Home Forums Hunting & Shooting Custom Rifles & Wildcats More testing......

Folks
A few weeks ago when I was able to shoot I started to do a little more testing. I always question my equipment because I dont have a different system to compare it to.
Some loads in some cartridges will produce a secondary pressure spike. as an example, the first curve goes to 60000 psi then a few inches before the muzzle the pressure may go to 80000 to 90000 psi. I wasnt sure this was real. I had no way of testing that I had any faith in.
So what do I do ? Keep pushing things until something happens.... <img src="/ubbthreads/images/graemlins/crazy.gif" alt="" />
I had a 338 Win mag with a # 5 contour barrel at 24 inches with a muzzle brake. The brake was incorperated into the barrel, meaning the ports were drilled directly into the barrel. The barrel diameter was .712. The ports were .250 in diameter and with .250 of unaltered barrel in between each port. I go in with a carbide piloted muzzle brake reamer that reames .020 over bore size , in this case .358.
So, .712 minus .358 equals .354.divided by 2 equals .177 wall thickness.
I was using 225 grain bullets, Winchester brass and GM215M primers.
Under advisement from my lawyer I wont list the powder or charge because this is dangerous.
I started loading up with a load from a popular manual. Went all the way to max load with no typical pressure signs.
My computer was showing a primary pressure of about 65000 psi and a secondary of about 80000 psi. Well I didnt believe the secondary spike.
So I decided to keep going up until I say something happen. When I got to about 67-68000 the pressure stopped going up on the primary spike, and was going off scale on the secondary. I kept going up on the powder charge, nothing out of the ordinary, no extraction problems, no sticky bolt, nothing.
Kept going up and on the next shot the rifle kicked like he##! Pressure was still off scale, round ejected nicely, no flatened primer, nothing out of the ordinary. I checked the graph, same things only a little longer off scale on the secondary. Chronograph showing the same readings.
Fired once more.....kicked like #$%^ again ! Still cant find anything wrong ! Brass looks good, speeds are the same, everything is normal.Pressure goes off scale at about 90000 and is staying off for a while.
Fired once more......kicked like !@#$ again . <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />
Whats going on here ?
I looked down at the muzzle and I had blown the muzzle brake completely off the rifle.....blown it off at the first row of ports... ..blew the brake completely off the barrel.
I think I am starting to put a little faith in this equipment. I am going to run this same test again as soon as I can start shooting again. If the same thing happens twice I'll say its real.
Please read the post at the bottom of this page and dont try this without the proper equipment. Better yet, just dont try this at all.
Charlie

Don't worry bout me trying that!!!

I was wondering if the second preassure spike is powder specific. As the burning properties of each powder would also change where and the amount of the 2nd spike?

I was thinking , and this is purely unintelligent speculation, that the primer fires and builds up enough preassure to launch the bullet and then the rest of the powder in the case going off gives you the 2nd spike? If this is true a faster powder would give you a bigger spike and a slower powder less of a spike?

I have heard of the 2nd spike but NEVER really thought about it or seen any reporting on any testing on such.

Soo just how far off am I on this?

I have read that the 7mm Rem Mag has some high pressure spikes. Have you noticed anything out of the ordinary with the 7mm Rem Mag as compared to other cartridges?

teal325
You are right. I have been told that with all calibers using a very light bullet with a slow powder that the primer pushed the powder and bullet down the barrel faster than the expanding gas can keep up. Then barrel friction stops or nearly stops the bullet, then it gets hit by the gas catching up to it. I dont know if there is any truth to this or not. I dont have the equipment to test.
What I have learned so far is that using a powder that completely fills the case doesn't seem to be the best idea. The powder manufacturers say to always use a powder that completely fills the case....why ?????? because they are in business to sell powder....
Seems a powder in the mid-range for a given cartridge/bullet combination works best. But then again, I'm learning something new every day... <img src="/ubbthreads/images/graemlins/shocked.gif" alt="" />
Charlie

rdinak
I haven't saw anything crazy with the 7mm Rem mag yet. I think throat diameter and leade angle and friction (or lack of) may play a big part in pressures. I plan to do some test with that one of these days.....when I get a round to it....where can I buy a sack of round to-its ? <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />
Charlie

Now the big question-- Have you noticed any accuracy quirks that corespond to the second spike? Say calibers A, B, and C.
If the spike is proportional to MV as in a gain of 200fps usually means a 2nd spike of 10000 psi across the board for the calibers? . I guess I don't really know how to explain what I am trying to ask but maybe there is a a measurable correlation to accuracy/MV and the 2nd pressure spike?

