257 stw blowing primers

[Trickymissfit]

The rifle is a 700 remington, pacnor 26 inch barrel, trued, oversized threads sleeved bolt, and a few other things.
I got the rifle last winter and worked up a load 81 gr R-25 with a 100gr nosler e-tip. it is loaded .090 off the lands and around 3850 fps. All was good. It put 15 shots into a 1 inch square at 100 yards.

So this fall I took it back out and loaded a few bullets to sight in the scope ( I had swapped out the VX-7 for a Vx-3 LR). That is where it all starts. Now it won't shoot a group. And it wants to blow the odd primer out. So I double checked everything thought the brass was getting used up. Sized up some new Remington brass (7mmstw necked down the same way as the last stuff) same thing. Then I realized I had been using federal 215 primers, last year I had been using CCI magnum primers.

Went back and sized up 3 more brass loaded them with CCI primers and only 80 grs of powder, first 2 shots almost touching (at 200 yards) bolt lift was all good, no extracor marks thinking this is all good now, then the third shot blew the primer out and was hardly on the paper.
Temperature is very similar to last year, same powder.

Any Ideas?? Would like to try something but not sure what.

Thanks

now I'm assuming that you are having the primers move out of being seated in the case. Right? If the primers are pierced, I'd be checking the firing pin protrusion. If by chance you reamed the primer pockets, I'd be checking the diameter of them. I've seen them open up rapidly with high pressures. I have no real data on the .257 STW case. It is excessive overbore so that may contribute to an over pressure problem. But I'm think the problem is opposite, and may need another grain of powder. Big overbore case don't like being down loaded much, and your load isn't all that much greater than the same bullet in a .257 WBY mag. On the otherhand something like 4831 might be better (80 grains of 4831 with a 120 grain bullet is max in 7stw).
gary

 

[Cheyenne 1]

now I'm assuming that you are having the primers move out of being seated in the case. Right? If the primers are pierced, I'd be checking the firing pin protrusion. If by chance you reamed the primer pockets, I'd be checking the diameter of them. I've seen them open up rapidly with high pressures. I have no real data on the .257 STW case. It is excessive overbore so that may contribute to an over pressure problem. But I'm think the problem is opposite, and may need another grain of powder. Big overbore case don't like being down loaded much, and your load isn't all that much greater than the same bullet in a .257 WBY mag. On the otherhand something like 4831 might be better (80 grains of 4831 with a 120 grain bullet is max in 7stw).
gary

ound
Haven't reamed the primer pockets, and yes the primers are popped out of the pockets. The load 80-81 gr of r-25 is on the upper end of the scale, it is pushing the 100gr bullet at over 3850fps.
I ran my bore scope through it, and checked for a carbon ring. I found no checking or cracking in the bore. It did seem like there was a corbon ring building up. I started cleaning it with Jp paste. I really can't believe how dirty it actually was. Even though I had cleaned it.
The rifle has about 125 rounds total.
I guess what was confusing to me is that all the rounds I put through it there were no signs of pressure, it shot good, and all I had done was put it away till now and then all these problems started.

 

[Lefty7mmstw]

ound
Haven't reamed the primer pockets, and yes the primers are popped out of the pockets. The load 80-81 gr of r-25 is on the upper end of the scale, it is pushing the 100gr bullet at over 3850fps.
I ran my bore scope through it, and checked for a carbon ring. I found no checking or cracking in the bore. It did seem like there was a corbon ring building up. I started cleaning it with Jp paste. I really can't believe how dirty it actually was. Even though I had cleaned it.
The rifle has about 125 rounds total.
I guess what was confusing to me is that all the rounds I put through it there were no signs of pressure, it shot good, and all I had done was put it away till now and then all these problems started.

You could have been very close to trouble to start with but saved by slightly cooler temp., a slightly slower rate of fire(fire rate will affect pressure with barrel heating), and/or a slightly cleaner barrel helping you out. I should think you can drop back a bit charge weight and be fine.
I mentioned this a few weeks back on a thread about bore cleaning; a patch will lie to you, as it will only tell you that THAT solvent is done picking up dirt, not that the bore is clean. Visual inspection is about the only way to go.

 

[SidecarFlip]

Too bad we don't have eve balls the size of a mouse attached to extension cords. That would save the cost of a borescope because you are 100% correct, the only sure way to ascertain if it's clean and undamaged is scope it.

There are some good alternatives out there to a Hawkeye and some are electronic. Problem is, there isn't a camera made small enough to fit small bore diameters that you and I can afford.

 

[Lefty7mmstw]

Too bad we don't have eve balls the size of a mouse attached to extension cords. That would save the cost of a borescope because you are 100% correct, the only sure way to ascertain if it's clean and undamaged is scope it.

There are some good alternatives out there to a Hawkeye and some are electronic. Problem is, there isn't a camera made small enough to fit small bore diameters that you and I can afford.

I don't have a bore-scope, but have good eyes. I look for dulling at the throat(and down the bore) and darkening at the edges of the rifling. You need a decent light source but not so much as to wash out the color. If everything is bright and shiny you are clean, assuming you've gone after copper too. You can also see what is left of your rifling then. If you have a lever or auto and don't have access to the breach a cotton patch or bore-light will get enough light where you need it to see the bore pretty well.

 

[Cheyenne 1]

I don't have a bore-scope, but have good eyes. I look for dulling at the throat(and down the bore) and darkening at the edges of the rifling. You need a decent light source but not so much as to wash out the color. If everything is bright and shiny you are clean, assuming you've gone after copper too. You can also see what is left of your rifling then. If you have a lever or auto and don't have access to the breach a cotton patch or bore-light will get enough light where you need it to see the bore pretty well.

I am going to try and attach some pictures. There were some dark spots and 6 inches ahead of the chamber. This bore scope is from snap on. I think it was about 350 or so. I have cleaned it now and wil do a little more.
If the weather ever gets better I am going to start from square one and see what it does.
Thanks for all the help.