12FV 6.5CM - Unusually high velocity

Newbie question:

I have a 12FV in 6.5mm Creedmoor and had an unusually high velocity with one round recently.

I was using Sierra Match King 150gr with 41.0gr of Reloder RL16. Velocities for this batch of 10 rounds varied between 2678 to 2700 ft/sec, but the very last one kicked off at 3,050 ft/sec! I stopped shooting at that point, until I could resolve the issue.

I've already traced the production issue down. I'm certain it must have been a bullet seated a bit further into the case than normal, and it was caused by a slip of a bearing on the press. I have already fixed the press in such a way that this problem can't happen again. It looks like this round got through my final inspection process - which I'm also changing in response to this!

Out of an abundance of caution I've retired the case (Starline), but before I take the rifle out again, a 13% higher velocity than expected means there must have been a considerably higher chamber pressure inside the rifle than normal, so I wanted to know if I should be concerned about the rifle itself?

Thanks for any advice.

Ross.

Yes sir. Bullet set back can raise pressure in a hurry!

I wouldn’t worry about it though. The Rifle is fine. The combination of a modern Action & good brass keeps the pressure at bay. In order for it to have damaged the Action in any way, it would have first had to damage the brass. You retired the brass, but not because it was cracked or anything, right? I’m sure the Rifle is just fine.

Thanks Dave,
Yes, the brass looks perfect. I'll take that as the best indicator then.

I think I might still start off with a comparatively small charge and bullet though, and build back up to my normal levels, mostly just to rebuild my own confidence ;)

Thanks again!

Ross.

Where did that shot impact the target relative to the other shots? I would think 300 fps would put that shot noticeably out of the group. Maybe just a bad chrono reading on that shot?

My group wasn't very good to start with (I don't think the Sierra MK 150gr work as well as Hornady ELD Match in this rifle, with this powder) about 1.5 inch spread at 100yds, but this one was definitely an outlier - a good 2 inches above any of the others. Given that physical difference I don't think it was a dodgy chrono reading this time - although I have had one or two of those too.

To get that much vel change the difference in OAL would have been a lot, like 1/4". Very noticeable. One of the reasons I put my reloads in the plastic boxes. I can look and see if any are grossly out of whack. I'd also check my other processes, like charge weight consistency. When using some powder with charge dies I have had bridge issues where one round gets a partial charge and the next one gets an overage.

If the pressure was really bad the brass would have signs, like a huge primer pocket and extraction that would need a hammer (yes, BTDT). Milder over pressure shows completly flattened primers and imprint of the ejector on the case head.

I agree. Reason I’m so methodical with reloading. I charge by weight, using the Lee Powder Measure Kit & a Powder Trickler. I use an electronic scale, but I even test it against my beam scale every 25rds or so. And then yes, all rounds go in a plastic ammo boxes. Very, very SLOW! LOL! But, it eliminates any simple mistake. And luckily I enjoy reloading. So going slow doesn’t bother me. It’s just part of the hobby.

Charlie B, agreed regarding the box - I do exactly the same and although I'm still new at this, I would have definitely noticed a difference of 1/4 inch - that's huge!

For a different hobby I design and print my own N gauge model trains, so I'm pretty good at noticing very small differences in things. At most, the difference here couldn't have been more than about 1/16 inch or I would have visually seen there was some inconsistency. I wish I had measured every round in the batch and know what the difference was, but it's obviously too late now. With my more recent batches I am now recording everything for every round, so I have data to help me trace any issues in the future.

As for charges, I literally measure everything to the final grain with a laboratory-grade precision digital scale - to get the exact quantity I'm after. I've been known to use a needle-point tweezer to swap a big grain for a smaller one to get my measures exactly right! That's probably more precise than I need to be, but I am *trying* to get every round as consistent as possible.

Thanks for describing the sort of things to look for on the brass if things go wrong. Hopefully I won't need it, but it's a useful reference should it happen down the road!

Ross.

The Bad CHRONY reading sounds more like what happened? if there was that much of a spike the pressure on the brass probably would have made it a bit hard to remove, did the bolt lift feel any different on that case?

Quote:

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Originally Posted by Mark611

The Bad CHRONY reading sounds more like what happened? if there was that much of a spike the pressure on the brass probably would have made it a bit hard to remove, did the bolt lift feel any different on that case?

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OP already stated that round’s POI was higher by 2”. That is a result of the velocity.

Glad you are careful. It pays off in the end.

One of the best investments I made was the Labradar (and now Garmin makes a better one). I measure the vel of almost every round I shoot. I still get some data that looks fishy, but, it's usually only one or two out of 50. Like when it reads a vel 100fps off and the bullet is in the middle of a 0.5MOA group.

Not trying to argue Dave, 2'' could be a flier, my brother has a LAB Radar, sometimes it's not working correctly, Ross, how do you measure your powder?

Mark, there didn't seem to be any difference at all when I removed the brass after the shot. The kick felt normal, the sound wasn't unusually loud, the temp of my barrel didn't climb by an unusually higher degree, the bolt worked normally without needing any extra force, the brass popped straight out and into my catcher.

