Looking for suggestions on a problem I'm having with loads for my Tikka T3 in 6.5 x 55SE. I developed a hunting load over the summer and made up a new batch to do final sighting-in. Thought it would be routine, but no such luck. My bolt locked up. Dealer got the case out - blown primer and ironing out of headstamp. Not good to say the least. I pulled the remaining bullets and re-weighed the charges with no variations found. This was the 3rd loading of new Rem brass. No previous pressure signs with this load, even on +90 degree days. Barnes 130 TSX with 46.5g of H4350 EXT and CCI BR-2, 78.6mm OAL. Cases trimmed each time. I had recently bought new boxes of the same primer (No lot # because they were 100 packs.) I weigh each charge with 502 scale checked with Sierra MK Bullet. Any ideas would be greatly appreciated.

47gr of H4350 and a 125gr partition is a nosler max book load. You're probably close enough to max (or even slightly beyond it) that apparently innocuous changes can have BIG effects.

The books oft repeat that you should work back up if you change any component - changing primer lots satisfies that criteria.

Potential reasons are:-

Powder lot faster (lot change or inadvertant contamination from)
Bullet variation
Inadvertant over charge
Foreign matter in case (eg tumbling media)
Untrimmed cases pinching bullet
Oil in chamber

Or any combination of the above

BTW why don't you use check weights - could you have used the wrong MK bullet to zero the scale?

This could be headspace issues, rather than excess pressure.

You said you'd trimmed the brass each time - did it need it each time? It shouldn't - if so, it sounds more like headspace.

What weight bullet were you using?

Sometimes low pressure can do this. The firing pin hits the primer and drives the case forward. (Too far forward, in the case of excess headspace.) The charge ignites, but with insufficient energy to drive the case head back against the breech face and the primer backs out.

Are you neck-sizing, or full-length sizing?

Also, though not a cause of the problem, how's your firing pin acting now? All the gas and molten metal could well have coated the firing ping/spring, bogging it down.

Jaywalker

Thanks for your replies. To avoid media problems I have been tumbling prior to decapping and then using flashhole uniformer as last step. I will now do visual check of interior to be sure. It is possible that some breakfree got into the chamber after cleaning out the lug recesses. I swab out chamber after cleaning but now I will do it before shooting to be sure. I use a Lee hand trimmer which limits trimming to only what is necessary. I was shooting Barnes 130g TSX, but I checked with a 140 MK. Sounds like a 50g check weight should be my next purchase. I have been only neck sizing and have had no problems due to apparent concentricity of chamber. I will strip and clean bolt - thanks for the tip. I'm starting to get my courage back, but dropping down a least one grain seems like a good idea. I have had good results at 45.5g (2810fps with some sub .5" groups). Thanks again.

I had a similar occurence with a Ruger M77 MkII 6.5x55 using a Lee neck sizer. After using full-length sizing dies the problem never recurred, and I never conclusively figured out what the issue was.

Jaywalker

Sorry I didn't see the trimming thing.
Sounds like you have a great potential load with the 45.5gr BUT do work back up to it from start loads rather than take a grain off the high pressure load.

I don't agree the headspace explanation. It can certainly cause a primer to back out but not to blow, erase case head writing and to lock a bolt. That is as clear a presentation of XS pressure as you will get without a basket of metal pieces.

I would imagine that the pressure required to blow primer/lock bolt/remove casehead writing is around 70-80kpsi?

It's a while since I worked with a beam scale but don't ALL scales require to be calibrated before use?

quote:

1894mk2: That is as clear a presentation of XS pressure as you will get without a basket of metal pieces.

I certainly thought so, until it happened to me. And I might be wrong - which is why I asked whether the cases needed trimming, or he just did them regardless. Cases that have to be trimmed after one firing do point to excessive case stretch. Still, I never did figure out what casued the problem for me - I just fixed it by going to FL sizing.

