Compressed loads and pressure

[Marble]

So I am developing a new for my 7-08 AI. I'm happy to say I have the time and excess components to play a little.

I'm looking at loading H4350 based on a few recommendations. I tried IMR 4350 @47 grains and got really good ES of 13 FPS averaging 2840 which is less FPS than my previous load, but marginally more accurate. Grouped around 7/8", I'm looking for 1/2" or so. I have room to load about 4 more grains. But the H4350 calls for MAX load of 48.0, with the AI generally I can add 10% to the load, obviously working up slowly. 48.0 is 100% capacity I think, or at least it is a compressed load. So I wonder how much my theoretical MAX load of 52.0-53.0 grains will fill the case up and, if having a compressed load will be good or bad. When I work up a load I usually do .5 grain increments and inspect cases for pressure signs one at a time.

Gun is an A Bolt 1, 22" barrel.

 

[g0rd0]

It sounds to me that you really want to push beyond the safe limits and expect your rig to take it. Don't go there.
If you have a published max at 48.0 grains and up it by 5% that is 50.5 grn BUT that 5% extra powder can give an extra 10% psi.
So, if that 48 grn load equals 52000psi a 50.5grn equals 57200 psi apx. Are you sure you want to do that for a mere 200fps more?

 

[Marble]

It's a published MAX of 48.0 grains with a standard cartridge. This is in Ackley, which generally go up to 10% greater powder volume.

 

[gohring3006]

It's a published MAX of 48.0 grains with a standard cartridge. This is in Ackley, which generally go up to 10% greater powder volume.

Pressure is relative to rifle and components. The only way to find max is work up in your rifle. And if you change a component start again. I do know that most of my 30-06 and 4350 are compressed with no pressure but I don't know how a 7-08 will handle it. But if your load books call for a compressed charge then it usually safe it seem like when I try to compress a charge that a manual says that max is not compressed the I get unpredictable pressure spikes and that's bad.

 

[pods8]

Sounds like you're shooting something ~140gr based on the velocity? Any reason you don't go a slightly faster powder? I've been running Varget in my standard 7-08. I've heard good things about H4350 too but haven't seen any in the last 2yrs to bother trying. IMR4350 was slower and less accurate in my initial loadings versus varget so I just focused in on varget since it takes less powder and is more temperature stable. Biggame is another powder that throws up good numbers, haven't see any of that either.

I can't readily comment on the compacted load, I don't think it does anything in terms of pressures (the compacting action itself which I think is your question) but I'm not the expert.

 

[Marble]

I have been using RL 15 for the past few years and my supply is low and it has been hard getting ahold of it. The load I was shooting was pretty good, about an inch at 2950. But I am just trying to see if I can get something a little more accurate and maybe a little more velocity. I use the gun for blacktail hunting so I don't really need anymore power, but I plan on letting my wife use it for mule deer and antelope next year so I am just looking to see if I can squeeze a little more out of it, as long as accuracy is the same or better. I do not mind shooting a little slower if accuracy improves, but velocity at safe levels is always a plus. Secondly, it's easier for me to use H4350 or IMR4350, RL 22, retumbo or something that is easier to acquire and that I normally have in stock in the garage. I already shoot those powders so having less variety to search for is easier for me.

I loaded up some H4350 in 48.0 through 50.0 this morning, in half grain increments. I shot IMR 4350 the other day at 47 grains and the load was just fine. Chrono'd at 2840.

I shoot the 150g Sirocco in my sons 7-08 (standard cartridge). I may try that bullet too. It's performed very well on about 10 bulls and 5 cows over the last 10 years out of my 7mm on distances up to 500 yards.

The gun I am shooting generally likes a fairly hot load. It tends to tighten up it's group at the upper level of powder charges.

 

[Marble]

Pressure is relative to rifle and components. The only way to find max is work up in your rifle. And if you change a component start again. I do know that most of my 30-06 and 4350 are compressed with no pressure but I don't know how a 7-08 will handle it. But if your load books call for a compressed charge then it usually safe it seem like when I try to compress a charge that a manual says that max is not compressed the I get unpredictable pressure spikes and that's bad.

When you say you get unpredictable pressure spikes, does that mean unpredictable with the same load over time or as you go up in powder charges while testing loads?

And I totally agree with you about starting a load and working up. Some rifles that are identical in make and cartridge cannot shoot the same as another. My buddy and I have identical 7mm's, his will only shoot 67 grains of RL 22, but mine likes 68. Same bullet, same gun, same brass and primer, same lot of powder, same temp outside when we shoot. But each shoots differently.

 

[gohring3006]

When you say you get unpredictable pressure spikes, does that mean unpredictable with the same load over time or as you go up in powder charges while testing loads?

And I totally agree with you about starting a load and working up. Some rifles that are identical in make and cartridge cannot shoot the same as another. My buddy and I have identical 7mm's, his will only shoot 67 grains of RL 22, but mine likes 68. Same bullet, same gun, same brass and primer, same lot of powder, same temp outside when we shoot. But each shoots differently.

