Just got back from the range with the results of shooting 150 gr Nosler Ballistic Tips in the 270 WSM. I started with a clean/cold barrel and fired 1 fouling shot followed by 4 three shot groups at 200 yards. I let the barrel get slightly warm but never more than that. The ES of velocities for all groups was right around 20 fps Ė so not horrible. Loads (all Ramshot Magnum), average velocities and group sizes were as follows:
All groups but the one with 69.0 gr had two shots about 0.5Ē apart and then one flyer to open up the group. A classic indication that there is some barrel vibration going on.
This performance sucks and I need to see what these bullets do running closer to 2,900. Iím guessing that they will shoot a lot better as did the 150 ABLR bullets however all shots today landed on my 8.5Ē X 11Ē target paper whereas the ABLRs wouldnít stay on 4 of those targets thus I donít know what group size they shot when they went bad but it had to be at least a foot to miss all that paper.
Conclusion: The 150 ABLRs shoot MUCH WORSE than the Ballistic Tips in this rifle while running similar velocities. What does that mean? Beats the hell out of me. Maybe this barrel does have a harmonics issue as Kirby suggested and the 150 ABLRs just really hate barrel harmonics. Now what? I suppose Iíll run them down around 2,850 fps and call it good. Then again, with all this messing around Iím about out of them so the problem may just go away for this hunting season as I likely wonít be able to get any more of these ABLRs until Nosler does another production run next year.
I would love to see what a conventional cup jacketed lead core bullet did with this same test, say 150 berger or 150 gr SST or something similar. May be the very heavy jacket on the Nosler, may be the fact that its not able to bump up under pressure. Not common but two bullets with the same jacket design do the same thing.
Shake things up, go to a conventional lead core, cup jacket design and see what happens, hell, just for test sake, any 150 gr bullet will do. The 150 gr Speer would even work, just shake things up and try something totally different then the AB and see what happens.
For me, my guess would still be a barrel harmonics issue but that is pretty extreme.
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Good try on the twist JD338. This barrel is a 1 in 10 per Numrichís site. But for the reasons stated by MontanaRifleman, that isnít the problem. I know what marginal stability looks like (oblong holes in the paper) and this is not doing that. All holes are straight through. Plus it will shoot MOA down at 2,770 fps Ė still with nice holes.
Interestingly no where on the bullet box does Nosler spec twist so Kirby is right, Nosler knows that a 1 in 10 is plenty fine. They also know that there are boxcar loads of 270ís Winchesters out there with that twist and I just canít see Nosler making a bullet that wonít work for those rifles. It would literally be a disaster for them.
By they way, thanks for the tip on the seating depth. Iíve been running these about 0.016Ē off and apparently need to increase that by a factor of 10 or so! If I can get them to shoot just a tad better that they do at 0.016Ē, Iíll be good to go.
It turns out my worries about running out of these was unfounded. I just got back from Sportsmanís Warehouse down in Federal Way and they had 3 boxes on the shelf along with a box of 150 gr 7mms at $50 per hundred. Thatís cheap enough to use them for practice.
They also had one 8 lb jug of Retumbo sitting right there on the gun counter for $168. I picked it up and almost bought it out of reflex until I remembered that I have an 8 lb jug of RL-33 that works plenty fine in my 300 RUM.
But back to the 270 WSMÖ. Kirby, Iíve got 150 Sierras Game Kings, 150 Bergers Hunting VLDs, 150 Ballistic Tips that I used this morning and now bunches of the 150 ABLRs. I think Iím going to get the ABLRs working (with some seating depth tweaks) the best I can at whatever velocity that happens to be since hunting season is NOW. Then Iíll see what it does with the Sierras and Bergers. Iíve attached a JPG scan of the target from my range session below. Pretty interesting how the bullets land either low right or high left except with the 69.0 grain load.
I thought the twist might be the answer and glad its not. In fact, I was surprised when I saw the recommended twist rate was 1:9 as I had thought 1:10 was the standard twist rate. Someone recently rand into a stability issue with this bullet in a 270 Win and now its got me thinking....
Bigngreen Ė you are of course dead right not to trust the website. That same wesite lists the diameter of the barrel shank incorrectly so they sure could have the twist wrong. However, the twist measures to be 1 in 10.5 inches and I figure Iím getting about 0.5 inches worth of slippage on the dry patch I used so it probably is a 1 in 10 since a 1 in 10.5 would be non standard. And there is also the fact that whatever the twist is, it does not exhibit even marginal stability when shooting the 150 gr ABLRs.
By the way, bullets that are unstable and are putting oblong holes in the paper can still group surprisingly good. Iíve done it with the Barnes 7mm 168 gr LRXs in a 4 groove Brux with a 1 in 9 twist. I had to run those up at 3,080 fps to get round holes down here at sea level but they still grouped better than MOA going much slower when the holes were oblong. And oh by the way Barnes prints 1 in 9 on the box but tells you separately that 1 in 9 is only good above 5,000 feet!