Is IMR 8208 XBR Only Accurate Above Max Load?

[ConcernedCitizen]

If you've tried IMR 8208 XBR, would you mind sharing your results, good or bad? I'm having a hard time working up a load with this powder, and have had an even harder time finding any good load data online. IMR's load data seems overly conservative, and Hornady seems to be the only other published source I've found so far. Most posts that I've found mentioning this powder seem to indicate that the best accuracy is found the closer you get to max, and most people seem to be running their personal load at or slightly over the published max.

I'm currently experimenting in .223 with Hornady 55 gr. FMJ-BT and 60 gr. SP. I've worked all the way up from IMR's minimum loads to Hornady's maximum loads with IMR 8208 XBR using both CCI-400 & CCI-450 primers, and the only decent groups I've seen so far have been right at Hornady's max load. No visible pressure signs at all, even at max. Didn't have time to break out the chronograph, so no velocities yet on the max loads.

Does this match everyone's experience so far? If you've tried venturing above max, how far have you gone, and where did you see your best accuracy? Where did you see pressure signs, if any? I know that many are hesitant to post load data above published max, so please feel free to PM me if you prefer.

I'm fully willing to attribute my lousy groups to my poor shooting skills, but would like to hear others' experiences before I spend too much more time chasing groups at max load. I have other powders to choose from, but was hoping to find a good load with this one due to the temperature insensitivity and good metering. Any and all feedback is welcome.

Thanks!

 

[Shmackey]

My results have been excellent without going over Hornady max. It's my favorite rifle powder.

Granted, I haven't tried loading it hotter, but I never saw a reason to do so. My current pet loads are all just a few tenths below max.

 

[Grumulkin]

The published "max" is what the publishers of the reloading manual got with THEIR gun, primers, lot of powder, etc. If you're not having signs of high pressure, then you're not at your "max." In addition, I believe it's pretty worthless to rely on velocity to determine if your load is at max.

I have tried IMR 8208 XBR in a number of loads. I get EXCELLENT results in a 270 Winchester. I've also tried it in a 223 Remington, a 30/06 Springfield and probably some others and got better results with other powders.

 

[steve4102]

The published "max" is what the publishers of the reloading manual got with THEIR gun, primers, lot of powder, etc. If you're not having signs of high pressure, then you're not at your "max." In addition, I believe it's pretty worthless to rely on velocity to determine if your load is at max.

This comment from Grumulkin really got my attention and I could use some clarification.

What pressure signs are we looking for that we "must" see before we are actually over pressure?
The 223 runs at 55K psi, these pressure signs that we must see show up in the 223 Rem at what psi, 56K, 60K, 65K or 75K and do they show up at different pressures for different cartridges?

The 5.56 runs at 62K psi, how do these pressure signs Know to show up just over 55K in the 223, but wait until over 62K in the 5.56?

Flattened primers is always used as an indication of an over pressure load. How does this work?
The 7.62x39 runs at a SAAMI max of 45K psi while the 270 Win runs at 65K psi, both take the same primer. How does this primer know to flatten just over 45K in the 7.62 x 39 and wait until over 65K psi in the 270 Win?

Sticky bolt lift is another sign we look for. At what psi does this occur? I'll use the same cartridges, the x39 and the 270, how does the rifle know not to "go stiff" just over 45K in the x39, yet wait until over 65K in the 270?

 

[MtnCreek]

Don't expect much from Hornady 55gr FMJ's. They're good bullets for what they are, but they are not target bullets. For a good shooting 55gr bullet, look at the Nosler BT.

My results w/ 8208 / .223 have been great and I have not exceeded published max.

 

[ConcernedCitizen]

I appreciate everyone's feedback so far.

I know that the 55 grain bullets are not the most accurate, and was focusing more on the 60 grain SP. I don't have the targets in front of me to measure, but groups were averaging 2"-2.5" right up until I hit max, and then immediately shrank to approximately 1.25". On one target, I had 3 rounds touching out of a 5 shot group.

My concern was regarding running right at max load. I'm keeping a close eye on primers, and looking for ejector swipes or extractor marks on the brass. So far everything looks good, but I am somewhat cautious given the lack of data available. That was the reason for this thread, to get a few real world experiences from this forum's members.

I plan to work up the same load in another rifle, but with better magnification this time. I have a feeling that I am somewhat limited by my equipment, as I'm currently using a 4 power scope and did not have good sandbags for a rest. Even with my limited equipment and mediocre shooting skills, there was a noticeable difference in accuracy once I hit max. I plan to load up another batch at max, and shoot a few 10 shot groups to get a better feel for the load.

Thanks again for all the feedback!

