trouble with 160 gr partitions in my 7mm mag

[phutch30]

Back ground- Ive shot 160 gr partitions from 3 different 7mags in the last 18 yrs. All shot well under an inch with 62.8-63grs of imr4831 seated 10 off the lands. 3 yrs ago I had my current rifle rebarreled and it also shot this load very well till last yr. Suddenly my groups went to around 2". initially I though for some reasom IMR had changed the power formula but I went through several other powers with no luck.

Ive tried imr 4350, R22, R19 and imr4831 in different charge weights and different seating depths. I could write it off as the barrel went out, but I loaded up a generic 60gr load of imr4350 with 160 game kings 10 off the lands, that puts 4 rounds into a 5/8ths inch group consistant.

Best group Ive gotten recently with partitions was 1 1/4 with imr 4350, for what ever reason my old standby with 4831 wont go under 2"

Why not stick with the game kings?? Ive never shot an elk with one so dont know how they will perform and from googling Im thinking I would prefer a sturdier bullet for elk hunting.

Any ideas why the partitions wont group? Ive gone through close to 3 boxs of them in the last 2 yrs trying to figure it out.

 

[MAinAR]

Good Luck. I have seen this too with Partitions in not only the 284's but other calibers as well. Don't have any idea why, but know that the 160AB's will give near exact same on game performance with higher BC and very easy to make shoot just like the game kings. It the reason you can't find any in stock also. But maybe someone here who has some "stock" could send you a few to test shoot. All I have are "loaded".

You said you have tried different seating depths, I have found the AB's and Partitions both have shot best at as much as .100" off. Have you been that deep?

 

[phutch30]

havent tried anything deeper than 25 off. Ive tried the accubonds and they shoot a little better but they are very tough to get around here. Havent seen any instock for months

 

[MAinAR]

havent tried anything deeper than 25 off. Ive tried the accubonds and they shoot a little better but they are very tough to get around here. Havent seen any instock for months

Nothing to lose to seat deeper and see. I usually test shoot at 50 off first then go deeper to 75 then 100 off. I do that before I go closer after shooting many of them in different guns.

Worth mention as well that with all IMR4831 loads from 243 up I have found that the nearer 100% case fill the better it did. Seating deeper helps in that area as well.

 

[SJB358]

I'd agree that it may be worth giving the 160's a bigger boot out of the muzzle. I've seen PTs usually respond to a faster powder or more PSIs to get them to come around.

 

[Gunner46]

Is it grouping 2 tight, with a flyer ? Or are they an over-sized triangle ?

(FWIW, when I was shooting a 7RM, H4831 always gave me better groups & velocity than IMR4831)

 

[Jgraider]

I'd agree that it may be worth giving the 160's a bigger boot out of the muzzle. I've seen PTs usually respond to a faster powder or more PSIs to get them to come around.

I agree 100%. I've gotten the best accuracy when near max pressure/velocities. Are you running these loads through a chrono?

 

[phutch30]

the 4831 gives me an over sized triangle. The 4350 is a ragged hole/cluster.

Just really wondering why it went south.

chroni yes. 63 gr 4831 runs 3030fps
R22 max load is about 3020ish
60 gr 4350 runs 3003fps- very very consistant velocity with this load.

I'll try a sqashing a few down the case and see.

 

[OU812]

What seems odd to me is that the rifle at one point shot the 160 partitions well and out of the blue won't shoot them to the same degree of accuracy any longer.

Are you still using the same lot number of brass, primers, powder?

How many firings are on the brass you used recently with the partitions?

 

[phutch30]

I agree, it puzzels me how/why it went from real nice groups to crud all of a sudden. I cleaned it with foam and barns copper solvent and shot it squeeky clean and Ive shot it dirty, same groups with partitions.

I cant say its the same lot of brass and cant say for sure how many reloads (8-10 or so). But its all the same make, trimed to the same length and all cases have within a couple firings of each other. I rotate through 50 brass at a time. Then resize and trim the batch and start thru it again.

Its a new lot of imr 4831 but ive played with charge weights between 62.5 and 63.2. Primers were all the same till this yr I switched from fed mag primers to CCI mag primers. I had bad groups with the Fed also.
To be honest my first thought was maybe I got a bad can of powder.

Going to try some seated .100 off this weekend see what it does

 

[Ridgerunner665]

Do you anneal the case necks?

If not, I think you might like what you see if you try it...

 

[JD338]

I had that happen once in my 338 RUM. The cases were loaded 6-7 times. I went to once fired brass
and my groups went back to sub MOA. Try some once fired brass.

JD338

 

[SJB358]

Annealing may be your answer. I'm betting your getting pretty hard brass by now. Speeds seem right on to me.

 

[OU812]

I agree, it puzzels me how/why it went from real nice groups to crud all of a sudden. I cleaned it with foam and barns copper solvent and shot it squeeky clean and Ive shot it dirty, same groups with partitions.

I cant say its the same lot of brass and cant say for sure how many reloads (8-10 or so). But its all the same make, trimed to the same length and all cases have within a couple firings of each other. I rotate through 50 brass at a time. Then resize and trim the batch and start thru it again.

With that many firings on the brass you need to either anneal the brass or get new brass of the same make and I would bet your accuracy will go back to normal.

I went down the same road many years back and it puzzled me as well. I talked with my friend Rick S and he told me to either anneal or new brass, problem was solved.

 

[lhsako]

I'd agree that it may be worth giving the 160's a bigger boot out of the muzzle. I've seen PTs usually respond to a faster powder or more PSIs to get them to come around.

> I agree! in the magnums especially, top end loads tend to produce best accuracy.

 

[preacher]

I just played with R26 and the Sierra 160 Gameking HPBT (which is tougher than the Gameking SBT) with great results and speed in my new 7mm Rem Mag ( it has a 26" barrel). I also just finished using R33/175 Sierra SBT. I could use those two loads the rest of my life, but I also like Partitions. I haven't tried any Partitions in this rifle yet, but will get around to it. I build my hunting loads on new or once fired brass, especially in magnums. I suspect your work hardened brass also, it doesn't have the same neck tension/bullet pull characteristics as new or newer brass. I could be all wrong but each rifle has its own preferences, ha. I wouldn't worry about killing elk with those Sierras, they are just fine. Good luck to you pard.