Fast Twist Effects on Lighter Bullets

Barks

Barks

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Okay. I have a benchrest shoot coming up and Im haveing a hard time finding 69gr Matchkings locally. I have on hand about 160 53gr MK. I figured that this could work. I just need to go back to the reloading drawing board and do some testing.

The rifle is a Savage LRPV RB-LP with a 1:7 twist. I have shot 40 grain blitzkings as well as 40 grain V-Maxes before. Not in volume, but just to try.

I was using H-335 as it was listed as Sierras "Accuracy" load for this bullet.
I match prep all my brass. Lapua, CCI BR4 primers and I am loaded 10 thou off the lands to start. I was going to work up in .3 grain incriments. Shoot 2 three shot groups and then fine tune from there with seating depth and .1 grain incriments if needed.

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I have the rifle in the bags and everything is rock steady. The wind is a bit shifty but nothing severe. I shoot my first 3 shots loaded with 25.4 grains of powder. And I distinctly remember shooting 6 rounds. From 100 yards away I thought my first group was 2 in 1 hole and the 3rd opened it up to about .350"c-c The next group I can see through the scope and its .563" c-c

I fired off the next 3 but I couldn't tell where shot 1 went. I fired the second and it lands right at 1 o clock on my bull. Now I'm thinking, I must have put the first one in the center. The third shot lands a bit low and right. Same powder charge but the next group I shot a bit high left....but I called that one. The second shot can't be found...but I felt the recoil of the rifle. And the third shot lands low right as predicted.

I now move on to the next charge of 26 grains and the first three don't even make it to paper. Now I'm scratching my head. I fire the next group only to have shot one hit slightly low in the bull the second a bit high and the third one is not there???

I am now considering the velocity is just too much for this bullet and its coming apart in flight. However this should only be 3150fps.
Only one of the three shots made it to the next target, None onto the same charge after that.

When I made 0 for 6 hits on the 26.6 grain charge test:eek:, I figured I'm just wasting ammo now. Its frustrating when you shoot 30 rounds and only 12 make it to the target.

Other than the twist rate, I don't really have any explanations. Guess I need to order some 69ers. I have done exhausting testing with a variety of heavier bullets that all perform well. None are as accurate at 100-200 yards as the 69gr SMKs. And they stay together.:)
 
1-7" is way too fast for the 40s, especially thin skinned oned like blitzkings. I'm surprised they worked for you at all. Unless my math is way wonky you're spinning those bullets at 324,000 RPM (I think the formulas are somewhat facile because they don't take into account the decelleration of the projectile)! That's probably a bit much for thin skinned bullets like the SMK. You can spin thin jacketed bullets fast enough that centrifugal force will tear them apart (see any bluish mist when you shoot?). Solutions? If you really want to shoot those light bullets you might try downloading the load to get less velocity. I know, What the hell good is a 223 shooting velocities of a 22 Hornet? Well, limited, but at least you'll make marks on the paper.

In reality, 7 is a wicked fast twist. You'd be much better served with 75 gr AMax, 80 gr SMK or Berger or even 90 gr Bergers. That's what they fast twist is for. Don't try to make that rifle something it isn't. It's designed for longer range than 200 yards. With some tweaking it should perform quite well out to 6 and 700 yards. Talk to Mysticplayer and get some heavy target bullets.
 
The previous post said it all.
Your 69gr sierras will work but the 80gr Sierras will work better, Good friend shot last Wed night at Connaught with same gun as yours with 80gr Sierras And Varget I was scoring for him his first time at 1000 yards shot a 15 round his score was 75 of 75 with quite a lot of V bulls. Conditions where good.
got to love them 223 Rem
manitou
 
Thanks for the info guys. I don't intend to try make this rifle something its not. I got it first and foremost to replace my 700VS in .308 as my Long Range Rifle. Half the cost to shoot in .223.

The local Benchrest shoot is devided into two catagories. Custom rifle and Factory rifle. Up until Savage made their new F class rifles, there really is no such beast as a "Factory Benchrest Rifle"..........to my knowledge anyway. As bought off the store shelves, trigger can be tuned and it can be bedded. But thats ALL. I had some defending to do when I showed up with this rifle. "Thats not Factory"!!

