Obturation maximized by pressure or speed

[rangeball]

This might not make any sense at all.

From what I understand solid copper bullets like the barnes have a better chance shooting accurately if you can maximize their obturation. Is this best achieved via higher speed or higher pressure?

If I remember right it seems high pressure doesn't necessary always mean high fps. The reason I ask is I just had another nice conversation with Dan @ SMI. He told me he is shooting the barnes 250gr TEZ in a regular black harvester very accurately with 65 grains of 4198 at 2500 fps. I plan to try this same bullet in the same sabot from the same make barrel with 42 gr of N110 to 2300 fps.

Since N110 is a faster powder than the 4198, at these speeds would you expect them to be producing similar pressure levels? Or is the faster speed of the 4198 load likely to be producing the what I believe to be better obturation?

[Dave W]

I remember RB saying an ideal 65gr duplex load would be close to 2600, just guessing that this would be close to a book load for pressure. Going by this, I'm guessing the N110 load would have more pressure. Again I'm just guessing, maybe RB or Edge can verify.

[rangeball]

Before my conversation with Dan, I had thought the N110 would provide good accuracy potential with the barnes, since it's fast and would give a quick thump out the gate. That was my theory anyway

[jims]

Rangeball: I had an SMI barrel on my Savage for awhile. It shot well when I used the SMI recommended loads. It did not like 4759 or VV120 very well. Maybe mine was an unusual occurrence but I might suggest sticking with their powders.

[fowlplay]

I'm going to say something that may be controversial.

Show me a Barnes TMZ or TEZ that has obturation to it. I have shot these TMZ's with H4198, N110, RL7, 4759, and 5744 powder from 1900fps to 2600fps and have never found a bullet that the base has obturated. The boatail bases after the shot looks just as perfect as they did before I put them in the sabot. These copper bullets are one tough mothers and the lack of obturation IMO is possibly why some have problems with the accuracy.
Steve

PS... I love these bullets in my gun.

[Al]

will bullets even obutrate in a sabot?

[screwbolts]

Apr 7, 2009 4:05:01 GMT -5 Al said:

will bullets even obutrate in a sabot?

YES!!! ;D

Notice how the numbers and letters engraved the base of these soft Pure lead Boolitz None of the following pure lead bullets were shot with more than 32 gr of 4759:


Notice how the lead flowed to between the pedels of the sabot, contrary to what ahs been posted before no leading of the barrel has ever been detected in my guns shooting sabots and pure lead.

notice that the boolets on the left are considerable shorter, these were fired with between 25 and 32 gr. of 4759.


Now some Condom wrapped bullets: all picked up from snow bank backstop, none fired with more than 38 gr. of 4759. XTPs and a couple SSTs all 250 gr. and they are now .459+- at the base ;D


now even my hard cast 333gr. LFN is .460+-

Some of the oicked up boolitz from my Snow bank backstop ;D ;D




Ken

[rbinar]

Apr 7, 2009 8:28:20 GMT -5 screwbolts said:

YES!!! ;D


Now some Condom wrapped bullets: all picked up from snow bank backstop, none fired with more than 38 gr. of 4759. XTPs and a couple SSTs all 250 gr. and they are now .459+- at the base ;D
Ken

Could the bases be spread by deceleration as easily as acceleration? I say that because I see the jacketed bullets obviously were deformed when they stopped.

Pressure and speed are both forces. As long as the force applied to the bullet is enough to start deformation the source is not a factor. The reason one load works as compared to another is likely dependent on other factors. I say that because relatively high pressure slow loads (like a 300 grain bullet with 44 grains of N110) work in some rifles, and opposite loads (like 71 grains of H4198 with a 250 grain bullet) work in others.

[screwbolts]

rbnar,

I suppose anything is possible, If I was to push on of the comdom wrapped bullets threw my bore, I usually find just light rifling marks on the pedels of the sabot. Now load the same sabot and bullet and shot it. the sabot now will have complete contact with the bore Hence bullet obterated and caused the sabot to be forced tightly into all nooks and crannies of the bore.

If I understand Obteration, it is a result of Newtons Law, something or other about an object at rest resists being moved. so when the back of a bullet is pushed forward the front resists and the bullet swells. IMHO Actualy the only velocity involved at this time is the back of the bullet trying to catch the front.

In he upper right corner of the Condom wrapped picture is a SST notice the tip is nearly perfect ( it doesn't show well in the photo.) I will go measure that particular Bullet. JMO I have very little use for condom wrapped bullets in a ML. the bullet measures nearly .454( it looks like .453+ in the photo I actualy have the caliper tiped to try and get that reflection from obscurring the needle. it is acyualy very close to .454 when read straight on) now that is with no/very little nose reshaping. This bullet was probably shot with 28 gr. of 4759.



Ever notice that when a car or truck that is in a head on the trunk doesn't normally get wider and deeper! or the tail lights on a pickup don't get farther apart but the front does the Obterating and the back just stops.

Ken

[screwbolts]

Could the bases be spread by deceleration as easily as acceleration? I say that because I see the jacketed bullets obviously were deformed when they stopped.

Pressure and speed are both forces. As long as the force applied to the bullet is enough to start deformation the source is not a factor. The reason one load works as compared to another is likely dependent on other factors. I say that because relatively high pressure slow loads (like a 300 grain bullet with 44 grains of N110) work in some rifles, and opposite loads (like 71 grains of H4198 with a 250 grain bullet) work in others.

IMHO, Loads that seem slow to hot rods are fast to regulars.

Never shot or owned any N110, nor do I have any plans to. But I do know from my own chronograph that a meeker load of 33 gr of steel can 4759 records the same velocity as 105 gr. of BH209, with a 333 gr. boolit. So the Slow load of 44gr. of N110 is slow compared to what? What is the Standard? I guess we all have different standards to rate slow and fast. ;D ;D

I am not an expert in the field of Obteration, but I do know it has a lot to do with Newtons Law. IMHO speed has nothing to do with it because it happens as a still object is FORCED to move. ;D a pellet in a pellet gun obterates. no gun powder used there. Oops. OFF topic.

Ken

[Dave W]

I also believe jacketed bullets like the 250 SST obdurate because when the petals on a recovered sabot are folded up to their original position, the area where the base of the bullet sits looks flared out and compressed like the base of the bullet swelled out toward the rifling.

I also agree with Steve about the all copper Barnes bullets. I have looked at many recovered yellow sabots from the TMZ line and if you fold the petals up to their original position, they look like there are no signs of the bullet obdurating. I also found one of the 290 TMZ's that I shot sabotless laying on top of the grass out at the 200yd line, it had not swelled up to engage the rifling, other than the tip missing and some dirt on it, you could not tell it had been shot.

[artjr338wm]

Does anyone think that this supposed lack of obturation is one of if not the reason people report shooting V-good if not excellent groups with the TMZ and Spitfire types of all copper bullets but then have their 200 yard groups fall apart in terms of accuracy?

I ask because I have read quite a few posts detailing were people could get the all copper Barnes TMZs to shoot 1.5" three shot 100yrd groups and often much smaller only to have the same exact loadings accuracy open up to as much as three or four inches at 200yrds.

Are the two related in any way?

Thanks,
Arthur.