6.5 CM Load with Viht N555

[urban]

Another newbie question...

I am preparing my first load. I have Viht N555 because it was available and specifically designed for 6.5 CM. Bullets are Berger Classic Hunter 135g. I can't find a load for this exact bullet. It seems that N555 is quite new so there are limited number of published loads.

Vihtavuori publish a load for Hornady A-TIP 135g - starting 39.5

Loads for slightly larger bullets:
Lapua Scenar 136g - starting 40.1
Fox Bullets Classic Hunter 139g - starting 40.4

Given my understanding that a load for a heavier bullet is generally safe for a lighter bullet ("...if you can't find a charge for the exact weight bullet you have selected, use the data for the next heavier bullet...") - can I safely use the starting load for the Hornady A-TIP and work up carefully from there? Or should I start half a grain lighter?

Cases are Starline. Primers are magtech large rifle.

Load data

 

[paul o']

starline brass. Nosler 130 GR RDF

 

[ChesterP]

I've got the same powder and have been working up loads for calibration using GRT but for the 140gr SST. I've calibrated the powder chart for RS62 actual results, then calculated the equivalent charge using large rifle primers to achieve what I'm getting with small rifle magnum primers. The model shows the correlation with my MV's to have LR primers needing a 1.2gr lower charge than with the SR primers which from actual testing seems spot on.

I've taken that correlation as a good place to start with the model for the only case it offers (LR primer cases) and it's come out for my 24 inch barrel (1/8) with a suggested OBT charge of 42.1gr N555 (LR brass) or if using SR primers, you may find the equivalent load to be around 43.3gr N555. MV's are circa 2,700fps for this load.

Be careful with the Fox bullet data as it won't correlate well between LF bullets and jacketed lead bullets. LF typically have a longer bullet wall (length) therefore swaging pressures, hence PMax tends to be slightly higher for similar given weights and velocities. However for your 136gr Scenar load I'd recommend a starting load of 41gr and work up. GRT shows (for my brass) a decent load at 42.8gr N555 with LR brass but please bear in mind this is for a cart H20 vol of 52.4gr water. If you confirm your case volume and intended OAL, your barrel length and twist, I'd be happy to re-run, but you should find a decent (and safe) load between 41 and 43gr.

 

[urban]

@ChesterP thanks for the offer.

I'm working on a load for the Berger Classic Hunter 135gr, not the Lapua.

Case volume is 51.9 gr water. I was going to load to 71.0mm OAL (Berger's recommendation for this bullet). Barrel is 24.3 inch 1:8 twist.

 

[jcampbellsmith]

Spookily, I was testing N555, with Sierra 130 TMKs, new Starline brass and Fed 210M primers last week. I loaded up 3 rounds from 41.8 gr to 42.8 gr in 0.2 gr increments and achieved the following results at 200 yds. Your noted load of 39.5 gr using a Hornady A-TIP 135gr would I think could be a good starting point for you. I've picked 42.1 gr as a likely powder weight for my rifle and will load some more up tomorrow morning.
Regards
JCS

 

[scotch_egg]

That’s a nice 200 yard group. You must be happy with the new barrel.

 

[jcampbellsmith]

That’s a nice 200 yard group. You must be happy with the new barrel.

Yes, Andy Massingham has done a great job. Shot 14 was an error on my part.
Thanks
JCS

 

[ChesterP]

@ChesterP thanks for the offer.

I'm working on a load for the Berger Classic Hunter 135gr, not the Lapua.

Case volume is 51.9 gr water. I was going to load to 71.0mm OAL (Berger's recommendation for this bullet). Barrel is 24.3 inch 1:8 twist.

I've run the model for you:

Several nodes identified as follows, all at a COL of 2.874":

43.53gr/2,785fps/55,000psi (recommended max node)
42.4gr/2,710fps/50,280psi;
41.8gr/2,672fps/48,006psi.

 

[jcampbellsmith]

I've run the model for you:

Several nodes identified as follows, all at a COL of 2.874":

43.53gr/2,785fps/55,000psi (recommended max node)
42.4gr/2,710fps/50,280psi;
41.8gr/2,672fps/48,006psi.

Very interesting. The batch I've just loaded using 130 TMKs is COL of 2.847 and 42.1gr of N555 is estimated to give me 2698 fps.
Thanks
JCS

 

[ChesterP]

Could be the difference is due to barrel length differences and case volume JCS? It only takes a slight difference in case volume to make quite a pressure difference. Also the 42.1 load on a 130 I'd guess would give lower MV's than a slightly higher load for a slightly heavier bullet (135).

 

[Ronin]

Yes, Andy Massingham has done a great job. Shot 14 was an error on my part.
Thanks
JCS

Thank you John

A pleasure as always

 

[jcampbellsmith]

Could be the difference is due to barrel length differences and case volume JCS? It only takes a slight difference in case volume to make quite a pressure difference. Also the 42.1 load on a 130 I'd guess would give lower MV's than a slightly higher load for a slightly heavier bullet (135).

Yes, there will be lots of differences to factor in. I'm pleased that my numbers are in the same ball park.
Thanks
John