Why do some rifles prefer different commercial loads

[alaskan9974]

I have a rem 700 in 308, been bench rest shooting trying to see what works at 100 yards before I shoot farther. I've shot a few hundred rounds of different match ammo seeing what works best in it.

The biggest difference I've seen in match ammo is between Federal gold 168 SMK at .75moa moa and Hornady super performance amax 168 at 1.25-1.5 moa. What's with the big variance? Even cheap Walmart zq1 has no issue hitting 1.5 moa.

 

[witchhunter]

All rifles are different enough that it matters. If you are going to use only factory ammo, find what it likes and just shoot that. When you start reloading, that same rifle will like a certain bullet, powder or velocity. Can't explain it, but it is true.

 

[splattergun]

fouling yes, fouling no, bullet velocity, bullet shape, barrel temperature, barrel twist, air temperature, rifle rest, &c &c

Shoot the ammo your rifle likes best on a consistent level through various conditions.

 

[Snyper]

I believe barrel harmonics are what makes a rifle prefer one load over another, but there are other variables involved

 

[jmr40]

Superformance ammo is loaded to give you more bullet speed. It isn't intended as a super accurate load. I'd test something else if accuracy is your goal.

Every rifle is different. All will shoot somewhat better with certain ammo. But many rifles will shoot most anything decently. Other rifles are very picky only shooting certain loads well and throwing others all over the target.

 

[climbnjump]

I once bought a box of Hornady Superformance 53 gr V-MAX for my .223 just to see if I could get the velocities listed on the box. My rifle actually exceeded the box velocities. But... I could only get 3" groups - at 50 yards - with that stuff. Yes, it was fast, but wasn't even accurate enough for casual plinking.

But I had already bought some of those same bullets for handloading so went ahead and worked up a load that shoots 2" groups - at 200 yards. Same bullet, same rifle, but of course different powder type, charge, case and primer. And perhaps more importantly, a different COAL.

Different rifles even of the same make and model, may well shoot differently because they are - wait for it - different... Due to manufacturing tolerances in machining, materials and assembly, no two barrels are the same, no two chambers are the same, no two barrel crowns are the same, no two action bedding screws are torqued the same, etc. And that doesn't even cover manufacturing tolerances of factory ammo of the same type not to mention differences between brands. So lots of variables simply means lots of variability.

 

[Liberty1776]

I wonder if bullet length makes a difference? My Win 94 groups Federal 150gr in a hand size group. It groups Winchester 170 gr in a quarter size group. Of course primer and powder are also different. Dunno, just glad sometimes I find the right load.

 

[CB900F]

Alaskan9974;

Snyper has given you the extremely short version, here's a longer one.

Every time you shoot, the barrel vibrates, mostly in the vertical plane. As the muzzle reaches the end point of a swing, it slows, stops, and reverses direction. In the mid-point of the swing, it's at it's highest swing speed. If the muzzle pressures the rear of the bullet to one side or the other as the bullet leaves the muzzle, accuracy is negatively affected. If you can get the bullet to exit the muzzle at an endpoint, accuracy is improved.

Look up the Browning/Winchester B.O.S.S system data. There they put a micrometer type weight on the end of the muzzle & you could dial it to make the barrel vibration match the load rather than try to find a load that matched the barrel.

900F

 

[Nature Boy]

Here's 3 different 10 round groups I fired with commercial "match" ammo at 100 yards in my Springfield M1A. All 168g .308 and all fairly close in performance. Make sure you're comparing similar quality and shooting a large enough sample to be a significant comparison. I'll bet you'll find less of a difference. If you'll note, one thing this did show was a big difference between point of impact between brands.

 

[CraigC]

Why do some rifles prefer different commercial loads

That's a million dollar question. Every firearm is a law unto itself. They will ALL show preferences. Just like people and ice cream, some like vanilla, some like chocolate, some like cheap, some like expensive, some only like one flavor, some like a little bit of everything.

 

[Slamfire]

Why do some rifles prefer different commercial loads

Why don't you ask something easy, such as, "What is the meaning to life?", or "the answer to the Ultimate Question of Life, the Universe, and Everything?" .

Our current state of the art is such, we don't know and I am certain that in my lifetime, we will never know. You just have to go out and test and find the stuff that works best.

By the way, the answer to the second question is 42.

 

[Art Eatman]

The generally accepted answer is barrel harmonics. For whatever reasons, different loads vibrate differently.

CB900F's answer may well be correct, SFAIK.

 

[HankC]

The generally accepted answer is barrel harmonics. For whatever reasons, different loads vibrate differently.

