Transfering a load from one caliber to a similar caliber

[DLrocket89]

Hi everyone,

First, this thread is as a result of me reading the original post here: http://rugerforum.net/reloading/63267-short-barrel-7mm-08-powders.html

I have a short-barreled 7mm-08 and my girlfriend has a short-barreled 243 Win. Most loading manuals assume a 24" barrel, so an 18" barrel can change things quite a bit. Per that guy's thread, I picked up a pound of Benchmark for use in my 7mm-08 and I already have H322 on hand. Now, that said, I'd like to try these same things in the 243 Win, which is the same cartridge as the 7mm-08 except the 6mm bullet/bore.

So...in that thread, he states he uses 38.8 grains of Benchmark (with a max recommended 38.3 so it's a bit over charged). If I try this 7mm-08 load in a 243 Win, what changes would I have to make? take it down 25% and work up slowly? Not even bother because the change from 7mm to 6mm is that big of a deal?

I've only ever played between the starting load and maximum loads direct from a manual, this would be my first excursion into using a faster burning powder to match a shorter barrel, so just looking for any experience people can share.

And just like the stickied warning for posting heavy loads, I totally understand I'm ultimately on my own and don't hold anyone (poster, THR, etc) liable if I go blow myself up. Just hoping someone is willing to share.

Thanks in advance!

Dustin
Wisconsin

 

[macgrumpy]

I'm confused, why not just follow the recommendations of a reloading manual or one of the major manufacturers online reloading guides? Why guess with something that can cause so much damage to your firearm and your person?

 

[DLrocket89]

Sorry - forgot to include that. I can't find any loading data on 243 Win for Benchmark or H322 for bullets heavier than 70 grains. The theory put forth in that thread is that those powders work like crap on longer barrels so they don't even include it, but with a barrel that's 6" shorter it makes more sense. So, basically, there's no book data available but it still seems to work.

 

[DLrocket89]

Also - there IS data available for benchmark in the 7mm-08 for all bullet weights, so perhaps it's just a stupid idea to try and transfer it to 243 Win...

 

[Walkalong]

So...in that thread, he states he uses 38.8 grains of Benchmark (with a max recommended 38.3 so it's a bit over charged). If I try this 7mm-08 load in a 243 Win, what changes would I have to make? take it down 25% and work up slowly? Not even bother because the change from 7mm to 6mm is that big of a deal?

Stop listening to someone who goes over max, look up data for the .243 and follow it, both starting and max. Don't go under, don't go over. Doing it as you ask is all wrong.

 

[DLrocket89]

Stop listening to someone who goes over max, look up data for the .243 and follow it, both starting and max. Don't go under, don't go over. Doing it as you ask is all wrong.

Aaaaand that's what I needed to know, lol. Thank you for the point blank statement.

Question on why not going under - I know you can have a situation where a half-full case with go dangerously overpressure (heard it called "overflash"). I assume why you say "don't go under" is to prevent this condition, correct?

 

[Walkalong]

Thank you for the point blank statement.

Sometimes brutally honest is the way to go.

 

[Jim Watson]

Apparently Hodgdon considers Benchmark to be too fast burning for decent velocity with game bullets in .243.
I suggest you do the same and get some listed powder like 4350 for the .243 and not try to transmogrify data promiscuously.
Contrary to your impression, 7mm down to 6mm is a LARGE difference.

If Benchmark was the only powder you had or could ever get, you could pay for Quickload and get something safely usable.

 

[Laphroaig]

And even though it seems logical to think faster burning powders will perform better in shorter barrels, that is generally not the case.

 

[DLrocket89]

Walkalong / Jim,

Thanks again for the comments.

4350 seems to be useful for pretty much every caliber I want to reload in, so I'll get some of that for sure.

 

[macgrumpy]

As others have said, if the book doesn't show a load combination that you are looking for then it's a pretty good bet that they don't think that it's a safe load. That being said, Hodgdon does show Benchmark powder charges for both the 7mm-08 and the 243. Hodgdon shows that you can use 36.5 - 39.3 grains of Benchmark under a 70 grain bullet in the .243 using a COAL of 2.625". H322 isn't shown for either cartridge in the Hodgdon 2016 manual.

Yes, you can experiment with powders and bullet weights that aren't normally listed but you are taking a risk. I use QuickLoad software to help build up new loads but I can't think of many cases where the powders that I used were not recommended by one of the manufacturers of either the powder or the bullet.

 

[DLrocket89]

Hi Mac,

True story on Benchmark, but I was hoping for something in 90-100 grain bullet weight class for the 243 win.