Have you noticed this 2nd spike in all calibers or just Mags- the larger case and such.

teal325
I havent tested a cartridge yet that I couldnt induce a secondary spike with the right combination.
Seems when you use a heavy enough bullet for a given caliber, you cant make a secondary spike no matter how hard you try.
Secondary spike and velocity , at this point, dont seem to be connected, but I'm still testing. I've got a lot to learn. Seems pressure and velocity are not nearly as connected as I would have thought they were. 9000 psi swings with 12 fps deviation over a chrongraph are common. Ask Richard Mann about the 358 we tested.
Charlie

That's an interesting tidbit! What kinda weights per caliber are we talking about here? Is it case specific or caliber specific?

TIA,

Mike

READY
In my 8 x 57, anything lighter than a 220 grain bullet makes a secondary spike, factory ammo included.
In a 338 Win, anything lighter than a 210 grainer will make a spike with any powder slower than 4198.
300 Win mag with a 150 grain using R-22 has a bad spike.
Ive tested factory ammo and handloads, got the same results with both.
Secondary spike may not be all bad, they have been there all along we just didnt know it. And there may be nothing to it, they may not exist. But if I can blow the end of a barrel off and extract the brass, reload it and use it again, something is going on.
I have saw and learned so many things since I got this equipment, I 'm nearly afraid to make any statements at all. Folks tend to not believe these things, still dont believe them when they see it with their own eyes. I still have a hard time digesting it.
OutlawPat..are you listening ???? tell us about your 338 with H380... <img src="/ubbthreads/images/graemlins/crazy.gif" alt="" />
Charlie

Appreciate the info........keep it coming!

Have you ever tested for this in 7mm or 300 Wby. mags with top listed charges of
H4831 and IMR7828? I never had brass problems or noted velocity irregularities
working with listed data from reliable sources, but you've got me wondering. Early on
I quit working with light for caliber bullets in these two cartridges however.

Dave

Charlie, an acquaintance of mine had the same thing happen up here with a Wby Mk V in 338-378 about 15-20 years ago.



The rifle was a 340 that had been rechambered. Recoil was pretty stout, so he sent it away to be Magnaported, the original system with the trapezoidal slots EDM'd into the barrel near the muzzle.



He was working up loads at the range one day and the muzzle came apart. Everybody was shocked, of course, as we had never seen anything like it!



He sent the rifle back to Larry Kelly and they replaced the barrel gratis.



Sounds pretty similar, eh?

Charlie -

The more I think about it the more the fact you can extract the brass without problems, reload them and use them again makes me scratch my head.

I would have thought you would have brass failure LONG before the end of a quality barrel would give away. In essence that 2nd spike is saving your brass and or reciever- transferring the pressure of an over load to the end of the barrel - farther away from your face! I wonder if the action destroying loads we hear about aren't getting the pressure spike like yours.

Yukoner, Sounds like pretty good service.

This is invaluable information, and another compelling reason to not exceed listed velocities (OR) charges. I one time split the muzzle on an '06-AI that had been xxx-xx-ported, (I was shooting 150's.....fast!.........hmmm, I wonder????)

This among other things that you and JB have written makes me thankful that I survived my years as a "push 'em faster" reloader.

Further proof that "she ain't blowed up yet" is not a sign of safe loading practices.

JimF

Thanks Charlie!

I was wondering if you had any .277 info..

Between this and your true tests of velocity loss with shorter barrels I'm wondering why I would want anything longer than 22" on anything..

Short barrels, heavy bullets, faster powders..

Mike

Seems to me you have some preferences as to how light a muzzle you will put on a rifle of certain bore diameters. Perhaps this is why.
No pressure signs. Fascinating. E

Turok mentioned the same secondary spikes on a couple of threads.After testing some bullets and powders,he is using Varget and Hornady 225gr bullets.

Keep posting intersting things,we are getting into new territory.

I've got a theory about the secondary spike. Apparently, it is being circulated on some of the boards.

When you fire a rifle, by the time the bullet exits the muzzle, the powder is entirely burned, and there is no oxygen left to support combustion.

The gasses are rich in hydrogen, and hot enough to glow. When they hit the air, they re-ignite... BANG! Secondary spike.

I have a test planned to see if this is really the case... but it does seem to fit the data.

Some of my work has been done with a milsurp Finnish M39, with 27" barrel. It's very easy to see the secondary spike on several loads.

what intrigues me about this is the relationship of light-for-caliber bullets to the spike. looks like chemistry and physics are stating blatantly what the most efficient combo is for each chambering, i.e. heavier bullets goodest; screaming light bullets not so gooder. hmmmm ....