Accuracy: Tale of Two New Model 70s

[Highbrass1227]

Hello Forum Mates. Need your advice. Below is a picture of two new Model 70s that I own. Both were purchased within the last 18 months. I handload for both.

The targets below the stocks show the respective groups. As you can see the maple Super Grade in .270 is shooting sub MOA. The Featherweight in .308 is spraying all over the place. I just shot these back-to-back last weekend.

Any advice before I call Winchester? I'm terribly disappointed by the accuracy of the .308. My protocols and even optics for the rifles are all very similar.

BTW my starting .308 load for the featherweight is a 150 grain Hornady SP over IMR 4064. I can let you know the power charge if you need that. (The .270 is a 130 grain Hornady SP over H4831sc)

Thanks!

 

[marksman1941]

Some rifles simply dislike certain bullets. I've found that it's worth trying 4-5 different bullets and bullet weights before getting too upset at it. Find a near the top load with your preferred powder, seat the bullet to book depth, give it a try. If you call Winchester after one load test they'll likely tell you to try more loads/factory ammo before they'll do much with it

 

[JKB57]

your super grade has a longer heavier barrel thus does not heat as quick,the featherweights have a pencil barrel that heats up quick so 3 shots on the 308 and the barrel is to hot to get good accuracy beyond that unless letting it cool

 

[Highbrass1227]

Some rifles simply dislike certain bullets. I've found that it's worth trying 4-5 different bullets and bullet weights before getting too upset at it. Find a near the top load with your preferred powder, seat the bullet to book depth, give it a try. If you call Winchester after one load test they'll likely tell you to try more loads/factory ammo before they'll do much with it

By top load are you suggesting to keep laddering up? I have a variety of .308 bullets and weights, so experimenting with them will not be an issue.

 

[Highbrass1227]

your super grade has a longer heavier barrel thus does not heat as quick,the featherweights have a pencil barrel that heats up quick so 3 shots on the 308 and the barrel is to hot to get good accuracy beyond that unless letting it cool

Great point on the barrel contour. I hadn't considered that. That center target is my original 3 shot group. Discount the flyer on the left and the other two shots are reasonable and load optimization can take over from there. Vertical is good so looks like my powder charge is in the ballpark.

 

[marksman1941]

By top load are you suggesting to keep laddering up? I have a variety of .308 bullets and weights, so experimenting with them will not be an issue.

Take this with a gigantic grain of salt, as your mileage may vary. In a modern rifle, with a modern load book, loads are typically neutered substantially to the point that "max" is still well within safe realms. So for example, if a load book offers a range of 40-44gr of imr4064 under a 150gr bullet, starting at 40gr tends to be a massive waste of time and resources. In this case I'll typically start at 42.5-43.0gr or so and work up from there.

I've found that if a rifle is going to be picky with loads, it simply isn't worth fighting that load. Doing a ladder of 0.2gr and finding accuracy nodes is all fine and dandy if that node is 1.0gr wide, but if it's smaller than that then ambient temperature is going to change your group size beyond acceptable levels.

IMR 4064 is relatively temp stable, and changes about 0.5fps per degree F change. So if you do your load development at 60F, and hunting conditions vary 30 degrees either way, you have a 30fps spread of your average muzzle velocity. If your accuracy node is 0.2gr wide, and groups open up outside of that, odds are good temp variations will push you out of your accuracy node at some point.

Sorry for the rabbit hole here. This will likely go against some advice from others, it's just what I've experienced. Basically pick a bullet, test a small range of powder charges up near max and make sure groups don't deviate massively (or one charge tested in a variety of temperatures) and if it doesn't work move on to another bullet. Seating depth also plays into it, more so with some bullets than others, but that can be its own rabbit hole to chase.

 

[moses42ak]

My 7mm-08 featherweight wasn't giving me what I wanted after trying a bunch of different loads. I bedded the recoil lug and tested the same ammo and the group shrunk considerably. Bed the recoil lug and keep the strings to 3 rounds. At this point, it can't hurt.

 

[Highbrass1227]

Take this with a gigantic grain of salt, as your mileage may vary. In a modern rifle, with a modern load book, loads are typically neutered substantially to the point that "max" is still well within safe realms. So for example, if a load book offers a range of 40-44gr of imr4064 under a 150gr bullet, starting at 40gr tends to be a massive waste of time and resources. In this case I'll typically start at 42.5-43.0gr or so and work up from there.