Think I just need to buy QuickLoad and be done with it. The basic idea around this whole post was "because the standard test barrel is 24 inches and mine is 16-18 inches, are there better powders out there for my situation? And if so, how do I find them?" Used 7mm-08 vrs 243 as the example. Basically, is there a powder where the performance out of a 24" barrel is crap but is better out of a shorter barrel? Seems like if I were to even consider playing around with this whole thing, I really need to get Quickload, and even then I need way more experience than I have now. And even then still probably not.

 

[Bart B.]

There was an incident on a military rifle team where their rifle shop built a 7-08 for the team to test. The Team Coach said to use the same load for it's 168's as the .308 Winchester used for its 168's. That was challenged by a team member stating 44 grains of IMR4064 was too much for safety and about 40 grains or less would be max, then he told the OIC that he would load it but took no further responsibility for it.

So, the Team Coach took the rifle to the pistol range to shoot a round or two to ensure it's OK to shoot. Chambered the first one, tilted the rifle away from him a little, fired it then screamed. The floor plate was blown off burying it an inch into his leg. Other metal and wood parts splintered into his lower torso. The bolt could not be opened as the case head jammed the bolt closed. That beautiful walnut stock was barely held together in the magazine area. The 'smith at the local shop couldn't get the barrel off. The rifle, as is, was shipped cross cross country to the shop it was built.

I was the one who challenged but loaded it then packaged up all the pieces to ship back to San Diego. The Team OIC said he should have taken my advice when I mentioned it, but he, too, thought it would be OK.

 

[Arkansas Paul]

Sometimes brutally honest is the way to go.

This is absolutely the best way to go when talking about reloading.
There is no room to beat around the bush. Tell it like it is, politely but plainly.

The potential repercussions are too dire for anything else.
Guns are expensive and fingers/hands are priceless.

 

[Arkansas Paul]

Question on why not going under - I know you can have a situation where a half-full case with go dangerously overpressure (heard it called "overflash"). I assume why you say "don't go under" is to prevent this condition, correct?

The reason you don't go under is to prevent pressures that are too low. There is a sweet spot you need to be in and that's why both the minimum and maximum are there.

If the pressure is too low, the primers can back out because they don't get blown back into the bolt face like they're supposed to. A primer backing out too far can cause extraction issues and if it backs all the way out, escaping gasses are right by your face. (I've never seen one back all the way out, but have read about it happening).

 

[Jim Watson]

because the standard test barrel is 24 inches and mine is 16-18 inches, are there better powders out there for my situation?

The answer to that is no.
Barrel length does not affect chamber pressure.
The rather slow burning powder that gives top velocity for a 100 grain 243 in 24" will probably do so in 16".
Muzzle blast will be greater and the gain in muzzle velocity versus a faster powder might be less, but it will still be there.

 

[horsey300]

Hi Mac,

True story on Benchmark, but I was hoping for something in 90-100 grain bullet weight class for the 243 win.

Think I just need to buy QuickLoad and be done with it. The basic idea around this whole post was "because the standard test barrel is 24 inches and mine is 16-18 inches, are there better powders out there for my situation? And if so, how do I find them?" Used 7mm-08 vrs 243 as the example. Basically, is there a powder where the performance out of a 24" barrel is crap but is better out of a shorter barrel? Seems like if I were to even consider playing around with this whole thing, I really need to get Quickload, and even then I need way more experience than I have now. And even then still probably not.

I run h1000 under 95-100 gr bullets out of a short barrel 20", at or above 2930ish (over a chronograph in cold weather) that is a SLOW powder for this cartridge. I would say that your bigger problem will be finding bullets it likes, the 788 18" was keyholing the same fusions that my 20" was one holing. Stay with the short bullets and pick a powder that will get you close to the velocity you want accurately and you'll be fine. Sierra makes the best flat bases in the business imo and if you two can get past the blast of the 18" barrel, you'll be fine!
ETA that is meant in the terms of NOT trying to match powders for both cartridges, even with a tool like quickloads, it doesn't make a bad idea feasible.

If you REALLY want a powder for both cartridges, look at the new imr 4166, 55-100 gr for the .243 and 115-175gr for the 7-08

 

[Bart B.]

Barrel length does not affect chamber pressure.

Right.

But faster powders can produce more uniform pressure curves before bullet exit. That makes lower muzzle velocity spreads. Especially with lighter weight bullets.

 

[DLrocket89]

Bart - Crazy story, thanks for sharing.

Paul - Agreed...when doing things that could get one maimed or killed, one needs to be able to take criticism. This is why I'm not this forum, don't want to hurt myself. Gottcha on the low pressure. One of my favorite loads for my Mini-thirty is about 10% below starting, because it recoils like a 22 and is still accurate. I wouldn't go more than that. I used to shoot USPSA about 10 years ago, ran a 45 ACP, 230 grain FMJ running about 700fps...it was below a starting load and recoiled like a 9mm, but never saw backed out primers.

