I went back for another go at it and put up some fresh paper to terrorize. I was out of the AE ammo so I pulled out a baggie containing about 30-40 rounds of loose PPU that I had brought along for ringing the gongs and plinking. I had not intended to use this ammo for sighting or precision but figured what the hell, and proceeded once again to attempt firing a decent shot group. I was quickly astounded to see these shots coming together to create some tight little groups! My first group of four shots with the PPU impressed Jim and I so much that he insisted I go take a picture to document my achievement. Here it is:



    I just figured the break I had taken was responsible for the improvement in my marksmanship but Jim tipped me off that it was probably the ammo that was to blame. It would seem that the Mega preferred the PPU over the AE ammo.

    So this leads me to my question.

    If I want to repeat these shot groups, do I need to buy the exact same ammo, PPU .308 WIN 150gr SP?? Or.... can I buy any brand .308 in 150gr to repeat the groups? Will it make a difference if I don't buy the SP (Soft Point)??? Will it make a difference if I buy a different brand ammo but with all the same specifics as this PPU I was using? Shit I don't know.

  2. #2
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    Your barrel is going to like some ammo, and not like others. Just because your rifle didn't like the AE 168gr OTM doesn't mean it won't like a 168gr projectile. Even if you get the same factory ammo, different lots can produce different results with varying levels of repeatability. High quality match grade ammo is generally going to be the most consistent from lot to lot. My recommendation is to try 5-6 different kinds of ammo and see what works best. For measuring accuracy/precision...try comparing 4-5x 5 shot groups (ie 20-25 rounds) or more if you can, instead of focusing on the best groups. Keep a record of your shot targets and what ammo was used...using something like OnTarget helps. After a few hundred rounds you'll have a decent amount of data that you can reference to see what works and what doesn't.

  3. #3
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    I'll second what DeviantLogic said. Individual barrels should be tested against a variety of ammo, even if the barrels are from the same manufacturer. A 1:10 twist will generally perform better with 150-180gr bullets so that should give you a reference point to start at. I plan on breaking-in a bolt gun in the coming weeks and I've bought about 8 different kinds of ammunition, all in the 168-175gr range.

    Some more things to think about:

    - Barrels take time to break in. If you are shooting a barrel for the first time groups have a tendency to shrink as time goes on. More often than not the graph of accuracy over time for a .308 barrel (I've only looked at data for a bolt action, but I assume a gas gun is similar) it looks like a shallow bell curve, with the highest point of the curve (tightest groups) at the center around 2000-3000 rounds depending on barrel manufacturer.

    - If you find a factory load that performs well or even if you develop your own load, there is a limit to the accuracy you can squeeze out of the gun. Be realistic in your expectations and be prepared to accept that you may not be able to produce cloverleaf groups or something like that.

  4. #4
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    Just how accurate do you want to get? Is that group you have there acceptable or do you want more out if your gun?

    Do you have a led sled and a chronograph?

    To really get down to brass tacks for good accuracy I will tell you my routine. You can take away from it what you will.

    First thing I do is I keep those big foam insulation boards laying around. They only cost a few bucks at home depot. They are like 8 feet long 4 feet wide.

    Put your target on there dead center. Set up your led sled and line up a dead center shot. Fire ONE round. Go inspect but bring a tape measure. If you are 10" to the right and 8" high make note of it and come back and adjust the sites to the hole you just made.

    Next do something along the lines of what Deviant Logic suggests. But one box of 20 rounds of various grain weight bullets. You can either do 3 or 5 shot groups. It's up to you. You will notice your aim point and your point of impact will be off when you change grain weights. Disregard this for now. What you are looking for is GROUPS. If you can chronograph these shots (all of them) that is that much better.

    Write everything down in a notebook. The way you have your target labeled there with shot 1, shot 2, shot 3, etc... I make a small sketch of the target noting just that. Later on up the road there is more things to do with shot mapping (that's what I call it).

    Move to the next ammo. Rinse and repeat.

    It might take 20-25 rounds total. But they will be a SLOW 20-25 rounds. It might take you an hour or more than that even.

    I have found that when you do the tests if you buy nicer ammo all of the same brand (if possible) to do your tests it helps. Don't scrimp or you can get frustrated because your gun might be great but your ammo might just suck. You want to eliminate as many variables as possible and have notes on everything. Personally even though it's expensive using nice ammo is better for these initial tests.

    When you notice better groups with one grain weight over another and think that might be your go to ammo then you can buy 3 or 4 boxes of that grain weight from different manufacturers. Chronograph is vital if you have it.

    Doing all this might go from a few hours to two or three sessions across a couple days. I shoot in my back yard so I just shoot and make notes until I get tired or bored and then go do something else for a while.

    After you've settled on grain weight if you want to tighten the group even more then we can discuss reloading. If you however are fine with a 1" group then buy ammo accordingly. And buy the SAME ammo. Same brand, weight, everything.

