7mm mag with 180 grn smk's

[vegas steve]

i have a 28" cbi barreled 7 mag that always shot 168 vlds extremely well,and i recently switched to a 180 grn sierra matchking,and once in a while i get a tumbler that keyholes way off course. im loading with 70.0 grns of retumbo and using federal 210m primers in weigh sorted remington brass. i figured a 28" 9 twist barrel wd stabilize a 180 smk just fine. i'll get 4 shots into one ragged little hole and the fifth shot goes rouge away from the group and completly sideways thru the target.never seen anything like that before. bad batch of bullets? i'm baffled.any ideas on what might be going on sure wd be appreciated.

 

[vegas steve]

anyone?

 

[vegas steve]

Wow i guess there isnt any 7 mm shooters on this forum

 

[vegas steve]

By the time someone finally chimes in i will have already figured it out.this place has really went downhill

 

[wbm]

i figured a 28" 9 twist barrel wd stabilize a 180 smk just fine. i'll get 4 shots into one ragged little hole and the fifth shot goes rouge away from the group and completely sideways thru the target.never seen anything like that before. bad batch of bullets?

7mm magnum is my favorite all-around cartridge so I have loaded for it a lot. Twist rate should not be the problem. A 1-9.5 twist will stabilize the 180gr Sierra so I would put twist rate at the very bottom of the problem list for right now.
Also, 100 yards is not a good range to test bullet stability....move to 500-600 and see what happens. If you get more keyholes at those ranges then you will know more than you do now. Personally I would give Sierra's tech line a call and see what they think.

 

[vegas steve]

well if the sierras are going thru paper completely sideways at 100 yrds then they will surely be way off course at 500.sierra claims their 180 smk shd be shot out of an 8 twist barrel,but everyone i know shoots them out of a 9 twist just fine.the barrel only has around 600 rds thru it so it cant be the barrel.

 

[Lefty7mmstw]

I'm dumping 180 smk's out of a 9" and change 7rum barrel at 3150 fps pushed by retumbo and all is well at about 1/2 moa...

I'd get your speed up a bit; you should be fine... if that doesn't work your bb. likely doesn't like the pill...

As to round count; I've got a 25wssm that just had the wheels fall off a h4350/ 120 speer bt load and she is around 600 rounds down the barrel (the bbl. still looks good)... My 7rum looks rather fried (bought used and have hundreds of rounds through it myself) but she is a solid 1/2 moa rifle with the 180 sierra, the 175 hdy, and the 168 berger...It all depends...

 

[Lefty7mmstw]

.this place has really went downhill

a few of us work out and about and can't get to a computer every day.... it is rather quiet here lately though..... Not necessarily bad either; the real mouths have mostly gone away...

 

[vegas steve]

I had the barrel bore scoped and the smith said it looked really good.he said even the throat looked really well.im gonna try some hornady eld match bullets and see how they do.maybe this barrel only could stabilize the big 180 smk's for the first 500 rds,and now it wont.wierd tho cause it was shooting 3 of em into groups as small as .184 at 200 yrds

 

[vegas steve]

i bought a box of 162 eld match hornadys today and loaded a few. i tested them at a private spot i go to to test guns after smith work.laying prone with no rear bag i put 10 shots into 2 inches at 515 yrds. at least i know the barrel is ok now.i was worried she was already toast after only 600 rds thru it. i didnt chrono it yet but my dope was right on with me plugging in a speed of 3225 on my shooter app

 

[Lefty7mmstw]

i bought a box of 162 eld match hornadys today and loaded a few. i tested them at a private spot i go to to test guns after smith work.laying prone with no rear bag i put 10 shots into 2 inches at 515 yrds. at least i know the barrel is ok now.i was worried she was already toast after only 600 rds thru it. i didnt chrono it yet but my dope was right on with me plugging in a speed of 3225 on my shooter app

good; glad you got something to work...