Need some help figuring this out

I bought a 338 Lapua recently, and finally have had some time to work up loads for it. After barrel break in, I did the Berger protocol to find the best seating depth for the bullet I plan on using.
I purchased some 225gr Nosler E-tips and I'm using Retumbo. I contacted Nosler to make sure that it was ok to use the starting charge of 93.0 gr they had listed in their manual even though it wasn't one of the bullets listed in that grain. I got an email back stating that I can start with that load and work up. So, a couple weeks ago, I did. 93.0 gr gave me 2977 fps and extracted with no issues and no signs of pressure. Next round was 94.0gr which gave 3022 fps and sticky bolt lift with a slightly flattened primer. Fine, I figured I found the max in my rifle and would work up 1.5-2.0 gr below that max. I loaded up 7 rounds in 0.3gr increments from 92.3-93.5 and would use the magnetto speed to find the velocity node since I've been using the 6.5 Guys velocity node method to find the nodes.

Now comes the issue and what the heck is going on. Today, the first round of 92.3 gr Retumbo gave me a stuck bolt and had to use a cleaning rod to get the stuck case out. Velocity was 3076 fps!!
I'm using the same exact components (Nosler Brass, CCI 250, Same 1 lb of Retumbo, 3.55 COAL, one time fired and FL resized brass). It was 25-30 colder today than my last visit to the range. I can't figure out how a 1.7 gr less powder charge yielded more velocity and pressure. I carefully number each round and use a RCBS chargemaster (I always calibrate it after it warms up) and I have checked it's accuracy against my Lee beam scale in the past and it was dead on. My barrel was clean and I always run a dry patch through any rifle I'm taking to the range before I put it in the gun case.

Does anyone have an idea what the heck is going on here??

When I first started reading your post, I thought you were going to say you were using Hornady brass. This is common with soft brass. I started with Lapua brass and never have encountered the problems others have had with different brands of brass.

Tag

dougduey said:

one time fired and FL resized brass).

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Does this mean the brass was or was not the same condition used with earlier/lower MV testing?

would like to see where this goes.

Mikecr said:

Does this mean the brass was or was not the same condition used with earlier/lower MV testing?

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It was exact same condition. Fired once and FL resized.

Doigduey, FWIW,a couple of years ago I had a good safe load for 264wm with Retumbo in 50° temps.
Right before my hunting trip the temp droped to 20°. The same load with the same component lot# blew my primers right out of the case! Velocity increase 150fps.
I blamed the barrel for its stress relief (or lack of) for bore contracting. It still baffles me to this day. But the more I think about it, maybe it was the Retumbo, the cartridge and the barrel.
Slightly different scenario but just a thought.

Maybe you accidentally got one jammed onto the lans somehow.

Nosler book shows this for the 225:
Using Norma cases.
Low 93 Gr. at 2953
Mid 95 Gr. at 3013
Max 97 Gr. at 3080 * This was the most accurate load at 97% capacity.

I just don't understand why things are suddenly blowing up on at 92.3 gr.

Also, they show COL to be 3.681 and you are at 3.55, unless you are measuring from the ogive.

Barrelnut said:

Maybe you accidentally got one jammed onto the lans somehow.

Nosler book shows this for the 225:
Using Norma cases.
Low 93 Gr. at 2953
Mid 95 Gr. at 3013
Max 97 Gr. at 3080 * This was the most accurate load at 97% capacity.

I just don't understand why things are suddenly blowing up on at 92.3 gr.

Also, they show COL to be 3.681 and you are at 3.55, unless you are measuring from the ogive.

Click to expand...

Barrelnut said:

Maybe you accidentally got one jammed onto the lans somehow.

Nosler book shows this for the 225:
Using Norma cases.
Low 93 Gr. at 2953
Mid 95 Gr. at 3013
Max 97 Gr. at 3080 * This was the most accurate load at 97% capacity.

I just don't understand why things are suddenly blowing up on at 92.3 gr.

Also, they show COL to be 3.681 and you are at 3.55, unless you are measuring from the ogive.

Click to expand...

i never start with the lowest charge in a reloading manual. i am never concerned about jamming in the lands but i would never load a case below or even at the minimum charge. i always start in the middle and find my node in the upper third. the closer to capacity a case the more reliable ignition is. weird things happen with low charges.

Would air density due to a lower temp and likely higher humidity do it? Maybe the rounds were warmer this time causing a fast burn rate? (I know that sounds crazy but think about having your ammo on the floor board of your car with the AC on in the summer vs heat now). I read this post this morning and contemplated it at the range while firing a 6.5cm load with H4350 that I developed this summer at 83 degrees and 17% humidity, No issues. Today I had several heavy bolt lifts at 29 degrees and 67% humidity. I am always careful to transport my ammo in a location in the vehicle that is out of direct sun as well AC or heat so I am pretty sure it has to be the atmospherics making the air in the bore "thicker" thus creating more resistance to get the bullet moving and driving up pressure. I know everyone always expects to see more pressure at higher temps and I do believe that's typically the case but if your ammo temp is the same (you mentioned it was your first round so I am assuming you store your ammo between 60-70degrees year round) then the environment would be the only thing that could drive up the pressure.

Barrelnut said:

Maybe you accidentally got one jammed onto the lans somehow.

Nosler book shows this for the 225:
Using Norma cases.
Low 93 Gr. at 2953
Mid 95 Gr. at 3013
Max 97 Gr. at 3080 * This was the most accurate load at 97% capacity.

I just don't understand why things are suddenly blowing up on at 92.3 gr.

Also, they show COL to be 3.681 and you are at 3.55, unless you are measuring from the ogive.

Click to expand...

i don't think temperature had anything to do with this.

did you check the charge weight on another scale or just straight out of the chargemaster?

did you fire any more of those rounds? might have been a heavy charge in that one case.

if you didn't fire any more you might want.to pull a.couple down and check the charge weight on a reliable scale.

i just don't like light charges. funny things happen.

Not sure that it is the problem, bu the problem with mono bullets has always been how big to make their dia in order to seal the bore but not create over pressure problems.

We cured this problem with our patented PDR design. We can cut our bulleta over groove dia without pressure issues and still always seal the bore. We don't see changes in pressure from day to day like other monos.

Steve

RockyMtnMT said:

Not sure that it is the problem, bu the problem with mono bullets has always been how big to make their dia in order to seal the bore but not create over pressure problems.

Steve

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This was my thought and why I prefer to stay with lead unless it has a sabot around it...

Did you make a dummy round using the same bullet used to determine the over all length of the loaded round? If you are seating close to the lands (0.020 inches or less), this could be your problem. The length of the bullet can vary enough to cause this problem.