.308 Sub-Sonic with VV N32C & Lapua 200gr Sub FMJBT Bullets

[UK_Mike]

Hi Guys
I am in need of a little help and guidance on starting a load development for a .308 sub-sonic round. All the info I have managed to obtain relates to Trail Boss and the most suitable power for this. As I live in London England and were up until recently part of the EU who decided that certain powders were bad for our health and banned them from sale, this included Trail Boss amongst a myriad of other powders you guys use and recommend.

After some additional searching I found a power made by VV, it is N32C and it has the same characteristics and burn rate as TB, but not quiet the same call fill properties, its said to be around 70% the volume of TB for same weight.

As I have no experience of TB nor N32C, I was hoping someone has some limited experience with N32, I am looking for a starting load for my .308 and aiming for 1050fps.

As the range I use is part of the UK National shooting center the rules are quiet srict of load development, I once I have a load range, I need to gauge point of impact drop at 100yds. If I am to far off on my initial shots they wont be happy and may ask me to leave and never return.

We have very limited range opptunities here and this is far and away the best, we can shoot out from 25 - 1200yds.

I will be using Lapua 200gr Subsonic bullets (4PL7060) and my rifle is a Rem 700 Police with 26" barrel and 1:10 twist. I have found that the Lapua bullets are slightly slimmer than what I am currently loading (168gr SMK HPBT) and additional neck tension is required on te cases.

My cases are once fired Federal brass which were fire formed in the rifle I will use the load in, I plan to neck size only using my Lee press and neck size die.

Based on teh powder being mainly european, I may be hoping for a lot but deffinatly worth a try, I appreciate the time you have taken to read this post and hope someone is able to point me in the right direction.

 

[csjavi]

I'm running 11.5 grains of N32C in a Sako case with a COAL of 2.83". It gives me about 1020 fps @ 0 C from an 18.5" 1:10 Remington 788. POI drops about 15" @100 m compared to most normal rounds. As per usual reloading development process for subsonics, you should start with more powder (say around 13 grains) and work your way down.

 

[UK_Mike]

Thank you for your comments, I have done some initial loads of N32C based on some research. The loads are 14 to 11 in 0.5 increments.
I am using fire formed federal brass which was neck sized only. I am using 200gr Lapua Subsonic bullets (4PL7060) and CCI 200 primers.

I am using a REM 700 Police 26" barrel 1:10 twist.

I am loading based on CBTO and not COL, with the bullet into lans my length was 2.428 so wanted to load CBTO at 2.400, but due to mag restrictions I have loaded to 2.310. The COL ranged from 2.79 to 2.83.

I have range time booked for next and hopefully will get some good data and end up with a load close to 1050fps. I was very interested in the POI shift at 100m, I had no idea of what to expect and this info has really helped me gauge what to expect.

 

[csjavi]

Thank you for your comments, I have done some initial loads of N32C based on some research. The loads are 14 to 11 in 0.5 increments.
I am using fire formed federal brass which was neck sized only. I am using 200gr Lapua Subsonic bullets (4PL7060) and CCI 200 primers.

I am using a REM 700 Police 26" barrel 1:10 twist.

I am loading based on CBTO and not COL, with the bullet into lans my length was 2.428 so wanted to load CBTO at 2.400, but due to mag restrictions I have loaded to 2.310. The COL ranged from 2.79 to 2.83.

I have range time booked for next and hopefully will get some good data and end up with a load close to 1050fps. I was very interested in the POI shift at 100m, I had no idea of what to expect and this info has really helped me gauge what to expect.

Sounds reasonable. Remember to shoot first without the suppressor just to check that the bullets stabilize. They should, but it would suck to hit the baffles.

 

[UK_Mike]

Sounds reasonable. Remember to shoot first without the suppressor just to check that the bullets stabilize. They should, but it would suck to hit the baffles.

Thanks for advise, I have read about some issues with baffle strike and bullets stuck halfway down the barrel. Not a good situation.

 

[UK_Mike]

Sounds reasonable. Remember to shoot first without the suppressor just to check that the bullets stabilize. They should, but it would suck to hit the baffles.

Completed phase one testing, found a good starting load using N32C and 200g Lapua Subsonic Bullets, thanks for advise

Charge Shot Speed Average of 3 shots
14g 1 1266 ft/s 1272 ft/s
14g 2 1270 ft/s
14g 3 1282 ft/s
13.5g 4 1234 ft/s 1220 ft/s
13.5g 5 1212 ft/s
13.5g 6 1216 ft/s
13g 7 1192 ft/s 1187 ft/s
13g 8 1185 ft/s
13g 9 1186 ft/s
12.5g 13 1061 ft/s 1081 ft/s
12.5g 14 1100 ft/s
12.5g 15 1083 ft/s
12g 16 1021 ft/s 1015 ft/s
12g 17 1022 ft/s
12g 18 1002 ft/s
11.5g 19 923 ft/s 950 ft/s
11.5g 20 957 ft/s
11.5g 21 971 ft/s