7mm lrm

[toddc]

I used to build two kinds of guns. Turtle shooters and coyote/deer rigs.
Turtle guns were shot in hot weather and hundreds of shots a day at times. Since the turtles were from 800 to 2500 yds I always shot pretty hot stuff.
I would smoke 4+ barrels a summer and yet after the turtles went to bed I would run a hunting barrel for the winter. My hunting barrels would last 5+ yrs. Turtle barrels? 2 months. Got 50% to twice as many rounds on the hunting barrels. Of course I never ran over 2 or 3 shots an hr on them and the accuracy requirements for hitting a whitetail in the vitals to 800 yds are way different from shooting small turtles off of logs past 800.

 

[MudRunner2005]

The last couple of years I find my self not engaging in a lot of debates. I think it's a waist of time debating cartridge choice, rifle brand choice and similar type of debates the seem to fire up on some threads.
People are going to have their opinions and I have mine. So screw it, I'm not going to convince anybody that doesn't want to be...
I'll engage on some ballistic threads, I like to talk about Optics, and I'll ask some questions when I feel like it could spark a multiple page conversation... But yea, I see where a "ahh screw it filter" is used a lot with me lately as well..

I left 8 gun groups on Facebook this past week because of the repetitive debates, and questions... I'm getting to old to argue why I anneal and some one telling me I'm waiting my time. Or my 30-06 won't shoot to 1000 yards because the 6.5 Creedmoor is only capable of 1000 yard shooting... lightbulb

Don't even get me started on the 6.5 Creedmoor supporters...

But yeah, the last year or so, I've slacked off a bit on engaging in threads certainly headed for destruction, or those threads that pop-up weekly like clockwork with the same questions over and over and over.

I especially try to avoid them when I'm not feeling well, drinking, or physically injured and in pain...Usually, the worse I physically feel, the more it shows up in my posts. LOL

Occasionally I get bored and like to engage in some lively debate.

 

[MudRunner2005]

All valid points. The belt thing is personal preference. I know you can headspace as normal and basically ignore it, but to me, it is an outdated design point, there really is no benefit to it and there are more interesting cartridges out there. Honestly, I could have made life easier and gone with the 7RM or STW and be done with it. I'm not saying that they are bad, I just don't want to worry about it. Call it ignorance if you'd like, but with so many good choices out there, one has to find a way to narrow it down.

I'm sure most of the barrel life issues are from guys that like to hot rod them or otherwise abuse them, which leads to reports of low barrel life spreading. It happens. But it is well known that "overbore" cartridges have lower barrel life as they aren't efficient. I wanted to strike a balance, so...different strokes, I guess. A barrel is a big investment for me and I wanted to make it count while achieving my goals.

I'm glad you are getting good life out of your STW. That gives me hope for the LRM. They seem to be similar enough performance wise that a barrel life comparison would be relevant.





Man, I didn't mean to get anyone wound up. No p!$$!ng match required and no need to prove anything. I'm not here to perpetuate false narratives and argue...I was simply sharing my perspective, respectfully (or so I thought). One cannot be an expert in all things and when building a rifle, I only know what I have read and can be picky about certain aspects.

I think the 280AI is a great cartridge and doesn't give up a whole lot to any smaller magnums. Again, balancing barrel life and performance was my goal. Others may have different goals. If this were mostly a plinking barrel, the 280AI would have been my pick hands down, but since I have a switch barrel, I didn't need to compromise that much. It may not be a huge difference, but I'll take 195s at 2900 and 180s at 3000-3100 over 180s at 2900 all day.

That being said, once can never have too many rifles and I wouldn't kick any of the aforementioned out of the safe! Good luck and feel better.

It's all good. You have your preferences, and I have mine. We all do. That's what makes the gun-world go round.

As an avid AI cartridge enthusiast and wildcat designer, I can appreciate your "I'll take the extra 100fps all day" comment. That extra 100-150 fps is what validates a lot of my wildcat design work.

I also want to clarify, because the word has gotten quite misused the last few decades, but when I say "ignorant" I don't mean that as an insult, I mean that as the proper definition of the word, which is uninformed or misinformed. I just wanted to clarify that, so you didn't think I was being insulting towards you or your intelligence level.

 

[WildRose]

It's all good. You have your preferences, and I have mine. We all do. That's what makes the gun-world go round.