There really was no indication that anything was different to the other shots, aside from the chrono reading and the hole in the target being a bit high.

I use a US Solid precision digital scale that I got from a previous job. It has recently been laboratory calibrated to 0.001g accuracy. I hand pour each load into a small aluminum pouring tray, and I then pick individual grains by hand, to get each load to within 0.01g of my goal. That then goes directly into the brass. I work in a quiet room where I won't be disturbed, so I can keep my concentration and focus on the task at hand. While I can't completely rule it out, I don't *think* I made a mistake with the charge.


Charlie, I've probably not shot even 500 rounds so far, but I've only noticed two bad readings from the big green Caldwell type chrono that I use, and both of those were simply failed null readings. I collect all the data automatically on my phone and then I review and chart everything in excel later, which has worked really well. The next thing I want to improve on, is to setup a camera that records the target, so I'm not trying to rely on my memory for which shot is which, and I can then plink 100+ shots and simply review the footage when I get back from the range.

Ross.

I really have no explanation for you on the errant shot. I've had a few over the years that were 100fps off and I had no explanation for them either. Sometimes I think we are just victims of a culmination of errors in material. It doesn't take much to throw off a load by that much so a small sample of the powder might be off enough to cause the issue. As much as we'd like to think the components are all the same, they really aren't. A bullet that weighs a grain or two less, a primer that has a bit more power, powder that has a disproportionate number of half grains, a case that has a different neck tension. Add them all up in one round and maybe....

Sounds like you have a decent setup. I'd probably still be using a Chrony if not for the time of day I shoot, ie, I start a bit before sunrise and optical screens aren't reliable in a light like that.

I mounted a good camera on the bench and it works well. If mirage isn't bad I can even see bullet holes at 500yd. The video gives some great information, especially when the shots are erratic. Watching the 'bullet trail' as the bullet descends into a target at long is fun by itself. And being able to go back and see shot placement is a bonus.

Ross sounds good on the measure

Thanks guys, you've put my mind to rest. I'm happy to go back out to the range again next week!

And a happy thanksgiving to you all!

Ross.

Alright, my take.....A 6.5 Creedmoor with a 150 grain bullet doing over 3000 fps, would probably
need a mallet to open the bolt. It is possible though to have an errant piece of brass way thicker
then spec with way less volume. That piece of brass could cause excess pressure, and at the same
time not expanding as much, and give easier bolt lift. Of course that piece of brass would need to
be water weight sorted to find out

I do have a question on why the use of a 150 grain bullet to begin with ?? The trick with a Creed-
moor, is to go the other way. Get some 130gr bullets and H-4350, and don't look back.

Hi Fuj', The Sierra MK 150gr are from a pack that I bought during Covid, when it was really difficult to find my usual bullets and powders at anything approaching a reasonable price. H-4350 was simply impossible to find!

I got a few different brands and sizes at that point, and they've been quite interesting to experiment with. I've just been depleting my excess stocks. The groups have never been very good with these 150gr at any of the charge levels I tried, so I have no real interest in getting any more.

So far, my fave is the Hornady ELD Match 140gr, which seems to work really well in this rifle, with both H-4350 and RL16.

Ross.

Quote:

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Alright, my take.....A 6.5 Creedmoor with a 150 grain bullet doing over 3000 fps, would probably
need a mallet to open the bolt....I do have a question on why the use of a 150 grain bullet to begin with ?? The trick with a Creed-
moor, is to go the other way. Get some 130gr bullets and H-4350, and don't look back.

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My take also.

Quote:

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Originally Posted by RBT321

Hi Fuj', The Sierra MK 150gr are from a pack that I bought during Covid, when it was really difficult to find my usual bullets and powders at anything approaching a reasonable price. H-4350 was simply impossible to find!

I got a few different brands and sizes at that point, and they've been quite interesting to experiment with. I've just been depleting my excess stocks. The groups have never been very good with these 150gr at any of the charge levels I tried, so I have no real interest in getting any more.

So far, my fave is the Hornady ELD Match 140gr, which seems to work really well in this rifle, with both H-4350 and RL16.

Ross.

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I shoot 140 eld-m with h4350 and it is a fantastic combo. my brother shoots 140's and RL-16 in his backup match rifles with considerably higher speeds and more powder. Both seem to work great! I was lucky, when H4350 was scarce i was still sitting on 10 LBS, and when it wasn't hard to find anymore i stocked up with enough to last the rest of my life for my 300 WSM's and 6.5 Creedmoors.
I did pick up some 130 Game Changers, but just haven't seen a need to try a lighter bullet for hunting when all of the break-in rounds for my two new 6.5 Creedmoor hunting rifles shoot VERY well with the 143's i load for my other brother and his son.
I have other options for hunting and mainly use my 6.5 Creedmoors for target, and while they may not be perfect for either, they are adequate for hunting and very good for a target round. I like them!