Where in the HE!! are these pressue signs coming from !!!

8

8541

New member
I have been shooting and reloading for 30 years, never had a rifle so frustrating as this new one.

30-378 Wby .333 NK. Loaded rounds are .3300-.331
Hall single shot
3 / 3 34 in barrell.
Annealed brass
trimmed
Brass all weighs within 1% of each other.
240 SMK
H50BMG and US 869 powders

I get out of the nowhere pressure signs. Rifle is very happy with these bullets at 3050 and less. But every now and then I wil have pressure spikes that send the chrono to 3150+, stick the bolt, etc. I have tried everything I can think of. I measure every single bullet for OAL, NK dia. etc. I can not find anything that would be causing this. It will happen with the same load on different days. I went to the range last week with a load of 105 grs. of US 869 (brass was a mix of virgin brass and annealed, 3000 FPS) went home, fully prepped some brass (annealed, trimmed, etc) went back to the range yesterday to test.....3084, 3150, 3180 (stuck bolt) I pulled the remaining rounds and the powder charges were where they should be. The barrell was clean yeasterday.

I have been chasing my tail with this rifle for 125+ rounds....it does the same thing whether it is H50 BMG, or US 869. The actual powder charge does not seem to matter. I have had 105 grains of each powder cause the same issue, and I have had 108 grs shoot fine.

One tip: another experienced shooter at the range was looking at my brass and noticed that a fired piece of brass still had enough NK tension that a loaded rounds projecticle would not slip easily into the mouth of the fired round. He therorized that I did not have enough NK clearance. As posted above, NK in rifle is .333 loaded rounds are .3300-.331, so .002-.003 clearance. A fired Nk is .3305, so .0025 spring back?

Weather was cool yesterday, not a weather related issue

I have the reamer used to chamber the rifle. It is indeed .333.

Any thoughts?

Thanks,
John
 
Let me start by saying I don't know. All I've got is a story.

Dave Tooley -- if you don't know who he is, look him up -- had a 7mmBooBoo he made a new set of cases for. Everything the same as before, but he kept blowing primers. Could not figure out why, and he tried everything he could think of. And that's a lot.

He took the cases and necked them up to .30 BooBoo. They worked just fine, no signs of pressure with the loads he long used. Necked them back down to 7mm, and pressure again.

I don't know if Dave ever found the cause, but it sounds like the problem you encountered. Given what you switched around, the only thing you've not tried are different cases. I'd get a few pieces of a different lot & see what happens.
 
Did the 3180 (stuck bolt) expand the fired neck more than the normal .3305? I have seen slow burning powder, light charge, not expand the necks of 243win brass. Could the pressure spike come from detonation of the powder? Magnum primer being used? Bullet jamed into rifling or .005" off? Neck tension- might need more to keep bullet from moving when primer fires. Annealed brass that is to soft can have shoulder set back from the firing pin strike. If bullet ogive is .005" off rifling, the shoulder set back may seat the bullet into the rifling, causing pressure spike? All a guess on by part. No experence with your cartridge.
 
You might try trimming your brass for more clearance at the end of the neck, in the chamber. If your shoulders end up very soft, from the annealing, and your necks are close to the end of the chamber. The cases may be pushed too far forward into the chamber by the force of the firing pin and the primer explosion which could jam the end of the neck inward against the bullet. Try trimming some cases for .030 clearance in the chamber. It shouldn't hurt accuracy at all. Just be sure to thoroughly clean the neck of the chamber before using any longer cases.
 
OK..... bear with me..... when I had this problem it was because I was throwing charges. Once I started weighing EVERY charge to within tight tolerances my spikes disappeared.
 
Sounds to me like a carbon ring inside your chamber, look with a bore scope and I expect you'll see a carbon ring somewhere between where the case ends and the rifling begins. If you don't have a bore scope borrow one and clean until it is gone.
 
Here is a list of questions that I think need answered for these guys to give you a better answer.

1. Has the chamber specs been verified? Overall case length, nk is actually .333, etc.
2. Are cases trimmed to proper length.
3. Tight bore on barrel?
4. New rifle or just new barrel?
5. Actual neck diameter of loaded round verified after initiall fireforming.

I bet you will find the reamer has a small neck. I haven't ever seen that much spring back. Not to say it can't happen, I just haven't seen it.

Hovis
 
0ne percent is pretty big on that case...plus or minus .8 ,or plus or minus .4
just one more thing to check
mark the cases that gives high pressure...se if it is the same ones ??
mike in co

8541 said:
Brass all weighs within 1% of each other.
Any thoughts?

Thanks,
John
Click to expand...
 
Wow, lots of help.....thanks.

A little more to this. I have fired approx 20 rounds of 190 SMK's with 115-117 grs. og H50BMG, not one problem, 3400 +fps. I have no interest in these bullets for this rifle, but wanted to test two things. First, I thought that maybe I was at that spot (with 103-106 gr. H50BMG) that it was not enough powder, and too much at the same time (hence the switch to US 869). Also, the only thing I do not measure on the 240 SMk is bearing surface lenght. I wanted to eleminate the bullets themselves as an issue.

