6.5x55mm Viht N160 overpressure at 44gr - any wisdom?

[Alantoo]

I suspect it is a bit of both.

I use a Lee Precision tool to size the cases View attachment 162202 and whilst the case is chucked up in the drill, I also offer up the RCBS chamfer tool to deburr View attachment 162203


What I discovered is that if you offer the deburrer up to the case mouth of an un-annealed piece of brass, you can get cutting edge chatter which renders a rough edge to the chamfer. Even at higher rpm.

Later trials have born out my theory: if I anneal first, the same set up gives me a smooth chamfer. And almost nil bullet swarf.

I trim and chamfer in the drill in the same way as you.

The chamfer tools themselves throw up a bit of burr, which you can feel if you run your thumbnail up the outside of a trimmed and chamfered case. That little burr is going to be the hardest part of the case mouth having been work hardened through forming by the chamfer tool pressure.

What I was trying to get at is that even were the materials of case and bullet of equal hardness, the sharp edge burr thrown up by the chamfer tools is a point loading (stiletto heel) and is therefore going to scrape or shave the bullet rather than the other way round.

But if the case mouth is flared the bullet can only make contact with the soft radiused form. The action is then one of burnishing rather than scraping.

The sketches may help explain what I am trying to describe...the chamfer burr and flare obviously exaggerated...but I found with Barnes Bullets it not only catches on the base of the bullet but also on each of the driving bands and produces those shavings seen in your seating die. You can feel the notchy seating action as the case mouth springs back into each of the cannelures and then is expanded again...

If your chamfer tools are sharp and cutting clean...you might find just a heavier internal chamfer will improve things, if the face of the case mouth is hitting the bullet rather than the chamfer, i.e. the chamfer OD is not greater than the interference with the calibre.

The expander / flare tool removes the risk of scraping completely.

Alan

 

[zambezi]

If your chamfer tools are sharp and cutting clean...you might find just a heavier internal chamfer will improve things

Thanks Alan. Good advice indeed. To deliver that smooth internal chamfer you describe, what I might do is chuck up an appropriately dimensioned Dremel fine-grit stone and offer the case mouth up to that

 

[Alantoo]

Thanks Alan. Good advice indeed. To deliver that smooth internal chamfer you describe, what I might do is chuck up an appropriately dimensioned Dremel fine-grit stone and offer the case mouth up to that View attachment 162230

Hmmm I think the grinding action is likely to throw up even more of a burr than the countersink cutter you are already using...Mind you that stone is much the same profile as the flaring tool so you could just tap it in to flare the mouth rather than rotate it to cut! You will still need a Lee Factory Crimp die to squish the case mouth back in though!

You can see the acute angle of the VLD cutter which is why the pressure required and therefore the burr is much reduced.

The flare tool has a bit of brass burnished on to it between the start and stop points which indicates how minimal the diameter increase is.

 

[Rutland lad]

Hence why I fancy one of these. But not until I get the load sorted.

Giraud Power Trimmer

Key Benefits

www.giraudtool.com

 

[zambezi]

Hence why I fancy one of these. But not until I get the load sorted.

Giraud Power Trimmer

Key Benefits

www.giraudtool.com

Howwww much??!

 

[Rutland lad]

That’s the wrong one ! Bugger.
The small one that works off your drill is better. Still not cheap but looks well made and saves a lot of farting about.

 

[zambezi]

A recurring question throughout this development has been whether I can be sure of my powder measurements. It seems odd that 42gr N160 in my 6.5x55mm rifle can be pushing a 120gr Barnes bullet at 2900fps as seen by my Magnetospeed V3 . Both Viht tables and GRT expect lower MVs at that charge weight.