As an avid AI cartridge enthusiast and wildcat designer, I can appreciate your "I'll take the extra 100fps all day" comment. That extra 100-150 fps is what validates a lot of my wildcat design work.

I also want to clarify, because the word has gotten quite misused the last few decades, but when I say "ignorant" I don't mean that as an insult, I mean that as the proper definition of the word, which is uninformed or misinformed. I just wanted to clarify that, so you didn't think I was being insulting towards you or your intelligence level.

When asked about belted vs non belted magnums a very good friend who happens to build incredible long range rigs pointed out that trying to get your headspace correct on a pont a few millimeters ahead of your bolt face is a whole lot easier than doing it on a point several inches ahead.

 

[WildRose]

All valid points. The belt thing is personal preference. I know you can headspace as normal and basically ignore it, but to me, it is an outdated design point, there really is no benefit to it and there are more interesting cartridges out there. Honestly, I could have made life easier and gone with the 7RM or STW and be done with it. I'm not saying that they are bad, I just don't want to worry about it. Call it ignorance if you'd like, but with so many good choices out there, one has to find a way to narrow it down.

I'm sure most of the barrel life issues are from guys that like to hot rod them or otherwise abuse them, which leads to reports of low barrel life spreading. It happens. But it is well known that "overbore" cartridges have lower barrel life as they aren't efficient. I wanted to strike a balance, so...different strokes, I guess. A barrel is a big investment for me and I wanted to make it count while achieving my goals.

I'm glad you are getting good life out of your STW. That gives me hope for the LRM. They seem to be similar enough performance wise that a barrel life comparison would be relevant.





Man, I didn't mean to get anyone wound up. No p!$$!ng match required and no need to prove anything. I'm not here to perpetuate false narratives and argue...I was simply sharing my perspective, respectfully (or so I thought). One cannot be an expert in all things and when building a rifle, I only know what I have read and can be picky about certain aspects.

I think the 280AI is a great cartridge and doesn't give up a whole lot to any smaller magnums. Again, balancing barrel life and performance was my goal. Others may have different goals. If this were mostly a plinking barrel, the 280AI would have been my pick hands down, but since I have a switch barrel, I didn't need to compromise that much. It may not be a huge difference, but I'll take 195s at 2900 and 180s at 3000-3100 over 180s at 2900 all day.

That being said, once can never have too many rifles and I wouldn't kick any of the aforementioned out of the safe! Good luck and feel better.

To have relevance an opinion must be based on fact. No, the design isn't outdated, it's still working perfectly more than a hundred years since it was first envisioned and as far as "efficiency" goes, one of the reasons we use slow powders on large volume cases is so that it doesn't all burn in the case giving us much higher possible velocities with much lower pressure.

As long as you are burning more than 99% of the powder before the bullet leaves the barrel how much more efficiency is needed and what is gained from it?

Perhaps if we had only one powder to choose from instead of dozens I could buy that argument but that's not the world we live in fortunately.

I found this post and it's well worth quoting.

SU37,

In looking through my reference library to try and prove 'your' supposition, I happened upon a couple paragraphs from Julian S. Hatcher, whom certainly should need no introduction.

From pages 309-312 of "Hatchers Notebook" (pages 310-311 are pictures only), he discusses burning rates and methods to slow burning to extend the pressure as the bullet proceeds down the barrel. The following is quoted, any typos are certainly mine. I've highlighted portions that are directly relevant to our discussion.

" The great trouble with getting high velocity in a gun is the fact that when the powder in the cartridge is ignited it turns into gas, and this gas, confined in the small space of the cartridge case, creates a very high pressure which pushes the bullet along the bore of the gun. But as soon as the bullet starts to move along the bore, that leaves more space for the gas to occupy, hence there is less pressure, and the effect of the powder will rapidly fall off to nothing unless special means are taken to keep the pressure up.

One of these special means is the perforation of the powder grain, which causes it to have a larger burning surface as the combustion proceeds. This is because the primer flash ignites the inside of the tube as well as the outside of the grain. As the grain burns, the outside surface gets smaller, hence the rate of evolution of gas would burn away, and the diameter of the hole becomes larger, with a corresponding increase in the interior burning surface.

The balance between these two surfaces can be controlled by the ratio of the inside diameter to the outside diameter in the finished grain of powder. In cannon powders with their larger grains, there are usually seven perforations instead of one.