Ok, now to your questions;

The hot loads did not expand the cases more than the others,
215 Federal Magnum primers.
The point of the testing that day was to load -.015, .000 and +.010 into the lands. The last time out the .000 shot very well, so I wanted to fine tune a bit. The first 3 shots I fired was the -.015. Hmmm......maybe there is something here I need to look at further.

I do trim the cases pretty short, in fact all of these are freshly trimmed. The shoulder issue is something I will keep an eye on.

The issue "seems" to happen in a string. Again, it seems that things are going to go well, or not; 3000 fps...... or 3080 to almost 3200, stuck bolt etc. I have already pulled the rest of the loaded rounds and the the powder charges are all right on....fwiw.

I weigh every charge.

The carbon ring is on my list of things to investigate.

Chamber specs: I have the reamer and the reamer print, and while the reamer is a little difficult to measure, I was able to get .3329 or so on the neck
Cases are trimmed
I do not know the bore specs. Fwiw, it is a Pac-nor 3/3 land and grooves, 10 twist.
New rifle
.3300-.331
The spring back has me wondering too.....seems excessive. A piece of fired brass has a neck so tight you can not seat a bullet with hand pressure.
I will start marking the hots ones
The brass is Weatherby, made by Norma. As far as I know they are the only guys who make brass for the big Weatherby's.

1% on these cases is around 3 grains. They weigh 313 to 316.

Thanks again for the help.

last tid-bit. After the 240 SMK's did their thing I also had some of the new 230 Bergers. 105 grains of US 869, seated right at and .030 off the lands. All 7 shot fine (as far as pressures) the 3 I loaded that were .030 off the lands had an ES of 3, 3177-3180.

John
 
my 1000 yd light gun brass( 300 win mag rws) is plus or minus 0.1

just saying....
mike in co
 
software excercise..

i manipulated case size to get the velocity listed with your components.
i then decreased case vol 1/2/3%
117.8 is 3084
116.6 is 3103
115.4 is 3123
114.26 is 3142......

so maybe you should spot check the case volume, and on offending cases...

no proof just info

mike in co
 
John also what are your necks trimmed to. Norma, Nosler, and HSM also make brass for the 30-378. Norma would be my first choice! Norma makes brass for Weatherby but I think the specs are a little different, ran into this with the 308 Baer, with 340 weatherby brass.

Joe Salt
 
minus % case volume from the volume that gave YOUR velocity
[
QUOTE=8541;677783]Mike, do you mean + or - .001 ? NK diameter?[/QUOTE]
 
plus or minus .1 gr wieght variation in fully prepped brass
ps..i am a newbie in 1000yd.....so use your own judgement on my comments
good technician......ammo crafter...vs relaoder

mike in co said:
my 1000 yd light gun brass( 300 win mag rws) is plus or minus 0.1

just saying....
mike in co
Click to expand...
 
Last edited by a moderator:
John another thing I forgot, what do your primers look like flat, cratered, are there any ejector marks! Sorry John not like being on the phone or there with you!

Joe Salt
 
On the hots one, obvious pressure signs, deep ejector marks, flat primers.

Thanks Mike.... I will look into that as well
 
A number of these responses strike me as crap. First of all, if the shoulder is soft & prone to move forward, by the time the case moves .002-.004, the belt will pick up & stop further forward movement. Unless the poster meant the cases were stretching -- in which case, they'd only snap back so much, and you could measure how much.

As to weighing cases: I don't do it. I checked for fun, and my cases are all within 2.5 grains of each other, with almost all within 1 grain. Of course, they hold 90 grains of water...about like .5 grains with a PPC.

I know Matt Kline weighs cases, and he shoots in the 3-4 inch region (his record is 2.815). I shoot in the 4-5 inch region. Maybe that's where weighing cases is helpful.

Weighing charges for pressure reasons is important if you're right on the edge, or if for whatever reason, you/your thrower can't throw within a half grain or so, and that would put you over. Seems unlikely. Having said that, I think weighing charges is vital for long-range accuracy, but when I check thrown charges, they're usually within .2 grains. Of course, there is always that one that's 2 grains out, and that can get you. I weigh to the nearest .1, trickling up.

* * *

There are some experienced long-range competitors who've replied to you. Stick with them. You've answered Dave Tooley's question, maybe he'll respond. Or get Joe Salt to give you his phone number, he can help, too.

* * *

Here's another story to make a point: Last Saturday, it was about 68 degrees in the morning. We couldn't quite decide whether or not to take off our jackets. I had three newbees shooting my guns, same loads I'd used two weeks before at White Horse, West Virginia, where it got up to 80 degrees. Now in Carolin'a 68-degree weather, we blew a few primers. (I shot in the warmer afternoon, same rifle & loads. No problems.)

They had left the ammo boxes in the sun, something I never do. There's energy in that sun, whatever the air temperature.
Now I'm sure that isn't your problem, but it just goes to show how unexpected variables can get you.

Another very experienced shooter, Charles Bailey, felt you shouldn't anneal your cases until after enough fireforming sessions (usually 2) until the shoulder edges were sharp. After that, he annealed every reload. Like you, I anneal after initial sizing. I don't reanneal until neck tension changes. Point here is there are a lot of ways to accomplish things, and newbees all too often seem to feel theirs is the only way. That's usually not true.

My best advise is (1) See what Dave Tooley has to say, and (2) try a new set of cases, or even a few new pieces. Make sure it's a different lot.
 
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