Barrel break in or temperature\pressure related velocity gain?

[tomcat818]

Hello LRH! been reading since I started reloading about 1.5 yrs ago but this is my first post.
Rifle:
68' 270 WIN model 700 22" barrel
Load:
56.6 gr H4831-SC
Speer 150 BTSP
CCI #34
Nosler Premium 2x and 3x fired
CBTO: 2.882
COAL: 3.361
Initial Velocity: 2837 avg
SD: 10.2
ES: 15.5
Case fill: ~98%
This was my grandmothers rifle and she only hunted with it once. When I inherited it there were maybe a dozen rounds thru it. About 5 yrs ago I slapped a VX II 4-12 on it was very picky about factory ammo with the best grp being 1.25". Fast forward to a year ago and I've now developed a load for my 300WM and so the 270 is next. Using the Eric Cortina method of finding the jams and having a hand loaded round my grandfather loaded for the rifle in ~ 1970 (can you say pack rat). I seated the Speer BTSP .035" off the lands (mainly to keep bearing surface contact at > .25") which was withing .010 of my grandfathers load which used a 150gr bullet only flat based. (most likely a Speer Hot Core or Nosler partition) Then I loaded up an optimal charge weight test using of six charge weights 55.5, 56.0, 56.5, 57.0, and 57.5 (Speer max for bullet). 56.5 3 shot grp was best @ 0.694" 57.0 .910 strung vertically both with very faint ejector\plunger marks but no heavy bolt and primers almost pancaked. Velocity for 57.5 dropped slightly so I figured that was showing overbore charge weight signs and there was a half groove from the plunger impact. I decided to do a .1 incremental from 56.5 at the same seating dept 56.6, 56.7, 56.8. 56.6. The 56.6 charge weight produced a .437 3 shot grp @ 102 yds wow!!
This brings me to today where I loaded the same load with a .002 shoulder bump to zero at MPBR to use the rifle for deer this season. Last year when I shot the charge weight test the average temp was ~ 36 F and today it was 52 F. My avg velocity for 10 shots using 1x fired brass was 2858 with a low of 2844
SD: 10.2 same as before ES: 16.1. with the 2x fired brass 9 shots CCI primers averaging 2871. It's been hot here in E. Oregon and will continue to be for at least the start of deer season so my concern is I'm pushing it on max pressure in above average heat (forecast near 80 first 2 days of season). Can someone run the numbers for this load and tell me where I'm at pressure wise? Since this rifle barrel is still breaking in(only 90 rounds) could the velocity be the result of this? Since I've heard H4831-SC is very temp stable powder I'm leaning toward barrel break in for the increase but would be nice to know what the software says the pressures are.
Side note: I think the BC Speer shows for this bullet is low considering the MPBR calculator (Hornady) called for 3" over at 100 for a drop of 3.2" at 300yds. I sighted it at 2.75 over at 100 and shot three 3 shot grps which average 2.71" drop at 300 with average group size of 2.05". I should have pulled this rifle out of the safe a long time ago she's a shooter.
Sorry about the length rookie mistake however in reloading as in life "The devils in the details"

 

[HSmithTX]

I think you will be fine with the H4831, 50 to 80 degrees isn't a big change for that powder in a 270-280-30'06. It is shooting superbly for a factory rifle, I'd be inclined to roll with it. I don't have software to do the pressure calculations you have asked for, but what is the velocity for the max charge in the load data and how long is the barrel they tested? If you are at or over that velocity chances are really good you will be running at or over max pressure. I would still be inclined to go hunt as is.

 

[tomcat818]

I think you will be fine with the H4831, 50 to 80 degrees isn't a big change for that powder in a 270-280-30'06. It is shooting superbly for a factory rifle, I'd be inclined to roll with it. I don't have software to do the pressure calculations you have asked for, but what is the velocity for the max charge in the load data and how long is the barrel they tested? If you are at or over that velocity chances are really good you will be running at or over max pressure. I would still be inclined to go hunt as is.

Speer shows 24" test barrel with 57.5 gr going 2860 so my average is just below that now at 2857. Considering I used the exact same component batches, load parameters, and testing at the same range my expectations were for velocities fairly close to the 2837 avg I had initially. The only thing different this time is I bought a bore scope and used ISSO instead of old #9 and it removed all the carbon\lead in the grooves
Really the only thing making sense to me is the barrel is fast and is breaking in and maybe the deep cleaning helped facilitate this.

Appreciate the response. I've learned a lot from this forum during my short time reloading and its saved me a bunch of time and components. Eventually I can pass on my knowledge to someone else in need of advice.

 

[HSmithTX]

Based on that info I don't think you are wildly over pressure, I think you are pushing the upper limit pretty hard and a bit more based on my guess that you lose about 20fps per inch in a 270, your barrel being 22 and the data being in a 24. If it were me and my season is starting soon I'd load a handful and go.