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

[Flash9919]

I’ve loaded Lapua brass to 48.5grns of n160 at a col of 2.995 giving an MV of just below 3000fps with the 120grn ttsx, it was hot but never gave any over pressure signs. I originally had a load doing about 2700fps but had expansion problems at ranges far less than what you’re talking about...actually it was lack of any expansion that was the problem! I like to be able to drive any Barnes I use now at a minimum of 3000fps at the muzzle just for piece of mind.

 

[Odders]

How old is your N160?
Any dust at all when pouring it from the container?

 

[zambezi]

How old is your N160?

Powder is brand new to me, date stamped by manufacturer in 2018.

No dust in container. All grains appear as originally manufactured.

 

[Blobby159]

Are you seating the bullets to engage with the rifling perhaps??

 

[zambezi]

Are you seating the bullets to engage with the rifling perhaps?

Nope. Cottis asked same question. See my reply above. Cartridge OAL leaves 0.200" jump available.

 

[Greyscout]

I originally had a load doing about 2700fps but had expansion problems at ranges far less than what you’re talking about...actually it was lack of any expansion that was the problem!

This is the issue I am having, last load was 45gr and the result was black streaks right down the cartridge indicating what I think is a lack of obturation. I appreciate you are talking about projectile expansion in your post though.

 

[CerebralDistortion]

Excuse my tongue in cheek reply, but I think the problem is spelled Blaser.

No seriously. VV160/560 are a bit slow when loaded low in 6.5x55. If you then over calibrate the case to facilitate Blasers locking mechanism it will increase the problem.

So, less calibration and stouter load.

And if I mistakenly found a Blaser where there was none. I apologize. The conclusion remains the same.

 

[25 Sharps]

This is the issue I am having, last load was 45gr and the result was black streaks right down the cartridge indicating what I think is a lack of obturation. I appreciate you are talking about projectile expansion in your post though.

Try annealing your cases or if safe upping your load. 6.5x55 is bad for this, I had same issue with 120s at 44 gr particularly on cold frosty winter mornings, went up to 46 and problem solved, almost, as still get the odd one so will anneal next time they’re loaded

 

[zambezi]

If you then over calibrate the case

Not 100% sure what is meant here but understand you to mean some excessive re-sizing? I use a standard RCBS full resizer and bump the shoulders of the Blaser fire-formed brass just 0.002". I.e. no different to my approach with the Sako bolt action 30.06. Certainly the fact that I am reloading for a Blaser rifle does not cause me to treat the brass in any special way.

 

[Greyscout]

Try annealing your cases or if safe upping your load.

Brand new Lapua brass so shouldn't need annealing. It is interesting that the OP is using much lighter loads with no obturation issues.

 

[25 Sharps]

Brand new Lapua brass so shouldn't need annealing. It is interesting that the OP is using much lighter loads with no obturation issues.

Think we’ve established it softer brass, which I a pain as I’ve just sourced 400 Sako cases in 6.5creedmoor.

Only option for you is to up your load or try a different powder/primer combination then

 

[Greyscout]

I have a tub of N140 and some Reloader 19, both should be slight faster burn rates, so may have to try that.

 

[CerebralDistortion]

Not 100% sure what is meant here but understand you to mean some excessive re-sizing? I use a standard RCBS full resizer and bump the shoulders of the Blaser fire-formed brass just 0.002". I.e. no different to my approach with the Sako bolt action 30.06. Certainly the fact that I am reloading for a Blaser rifle does not cause me to treat the brass in any special way.

Yes, excessive resizing. Substituted in translation...

Flattened primers is not (necessarily) a sign of excessive pressure, but a sign of excessive resizing.

And of course you need to take into consideration if you are reloading for a bolt or straight pull action. How often do you load for a crush fit in a Blaser?

Bumping the shoulder on a case that still has a way to grow before fully filling the chamber is not only unnecessary but also counterproductive.

Is it possible to chamber a fired round without problem or resistance? Then there is no need to bump the shoulder, the case is small as it is.

 

[zambezi]

Is it possible to chamber a fired round without problem or resistance?

I am able to re-chamber a spent round, but final close feels more snug than that offered when chambering an unfired round.

Bumping the shoulder on a case that still has a way to grow before fully filling the chamber is not only unnecessary but also counterproductive.

OK. So I have measured the shoulders on the Sako factory ammo which delivers half MOA accuracy and it is 1.761". So a cartridge with that dimension delivers very good performance. All Sako and Hornady cases fire-formed in the Blaser grow to 1.766". So based on the uniformity of case extrusion from two makers, I am guessing the chamber is about 1.766". Thus the idea of a 0.002" shoulder bump still sounds right/not excessive/par for reloading any rifle. Please explain if I am missing something in your argument.

How often do you load for a crush fit in a Blaser?

I do not understand that statement. Are you describing an excessive COAL where the bullet engages the lands upon chambering? If so, that has already been shown by measurement to not be the case. Are you proposing the re-use of a fire-formed case with zero body or neck resizing?

