Pressure signs

[greener280]

I am having a bit of trouble with a recent load I developed for my 7mm WSM 160 accubonds. I am shooting 60.5 grains of IMR 4831, and .005 jump. I am seeing some signs of pressure (cratered firing pin strike, primers might be flattening a very small amount, and a very slight impression of the extractor). I would like to still keep up my velocity, and suggestions. I was thinking about backing off of the lands a bit.

 

[Broz]

Sounds a bit hot. If you do back off the lands it could reduce the pressure a bit. But as you do you will also be taking up case volume space with the deeper seated bullet and that could offset it. If you are seeing pressure like you are describing, I would suggest backing off a grain or two. You may even find better acuracy. I will take that to velocity any day. If you feel you have to have the velocity then I would look at changing powder and working up again. You may even find a load with better velocity that will save your rifles throat and make your case life better.

JMO
Jeff

 

[Tikkamike]

+1 to broz.

Are you sure your primers are actually showing a sign of pressure? I have several guns that have craters in the primers with light loads and factory loads. also the ejector marks are very common. Just saying make sure what you are seeing is not common to your rifle.

 

[greener280]

Here is a picture of the last two cases that were shot.
Extractor marks on the left case is on the E and R, on the right is on the W in WSM.

 

[Tikkamike]

I cant tell for sure but they do not look the same. the one on the left looks like it has more of a crator? is that right? If so I have never had a rifle do that inconsistently so it could be a pressure sign. Measure the case head and see if you have any head expansion. Also deprime and measure your primer pockets. if they measure more than .2085 they are too big and you have too much pressure. .2085 is the absolute max before your primer pockets are too loose.

 

[greener280]

The one on the left does have the worse signs of pressure. Primer pockets are exactly .2085. This is about the third go around with this brass as well. These loads are also fairly consistent in velocity ES 20 fps and grouping 1/2 in so I would like to keep it. That is why I am considering just backing my bullets .015 off the lands instead of .005

 

[bassin93]

Greener280

I have a remington sendero in 300rum that craters the primers no matter how hot of a load i shoot. I am pretty sure that the firing pin hole is to large for the pin and get flow back. Just wondering if yours is the same way.

 

[Tikkamike]

well if they are .2085 after 3 reloads i would guess your pressure is either fine or just barely over I would back it off a half grain You will see minimal if any velocity decrease as a lot of loads tend to Plateau as far as velocity goes once they hit the peak until they hit a certain over pressure then velocity shoots up. sounds like your accuracy sweet spot is right where you have them seated. if you back them up your group is likely to increase in size. I would bet if you backed the powder off a half grain maybe even a full grain if that makes you more comfortable you would still have great velocity and keep your accuracy. I hate to see you sacrafice accuracy for velocity which is no more than a number. Not to mention even if you lost 100 fps (which you wont)you would probably never even see it.

 

[Tikkamike]

Greener280

I have a remington sendero in 300rum that craters the primers no matter how hot of a load i shoot. I am pretty sure that the firing pin hole is to large for the pin and get flow back. Just wondering if yours is the same way.

I think that is exactly what is going on. What velocity are you getting? should be around 2900 -3000 I would have to look it up to be sure

 

[greener280]

I figured that it would come down to reducing the powder charge. Except I have and anything below 60.5 grains is shooting somewhere around a 1.5 inch group. I will need to try a different powder possibly to get better accuracy in those lower charges.

 

[Tikkamike]

Well if you feel you can not go down with your powder charge I suggest you pick 5 shells and keep loading those same 5 with the load you have worked up right now and see if the primer pockets expand eventually. they very well may not. If they dont expand after another 3 or 4 loads I say shoot that load and call it good. If you are getting good results and not wearing out brass and nothing dangerous is happening I would say you have a great load!!

 

[greener280]

Sounds good thank you.