N540 vs N550 for .308

[bolt_action]

May I have the benefit of your collective wisdom on the importance (or otherwise) of combustion ending before the bullet exits the muzzle?

I use Quickload to predict the internal ballistics before working up a load, and I find that if I use the actual dimensions of my case and bullet instead of the figures in the database it agrees closely with reality.

For example, QL predicts an MV of 2578fps for 45gn N550 with 175gn Berger LRBT and I measured an average of 2555fps. It also says that only 96% of the powder is burnt before the the bullet exits the muzzle (the barrel is 26").

QL also predicts that I will get a very similar MV for 42gn of N540 for a slightly higher chamber pressure but with 100% of the powder burnt.

Given that my N550 load is giving me very good results at 1,000 yards, does it matter that not all the powder is burnt?

[tony h]

it does not matter, but it would be better..
alot of people chop there barrels and so the powder does not all get burnt, but the rifles are still acccurate ...


tony

[bolt_action]

It's nice to know, because my curious half wants to buy some N540 to try it and my sensible half says don't spend the money!

[Stover Rover]

May I have the benefit of your collective wisdom on the importance (or otherwise) of combustion ending before the bullet exits the muzzle?

I use Quickload to predict the internal ballistics before working up a load, and I find that if I use the actual dimensions of my case and bullet instead of the figures in the database it agrees closely with reality.

For example, QL predicts an MV of 2578fps for 45gn N550 with 175gn Berger LRBT and I measured an average of 2555fps. It also says that only 96% of the powder is burnt before the the bullet exits the muzzle (the barrel is 26").

QL also predicts that I will get a very similar MV for 42gn of N540 for a slightly higher chamber pressure but with 100% of the powder burnt.

Given that my N550 load is giving me very good results at 1,000 yards, does it matter that not all the powder is burnt?

A top gunsmith told me that the Vit 5** series double base powders wreak havoc on throats and erosion rate is far quicker than with single base. I would be looking at IMR4895 as a really good powder for 308 and it burns fully.

[Parabuteo]

A top gunsmith told me that the Vit 5** series double base powders wreak havoc on throats and erosion rate is far quicker than with single base. I would be looking at IMR4895 as a really good powder for 308 and it burns fully.

That is very interesting....

I am no expert, and have only been re-loading for just under a year.

My main interest is in F/TR, so although I currently have a rifle that wont cut it competitively, that is the direction I am heading in eventually.

Due to difficulty in obtaining Lovex DO73.6/Accurate 2520 (a Double base .308 orientated powder), and an interest in sorting out my .303, I have switched to N140, which is a single base powder, but apparently close to the burn rate of the accurate powder.

Until they started using the Vhit 5 series N140 was the fave of the F/TR lot.

All I can say is that My barrel is only 26" so it wont allow the sort of performance for competitive F/TR shooting (usually out t0 30" plus now) but Russ Simmonds suggested it would do me very well.

So far, I have found it to be much cleaner burning than the double base 2520 (is this a mark of efficiency?) and the accuracy from the .308 seems the same....hopefully!!

It is supposed to be marginally slower than the 2520, but so far seems like a nice powder to use.

With a 26" barrel I am sure I could push the gun hard to shoot to 1000, but since I will only be doing that a few times a year, logic (and a chat with Russ) suggests I keep the stress/erosion down on the rifle and stick to producing best grouping out to 600...then pray at 900-1000...until I get a dedicated F/TR rifle that is.

[kennyc]

That is very interesting....

I am no expert, and have only been re-loading for just under a year.

My main interest is in F/TR, so although I currently have a rifle that wont cut it competitively, that is the direction I am heading in eventually.

Due to difficulty in obtaining Lovex DO73.6/Accurate 2520 (a Double base .308 orientated powder), and an interest in sorting out my .303, I have switched to N140, which is a single base powder, but apparently close to the burn rate of the accurate powder.

Until they started using the Vhit 5 series N140 was the fave of the F/TR lot.

All I can say is that My barrel is only 26" so it wont allow the sort of performance for competitive F/TR shooting (usually out t0 30" plus now) but Russ Simmonds suggested it would do me very well.

