I did my barrel break in today and instead of just burning powder and slinging bullets, I decided to do a ladder test with the 125gr Nosler Ballistic Tip, RL7, Remington 7-1/2 Primers and Federal pull-down brass (first firing since form). I don't consider anything in this test final but just wanted to get an idea of what i was looking at on potential accuracy and approximate velocities with this combo. I loaded at 2.300" and this bullet hits the lands in my rig at 2.485", so I'm jumping an obnoxious .185" on this one. I did not begin the day hopeful with this load as I usually don't have great luck with such great jumps but I still went into it with an open mind. At 2.300"load length and brass trimmed to 1.620", this bullet seats just barely into the ogive. I measure .305" bullet diameter where it mests the case mouth. I lack the mathmatical knowlege to calculate exactly how much longer the bullet would need to be seated to avoid seating into the ogive but it's irrelevant for my application anyhow since I'm stuck with mag length of 2.300" Again, I've not had great success seating bullets in this manner but still an open mind.
Beacuse I wasn't doing refinement loads or a 'real' ladder test, I did all my shooting at 100yds today instead of my usual 200 for load development.
After digging around in everyone else's load info, I put together a ladder from 28.1 to 29.3gr charges in 0.3gr incriments. I'm not sure what kind of pressures I'm making with this but saw no indication of excess today (85 deg F). My headspace seems to measure longer than everyone else with this caliber and today's loads measured consistent with my test load from a few days ago. (1.371-1.374 with Hornady Headspace Tool) so YMMV with pressure / pressure signs.
Low velocities were just a few FPS below 2500 and high velocity loads measured just a few above 2600 out of my 18" tube, velocities were a smooth climb between loads with nothing erratic. All of these measurements were at the muzzle with my Magnetospeed chrono and it seems to map right along with my more traditional chronos.
The best group of the day was 0.60" and that was the lowest load at a smidge below 2500fps. The worst of the day was right in the middle of the charge ladder at 1.50" and things looked like they were starting to tighten back up at the next two higher charge ladders, the final group on the highest was just a little over MOA.
Finally, I have some kind of gas problem as nothing during the day cycled reliably but that's its own issue that I'll get figured out. I ordered a standard profile barrel and had a .750 BTE gas block set aside for the build but ended up receiving a semi-bull barrel and only had a non-adjustable .875 gas block on hand. The adjustable BTE is ordered now but I'm guessing that isn't the root of my problems since even my significantly lower-charged break-in loads cycled the bolt to the exact same point before hanging up, so I don't think I'm over-gassed and all of these loads should have plenty of juice to cycle on their own.
All-in-all, I'm not completely upset with the results. I'm hoping to get significantly better groups after break-in and I'll probably revisit this exact test and add a few more charge ladders at the top. I'd still like to shorten the jump to the lands a bit but I don't think I can get JB Weld to hold so what's a guy to do?
That is all for now, more to follow in upcoming days.
Interested to hear how your test goes, keep us posted!