Very furstrating pressure issues....

8

8541

New member
I have a 30-378 I built on a Hall G action with a pac-nor 34 in. 3/3 .333 neck

I am getting (to me) unexplainible pressure signs. I have had as much as 106 grs. of powder (H50BMG) with no pressure signs (same bullet, same seating depth, etc, etc) and yet sometimes as little as 103 grs. will have so much pressure I have to whack on the bolt a bit to get it open, primers flat, deep ejector mark, etc.

Over a chonograpgh one day recently 103 grs. produced 3050 fps (perfect and what I am looking for, accurate, easy bolt lift, etc.) but then a few days later the exact same load will go 3150+ and give me pressure signs. On 2 days when the 103 loads pressure was high I came home, pulled and weighed the remaining 103 loads and verified the powder charge was accurate (over 2 different scales)

I make sure not to fire the rifle when the barrels is hot, last time out the temp was 60 and the 2nd-4th round of the day had terrible pressure. I was using 240 SMK's and 230 Bergers with the same 103 powder charge.

I have weighed brass, only a 1% varience, weighed bullets, weighed powder charges twice, never let the barrel get dirty.....what the heck is going on? Just some days the load is happy, some days not.

This is not a weather related problem, warm or cooler weather does not seem to influence the issue.

Basic load:
30-378
103 grs. H50BMG
touching lands or .030 off (does not seem to make a difference)
333 chamber, loaded rounds are .3305-.331
.003 nk tension
240 SMK or 230 Berger OTM, 99% have been 240 SMK's

Thanks,
John
 
i don't think it is your issue, but i run my brass at plus or minus a tenth...or less...300 win mag....

how much is 1% on your cases....maybe resort in smaller groups and see how it does.

mike in co
 
not straight across data but it looks like you are low in the pressure band for 50bmg powder.....and when working below its perfered burn pressure strange things happen..

i get pressure at 47kpsi with a 240 sie in a 34 in bbl..in quickload...its only a tool not a bible....

would need more specific data to get closer....as in ql does not have a 30/378 in thier data base....

mike in co
 
so 1% or plus or minus 1%.....3 gr vs 6 gr.........i do not know if that is an issue..but if it was 3% of volume it might be...
mike
8541 said:
The 30-378 cases weigh around 315 grs.
Click to expand...
 
To me, I would check the loaded necks on all rounds, I do not think a little more clearance would hurt, I have nothing back my thoughts, other than its a good place to start. may be some build-up in the barrel in the neck area. Is the powder all out of the same can? not blended powder? Good luck! Ron Tilley
 
3 gr. spread in weight. Intersting thoughts on the H50BMG burn rate..that thought has crossed my mind. I have some Retumbo I ought to try. I measure every loaded round and the necks are all within .0005.

All powder is out of the same keg.

Thanks for the tips, new powder is the first thing I will try.
 
Could you possibly be oversizing the cases....enough to affect the headspace? I've seen this happen and some rounds produce excessive pressure while others don't.
 
John, sometimes we just don't find the cause. A very good gunsmith decided to make up some new cases for his 7mm BooBoo for the Nationals (I guess I've given away who . . .) No changes except for a new lot of RWS 8x68 brass. Using the old load, very high pressure. Drop the charge, still high pressure. Primers fall out kind of pressure.

Hmm. He checks everything he can think of, and you'd better believe that's a lot. Still high pressure. So, he expands the necks up to .30 to fire in his .30 BooBoo. Now these case perform just like the old .30 Boo cases -- no difference between the performance of the new & old, certainly no sign of pressure. Neck back down to 7mm. Pressure with the new cases reappears.

Let's hope a powder change solves yours, otherwise you may be lost forever 'neath the streets of Boston . . .

Edit:

But try Wilbur's idea first . . .
 
8541,

Several things come to mind. I can't find a mention of primer choice. If you're not using a Fed 215 or 215M I would try that first.