  5. #5
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    Probably the best examples of testing ammunition can be found in Molon's posts. He uses 10 shot groups, and layers the groups to form composite groups which can then be used for comparison purposes. The below is an example of his comparison of 3 types of 6.8mm SPC loads, using 30 shot composite groups (3x 10 shot groups).

    Name:  6_8 mean radius comparison 03.jpg
Views: 346
Size:  78.3 KB

    I'd highly recommend reading his thread The Trouble With 3-Shot Groups, which provides explanations as to how/why he tests this way.

  6. #6
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    The ammo designed for the 7.62x51M1A. Try some Federal Gold Medal Match .308 with 168gr and 175gr Sierra Match Kings. The head stamps on the ammo are different and your chamber may prefer the .308 Win to the NATO round. My R700 does not do well with Lake City or other NATO brass

  7. #7
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    I won't get so lengthy as Alamo..

    Shoot it more, buy some various kinds of ammo 155-175's, and get out and put some more rounds thru it, dont be so quick to clean out the barrel either.

    Curious shooting off a bipod & bag or bags or?

  8. #8
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    Quote Originally Posted by mustangfreek View Post
    I won't get so lengthy as Alamo..
    I am working on my one line responses. It's hard.

  9. #9
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    Quote Originally Posted by mustangfreek View Post
    I won't get so lengthy as Alamo..

    Shoot it more, buy some various kinds of ammo 155-175's, and get out and put some more rounds thru it, dont be so quick to clean out the barrel either.

    Curious shooting off a bipod & bag or bags or?
    Yes it rests on an BT10-LW17 V8 ATLAS Bipod and I am using bags under the stock.

  10. #10
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    A couple of PDF files attached. One is a range log for rifle use; the other is just an example of how to fill in the blank one. You may not find it useful, or you might build on it to gather the information you want to keep on range trips. Advice above pretty much covers it, and maybe these will help.
    Attached Images Attached Images
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    NRA Certified Instructor

    "I won't be wronged, I won't be insulted, and I won't be laid a hand on."
    John Wayne - "The Shootist"

  11. #11
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    Awesome Jerry!! Thank you!!

    Here is the build list for the rifle I'm using.

    MEGA MATEN 18” AR10 Marksman Rifle
    Mega MKM Maten Extended Rifle Length Keymod Set
    Mega .308 Billet Upper Receiver
    Mega .308 Billet Ambi Lower Receiver
    Mega Lightweight Extruded Keymod Handguard

    Lower
    Rainier Arms Buffer Tube Tube/Buffer and spring Assembly
    Magpul ACS Mil-Spec Stock W/Limbsaver Butt Pad
    Mega Branded Hogue Rubber Finger Grooved Pistol Grip
    JP Lower Parts Kit Mil-Spec Minus Trigger Assembly
    Geissele Hi-Speed National Match DMR (Designated Marksman Rifle) Trigger
    Battle Arms Development Combat Ambi Safety Selector Switch
    Battle Arms Development Enhanced Magazine Release
    Norgon Ambi Bolt Catch/Release

    Upper
    Mega Arms .308 Charging Handle
    Mega Arms .308 Barrel 18” Mid Length Gas .750 Block Journal 1:10 Twist
    Rainier Arms Ultra Match .308 Bolt Carrier Group
    Syrac Ordnance .750 Set Screw Low Pro Adjustable Gas Block
    SLR Synergy Comp 30 Cal 5/8x24 Thread
    Lewis Machine Tool .308 Flip Up BUIS Set Front/Rear
    Gear Sector Rail Mount QD Socket/Swivel Set
    B&T Atlas Bipod Lever With ADM 170 Lever

    Optics
    Bobro Precision Optic Mount Extended 30mm Rings
    Vortex Viper PST 4-16x50 30mm Tube FFP Illuminated EBR-1 MRAD Reticle
    Aadmount Objective/Occular Lens Cap Covers and Throw Lever

  12. #12
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    Quote Originally Posted by alamo5000 View Post
    I am working on my one line responses. It's hard.
    Lol..obviously your posts are longer then my Add can handle....

  13. #13
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    With the 1-10" twist it's going to prefer the heavier bullets. The 175gr. HPBT's shot very well out of my 16" Mega barrel. Decent shooting barrel but damn those gas ports are huge. Mine is severely over-gassed.

  14. #14
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    Quote Originally Posted by SINNER View Post
    With the 1-10" twist it's going to prefer the heavier bullets. The 175gr. HPBT's shot very well out of my 16" Mega barrel. Decent shooting barrel but damn those gas ports are huge. Mine is severely over-gassed.
    Yes! I had to replace my standard gas block because it was ripping the primers out of my casings when I shot it! I installed a Syrac Ordnance adjustable gas block and got it tuned up nicely!! Shoots like a dream now.

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