VV N135 speed/pressure/velocity?

[BringBackThe80s]

Has anyone else found pressure versus velocity discrepancies with Vihtavouri's listed loads for N135?

I have been working on loads for Barnes 130TTSX and 175LRX (a bit heavy, but I had a good number on hand). I don't have a chronograph at the moment, but I have chrono'd a bunch of those bullets with other powders and have parameters in Gordon's Reloading Tool dialed so it consistently predicts my rifle's velocities and nodes within 10-25 fps.

Burn rate charts list N135 next to H4895/IMR4895 and just a bit slower than Varget, so a great zone to fill a 308 case and achieve 100% burn. However, the max loads in Vihtavouri's manual are all listed with charges weights 2-4 graines less than, velocities well below, equivalent powders in other manuals (e.g., ~200fps less than 4895 and Varget in the Barnes and Hodgdon manuals, etc.). That makes it look like Vihtavouri was just very, very conservative on pressure.

But then I plugged those loads in Gordon's Reloading Tool, and using default values for cartridge, bullets, and powder, it predicts VV's listed max loads would produce velocities exceeding 4895 and Varget, but with pressure exceeding SAAMI by several thousand PSI--despite being a lot lower charge weights! That could make it look like N135 has a much faster burn rate than burn rate charts suggest. However...

When I adjusted the bullets' Initial Pressure to the same value that consistently trues up velocities yielded by other powders (750psi), GRT predicts N135 velocities in between: ~100fps above VV's manual and 100fps below velocities listed (and shot) with equivalent powders. When I used OBT function to adjust the powder's values to produce book velocities, GRT predicts that VV's listed max loads will produce pressures in the mid-40k's.

So, is VV's manual just hyper-conservative with pressure, staying 25% below max when they could safely top out 200fps higher? Or do VV's max charge weights reflect pressures nearing 60000psi, indicating N135's burn rate is faster than generally thought?

For those who have used N135, did VV's manual reasonably predict the velocities you got (after adjusting for barrel length)?

 

[divingin]

Chart that I've got (no idea where it originated, but has a date of Feb 2024) has N135 listed as #102 (slower than IMR4895 at #101, N540 at #100, and IMR4895 at #99; and just just faster than RL12 at #103, Acc 2495 at #104, IMR 4166 at #105, and IMR 4064 at #106.)

Varget is listed at 113.

I haven't used much N135; I generally go for N133 and LT-32 for shooting light 6BR bullets, and RL15, Varget, or N140 for heavies. I also just use the manual for reference to get a load range, rather than for expected results.

 

[CJ6]

Manuals = Guides not absolutes.

 

[HandgunHTR]

Book pressures and velocities are based solely on the pressure barrel used for testing by that manufacturer, and are only a predictor of what you may see in your barrel.
The only way to truly know how your barrel is going to behave is to work up your loads using the old tried and true, start low and work up.
Also, without a chronograph, unless you plan to shoot at various yardages and do the math, you are just guessing.

 

[Doom]

I can't comment on any 6 mm data but VV recently posted new data for N135 (2024 Manual) for 308 and the max charge dropped to (40.1gn, 2569fps) from (42.1gn, 2697fps) for the 168SMK. I quizzed them about a change in the powder and got a response to use the new data. My lot is from 2015 and I don't remember the speed but I think it was around 2500 fps with 40.9 gn. That with a 20" barrel.

I agree something is amiss with either the data or the powder. I was about to order some more but with the new data I don't think it will do what I want in 308. I use it 223 also with 52 Berger Target bullets.

 

[jelenko]

My load for a 69 grain sierra in a 24" barrel [on an AR15] is 2970 fps at 24.0 grains of 135 with 53.6K PSI .

VV's book max [in a 25" barrel] shows 2871 at 23.8 grains of 135.

=> I'm seeing 100 fps more with a little more powder but an inch shorter barrel.

 

[BringBackThe80s]

Also, without a chronograph, unless you plan to shoot at various yardages and do the math, you are just guessing.

I agree on the chronograph. I'll replace it when possible.

As far as load development, yes, I always start low and work up. I did shoot N135 from min to max with no sign of pressure, but if the velocities match the VV manual, it seems like there should be a lot more space to go higher. But I'm hesitant to go beyond book max without a chrono to clue me in if velocities indicate excess pressure

Book pressures and velocities are based solely on the pressure barrel used for testing by that manufacturer, and are only a predictor of what you may see in your barrel.
The only way to truly know how your barrel is going to behave is to work up your loads using the old tried and true, start low and work up.

Agreed, but usually Hodgdon, Hornady, etc. list max velocities that do correspond decently with max SAAMI pressure predictions, even if a greater or lesser amount of powder is needed to hit that velocity due to differences in a particular barrel, cartridge/case, and bullet combination.

Here, though, the *velocities* (not just the charge weights) listed by Vihtavouri seem completely incompatible with SAAMI pressure limits, or even Europe's lower C.I.P. limits, unless N135 has a burn rate much more like 4198 instead of 4895.

 

[BringBackThe80s]

My load for a 69 grain sierra in a 24" barrel [on an AR15] is 2970 fps at 24.0 grains of 135 with 53.6K PSI .

VV's book max [in a 25" barrel] shows 2871 at 23.8 grains of 135.

=> I'm seeing 100 fps more with a little more powder but an inch shorter barrel.

