pressure problems with new 6.5x47 brass?

[AusFclass]

gd day gurus!!

at the shoot on saturday i blew primers out of two consecutive rounds and was slightly shocked to ruin my brand new 6.5x 47 cases! ???

i was useing a new batch of lapua cases ( 4ph6010) loaded with a warm charge of 37.5gr of varget and a 139gr lapua with cci BR4's. i had loaded these before xmas. i throw then weigh my charges to within 1/10 of a grain and am useing the same batch of projectiles/primers/powder i did the load work up with.

i fired one shot on a clean barrel and then blew primers on the next two sighting shots. i switched to some rounds that i loaded during the week to exactly the same specs and had no problems. after useing all the rounds that were loaded during the week i went back to the previous batch loaded before xmas to the same spec and had no problems for the 3 shots that i had to use. there was no elevation change noted at 500yds between both batches.

there was no stiff bolt lift. this rifle will tend to pierce SR primers at high pressure because of the pin size and this didnt occur.

there is probably 10-15 deg c difference in temp to when the load was developed. i have never had an issue with ADI powders with realatively small tempreature changes but there is allways the first.

i am yet to do a full diagnostic on the cases but id like to know if anyone has had this problem with new brass or can point me in another direction??

thanks for reading!

 

[ChrisNZ]

same can of Varget?
Nothing else obvious

ChrisNZ

 

[ThunderDownUnder]

What action have you got in your rifle?

You are using a full grain less than I am with the Scenar 139gr bullets and I dont get problems. I keep my ammo in an insulated bag so it doesn't get the full 50+C in car or direct sunlight temperature overdose.

Maybe consider bushing your firing pin if you know it might be contributing to the problem. Did you make a mistake measuring your load? How old is your brass? Old brass may be suffering from loose primer seating tension.

Ian

 

[AusFclass]

these are brand new cases and i allways use a dry patch and swab out my chamber before firing the first round.

i am cautious about overheating loaded ammo and during my second range the ammo would have been at a slightly higher temreature and had no problems. i do not colse the bolt with a round in a hot chamber untill im ready to fire.

i pulled two loaded rounds that i had left and weighed the charge and it was perfect!

you may be on the money with that comment lynn!! ;D

the bullets were very hard to pull. i know new brass has more neck tension, even after i put the mandrel through them, than once fired brass sized with a bushing.

these rounds were not dirty at all BUT because both the case and bullet were perfectly clean when seated MABY during that period they had time to fuse together?

i weighed several cases from the lot that i used during load development and found no sigifficant difference.

 

[Rem06]

how about neck wall thickness on the new brass?? or not enough clearance for bullet release,tight neck? worth a check

 

[AusFclass]

yes i thought the neck clearance could have been an issue with the new batch of cases. i had a friend measure loaded and fired round dimensions with his uber gooood micrometer (mine is in mm only) and found that the loaded round was .291 with a ".293" chamber and the fired rounds were measuring around .2925. so there should be enough clearance.

once again lynn i think your on the rite track. after thinking back to year 11 highschool chemistry while studying "active corrosion prevention" and understanding how the electron transfer works i can see how the bullets can effectively fuse themselves in the case.

i think it is a combination of cases fuseing to the bullet and new brass having more neck tension than once fired cases.

in the future i will load closer to the time of use, maby back off the charge on brand new cases and turn up an oversize expander mandrel that produces similar neck tension to brass sized useing a bushing.

i guess it one of those things you would would never believe untill it happens to you!