Finding a load- ES, SD, speed and accuracy question(s)

[VO2Max]

Hi,
I have a question for those who have been reloading for longer than me: I am working up loads for my hunting rifles (7mm RM and 7-08) and am looking at data collected... I’m finding that my 7mm RM loves higher charged loads and shoots tighter groups with those loads. But, with my 7-08 I found one group at around 2500fps which shoots incredibly tight groups with low ES and SD and then I found that it likes a higher charge with low (not as low as the lower mentioned above) SD and ES but at 2700fps. Chase speed a bit or chase accuracy and slightly better consistency in this case? The 7-08 will be my 300yd max deer rifle (occasional bear if in high alpine).

thiughts appreciated.

 

[cahunter805]

What grain bullet and what brand? 2500 is pretty slow and I’d probably just work around the 2700 load and fine tune it a bit more.

 

[VikingsGuy]

Bullet type, game type, max yardage, will all play a role in answering the question. If for deer under 250y with lead bullet I don't think the extra speed is necessary, but if shooting mono-copper, elk, over 300y I would try a different powder or different bullet to get your 7mm08 up over 2800.

 

[ImBillT]

Accuracy “nodes“ are entirely velocity based. Accuracy nodes are essentially the velocity at which barrel vibrations will slightly correct for velocity variation. At 100yds the effect can be quite pronounced and under the right circumstances you can shoot teeny tiny groups with horrible SD/ES numbers. There are multiple nodes that will all have relatively similar effects. Once you find the velocities that those occur at, you can get back on them with other powders and bullets. Some powders may not be able to reach the upper nodes due to exceeding safe pressures or running out of case capacity before the required velocity is reached.

Low SD/ES is more a function of consistent charge weight and consistent ignition. Improving those numbers happens through several ways. Charge weight can vary a lot more than you think without making much difference. Even plus or minus .5gr can yeild some pretty good SD/ES numbers. Using good primers is a requirement. Wolf, PMC, S&B, Federal Gold Metal, and CCI-450’s all have good reputations. Next, getting good conditions for the powder at hand is important. Ball powders are hard to ignite and sometimes require magnum primers, not just consistent primers. Jumping or jamming a bullet can change how consistent your ignition is. Some powders are most consistent at very high pressure. Others get erratic at high pressures. Regardless of pressure, you’ll almost always get your best SD/ES with a nearly full case.

You can wear out a barrel tuning. Just get on a node with a powder that lets you fill the case and you’re most likely about as good as you can get. Let the paper tell you if you’re shouting ok. Only worry about SD/ES if you know you’re on a node and the paper tells you that you’re still not shooting great. In that case, improving SD/ES by changing primer, seating depth, or powders MIGHT be of benefit. Sometimes a particular powder will only give good SD/ES numbers on the higher or lower nodes. Rarely a certain powder may only yield good SD/ES numbers above any of the nodes it can reach before going over pressure.

Off-center primer strikes can cause bad SD/ES, and the fix is to bush the firing pin hole. That’s going way down the rabbit hole though.

 

[Dougfirtree]

For the 7mm-08, you could just try a different powder, but you could also take the most accurate charge weight that does give you a velocity you're happy with, even if the group is like, 2" and then play with seating depth. You may find that you can shrink it right down. In my experience, seating depth can make a massive difference.

I'm no expert, but I'm not sure I buy into the idea that accuracy nodes are 100% about velocity. I think they're about vibration and that vibration can be caused not only by the velocity, but also characteristics of the powder and its burn rate. I've definitely noticed accuracy differences between different powders using the same bullet and same velocity. So, anyway, for what it's worth, I wouldn't be afraid to try a different powder. What is the powder you're using? Most people seem to be able to find accuracy with Varget in the 7mm-08. I've had great luck with H 4895 and IMR4350 too.

 

[Dougfirtree]

Also, for general hunting, if there are big differences between velocities with a certain load, from shot to shot, but every shot is still hitting where you want it to, I think that's fine. I put way more emphasis on the groups I'm shooting than on what my Chronograph is telling me. I might feel differently if i was shooting long range in competitions, etc.

 

[Deleted member 16014]

For 300 and under it really isn't gonna matter much either way. I guess given the choice I'd take the speed unless velocity variation was a total disaster. 600+ and that ES/SD starts to matter a lot more. My two cents.

 

[std7mag]

The 7mm-08 is quite capable of taking game, including elk out to 400 yards. Ask our fearless leader.
I have taken deer at 400 yards with mine.