 

[Sunray]

"...right at max load..." That's not a big deal. Max loads aren't something to be worried about. Going over 'em can be though. Some rifles just like 'max' loads. IMR 8208 XBR's pressure with a 60 grain bullet isn't the highest anyway.
"...I'm keeping a close eye on..." Look for hard extractions and difficulty opening the bolt.

 

[BoilerUP]

Just came across this thread so I figured I'd bring it back to life...

I have an 18" 1:8 BHW 5.56 barrel on my FrankenSPR. I get very solid sub-MOA accuracy with 8208XBR and a 77gr Nosler CC @ 2660fps with 23.5gr 8208XBR, which is over the Hodgdon max load of 23.2gr. I've tested as high as 24.0gr XBR with ZERO pressure signs and velocity similar to Mk262Mod1 at that charge weight.

I tried Hornady 55gr FMJBT from 24.2gr up to 25.8gr XBR and accuracy was disappointing; UMC 55gr Metal Case shot equal or better than my best groups. 25.6gr was the 'best' I tested with velocity equaling the UMC ammo, though I have not loaded up a bunch to retest as the barrel loves 77s.

I also have a 22" 1:7 223AI bolt gun that I shoot 8208XBR out of with 80gr A-Max, and its best accuracy (and its been spectacular) comes right on the edge of too-hot.

 

[ConcernedCitizen]

I appreciate the bump, as I forgot to follow through with an update.

My best groups with the Hornady FMJ-BT were at 25.0 and 25.8 grains. I decided to go with the 25.0 grain load for practice ammo, to conserve powder and reduce wear and tear. The velocity for the 25.0 grain load also matches my BL-C(2) load, and seems to shoot to the same point of impact, so I'm happy about that. I might revisit the 25.8 grain load, just to get some chronograph data in the future.

For my 60 grain SP loads, 25.0 and 25.3 were almost indistinguishable, with perhaps a slight edge to the 25.3 grain load. I was noticing some slight flattening of the primer when using CCI-400s, but no visible signs when using CCI-450 primers. I went with 25.0 grains along with a CCI-450 primer to give myself a bit of a safety margin. I might revisit this load later on, and work up in .1 grain increments, just for fun.

I'm also happy that the same charge works well with both bullets, which lets me leave a powder measure set just for this powder.

 

[Grumulkin]

This comment from Grumulkin really got my attention and I could use some clarification.

What pressure signs are we looking for that we "must" see before we are actually over pressure?
The 223 runs at 55K psi, these pressure signs that we must see show up in the 223 Rem at what psi, 56K, 60K, 65K or 75K and do they show up at different pressures for different cartridges?

There are multiple pressure signs and they vary depending on the cartridge and the gun they're shot in. The mistake most people make is to focus on one to the neglect of others. By the way, using a chronograph to get the velocity is the least dependable of them.

For example, in a cartridge for a lower pressure load to be fired in a not so strong gun, the first pressure sign may be the gun blowing up in your face. In a stronger revolver such as the Freedom Arms Model 83, the first pressure sign will be difficult ejection of cases. In a Thompson/Center contender shooting something like 222 Remington, the first pressure sign may be a pierced primer, a primer leak or difficulty opening the action; the primers will not be in a so called "flattened" state. I could go on.

The 5.56 runs at 62K psi, how do these pressure signs Know to show up just over 55K in the 223, but wait until over 62K in the 5.56?

Regarding pressure signs, they don't know.

Flattened primers is always used as an indication of an over pressure load. How does this work? The 7.62x39 runs at a SAAMI max of 45K psi while the 270 Win runs at 65K psi, both take the same primer. How does this primer know to flatten just over 45K in the 7.62 x 39 and wait until over 65K psi in the 270 Win?

Flattened primers are highly touted by some and disparaged by others. Sadly, both views are wrong. When applied to a specific gun and cartridge flattened primers can be a very useful pressure sign. For other guns and cartridges it is a worthless pressure sign.

Sticky bolt lift is another sign we look for. At what psi does this occur? I'll use the same cartridges, the x39 and the 270, how does the rifle know not to "go stiff" just over 45K in the x39, yet wait until over 65K in the 270?

Just remember what "maximum" pressure is. It is the pressure at which the best performance of the cartridge occurs while still maintaining the safe integrity of the cartridge case, the primer and the firearm.

Going back to the Freedom Arms Model 83 revolver as an example; it will take 65,000 psi or more without blowing up as will a 454 Casull cartridge and primer. A 45 Colt cartridge (by the way, there is no such thing as the often mentioned "Long Colt") can also be fired in the same gun and since the constructon of that cartridge is different, if you shoot 65,000 psi loads with it, you're risking excess brass stretch or maybe failure.