308 How much do you back off when you see pressure signs?

[clearwater]

Have a new rifle and new brass so don't have much history to go on.

Brass is NT brand and holds 3 grains less of IMR 4895 than WW brass. Military brass, so I anticipated having to drop down a grain or two.

Nosler data for 168 BT, Nolser Brass, shows max at 43 grains, 2708 fps

When I hit 42 grains, 2590 fps (2 inch shorter barrel) I get hard bolt lift. No primer signs.
Gave MOA with Nosler seconds for 5 shots in this initial test. The groups had tightened as I increased the charge.

Ave Velocity went like this.

39 2382
39.5 2453
40 2504
40.5 2525
41 2529
41.5 2573
42 2590

I always learn something from this forum, so I thought I would ask.
What should I be considering when loading the next batch? Any rule of thumb for how much to drop back?

 

[DrMike]

When I see pressure signs with a given set of conditions as you describe, it would appear that half a grain would be sufficient to lower chamber pressure to safe levels. As the rifle gets broken in, you may see increased velocities with the same components. Also, anticipate that changing components (especially brass) may well yield increased velocity. The difference in velocity between the 42.0 grain charge and the 41.5 grain charge is insignificant in the field, so you're not losing much in terms of ballistics, but you would be dropping back to safer pressure limits.

 

[Guy Miner]

Agree with Dr Mike - you've got a good combination of components - 4895 is excellent in the 308 Win.

I'd probably drop back a full grain, but try Mike's recommendation of 1/2 grain. If it works well, run with it!

The 308 isn't tough to deal with. Pretty much a handloader's friend.

Guy

 

[TackDriver284]

Another thing to consider is that you are using new brass, once fireformed you may make more room for pressure to drop a bit, just a thought. Mike gave some good points as well.

 

[TXbaldhunter]

With a 168gr Nosler Ballistic Tip using IMR 4895,Win. brass,WLRM Primer,I'm loading 45.0grs of IMR 4895 at just over 2800fps tested in all three of my 308's.I've never seen any pressure signs with this load and all three rifles will group it around 1/2".If I would start to see signs of pressure on a 308 Win size case,I would back off at least one grain.

 

[ShadeTree]

My line of thought agrees with Guy and TX.......if I was getting noticeably hard bolt lift, I'd go back a grain. At the end of the day though Dr Mike has probably encountered that more times than I've sat down at a shooting bench. If he says 1/2 grain will do it, it likely will.

 

[clearwater]

I measure some fired, neck sized brass and got a 1 grain increase in volume with i4895.

Loaded some 1 grain and some 1/2 grain lower to try next time.