6XC Load Data - N550, IMR-4166, RL-23, H4350

[spamassassin]

There doesn't seem to be quite enough variety out there. 6XC can do wonders with quite a number of powders. It's not all H4350's world. Coach and I did some experimenting and we have some helpful results. We'll be doing some more testing with other powders in the coming weeks.

This data came from our initial efforts at load development for my new 6XC barrel for my prone/PRS match rifle. So far it looks like we'll be using a 39.5gn charge of H4350 to get just shy of 3,000 FPS and single digit SD's with groups at about half an inch. It was a very tight decision as I would normally have chosen the actual winner which was N550 in a slightly lighter charge. N550 is super expensive compared to H4350 and we have several 8lbs jugs of H4350 on hand and only about 3lbs of N550.

Since we'll be using the same load in both of our rifles (don't forget there's a 2nd new 6XC barrel identical to mine ready to go onto Coach's gun), we will of course have to make sure the load performs acceptably from that rifle but so far, I haven't made a test load I would feel bad about using in a match.

Chamber: 6XC (CIP)
Brass: Norma Large Primer, .013" neck thickness, .003" neck tension
Primer: Federal 210
Bullet: 115gn DTAC RBT HBN coated jumping .040"
Barrel: Columbia River Arms P3 (Polygonal 3 land) 25.5"
Muzzle Device: N/A

H4350 (well we did test it a good bit)
Brief: 37-40gn seems to be a decent window. Known solid performer. 3000fps is probably pushing pressures a bit for maximum brass life. Getting the case as full as possible seems to help SD's.
38.5gn: 2929 average, 13fps SD, .75" group
39gn: 2964 average, 15fps SD, .71" group
39.5gn: 2977 average, 2fps SD, .33" group

RL-23 (Reloader 23)
Brief: 37-40gn seems to be a decent window. Likes a full case. SD's really opened up without a pretty full case in multiple chamberings. Meters terribly. Burns clean. We estimated we could pop 40gn in the case and get 2950fps. More testing coming but this was a very soft load pressure wise.
38gn: 2837 average, 28fps SD, .65" group

N550
Brief: 35-38gn seems to be a decent window. Expensive powder but turned in a stunning pair of development groups at .1" and .2" with single digit SD's. Pressures were mellow and it was a very quiet shooting load. People should start looking closer at N550. We started very soft
36.5gn: 2892 average, 12fps SD, .2" group

IMR-4166
Brief: The load listed below is TOO HOT by at least a full grain. Reduce >2 grains minimum before attempting to use. We got brass flow into the ejector hole with this load on 2 of 5 shots. The above noted, this is looking like a possible stunner. Low SD's have been routine with this powder in every overbore case we've tried it in with a heavy bullet. Might be better for slightly lighter bullets than we tested.
37.5gn: 3086 average, 2fps SD, .53" group

 

[spamassassin]

6XC Load Development - Analysis Time

This little case seems to really like being as full as possible and/or run a little hard and put away a little bit wet if you get my meaning. We broke in the barrel with 15 shots but as you can see from the data below, around shot #6 things stabilized. By round 10 I had warmed up the barrel a bit and was vacillating between baking rounds in the chamber while I wiggled around trying to get a natural point of aim and firing quickly when I was already at a good NPoA.

All discussions of load data and charge weights come with the "don't copy me and hurt yourself" disclaimer. Don't just run my loads, work up to them. These are all on Norma brass, F210 primers, 115gn DTAC bullets and COAL at 2.8".

Around shot #6 things pretty well started to stabilize. Inconsistently going between firing quickly and baking rounds in a warm-ish chamber widened the ES a bit.

After grinding out the first 15 rounds to break in the bore and establish a zero; this was a BRAND NEW barrel after all, we took a little break and went to check the target. The new barrel shot to such a different POI than the prior barrel that it took quite a few shots just to get on steel at 100yrds. By round 10 we were on steel at what seemed like pretty close to POI=POA. Enough to move to the BoxToBench Precision 100yrd Load Development Target and dialed the zero in on the cold zero aiming point. 5 rounds at the cold zero put us at 15 shots and we were already seeing each set of 2 bullet holes (because: adjust, fire 2, adjust) either touching or very close to it. We're pretty excited about the performance we're seeing so far.

After the first 15 shots and letting the gun cool down I settled in to go for groups for record. Starting off we did the Coach's match load (CML) which is 38.5gn of H4350. Then the RL-23 was run followed by N550 and IMR-4166. To wrap things up we came back to the H4350 and did the 39.5gn load then finished out our paper punching with 5 at 39 grains. After that I had 5 rounds left and wanted to drop a shot on the 900 yard target so we went up there and I rang the gong for 5 rounds of 38.5gn. There's a called flyer (obvious) on 4 of the 6 aiming points. I wasn't in the most stable position and I knew it.

My velocities are a solid 150fps above what Coach gets from his Enfield rifled barrel of the same length with the same load. Ok, to be completely transparent, it's not EXACTLY the same load. We do actually seat the bullets about .100 deeper for my new barrel than Coach's barrel but I can't see 150fps difference from that. I think this is the polygonal rifling in full effect. Less friction because you're not engraving the bullet, you're swaging them.

