Relatively new to reloading 308 Win. I have had pretty good success with IMR 4895 and Hornady 168 grain Amax using the starting load of 41 grains, per what Hodgdon lists for 168 grain Sierra HPBTs in a 20 inch Aero M5 308, pretty standard all around. Last night I decided to try 42 grains, measuring on a Lee scale and pouring the powder from the pan to a funnel. What I notice was that when seating the projectiles at mag length (2.800"), I would hear some crunching. Given what the data says it seems like that shouldn't happen until closer to 45 grains. Comparing the 168 Amax to the 175 Sierra match kings, it looks like the Amax is longer tip to butt due to the ballistic tip. Is this normal? Should I lower the load, or increase the COAL to the longest my mag will actually fit?
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Compression with relatively light load - IMR4895 and Amax 168 .308 Win
- Thread starter westsidecamper
- Start date
If you're pressing in a longer bullet into the same casing to the same OAL as the shorter bullet then that longer bullet is poking into the powder. A little crunch is OK, but jumping one full grain is a bit of a large jump if your 41gr load was doing well as you say. Generally, when developing a load you would do 0.2 or 0.3gr jumps. For OAL, you can likely seat the bullet to mag length and be good to go. Try one and chamber it, as long as the bullet isn't touching the rifling, you're good to go. If it is toughing the rifling, seat it shorter until its about 0.020-0.030 off the rifling. Easy day.
So, as a general guideline, you could do, for example, 3 or 5 rounds each at 40.7, 41, 41.3, 41.6, 41.9, 42.2, 42.5 and shoot each group at 100y to see which one does the best in your rifle. If you are shooting the higher-end charges and you notice primer flow, primer flattening, primer cratering, light ejector swipes... take note and proceed cautiously as you are getting into the yellow/caution pressure area... if cases get stuck in chamber STOP SHOOTING and do not go any higher as that is definitely beyond the safe pressure area. Take note of what charge weight caused that issue and make the previous safe charge your MAX charge weight.
If you're looking for fun/accurate plinking, then pick the charge weight that gave the best accuracy and just shoot that load. There's a deeeep rabbit hole to dive into with reloading. I'd keep it simple because it will work, and be a lot more fun than constantly tinkering which can become frustrating and make reloading a chore, losing the fun of it.
Welcome to the reloading world! Be safe and HAVE FUN.
So, as a general guideline, you could do, for example, 3 or 5 rounds each at 40.7, 41, 41.3, 41.6, 41.9, 42.2, 42.5 and shoot each group at 100y to see which one does the best in your rifle. If you are shooting the higher-end charges and you notice primer flow, primer flattening, primer cratering, light ejector swipes... take note and proceed cautiously as you are getting into the yellow/caution pressure area... if cases get stuck in chamber STOP SHOOTING and do not go any higher as that is definitely beyond the safe pressure area. Take note of what charge weight caused that issue and make the previous safe charge your MAX charge weight.
If you're looking for fun/accurate plinking, then pick the charge weight that gave the best accuracy and just shoot that load. There's a deeeep rabbit hole to dive into with reloading. I'd keep it simple because it will work, and be a lot more fun than constantly tinkering which can become frustrating and make reloading a chore, losing the fun of it.
Welcome to the reloading world! Be safe and HAVE FUN.
Measure the length of that bullet and measure its weight to verify it's what on the package. Length should be ~1.265 for the Hornady 168 A-Max.
With a COAL of 2.800 42.0 grs of IMR 4895 only fills the case to 97.1% and so, I wouldn't expect the powder to be compressed like that. With 45 gr., then yes. . . there'd be some compression as the case would be at 104.1% of capacity.
What brass am I using?
- Good question, I'm using PMC and Hornady brass. I heard the crunching with both. I only loaded about 6 bullets because of this. I did confirm that 41 doesn't cause crunching but 42 does.
Bullet length
- 1.28x pretty consistently. That tip increases the length significantly.
Why did I jump up a full grain if I had good results?
- Good question as well. I want to see what results I get with a higher charge because I wanted to get more velocity. The public range I go to only goes to 100, so that's what I test at, but at a friend's range I can push as far as I want. The load I had before was good but it was dropping more at 300 than I would like. I don't have a trickler so it's been pretty painstaking to measure loads, so basically laziness motivated the jump. If there's good evidence that I'm missing out by not using 1/3 or 1/2 grain increments, please point it my way so I can motivate myself to do better.
- Good question, I'm using PMC and Hornady brass. I heard the crunching with both. I only loaded about 6 bullets because of this. I did confirm that 41 doesn't cause crunching but 42 does.
Bullet length
- 1.28x pretty consistently. That tip increases the length significantly.
Why did I jump up a full grain if I had good results?
- Good question as well. I want to see what results I get with a higher charge because I wanted to get more velocity. The public range I go to only goes to 100, so that's what I test at, but at a friend's range I can push as far as I want. The load I had before was good but it was dropping more at 300 than I would like. I don't have a trickler so it's been pretty painstaking to measure loads, so basically laziness motivated the jump. If there's good evidence that I'm missing out by not using 1/3 or 1/2 grain increments, please point it my way so I can motivate myself to do better.
Well, that length of ~1.28x is not out of reason (compared to a published length). And though yours are longer, it still shouldn't produce a compressed load when using 42 grains unless the case volume is much smaller than normal (like at 54.3 grs of H2O). So, the only other thing left to do is to find out what case volume(s) you're dealing with for those Hornady and PMC brass (FYI: normally, one would measure fired brass for other calculations).
Get a Hornady ogive tool and measure the distance to the lands in your rifle. Seating to 2.800 in a 308 is like putting a 3 cylinder in a Ferrari. I run 44.5gr of H4895 with a 180 Berger and am not compressed and still feeds through a 2.950 mag.
Not much I can do about this unfortunately. It's an AR so the longest mags are still only 2.87 inches. I think I can fit 2.83 in the magpuls I have. Which I bet would not crunch at all.
I think he simulated w/ a nominal case capacity in GRT or quickload
Knowing what I know now, there's a lot of variance in case capacity for 308 brass between brands.
