New Upper on M&P Sport - Accuracy Issue

wylie won

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I put a new barrel on my M&P Sport. I put on a Ballistic Advantage 20" 5.56 DMR Rifle Length AR 15 Barrel, Performance Series.

I've put about 100 rounds through it this weekend. It's all over the place at 100 yards. Here's a picture of the results. It cycles fine but the groups are everywhere.

After my trip to the range, I came home and made sure everything was tight. My optic is level and torqued to spec. Handguard looks fine.

Is it just the process of breaking in? Look at the groups (the orange target is 1") and let me know if you have any thought...

Thanks!
 

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Looks to me like I would keep going up on the charge and shoot some more,seems to tighten up as charge is going up. May have a sweet spot that you will find that the barrel likes. Have you tried any factory loads? Did you look at the crown of the muzzle?
 
The crown looks fine. That's all I loaded for today. I'll work my way up to max load next weekend. There's just NO consistency with those groups.

I haven't tried any factory ammo. I reload all my match grade stuff with GREAT success in my bolt rifles.
 
Suggest trying a different primer. Have heard that those AR match primers may not always give consistent ignition. Since it looks like your following Sierra's loads, try the Rem 7 1/2's.
 
What is the twist on the barrel? You might want to try some factory ammo as a base line. Your barrel might need some breaking in too.

Being that it's a new barrel, you essentially have a new rifle and will need to figure out what charge and bullet weights it likes to eat best.
 
Suggest trying a different primer. Have heard that those AR match primers may not always give consistent ignition. Since it looks like your following Sierra's loads, try the Rem 7 1/2's.

I agree, I'm not overly impressed with those primers. I have a few other brands I can try.
 
What is the twist on the barrel? You might want to try some factory ammo as a base line. Your barrel might need some breaking in too.

Being that it's a new barrel, you essentially have a new rifle and will need to figure out what charge and bullet weights it likes to eat best.

The Twist rate for my rifle is 1:7. You are right, I will definitely need to develop a load for this rifle. I just did not expect the Sierra match King groups to be so all over the place.

I have a Hornady 68 grain match load that I developed for a Savage 223 bolt action that is sub-moa all day long. The new rifle barrel on this AR doesn't like those at all

It's too early to blame the barrel. I'll try another load development this next weekend
 
The Twist rate for my rifle is 1:7. You are right, I will definitely need to develop a load for this rifle. I just did not expect the Sierra match King groups to be so all over the place.



I have a Hornady 68 grain match load that I developed for a Savage 223 bolt action that is sub-moa all day long. The new rifle barrel on this AR doesn't like those at all



It's too early to blame the barrel. I'll try another load development this next weekend



Agree on not blaming the barrel yet.

Maybe experiment with some heavier bullets? Buy some boxes of different weight bullets to see what it seems to prefer before putting a bunch of work in load development might be the best approach.

It depends on how much you value your time vs paying store prices for ammo.


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Agree on not blaming the barrel yet.

It depends on how much you value your time vs paying store prices for ammo.


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I actually really enjoy load development. I already have a few ideas for the next loads. Hopefully the groups will tighten up.
 
I use CCI-450 for everything AR. The 450 is the same as the 41, but has a slightly "softer" cup.

What is your bench set-up? A poor bench and poor technique could easily be part of the issue.

Like Vonn mentioned, you may wish to up the charge. I seem to have best luck just a bit off max.
 
I'm shooting off a bench with a Harris bipod and Rabbit Ears rear bag. I'm a pretty good shot. I'm not worried about technique.

My next loads will come closer to max at 25.5, 25.7, and 25.9.

I'm also going to run some Hornady 75 gr BTHP Match to see if the 1:7 prefers the even heavier projectiles.
 
I am getting 1 1/2" group at 300yds with Hornady Black 75gr bthp in my 1/7 barrel. You might try those for a baseline. I don't think I could reload any that would be much better, but I am about to start trying.
 
I am getting 1 1/2" group at 300yds with Hornady Black 75gr bthp in my 1/7 barrel. You might try those for a baseline. I don't think I could reload any that would be much better, but I am about to start trying.

That's sub-moa... very nice! Next time I'm at the sporting goods store, I'll buy a box to try.
 
Question, how snug was the fit between the barrel extension and upper receiver? If it slid in easily or even had a bit of wiggle there is the reason for your poor accuracy. The ideal fit is one where you have to get the extension perfectly aligned in the receiver and has noticeable drag as you push the barrel "home".

I have a precision AR I put together using a Shillen barrel in a Gibbz Arms side charging upper and the fit between the barrel and receiver was so perfect I had to use a small nylon hammer to drive the barrel in the last 1/4 inch. With a 68 grain Hornady BTHP over 23.7 grains of Varget this rifle will shoot under 3/10 inch 3 shot groups at 100 yards and under 1/2 inch for 5 shot groups. Yeah the barrel does drift a bit as it warms up but I can live with 1/2 MOA and single cut barrels are $$$$.

BTW, you may want to take note of that powder charge of Varget that works best for me, did a fair bit of testing to find the sweet spot for my barrel and it's a lot lighter charge than what you are using. I'll also note that I tries the Sierra Match Kings and the result was identical to the Hornady bullets and the Hornady's are a lot cheaper than Sierra. IMO anyone who claims that Hornady bullets aren't accurate hasn't actually shot with Hornady bullets because they are very accurate.
 
Question, how snug was the fit between the barrel extension and upper receiver? If it slid in easily or even had a bit of wiggle there is the reason for your poor accuracy. The ideal fit is one where you have to get the extension perfectly aligned in the receiver and has noticeable drag as you push the barrel "home".

