Compressed load for 7mm-08?

[wsryno]

I'm loading for 7mm-08 using Winchester cases (2.025 trim length, 2.755 COL), WLR primers, IMR4350, and Hornady 139gr SST. This is the first time I've worked up this caliber. I started at the low end with Hornady's load data: 39.5gr then 41.3gr then 43.0gr, and by the time I got to 43.0 the loads started compressing. Just a little. So I loaded 44.8gr and it seemed like a lot of compression. The max load is listed as 46.5, and it's not listed as a compressed load. I stopped at 44.8 because I was a bit uncomfortable. I shot 3 rounds of each of the 4 loads with no excessive pressure signs; all the fired cartridges looked the same and I noticed only a very slight increase in recoil.

But the question remains in my mind: how much compression is too much? Thanks in advance.

 

[GJgo]

I would suggest that "too much" compression is when your OAL starts growing with compressible powders like 4350, or when you start to dent the bullet as with non compressible powders such as the AA9 I use in some pistol cartridges.

 

[helotaxi]

Just because you're crunching powder when seating the bullet doesn't mean that your load is compressed. It isn't really compressed until their is no space between the kernels of powder within the case. FWIW it is very difficult to get to that point. If I find that I'm getting to the point of filling the case to or above the bottom of the bullet, I'll try to settle the powder down into the case better by either slowly pouring powder from the scale pan into the case while rotating the case in my fingers or gently tapping the case on the bench ot settle the powder in. I've gained significant usable case volume with these techniques and the longer the powder kernels, the more the gain typically.

 

[ArchAngelCD]

Why are you using IMR4350 in the 7mm-08? IMO that powder is slightly on the slow side for that small a case. That's why you are having trouble getting to the Max recommended charge weight without running out of case space. IMO H414/W760 will give you the same velocity and pressure but not compress. Also, most any powder that will work well for the .308 will work in the 7mm-08 too but my buddy prefers W760/H414 but also uses BL-C(2) when he has a lot around for loading his .308 ammo... This is just a guess on my part but I'm betting Varget would also play well with the 7mm-08.

 

[wsryno]

Based on what helotaxi and GJgo have said, my loads were "crunched" but not compressed. I didn't meet any extra resistance when seating bullets on my max load, and I would expect that if the case was being damaged or COL was getting longer there would be some extra resistance.

My concern was not over-charging, because I am being as careful as possible weighing each charge. My concern was the relative safety of crunching the powder in the case with the significant leverage afforded by the press. I want the bang while the round is in the gun, not on my press.

Why are you using IMR4350 in the 7mm-08? IMO that powder is slightly on the slow side for that small a case. That's why you are having trouble getting to the Max recommended charge weight without running out of case space. IMO H414/W760 will give you the same velocity and pressure but not compress. Also, most any powder that will work well for the .308 will work in the 7mm-08 too but my buddy prefers W760/H414 but also uses BL-C(2) when he has a lot around for loading his .308 ammo... This is just a guess on my part but I'm betting Varget would also play well with the 7mm-08.

Convenience. I wanted a powder that I could load for .270, 7mm-08, and .308 (not loading .308 yet but will) with several different bullets (Hornady SST for lower priced practice/fouling rounds and Barnes TTSX for hunting). When I put all the data from numerous sources into an Excel spreadsheet and cross referenced the calibers, bullets, and powders I was left with about 5 choices. I chose the slowest of those 5 for apparently no good reason other than it would work with everything I plan to load in the near future, and it was in-stock.

I hunt deer in thick cover which limits 99% of my shots to 75 yards or less, which is also why I use iron sights most of the time. I have mounted a scope on my rifles as I'm working up a load, as I think this will give me much better feedback on the relative "accuracy" of the load. But once I've nailed down an accurate load, I'll only leave a scope on one of my rifles, whichever one has managed the smallest group. What I'm trying to say is that I don't need ridiculous accuracy.

FWIW I found my 7mm-08 loads to have relatively low recoil. Maybe this is another thread but is there a relationship between powder burn rate and recoil, everything else being the same?

 

[GJgo]

The 7mm08 I load for prefers RL17 (fast version of the 4350s) to Varget, so you just need to let the gun tell you what it likes. Personally I like the slowest powder I can hit my veloicity & accuracy goals with.

 

[helotaxi]

FWIW I found my 7mm-08 loads to have relatively low recoil. Maybe this is another thread but is there a relationship between powder burn rate and recoil, everything else being the same?

Assuming the same muzzle velocity and same bullet, total recoil impulse will be the same (very slight variance for the difference in powder weight) regardless of powder burn rate. What will change is the character of that recoil. The faster burning powder builds pressure more quickly and the initial bullet acceleration will be quicker. That results in a sharper initial recoil impulse which, to most people, seems like more recoil.

 

[GooseGestapo]

With my 7mm08, it's no contest between the "4350's" and the faster powders. Until RL17 came along, it's what I used (4350's). The only "exception" was BLC2 with a 139gr Hornady. At 44.0gr (hot), it's almost as good as IMR4350.