That's fairly consistent with the discrepancies I am seeing between the VV manual and simulations. The max charge weights in the book are not far off of predicted charges to hit max pressure. But the listed velocities for those charge weights are ~200fps lower in the book compared to simulations.

I suppose that would make for a lot of happy customers if they universally see their velocity results--even with a shorter barrell--beating out Vihtavouri's velocities in the manual.

 

[Jeff Porter]

My work with N135 and other VV powder shows the published data to be very lawyer proof. I always get best results above the listed maximum.

 

[KMW 1954]

Need to follow this.

 

[Doom]

My load for a 69 grain sierra in a 24" barrel [on an AR15] is 2970 fps at 24.0 grains of 135 with 53.6K PSI .

VV's book max [in a 25" barrel] shows 2871 at 23.8 grains of 135.

=> I'm seeing 100 fps more with a little more powder but an inch shorter barrel.

I checked the 223 52 Berger data and a 25.4 gn load chronographed at 3307 fps in Lapua brass out of a 26" Rem 700 (2015 N135)

The 2023 data max was 26.1 gn at 3402 fps with Lapua Brass at 2.26 COAL. I loaded that and if memory served me right it chronographed at 333x as I remember. It was a compressed load but did show pressure but tended to push the bullet out.

 

[HandgunHTR]

That's fairly consistent with the discrepancies I am seeing between the VV manual and simulations. The max charge weights in the book are not far off of predicted charges to hit max pressure. But the listed velocities for those charge weights are ~200fps lower in the book compared to simulations.

I suppose that would make for a lot of happy customers if they universally see their velocity results--even with a shorter barrell--beating out Vihtavouri's velocities in the manual.

Maybe they get all their test barrels from Sako/Tikka who have a reputation for slow barrels.

 

[Webster]

Has anyone else found pressure versus velocity discrepancies with Vihtavouri's listed loads for N135?

I have been working on loads for Barnes 130TTSX and 175LRX (a bit heavy, but I had a good number on hand). I don't have a chronograph at the moment, but I have chrono'd a bunch of those bullets with other powders and have parameters in Gordon's Reloading Tool dialed so it consistently predicts my rifle's velocities and nodes within 10-25 fps.

Burn rate charts list N135 next to H4895/IMR4895 and just a bit slower than Varget, so a great zone to fill a 308 case and achieve 100% burn. However, the max loads in Vihtavouri's manual are all listed with charges weights 2-4 graines less than, velocities well below, equivalent powders in other manuals (e.g., ~200fps less than 4895 and Varget in the Barnes and Hodgdon manuals, etc.). That makes it look like Vihtavouri was just very, very conservative on pressure.

But then I plugged those loads in Gordon's Reloading Tool, and using default values for cartridge, bullets, and powder, it predicts VV's listed max loads would produce velocities exceeding 4895 and Varget, but with pressure exceeding SAAMI by several thousand PSI--despite being a lot lower charge weights! That could make it look like N135 has a much faster burn rate than burn rate charts suggest. However...

When I adjusted the bullets' Initial Pressure to the same value that consistently trues up velocities yielded by other powders (750psi), GRT predicts N135 velocities in between: ~100fps above VV's manual and 100fps below velocities listed (and shot) with equivalent powders. When I used OBT function to adjust the powder's values to produce book velocities, GRT predicts that VV's listed max loads will produce pressures in the mid-40k's.

So, is VV's manual just hyper-conservative with pressure, staying 25% below max when they could safely top out 200fps higher? Or do VV's max charge weights reflect pressures nearing 60000psi, indicating N135's burn rate is faster than generally thought?

For those who have used N135, did VV's manual reasonably predict the velocities you got (after adjusting for barrel length)?

I don't trust computer programs. I just shoot for small groups without signs of pressure. I trust the manuals as a guide if you use common sense. A load either shoots small or it doesn't. The targets tell the truth.

 

[Murray Brook]

I've used quite a bit of N-135 in my 6BR. Looking at my notes I would say that the amount of powder ( max load) lines up fairly good with Vit load date but the Vit velocity is any where from 50 to 75 ft/sec below what my velocity was.

 

[jpjulian]

VV N-135 seems faster than IMR4895 in my .308 loads for my M1A, definitely not slower. With 168 MK's I just have not been able to get function right with 135 where 4895 works like a charm as for decades. N-135 seems just a hair too fast.

 

[HTSmith]

Maybe @Laurie will chime in. He knows a lot about this.

 

[RegionRat]

Here is a way to look at how N135 compares to H4895. Here are the default models for the GRT code.

And here are the QL models


I realize lots of folks want very simple one or two term descriptions, but mother nature is a bitch and demands her dues. It takes at least all of the above to simplify a powder behavior, and some of us would argue the above fall short. YMMV

 

[Laurie]

Maybe @Laurie will chime in. He knows a lot about this.

https://www.targetshooter.co.uk/?p=3934

N135 (and others) compared to H4895 in 223 with the 77gn SMK. Note a long freebore chamber allows higher loads than those in reloading manuals.

 

[Murray Brook]

Just checked my 6mm ppc usa data against the data on the Vit site using N-133 with the 70 gr Sierra. Same as the N-135 data. Max loads line up but the velocity is appx 100 ft/sec lower. Vit uses a 23" barrel for their testing. My barrel is 24".