Interesting anomaly.

[XTR]

I've recently been re-visiting my Berger 215H loads (I've got ~1500 of them so I may as well shoot them) and doing some testing with both HBN and Moly compared to naked bullets. I'm running all of my tests with a Pressure Trace attached to a strain gauge and over a 2 Box chrono. Since the my Pressure Trace is in no way calibrated I've been using a known load as a benchmark for this evolution. My benchmark load has been some leftovers of my 200.20x load that I've been shooting the last yr and a half. Running 200s at 2675 or so is a pretty pedestrian load in the F-TR world.

At the beginning of my testing last week, starting with a clean barrel I shot a couple of my benchmarks and got smoke from the breach.... Huh, did I blow a primer... nope soot back down the side of the case, in fact on my first 3 cases before I switched to the 215 load were sooted up. I thought I must have left some cleaning solution in the chamber or some such.

Today I ran my 215 tests and at the end I fired 3 of the 200s for a reference because the temperature was quite a bit lower... again, soot all over the cases. At this point I'd fired close to 30 rounds so it wasn't cleaning solution.

This got me thinking. My 200 load has the bullets seated with very little bearing surface in the neck. My 215 barrel freebore is much longer than the barrel in which I normally shoot the 200s. In fact they will fall out of the case before reaching the lands, by a pretty good distance.

I measured the necks on the sooted up cases, they measured .337, I size to .336, and my chamber neck is .342; my fired cases are usually .340 or so.

Best I can guess the primer ignition is popping the bullet and powder forward and out of the case, the result is some of the powder igniting in the neck area, not expanding the neck, and blowing gasses back into the chamber.

The point here is that over long throats and short seating depths can get unwanted results. (no more shooting those bullets in that barrel)

 

[Zero333]

You brought up a very good point about the relationship between the case neck, the neck tension, the freebore and bullet bearing surface in the neck.

 

[fguffey]

Low pressure, there is not enough pressure to expand the case. The bullet could be too small in diameter, the barrel could be shot out, the burn rate could be too slow. I understand there is a lot of cute shooting going on, I suggest you pull a few bullets and replace the powder, I do not care if you sized the neck and or full length size the case, I do suggest you measure the length of the case from the shoulder to the case head; a short case can be the cause of reduced pressure.

F. Guffey

 

[Papa Charlie]

I had the same problem with my factory barrel. To get the rounds to within 0.015" of the lands, I had to load the bullet very long with maybe 0.100" of bearing surface. Add to this that I use a .336 bushing on my .308 and that makes for a very loose round sitting in there.
Couldn't figure the powder soot around the neck, as I was only neck sizing for some time, when I went to full length sizing I notice the soot had traveled farther down the case.
I tried loading the rounds deeper and the soot diminished greatly. Increase the neck tension to a .335 bushing and soot gone.
Thankfully, I am replacing the factory Remington Barrel with a Benchmark and the chamber will be sized to a SAAMI Match Reamer with a 0.110 Freebore. I know that sounds short for shooting the Berger 185 and 200.20X but I loaded a dummy round with the 200 with only 0.240 bearing surface and with the Match Reamer, it moved the round in exactly 0.004". I have more than 0.114" from the bottom of the bullet to the powder with an overload of 40.0gr of Varget. So plenty of room to seat back another 0.015" off the lands and still have 0.095" of expansion area for the powder.
Can't wait to start load development.

 

[T-shooter]

I'm still working up a load with the 200.20x in a stock Savage. It seems to group better at .005" to .000" jump. I have ran as much as 43.5g of Varget without any pressure signs so far. These are the dimensions I have for that load. I have enough bearing surface in the neck to hold the bullet. Having the bullet seated out so far increases case capacity allowing more powder. In a 22" barrel, it's just under 2,600 fps. A longer barrel would have a substantial increase in velocity.

 

[fyrewall]

Some time ago I loaded some .30-06 rounds with Re 19 and 150 grain bullets using unturned necks, F/L dies, with bullets seated deep enough so loaded rounds would fit inside the magazine - no more thinking other than to try to duplicate a max accuracy load as shown in my Nosler manual. I got a major amount of soot and in addition to the soot, a dented case shoulder. I pulled the bullets and loaded everything with H414 and got beautiful results with out any other changes than switching powder - high velocities and great accuracy. Same seating depth, same relation to bullet ogive and leade, same primer, same neck tension (really tight with factory F/L dies and unturned necks) and no soot. Possibly, I failed to get enough Re19 into the .30-06 case to generate working pressures with 150's but Re19 worked super good with the solid copper, long for weight Barnes TSX 180 grain bullet.

I now shoot a 6.5-06 with turned necks, bullets seated almost touching lands or 1 caliber deep (.264), 100 to 140 grain bullets, and, what I think are suitable powders, 4350 types with 100's, H4831/Re23 with 123's, and H1000 with 140's. No soot, shiny turned necks, and despite a big jump with the 100's, great accuracy at all ranges. My neck tension is sort of minimal with those shiny turned necks but after firing they are still clean and shiny. Same story with .20P to .375-.338.

I did not get what powder was used and by 215 and 200 tests did that mean those bullet weights? What type primer was used? Were velocities of your sooty cases measured as compared to your standard or bench mark load? I assume this is with a .308 that has major free bore to shoot long heavy bullets. I assume no pressures were obtained as your device was not calibrated.

Obviously, the soot comes from powder burning under low pressures. .337 for sooty necks vs. .340 for normal necks would indicate inadequate neck expansion. Would not, normal expected chamber pressures obtained from shooting 200 grain bullets @ 2600 fps plus from a .308, with pressures in the 60K psi range, cause total case expansion including the neck to primer and expand those necks to the expected .340 ?

Possibly, an analysis of the powder used in these soot producing rounds might be useful. I would assume that the match grade bullets would not be under size diameter or markedly under weight.

I don't intend to be pedantic, but my inclination is to dig at stuff.

Great diagram T shooter.

 

[Homerange]

The point here is that over long throats and short seating depths can get unwanted results. (no more shooting those bullets in that barrel)

And yet long throats can and are used to advantage.

The RUM's are an example, where if the same charge was used in a short throated rifle it would result in a significant overcharge.
Long throats by design can work.

 

[mikecr]

Huge neck clearance.
And how far from chamber end are you trimming to?

 

[fguffey]

And yet long throats can and are used to advantage.

The 300 Win mag has a short neck, it is close to .268" long, in the old days relpaders would throat the 300 Win mag chamber to allow for seating the bullet out of the case and into/near the rifling. Those that knew what they were doing got good results. Another chamber from the old days that had a short neck was the 30 Gibbs, the neck on the 30 Gibbs was .217" long, again, seating the bullet out of the case allowed for more powder. By using longer cases I was able to add .030" to the length of the case neck.
Failure was designed in to the forming process, when using 30/06 cases to form 30 Gibbs cases the case shorten .045" from the end of the neck to the shoulder/neck juncture, as opposed to lengthen from the shoulder to the case head.

F. Guffey