I've never used Sako brass in the 6.5X55mm, but have found it to be both heavy and extremely 'soft' in other common cartridges

One thing to really jump out as I sifted through all the cases and cartridges and measured a hefty sample was this: Whereas both Sako and Hornady once-fired brass is measured to be uniformly 1.766" at the shoulder, once-fired Federal brass is just 1.760". This supports Laurie's assertion above that the Sako brass is a tad on the soft side. Perhaps Sako brass does not lend itself to reloading and/or loads in the upper range of the reloading tables.

The easy next test for me is to develop some Federal case reloads up to the 44gr N160 mark and see what, if any, impact that has on those cases.

 

[25 Sharps]

I have a tub of N140 and some Reloader 19, both should be slight faster burn rates, so may have to try that.

What weight bullet, N140 will be too fast if it’s 140 gr?

 

[Greyscout]

What weight bullet, N140 will be too fast if it’s 140 gr?
129gr SST - havent started load dev for the 140gr as yet - which is why this post caught my attention.

 

[25 Sharps]

N140 will be too fast, don’t know about RL19 as have had no experience with it

 

[CerebralDistortion]

I am able to re-chamber a spent round, but final close feels more snug than that offered when chambering an unfired round.

OK. So I have measured the shoulders on the Sako factory ammo which delivers half MOA accuracy and it is 1.761". So a cartridge with that dimension delivers very good performance. All Sako and Hornady cases fire-formed in the Blaser grow to 1.766". So based on the uniformity of case extrusion from two makers, I am guessing the chamber is about 1.766". Thus the idea of a 0.002" shoulder bump still sounds right/not excessive/par for reloading any rifle. Please explain if I am missing something in your argument.

I do not understand that statement. Are you describing an excessive COAL where the bullet engages the lands upon chambering? If so, that has already been shown by measurement to not be the case. Are you proposing the re-use of a fire-formed case with zero body or neck resizing?

One thing to really jump out as I sifted through all the cases and cartridges and measured a hefty sample was this: Whereas both Sako and Hornady once-fired brass is measured to be uniformly 1.766" at the shoulder, once-fired Federal brass is just 1.760". This supports Laurie's assertion above that the Sako brass is a tad on the soft side. Perhaps Sako brass does not lend itself to reloading and/or loads in the upper range of the reloading tables.

The easy next test for me is to develop some Federal case reloads up to the 44gr N160 mark and see what, if any, impact that has on those cases.

How snug is more snug? If you are still able to close the action without using excessive force, there is no need to bump the shoulder.

When you fire a case it grows due to pressure forming to the walls of the chamber. When the pressure is no longer there the case shrinks.
If the load is low, it may take several firings for the case to grow fully to the limits of the chamber. If ever. Bumping back the shoulder 2 thou if that is all it has grown, it will be in a continuous state of less than perfect fit.

The case length (base to shoulder) is not in my opinion related to the accuracy of the load since the chamber is the limiting factor in the expansion of the case. Load and distance to the lands are.

If the case grows to 1.766" and it is still possible to close the action, I would not bump the shoulder, because the case is still not fully grown. I would use a full length die and just resize the neck. If this resizing makes it hard to close the action then I would bump the shoulder.

My goal is to resize the case as little as possible. I have had 300 Win Mag cases light loads reloaded five times without them growing enough to need a bump.

And finally. If you resize your cases though they do not need it, you are using soft primers and a too slow power for the load. Then this is the reason you get pressure signs, not that the pressure is too high.

 

[zambezi]

black streaks right down the cartridge indicating what I think is a lack of obturation

Reviewing your lack of obturation experience and with reference to CerebralDistortion's statement below, I reviewed the twice-fired cases afresh. I see blacking of the neck and shoulders. It is not the full case streaking you have, but it does support CD's suggestion that bumping the shoulder is, at minimum, probably unneccesary. I.e. taking the shoulder back has given the hot gases some unrequired wiggle room.

So...on my 6.5x55mm development journey I am now going to add: "neck-sizing only, and recheck cases".

I would not bump the shoulder, because the case is still not fully grown. I would use a full length die and just resize the neck

 

[Blobby159]

Reviewing your lack of obturation experience and with reference to CerebralDistortion's statement below, I reviewed the twice-fired cases afresh. I see blacking of the neck and shoulders. It is not the full case streaking you have, but it does support CD's suggestion that bumping the shoulder is, at minimum, probably unneccesary. I.e. taking the shoulder back has given the hot gases some unrequired wiggle room.

So...on my 6.5x55mm development journey I am now going to add: "neck-sizing only, and recheck cases".

View attachment 149094

Just to back up one of your assumptions here 'zambezi', new cases in my first 6.5 Swedish reloads gave me lots of ash down the outside of the fired cases just like in the photo (further up in this thread). I too was mightily confused to start with, but persevered with the load and the next series were all clean and bright outside. The cases needed to grow to fill my rifle's chamber (a Tikka t3)...

P.S. I neck resize with a Redding Bushing die.

ATB ...... and shoot safely