6.5 142 mk comes unstuck

[rep]

after noon all ,had three projies blow in two shoots recently ,these are clocked at 3140 fps shoot very well bbl is 1/8 twist of 28" and is very smooth easy to clean ect ,sierra shows mv of a3200 fps and i have spoken to other users of same who run them at 3300 + with no ill efects. Has any body had this happen to them or know of it going on elsewhere these projies were brought 1 month ago from sara store any input would be great. thanks rod

[Ken L]

Rod
Try this before you do anything else.
Fire one of these projectiles at 10 metres thru a clean white sheet of paper and look for something like this :



Ken L

[rep]

thanks ken will try next w end was this 142 ?

[Matt P]

Rod
I've fired 1000's of 142SMK and never had a problem but I only drive them at 2900fps. There were reports overseas of this happening and was put down to a couple of maybe's one was the obvious "the bullet" the second was poorly preped brass with burs in the neck scratching the jacket and thirdly was rough throat and "Cut Rifleing".
Have you inspected the bullet metplate ?? Does it look like it hasn't formed right and look "odd".
I would also email sierra with a batch no and see if they have had any other issues with this batch.

Matt P

[AlanF]

Rod,

You must be using a seriously big case to get 3150 fps?

Alan

[Ken L]

thanks ken will try next w end was this 142 ?

Yes a 142 Sierra at 2906 fps

[rep]

hi mat , i have checked couldnot see anything out of the ordinary and sent sierra a email havent had responce as yet. Alan the round is a 6.5/06 imp . Ken what was the cause of your problem and what was the cure

[Ken L]

Ken what was the cause of your problem and what was the cure

The barrel in question had been removed and replaced with a new barrel for the 2002 FCWC and while it was sitting on a shelf a mud dauber wasp had built a nest in the bore. This was removed and after thorough cleaning the barrel was again fitted to the rifle for club shooting.
In the cleaning one a piece of fire cracking in the throat had broken away and this left a sharp edge that that subsequently picked up some copper. It built up to a level that it damaged the jacket and caused the problem..
Cure: cut off 150 mm and rechamber 6.5 X 57 AI for fire forming new cases.

But it happens

Out of interest how many rounds have you fired thru that barrel before the problem showed up?

Regards
Ken L

[rep]

ken this bbl had only about 300 rounds down it from new when this started going on.I thought the 1/8 twist might be the cause but if that was the case you would expect more than 3 out of 350 or so to come apart, or at least grouping to be poor, could it be that some jackets are weaker than others .any how its got me fingered should i just try lapua 139 s and see what happens

[AlanF]

Rep,

If you're more interested in just getting rid of the problem than finding out the exact cause, then I'd drop your loads down in velocity. I am not aware of anyone who recommends running the SMK142 at that velocity for good accuracy (or barrel and brass life). The common velocity range quoted for accuracy is between 2900 and 3000fps. Ask the question on benchrest.com and I think you'll be convinced.

Alan

[rep]

Alan ,those mv you have posted are they the best speed for these projies out of any case size or just in smaller br cases where they are at there upper limits ? , at the mv i have listed elavation, grouping is exelent could not be happier .During load testing started at 55 gr up to 60 gr but 57 gr was the go , that said i will reduce by 1_ 1.5 gr but how many would i have to shoot to see if it is the mv that is the problem if only 3 out of 350 let go ?. To my way of thinking those three jackets must have been a bit weeker or thinner than the rest other wise i would expect a lot more to have gone tits up or at least see poor grouping down range.Mabey wrong ,what say you.

[AlanF]

Rep,

I'm not an expert on jackets sorry - I've read fairly widely on 6.5 projectiles for my 6.5-284, and all the top US 1000 yd BR shooters seem to say that going above 3000 with the 142SMK is not recommended for accuracy, probably because of copper fouling and perhaps also because of blow-ups as you're getting. Sierra jackets are highly regarded though - see Dave Tooley's comments on this recent thread on benchrest.com. If you're getting good accuracy at a higher node then you're the exception - maybe your barrel is very good. But I can say that I haven't had a single blow-up with SMK142s in about 1800 rounds varying between about 2880 and 2980fps.

Alan