142gr SMK blows ups with newer pointed bullets

[Heman]

Friend of mine who shoots at Atterbury that is a HM had his 6.5x284 start acting up at Perry, shots going all over the place. Scrubbed it really good after and shot it again for the first time since CP. Bullets still were very eratic. Every other or multiple shots in a row weren't showing up on target. They were blowing up. He switched to some older non-tipped 142gr SMKs and had no problem at all. Shot 23 in a row (all he had) and all of them showed on target. Fired one of the pointed 142s and it blew up.


He's going to be calling Sierra this week, but thought I'd ask here. As anyone else noticed this?

 

[dkhunt14]

Typically Sierra has a heavier jacket. They are usually pretty tough. I wonder if something isn't wrong in the throat. Like really rough or a piece came out. Years ago when the Berger bullets were blowing up in 1000 yard BR. Most of them were 6.5-284's. Most of them had rough throats from firecracking and they were really pushing them. That was the reason Berger came out with the target version with the heavier jacket. I haven't heard of any bullet not making it to the target in a long time. Matt

 

[JohnKielly]

Could be a velocity thing. Hereabouts, we found that the 6.6/284 was problematic, particularly when pushed hardish. Haven't seen the profiles of both SMKs, but if, for example, the newer has a smaller bearing surface & runs faster with the same load ........

 

[Heman]

I thought it may be a velocity issue. So I put my magneto speed on it. The pointed 142s were going around 2918-2912, the non pointed 142s were going around 2930ish. So the ones not blowing up were a tad faster but still within the normal 6.5x284 range.

I was thinking it was somthing in the barrel also as every other or 1 out of every 3 was showing up on the target. But like I said when he went to a box of the older non-pointed 142s he shot 23 in a row with no blow ups and as soon as he went to a pointed one, poof.

 

[FatBoy]

I have shot about 1300 of the "new" pointed 142s. About 800 from two 8.5 twist 6.5x284s at 2980 and about 500 from two 6.5x47s, one at 2745 (8.5 twist) and one at 2835fps(8 twist) . No issues.

I have "lost" four or five 142s over the years. Most of them in the early to mid-2000s. It happens, but to lose that many, I would be scrubbing it down, flushing it and getting a bore scope in to see if an ecclusion opened up or the fire cracking is so bad it's tearing the jacket . Sierra may have used a thinner jacket on the pointed units but I would think something is probably wrong with the barrel causing jacket damage. Those are hot 260 speeds, they shouldn't hurt that bullet.

Edit: were the old box 142s on call?

 

[Heman]

Yes the old box 142s shot like they always have shot for him. It was at Perry he went to the new box and his gun shot like hell, figured it was a gun issue. Found out it wasn't yesterday. I thought it was a barrel issue also. When 2 of every 3 were blowing up, but then when 23 of the old box were fired with no blow-ups not sure you can say barrel related. He's going to call Sierra, but just thought I'd see what others have experienced.

 

[dkhunt14]

In almost every case i saw with bullets blowing up had a rough throat from firecracking. Or hey were shooting them really fast in a big case. I think the gun Needs borescoped, to look for cracking, a piece missing or carbon in the throat. Hard carbon looks like weld. The 6.5 caliber seemed to blow up more then others. Matt

 

[johnfred1965]

Rough barrel or not, from your description, it is obvious there is a difference in the bullets. No one likes to admit a mistake, but a call to Sierra may be the only way to find out if something has changed or a problem has come up. I don't have any of the pointed bullets, but my old stock shoots fine

 

[1shot]

Shawn,
If you recall I had a new barrel that kept blowing up bullets a Atterbury. It turned out that the barrel had an 1.75" tear in the rifling from the factory. It was in 6mm, but the bullets would get 600-700 yds. before letting go. The mfg. got me a new bbl. and paid for all the chambering costs associated with it.
Bottom line,
I'd scope the bbl. very closely and if finding nothing, I'd contact Sierra.

Lloyd

 

[billlarson]

In almost every case i saw with bullets blowing up had a rough throat from firecracking. Or hey were shooting them really fast in a big case. I think the gun Needs borescoped, to look for cracking, a piece missing or carbon in the throat. Hard carbon looks like weld. The 6.5 caliber seemed to blow up more then others. Matt

+2......... SO TRUE......... happened to me at 400 rnds..basicly a new barrel.......... 6.5x284.... 142 at 2950 ft/sec.

 

[DukeDuke]

I have fired just 25 of the 142s out of my 6.5x47 at 2900+fps in 94F temperatures with not only no problems, but with stellar performance.
I was planning to buy some more, now I'll wait.

 

[MattPeetz]

Regardless of barrel or conditions in it. Fast speed or slow speed. One lot is fine and one lot is bad. Its been demonstrated.
Something changed and the change is the bullet. Whether construction or bad lot of brass. Whatever it is Sierra needs to find out.

 

[Liven The Dream]

I have shot 100 New 142's in my 6.5x55 at 2910 AV. Vol.
No trouble at all . They are better in my rifle.
Don

 

[Heman]

He's going to call Sierra here to see what they say. Again was just strange that an old lot of 142s shot fine, the new lot were all over the place and would blow up.

 

[Shaggy357]

If you have any of those bullets left, send a couple to Sierra and have the lab examine them. What is thickness and does hardness testing come out normal? I have a load that shoots phenominal....except when the moon and stars align just right....Hot day with a little humidity and after about 5 shots, the velocity goes up a little and the bullets comes apart due to the jacket failure. Copper is getting expensive. Just a few .001" in cup thickness is a significant savings in raw material....something to think about.....

Steve

 

[rifleman700]

I have a friend in NZ who said that the new TMK's have a different jacket than the previous MK's. May just need to scrub bore to get all of the foreign jacket material out and try them again.

 

[KAIFS]

I shoot tons of 142gr SMKs, mostly because it mimics Swedish M/41 projectile the best, weight wise (141.5gr). Granted I am nowhere near the velocity you guys are talking about- but I have not had any issues with mine from both military swedes and a fair number of modern 6.5x55 rigs. First I heard of this issue with this particular pill.

 

[SF-Guy]

Shawn,
If you recall I had a new barrel that kept blowing up bullets a Atterbury. It turned out that the barrel had an 1.75" tear in the rifling from the factory. It was in 6mm, but the bullets would get 600-700 yds. before letting go. The mfg. got me a new bbl. and paid for all the chambering costs associated with it.
Bottom line,
I'd scope the bbl. very closely and if finding nothing, I'd contact Sierra.

Lloyd

Lloyd,
I have had trouble years ago with a 308 barrel and when I was at my whit's end and screwed the barrel off, I pushed 19 168's through it just to gauge and inspect them (almost valid test as there is no pressure behind them but enough to average and inspect under my microscope). There was a length of land which was cutting a groove in my jackets and it ran the whole bearing length. I used some of David Tubb's Final Finish ( a whole regimen of them) and it smoothed it right out. I might have hand lapped but too lazy and was really happy with the outcome. I put that barrel on another action a year later and it gave me good long service and never blew up another bullet.