So to give added certainty re powder charge weighings, I have now purchased a cheap electronic scale which comes with a reference 50gram mass. Obviously not E1 spec, but it is a good starting check. Thereafter, I offered up same sample masses to both measurement sytems and compared values declared:

First up, the electronic scales read the 50gram reference mass at 50.101grams. Next I tared it out and applied a Barnes 270grain bullet . And then I transferred that bullet to the RCBS beam scales . What the electronic scales declared to be 270.3gr, the RCBS beam scale declared to be 269.7gr. That is a 0.6gr difference or less than 0.2% discrepancy. Given that the 50gram reference mass was called 50.101grams [which is 0.2% higher than its declared mass!] , I can have a lot more confidence that the RCBS beam scales and my operation thereof is on the money.

 

[zambezi]

Two (related) epiphanies in the last bout of reloading:


(A) All Sako factory ammunition I have purchased is manufactured to be taller than the all Winchester, Federal, Norma and Hornady that I have. That is not a COL or CBTO measurement. I am referring to a shoulder measurement of case alone [see image below].

1. Sako shoulder measurement of 100 unfired factory cartridges all fall in the range 1.761" to 1.763".
2. Sako once-fired brass [in my rifle] measures exactly 1.766" at the shoulder. [not some of it, not most of it, all 250 pieces fired so far] Clearly that indicates chamber fire-forming max dimension*.
3. All other once-fired brass grows somewhat but none measure longer than 1.760". [I.e. it will take non-Sako brass more than one firing to stretch to chamber dimension]

(B) In most of the reloading thus far I had tried to retain fire-formed case dimensions and only re-size the neck of once-fired brass. But I do not have a neck-only sizer die. So I have been using a FL sizer that had been backed so far out of the press that cases were not fully ingested by die [no cam over] with the hope that only the neck was being modified. That was a false assumption debunked by specific batch measurement of case shoulder height, obturation at widest point above head.

1. Even when the FL die is demonstrably engaging only a portion of the neck, some body resizing still occurs
2. With FL die backed off such that it sizes only half the neck, case body is still swaged in by 2 thou and that causes...
3. ...case to lengthen! Whereas all cases were 1.766" at shoulder after fire-forming, all grew 3 thou after resizing.

Where reloading steps for the 30.06 and .375H&H have been near linear, the 6.5x55mm excercise has been far more multifaceted. But it has been a hugely fascinating journey of discovery too. My next step is to buy a neck-only sizing die.

*obviously, allowing for brass spring-back, chamber is going to be a tad bigger. However, absolute uniformity of once-fire dimensions leaves no doubt that limit was reached

For utter absence of doubt, the relevant dimension is highlighted:

 

[Alantoo]

Even when the FL die is demonstrably engaging only a portion of the neck, some body resizing still occurs

The knee bone is connected to the thigh bone, and the thigh bone is connected to the hip bone...?

I imagine that when you reduce the diameter of the neck, the shoulder is also dragged down a bit smaller by association...it will still happen to a degree with a neck-only sizing die. The associated reduction will become progressively less as you move down the case away from the neck until you reach the point where the movement is not sufficient to pass the yield point of the brass and then a further bit where it will be held in tension against the spring back.

Alan

 

[zambezi]

The knee bone is connected to the thigh bone, and the thigh bone is connected to the hip bone...?

I imagine that when you reduce the diameter of the neck, the shoulder is also dragged down a bit smaller by association...it will still happen to a degree with a neck-only sizing die. The associated reduction will become progressively less as you move down the case away from the neck until you reach the point where the movement is not sufficient to pass the yield point of the brass and then a further bit where it will be held in tension against the spring back.

Alan

100% agree. I doubt you can apply pressure to any part of a case and not see some knock on effect.

However...online research does suggest that the collateral modification of case dimensions [when attempting neck-resizing] is greatest when using dies that utilise the concept of over-swage+expander-ball correction. I.e. because the final setting of neck tension in those types of dies is achieved by dragging the [now semi-captive] expander ball back out of the case void, the probability that the case shoulder height is increased becomes greater than is the case with bushing dies that only impinge the outside of the neck, and then only in a downwards motion, not upwards. If anything, a well adjusted bushing die could probably incorporate a half thou shoulder bump rather than an unintended stretch. Careful selection of bushings also means working the brass minimally, which will improve case life.

