OzFclass

I am shooting my 7mmWSM with 162gr Hornady A-Max projies. Nice and accurate - if they reach the target! Was using 64gr REL22 then 64gr AR2213sc which is 2gr above book max. so I changed to 70gr AR2225 (Retumbo, REL25)which is a half grain below max. Bullets still blowing on the way to the target. Barrel is 500 rounds old and MAB 1 in 9 twist stainless steel. Normally clean the barrel with Ed's Red with ammonia but checked out if there was any copper still in it by using Sweets 7.62 - no copper fouling. Happens more in warmer weather. I am using Federal large rifle magnum primers, cases are annealed and neck turned. Any help will be appreciated!!

I have some experience with this phenomenon

It would be interesting to get a borescope down and see if there are a lot of tooling marks or maybe if the rifling is extra deep in your barrel .....

Basically if the bullet jackets are giving way then when the barrel gets hot and the spinning lead can soften a bit more will give way. Even one blowup is too many so you need to change bullets to eliminate the problem (I don't recommend noslers !) In my experience a lighter powder charge makes little or no difference.

Try switching to the BTHP version of the 162gn A-Max it has the same BC and possibly thicker AMP jacket.

http://www.hornady.com/store/7mm-.284-162-GR-BTHP-Match/

What speed are you running at?

You don't need to run in the 3000's just to get accuracy. I'd suggest staying around 2900's for a safe and reliable speed. Just find the node in that speed range, and you shouldn't get blow up's.

I run a SAUM (just slightly less powder), and using the AMP jackets on the 162's have had no blow ups!

Stay safe.

I have had some feedback about hard carbon build-up. I have started cleaning the bore with a mild metal cleaner and the crud coming out is black and plentiful. I have had bullet blow-up with the Hornady 110gr V-Max in my .308 as well - I am using 10X for this but was using AR2208 when it was my target rifle - could be the same issue. Will continue cleaning until the bore comes clean then will head to the range and see if it has made a difference. With the Hornady 162gr at $55 per 100 versus the Bergers at $98 it is not an option to change bullets as I am on a disability pension. Any more suggestions greatly appreciated.

Berger 168gr VLDs are $58 per hundred at BRT, not the ridiculous price you have seen at some rip off gun store.....

I hope the cleaning regime works for you but really you should consider other projectiles, too. What about lapua ? (when available) I found when i changed jackets my probs went away

good luck
andrew

6shooter wrote:I am shooting my 7mmWSM with 162gr Hornady A-Max projies. Nice and accurate - if they reach the target! Was using 64gr REL22 then 64gr AR2213sc which is 2gr above book max. so I changed to 70gr AR2225 (Retumbo, REL25)which is a half grain below max. Bullets still blowing on the way to the target. Barrel is 500 rounds old and MAB 1 in 9 twist stainless steel. Normally clean the barrel with Ed's Red with ammonia but checked out if there was any copper still in it by using Sweets 7.62 - no copper fouling. Happens more in warmer weather. I am using Federal large rifle magnum primers, cases are annealed and neck turned. Any help will be appreciated!!

See Eric Stecker's post in this benchrest.com forum post:

http://benchrest.com/archive/index.php/t-65740.html

You can take your pick from Eric's list, but this might go right back to how the barrel was run in. When you think you have the barrel squeaky clean just check for copper again you might get a surprise.

Excellent article aaronraad, thanks for that. I am confident I now have the barrel as clean as I can get it and will head to the range tomorrow to see what happens. Is 31" "too long" for a 7mmWSM? most target shooters only go to a max of 30" with their .308's.

6shooter wrote:Is 31" "too long" for a 7mmWSM? most target shooters only go to a max of 30" with their .308's.

I think getting the barrel borescoped by someone familar with signifcant rifling defects would be a good start. Recrowning the muzzle is relatively simple to organise and might give you the result you're looking for. Do you know what the load was doing over a chrono in warm weather vs cold weather? I assume its hard to check now unless you want to risk spraying a chrono with shrapnel?

I have spoken with a well known 6.5mm F-Class shooter that had a pair of barrels from the same batch. Coincidently at the 500 round mark one barrel started popping bullets downrange. The sister barrel is still going past the 500 round mark. After some thorough investigtion he is still unable to determine any significant difference between the two barrels?

Come to think of it, I'll send you some 168gr and 180gr 7mm projectiles. I'd be keen to see if you can get them to fly apart.

What speed are you getting with the 162s? I would say with that load you are getting them pretty fast by the time they leave the barrel. Can you switch to 180s and shoot them at the next lower node? I have been looking into barrels heating up in WSM type cartridges and am switching to Vihta Vouri N165 powder which is slightly cooler burning and will also be switching to coating my projectiles in HBN, not so much for reduced fouling, but but mainly to reduce barrel and bullet temperatures.

The only bullets I have had blow up are 75gn A maxes in a 22 cal fast twist, while the other brands didnt blow apart, I had heard these particular bullets had thin jackets, maybe the 162 gn 7mms are the same? If Aarons jackets are thicker, it could solve the problem???

The only bullets I have had blow up are 75gn A maxes in a 22 cal fast twist,

Hi 6shooter,

I'm running a faster twist at 1:8.5 and don't see these issues when running at 2950fps, so I suggest that you may be going a bit too quick.

Good luck.

8.5 is a slow twist..... 1 in 7 is fast, thats what blew nosler 223 80gr for me, but they were fine in 1 in 8.....

As I said their muzzle velocity is not the main thing.... its the rifling, twist and projectile jacket thickness/hardness that makes the bigger difference. My 1 in 7 223 spins em faster than a 1 in 8 22-250, for example...

8.5 is a slow twist..... 1 in 7 is fast, thats what blew nosler 223 80gr for me, but they were fine in 1 in 8.....

Hi Andrew, it's all relative

In comparison to his 1:9 twist, my 1:8.5 is faster, and I don't have the issue with my SAUM pushing the 162 AMAX's at the 2950fps speed. That's why I'm curious what speed he is pushing them at.

After all, any twist rate could conceivably cause this issue if the speed was too high.

I've been able to push Berger 180's at 3100 fps with my SAUM, and the jackets stayed on, and they were accurate. I just made a value judgement on what speed I considered was fast enough.

Some drive Ferrari's at 200+ Km/Hr, others cruise at 100 Km/Hr. So long as you get home in one piece at the end of the day, that's all that matters

Sure its relative, your getting 262000 RPM with those 180 bergers @ 3100 in 1 in 8.5

My 223 was getting 298000 RPM with 80 noslers at 2900 fps in 1 in 7

I hate to think what a 22/250 with a 1 in 7 could do to a projectile

I guess thats why the ones i have seen are 1 in 8 !

[/quote]

Some drive Ferrari's at 200+ Km/Hr, others cruise at 100 Km/Hr. So long as you get home in one piece at the end of the day, that's all that matters [/quote]

I like that anology.