CB900F's answer may well be correct, SFAIK.

Heavy barrel tends to be less ammo sensitive while stiffer and the weight helps.

 

[Tirod]

What causes harmonics to be different one load to the next? First, the powder charge and it's "impact curve" going from rest to full burn. How the charge "rings" the barrel and starts the vibration node, it's amplitude, and then, the dwell time in the barrel where the bullet exits just as the muzzle comes to the most coaxial point in the vibration.

In a general sense, loading for more velocity eventually reaches a point where it "rings" the barrel harder and harder, which causes more dispersion. It's why handloaders working up loads note that they get the best accuracy with a charge under the safest maximum load. You can get more speed but it is usually at the cost of the group opening up.

Another element is just how far the bullet sticks out of the case and where it's positioned in relation to the rifling. As the bullet exits the mouth of the cartridge under increasing pressure, was it coaxial to the bore, does it stay coaxial, and does it travel in line to exit that way? Some ammo might be close enough in the box but that specific gun might be knocking it back slightly or causing the bullet to tip when loaded into a chamber - and that is why all self loading military ammo uses a crimp. That also brings up bullet setback, where it's not held tightly in the case mouth and gets shoved back compressing the powder charge.

It's complicated, is what it is.

So the bullet actually has to be straight in the bore to come out the muzzle straight, if it's tipped off axis it then gets a poor start. Then the muzzle has to actually be in line with the rest of the bore and not slightly offset from vibration.

Crooked bullets and a muzzle off target, big groups. We are talking tenths of a thousand and smaller dimensional variances, or changes of less than 50fps in velocity, or using one powder compared to another. Even adding a muzzle weight and it's position relative to the crown changes things, along with how hot the barrel is - they get more flexible when warmer.

It's been reported that pushing the bullet out just a few thousandths of an inch further out to engage the rifling can clean up a run of the mill group and make it to bragging rights turf.

It's why handloaders have so much fun!

 

[CraigC]

I think it has to do with a lot more than just barrel harmonics. By that logic, a 3" diameter barrel would shoot all loads using the same bullet with the same degree of accuracy. I think it has to do with everything that falls under the umbrella of internal and external ballistics, including every dimension imaginable of both the firearm, the ammunition and all its components. Not to mention how all that impacts the bullet's flight. It's countless seen and unseen, measurable and immeasurable factors.

It's why handloaders working up loads note that they get the best accuracy with a charge under the safest maximum load.

I think this is mostly myth. It just doesn't withstand scrutiny. For example, take a rifle chambered in .222Rem. It may reach peak accuracy just under its limit of 46,000CUP. Now rechamber it to .223WSSM that runs up to 65,000psi. If the myth were true, the rifle would never be able to match the .222's accuracy running anywhere near the .223WSSM's maximum pressure, especially when the case is a good bit larger which equates to a weaker chamber wall.

Another example. Take a new production Winchester 1886. The SAAMI maximum pressure is 28,000CUP. According to the myth, the rifle would shoot best somewhere just under that maximum. For argument's sake, 26,000CUP. If the myth were true, loading that rifle up to 40,000CUP or more, which is perfectly safe for the rifle, would result in degraded accuracy. We know this is false.

And how would you know that any firearm wouldn't actually reach peak accuracy with a load slightly over maximum? It is obviously a bogus theory.

 

[Bart B.]

Tirod,

Where is the most coaxial point in a barrel's vibration for optimum bullet exit for accuracy?

Why is that the best place?

Just curious as I've never heard of a "coaxial point" someplace in a barrel's vibration properties.

 

[FL-NC]

Price and performance- both in accuracy and terminal performance. Not all ammo agrees with all rifles.

 

[bikemutt]

alaskan9974, I've noticed the exact same thing with my Rem 700 .308. I will say though, I have yet to find a rifle that isn't more consistent with Federal Gold 168 grain.

I have also seen variances in Hornady according to lot, albeit with 140 grain 6.5 Creedmoor fired from a Savage 12 LRP rifle. I'd been having great success with a small batch of that ammo. When I ran out and changed to a new lot, accuracy was off by a noticeable amount. Now that I've burned through that batch, I'm back to feeling the Hornady love.

Here's a group from the latest lot, 100 yards off a bench. The last shot choke is typical of the dumbo pulling the trigger

 

[alaskan9974]

Thanks. My 700 is loving the GMM, my lr308 ap4 is happily eating the superperformance and getting decent groups with the p308 scope. Win/Win for me as I bought a ton of both.