Jim - understood about chamber pressure. Fair enough on the muzzle velocity, thank you for sharing your experience!

Horsey - Thanks for the input there. And yeah, good point about Quickloads.

Thanks everyone, I really appreciate it!

Dustin

 

[Jim Watson]

Right.

But faster powders can produce more uniform pressure curves before bullet exit. That makes lower muzzle velocity spreads. Especially with lighter weight bullets.

I can see that. Might be why a lot of target shooters stick to 4895 when a sharp pencil on the chart might gain them some velocity.

 

[blue32]

I've done it. But I was going from 7mm-08 to 260 rem. And using Unique with cast loads. Jacketed bullets using data from .284 to .243? That's not a small jump. I have to vote no on this suggestion.

 

[horsey300]

It is doable just not well with most powders,
http://www.hodgdonreloading.com/data/rifle
Imr 4166

I've done it. But I was going from 7mm-08 to 260 rem. And using Unique with cast loads. Jacketed bullets using data from .284 to .243? That's not a small jump. I have to vote no on this suggestion.

Bart - Crazy story, thanks for sharing.

Paul - Agreed...when doing things that could get one maimed or killed, one needs to be able to take criticism. This is why I'm not this forum, don't want to hurt myself. Gottcha on the low pressure. One of my favorite loads for my Mini-thirty is about 10% below starting, because it recoils like a 22 and is still accurate. I wouldn't go more than that. I used to shoot USPSA about 10 years ago, ran a 45 ACP, 230 grain FMJ running about 700fps...it was below a starting load and recoiled like a 9mm, but never saw backed out primers.

Jim - understood about chamber pressure. Fair enough on the muzzle velocity, thank you for sharing your experience!

Horsey - Thanks for the input there. And yeah, good point about Quickloads.

Thanks everyone, I really appreciate it!

Dustin

 

[Arkansas Paul]

Paul - Agreed...when doing things that could get one maimed or killed, one needs to be able to take criticism. This is why I'm not this forum, don't want to hurt myself. Gottcha on the low pressure. One of my favorite loads for my Mini-thirty is about 10% below starting, because it recoils like a 22 and is still accurate. I wouldn't go more than that. I used to shoot USPSA about 10 years ago, ran a 45 ACP, 230 grain FMJ running about 700fps...it was below a starting load and recoiled like a 9mm, but never saw backed out primers.
Dustin

Keep in mind that handgun rounds manifest pressure issues differently than do rifle.
Looking at the primers on handgun stuff isn't a good way to judge pressure.

Low pressure rounds in a handgun will show by the cases being sooty and dirty, caused by there not being enough pressure to expand the brass to seal in the chamber.
And pressures will be well past the dangerous level on the high end well before primers start to flatten out.

As for the rounds in your mini thirty that were 10% below starting, did they cycle the action okay? Of did you get failure to ejects?
Just wondering if it effected that part of it.
My experience with loading for autoloaders is limited to handguns. I'm a rookie as far as auto rifle loading.

 

[DLrocket89]

Paul -

Good point about pistols. This was all 10 years ago and I don't have any records from then. I do remember I went to a lighter recoil spring on the pistol I was using (Ruger P345) to get more reliable function. I ran two different types of powders, one made the cases all sooty so I discontinued it, but the other one (Win 231??) ran well at low charge weights.

Referencing my current activities, the 10% below starting load cycled the action fine, locked back on empty mag and everything. The Mini-Thirty, stock from Ruger, is waaay overgassed though, so I'm not surprised by this. Once I settle in on a final load I'm probably going to install an adjustable gas block and tone it down some.

Dustin

 

[Bart B.]

Might be why a lot of target shooters stick to 4895 when a sharp pencil on the chart might gain them some velocity.

I don't think so. My queries as to why folks did that for 30-06 and 308 target rifles revealed they wanted to use what Lake City Arsenal did in their 30 caliber match ammo. Yet best accuracy happened when IMR4064 was used for 168 to 180 or 190 grain bullets in both when charge weight spreads were 2/10 grain at most. One Arsenal proved that was true, but had to weigh charges to do it. Metered charges of 4895 produced better accuracy than 4064 did with half the charge weight spread in the high speed loading machines used.

However, when 150 and 155 grain match bullets were used in both cartridges, 4895 was best for accuracy. Heavier bullets clustered smaller on target when 4320 and 4350 were used. From one national champion, an old axiom is velocity should equal powder: fast bullets need faster powders; slow ones, slower.