So far, I have found it to be much cleaner burning than the double base 2520 (is this a mark of efficiency?) and the accuracy from the .308 seems the same....hopefully!!

It is supposed to be marginally slower than the 2520, but so far seems like a nice powder to use.

With a 26" barrel I am sure I could push the gun hard to shoot to 1000, but since I will only be doing that a few times a year, logic (and a chat with Russ) suggests I keep the stress/erosion down on the rifle and stick to producing best grouping out to 600...then pray at 900-1000...until I get a dedicated F/TR rifle that is.

I have also moved from 2520 to n140, mostly because I was finding 2520 very dirty in use, I suspect that the harder you drive it the cleaner it gets, but with rifles with barrels in the 21-25" range I am loath to waste powder just to get a cleaner burn, the N140 burns cleanly and gives me good accuracy with out any hassle, I have also heard the stories about the n5** range and erosion. PS I have always found the NRA a good source of 2520 in the past and Andy Allwood is good for the N140 and the Lovax version of 2520.

[bolt_action]

That is very interesting....

I am no expert, and have only been re-loading for just under a year.

My main interest is in F/TR, so although I currently have a rifle that wont cut it competitively, that is the direction I am heading in eventually.

Due to difficulty in obtaining Lovex DO73.6/Accurate 2520 (a Double base .308 orientated powder), and an interest in sorting out my .303, I have switched to N140, which is a single base powder, but apparently close to the burn rate of the accurate powder.

Until they started using the Vhit 5 series N140 was the fave of the F/TR lot.

All I can say is that My barrel is only 26" so it wont allow the sort of performance for competitive F/TR shooting (usually out t0 30" plus now) but Russ Simmonds suggested it would do me very well.

So far, I have found it to be much cleaner burning than the double base 2520 (is this a mark of efficiency?) and the accuracy from the .308 seems the same....hopefully!!

It is supposed to be marginally slower than the 2520, but so far seems like a nice powder to use.

With a 26" barrel I am sure I could push the gun hard to shoot to 1000, but since I will only be doing that a few times a year, logic (and a chat with Russ) suggests I keep the stress/erosion down on the rifle and stick to producing best grouping out to 600...then pray at 900-1000...until I get a dedicated F/TR rifle that is.

I use N140 too, and also have a 26" barrel. It does perform well at 1,000 yards but N550 gives a higher MV for the same chamber pressure. Your bullet needs to be above transonic speed at the target to stay stable, and you can work back from there to see what MV you need to achieve. For the 175gn Berger LRBT it's around 2,600fps. You can achieve this with N140 but you will exceed Viht's recommended maximum load of 41.4gn (!!obviously work up carefully and look for pressure signs!!).

[Parabuteo]

I use N140 too, and also have a 26" barrel. It does perform well at 1,000 yards but N550 gives a higher MV for the same chamber pressure. Your bullet needs to be above transonic speed at the target to stay stable, and you can work back from there to see what MV you need to achieve. For the 175gn Berger LRBT it's around 2,600fps. You can achieve this with N140 but you will exceed Viht's recommended maximum load of 41.4gn (!!obviously work up carefully and look for pressure signs!!).

Yes, I understand that, cheers

It is why our lot are running 30-32" barrels and driving Moly Coated VLDs like the clappers but...

I have a little 7.62x51 (yes...old) M67 Kongsberg target rifle that although it has a Mauser action, dont have a cat in hells chance of competing with the genuine F/TR boys .

I had the poor little thing running at 2859 on 46gr of Lovex, but then I thought what's the point?

Russ Suggested the N140 would be better for my barrel, and just to shoot whatever gave the best group.

It wont compete at 1000 within our lot, so I am going to learn what I can while I save up for my propper F/TR rig in a couple of years.

In the mean time, I need to understand everything I can re wind, plotting, the .308 etc.....so maybe a 5 year plan

This way I will have a sweet little rifle I can put the aperture sight back on and shoot with a sling...properly

And it needs to last a bit.

