Something really bizarre happened to me this weekend. I was working up a load for a Remington 7600 in .30-06. From IMR's web page, I see the 150g Ballistic tip has a max charge of 59g of IMR 4350 for 2960 fps and 57,000 PSI. I used Federal 210 Primers and WW brass.

I substitued the Ballistic Tip for the SST and started at 54.0g of powder. This was followed by 55.0g, 56.0g, 57.0g, 57.5g, 58.0g, 58.5g, and 59.0g.

At 57.0g I was getting avg 2816 fps, at 57.5 I got 2843fps. OK, sounds reasonable. At 58.0g the avg velocity dropped to 2790 fps, 58.5 2775 fps, and 59.0 2743 fps.

What in the world is going on here? I have been handloading for a good while and I have never seen this before. Perhaps the battery was dying on the chronograph? These were the last shots I fired through the chronograph for the day, so I don't know what would be next.

Since this was bizarre, I kept 2 of the bullets from each "step", pulled the bullets and weighed the charges. The powder charges were all correct. Examining the fired cases showed measurable change in pressure from any of the loads fired.

This has me scratching my head. Any ideas other than a faulty chrony? This Chronograph has been very reliable in the past.

There is a theory out there that presents the idea that when you pass the most efficient load for a given caliber (with some powders only0 the velovities go down instead of up. I forget anymore of the details. - dan

Yes, the 7600 has a 22" barrel. Perhaps IMR 4350 is a bit slow for a 22" barrel with 150g bullets.

Well, it could be a battery problem, but usually when I have battery probems, velocities are erritic to the high side. Who knows?
What does concern me though, is were there any signs of excessive pressure? I ask this, because with some powders, as pressure goes to the limit for the particular powder, velocity may either jump or drop dramaticly.
If you check the max load for your cartidge in six different manuals, you'll most likely find six different max loads for the powder you are using. Your powder choice is OK. What I think I would try, is load up another batch of the suspect ammo and run them through the chronograph one more time using a fresh battery. If it was the battery, then the problem has been solved. If the same thing occurs though, then you have most likely reached the maximum load for that particular combination in your rifle. Drop back one grain and accept the load or try a different propellant.
Paul B.

Paul,

There were not any signs of high pressure. The primers were not flattened at all, no ejector marks, no measurable case head expansion, no sticky extaction etc.

I am going to get a new battery for the chronograph and try again this weekend.

I may drop back down to the minimum charge and try a magnum primer to see what happens.

Buzz -- I have had what you described happen to me a couple of times. I don't remember exactly which rifle without checking my charts. More than likely it was my 257 Wby. Good shooting.

As with everything in life, you reach a point of diminishing return...

Check your manual and see what barrel length they tested their loads.

I recently saw an advertisement on TV that too much of a good thing is a great thing...well, only in TV advertisements...

Was the angle of the sun changing dramatically between the different charges you tried? I've had similar weird results very early and very late in the day.

It was about 4:00 pm in the afternoon with mostly sunny skies. Temperature was ~ 80 degrees.

You ran out of barrel.

I've experienced that several times. Tip for the Day: Go back to your 57g load. No charge for that one!
See the previous posts about diminishing returns. It is not an uncommon occurance. Nothing wrong with your speed meter.

Buzz

How many of each powder charge did you fire?

I suspect that you got the low end of the extreme velocity spread with the 59 grain load, and the high end with the 57 grain load.

A charge increase of 2 grains will only cause an increase of about 100 feet per second in the 30-06. Extreme velocity spread could appear to erase the increase in powder charge.

Good luck

Jamie

I had 5 for each load. The highest extreme spread was 25 fps and that was the 59g load.

Buzz,
I would bet that the increase in powder was fine until the velocity began to drop. At some theoretical load density SOME powders with begin to "snuff" the ignition process causing extreme spreads to increase and average velocity to decrease. Although this is not common with the powder you are using it may be a result of the primer / powder / load combination.

Back the load down about two grains from your highest velocity and put in a magnum CCI primer and work it up again - you may see a big difference in performance.

PaulS

Paul S. has hit the nail on the head...

I loaded 250gr X bullets over 4350 and noticed the same exact thing, only much more dramatic loss too.

I was at, or just over max load when velocity dropped 150 - 200 fps in a 1gr higher charge.... it did this consistantly too. The only way I was able to get a bit more speed from it with the higher charges was to use Federal High Energy brass, I picked up another 150 fps and then got pressure signs... velocity never fell on it's face like it did with the normal Fed or Rem cases either. Case capacity vs. charge wt had a significant effect on the burn process indeed.

If it were bbl length, I'd guess you'd just not get anything more out of it, but not loose velocity. You never know though, it may delay the burn with that much more in the case and a longer tube may recapture a loss if a delay in burn was really what was happening.

I agree Paul cut to the root of the problem. Increase primer strength and/or increase neck tension. My Whelen behaves much better when I seat the bullet deeper.

I think it is a case of powder being shoved into the barrel after the bullet, before it has a chance to properly ignite with the rest of the charge. JMO, Dutch.

Brent,
You've got my curiosity aroused, here. What difference do you think the Federal high-energy brass made? Other than there being a difference in average weight between makes, or a difference in neck tension, I cant figure it. And, I would give these only slight significance at longer range - usually some vertical stringing at >300 yds. I'm not arguing, just trying to learn something, here.Thanks>>>>>>>>>>Bug.

Bug,

I purchaced the 338WM Fed HE brass in loaded form with TBBC, $45 a box I believe! Had a buddy that was getting over 3000 FPS in his Ruger with 250 X bullets so I worked up the load, an awfully compressed load too, seating bullets was done REAL slow. I couldn't get more than 2850 out of them in my rifle with Rem or Fed brass no matter what I did, even tried IMR4831 and about the same with 2gr less powder.

That all changed when I used the HE brass. It was the the ONLY brass that I could get the 3050 fps I was now getting. Logic dictated it was only the brass that made the difference, for whatever reason, it's the only component I changed while testing. I never did see what the case capacity was on any of them, but there was obviously a difference, although you'd think it would have to have been a freaking HUGE amount to get that much more speed, least I thought. I think, it was just enough difference to change the dynamics on combustion that pressure rose quite quickly, maybe a different design around the primer hole... who really knows... I wish I'd looked into more then.

My buddy who was getting those speeds in his rifle too, he has my old Ruger now as well. I'll hook it up to the Oehler 43 sometime when I get more strain gages and work up the load with some HE brass for a comparison test sometime, I still have the same two cans of 4350 and 4831 I was using with them loads.

The primer pockets lossened and brass lasted only three loadings, some four, and that's it, so pressure was way up there, that's a fact. One things for sure, that Federal brass is tougher than snot, way, way tougher than Rem anyway.
I was getting 2850 fps with the Fed TBBC factory loads, so PSI had to be in the 75-80 kpsi range on my handloads... NOT good!

I switched to the 416Wby to get even beter results, trajectory was about the same and energy and bullet diameter just made it all the more powerfull... with normal pressure levels. Never looked back.