PDA

View Full Version : Cratered primer: A problem?


ronas
06-29-2011, 4:31 AM
Photo is of 308 Plama Lapula brass with CCI 450 primer using Berger 155.5 with 47.5 gr. of Varget.

Crater is barely visible without magnification. Photo was taken using super macro. Primer is not flattened at all and has not backed out any. Primer is still round around the edges.

Chronograph was on the bliz when I shot this but a few mins. earlier we chronoed 47 grains with no crating at all. Average fps was 2824 fps and standard deviation was 10 fps. I am shooting these round at 600 and 800 yards, with a TRG-22.

So question is how significant is the cratering I'm getting at 47.5 grains of varget?

http://forums.rennlist.com/upload/p1010306.jpg

Jonathan Doe
06-29-2011, 5:24 AM
The cratering itself is not a sign of high pressure. There will be other signs for that. The cartridge case looks okay. I see that once in a while on my 308 Win cartridge cases.

XDRoX
06-29-2011, 5:48 AM
I wouldn't worry about it either. Doesn't look that bad to me.

How the hell are you getting a SD of 10? That's amazing! Are you talking about 10 rounds or less? If you're getting a SD of 10 within 10 round strings you should be a precision reloader for Winchester:D

ronas
06-29-2011, 7:08 AM
Are you talking about 10 rounds or less?

Only 5 rounds but I would expect same results based on how accurate they are.
1-2877
2-2868
3-2875
4-2874
5-2868

I have several benchrest shooter I shoot with so they have taught me quite a bit. I did not even weight group of brass I used above. If I had I think the results would have been better. That group of brass all weight within .5 of a grain of each other. I also measure bullet seating depth from base of case to ogive.

However, I refuse to shoot benchrest with a gun in a vice with a trigger you breath on and it goes off.

XDRoX
06-29-2011, 8:18 AM
Only 5 rounds but I would expect same results based on how accurate they are.
1-2877
2-2868
3-2875
4-2874
5-2868

I have several benchrest shooter I shoot with so they have taught me quite a bit. I did not even weight group of brass I used above. If I had I think the results would have been better. That group of brass all weight within .5 of a grain of each other. I also measure bullet seating depth from base of case to ogive.

However, I refuse to shoot benchrest with a gun in a vice with a trigger you breath on and it goes off.

Very impressive. You loading this on a single stage I assume?

I like Varget a whole lot better all of a sudden.

ronas
06-29-2011, 11:07 AM
You loading this on a single stage I assume

Yes loading on single stage and drop each charge with uniflow into scale pan and trickle to exact weight using RCBS 10-10 scale.

While working up load for trg-22 I tried Reloader 15, Ramshot, BLC2, Varget and two or three others my buddy gave me to try out. Most were quite good but the Varget was just a little bit better.

Jonathan Doe
06-29-2011, 2:52 PM
How the hell are you getting a SD of 10? That's amazing! Are you talking about 10 rounds or less? If you're getting a SD of 10 within 10 round strings you should be a precision reloader for Winchester:D

I test 10 round batches for my reload tests. Using Ohlers 35P chronograph, I used to get SD of 10 or less consistently. That is of course with usual case prep and single stage loading with all match components.

Pthfndr
06-29-2011, 6:27 PM
If this is a factory rifle with a factory bolt, what you are seeing is not actually cratering, but just where the primer has been driven into the firing pin hole slightly. Perfectly normal.

This why most competition rifles have a bushing installed in the firing pin hole. To keep tolerances as close as possible.

ronas
06-30-2011, 2:27 AM
If this is a factory rifle with a factory bolt,

Yes it is it's a Sako TRG-22 entirely milspec with no alterations at all. It was the best milspec 308 bolt action I could find. It even has a cold hammerforged barrel with the end of the barrel threaded for a suppressor.