I have a precision AR I put together using a Shillen barrel in a Gibbz Arms side charging upper and the fit between the barrel and receiver was so perfect I had to use a small nylon hammer to drive the barrel in the last 1/4 inch. With a 68 grain Hornady BTHP over 23.7 grains of Varget this rifle will shoot under 3/10 inch 3 shot groups at 100 yards and under 1/2 inch for 5 shot groups. Yeah the barrel does drift a bit as it warms up but I can live with 1/2 MOA and single cut barrels are $$$$.

BTW, you may want to take note of that powder charge of Varget that works best for me, did a fair bit of testing to find the sweet spot for my barrel and it's a lot lighter charge than what you are using. I'll also note that I tries the Sierra Match Kings and the result was identical to the Hornady bullets and the Hornady's are a lot cheaper than Sierra. IMO anyone who claims that Hornady bullets aren't accurate hasn't actually shot with Hornady bullets because they are very accurate.

The barrel fit right in... it wasn't "snug" at all. I wonder if that has an effect on my accuracy???

I agree about Hornady. The 68gr Match with 23.8 gr of Varget is my go to load out of my Savage FV12 223. I'm attaching a pic. I can do that pretty consistently with that rifle. The new Barrel does not like it though.

In my 308, my go-to round is the Sierra matchking 168 grain. However, the Hornady 168 grain Eld match is a great round! The grouping with the Sierra is a bit better, but not by much. The ballistic coefficient of the Hornady Eld is so much better by comparison and I can get the Hornady over 2700 fps.
 

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It's pretty obvious that Savage of yours is quite accurate and you know how to use it, so we can rule out the Shooter as the cause of your accuracy problems. IMO the problem is that "drop in fit". Because any "wiggle room" will allow the barrel to vibrate inside the receiver with each shot fired.

I had a similar issue when I put together my 300 Blackout using a Wilson Combat barrel and a Detroit Gun Works upper. In my case I got a bit lucky and there was enough clearance between the barrel extension and receiver to allow me to insert a single wrap of 0.001" stainless shim stock. With a bit of red locktite to "glue" that shim to the barrel extension I now have a rifle that will shoot to 3/4 MOA. BTW, I had hopes that after the locktite set I would still be able to slide the barrel out of the receiver but that locktite did bleed a bit so the barrel is now locktited in place. If I ever have need to remove the barrel I will most likely have to "bake" it in an oven to 165 degrees to melt the locktite and allow it to release.

I learned a lesson with my Blackout and when I put together my 223 Carbine I took my Odin Works barrel for it to a local gunshow and test fit it in the various uppers on display until I got a good snug fit.

This is probably your best option if you have gun shows in your area because as I have discovered there is a lot of variablilty in "mil Spec". Another option is to locate a machinist who will measure the diameter of your barrel extension with 4 place micrometers so you'll know the diameter down to 1 ten thousandth of an inch. Looking on the Net that diameter should be 0.9997 to 0.9998 inch and the receiver spec is 1.000 +/- 0.002 inch. Yeah a whopping 0.004 inch range. Once you know the exact diameter of your barrel extension Midway or Brownell's and see if they could sell you an upper selected for size.

A much more spendy option would be to contact Gibbz Arms and talk to them about one of their Side Charging Uppers. As noted when I put together my precision AR the Gibbz side charger fit the barrel extension on my Shilen barrel as perfectly as possible.

Final option is to locktite the barrel extension into the receiver. The downsides to doing this is the barrel and receiver will require heating to the point where the locktite will release enough to remove the barrel. After that you'll have to clean the residue with MEK, a rather nasty solvent to use (thinks LOTS of fresh air and don't even think about doing it inside or near any open flame). The other thing you'll have to keep in mind that you will need to keep the barrel extension below that release temperature when shooting so NO high volume rapid fire.

Attached you'll find a pic of my precision rifle after it's first outing. That lever at the top front is the charging handle so no need to reach under a scope to charge the rifle. I will also note that I was so impressed with Gibbz method of mounting a handguard that all 3 of my AR's have a Gibbz handguard even if they feature standard uppers.
 

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That's a nice rig...

I took it apart this evening. There was a tiny (very minimal) wiggle. I would not describe it as snug.

Something I did notice was the barrel nut. I don't think it was torqued down enough. I couldn't get it tight enough to make it to the next screw hole. I used a shim and it helped me get a bit more torque on it. But I have no faith in that barrel nut and handguard.

I'll take it out this weekend to run a few more 100 yard groups. We'll see...
 
I'm having a similar issue with a .308Win LR-10. I just can't get it to group. I haven't messed with it in a while. I will follow this closely. Maybe the progression you go through will help me with mine.
 
That twist SHOULD.....

The Twist rate for my rifle is 1:7. You are right, I will definitely need to develop a load for this rifle. I just did not expect the Sierra match King groups to be so all over the place.

I have a Hornady 68 grain match load that I developed for a Savage 223 bolt action that is sub-moa all day long. The new rifle barrel on this AR doesn't like those at all

It's too early to blame the barrel. I'll try another load development this next weekend

...be able to stabilize heavier bullets and have no problem with lighter bullets so changing the load the next thing I'd try. if that doesn't work, try different weight bullets. Unless your barrel is free floating, weird harmonics may be introduced. That looks like it could be the problem here because the groups don't show consistency in pattern. Except maybe low right is a bit prominent, but like you said they are 'all over the place'.
 
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