308Win, IMR4064, 155LS question

[wapiti25]

You might look for some thinner brass (larger volumne). A full case/slight compression has work well for me. I would work up and shoot first you may not have any problem.

 

[Bart B.]

Don't forget palma uses some serious hot loads too. Just too push the 155s to 3000fps.

As one of the 5 or 6 people who developed loads for the US Palma Team rifles using prototypes of Sierra's new 155-gr. bullet back in 1991, we pretty much duplicated load data for 150-gr. bullets with all sorts of powders to see what shot the most accurate. These loads developed about 52,000 CUP (61,000 PSI) which are SAAMI specs for the .308. The load selected was 45.3 gr. of IMR4895 with a Fed. 210M primer. Check that out against published loads listing pressure it had in their barrels. In my 30" barrel, they left at 3015 fps chrono'd at 15 feet. We later used about 46 grains of Varget under the 155's.

No serious competitor uses serious hot loads; they're not all that accurate.

M80 7.62 NATO ball ammo's 147-gr. bullets leave 30" Palma barrels at the same speed. The Brits were the first to use that ammo in serious competition back in the '50's. They had to use 30" long barrels to shoot those bullets fast enough to keep them supersonic through 1000 yards. It wasn't until the 1990's that US Palma rifle shooters using 155's had 30" barrels. With the 172's through 200's used before then, a 26" barrel was good enough.

 

[jbell]

Thanks Bart good info. I am not trying to make a load for book max but I do like to initially find out where I start to see pressure in a given bullet / powder combo just so I know. I don't chase velocity but there is a velocity I need to be able to meet to do what I need to do.

 

[jbell]

2500 feet below sea level?

Yes, one of the spots where I shoot is at 250' ASL and in the winter it can be down to -10f. We usually will not shoot much colder than the single digits on the plus side of the thermometer. The pressure can be between 29.7 - 30.3 in.hg. That makes for some pretty thick air and will test a load fast...

 

[Dans40X]

47gr of Dupont IMR 4064 or VV N135 will fit w/o a drop tube or issue in Rem URBR brass w/ a 155 MK seated atop.
I've toasted a couple barrels w/ the load for 1K prone use.

 

[jbell]

Dan thank you. Did these barrels have a long throat / freebore?

 

[Dans40X]

No,
7.62 NATO chamber throated for 155 MK's pushed thru 27.25" 1:10"twist cut rifled Bbls.
Fwd end of BT @ wheelbase seated to neck/shoulder junction.

Early production Rem URBR brass was produced w/.062"ish diameter flash holes.
Late production URBR small pocket brass was produced w/.078" diameter flash holes.

I never experienced ignition problems w/ the .078" flash hole URBR brass,the .062" had issues igniting 45+gr of extruded powder.