primers

[reynolds357]

I'm changing primers in my 6.5 prc load. Should I rework the load or stay with the same powder charge? I'm going from a fed 215 to a rem 9 1/2m.

Since you are going to a milder primer, I wouldnt go down on powder. Maybe start where you are and work up a touch if you do anything.

 

[reynolds357]

You may be surprised at how well some of those work. Board member Slamfire said the Tula primers are his secret weapon in .30-06, getting some sub-ten fps SDs; lower than Federal Match gives him. (Note these KVB-7.62 primers are not the KVB primers that did poorly in the Michael and Amy Courtney experiment; those were non-toxic primers with DDNT instead of lead styphnate in the priming mix. I am hoping they will repeat that work when the Federal Catalyst primers become available to test.)

In the meanwhile, the only issue I found with the KVB's is the cups are crudely ground to length on something resembling a belt sander (from the marks on the cup lips). This leaves burrs and causes them to require some effort to seat. You'll want to swage or ream your primer pockets, as you can crush one on a tight pocket like the ones in IMI brass.

I love Wolf, wish I could still get them.

 

[sako2]

I dropped down 1gn and worked back up to 3 tenths above my original load. at 3 tenths over I started getting hard extraction. My velocity opened up but I think my chrono is acting up. I got a new 1 and will try it tomorrow.

 

[stagpanther]

I still have my top-secret stash of Tula small rifle magnum primers. My problem is that I use about 1,000 large rifle primers a month for much of the year and didn't plan for the supply to dry up for months. Only thing left AFAIK is Unis Genix primers at Graf's.

 

[Unclenick]

…at 3 tenths over I started getting hard extraction.

That's a high-pressure sign, so, regardless of reputations, the primers don't seem to be igniting the powder as if they are milder. Indeed, the old rule of thumb, when you get sticky bolt lift, is to back the charge down 4-6%. You may not want to give up that much velocity or an accuracy sweet spot you seem to be on, but either the brass is flowing (you may need harder brass, like ADG) or you are stretching the steel enough on firing to snap back over the brass. In that instance, the pressure is fatiguing the steel faster than normal.

 

[hounddawg]

what Nick said, hard extraction is a definite warning sign

 

[sako2]

Yes i did back it down to my original charge. Trying find out why I lost velocity and my es is 70 fps. Unclenick I am using adg brass. If I remember right the ones with hard extraction have 12 firings on them.

 

[Unclenick]

Sako2,

Velocity decreasing as charge increases is another high pressure sign. What happens when pressure gets high enough is the chamber itself starts to stretch (what allows the brass to expand enough past it's yield point for the steel to snap back down on it and make extraction sticky). The stretching messes up the combustion volume and produced gas quantity ratio, dropping final velocity by not burning the powder as quickly as the bullet goes down the barrel as the increase in charge would do without the stretch. That is causing acceleration and therefore the velocity to lag. The stretching of the chamber is very accurately proportional to pressure, so any shot-to-shot pressure variation makes the stretch vary as well as its effects. That's what makes the velocity spread increase.

 

[hounddawg]

Thanks Nick, that is my something new for the day. I have often wondered why near the top of my load tests I started seeing diminishing returns comparing velocity to the of the amount of powder being used, now I know

 

[sako2]

I'm 8 tenths of a gn under the the max charge and right at the velocity for the data I have. I can lift the bolt handle with the back side of my hand. Most shots are within 20fps of each other. Then I get 1 that's 50fps faster then a couple shots I get 1 50fps slower.