Head scratcher!

[Downhill]

XP 100, 14" 12 twist Hart, 6BR- Barts 68gr Headhunter 6, 32 gr Varget, CCI 450 in Lapua brass fired 3x.
Loaded these rounds a year ago (50). Shot 18, no problem back then. Same time of year so temps would be close 90 degrees. Went to shoot the rest this morning, #1 hard bolt lift, #2 blown primer, #3 blown primer and #4 hard bolt lift. Over pressure I know. Bore scoped fine, no fouling or carbon ring. Neck tension light (1 to 2 strikes with impact puller). Powder weight checked-32 grains.
What happened when the load shot fine a year ago and now is too hot?

 

[BoydAllen]

XP 100, 14" 12 twist Hart, 6BR- Barts 68gr Headhunter 6, 32 gr Varget, CCI 450 in Lapua brass fired 3x.
Loaded these rounds a year ago (50). Shot 18, no problem back then. Same time of year so temps would be close 90 degrees. Went to shoot the rest this morning, #1 hard bolt lift, #2 blown primer, #3 blown primer and #4 hard bolt lift. Over pressure I know. Bore scoped fine, no fouling or carbon ring. Neck tension light (1 to 2 strikes with impact puller). Powder weight checked-32 grains.
What happened when the load shot fine a year ago and now is too hot?

I would check for bullets becoming cold welded in the case necks. You can set your seater to seat the bullets say, .010 deeper, if some of them take a lot of effort to move and make a loud popping sound when they do, that is what you have.

 

[searcher]

You might have had that load right to the top of what your gun would handle both times. The second time, cold welding (the bonding of bullet and brass) could have been just enough to push you over the edge. I had long ago noticed that varmint ammo pre-loaded well in advance of a varmint hunt (or left over from a distant-past hunt), always shot with higher velocity months after it was originally loaded and chronographed. You can't really tell how much cold welding took place when using an impact pullet to remove the bullet. I moly coat my .223 and larger varmint bullets just for this reason. It isolates the bullet from the neck (or at least provides the lubricity to stop it from doing this over time. You could verify this by taking several of your old rounds and tapping them with your impact puller - but not enough to unseat the bullet. Then re-seat to your proper depth again. If the symptom goes away when firing them- that was likely your problem. Still, I'd probably back that load off a minimum of a full grain.

 

[farmerjohn]

Hi Feller, I've run that exact same load except for using a 55gr Nosler BT, in an XP with a 16" barrel for P dogs for several years and it's pretty warm in my rig. I'm just wondering if those 2 strikes with the puller are the blown primers and the 1 strike ones are the stiff bolts. Only thing I can imagine is bullet "welding", why don't you try seating the bullet just a hair deeper, just enough to break it loose from the original spot and see if it cures it. If not I'm scratching too.... John

 

[farmerjohn]

Looks like somebody can type faster than me and thinks like I do.... John

 

[K22]

I would be interested in hearing back from the OP if he tries the recommendations offered regarding cold welding. I hope he does.

For more years that I can remember, I have loaded my varmint rounds in the winter to prepare for the upcoming varmint season. In addition, some unused reloads carry over from season to season and I have never detected any performance changes in these reload compared to those loaded and shot recently.

However, it sure does look like "cold welding" could be the only explanation. I am scratching my head too on this one.

PS: The only time I ever experience pressure problems (published load data) is with ball powder in the field in 90 degrees+ weather. (H380 / 22 -250).

 

[ebb]

I had that happen with a Retumbo load.

 

[LHSmith]

Lately I have been loading my match rounds 30 thou long and final seat between relays on match day to eliminate any chance of cold welding on any left over rounds which may not get used in the near term-perhaps into the next season. It also allows for another parameter to adjust tuning by seat depth changes.

 

[Downhill]

I would check for bullets becoming cold welded in the case necks. You can set your seater to seat the bullets say, .010 deeper, if some of them take a lot of effort to move and make a loud popping sound when they do, that is what you have.

I really don't think cold welding is the issue, although could be as I have been wrong before. But a couple decades ago a BR shooter told me to keep a small container of steel BB's with graphite on the bench, swirl the bullet in the graphite coated BB's a couple of times then seat it. Has become second nature as I am a bit OCD when it comes to handloads, does it hurt- don't know, does it help- maybe. Would think at the very least the small film of graphite would prevent cold welding. On a side note I borrowed a buddy's tuned beam scale to verify my two scales- spot on. Only thing I got left to blame is some goof ball reaction with the powder but Varget??? Hope not as I have 12 lbs of it.

 

[Hal]

Pull a bullet and look at your powder to make sure it's still okay.
Than pull 5 bullets and reseat them with the same powder charge and see what that does.
Hal

 

[Tesoro]

has to be the obvious.

 

[Old Navy]

If they were mine, I would tear them all down and start over.

 

[Kracken McGraw]

It’s hard for me to believe in cold welding with all of the factory rounds produced and used many years later.

 

[mfendley]

It’s hard for me to believe in cold welding with all of the factory rounds produced and used many years later.

True, but factory rounds are not close to a limit as far as powder charge. So even if the cold welding is occurring, you wouldn't see anything close to a hard bolt lift or blown primer.

 

[ebb]

My 300 RUM with the Retumbo were not close to max. I think it was the powder.

 

[mikecr]

What sizing was done on the brass last year?

 

[BoydAllen]

It’s hard for me to believe in cold welding with all of the factory rounds produced and used many years later.

So you totally discount all of the well written accounts and pictures relating to this subject? Many of us have personal experiences with cold welding. It is one of the main reasons that some competitors load their rounds long and then seat them to final length just before a match.

 

[Kracken McGraw]

So you totally discount all of the well written accounts and pictures relating to this subject? Many of us have personal experiences with cold welding. It is one of the main reasons that some competitors load their rounds long and then seat them to final length just before a match.

No Sir, I didn’t say I was Right. It’s just hard to picture it happening when the explosion happens in the chamber and the case neck expands several thousandths when releasing the bullet to go down the barrel.

 

[mgunderson]

Curious on how the brass was cleaned and how the ammo was stored.

I like the idea of tearing 5 of them apart, inspecting them, and reassembling. Credit to one of the above comments.

I would suggest double checking the distance to the lands.

 

[Downhill]

Went ahead and pulled them all, starting over.