What caused sticking bolt?

Ruger precision rifle .223 caliber, had 50 rounds loaded with 24 gns Varget with 68 gn HPBT bullets. All fired perfectly except for one. That one sounded and felt the same as the others and had the same point of impact. But when I went to open the bolt, it would not lift. After hitting it quite hard with the heel of my hand several times it finally lifted and I was able to eject normally. Cartridge looked normal with no flat primer or anything different than the others. Brass was Lake City. Any idea why this one round stuck?

 

Normally high pressure. Look for bolt print marks on the base of the brass. The OAL may have been longer into the lands? The load you listed is on the low side according to my notes, but over pressure can happen if the OAL is too long.

 

It could be pressure, like Blue posted, or it could be that your bolt needs to be disassembled, cleaned and lubed. I trim all of my brass before I load it for the first time and closely monitor it after that.

 

Your load was a common across the course load, at least out to 300 yards. I would have not expected high pressures, but then, without pressure gages on your barrel, we really don't know what the actual pressure curve is in your rifle. What I am going to recommend is that you cut your loads by a half grain, and continue cutting by a half grain until all over pressure indications stop.

I would like to comment on the shooting communities attitudes on pressure. If the book value is lets say, 50,000, the majority of the shooting community believes each and every cartridge will be 50,000 psia. That is not so. You can look at SAAMI documents, but pretty much for ammunition, they allow an lot average of 50 kpsia (for example), but with 20% overs and unders. So it is perfectly OK if the occasional round hits 60,000 psia, as long as the average is 50 Kpsia. What that means to the hot rod community, the types who have to push things to the max, is that when they move the average pressure up, lets say to the 60 kpsia level, and assuming the 20% variance still holds at those pressures, then they are going to get the occasional 72 kpsia round, which happens to be above typical proof pressures. Proof pressures are kept just below material yield, so the hot rod types are clearly going to have the occasional round which is going to be at or above material yield. Since pressure data is scarce, it may be that when average pressures are pushed up, the variances also increase. At least on the high end. Gunpowder does not burn like a candle, nice and linear, it has an exponential slope to the curve. I am of the opinion that higher pressures will result in much greater high end variances, but without data I can't prove it.

Based on my decades of reloading experiences, I am going to say that pressure is not your friend. You are not the master of it, it will hurt you when it can, because it can. You get complacent with pressures and pressure will show you, that your complacency is all hubris and arrogance.

So, cut your loads. You had a high end pressure excursion that is telling you, your load is too hot with that combination of cases, bullets, powder, primers, and gun.

 

Bolt hard to open- High pressure https://www.thehighroad.org/index.php?media/albums/high-pressure-signs.148/

Range brass- case head may have been expanded in the web area , when fired in a different rifle. A small base die may be needed to size it smaller. Or scrap the brass.

Some tumbling media may have stuck inside the brass. This reduces case volume and raises pressure.

Trim length to long. Bullet pinched in chamber.

Loaded round neck diameter larger than .253" not common. Bullet pinched in chamber

Brass case is a lot heavier, less volume, then the others. Compare weights.

Powder bridged in drop tube of measure. One round got 2 or more grains less powder. The next cartridge got the extra powder. High pressure. Common with some larger flake powders.

 

Check your OAL you might set the bullet in a little my book calls for 2.260 OAL

 

“Usually high pressure” is usually correct, but...

Over sized bases can cause sticky bolt. The sizing die takes it small enough to chamber, but then the “memory” of the brass causes it to NOT springback, sticking in the chamber.

 

I'm not 100% convinced the OP has high pressure, but this is too good to pass up...

That is my opinion too. Smokeless powder seems to burn more efficiently under pressure, so as you pass the halfway point, it takes less and less additional powder to do the same job. Here a simple graphic to show the problem...



Additionally, pressure and bullet velocity seem to move together only within the recommended load range. After that, adding more powder may not result in the anticipated velocity increase, but it always contributes to additional chamber pressure.

Which is why I tell novice reloaders... every step, every process, every precaution we take in our hobby is to control chamber pressure. Don't ever let your quest for "accuracy" or "penetration" take your eye off of chamber pressure.

But I must say Mr Fire, you said it better. Thank you.
.

 

Additional thoughts...
Here's how seemingly innocent process steps can lead to high chamber pressure...
• The reloader dry tumbles with corn cob media sold as "gerbil litter"
• The litter product is larger than most corn cob media
• During 1 hour tumbling, corn cob enters the cartridge case
• During 5 minute separation tumbling, not all the media is extracted from the small neck 223 case
• 223 case gets loaded with powder on top of large corn cob "kernels"
• One cartridge in 50 ends up with reduced internal volume and thus much higher pressure

So easy to do. Nothing obvious at all. No warning given.

 

I use a micrometer set at 1.760 and check each case after sizing. Any case that is longer is trimmed with a Lee trimmer and then rechecked for length before being placed in a bin for reloading. I was told that as long as the resized case is shorter than 1.760 it is good to go. Is this correct? I should mention that I have loaded more than a thousand .223 and this is the only one that was sticky.

 

I examined the case carefully and saw no difference between it and the other cases so I tossed it in with the others to reload. I probably should have thought to keep it aside but too late now. This was the second reload on Lake City brass, all relatively mild loads

 

Trim Length- Most chambers have what i call a "Safety Zone" There is about .010" free space in front* of the maximum chamber length. It can be measured, but not necessary unless running over maximum case trim length.

Did see untrimmed brass ruin a nice M70 years ago. But not a common problem.

 

If you’re diligent with trimming that may not be the issue. If you don’t pour and weigh every charge before dropping it into the case the powder-bridging theory seems very plausible to me.
I had wonky charges happen to me once, every load since then I tap the powder dispenser 6-7 times and weigh charges a lot until I’m sure all is pouring well. It could still happen to me again, but I try to reduce the chance.

Good luck with finding the cause!