When I compressed loads that shouldn't be compressed I would find that I wouldn't get any pressure signs then I might go out a week later and **** near blow a primer,or I might get one case that shows no pressure then the next shot, show pressure. I don't know if its the slight variance in neck tension or capacity. But compressing loads that do call for it leaves no margin for error.

 

[Marble]

Ok. I will error on the side being cautious.

When I loaded 49.5-50.0 were compressed. For standard cartridges it said 48.0 was compressed. I'll have to go shoot and see what happens!!

Thank you everyone for your help. ,

 

[Canadian Bushman]

I like compressed loads and my experience with 4350 in the 08 case shows that it likes it. If youre not getting definite pressure signs i would not hesitate to load past 48gns.

With your increase case volume and seating the bullet out further your gonna burn a bit more powder than a standard 7/08 case.

My go to load for my 308 is 48 gns of 4350 under a 215 berger and i get a slight crunch seating every bullet. This load consistently shoots 1/4-1/2 moa out to 1200 yds. Ive shot this load from 40 deg f to 98 deg f and no pressure spikes.

In testing i shot up to 49.5 gns of 4350 which was heavily compressed. But still had no pressure signs. It was so compressed my seating stem was leaving rings around my bullets.

Just creep up on it and pay close attention to your primers, case heads and velocities when you think youre getting hot, stop.

 

[gohring3006]

I like compressed loads and my experience with 4350 in the 08 case shows that it likes it. If youre not getting definite pressure signs i would not hesitate to load past 48gns.

With your increase case volume and seating the bullet out further your gonna burn a bit more powder than a standard 7/08 case.

My go to load for my 308 is 48 gns of 4350 under a 215 berger and i get a slight crunch seating every bullet. This load consistently shoots 1/4-1/2 moa out to 1200 yds. Ive shot this load from 40 deg f to 98 deg f and no pressure spikes.

In testing i shot up to 49.5 gns of 4350 which was heavily compressed. But still had no pressure signs. It was so compressed my seating stem was leaving rings around my bullets.

Just creep up on it and pay close attention to your primers, case heads and velocities when you think youre getting hot, stop.

your right about imr 4350, I swear I think I could pour it to the top of my 30-06 case rim and stuff a 178 Amax in it and not even use a scale. I don't of course but I don't think you can get enough of it in a 06 case to be over pressure...

 

[pods8]

What bullet are you shooting currently that is 1" groups? Hornady is my plinking load at about 1" but I worked up the bellow 145gr barnes LRX for hunting (left target).

 

[Canadian Bushman]

your right about imr 4350, I swear I think I could pour it to the top of my 30-06 case rim and stuff a 178 Amax in it and not even use a scale. I don't of course but I don't think you can get enough of it in a 06 case to be over pressure...

I know you could definitely do that with a 308. Technically its too slow for an 08 so it should be better in a 7-08. We will have to wait for marble's test to know for sure.

 

[Marble]

I like compressed loads and my experience with 4350 in the 08 case shows that it likes it. If youre not getting definite pressure signs i would not hesitate to load past 48gns.

With your increase case volume and seating the bullet out further your gonna burn a bit more powder than a standard 7/08 case.

My go to load for my 308 is 48 gns of 4350 under a 215 berger and i get a slight crunch seating every bullet. This load consistently shoots 1/4-1/2 moa out to 1200 yds. Ive shot this load from 40 deg f to 98 deg f and no pressure spikes.

In testing i shot up to 49.5 gns of 4350 which was heavily compressed. But still had no pressure signs. It was so compressed my seating stem was leaving rings around my bullets.

Just creep up on it and pay close attention to your primers, case heads and velocities when you think youre getting hot, stop.

That's why I stopped at 50.0 yesterday and loaded three. Going slow is better when working up a load. Normally when you get a good hot load I'll get some primer flattening. I didn't have any at all with 47.0 of IMR4350. These Ackley cases really last. The primer pockets don't grow much if any, the cases don't seem to stretch much either. The necks don't grow, but they will split after 4 firings or so. SO I anneal them and they last another 4-5 firings.

your right about imr 4350, I swear I think I could pour it to the top of my 30-06 case rim and stuff a 178 Amax in it and not even use a scale. I don't of course but I don't think you can get enough of it in a 06 case to be over pressure...

What bullet are you shooting currently that is 1" groups? Hornady is my plinking load at about 1" but I worked up the bellow 145gr barnes LRX for hunting (left target).

I'm shooting the Nosler AB 140. I use it for deer and blackbear here locally. I eventually will have to make a copper only bullet load because I live in CA. It's such horse****.

I know you could definitely do that with a 308. Technically its too slow for an 08 so it should be better in a 7-08. We will have to wait for marble's test to know for sure.

I was thinking the same thing. I think that a lot of info on .308 loading should be able to partially applied to the 7-08.

I'm packing up for a backpacking trip today, taking a friend to go kill a muley up in the warner mountains.. So hopefully next week I'll get enough time to go over to the range to shoot and chrono my loads.

I love this little gun. Eventually I'm going to put a custom barrel on it around 26".