bearing surface length VS pressure

A

alinwa

oft dis'd member
Has anyone here documented a pressure rise when bearing surface is increased for a given weight bullet?

al
 
you sayin' "I fired some 125's that had XXX long bearing surface, then some others that were longer/shorter.....and the pressure/velocity changed by XXX."

al
 
You gotta be kidding. It's Holy Writ. Revealed Truth. No need for documentation. Heresy. What is the prescribed punishment, I forget?
 
good question. only problem is getting someone to find out.
given load as you said different bullet bearing surfaces. IE tanget vs secant ogives also different length jackets.
 
I am amazed, I've said this before! There is a difference when bearing surfaces are different. I have one rifle that likes them short and one that likes them longer, and there the same cal. 300 wsm. and I'm talking 30 thou. difference. So is it pressure or the twist? Same barrels same twist. I'm not getting any pressure signs they just shoot different.


Joe salt
 
Using the info

After sourcing this information I am not sure how it could be used to develop a load or get a rifle shooting more accurately. I am interested in how you will apply this information in a practical way.
Andy.
 
I forgot to mention same bullet design {ogive} Right now the way we test is just to use different bullets to get a tune.{load}
 
Andy, once you have a load worked up just change lenghts, nothing else just bullet lenght and see which ones shoots the best. If you only change one thing at a time this will give you better information on what is going on! If you change two things or three you might just as well not waste your time or ammo. GerryM if your saying what i think your saying, Different bullets, you just messed up the test [apples to apples]

Joe Salt
 
Charles E said:
You gotta be kidding. It's Holy Writ. Revealed Truth. No need for documentation. Heresy. What is the prescribed punishment, I forget?
Click to expand...

IIRC it's banishment to The Great Range In The Sky, with no bullets....

yeahhh, Revealed Truth has cost me lots of money.

al
 
Yep I understand but

Joe Salt said:
Andy, once you have a load worked up just change lenghts, nothing else just bullet lenght and see which ones shoots the best. If you only change one thing at a time this will give you better information on what is going on! If you change two things or three you might just as well not waste your time or ammo. GerryM if your saying what i think your saying, Different bullets, you just messed up the test [apples to apples]

Joe Salt
Click to expand...

Yep I understand the principle but by knowing what pressure changes and velocity changes were with changes in projectiles ( ie assigning numbers and graphs to the scenario ) I don't think would hels in predicting what the best combination is going to be or alleviate any testing that's necessary. It would also take a lot of work and testing to document such conditions.
Andy.
 
Charles did you find out that long and short bullets give you bad reading with your Oehler. Because if you measure from tip to base and find one longer than the others, you will get a different reading. Mark one then try it!

Joe Salt
 
Joe, he's asking for numbers.

Take the 187 BIB. R.G. Robinette made up a few with a very short boattail. We shot them at 100 yards, using the same load as the FB. Now, they have a different bearing surface -- the length of the BT. After shooting groups separately, we shot a two groups, one with Joel's rifle, one with mine, mixing the FB and the BT. Using the same charge, they shot into a nice small hole, no different than the "pure" groups. Sure, at 1K they wouldn't, but I doubt that's due to pressure differences, it's due to ballistic coefficient differences.
 
Well I guess I'll have to give you numbers in April, right now all I have are facts from last years shooting.Don't know how I can give you pressure readings other than you take my word, that the long ones are giving me problems, maybe its just the barrel. Found some bullets with the same lot # as last years and the bearing surfaces all measured the same, on the short side so if I'm right I should have a good year in Heavy gun.

Joe salt
 
Al, I was talking with you before about the 300gr SMK's and how they vary greatly in bearing surface length (even offered to borrow you my measureing equipment) never really noticed a "pressure rise" or even a FPS difference in my chronograph.
The difference was noticed at long range in the form of "vertical"........yes it is documented.
 
Alinwa
Get some 6mm 107 grain MatchKings and shoot them in a 6BR.You can find the new ones at 1.208 to 1.220 inches long and compare them to the older ones that were 1.260 inches long.
I think will find Joe Salt is correct that the pressure doesn't matter as much as the barrel does.Hart 8 twist barrels seem to like the longer bullets and Krieger's seem to prefer the shorter bullets.
No scientific data just years of looking at targets.
Lynn
 
In the faint, forlorn hope of staying on topic, this was the original post:

Has anyone here documented a pressure rise when bearing surface is increased for a given weight bullet?
Click to expand...

Usually, Al's like Horton -- he means what he says. Best I can tell, no one with strain gauges to measure pressure, and posting to BR Central, has run this test.
 
There is a lot on here that i agree with, what Joe and Charles have said, and more pertinent to me, what Lynn has said about the 107 SMKs. Just this weekend gone i tested two different bearing lengths head to head in my 6BR light gun where the longer shot a 6.1 and the shorter shot a 4.1. Now that may not mean much because the time between groups (relays) was over an hour and anything can happen between that time, but if i had to choose, i would go with the shorter BL just purely on what i saw on the sighter prior to the group being shot. So i do not discount what Joe has said in any way.
I cannot say what the cause and effect is of bearing length variation on either internal and external ballistics, but there is enough people "seeing" an effect to be worthy of the time and trouble it takes to sort bullets this way. Which ever way it goes and what is dicovered in the future, this is not pie in the sky stuff. I can show clear evidence of recorded targets spanning a couple of years now where i have reduced my vertical dispersion by BL measurement alone.
 
Charles E said:
Al, it strikes me you have the two most important qualities for needing an Oehler -- the curiosity, and a range at home. I don't know if you can find a used 43, or what the price for the newer 83 is, but that would answer a lot of questions.

http://oehler-research.com/system83.html
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We had a 43 set up here for a while. My range is wired for cat-5, RG-6 and 110VAC. I'll look into the 83, I musta' got busy and lost touch :) I didn't know there WAS such a beast.

weird

By end of day tomorrow I'll know all there is to know about it...

I shoot thousands of rounds over other chronographs though.

al
 
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