pressure issue

[gr8hntr]

Hey yall
got a 30-378 and have worked through 2 different powder ladders and found a .644 3 shot group .
here is my question. . Why would this load have a stiff bolt only after 1st shot when hunting but no signs a month ago when workin up the load .. book says 113gn is max but I started showing pressure signs at 108gn and best group is with 106.5gn .. the 2nd shot if needed when hunting shows no pressure sign .
the 106.5gn chronos at 3370fps with 180 nosler BT

thanks for any help

 

[Guy Miner]

Welcome to the forum!

How's your very accurate load compare with factory ammo, same bullet weight? Velocity, accuracy, pressure issues?

Were the cases trimmed to proper length?

That's a rompin' stompin' cartridge - we'll try to help you get it figured out. Buddy of mine shoots one for bear, mule deer & elk.

Guy

 

[DrMike]

Welcome to the forum. Several questions may assist in suggesting reasons for your observation.

What was the temperature differential between time you developed the load and when you were hunting?
Are you possibly tickling the dragon's tail? Is your pressure curve just at the critical plateau?
Were you using new brass for hunting? Or was this once- (or twice-) fired? If previously fired, was it trimmed properly?
Did you use the same lot number for your hunting loads that you used for your load development?

 

[gr8hntr]

Thx yall
the temp was close both days cold enough for a coat ... this is new brass and once shot trimmed brass .. did the ladder with new brass and the few days later did the speed test of the pet load .i just ran out of my 1st lb of powder so not a mixed lot. I havent shot any factory ammo in it @ $150 a box I dont plan on it haha .. the powder is retumbo im using . I leave my gun in the truck overnight so im not heatin it up inside the house then bringin it out in the cold ... could the colder temps even 10 to 20 deg cause this ? I have a electric cart and the gun rides vertical in a gun rack .. could the powder be gettin packed on the ride in and do this ? (dont think so but racking my brain tryin to come up with something ) .. it has happend both deer I have taken this year . Could the wby brass be gettin weak after once shot if so why is it only the 1st shot of the morning ? Lots of questions runnin through my mind lol

 

[Ridgerunner665]

Oily chamber...

 

[DrMike]

The Wby brass assuredly can be weakened by one firing; however, that shouldn't be a source of increased pressure unless it is actually splitting, which you would note. The usual point of weakness will be first seen in the primer pocket. Thus, you would know it when you loaded it. RR has a valid question when he asks about an oily chamber. I had a case once of a fellow who insisted that his ammo was serious seriously over pressure. A cursory examination demonstrated a thin, almost invisible, film of oil on the cases. This was in a 7.62 Warbird. Consequently, his first shot generated abnormally high pressures.

 

[kraky]

I lost alot of my 30378 data in a computer crash years ago. I have a Sako. I do remember in my gun (26") factory ammo ran 3290 fps. In my gun I wouldn't want to push 180s any faster than you are. Wby/Norma brass is soft and if you get a little speedy for your gun ....especially the 30378...the brass shows it quickly. Only other thing i can think of that hasn't been covered is an oily barrel can certainly jump pressure on the first shot. Many people think it would reduce pressure but the hydraulics involved in pushing oil out of the way can actually spike things.

 

[w8n4rut]

i have a 30-378 built on a ruger no.1, mine maxes with 108 and the 180's. I had pressure issues as well and the problem is retumbo. it spikes something terrible.

 

[gr8hntr]

How bad is a foggy day and or misting rain? is this something that can cause this spIke ... i hunt almost every day of TN 100 day season and tend be in this type weather some

Thx for all the help yalls

 

[gr8hntr]

I really don't want it to be the retumbo because of the accuracy I'm getting with it

 

[DrMike]

Retumbo is marketed as an Extreme Powder. While anything is possible, it is highly improbable that Retumbo is causing the pressure spikes you report. It is more likely that some other factor is in play. A difference in brisance resulting from differing primer lots, a change in metallurgic properties and/or neck thickness of brass, a residue of oil in the chamber and other such seemingly insignificant changes in conditions is the more likely culprit.