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Old August 12, 2009, 05:03 PM   #1
.284
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Accuracy Question- Barnes TTSX loads

Okay, so I have a "new to me" Rem 700 280. I have experimented with a few loads so far. The gun shot a 140 gr. Nosler BTSBT with IMR4350 real real well. I don't have the exact data right in front of me but, around 2600 ft/second, great 5 shot group. The Barnes 120 gr. tipped triple shock was loaded with H4831SC and was around 3025 ft/second. Still a good group, just not as good as the noslers.

Before you say stay with the noslers, let me tell you what I like about the Barnes load and what I did. 62 grs of the Hogdon SC filled the case which I like (although I can go to 63 grs compressed load) I like the lighter bullet weight and speed. I started the load with .050 free bore (which is about what Barnes recommends). The lighter powder loads didn't shoot all that well so, I have about a grain to play with. Also, I am loading these strictly for whitetail.

My question is this. Should I play with the powder first or move the free bore out or in (Barnes recommends .030-.070)? Or, does somebody have any other info for me?
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Old August 12, 2009, 05:21 PM   #2
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If you aren't using them already, switch to magnum primers (see this link that Hardcase found originally as to why) for the reduced charge, then play with the seating depth. Some combinations even work best with the bullet way back about one caliber into the case neck. Usually, though, the bullets have to be seated straight for that. This likely means you will need a competition type sliding sleeve seater die, or an arbor press seating die like the benchrest folk use. I can vouch for the Redding Competition Seating Die cutting runout by a factor of 8 for me, and have heard others say they like the less expensive Forster version.
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Old August 12, 2009, 05:45 PM   #3
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I don't know if it is true for all .284 diameter bullets or if it's even true for any rifles other than mine. But when reloading my 7 mm mag, I have been having more trouble getting good accuracy out of the lighter bullets. The 154 gr and 162 gr bullets were pretty easy to find good accurate loads for. But the 139 gr bullets seem to be more sensitive to powder weights. I haven't even tried any 120 gr bullets yet. Maybe it's not the same situation with the .280 cartridge, but it might be similar. Those lighter bullets are not as long, so I'm guessing they might not be quite as stable.
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Old August 13, 2009, 10:39 AM   #4
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The lighter bullets, assuming they are shorter than your heavy ones, as is usually be the case, will actually be more highly stabilized by a given rate of twist. A few things can go wrong, though:

Short bullets are easier to tip and experience runout. If you don't have a concentricity gauge, get one. NECO has a fixture for straightening the crooked ones. A couple other outfits have combination gauge/straighteners.

The powder for the light bullets needs to be faster to avoid erratic ignition. Light weights offer less reaction force for the burning powder to build pressure against.

Depending on design, a light bullet can get going so fast that a barrel with too much twist will cause core stripping. This is where the jacket is spinning faster than the bullet core, which slips inside the jacket. This distorts the core, a bit, as you might imagine. Harold Vaughn used a magnetometer to demonstrate it occurring above 3150 fps MV (IIRC) with a particular bullet and barrel twist he was using. I think it was a .270, but might have been a 6 mm; I'd check but my copy of Rifle Accuracy Facts is hiding at the moment.

Whether core stripping can happen in your gun or not will vary with the bullet design and barrel twist and the peak acceleration you subject the bullet to. It is caused by rotational acceleration being too fast for the bullet construction. The result is an under-spinning core that slows the jacket spin after exiting the muzzle, and it will have a slight asymmetrical core distortion, so the bullet wobbles a little in flight. Vaughn's groups opened up when he surpassed the velocity at which it occurred in his gun.
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Old August 14, 2009, 08:16 PM   #5
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Guys, thanks for the advice. To answer some of your questions, I am using a RCBS gold medal seating die (next step up from competition that wasn't available). I use magnum primers. The Barnes is actually a bit longer than the 140 grs as all copper is lighter that the jacketed counter parts. So, runout and core stripping should be non-issues. The rate of twist for my gun (per remington tech support) is 1 in 9 1/4" so if I wanted to, I should be able to go heavier gr weight bullet with no problem.

Doodlebugger, we share the same bullet diameter but, our cases are way different. My case is much smaller. You're obviously over compensating for your other short comings. Just kidding....7mm mag is way cool.

I think what I'm going to do is load 62.5 grs and 63 grs and see if I tighten my groups, if not, then I'll move my free bore in or out at .010 increments
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File Type: jpg barnes vrs. sierra.jpg (108.4 KB, 39 views)
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Old August 15, 2009, 05:31 PM   #6
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How long is the 120 grain tipped TSX?
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Old August 18, 2009, 04:55 PM   #7
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Sorry it took a minute to reply. The Barnes is 1.220" and the Sierra (in the picture) is 1.150"
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Old August 18, 2009, 05:24 PM   #8
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Dude, if your minutes are three days long, don't make me wait an hour.

I took your data and ran it through my twist estimator. It calculates the approximate gyroscopic stability factor, s, for the weight, length, and velocity of the bullet. Using standard meteorological condition (Army, Std. Metro), it looks like you have plenty of barrel twist. Harold Vaughn's criteria (s=1.4 for best accuracy) would put you at a 10.5" twist. You've got about s=1.8. Any time you spin faster than necessary, there is some exaggeration of any mass distribution errors in the bullet, but you're not that far off. So I think this will come down to being sure the bullet is in straight and getting the right barrel time to hit a barrel time sweet spot.

Take a look at Dan Newberry's OCW site for a way to try to find a good load. I like to experiment with seating depth rather than take a recommendation. You may actually find a much deeper seat does better in your particular gun. It's not uncommon for a bullet with the bottom edge of the bearing surface about 1 caliber into the case mouth to do well, too. Just use a starting load and change the seating depth not over 0.02" at a time and see if you get a better accuracy spot?
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Old August 31, 2009, 12:15 PM   #9
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Here is a look at 63 grs H4831SC and a 120 gr Barnes TTSX. The 100 yard group got a little tighter, velocity average was 3079 ft/sec and the spread was 26 ft/sec. I think moving the free bore .010 in or out should get me the rest of the way there. Any thoughts?
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