The Sightron scope will be a huge leap forward (and will go on the Dolphin Gun Company beast when I can afford it...if I am any good too).

Oddly I have some test 175s loaded ready to go, and have been briefed that teh Vhit figures are very conservative, but never the less I have still gone 10% low to start with.

The effects are broadly similar with the 155s in any event.

I have been told to stick with the 155s and just do my best to get them shooting well from my rifle....by a very reliable/experienced source....but I still fancy trying the 175s out of interest

In the mean time I will just concentrate un upsetting the apple cart with those using a like rifle

[bolt_action]

Yes, I understand that, cheers

It is why our lot are running 30-32" barrels and driving Moly Coated VLDs like the clappers but...

I have a little 7.62x51 (yes...old) M67 Kongsberg target rifle that although it has a Mauser action, dont have a cat in hells chance of competing with the genuine F/TR boys .

I had the poor little thing running at 2859 on 46gr of Lovex, but then I thought what's the point?

Russ Suggested the N140 would be better for my barrel, and just to shoot whatever gave the best group.

It wont compete at 1000 within our lot, so I am going to learn what I can while I save up for my propper F/TR rig in a couple of years.

In the mean time, I need to understand everything I can re wind, plotting, the .308 etc.....so maybe a 5 year plan

This way I will have a sweet little rifle I can put the aperture sight back on and shoot with a sling...properly

And it needs to last a bit.

The Sightron scope will be a huge leap forward (and will go on the Dolphin Gun Company beast when I can afford it...if I am any good too).

Oddly I have some test 175s loaded ready to go, and have been briefed that teh Vhit figures are very conservative, but never the less I have still gone 10% low to start with.

The effects are broadly similar with the 155s in any event.

I have been told to stick with the 155s and just do my best to get them shooting well from my rifle....by a very reliable/experienced source....but I still fancy trying the 175s out of interest

In the mean time I will just concentrate un upsetting the apple cart with those using a like rifle

Good luck with all that. My shooting is Practical oriented, i.e. we have to use high capacity magazines so can't adjust for bullet jump into the lands. That's why I use the tolerant LRBT instead of VLD.

If you haven't seen it already, I recommend Bryan Litz's book on Applied Ballistics for Long Range Shooting. It's a fantastic resource on everything from bullet choice to minimising the effects of wind etc.

[bolt_action]

A top gunsmith told me that the Vit 5** series double base powders wreak havoc on throats and erosion rate is far quicker than with single base. I would be looking at IMR4895 as a really good powder for 308 and it burns fully.

Yes I'm aware of the reputation it has for erosion, but to be honest I don't put that many rounds through the rifle so I'm not too concerned. Thanks for the tip on IMR, I will look at that next.

[NZ-Sika]

A top gunsmith told me that the Vit 5** series double base powders wreak havoc on throats and erosion rate is far quicker than with single base. I would be looking at IMR4895 as a really good powder for 308 and it burns fully.

I have personal experiance of using N560 and can that the 5 series powders massively accelerate throat erosion I have never used them since.

I have been told that it is all double base powders not just Vit N5xx but other double base powders such as RE17 that do the above.

[Ruger_shooter]

May I have the benefit of your collective wisdom on the importance (or otherwise) of combustion ending before the bullet exits the muzzle?

I use Quickload to predict the internal ballistics before working up a load, and I find that if I use the actual dimensions of my case and bullet instead of the figures in the database it agrees closely with reality.

For example, QL predicts an MV of 2578fps for 45gn N550 with 175gn Berger LRBT and I measured an average of 2555fps. It also says that only 96% of the powder is burnt before the the bullet exits the muzzle (the barrel is 26").

QL also predicts that I will get a very similar MV for 42gn of N540 for a slightly higher chamber pressure but with 100% of the powder burnt.

Given that my N550 load is giving me very good results at 1,000 yards, does it matter that not all the powder is burnt?

There is the answer to your question

[bolt_action]

There is the answer to your question

Ah yes, but I shoot against some competitive b*ggers and need every little advantage I can get!