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Target bullets blowing up

Back again after a fairly long absence! I am shooting my 7mmWSM with 162gr Hornady A-Max projies. Nice and accurate - if they reach the target! Was using 64gr REL22 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 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!!
 
Barrel is button rifled. Speed is unknown - Hodgdon book lists 70.5gr Retumbo in 24" barrel at 3,010fps whereas I have a 31" tube and am using 70gr. I don't have access to Quikload or a chrony at the moment - accidentally shot mine.
 
Not sure but sounds kind of like the bullets are getting pushed too fast and coming apart from too much velocity. The extra 7 inches would only account for another 175fps though so this seems curious
 
with a slow burning powder the +7 " bbl can give more than 200fps and that can account, reduce the load 2gr and try the same bullets, bet they hit the target.
Bob
 
What twist is your rifling? From what I've read, it is the RPM's or bore condition that cause a bullet to blow. I had Hornady 110 gr. V-Max shot from a 10tw .300 Ackley Magnum at an advertised 3900 fps do this. I would agree with Nomad and check the barrel for a rough condition. Also you can contact Hornady and they will let you know what they are rated for. FYI, I shoot the 162's in my 9tw RSAUM and (9 1/4?tw)Remington Magnum with out an issue.
 
I had a problem with my 6.5 X 284 at a State F-Class match. All of a sudden in the middle of the third match of the day my bullets started coming apart. Lost 4 or 5 of my last 7 shots. Same load I had always shot - although it was hotter than heck that day. I found out later that I had a carbon deposit which once removed cured my problem.

About a month later a buddy of mine was having problems with his 22-250 Imp. and bullets blowing up. After a long workout with JB bore paste his problem went away.

In both cased the bore was clean of copper (at least that is what the patches showed).

Scrub your bore really well and get the carbon out. I'll bet your problem goes away.
 
The early days of people using 7mm short mags for F Class in the UK saw several people suffer blow-ups short of the target, and nearly always with A-Max models. They are obviously very thin-jacketed and so if the twist / barrel condition / pressure / MV combination is 'pushing the envelope', this model seems to be the first to give way under the strains.

FWIW, Hornady bullets, both HPBT Match and A-Max are the only bullets I've ever managed to blow up - in a 1-8" twist .223 Rem. 52gn A-Maxes shot fine in cold weather, but started to string vertically as the barrel heated in hot weather, finally blowing up around 90 yards downrange, the HPBT Matches being the 75gn model when the barrel was well worn and the throat heavily eroded.

There was a lengthy discussion on this issue a few years ago vis a vis Berger VLDs and why the company had moved to thicker jackets on the US Rifle Teams' Long Range Shooting Forum in which Berger's Eric Stecker lists all the potential variables that can combine to cause this problem. After Berger Bullets received complaints about the original thin-jacket 140gn 6.5 VLD blowing after firing from 6.5-284 rifles, they tried to ascertain the likely causes, but didn't manage to get a bullet to fail in any of their test sessions. It says a lot for Berger that they listened to their customers and took action, while some companies would have tested the bullets, failed to reproduce the problem, and then denied it actually existed!
 
How about just chaging to a berger or sierra in the same weight variety and see if it does better. Remember lightning speed doesnt always make the best accuracy in most cases.
 
I would want to inspect the throat and bore with a borescope. My guess is a combo of excessive speed, thin jackets and a rough throat.

A good friend was shooting Fclass with a modified 7mm WSSM and the throat on his krieger bbl was gone in 700 rds. He was shooting the 180 gr Bergers a bit over 3000 fps in a 30 in tube.

He was shocked with it quit shooting at that round count. Borescoped the bbl and the question was where did the lands go and what is all that cracking in the throat of the bbl.

Speed costs money, how fast do you want to go? :-)

Bob
 
Several people have suggested carbon build-up which got me thinking - I have also had bullet blow-up with the Hornady 110gr V-Max in my .308. Don't have any JB paste but have run a fairly mild metal cleaner down the bore - it came out filthy with a LOT of carbon on it. Many patches later the black is getting less but more cleaning is needed. I shoot the Hornady mainly because of the price - $55 per 100 versus $98 per 100 for the Berger here in Australia. I am on a disability pension and already spend $100 per month on ammo just for target shooting, plus gas to get to the range. I re-read Vince Bottomley's article on this site about his 7mm and he is running his bullets at about the 2,850fps mark. I will go to the range tomorrow and see if the cleaning has helped otherwise it is back to load development. Any more suggestions will be greatly appreciated.
 
Looks like you are spinning the bullet over 279000 RPM at normal temp...Add a few degrees of temp and the RPM will approach 300000 and produce blue smoke balls at about 50 yds. Ask me how I know...LT
 
I had same thing happen in my 7mm rem mag shooting 162 a-maxes. was shooting 69? grains roughly and reduced to a cool 65.6 grains and they're still going 3030 fps and have had no problems again.
 
Depending on the cleaner used, the solvent/cleaner solution may simply react with the steel and will ALWAYS yield a black patch. Iosso also works well for controlling carbon......just don't expect patches to come out white.....or even gray once the carbon is removed.
 
Started load development again with the 162gr A-Max's. Settled on 67.5gr Retumbo which shot well under the inch - 3 shots - at 100 yards. Went to the range for the usual Saturday club meet and all bullets hit the target and were very accurate (damn those wind flags!!). Bettered my previous 400 yard score so am very happy. Thanks to every one for their input - speed was definitely the problem. Also added 3lbs of lead shot to the stock, mainly in the fore-end which improved recoil markedly - no more recoiling high and left! Rifle is now just over 18lbs with a 20lb limit in F-Class open.
 
J4 jackets are quite thin. Deep or sharp rifling, rough barrels from tool marks or carbon/copper deposits along with high pressure loads take their tolls on these bullets.

Another factor is your round count, hot loads, and known barrel burner 7mmWSM.

I would bet money the combination you mentioned would show heat cracking and flatten rifling, maybe missing rifling.

Fire the rifle in the dark and check for discharge of burning steel. Red and yellow sparks in the muzzle blast.

Nat Lambeth
 

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