A good friend of mine have a 6,5-06 built around a Tikka action and a Walther SS barrel 1-9". The rifle is built with the Swedish F-Class clone and longrange BR in mind. The rifle shot really well in the beginning with 123 gr. Scenars and everything was just fine. After a few hundred rounds strange high pressure starts to shows randomly even with moderate loads. A load of 50 gr N-160 behind a 123 Scenar works great but every now and then there´s pressures that makes the primer fall out of the case and heavy marking on the case from ejector etc

We have tried to find the cause of this behaviour but we can´t really se whats wrong!? It seemes like it´s a bit better when the barrel is really clean but the problems comes so quick that I really doubth that fouling build up is the problem. I checked the barrel tonight with my borescope and I can´t se anything out of order.

Any ideas?

Stefan

Check your case neck thickness on all the cases. You may have some that are too thick and you are not getting proper bullet release as there is insufficient space for expansion of the case neck. If you are sizing down 30-06 brass with no neck reaming this seems like a possibility.

quote:

Originally posted by stocker:
Check your case neck thickness on all the cases. You may have some that are too thick and you are not getting proper bullet release as there is insufficient space for expansion of the case neck. If you are sizing down 30-06 brass with no neck reaming this seems like a possibility.

+1 to that, and also, be VERY certain that in THAT specific chamber your brass is trimmed properly.

Along those same lines, if you/he are loading into the lands, you must be very careful with Ogive differentials, and how you are seating bullets--a couple extra thou into the lands can really drive up pressures....if you get one into the lands and the others aren't--same thing!

In that same caliber, I had a neck that was SHORT, and brass had to be trimmed shorter than anticipated by a good bit. Every rifle is an individual, but especially custom wildcats!

I fitted the barrel to the rifle and we are quite sure that the cases fits the chamber in the proper way both by length and neck clerance. I have been shooting benchrest för more than 20 y and are used to turning necks and looking after chamber/case fit.

The strange thing is that everything was working just fine first 3-400 rounds!? My friend whent for new unfired brass that he turned the necks on just to rule that out. The loads are quite mild and would not be in any zone that would generate these pressures unless something is really, really wrong

Thx. for the input so far!

Stefan

quote:

Originally posted by Stefan:
...but every now and then there´s pressures that makes the primer fall out of the case ...

WOW! Be careful, primers falling out are a sign of very high pressure spikes. As Fish suggested, I would check the distance from the lands and try to seat the bullets 0.2-0.3 mm deeper. Quickload suggests the existance of a "fast lot" of N160; in case he use that fast lot, 50gr. could give 3900/4000 bar of pressure.

The problem you describe is not that rare.

In some situations, buttonrifled barrels, that is not properly stressrelived, can "spring back" resulting in tighter spots.
This oftens occures just in front of the chamber, where the barrel gets pretty hot, during fiering.

Check specially the groove diameter just in front of the chamber.

Several people also reports of verry high preasure in those barrels after QPQ treatments 575deg centigrades.

In cutrifled and hammerforged barrels i have heard of no sutch problems

the kind of stainless steel used by LW is a very special one called (particle hardening )while this kind of steel has a much better corosion resistance than normal 416 ss steel used in usa, it has some draw backs too .
it is heat hardening . that means it can become harder when temprature rise and it is normal that temprature inside barrel can go high causing partial higher hardness in throat area which is the most exposed to the heat generated by powder burning.
when steel is hardening some degree of deformation occures which may cause some tightening inside barrel. i believe you should talk to LW about that.
best regards
yes.

Has the throat lengthened any during those 400 rounds?

If it has that would normally reduce pressures somewhat. As your pressures were already described as very mild, they could be dropping enough to cause "pressure excursions" when using a slow burning powder in a big case with a small diameter bullet.

Not likely, but a possibility? Especially if the throat is also a little roughened at the same time, which may be causing the occasional bullet at very low pressures to "hesitate" as it passes through the throat into the rifling.

Again, "Not very likely, but may be a possibility?" Quien sabe?

If it was my rifle, and nothing else worked, I would jack the load up a bit or try a faster burning powder, or both. I'd fire at least 30 rounds with that "hotter" load (from a safe remote distance with the rifle in a vice-like fixture) and check all that brass and its primers. If there were no more of the high pressure signs, I'd probably fire 20 more and check the brass/primers again. Then if all was okay, I'd permanently stay away from low pressure loads in that particular cartridge and barrel.

I AM NOT SUGGESTING THAT YOU OR YOUR FRIEND DO THAT; am just thinking through what I might try.

Anyway, hope you find the problem and can correct it. That sort of stuff gives me the heebie-jeebies.

Thx. for the inputs!

There could be a doghnut-problem! The bullets are seated quite far down the neck and I throated the barrel 3 mm today to se if that will make any difference. The pressure problems have occured with cases fired only two times so the throating is probably a long shot but we will give it a try. It´s late here in Sweden and the temperature is -20 C and dropping...... A trip to the range tomorrow? Hmmmm,I´ll give it a few days and hope for some better weather

Stefan

stefan
is this problem occures only in stainless barrels or crom - moly LW barrels too?

Haven´t seen this problem in any barrel before......

We whent to the range today after all, it was "only" about -13 C when we left We shot 10 shots with the new and longer throat and it seems like the problems are gone! Mabye the bullet seated close to the doughnut caused the pressure problems!?

We will give it another go when the temperature rises to a more "human" level