Another method of controlling the burning of the powder and making it more progressive, that is, making it holdup its pressure longer during the travel of the bullet, is by coating the powder with a substance which makes it burn slowly at first. As this coating burns off the outside of the powder, the speed of combustion increases. These progressive-burning powders tend to give a more uniformly distributed pressure, sustained longer during the travel of the bullet. Moreover, the maximum pressure is not so high because instead of being exerted all at once, the pressure is spread out more evenly during the entire travel of the bullet. The du Pont "Improved Military Rifle" powders such as I. M. R. No 3031, I. M. R. No. 4320 and I. M. R. No. 4064 are progressive powders.

Like black powder, smokeless powders are also controlled as to their speed of burning by the grain size. Powders with very fine grains burn up in a hurry and therefore are particularly suited for short-barrel weapons. Powders with very large grains take longer to burn up, and are adapted to long-barrel weapons such as cannon. ..."

The text continues to talk about granule size and ignition dynamics, but is not directly relevant to our current discussion.

I'll sit here on the same page as Julian S. Hatcher, I also suspect that Powley is sitting here beside us.


AJ

 

[Ragnarnar]

To have relevance an opinion must be based on fact. No, the design isn't outdated, it's still working perfectly more than a hundred years since it was first envisioned and as far as "efficiency" goes, one of the reasons we use slow powders on large volume cases is so that it doesn't all burn in the case giving us much higher possible velocities with much lower pressure.

As long as you are burning more than 99% of the powder before the bullet leaves the barrel how much more efficiency is needed and what is gained from it?

Correct me if I'm wrong,

A 7stw and 7rm both of which have 25* shoulders (iirc) are going to stretch more when fired as compared with a cartridge with a greater shoulder angle. Thus more working of the brass when it's fired, more work for me in the reloading room and ultimately less brass life.
Additionally the improvements in angle would allow a few grains in powder added. Thus more potential velocity.

I thought this was the draw to an AIed case.

I'm also of the impression that the shape of the powder charge as it sits in the case has some measure on performance, in that a short fat powder charge will be more efficient than a long skinny one.
I thought this is why the 375 ruger bests the performance of a 375 h&h in a shorter action and shorter barrel with the same amount of powder. Or the 6.5saum beating a 6.5 win mag with the same amount of powder and shorter barrel and action. And reportedly much better barrel life too. .

 

[WildRose]

Correct me if I'm wrong,

A 7stw and 7rm both of which have 25* shoulders (iirc) are going to stretch more when fired as compared with a cartridge with a greater shoulder angle. Thus more working of the brass when it's fired, more work for me in the reloading room and ultimately less brass life.
Additionally the improvements in angle would allow a few grains in powder added. Thus more potential velocity.

I thought this was the draw to an AIed case.

I'm also of the impression that the shape of the powder charge as it sits in the case has some measure on performance, in that a short fat powder charge will be more efficient than a long skinny one.
I thought this is why the 375 ruger bests the performance of a 375 h&h in a shorter action and shorter barrel with the same amount of powder. Or the 6.5saum beating a 6.5 win mag with the same amount of powder and shorter barrel and action. And reportedly much better barrel life too. .

Not really, I neck size usually for four or five firings and then when the bolt starts getting snug I'll do one full resizing for each of them. That isn't much work. I also will anneal them usually every other firing just as I do with my 300 Rum's, 3 of which I load for.

It's not more efficient to get the bulk of your powder burning before the bullet even leaves the chamber, doing so is counter to the benefits we get from slower powders like RL25, 26, 33, H1000 and US869 or BMG. When pressure peaks too quickly you have to back off of the charge and with faster burning powders that puts a hard limit on your potential best MV. We can run the same bullet faster with slower powders, lower heat and less wear and tear on the throat because more of the powder burns down the barrel rather than in just the first 8-10" after the bullet exits the chamber.

The Ruger has about a 2CmC H20 increase over the H&H. Isuspect that the extra volume combined with different, newer powders designed specifically to keep burning and pushing the bullet right to the end of the barrel has a lot to do with it.

I know I like mine well enough that I'm probably not going to be able to talk myself out of putting together a 26" or 26" version together to see just how far I can stretch it out with good accuracy.

