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Old November 27, 2021, 10:03 PM   #1
Dgr6
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Advice on consistency issue

I'm relatively new to reloading so I might be overlooking something simple. I developed a 300 win mag bolt gun successfully down to repeatable .25 moa groups as my first foray into reloading. Once I got that done, I started on a 308 ar10 I built with a rainier 18" ultramatch mod2 barrel. I have gotten a few loads to group down at around .25 at 100 yards, but each load I've developed has been wildly inconsistent when I test further. With the same exact recipe I've had swings as wide as .25 up to 3.1 moa. My 300 magnum never had this issue, and was very consistent with all the loads I tried during development, whether they were good or bad. I've looked the gun over thoroughly and don't see any obvious issues there. I've tried 2 different powders and 3 different projectiles. Im not a regular cleaner, but I gave it a deep clean to rule that out as a variable. All loads exhibit the same inconsistent swings. Right now I'm playing with neck tension but haven't seen any useful results from that yet. I'm hoping there's something obvious to a more experienced reloader that might steer me in the right direction. I'm starting to wonder if the barrel has some sort of manufacturing issue, or there's some weird harmonic problem going on with it. My goal for this gun is consistent 1/2 inch groups at 100, so the best groups have exceeded that, but the consistency problem is driving me up a wall. Any suggestions would be greatly appreciated.
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Old November 27, 2021, 10:50 PM   #2
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Do you have a chronograph? What's the twist rate of the 308 barrel and what bullets are you trying?

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Old November 27, 2021, 11:04 PM   #3
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I do have a chrono. It's 1:10 and right now I'm using lapua brass, cci 200s, n540 and Sierra matchking 175s.
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Old November 27, 2021, 11:10 PM   #4
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Do the groups open when the gun is hot? Could be your shooting faster with the semi auto. Could be barrel heat, or a poor barrel to receiver fit causing the groups to open up when the gun is heating up.
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Old November 27, 2021, 11:15 PM   #5
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That might be too fast a twist. Using the jbm stability calculator, at a velocity of 2500 it's putting out a stability factor of 2.369. you generally want around 1.5. that barrel should work great for the heavies looks 230's, which at a velocity of 2000 gets a stability factor of 1.5 ish.

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Old November 27, 2021, 11:38 PM   #6
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I've been shooting no more than 3 shots at a time without a break to try to keep temperature out of it. The other bullets I tried were berger 168s and matchking 168s. I also tried H4895 powder with similar results.
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Old November 27, 2021, 11:47 PM   #7
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Originally Posted by Dgr6 View Post
I've been shooting no more than 3 shots at a time without a break to try to keep temperature out of it. The other bullets I tried were berger 168s and matchking 168s. I also tried H4895 powder with similar results.
Yeah that barrel's twist rate just seems to fast for really anything under 200 almost, doesn't matter the powder, they could just be getting spun too hard with that fast twist. Try something in the 220-230 grain class and see if the problem goes away

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Old November 28, 2021, 05:38 AM   #8
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1 in 10 is perfect for 175.

In our local competitions we shoot F class and Tactical at the same matches. Tactical class uses AR10's and 15's and their targets have X and 10 rings twice the size of the F class for a reason. Unless you are a special case you will need a few thousand rounds of practice to get consistent .75's let alone .5's. Internet experts aside consistent .5 groups with a AR are about as common as a honest politician
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Old November 28, 2021, 08:40 AM   #9
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Yes! Consistent 1/2" groups at 100 yards in a large platform AR! Every human has that goal.

Consider a Kreiger instead of a factory barrel to start. While at it, throw in a JP bolt.

I think your load development is whats getting you. You can't pick 1 tight group in a sea of big groups. Ideally you will have very tight groups before the best one, and very tight groups after the the best one.

The fly in the ointment is the POI shift from group to group. If the group you picked in the clusters are moving all over the place, you end up with big fliers the next time you go out.

If you tweak your expander ball de-capping instead of using a universal die for that you can have lots of problems.
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Old November 28, 2021, 08:47 AM   #10
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Consider a Kreiger instead of a factory barrel to start. While at it, throw in a JP bolt.
good advice
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Old November 28, 2021, 08:59 AM   #11
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I have about 4 factory stock ar-15 223 caliber and one Smith and Wesson factory stock AR-10.
I have given up on making them shoot as well as my heavy barrel bolt action rifles, for me they are about a 2 or 3 moa gas gun and I just shoot them for fun, 1/4 moa out of them consistently is out of the question.
I hope you have better luck.
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Old November 28, 2021, 10:20 AM   #12
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I thought initially I was dealing with powder that was very temperature/condition sensitive. I had a load that shot under .5 for 3 groups on one particular day, and I've probably made that same recipe 10 more times since then and can't get it under 2 inches now. That's what prompted me to try switching powders. What gets me is most of the factory match ammo I've tried seems to group around an inch pretty consistently, so that leads me to believe something is off in my process thats causing it to open up to these 2 and 3+ inch groups randomly. I'm going to try borrowing a different set of dies to see if maybe something is wrong with my set to rule that out. It could also be that I was just lucky with my 300 and it's created an unrealistic expectation for this new gun.
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Old November 28, 2021, 12:29 PM   #13
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Dgr6, you did not mention what powder you were using...