I've found that if a rifle is going to be picky with loads, it simply isn't worth fighting that load. Doing a ladder of 0.2gr and finding accuracy nodes is all fine and dandy if that node is 1.0gr wide, but if it's smaller than that then ambient temperature is going to change your group size beyond acceptable levels.

IMR 4064 is relatively temp stable, and changes about 0.5fps per degree F change. So if you do your load development at 60F, and hunting conditions vary 30 degrees either way, you have a 30fps spread of your average muzzle velocity. If your accuracy node is 0.2gr wide, and groups open up outside of that, odds are good temp variations will push you out of your accuracy node at some point.

Sorry for the rabbit hole here. This will likely go against some advice from others, it's just what I've experienced. Basically pick a bullet, test a small range of powder charges up near max and make sure groups don't deviate massively (or one charge tested in a variety of temperatures) and if it doesn't work move on to another bullet. Seating depth also plays into it, more so with some bullets than others, but that can be its own rabbit hole to chase.

Yes, I have a similar philosophy as you on load data-typically start around mid. I believe mine were 42.0 and 42.5 grn of IMR 4064. I can try some more powder/velocity, but my stringing was horizontal, not vertical.

Regarding seating depth, n my .6.5 CM's and .270, I set the bullet .02 from the lands with great results. I found that the .308 and .30-06's have much deeper throats due to their military lineage and vast bullet varieties. I wanted to keep more bullet in the case and am probably like .05 from the lands, so can can due some experimentation there as well.

Thanks for the thoughts!

 

[FireFlyFishing]

Barrel free floating on the .308?

 

[toptom60]

My dad has a featherweight in 308 and shoots basically same as you 150 sp and 4064 powder and it's very accurate in his gun. Our model 70s have been pretty easy to get a good load for, there is a small chance it doesn't like that bullet. My first thought would be may have barrel contact or need lug needed as said above. Also definitely with featherweight barrel they get warm quick.

 

[Highbrass1227]

Barrel free floating on the .308?

I was under the assumption that all modern firearms were free-floated?

 

[hesse]

Check the bedding I always do a bedding job on the 70s and try factory ammo. Because Winchester will want to know I don't know of any factory that will warranty any guns that you shoot reloaded ammo in. Have you put a bore scope in it to look at the. Rifling in the barrel

 

[FireFlyFishing]

I was under the assumption that all modern firearms were free-floated?

 

[IridiumRed]

Like to add to everyone mentioning barrel contact... i bet that stock is pushing on the barrel. You MIGHT be able to do a "quick fix" by putting something down inside stock / under action to shim it higher (like cardboard stock from a cereal box), if you can shim front and rear equally, not put a bunch of unequal load / bending force on it, and if the barrel is now not touching the dtock, it -might- just shoot better (if it does, then it indicates rifle needs a good bedding job done and barrel channel clearanced as necessary). Thats achange that could be easily undone too if you wanted to explore warranty options

Also! Check the crown! Could have a big nick / burr / cleaning damage.... or just be uneven

Bad crown will destroy accuracy!

One other thing, it could be scope / mount issue. If it comes down to it swap everything over from good shooting rifle. Make sure everything is tight, make sure mounting surfaces are clean (no crap caught in between, making mount want to rock around). Make sure that the scope mount bases arent putting a lot of bending moment on the scope by pointing in different directions.

All of this wild shooting could simply be a loose scope mount, or a bad scope. Or hell, could be a too long front scope mount screw hanging down far enough inside front ring to make light contact w upper bolt lug when locked into battery (thats a super oddball / rare condition... but can cause wild shots... that will make everyone pull their hair out trying to find... again, rare, but i remember things like that as stuff to try / think about if you start running out of options / have tried everything else...)

And, ill echo what was said earlier about pencil weight barrel. Could just be moving while hot (which could be due to / influenced by bedding, or could be a bunch of internal stress literally hammered into barrel). Id try bringing rifle to range w something else, and shooting one round at a time w like 5 minutes between every shot.. just to see how that goes

One final thing, if you had bore scope, would be interesting to start w clean barrel, scope it, start shooting, and check barrel after a few shots. Could have rough / defective spot in barrel that picks up a ton of fouling... could be anywhere in barrel but id be looking particularly at the first and last inch or two.

Wow, didnt intend to write a book, just kinda came out

If it were me, i might start w the barrel scope if the barrel is in fouled (shot) condition, just because that only takes a few minutes, but i have a borescpe / wouldnt buy one just for this reason. Id try to check crown if you have any way to see it w magnification (again, fast easy). Then id be looking at bedding, scope / mount

Whatever happens, best of luck to you, and let us know if you figure it out!