I use 46.0gr of IMR4350. Not as fast as 46.5 but slightly more accurate (barrel harmonics?).
However, RL17 is slightly denser, smaller grained, and quite a bit faster velocity wise.
I'm getting 2,900fps from a 20"bbl with 139-140gr bullets and 2,800fps with 150gr Bullets. I'm only getting ~2,800 with 139's and high 2,700's with 140's with the "IMR".

My rifle isn't MOA but approaches for 3-shots with 48.0gr w/139gr Hornady's, 47.0gr w/Nosler and Sierra 140's, and 46.0gr w/150gr Nosler and Sierra's. These are seated to ~2.790" and are "slightly" compressed loads. Less so than the IMR4350's.
RL17 has accuracy of "IMR" and equal or better velocities of "H" 4350.....
My rifle also has a pronounced preference for 150gr bullets, especially the Nosler BallisticTips.
Just bought another 5lbs yesterday to start working up some loads for my .375Ruger..... And some "old" bullets with "old" prices.....
I'm not so sure if the wallet doesn't "wallop" me more than the rifle when shooting this monster..... But it sure is fun, and most accurate "Ruger" I've ever shot...

 

[Dthunter]

As far as compression is concerned, if you hear the "crunch",it is compressed....period.

But thats isnt a big deal normally. If a/some powder is "overly" compressed it can affect the burning characteristics. Normally an over compressed charge will exhibit larger standard deviations. This is where a Chronygraph is absolutely golden!

If you use a ball powder, compression is/can be a bad idea. First, ball powders are far more dense, and therefore less compressable. Try to compress a ball powder too much, and you can damage the bullet ogive on seating, misform a case, or both.

Second, I have found ball powders tend to not perform thier best when compressed. The pressures can be elevated, and the standard deviation of the load can increase.

If you use a Chronygraph as you target shoot, you can see how a compressed load affects "YOUR RIFLE".

"My 7mm-08 Loves IMR4350! Compressed slighly.

The OP says his shots are normally inside 75 yards. At this distance, just about any load in any manual (for his preferred bullet weight) for his .308win. Will do fine.

Have fun guys, and keep it simple.

 

[snuffy]

But that isn't a big deal normally. If a/some powder is "overly" compressed it can affect the burning characteristics. Normally an over compressed charge will exhibit larger standard deviations. This is where a Chronograph is absolutely golden!

In my experience and that of many others, the exact opposite is true. Compressed powder charges have lower standard deviations. You WANT as near 100% load density as you can get.

Also, the only reason a compressed charge will exhibit higher pressure is because you just added MORE powder! It has nothing to do with compressing the powder charge.

One trick, well actually two tricks, to getting more powder into the case, is a long drop tube under the funnel. Then to slowly pour the powder, not just dump it in. Second is using a standard funnel, but slowly pouring the powder on the edge of the funnel, let it swirl into the case. It "lines up" the powder granuals to take up less room. Doubts? Try it and see.

If you use a ball powder, compression is/can be a bad idea. First, ball powders are far more dense, and therefore less compressible. Try to compress a ball powder too much, and you can damage the bullet ogive on seating, misform a case, or both.

Very true. Ball powder can't be compressed much at all. But it seldom has to be, because it's denser that extruded powder. Again, the long drop tube will allow it to settle better.

If you use a Chronograph as you target shoot, you can see how a compressed load affects "YOUR RIFLE".

Very true also. Maybe what I wrote above isn't always true, but has been true for every rifle I've owned/loaded for.

 

[sourdough44]

Varget here with 120 & 140 grn bullets.

 

[primape]

I have found that in my Mod 7, even though the max load for IMR 4350 is listed at 46g for 140 Nosler BT's, a little over 46 is more accurate and shoots better than factory Remington 140g bullets without a scope adjustment. That loading of 4350 does compress the powder.

I don't understand why a slow powder like that shoots so well in a 20" barrel. It is so much more accurate than 4895, 4064, and Varget in my rifle.

 

[GJgo]

The 7mm-08 I load for has an 18" barrel & it likes RL17 best. My Swede has a 22" barrel & it likes H1000 best. I don't know why, but if it works it works.

 

[wsryno]

Interesting discussion, thanks for all the feedback. I just wanted to know if what I was doing sounded safe but I learned a lot more.

For this rifle (Rem Mod 7 18.5" bbl) if I can consistently group under 2" @ 100yds then I'm done working up my load. At that point, my time and money will be better spent practicing than working up the .75" group (which may not be possible with this shooter behind the glass anyway ). Remember, I'll be taking off the scope and using the iron sights and I won't have a shot over 75yds. I suspect the deer would only be slightly deader when hit at 2800fps than 2700fps

Later on, when I work up a load for one of my rifles that I will leave scoped, I will work as hard as possible to get to MOA accuracy, so the critter that appears 200yds downrange doesn't have to suffer. It's the least I can do.

The OP says his shots are normally inside 75 yards. At this distance, just about any load in any manual (for his preferred bullet weight) for his .308win. Will do fine.

Have fun guys, and keep it simple.

Dthunter you nailed it!