That being said, It won the 100 and 200 yard score shoot in factory class 2 years in a row. My father was the trigger man at the time. First year I loaded 70gr Berger VLDs and this year was 69 SMKs. The SMKs were $9 cheaper and slighlty more accurate.

I recently sold my .222 for which I had these 53gr SMKs lying around and I thought I would try to get them to group like the 69ers do....... Not Going To Happen. Even if I backed off the velocity, the centrifical force is still too big a factor. I didn't realize these bullets had such thin jackets. Does the hollow point factor in at all?? I feel the reason the 40 grain polymer tips stay together is because of that plastic tipped insert. Nosler claims they have spun their 40 grain ballistic tips in a 6 twist test barrel at 5000+ fps and they still stayed intact. I have never seen proof of that though.
 
I had a bunch of 52grHPBT Match Hornady's loaded for a different .223 that I used in my 1-7 twist Savage and they shot reasonably well. I'm presently trying some 50gr V-Max in a load development, but need some time and a calm day. I've been using BenchMark only.
 
Those little NBTs must have thick jackets. A hollow point shouldn't make any difference as opposed to the jacket thickness. Still, the Blitzkings didn't vaporize so my theory could have holes.
 
I happened to post the various RPM vs FPS for a 7" twist barrel in the Reloading Forum

http://www.canadiangunnutz.com/forum/showthread.php?t=359438

Apparently most bullets will hold together up to about 300,000 RPM. A thicker jacket will help. Also, the larger the diameter, the lower the RPM threshold.

Also, the rotational speed downrange will decrease much slower than forward velocity. (It will keep spinning fast despite moving forward slowly.) Forward velocity is decreased by drag because of frontal area and related drag coefficients. Rotational speed will decrease only as a result of air friction on the skin of the bullet.
 
Barks said:
Nosler claims they have spun their 40 grain ballistic tips in a 6 twist test barrel at 5000+ fps and they still stayed intact. I have never seen proof of that though.
Click to expand...

That is definitely "rounded up" shall we say. Max theoretical velocities for any bullet is around the 5,000 fps range. That would also be 600,000 RPM

The 22 Eargesplitten Loudenboomer only achieved about 4,600 fps. It is a 22-378 with a 60" barrel

The 17 Flintstone Super Eyebunger got up to 4,798 ft/s. It is a 17-250 with a 52" barrel.
 
Barks said:
Does the hollow point factor in at all?? I feel the reason the 40 grain polymer tips stay together is because of that plastic tipped insert.
Click to expand...

I got this explination on another forum as I am having the same problem in my 6mm.

"Not exactly unheard of, and not too uncommon in some combinations. Berger had some problems with this some time back and have since modified their line to eliminate such problems. You've already touched on part of the answer here; heat. Eric Stecker of Berger Bullets did some very extenisive testing with MIT and high-speed thermal images of bullets in flight to determine what was causing this phenomenon. They took a serious look at the causes here, and spent the time, effort and money to do it right. It comes down to heat, migrating through the jacket and melting the core, or at least a boundary layer of it under the jacket. Once the core goes plastic or liquid, any void in the jacket will allow it to outgas, and the bullet blows. By reviewing the thermal images, Eric was able to discern the actual temperatures of various areas of the bullet in flight, and it's not what you'd automatically expect. The base, for example, stayed quite cool despite being in contact with the hot powder gases. The ogive (not surprisingly) didn't heat up too badly. The real hot spots were the meplat, due to the friction of the air and nose pressure. The worst, though, was the bearing surface, particularly where the rifling was engraved upon firing. This portion hit several hundred degrees, almost instantly. The analysis concluded that the jackets were thin enough to allow the heat to penetrate to the core, and bad things happened. To resolve this, they thickened the jackets to allow for better "insulation" of the core, and the problem now seems to be entirely resolved.""

it seems that there is a lot of heat on the meplat so the plastic tip may help by reducing the surface area and thus the extra heat generated.
 
That's interesting.

So the meplat is heating because of the compression of air as the bullet accelerates down the barrel. So the bullet is imparting energy TO the air, causing the air to heat and in turn heating the meplat. (think Fire Piston)

The air inside a hollow point will heat up, transferring that heat directly to the lead core.

This is different than the burning gases behind the bullet, which are imparting energy to the bullet. Theoretically, after 100% of the powder behind the bullet is burned, the decreasing pressure (expanding gas) will DECREASE the temperature of the gas behind the bullet.
 
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