Two weeks ago I tested a batch of hand loads in a 270, using 59.5gr of 4831sc and varying the jump. At 0.1, 0.3, and 0.4" groups were sub-moa, with 0.4 being the best (0.7 moa) Fast forward two weeks. I neck sized the brass from the last session and loaded about 20 to mimic that best group, with 0.4" jump. Those rounds loaded to jump 0.4 were well over an inch, at the next range visit.

I feel like the shooter and gun were proven with the first session. What direction would you go to figure this out?

Perfectly normal in my experience. I quit trying to figure it out years ago.

What kind of rifle, and has it been tuned up re trigger and bedding?

You say you neck sized the brass for the newer batch. Was the first batch neck sized? Also, what kind of die did you use to neck size? The "regular" type neck sizers don't always produce the straightest sized brass.

Do you know the runout of the assembled cartridges for both batches?

When the first batch was "proven," how many shots were in the groups, and how many groups did you shoot? Small sample sizes don't prove much.

Everything done for the first trip that produced good results was repeated. Rifle is an M77. Trigger could use work but it did ok on the first trip. Obviously I know what is imperfect about the setup, but those things were imperfect the first trip, too. That's my confusion. Maybe I'm thinking about it wrong.

Lee collet neck sizer used, btw. 3 shot groups, but with multiple such groups doing so well, I see it as statistically significant. What I mean is that, if I'd shot all 4 3-shot groups at one bull, there'd have been a 12-shot 1ish moa group. I am starting to put more doubt into this part, though.

On runout, I can only say it should've been similar for both data sets. Weather was similar both days.

If you shoot enough groups with a rifle that really does average 1 MOA, you will see groups 1/4 MOA on either side of that with regularity. This is particularly true if it's not a rifle with a light, consistent trigger, a stock designed to ride the bags, et cetera.

Ya seem pretty sure that things were the same from session to session so I'd have to guess maybe a paralax problem? If you've got a scope with an adjustable objective, is it possible the setting was changed between now and then?

A 1/4 moa problem can be difficult (if not almost impossible) to find sometimes!

I appreciate your input, gentlemen.

Let us know if ya figure it out! You've tweaked my curiosity!

Friend, no more than I get to shoot, it may be awhile before I solve this problem. A few years into this hobby and I'm definitely making more questions than answers. Frustrating, especially when you think you've finally broken through.

I'm starting to wonder if the way I was holding the rifle is the culprit. This is really the only thing that I consciously recalled being different. At the time I didn't think it'd make a dern. I was using sandbags both times, but, on the second trip, the way the bench was sized, it was easier (and noticeably more stable) for me to not have my forward hand holding the forearm.

I've often read that this can be an issue with lighter rifles. My complaint about this gun has always been that it is way too heavy, so I figured I was in the clear. Is the theory that recoil adjusts POA in the millisecond before the bullet leaves the barrel, and perhaps this is more pronounced on lighter rifles, understandably so?

Turk, I'm sure you found it. Something as small as an inch or two difference in the location of the bag on the fore stock can make all the difference, let alone hand holding/not holding the fore stock. Remember to make one difference only when shooting/loading ect. as well as some days you can shoot, some not. Good Luck-Muddy

That can sure make a difference! If your gonna do serious load testing you'll have to get your bench technique down to a science so you can concentrate on the loads instead of everything else. Eliminate variables as much as possible. Get yourself a descent front rest, get comfortable with it. Make sure the sling stud on the front of the stock isn't hitting and (for lack of a better word) bouncing around the rifle. Every shooter is different but I preferred to use free recoil for all my load testing. Get yourself a descent back bag also! Don't rely on the ranges canvas sand bags. Get your own setup and get real comfortable with it.

Your cheek weld can also make a difference and cause small parallax errors if you mount the rifle different each time you test a group. You can test parallax by mounting the gun as normal, watch the crosshairs and the bullseye. slowly move your head around and if the crosshairs are moving, you've got parallax. Play with your front adjustable objective until you can dial out the parallax. The yardage settings are usually off a bit on the Adjustable Objective.

Some ranges I've seen connect the benches together with lumber so you can stand your rifles like in a gun rack. These really suck for load testing as everyone down the line can cause all kinds of movement to your bench just by fooling around on theirs. One range even had the roof connected to the benchs and every time the wind would blow you could watch your crosshairs moving around! lol

Anyway there's a lot of things that can give ya a fit at the range and spoil your range testing and like I said, a 1/4 moa problem can be hard to find. If you have any benchrest matches going on in your area, it's a great place to learn. Those guys seem to love teaching and helping folks out in hopes you'll be joining them sometime.

I suspect that you have just answered your question. However, like 5sdad posted, sometimes it just happens. Phase of the moon, too much coffee, fight with the wife, bad day at work, etc.................

I have noted that when not holding the rifle secure groups always seem to drastically open up. I'm thinking it was shooting technique for sure.

Shod

In a hunting rifle I don't see any reason to sweat 1/2MOA vs 1 MOA. Sure, it's nice to see those little bug hole groups but are you going to be shooting off a bench when you are hunting? Is the game going to notice the difference?
Consistency is going to bring home the venison. Get off the bench as soon as you can and practice field positions. That will make a lot more difference in your success than 1/2 MOA.

You're exactly right blacktailer. I need to keep that in mind. I take comfort in knowing the groups from the second trip are still much better than those I lived with before starting reloading.

a lot of bench techniques can be improved by dry firing. You can set up on the kitchen table or in the shop, put a small target on the wall, and practice, practice, practice. When you break the trigger, if the cross hairs jump off of the target, you're doing something wrong.

I feel very confident I am not flinching. For many years I had a problem with it and got pretty adept at knowing when I had jerked the trigger. I'm still not perfect in high stress situations but generally have good trigger discipline on the bench.

Turkish you are varying holds and going from hand held to (l assume) firm sand bags which may cause more "bounce" from a firm rest. Especially if the barrel is bedded in the forend.

Add in that we really don't know runnout of the neck sized brass and any of these things can effect groups day to day. That said you will get a truer picture of the rifle's capability if you get it out to 300 yards. If it does well there, l would stop worrying about 100 yard groups which are just a place to begin but hardly an end game in and of themselves.

Unless you're shooting indoors at a climate controlled facility, the weather conditions likely were different too.