Brass life? As soon as I get some of the VRG4's in .375 I'll load up a box and they will be on their 4th firing. Not seeing any signs of stress or work cracking in them and I tend to load them pretty stout.

As for the case itself If I didn't already have pretty much everything I could ever hope to need in the gun cabinet already I like it well enough I'd prbably be trying some wildcats of my own.

 

[gunnar andersen]

Rifle not liking brass? That's a new one... I can guarantee that YOU wont like it though. All mine required neck turning for consistency in tension. They used to have issues with weight variance, but they now sort it to something like +/- 1 gr. I have heard some having issues with brass life, but I can't comment on that as of yet. Would it be nice if some other mfr would make consistent brass? Oh yeah. Would neck turning one time over the whole life of a case turn me off of a great cartridge? No way.

Single source isn't really an issue for availability. I can call Gunwerks or Primal Rights at any time and order many thousands of cases. That, to me, is better availability than almost any cartridge.

Any brass could become unavailable at some point. If you are that worried about it, buy a bunch of cases up front.





I had a similar process of elimination. Nothing with a belt, to start.

280AI and smaller doesn't have the horsepower for the heavies, feeding issues, brass availability, and slower speeds deterred me from the SAUM (for a hunting rig), barrel life is an issue with the 28 Nos and bigger (as well as the WSM due to short neck).

The LRM seems to be the best of all worlds, as long as the barrel life turns out to be what I expect (1200 rds...will be tickled if I can get 1500 out of it). I was originally wanting to build a 28 Nosler, but the anticipated barrel life of 6-800 rounds I found unacceptable for me. Perhaps running 195s or some other heavy bullet would extend that some, but who knows.



That also seems like a great cartridge, from what I have read. Did you consider the Dakota? I would have went that route if I were to want to mess with the bolt face. Brass cost kept me from it as well, but I was under the impression that the LRM was still like 1.30/ea...but when I went to order the price was around 2 bucks. Talk about a price hike!

The 7 mm Blaser is suppose to fit on a magnum bolt face as the rim is slight rebate, I'm not sure where the problem is, first I thought a none aligned/over sized chamber. The chamber size is slight under max tolerance, Perhaps a chamber reamer with close to min. dimension would have done the trick.
Can the problem be of another nature????. I believe the rim on lrm is same as belted cartridge, where as the Blaser is same diameter as the WSM. Before I enlarged the bolt face the rim of the fired brass would catch the edge of the bolt face if not the case where chambered exactly the same as it was extracted. Is there any suggestions, as I will likely chamber an another barrel in the same cartridge.GA

 

[Ragnarnar]

Not really, I neck size usually for four or five firings and then when the bolt starts getting snug I'll do one full resizing for each of them. That isn't much work. I also will anneal them usually every other firing just as I do with my 300 Rum's, 3 of which I load for.

It's not more efficient to get the bulk of your powder burning before the bullet even leaves the chamber, doing so is counter to the benefits we get from slower powders like RL25, 26, 33, H1000 and US869 or BMG. When pressure peaks too quickly you have to back off of the charge and with faster burning powders that puts a hard limit on your potential best MV. We can run the same bullet faster with slower powders, lower heat and less wear and tear on the throat because more of the powder burns down the barrel rather than in just the first 8-10" after the bullet exits the chamber.

The Ruger has about a 2CmC H20 increase over the H&H. Isuspect that the extra volume combined with different, newer powders designed specifically to keep burning and pushing the bullet right to the end of the barrel has a lot to do with it.

I thought about your point for awhile and it was beginning to make sense to me, but I reread it and you've confused me again.

How is putting X amount of powder in a short fat case, igniting it all at once and getting Y velocity from a shorter barrel less effective and efficient than putting the same X powder in a long skinny case and needing a longer barrel to get the same Y velocity?
By way of another example a 6BRX which is a short fat case can sling a 105 Berger at 3030fps with 33 grains of powder. A 6X47 lapua which is thinner can hit 3100 with the same bullet but takes an extra 6-7 grains of powder. How can a difference in performance that big be accounted for if not something to do with the shape of the powder?

Also I've had issues with reliable feeding on NS only cases. I don't think I'd trust them personally for hunting.

 

[WildRose]

I thought about your point for awhile and it was beginning to make sense to me, but I reread it and you've confused me again.

