Barrel break in or temperature\pressure related velocity gain?

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"

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.

HSmithTX said:

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.

Click to expand...

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.

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.

HSmithTX said:

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.

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Thanks I've got a bit of time so I think I'll load .1gr increments down from 56.5 and see if there's a decent node there somewhere. 56 gr was not bad during optimal charge weight testing at right at MOA. I'd like to see velocities down around the 2840 mark and 56 gr avg velocity was 2828.

Powder charge weight has very little influence on accuracy. So shooting increments of 0.1 grain is a waste of time regarding an accurate load. Good shooting practice but no value for finding an accurate load. Most experienced reloaders would try 0.5 or 1.0 grain increments. Then there is the factor that small groups are just random chance. It takes about 30 shoots to get a valid accuracy for any load. The three shot group at 56.6 gr of 0.437 was random chance. That load is no more accurate than 56 or 55. Shoot the 56.6 again and see what you get. Or load up 30 at 56.6 and shoot ten three shot groups. That will tell you a lot about load testing. Best idea, read below first. A guy did what you are doing with three hunting rifles similar to yours.

Your bullet/powder combo is accurate in your rifle. So choose a safe charge weight that gives the velocity you want. Then you are done testing charge weights.

Read this for more info on charge weight effect on accuracy: https://www.msn.com/en-us/news/crim...S&cvid=9af54efac6ab4349d188fa53423798e0&ei=51

"This was my grandmothers rifle"

fruitnut said:

Powder charge weight has very little influence on accuracy. So shooting increments of 0.1 grain is a waste of time regarding an accurate load. Good shooting practice but no value for finding an accurate load. Most experienced reloaders would try 0.5 or 1.0 grain increments. Then there is the factor that small groups are just random chance. It takes about 30 shoots to get a valid accuracy for any load. The three shot group at 56.6 gr of 0.437 was random chance. That load is no more accurate than 56 or 55. Shoot the 56.6 again and see what you get. Or load up 30 at 56.6 and shoot ten three shot groups. That will tell you a lot about load testing. Best idea, read below first. A guy did what you are doing with three hunting rifles similar to yours.

Your bullet/powder combo is accurate in your rifle. So choose a safe charge weight that gives the velocity you want. Then you are done testing charge weights.

Read this for more info on charge weight effect on accuracy: https://www.msn.com/en-us/news/crim...S&cvid=9af54efac6ab4349d188fa53423798e0&ei=51

Click to expand...

After I zeroed at 2.75" over at 100 yds I did test for repeatability with 56.6 gr charge weight and shot 0.616 3 shot grp. Then to verify my 2.75" over at 100 I shot a 5 shot grp that I just measured at .968 before moving on to the 300yd drop test. I attributed the increase in grp sizes partly to my scouting about 7 miles a day at > 5,500' elevation so I didn't feel as steady as last year when I didn't draw a tag (I'm 63yrs old). My charge weight test was in .5 gr increments and then I fine tuned from there with the 56.6 being about 50% improvement over the 56.5 grp at 0.895. I believe barrel harmonics play a big role in accuracy (outside the shooter) with seating dept coming in second. Harmonics are directly related to the size of the source of the energy that creates the harmonics which to me translates to charge weight, powder burn rate, and projectile weight interacting with the physical aspects of the barrel I.E. bore, length, contour, number of grooves, and twist rate. As far as random chance when shooting goes a shooter is much more likely to be the source of random results by not being consistent in point of aim at trigger break and a myriad of things shooters do to compromise accuracy. The load and the mechanics of the rifle can be reduced to load consistency and then physics which is very repeatable if the nut pulling the trigger does his job.

When doing charge weight testing on my 300wm with two different powders and same projectile with 6 charge weights 3 shot grps per powder (I believe .6 gr increments) 7 out of 12 where < 0.810' grps which I attribute to research on load data as it relates to all mentioned above. The probability that random results produced these results is .417 with 1.0 being a certainty.

Harmonics and nodes are artifacts produced by reliance on 3-5 shot groups. Did you read the link? It would be worth your time.

Good luck with your hunt. If nothing else all that exercise is great for your health.

What I've experienced is a thinner hunting profile barrel will only hold the first couple shots close together before heat effects the group. I test two shots at a time, (two shots in a minute) allowing the barrel to completely cool between groups. I select the recipe that prints the smallest two shot group that still meets my desired velocity. I go out on different days and fire the two shots and keep a record how they perform. I zero the gun to the first shot POI. Easy way to look at it, I want a gun that puts those first two on orange 1" dot at 100yds.

This highly contrasted to my 25 shot groups out of my MTU profile range guns.

Brathany said:

What I've experienced is a thinner hunting profile barrel will only hold the first couple shots close together before heat effects the group. I test two shots at a time, (two shots in a minute) allowing the barrel to completely cool between groups. I select the recipe that prints the smallest two shot group that still meets my desired velocity. I go out on different days and fire the two shots and keep a record how they perform. I zero the gun to the first shot POI. Easy way to look at it, I want a gun that puts those first two on orange 1" dot at 100yds.

This highly contrasted to my 25 shot groups out of my MTU profile range guns.

Click to expand...

No doubt about the heat effect on this sporter barrel. When doing my OCW tests I allow the barrel to cool completely between shots so I plan for a cold day ~ 35 F to test on to minimize cool down wait times. (Also simulates avg temp I typically hunt in). This particular day the temp was ~45F and since I already knew this charge weight, bullet, and seating dept where accurate I wasn't as patient on letting the barrel cool. This could explain the .616 3 shot repeatability test grp vs .437 OCW 3 shot grp.
This heat effect really became apparent when shooting out to 300 yds when I shot a five shot grp with only a minute or two between rounds (See attached target note image loaded upside down for some reason). The first two (cold barrel) went into 0.296' and only dropped ~1.5" with POA at center of bullseye. I couldn't even find them with my spotting scope because they shouldn't have been in the orange (bullseye on this target is 3") or that close together. The next one hit more where I expected elevation wise at about 2.6" low and to the right (A bit of pull on my part I believe) On shots 4&5 the heat started to have an affect along with that I noticed about a 5-7 breeze(Wind drift for this Speer bullet is suspect) out of the right on the last 2 which grouped at 0.529 about 3" higher than the average of the first 3 shots which grouped at 2.05"
Note: the five shot grp I used CCI #34 primers and the subsequent 3 shot grp Fed 210 primers. I had read that the #34 primers where "hot" and could produce higher pressures so I compared them to a standard large rifle primer the 210 at 100 and 300 yds. The 34's where hotter with about 25 fps higher velocities and the two were similar accuracy wise. The 34's did produce better SD and ES over the 210's with the 34's averaging about 10.2 SD and the 210's about 17 SD.
This demonstrates and reinforces why developing a highly accurate load even for hunting applications is very important. If this load was 1 MOA instead of .5 MOA at 100 the hot barrel shots spread would have potentially doubled from 3.5" to 7" and opening the possibility of a wounded animal and miles of tracking with shots at this range. I get the first two where deadly accurate and no follow up shots would have been needed. However, I like the peace of mind when taking a shot at game that barring a screw up on my part the shot is going to find the kill zone no matter what reasonable scenarios might unfold out to maximum yardage which for this rifle is 300yds.