Gavin on UR extols the virtues of the Forster die that claims to do just that:

 

[25 Sharps]

A recurring question throughout this development has been whether I can be sure of my powder measurements. It seems odd that 42gr N160 in my 6.5x55mm rifle can be pushing a 120gr Barnes bullet at 2900fps as seen by my Magnetospeed V3 View attachment 162526 . Both Viht tables and GRT expect lower MVs at that charge weight.



So to give added certainty re powder charge weighings, I have now purchased a cheap electronic scale which comes with a reference 50gram mass. Obviously not E1 spec, but it is a good starting check. Thereafter, I offered up same sample masses to both measurement sytems and compared values declared:

First up, the electronic scales read the 50gram reference mass at View attachment 162523 50.101grams. Next I tared it out and applied a Barnes 270grain bullet View attachment 162524. And then I transferred that bullet to the RCBS beam scales View attachment 162525 . What the electronic scales declared to be 270.3gr, the RCBS beam scale declared to be 269.7gr. That is a 0.6gr difference or less than 0.2% discrepancy. Given that the 50gram reference mass was called 50.101grams [which is 0.2% higher than its declared mass!] , I can have a lot more confidence that the RCBS beam scales and my operation thereof is on the money.

2900 FPS from 42 is way over, I get 2750 with 44 gr and 2850 with 46 gr out of a 24” barrel, something is amiss

 

[Alantoo]

I guess the actual end result of the interaction dynamics between particular case batch and particular die is the only thing to go by. And @Muir will probably be along soon to tell you to quit measuring stuff!

Evidently in your example using the f/l sizing die to only squish the neck, the effect of compression and friction when reducing the neck diameter being transferred to the shoulder and thereby reducing its length/diameter without direct contact with die...was more than reversed by the lengthening effect to the shoulder created by the friction when dragging the expander out...intriguing why that should be...the neck would have work hardened a bit more between the in and out creating more friction possibly? The expander ball having a less acute angle?

I sometimes use a Lee collet neck sizer which does not involve as much axial stress as the F/L or bushing types...is that what you are considering?

Alan

 

[zambezi]

bushing types...is that what you are considering?

Yes. Specifically Redding Type-S with 73294 bush if that can be sourced.

 

[zambezi]

2900 FPS from 42 is way over, I get 2750 with 44 gr and 2850 with 46 gr out of a 24” barrel, something is amiss

I can only measure, re-measure, and chrono. The numbers are the numbers. Two other contributors to this thread have had a similar experience to mine whilst using same brass+powder+rifle combo. There is an answer in the data...somewhere.

I am beginning to wonder if those seeing over-pressure at lower loadings should compare N160 powder batch numbers. In similar vein, I have now made up some 30.06 rounds using the N160. If they also chrono above their charge rating, I will contact Vihtavouri and query if they have any batch issues.

Results will be in by Friday.

 

[25 Sharps]

I can only measure, re-measure, and chrono. The numbers are the numbers. Two other contributors to this thread have had a similar experience to mine whilst using same brass+powder+rifle combo. There is an answer in the data...somewhere.

I am beginning to wonder if those seeing over-pressure at lower loadings should compare N160 powder batch numbers. In similar vein, I have now made up some 30.06 rounds using the N160. If they also chrono above their charge rating, I will contact Vihtavouri and query if they have any batch issues.

Results will be in by Friday.

I can go a fair bit higher load wise but accuracy drops off. The velocity on the face of it is just too high for the load you are recording.

Have you tried on another chrono?

 

[zambezi]

Have you tried on another chrono?

Yup, two. Details in thread above. Chrony F1 and Labradar in addition to Magnetospeed V3. I.e. three different chronographs, albeit on different days. The Magnetospeed definitely declared the highest MV, but not by a huge margin. [both Labradar and Chrony F1 threw "err" results periodically]

More to the point, as per the OP, the initial sign was over-pressure at low charge values. I.e. the chrono work is really just cross validating what the shell observation flagged initially.