i agree with hounddawg that 1:10 is about as perfect as you can get for the 175 weight bullets

i have had really good luck with Varget and Nosler 175 custom comp bullets...they seem to fly a little better than the seirra and speer bullets in that weight class for me

also i would be very careful about the neck tension in a auto loader...lots of different things going on vs a bolt gun...just a thought....you dont have any control with the bolt picking up a round from the mag and slamming it into the chamber on an auto..so you could be getting bullet set back just from loading into the chamber...

for me i sure would not be expecting bolt gun accuracy out of my ar10....but im sure some people could make it happen....my gun will do pretty consistently 1-1.25 i know its just not a target gun...lol...so i dont try to make it one

my .02

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Old November 28, 2021, 01:17 PM   #14
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1:10 is an exceptionally common twist rate in both 308, 30-06, and 300 win mag with 150g bullets and up. I seriously doubt the twist rate is the issue.

Could be loose optics on the gun. I would go through and re-torque everything.

still say it could be barrel to receiver fit. you could pull and re-torque the barrel nut.

Could be the barrel conditions. depending on how you are cleaning it and fouling/copper buildup. may only shoot well when its squeaky clean....
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Old November 28, 2021, 01:48 PM   #15
Dgr6
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Ocharry - I'm using n540 powder now, and I was using h4895 previously with similar results.

I'm going to retorque the barrel nut next and make sure it's still in spec. It didn't seem to change after a deep clean from what it was doing previously when dirty. Optic was recently checked and is still good.
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Old November 28, 2021, 01:52 PM   #16
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Quote:
Originally Posted by arlaunch View Post

I think your load development is whats getting you. You can't pick 1 tight group in a sea of big groups. Ideally you will have very tight groups before the best one, and very tight groups after the the best one.
I'll definitely second this too. I never pick a load based only off 100 yard group size. I bet if you look at the Chrono numbers, they'll be all over the place.

I don't have any 308's, but I do have a 300 rum that's a 1:10 twist, which is why I suggested it might be a bit fast, and the jbm calculator defaults to a 12 twist. Apparently I was mistaken, so ignore that bit.

The vihtavouri powders should perform great. Go back to your load development and use the Chrono. I use the ocw method. Shoot 5 shot groups of .3 grain increments round robin style(one of each charge weight, then go back for a second, third, etc) there should be a cluster of charge weights that has a velocity plateau and all have a similar poi. Then try those at longer ranges.

As others have said, don't expect bolt gun accuracy from a gas gun. I'm not saying gas guns can't be accurate, but expecting it to hold .25 moa (hell, the fact you got quarter minute suggests something funny going on). From a bit of digging, most people get about half minute from them. They're actually(or at least were) shilen blanks.

Don't try to shoot tiny groups during load work, just try to do everything exactly the same, shot to shot to shot, and let the data tell you which load the gun wants. Don't use a vice either, and don't muscle the gun around. You should be able to relax and close your eyes, and when you open them again, you should be aiming at nearly the exact same spot.

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Old November 28, 2021, 02:31 PM   #17
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Dgr6,

Some more details would be helpful. If you got a 300 WM to shoot 1/4 moa, that is practically a miracle to most shooters. Don't let that rifle get out of your hands.

For the problem gun: Lots of things need to be determined, so let's start with some basic information: Are you using optical sights? An optic that is internally rattled can cause rounds to jump around sometimes and not others. Is your AR platform match accurized (handguard floated, target trigger that doesn't disturb POI, etc)? If not, intermittent handguard contact with the barrel could explain it. How many shots are you putting into each group? If it is just the three shots you mentioned between coolings, that number is so low that the normal group statistical variation is 6:1 for 95% of groups. Ten-round groups are much more useful for determining typical performance and differ by a quarter of that. But a gun sometimes shooting a quarter-inch and sometimes 3 inches is a 12:1 ratio. The odds against that being random are big, even with three-shot groups, so something else, like one of the above-mentioned mechanical issues, is more likely to be going on.

Bullets deformed by passing through heavy copper fouling can spread out badly. If you have a borescope, you should look at it. If not, I would use Slip2000 Carbon Killer to get the carbon out, and follow it with Bore Tech Eliminator, allowed to sit 10 or 15 minutes before patching out, and repeated until the blue stops coming out (note that a brass jag will color the patch blue using this stuff, so a plastic or steel military one or one of Bore Tech's Proof-Positive jags made of non-reacting alloy should be used with it. Then use the Carbon Killer again and allow it to sit, too, in order to get out any carbon that was previously covered by copper.