Varget, while known for it's excellent accuracy, doesn't give the velocities i'm looking for in a hunting cartridge.
You need enough muzzle velocity to still give you enough velocity at range for your bullet to expand.
Example would be a 140gr Nosler Ballistic Tip at your 2,500 fps would give you an effective hunting distance of 400-450 yards. Same bullet at 2,800 fps stretches distance to 600 yards. This is just for the minimum 1,800 fps expansion velocity.
Obviously your 2,800 fps is going to give you higher energy at closer ranges.

Consistancy is the name of the game for accurancy.
Primer seating depth, trim length, powder charge, etc..
But for your 300 yard max distance, it really doesn't pay dividends to be to ana (err, worried) about ES/SD.

 

[44hunter45]

Accuracy “nodes“ are entirely velocity based. Accuracy nodes are essentially the velocity at which barrel vibrations will slightly correct for velocity variation. At 100yds the effect can be quite pronounced and under the right circumstances you can shoot teeny tiny groups with horrible SD/ES numbers. There are multiple nodes that will all have relatively similar effects. Once you find the velocities that those occur at, you can get back on them with other powders and bullets. Some powders may not be able to reach the upper nodes due to exceeding safe pressures or running out of case capacity before the required velocity is reached.

Low SD/ES is more a function of consistent charge weight and consistent ignition. Improving those numbers happens through several ways. Charge weight can vary a lot more than you think without making much difference. Even plus or minus .5gr can yeild some pretty good SD/ES numbers. Using good primers is a requirement. Wolf, PMC, S&B, Federal Gold Metal, and CCI-450’s all have good reputations. Next, getting good conditions for the powder at hand is important. Ball powders are hard to ignite and sometimes require magnum primers, not just consistent primers. Jumping or jamming a bullet can change how consistent your ignition is. Some powders are most consistent at very high pressure. Others get erratic at high pressures. Regardless of pressure, you’ll almost always get your best SD/ES with a nearly full case.

You can wear out a barrel tuning. Just get on a node with a powder that lets you fill the case and you’re most likely about as good as you can get. Let the paper tell you if you’re shouting ok. Only worry about SD/ES if you know you’re on a node and the paper tells you that you’re still not shooting great. In that case, improving SD/ES by changing primer, seating depth, or powders MIGHT be of benefit. Sometimes a particular powder will only give good SD/ES numbers on the higher or lower nodes. Rarely a certain powder may only yield good SD/ES numbers above any of the nodes it can reach before going over pressure.

Off-center primer strikes can cause bad SD/ES, and the fix is to bush the firing pin hole. That’s going way down the rabbit hole though.

Lot's of gold in this post, @ImBillT .

 

[BuzzH]

Bullet type, game type, max yardage, will all play a role in answering the question. If for deer under 250y with lead bullet I don't think the extra speed is necessary, but if shooting mono-copper, elk, over 300y I would try a different powder or different bullet to get your 7mm08 up over 2800.

I might be tempted to pick up the 7RM he said he has if elk are the issue....

If my 7-08 was my primary deer rifle for 300 yards and closer, and velocity was lackluster with the 140's, I would be tempted to try some 120 BT's.

 

[RiverRatt]

I just did a Saterlee Ladder test with 150 ELDX, H4831SC, and Hornady brass. I am shooting a Remington 700 7mag and shot for a group at 100 yards. Using a Caldwell chronograph to record velocities I found a sweet spot around 3100fps. I have a friend who said he's seen 3100 to 3120fps for 150g bullets. This is the most consistent and accurate my gun has shot since I started trying to find a load around 300 shots ago. I was getting crazy frustrated but changed the stock and bedded recoil lug fixed my issues.

 

[Brian in Montana]

I've had similar results in my 7-08. With 140gn Accubonds, it shoots really good groups around 2500fps. I don't want to shoot that load, I definitely am a speed chaser. The best I've found in my 7-08 is with a 139gn Hornady Interbond, using Big Game powder. I can push that to almost 2900fps very accurately and with low ES and SD. This stuff really depends a lot on what you want to do with it. That lower velocity load is probably very comfortable to shoot and with the right bullet design would certainly be adequate for mid-sized game.

I worry most about how a load groups, but I seem to find that the best grouping loads also tend to have relatively low ES. I know a lot of guys geek out pretty huge on ES and SD. I pay attention to them, but at the distances I generally shoot an ES of 25 really isn't going to make much difference. You have to be reaching out there a ways for the difference to become that much of a concern. That's why the hardcore bench rest and competition shooters wring their hands over it so much.

I really don't hunt much with my 7mm-08. I've only shot an antelope and a WT deer with it. It certainly did the job.