Jaywalker

A little is cut away after each firing when using the Lee hand trimmer, even with lighter practice loads (140 MK over 41g H414 w/ CCI Br-2 primer, about 2500fps). I consider myself very lucky - out of the corner of my eye I saw a white flash emerge from the rear of the bolt. Only a plastic rear shroud on the bolt. The pressure must have been really up there! It's especially scary because I wasn't pioneering, just making a new batch of a previously developed load. I will back down the standard 10% normally recommended. Thanks.

My first question would be about seating depth. How close to the lands are you loading? Is it possible that somehow these were loaded long? Just picturing a near max powder charge combined with a seating length up against the lands. I've loaded some rather stiff charges in the 6.5x55 in modern actions and haven't had this happen. Another thought may also be the brass. I only use Lapua for serious work with the swede and occasionally S&B for light duty.



Eric

Barnes recommends .030" to .070". I have them seated .045" off the lands, which translates to 78.6mm OAL. I tried .070", with no apparent difference in accuracy or pressure signs. I don't dare seat them closer. I often check that the die lock rings are snug and measure them often. One of the nice features with the barnes TSX is the grooves, which give a quick, ROUGH visual indicator (not a substitute for measuring). I now use Remington brass for my hunting loads, which, until now has shown absolutely no pressure signs with these loads, where Fed, Graf and S&B could not handle them. I heard Lapua has a superb reputation for precision (machined instead of swaged flashholes, etc), but how is there strength?

Ok, that's cool, the seating depth question was what popped into my mind first. As to the strength of the Lapua brass, I have loaded and shot some of the brass at slightly hotter than "normal" levels up to 10 times (brass didn't fail, I just switched to newer to be sure). Also, I am using a Remington actioned rifle in F-Class chambered in 6.5x55 right now. I have pushed 142gr Sierras at over 3,000 fps with Lapua brass (I won't go into the powder charge for that load). No problems like you described at all, I did turn it down a couple notches when I had moderately stiff bolt lift.

Only other question I can think to ask would be this: How do you measure the length so you know where you are seated in relation to the lands? If it's bullet tip to base of case, could it be that the bullet in question was a bit long? I learned to measure the length with a comparator that gives a measurement to the ogive.


Eric

found the best for general hunting to be the 120 and 140 corelokts.
I use the 120's for most everything- at a bit over 3000 fps using european brass.

later
P

that took a lot of pressure, since it was a new batch,could it have been the wrong powder? simular but faster or differnt lot of the same powder,wrong powder returned to wrong container of powder? Maybe a bore obstruction, cleaning patch in the throat ?a squib with a bullet left in the bore, ect,,?
I had some pressure problems with my 6.5 x 55 with pmc factory ammo. It was very long loaded and really flattened the primers streching the pockets,difficult bolt lift ,turned out it was seated into the lands, I seated them a little deeper[a lot actually] and primers looked good , with easy case extraction

Here's another thought that I have encountered in my reloading. Is your reloading/powder storage area in a cool dry location? If not, the humidity on those 90deg days could have changed the size of your powder charge when compared to the size of the charge loaded on a dry autumn or winter day. Good Luck and Be Safe.

I regrouped and tried it again today. Went down to 45.5g and had no problems - .7" 3-shot groups - I'm happy with that as a hunting load and will stay there. I measure from base to tip, which isn't too bad with the Barnes TSX, but could be problematic with exposed lead soft points (very irregular). I do store my components in a cool and dry conditioned interior area, but that is a very good point. I have narrowed down my problem to the charge being max+, in comination with oil (breakfree) in the chamber. I decided to back off and keep the safety factors intact (along with my face and vision). Very important lesson - I doesn't matter how strong the rifle is - the brass is the weak link. Thanks.

same can of powder or new can?? if new can,..it very well can have a faster burn rate than the old can, causing high pressures,..VERY HIGH.

stiff bolts start at ~70k psi,..yours was probably at 75k or 80k psi when it locks a bolt and irons out the headstamp.