As mentioned, the 10" twist is not a problem with the bullets you are using. Shooting just under 1 moa is a very reasonable expectation for a 10" twist with the bullet you are using. They can stay in the X-ring of a 600-yard slow fire target with the best shots running them from the prone position with a sling. That's about 1 moa at 600. Using Litz's estimate based on the ratio of times of flight, that would be like shooting a hair under 0.8 moa at 100 yards in zero wind. I have a match accurized Garand that would shoot Sierra 168's into 0.75 moa for ten shots from the prone position when it was newly fit up. My Compass Lake match 223/5.56 AR shoots to 1/2 MOA consistently off the bench, but the match accurizing steps were necessary.

Some other factors may be at work. If factory new ammo shoots more consistently, check your case head for being out of square. Line the empties up on a flat surface and sight down the line to see if the mouths of the cases line up. If not, you may be bending rims on extraction. When such cases are reloaded, resizing can be inconsistent because sometimes the rim bend rests on the shell holder ledge and sometimes is down in the slot in front. Such cases cause recoil to be inconsistent because they randomly hit one side of the bolt face first before the rest, changing the lateral recoil moments that affect barrel vibration. Make sure your cartridges are concentric. Using a Lyman M-die rather than the expander built into the sizing die can help quite a bit with this.
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Old November 28, 2021, 03:06 PM   #18
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Competitive long range shooters using 30 caliber 150 grain bullets leaving 3000 to 3050 fps learned decades ago that a 1:13 twist barrel produced best accuracy. NATO M80 ammo often was best with a 1:14 twist.
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Old November 28, 2021, 08:18 PM   #19
Dgr6
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The 300 wm recipe is 67.4 Norma mrp, Hornady brass, cci 250s, and berger 230 hybrid targets for anyone that may be curious. Es and SD were very good, but I don't remember the values off hand. The gun is an xbolt max long range with a factory barrel, believe it or not. Nothing super high end in the target world. It definitely exceeded my expectations. It shoots everything lighter than the 230s that I tried pretty terribly, however. I was on the verge of selling it until I found that load.

The 308 is an m5e1 chassis, ssae trigger, Bushnell dmr 2 3.5-21, and aero bolt (until I can find a jp bcg in stock). I shoot off of bags with as little rifle contact as possible. I have a jp 556 I moved the optic to to test and it grouped like normal.

When I cleaned I used m pro 7, then butchs bore shine until patches came out clean. I tried groups with it clean, and then groups after a few mags to foul the barrel again. No significant changes.

When I installed the barrel I lapped the receiver and used a bedding compound. Torque was slightly off when I rechecked the barrel nut today, so I'll reshoot tomorrow and see if anything changes. All other torque values were good.

My normal process is 3 rounds each until I find a good group, then I shoot 3 more 3 shot groups over the chrono to make sure es and sd are acceptable, and the accuracy remains. Im only using unfired brass right now. I'll shoot over the chrono tomorrow and see what I get as I'm trying new loads.

As far as accuracy expectations, my jp and geissele rifles are sub moa with a variety of match ammo, but I've never dealt with an ar10 before. I'd be happy with anything sub moa at this point as long as it's consistent.
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Old November 28, 2021, 09:18 PM   #20
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https://ibb.co/sq1rKZP

https://ibb.co/Np2QRbh

Here's two groups from the same recipe on the same day (before and after zero adjustment, not a massive poi shift). When I came out to shoot it the next day I never had a sub moa group again. I wish I had chrono data from those days but I don't. I went further up the ladder and got a .29 on a different load, but that one never repeated so I moved on. I believe the load pictured is the one that eventually shot a 3.1 moa group. That seems like a pretty wild swing to me.
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Old November 29, 2021, 12:19 PM   #21
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That is a pretty wild swing. Something is changing. You can overlap targets to get a larger sample if you haven't changed anything. 3-shot groups by themselves can be rather variable, so unless they repeat, there is a good bit of luck-of-the-draw with them. Below is a computer simulation making groups with a random number generator that has its output constrained to produce a normal distribution on both the horizontal and vertical axes. This set contains something close to both the extremes of a 95% confidence limit for 3-shot groups, which makes it a bit of an outlier. I had to run the simulation a number of times to get an example this extreme, but you get the idea from it of what can happen at times and how drawing a conclusion about how the gun is performing is difficult with just any 3 of the nine shots. But combined, they give you a much better idea. Even if all the three-shot groups had been tight, when they combined, the group would be bigger because you can see that not only did the groups differ in size, the little red x's that mark the center of each three-shot group moved around. That center moving has a standard deviation equal to the standard error (sd divided by √n) on each axis.



Per the cleaning, I used to use Butches and other ammoniated cleaners, but the water-based chelating cleaners work so much faster and better for copper, it's a night and day comparison. This old article may be of interest.
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Old November 30, 2021, 04:20 PM   #22
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If you got a 300 WM to shoot 1/4 moa, that is practically a miracle to most shooters. Don't let that rifle get out of your hands.
I would not shoot it much! Once the barrel is gone......

You should be shooting 5 shot groups (not that I would want to with a 300 WM, but 5 tells the tale and 10 more so).

Pr Shadow and Unclenick, it seems like something is loose.
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