 

[25 Sharps]

Yup, two. Details in thread above. Chrony F1 and Labradar in addition to Magnetospeed V3. I.e. three different chronographs, albeit on different days. The Magnetospeed definitely declared the highest MV, but not by a huge margin. [both Labradar and Chrony F1 threw "err" results periodically]

More to the point, as per the OP, the initial sign was over-pressure at low charge values. I.e. the chrono work is really just cross validating what the shell observation flagged initially.

Reread the thread. Seems to have jumped up with the magneto.

I wouldn’t go much lower personally, I would try a different batch of N160 for comparison. The fact you are also getting pressure signs with the hornady still suggest something is amiss.

what’s your case capacity H2O? In a fired case Sako and hornady and COAL?

Nosler data agrees with everything else, Under 2600 for 42 Gr..

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[zambezi]

what’s your case capacity H2O? In a fired case Sako and hornady and COAL?

Genius. Problem solved. Maybe. At least I now have probable cause, and can build out new test loads based on this revelation:

In my attempt to mimic the accurate Sako factory load, including its CBTO of 2.337", I had not considered how case volume might be an issue for N160. I had assumed that because both factory and my rounds had some airspace, ignition should function broadly the same. I.e. neither are compressed loads. Clearly, the Sako factory powder differs greatly from N160 in that it functions well with just 49gr H2O case volume. Not so N160...



I found very little discernible difference in H2O case capacity between different brands of brass. As stated before, my reloads were built to mimic factory loads and thus have a COAL of 2.890" which means available case space starts 0.608" below case mouth. H2O filled to that point weighs exactly 49gr . Well...when I punch 49gr H2O into the GRT calculator, it predicts over-pressure at the lower charge weights I have seen.


There is good news: early on I did some measurements from breech to the lands in my rifle. It is 2.589". Barnes state ttsx requires a minimum 50 thou jump. That means I can seat the ttsx projectiles 200 thou further out the case and still satisfy the Barnes requirement. In turn, that will boost the H2O volume available and [per GRT] reduce pressures...tests to be performed on Thursday. Will update Friday. You may be the recipient of a small libation

 

[25 Sharps]

Genius. Problem solved. Maybe. At least I now have probable cause, and can build out new test loads based on this revelation:

In my attempt to mimic the accurate Sako factory load, including its CBTO of 2.337", I had not considered how case volume might be an issue for N160. I had assumed that because both factory and my rounds had some airspace, ignition should function broadly the same. I.e. neither are compressed loads. Clearly, the Sako factory powder differs greatly from N160 in that it functions well with just 49gr H2O case volume. Not so N160...



I found very little discernible difference in H2O case capacity between different brands of brass. As stated before, my reloads were built to mimic factory loads and thus have a COAL of 2.890" View attachment 164861 which means available case space starts 0.608" below case mouth. H2O filled to that point weighs exactly 49gr View attachment 164863 . Well...when I punch 49gr H2O into the GRT calculator, it predicts over-pressure at the lower charge weights I have seen. View attachment 164864


There is good news: early on I did some measurements from breech to the lands in my rifle. It is 2.589". Barnes state ttsx requires a minimum 50 thou jump. That means I can seat the ttsx projectiles 200 thou further out the case and still satisfy the Barnes requirement. In turn, that will boost the H2O volume available and [per GRT] reduce pressures...tests to be performed on Thursday. Will update Friday. You may be the recipient of a small libation

49 gr is LOW for 6.5x55! I have a feeling federal is around 53/54 gr but not sure without looking it up in my notes.

edit

just re-read that, that is not the capacity you’ve measured to a point.

what is the exact capacity of h2O with the miniscus at the case mouth?

if GRT works the same as QL this is the figure you should be inputting

 

[25 Sharps]

I also see your barrel is 20.5” I just can’t see how you are getting 2900 FPS from a 20.5” barrel and 42 gr of N160 it is just not possible!

looking at the Nosler load data this would potentially be possible with N150...... you sure you picked up the right tub?