Blown primer, mild load?

[ricehombre]

I had a Win M70 rebarreled to a #7 Krieger, 24", 1-10, and had good luck with RL22. But two loads with light loads, 39.5 IMR4350 100gr sierra 2.645oal, and 42gr Hunter 95 SST, had blown primers. I pulled the rest. Checked the powder in pulled loads and the loads were perfect. Had good luck with Hybrid 100, but what would cause the hot loads. They were hot, distinct extractor marks-cratered primers that didn't blow out. Quickload verifies the manuals I use. The chamber is tighter than stock but I don't crowd the lands. Thanks

 

[243winxb]

What Caliber? If you have a tight neck chamber you need to outside neck trun your brass.

 

[rcmodel]

I agree a tight neck could be causing your problem.

Try slipping a bullet back in a fired but not resized case and see if it will fall in.
If a bullet is tight in a fired case it means you will have to neck-ream or outside turn the case necks to get enough clearance for them to release the bullet during firing.

If we knew what caliber you are talking about, we might be able to cross-check your powder charges against other manuals.

rc

 

[ricehombre]

I'm sorry, it was .243 win with sierra 100gr pro hunter. And yes the bullet does slide easily in a fired case.

 

[rcmodel]

But two loads with light loads, 39.5 IMR4350 100gr sierra, and 42gr Hunter 95 SST,

I don't think your light loads are light loads.

Lyman #49 shows 39.5 IMR-4350 and 100 grain as a max load giving 57,000 PSI.
43.0 grains Hunter & 100 grain giving 57,700 PSI.

Maybe your tight Kreiger barrel + tight chamber is just raising pressure too much with max loads.

rc

 

[ricehombre]

Your right, didn't check my Lyman manual. The Hodgdon manual starts at 38.5 and goes to 42 with IMR4350. Speer goes to 41.5. I'll just have to back off on this barrel. Just never ran into this with a dozen factory rigs.

 

[rcmodel]

Which raises the question.

Did you start out with 10% reduced starting loads and work up until you got pressure signs?

Or just throw a max load in the case and go for it?

rc

 

[ricehombre]

I had assumed that I was starting on the low end and went from there. According to the Lyman manual maybe not. Fired only two round from the first group and pulled the rest. thanks

 

[Slamfire]

Win M70 rebarreled to a #7 Krieger

You said the magic word: Krieger.

I will bet you did not shoot your loads over a chronograph or you would understand that something weird was happening.

Krieger barrels are extremely tight. Loads developed in other barrels will absolutely zip along at warp speeds in a Krieger, and you will be blowing primers.

So, cut your loads. Yes they are "minimum" loads, but in a Krieger, they are maximum loads.

Hey, think of it as being environmentally conscious. You will get the velocity you want, but you will be using less resources to get there.

 

[ricehombre]

That's the first time I heard that but now that you mention it I also have a Kreiger barrel on a 270 that I have to load 1.5-2 gr less than my L61R Sako. Thanks for the comments.

 

[ArchAngelCD]

I just love a happy ending...