Over pressure at random

[wjarrell]

Gun is factory Model 7 308, 18" barrel, 1:10 twist.

Load is berger 155 vld seated to 2.810 43.5 grains of varget, fl sized new Winchester brass, cci 200 primers.

This load shoots 1/2 to 3/4 MOA but about 10 or so rounds I get an ejector swipe and heavy bolt lift. Can anyone explain or guess why my pressure signs are spread out between firings? Could it be inconsistent brass?

 

[Dosh]

W, could be brass or perhaps seating depth if not measured with a comparator at the ogive. Weighing powder charge precisely and cases inconsistencies can factor also.

 

[LoneTraveler]

Are you weighing your powder charges? What type of scales?
Is it a compressed load? It could be that the neck tension is not tight enough to hold the bullet. In handling the bullet may be sliding out and contacting the rifling when put in the chamber. This will make the pressure jump wildly.
Just some thoughts to check.

 

[dfanonymous]

I mean, I know every gun is different, but will copper build up in a barrel and a max load, it could easily hit over pressure. Although I think its like around 47gr for max load with a 155gr, so maybe its a combo of things...maybe seated not deep enough as well?

 

[rcoody]

Gun is factory Model 7 308, 18" barrel, 1:10 twist.

Load is berger 155 vld seated to 2.810 43.5 grains of varget, fl sized new Winchester brass, cci 200 primers.

This load shoots 1/2 to 3/4 MOA but about 10 or so rounds I get an ejector swipe and heavy bolt lift. Can anyone explain or guess why my pressure signs are spread out between firings? Could it be inconsistent brass?

well you are a full grain under max so your scale would have to be pretty bad to be getting an overcharge. i would check the accuracy of your scale against another one anyway.

even with a jam you wouldn't be getting that sticky bolt lift with that load. you should get a stoney point overall length gauge and hornady bullet comparators and learn how to use them. know where your lands are. check your seating depth for consistency.

did you check trim length after sizing?

i would suspect the brass is your problem. you are fireforming this brass on the first firing. it is growing. if you had the hornady headspace gauges you could see how much. you really want to set your sizing die to only bump that shoulder 1 to 2 thousands. with proper resizing you problem may go away on the next firing.

Many will argue this point. buy you some lapua brass and some cci br2 primers and try that.

 

[wjarrell]

I appreciate the replies guys, I will double check my scale and try some new brass.

 

[rcoody]

I appreciate the replies guys, I will double check my scale and try some new brass.

I appreciate the replies guys, I will double check my scale and try some new brass.

i would properly resize your fired brass and load it up and shoot it. now that it is fireformed you problem may be gone. You do know how to measure your fired brass to properly set up your resizing die for that 1 to 2 thousandth shoulder bump?

 

[dfanonymous]

Actually, not turning the neck...or the trim being to long, can be enough to cause enough for over pressure, thats a pretty common issue....it could have been the. Did you trim the neck at all?

 

[wjarrell]

Actually, not turning the neck...or the trim being to long, can be enough to cause enough for over pressure, thats a pretty common issue....it could have been the. Did you trim the neck at all?

Ya brass was freshly trimmed.