Running into pressure all of a sudden

I have a 6.5 saum with about 300 rounds on the barrel and ran into issues recently. Everything is the same on the load, same lot numbers on everything and even pulled a few rounds down to make sure the charge was correct. I had a hard to lift bolt on a couple rounds then popped a primer out of the case. Suspected a carbon ring, cleaned really good and soaked the area with C4 then scrubbed with a brush. Cleaned out the barrel and chamber then tried it the other day, it popped primer on the first round so I stopped.

I don't have a borescope to check for carbon. Is it possible that the barrel took longer than normal to speed up and I just need to back the powder charge down? 1sr gen hornady brass, 60.1 grains with a 140 hybrid. 015" off the lands. It wasn't a hot day and the load development was done on a hotter day when I originally did testing. I've gained right at 50 fps since this started, installed the chronograph just to see on the shot the other day to try to help figure out what is going on.

 

Looks like you've checked the usual suspects, the only thing I can add is to ask if you've changed your shoulder bump process. IOW, is it possible you've reduced the case volume by oversizing the brass? Or is case life the issue, too much pressure too many times and it's done. More possibilities include oil in chamber, new batch of powder or primers.

A cheap endoscope camera, about $35 on Amazon will suffice to see into the chamber and throat, as well as muzzle for copper build up. It won't give you stellar images you can frame, but it'll allow you to verify your cleaning procedures are doing the job you think they are.

 

I will confirm when I get home but I bump the shoulder .001-.002". Everything is the same lot number as far as components, these are even in the same 100 round box that i loaded up in one afternoon. The brass is shit, primer pockets don't last long but I throw out the cases that the primers seat too easily. I'm going to clean it again tonight and load up some rounds in new brass at lower charges to see how they work and check for velocity at the same time. I may end up buying a good borescope if I don't figure it out tomorrow.

 

I would check case length if you have someway to measure chamber length. Cases might need to be trimmed if too long.

 

Cant hurt to confirm neck dia of chamber and loaded rounds. Brass flow?

 

What powder were you using? Was your development load finalized in brass with dirty necks VS these with a clean ( bare) neck? How long have they sat around since you originally shot them?

 

How many firings do you have on that brass?

 

Finalized with once fired brass which is what this ammo is loaded with. They are a few months old, I could try seating the bullet a little deeper to make sure it's not the issue. I plan to pull some of them down to back powder charge down for tomorrow. I dry tumble too so I leave carbon in the necks.

Nature boy, they are once fired brass. I have shot about 100 rounds loaded with this batch of once fired brass.

 

I would not give up on the idea that you have a carbon ring causing this. I had the same issue last year or the year before, memory sucks. Anyway it took me the better part of a week to get the carbon out and that's when I started cleaning every 100ish rounds and began a JB and kroil throat cleaning regimine every cleaning as well. I tried most of the acclaimed carbon cleaning products and for me I have decided it takes elbow grease and bore paste.to truly remove the carbon in the throat.

 

I still didn't catch the powder you're using. Was it a max load? After experiencing it twice, I certainly wouldn't fire anymore of them till you find out what's up.

 

You load near max in cool conditions and now that the temperature is up a bit wondering why you are getting a sticky bolt? It could be the Ol' tried and true to much powder.

Ray

 

No. I'm not firing anymore of them. I'm using h1000 and mac load was right around 61 grain in the initial pressure test.

 

Try rereading the thread, I did load development on a hot day and this was done on a cooler day.

 

You can also get false pressure and bolt thrust from the brass not being clean from any kind of lubricants.. Chamber wet, brass got oil/ graphite or something of this nature. Over lubing the bolt and it's contaminating your brass..

Ray

 

Didn't so far find it listed. What kind of sizing did you do when all was well, and then when it was not well?

Danny

 

Redding type s die with a bushing .002" smaller than a loaded round.

 

Full length sizing die

 

I’ve had s couple new barrels that required a significant charge reduction after two hundred or fewer rounds. The odd barrels initially allowed more than normal powder loads which later sharply transitioned over about 15 shots, to brass flow, and then required backing the charge down to the nominal level.

I suspected that a lapping residue may have burned away that had been reducing friction, and that if that wasn’t the reason, the throat changed.

 

Neck Size? Full Length? Partial Full Length?

Danny

 

Full length with a .001-002" bump