Pierced primers question

[TheSnake]

Shooting - Savage 6.4X47, 28” barrel, 130 Berger VLD Hunting bullets, R7.5 primers, all brass factory Lapua new. 95F Temp

Doing some load development for my 6.5X47 and fire forming Lapua brass as I go. I have been using H4350 and worked up to 40.6gr getting an average Vel of 2790fps with new brass and 2830 on the 2nd reloading and after.

I switched to Reloader 15 for this test. Here are my loads and how they shot. This is with new brass 5 shots each lot.
# Gr. AvgV ES SD
1) 36.8 2784 30.4 11.3
2) 37.3 2816 10.4 4.3
3) 37.8 2855 9.1 4.0
4) 38.0 2880 40.2 16.5 <-QL Shows 38.0 getting close to Max at 70F so I stopped there.

Here is the problem. The primers were pushed out of the cases ever so slightly in all 20 rounds where the case will no longer sit square on a flat surface. In lot # 3 cases, 2 of 5 primers were pierced. In lot #5 cases, 4 of 5 were pierced. The bolt was not hard to lift on any of them and I don’t see extractor marks on the case heads. I have included a picture of lot #5 for your viewing pleasure in case I am missing something.

I know the firing pin pushes the case up to the shoulder taking up all slack before the primer goes off. It is possible since this is new brass, when the powder goes off, it forces the primer backwards slightly allowing the pin to pierce the primer? I am also surprised that the primer was not pushed back into the case when the case gets forced back from the pressure. Would you take this as 37.8gr is above max and stay below this or is it possible the piercings will not happen on the 2nd reload at 37.8gr?

None of the H4350 rounds show this extruding primer issue nor have any pierced the primers fire forming or otherwise.

Thanks for your assistance.

 

[Steve Blair]

Savage firing pin protrusion is not fixed, but adjustable. Measure the protrusion and ensure that it is within specs. While you are doing that, examine the firing pin tip. Is it round and smooth? Check the fit to the firing pin hole. Is there any visible gap around the tip?

Any or all of the above could be contributing factors. The Remington 7½ should be good but you could try CCI BR4 or Wolf KVB-5.56M as a control.

 

[TheSnake]

Thanks Steve. I would agree that the pin could have a problem but I fired 30 rounds of the H4350 at 40.6gr during the same sitting and none of them pierced the primer and none of the primers were extruded past the face of the case like all of the R15's were. All same brass same lot and all being fired formed. Bullet seating was the same for all. This should pretty much rule out a problem with the pin.

 

[Steve Blair]

H4350 is a slower powder with different pressure characteristics. You may be seeing evidence of the problem with the RL15 pressure curve that was not evident with H4350.

FWIW, QL shows the 37.8 g RL15 load about 5ksi higher than that the 40.6 H4350 load. The photo shows that the chamber diameter is a little large. Have you checked the headspace? Ideally, there should not be enough headspace to allow primer extrusion.

 

[milboltnut]

Can I ask a dumb question? Did you rebarrel this rifle?

 

[TheSnake]

I myself did not re-barrel this rifle but purchased it this way. It had 500 rounds through it when I purchased it and I have shot about 100 rounds through it so far. I do not have a go no-go gauge for this cal. Measuring the difference between the factory Lapua brass shoulder and fire formed brass is .014 longer. 1.4985 on new brass and 1.5125 fired in this rifle.

 

[DOGCAPPER]

The primer backout may come from bumping the shoulder back too far.....Lets the case slide foreward when the fireing pin strikes..Try a few neck sized only.....

 

[Steve Blair]

.014 is too much difference. You likely have excessive headspace. A set of headspace gauges from Pacific Tool & Gauge is $27. All Savage owners should have a set of headspace gauges. Failing that, you can set the headspace .001-.002 more than your unfired brass. You could also take the rifle to a gunsmith and have it set properly without buying the associated tools.

 

[NorCalMikie]

Or, just "neck size" the fired brass, reload with the same powder charge and see what happens.
New brass "might" take a couple of firings to completely form to the chamber and take up any excess space.

 

[Rust]

.014" is excessive headspace. The correct solution is to get a go gauge and set proper headspace.

While fresh brass can be fire formed to fit the chamber, it begs the question why bother when it is so easy to set correct headpsace in a Savage? It also begs the question why leave a potenitally hazardous condition uncorrected?

 

[jo191145]

.014 is definately excessive. Besides massive stretching of the brass you also have that much more unsupported brass in the web area. If of course this barrel was chambered correctly to begin with. Most likely its an installation error though. Its just a bad situation all around that should be fixed.

If you have the tools you can reset the headspace with the Virgin Lapua brass. This will usually give you a tight headspace condition. Not a problem for a reloader to deal with.
You need to assure the bolt face has clearence against the barrel stub.
After your brass gets difficult to chamber you'll then need to determine if your FL die is capable of setting back the shoulders with this headspace.
Both issues can be easily fixed.

Your brass will last much longer with a tight headspace and correct sizing. As it is now I would also consider it dangerous. Theres just no need to leave it that way.

 

[TheSnake]

I will give my local smith a call tomorrow and see if he has the gauges to check. Otherwise I will order me some. Thanks for the comments!

 

[TheSnake]

Dropped the rifle off yesterday and got a call this morning. Head space was 10 thousands too long. Had the smith make the correction. Looks like I get to start my load testing all over again after resizing all my brass. :'( I will post how I do with Vel max after a few runs.

Thanks again all!

 

[TheSnake]

Finally got to shoot a few rounds after having the head space problem corrected. Loaded up the same 4 groups of 5 that gave me pierced primers before. RL15 loaded 36.8, 37.3, 37.8 and 38.0gr shooting 130 Gr Berger's. This time I had no pierced primers and the brass only moved .008 from factory.

Best group came from the 5 shots of 37.3gr Avg vel at 2850, ES 6.1, SD 3.2, AD 2.7. .354MOA at 100 yards.

38.0gr avg vel of 2909, ES 9.4, SD 3.9, AD 2.7 but I think I like the 37.3gr just fine and will work from there.

Thanks again for the advice on getting this problem corrected. This forum and the people on it are GREAT!