Second, 103 gr H50BMG in your case provides slightly less than 90% load density. It doesn't register in my wet finger in the wind analog computer as a full power load. H50BMG is a relatively hard powder to light and combined with all that air space even a Fed 215 might not have enough stink to provide consistent results. I wouldn't be surprised to learn that very short, hard to detect, hang fires were occurring. More powder (to increase load density) and/or a hotter primer (if you're not already using a 215) may improve your results.

I think your best bet is to give up the H50BMG and try an easier to light powder. Retumbo that you mention, H1000, VV170, AA8700, H870, RL25 and even 7828 are powders that may give you better results. Even if they provide the same or even less load density than H50BMG they are all easier to light and present less of a challenge to a primer.

Greg
 
Could there be carbon in the throat? Are the cases trimmed short enough? Both of these can create pressure. Matt
 
Thanks for the help gents.....this has really been frustrating.

I use nothing but 215 primers in this case.

The cases are mostly virgin brass, some are neck sized. I am having a custom FL die made.

I have some Retumbo, H-1000, and 7828 on hand. I will try the Retumbo first. I should be able to get some rounds together for a little trip to the desert this weekend. I will let you guys know what I find.

I don't think I have any carbon / fouling issues.....the results are just too inconsistent. I am hoping for a simple explanation; powder. Powder makes the most sense, I have had 106 grains happy and 103 unhappy....nothing else changed, even .030 in OAL made no difference.

Thanks again,

John
 
Since dk hunt 14 just mentioned it I might as well admit it. Same thing happened to me recently while testing WC 872 in a 6.5 STW with 140 gr A-MAX. Worked up to 89grs for pressure then dropped back to 85gr and started over with different seating depth, then the bolt froze three times in a row at 86gr. Only reason I fired three times was disbelief!
I stopped all testing with that set up and began to test a light load with a 107gr MK. Bolt froze. Then dummy got out the calipers and the cases were 1 thou too long. I need to put my arbor press in time out til I can prove I'm a big boy and act as I should. There its off my chest.

Anonomus
 
thank you ballpowder, it needed to be said anyway!! I've done it. Anyone who's loaded for very long using short or min-spec chambers has or will run into this problem IMO

ya' done good coming clean :):):)

lol

al
 
That is the joy of using a belted case...if you FL size and happen to overdo it, you still have the belt for headspace. You should NEVER have headspace issues with a belted cartridge.
 
Usually with new brass you can be overloaded and sometimes it doesn't show pressure. Fire them again and pressure can be a lot higher. When the brass is new it is smaller and softer than after fired and resized and the chamber reamer can be tight also: so they are not sized enough, or your die doesn't size enough. If you are using neck die it isn't sizing at all. Big loads of slow burning powder usually makes carbon in the throat. When you clean can you feel the patch start harder then get easier as it goes through the barrel? If it does you have carbon. You can usually feel it. Matt
 
http://www.saami.org/PubResources/CC_Drawings/Rifle/30-378%20Weatherby%20Magnum.pdf

It would be interesting to see a print of the reamer used to chamber that barrel.
See above for the Saami specs.

"The cases are mostly virgin brass."

A friend has a factory Weatherby .30-378 chambered rifle.

It uses minimun spec brass in a maximum chamber.
The unfired brass was short at least .006 + to the bolt face in that chamber .
When fired you got ejector marks on the case head until the brass was fireformed to the chamber.

Wilson makes case head space gauges for the smaller Weatherby calibers.
You measure off the shoulder.

While this gun is probably headspaced tighter on the belt you still have to blow the case shoulder out to fit the chamber.

You can check this quickly using a cut off case to fit over the neck contacting the shoulder in the middle and a set of vernier calipers.


Glenn:D
 
When you take a 300 Weatherby or 340 Weatherby and neck down to fireform for 308 Baer; the case really gets blown out to make Baer. You can usually shoot stiff load and not get sticky on bolt because you lose about a half grain to blow the brass forward. After they are formed you have to drop a half grain just to stay with same velocity. Does not matter about headspace because they have belt. But i keep my bullets jammed because that is where they shoot the best. So by jamming bullets it keeps case against the boltface. Matt
 
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