I just spent the last hour pulling down over 200 loaded rounds of ammunition.

I shoot a few fringe cartridges that don’t have an over abundance of community support. One of these is the 7mm LRM. I’ve owned and reloaded for this rifle better than a decade. I always keep detailed notes on each of my rifles down to environmental conditions during load development, total round count, load count on brass, B.T.S., B.T.O., how many rounds between cleaning, the lot number of bullets and powder; you know just the really anal stuff.

I loaned this rifle to a friend for a Nelgai hunt back in October. I finally ran into him and asked about the hunt and also about getting my rifle back. He blamed me for almost not being able to shoot a trophy. Turns out when he went to verify the zero on the rifle it was definitely show signs of over pressure. He said he could barely open the bolt and he almost felt like he had to beat the bolt back t with a 2x4 to extract the spent brass. I looked at the shot brass and it all had extractor marks and flat primers. When I deprimed the brass all of the primer pockets were loose also.

So i got the rifle and ammo back and proceeded to deep clean the barrel since I didn’t know what he had done with it since he picked it up from me. Maybe the chamber and throat were fouled. I took the gun out to shoot and my first shot was 70 fps faster and had a sticky bolt. I chose another round at random and same results. I did this ten times.

I randomly broke down twenty rounds of my loaded ammunition and weighed the powder charge and it all matched my notes. Somehow this powder/load combination has gotten really hot for the rifle.

I honestly have no idea why this is showing signs of extreme over-pressure. I have shot and hunted with this load for a decade and have always thought it was perfect.

Right now I’m working on load development from scratch starting 6 grains under the original powder charge and chronographing every shot to make sure I’m not getting false positives from the brass while chasing the velocity I think the cartridge should deliver.

I have no clue what has changed since my original load development and that is really starting to bug me.
The pressure curve is definitely higher even though nothing else has changed.
Maybe the humidity/moisture content of the powder?
I am measuring case length, case weight, neck thickness and anything else I can think of.

If you have an educated guess let me know. I am definitely open to suggestions.

Same lot of powder? No powder mix ups?

Have you bore scoped the barrel after cleaning. What’s the throat look like.
I assume no change in lot#of powder? Am curious of type of powder I believe the LRM was loaded with H1000 from originators.

Yes, same powder lot number. Even same bullet lot number and the brass was purchased at the same time time.
If I had made the cardinal mistake of using the wrong powder at the charge weights I load I’m pretty sure I wouldn’t be around asking for some help.

I don’t have a bore scope to look at the throat but I can say that I suspected something like a carbon ring build up. I spent extra time cleaning the barrel with Kroil and ISSO paste to make sure that wasn’t the problem.

You’re right about the powder, it is H1000.
This lot of powder is about three years old My original load development was done when I first got the rifle. I have had to re-verify the charge weight when I switched to this lot number and according to my notes I saw no difference in charge weight to velocity.

I shoot the LRM to 1300+ yards often and would easily be able to recognize a difference in pressure/velocity

I tend to buy enough powder, brass and bullets to shoot a barrel out,
That’s why I’m starting to think that maybe the moisture/humidity content of the powder has changed enough to make this load stupid hot.

I have got to be missing something.

Moisture content was one of my first thoughts, but if that’s something you’re aware of, I’d assume you’ve stored it properly and not left the lid off for extended periods of time.

Could be rough fire-cracked throat or maybe if you loaded in winter when humidity was extremely low it could effect burn rate if load was on ragged edge of maximum pressure maybe could result it excessive pressure?

When you did the load work up, was it on new virgin brass? And is the loaded ammo you are getting pressure with, reloaded with fired brass? And is all the ammo the same exact powder charge?

I am starting to suspect that it is excessive carbon fouling in the throat. I have a borescope coming that should be here Saturday to let me confirm or rule that out.
The original loads were warm but not the maximum that was given to me by the cartridge designer (Gunwerks).
I still think humidity might be playing a role in this but I do not believe it could have the impact I have seen.




The original development was done with both new and fired brass. All of the brass i have for the LRM has at least two reloads now and the total round count on the rifle is just under 600.
The powder charges on all of the ammo I pulled down was within 0.06 gr +/-.



My WAG until I get the borescope is that my cleaning was polishing the carbon in the first 1 or 2 inches of the barrel and not completely removing it.
I cleaned the barrel over two days and then loaded 15 rounds 1.5 gr under my normal charge weight. The first two shots chronographed pretty close to what I expected. After that the velocity started to climb quickly with random extreme spreads in the 60 fps range. The fastest round were what I would call “clickers”, not a full blown stiff bolt but they had that definite click to them. They also had very faint ejector marks on the brass.

I am going to wait until I can visually inspect the chamber and throat before I do anything else with this rifle. I have also bought a new scale to just alleviate that worry of charge weight variables from the equation.