An experiment-Reading Primers - with a friends rifle

[cloverleaf]

I have had my share of issues, including broken rifle parts recently, and while things are looking up, I was looking at the fired reloads from my friends model 99 in 250- 3000 Savage and I noticed what looked to me to be "cratering" of the fired primers. Given my recent experiences I decided to be EXTRA careful and do a ladder test *(at least thats whet I'd call it) to see if there were changes in how the primers look. Speers load data for this 87 Gr. bullet, in IMR 4350, 250 Savage runs from 37 to 41c Grains. My initial reload for this rifle was 39.5 Gr. All loads tested fired w/o any notable indications of "sticky bolt". My load of 39.5 gr was as hot as I went. None of the loads on my " test" went any higher than that unless you count the 100 Gr factory loads (also in the pics).

So, the photo starts with Rem. 100 gr Factory loads (Sorry- red sharpie on these primers). The next load was 39.5 gr. Subsequent 2 round "groups" were reduced by 1/2 grain increments down to 37.5 gr. The results are pictured below.

Again, this is just a visual assessment of fired primers . From what I see, I will stick with my 39.5 Gr load. I am assuming the "cratering" I see is either "normal" or the function of a large primer hole in the bolt face.

The target dosent really mean any thing, I wasnt working really hard for groups.... more shooting of a 38 gr load might be worth while. 39.5 Gr is accurate enough.

Any thoughts, observations- just posting for the sake of conversation. CL

 

[RL338]

I am assuming the "cratering" I see is either "normal" or the function of a large primer hole in the bolt face.

Excessive firing pin clearance will show cratering like you’re seeing. If the 39.5gr is to your liking then there is no need to push higher.
I have several rifles that the firing pin was turned down and the bolt face bushed to eliminate the cratering issue.

 

[JD338]

What Rick said

JD338

 

[SJB358]

What Rick said

JD338

Yup, what Rick said. Firing pin holes that are a bit bigger will give cratering across the board. In my world, they aren't a great indicator of much other than machining.

Your friends 250 is pretty slick. Very nice rifle

 

[cloverleaf]

Thanks Guys- Little extra firing pin clearance in the bolt. Kinda what I figured. I get acceptable accuracy at 39.5 gr. so unless things change I will stay there. I have heard of shimming a firing pin, but I'm not sure its the best plan for a 100 year old rifle and my friends budget. If money was no object, I could send it to Mr. Turnbull, now that would be interesting......

My take away- cratered primers - yup thats what they look like- can be an indicator of over pressure, but not the only one, or always the cause. CL

 

[longrangehunter]

It really has to do with the type of primer you Test..... Standard CCI's will creator easy vs 41's, 34's and BR2/4's, F210M, F215M. Same for Remington 7 1/2, vs F205M. Same loads but each primer will tell a "Odd Ball Tale" when really that's not what to look for.... speed = pressure. Stay within the known velocity range for a given cartridge bullet combo, and bbl length. As that grows long add 20-25 f/s. Some barrels are just slow, and some are just fast..... they will all speed up for the first 100 or so rounds, so don't get to caught up until you do have it fully broken in. Oh, and some factory ammo is bogus unless you chrono the lot, and why hand loading and a chronograph are how you tune a rifle to make it fall into place for accuracy IMO. That said, I've seen a rifle shoot bug holes at 100 yards and suck the further out you go, or the 1" moa rifle still hold it's own out to 800 yards and not even skip a beat!

 

[TackDriver284]

Like RL mentioned, I would bush the bolt.

 

[clearwater]

I have one that craters even with starter loads that leave a smokey neck and give velocities lower than book for the charge. It's a shooter tho. It's on a 100 year old springfield action.

Is it something worth trying to fix? I just use book velocities and look for other signs to keep pressure in check.

 

[PJGunner]

The edges of the primers even at your top loads are still nice and round.
like others have said, I go with the thought that it's caused by a large firing pin hole in the face of the bolt.

Interesting as I have a Remington M700 BDL with a normal size firing pin hole that will craters primers. On inspection, I find that someone at the factory did a slight chamfering on the firing pin hole, for what reason I have no idea. All I can say about that one is regardless of what I run in that rifle, I get cratered primers. The load can be 5.0 gr. of Unique and a 110 gr. cast uller or a full bore 220 gr. round nose loaded balls to the wall, there will be a crater on the primer. You can imagine what people think whenI let them shoot the rifle and they look at the case after the shot. It does cause a few raised eyebrows.
Paul B.