How is putting X amount of powder in a short fat case, igniting it all at once and getting Y velocity from a shorter barrel less effective and efficient than putting the same X powder in a long skinny case and needing a longer barrel to get the same Y velocity?
By way of another example a 6BRX which is a short fat case can sling a 105 Berger at 3030fps with 33 grains of powder. A 6X47 lapua which is thinner can hit 3100 with the same bullet but takes an extra 6-7 grains of powder. How can a difference in performance that big be accounted for if not something to do with the shape of the powder?

Also I've had issues with reliable feeding on NS only cases. I don't think I'd trust them personally for hunting.

It's better in the long run for medium and large bore cartridges because instead of counting on one big pressure spike in the chamber and first inch or two it is spread out running most of the length of the barrel to attain higher velocities with lower pressures. Just think of it as a slow, gradual push down the pipe rather than hitting it with a hammer.

Slower burning powders by design have higher volume typically. Again, if we only had one powder or one single fast burn rate of powder to choose from the "efficiency" argument would have merit but of course that is not the case.

I would never for a minute think of using 92gr of H-414 in my .300 Rum's, if I did I'd be building a bomb instead of building a load, but 92gr of RL 25, 26, or 33 is a nice fit and gives great velocity, low ES's and very good barrel life.

I'm not sure what your point is about neck sizing only. Most people shooting belted magnums will full length resize most of the time, those of us looking for precision will neck size for two or three firings and full length resize when needed in between.

 

[Ragnarnar]

I see what you're getting at but I still can't reconcile it in my head, given the observed performance of smaller rounds. I can't believe it doesn't translate into a larger round the same Way.. I'm going to continue to think on it. Thank you for taking the time to explain it repeatedly.

About the neck sizing.
I thought you were hunting with neck sized rounds rather than shooting benchrest. I've always full length sized everything because I've had issues feeding on neck sized rounds. Additionally I find it to be more accurate and consistent versus neck sizing. With the exception of Rifles with tight chambers I'm not aware of any benefits to neck sizing, other than case life.

 

[4xforfun]

By way of another example a 6BRX which is a short fat case can sling a 105 Berger at 3030fps with 33 grains of powder. A 6X47 lapua which is thinner can hit 3100 with the same bullet but takes an extra 6-7 grains of powder. How can a difference in performance that big be accounted for if not something to do with the shape of the powder?

Also I've had issues with reliable feeding on NS only cases. I don't think I'd trust them personally for hunting.[/QUOTE

First, you are burning 6-7 grains more of a DIFFERENT, SLOWER powder in the 6-47L. Second, you are running at higher PSI with the BRX.

I get a kick out of people who say that xyz case is more efficiant........say a 300 WSM vs a 300 Win mag. Yes, you can nearly match the Win mag velocity with the WSM with less powder, but the PSI is MUCH higher on the WSM. It is simply a fact that the WSM brass can take it. This gives the apperance that you are equally matching velocity. Run the WSM and the WIN mag cases at the same PSI and see what you get.

Just my .02,

Tod

 

[Ragnarnar]

First, you are burning 6-7 grains more of a DIFFERENT, SLOWER powder in the 6-47L. Second, you are running at higher PSI with the BRX.

First, no you're not. I based that off same powder and the same bullet in both cases gleaned from load data from multiple sources.
I'm being honest. I don't own either, so I had to work google on this one. However half a dozen different loads from the internet while not scientific, is pretty indicative.

Second, no its not. If your theory was correct the 6BRX would have a massively shorter barrel life than a .243/6xc/6-47 and this is not the case. If you get 1100 rounds from a .243/6xc/6-47 loaded for competition you're lucky. People are reporting barrel lives beyond 2000 with the 6BRX.
The entire purpose of the 6.5X47 for a parent case was to take advantage of the thicker case head to handle the higher pressures.
32.5 grains of varget in a BRX generates 55k PSI according to quick load. Thats pretty mild compared to the other options out there. A factory .243 operates at 60K.

So even if you were correct, how is using less of a faster powder at a higher PSI to equal the performance of more powder in a longer case and barrel somehow less efficient?

 

[4xforfun]

F
So even if you were correct, how is using less of a faster powder at a higher PSI to equal the performance of more powder in a longer case and barrel somehow less efficient?

You are right. In fact, you should run 33 grains of Clays, Red Dot, or Titewad in your BRX with that 105. That would be really efficient and prove your point. No google needed.