So now on to the powder results. H4350 you see the curves change shape as you fill the case up. To my eye it almost looks like someone's grabbed on to the right side and started pulling the string taut. Group sizes went down as powder charges went up but we're talking about going from a .75" group to a .71" group to a .3" group. The academic in me is crying out to be let loose with a scale and all of my reloading supplies to do a 1/10th grain at a time experiment. But, that's expensive and I have other matters to attend to. The experienced rifle shooter in me says, "You do realize that any one of those is sufficient for the 1000yrd stuff you're doing right?" The competitive rifle shooter in me says, "Take the 39.5 and let's go home and load ammo before you change your mind again."

This is Coach's match load that he uses in his current barrel. Featuring a tight 10.87fps standard deviation from my gun and a not disappointing .75" group this load showed promise. I just don't want to tune it. In Coach's gun this load runs 150fps slower, has a 32fps SD and turns in the same .75" groups.

The group size collapsed on this load down to .4" until I popped a flyer into it (which I called) that took the final group to .71". 40fps ES is a bit on the broad side for me out of a 5 shot sample size. I could maybe do half of that.

When we give it 39.5 grains the dissonant came into harmony and it made a .3" group with 2fps SD's and 5fps ES. It's running mild pressures and making within a gnat's ass of 3,000 fps where I'd draw the velocity line anyway. ~2950 was our target and we're there with a solid load.

Onward and upward. We still have loads to analyze. Everyone knows that after my experience with it in .243AI and 6.5x55AU that I'm a big fan of Reloader 23. It's sloooooooow burning and has been returning impressive velocities with reasonable pressures from very heavy for caliber bullets in relatively long bores from very overbore cases... as you would expect it to do if you are at all familiar with Boyle's Gas Law. We had no idea how much to start with so we did exactly what Coach did with it for my .243AI. We filled the case up to the body:shoulder junction, dumped it out and weighed it and put that much into 5 cases. It came out at 38 grains with no drop tube, just a funnel and a weighing pan.

Reloader 23 showed me with my .243AI that it likes a full case (I'm sensing a trend here with these slow burning magnum powders) and that it's pretty hard to put enough into a 6mm case based on a .473 case head to blow the damned thing up if you're seating to SAAMI/CIP lengths. 38 grains produced pretty nice velocity. A testament to the efficiency of the 6XC case setup. Still with 28fps SD's, 66fps ES and a .68" group of 5, it would "do" but I'd want to develop it more if I were to use it. We did find that RL-23 is a great option. Somewhere around 40 grains should give high 2900's at reasonable pressures even when seating bullets deepish.

That right there is porn star sloppy.

Pressing on, we have N550. A double base NG/NC powder known for being a little temperature touchy after 90F and for being pretty darned expensive. 36.5 grains of N550 gave us a nice narrow 11.95fps SD's on ES's of only 29fps. Still a little tall but velocities were touching 2900 and pressures were VERY low. It also grouped a .2" group of 5 shots. Oh man am I tempted to increase my powder budget by 25%. We figure we could fill the case on this stuff somewhere around 39 grains at 3,000fps. But, I don't want to have to spend much more time or money to develop a load; much less an expensive one. If one jumps out at me maybe but that H4350 load at 39.5 grains is hard to beat even with slightly tighter groups.

A lot of promise in this one. .2" group OMG!

Now we cross into "Coach style load" territory. So far we've been on the very slow side of the slow side of the rifle powder spectrum. Now we're going to cross the street where the Beatles fans turn into Stones fans and start dragging their knuckles. Not really. Just making fun of coach. The defining line between a "Me" style and a "Coach" style of handload is I like my powder to burn all the way down the barrel giving as flat a pressure curve as possible all the way without a huge spike of pressure in the case itself. Coach likes his pressure to form in the case, for all the events to happen in that space and then to use the built up pressure. He also tends to jam bullets rather than jump them where I jump them at least a little bit normally.

Making a Coach style recipe means you know you'll see pressure sooner . That being the case and the fact that there was no data for IMR-4166 we elected to hot-foot bloody educated guess it. I calculated using wild approximations, generous rules of thumb and a little bit of plain old guesswork that 37.5 grains was about the most we'd want to try and so we tried that. It came back hot enough to imprint my ejector hole on the brass so that's at least 2 full grains too much juice for my money. It did however make 3080fps with a 2fps SD and a 6fps ES for 5 rounds. Drop a grain or two and you're right up around 2950-3000fps. What a smoker though! Too bad the pressures were simply too high.

If it wasn't running north of 70,000psi This would be my new load.

Below you can see the velocities as they came out of the gun during testing. You can see it took about 5 rounds to season the bore and then it's pretty much standard load development wavy gravy until you get to 2 very specific sections whose extreme flatness gives away that something very cool happened there and needed to be paid attention to.

So while N550 turned in the best group and ok SD's, the extremely tight SD's and the super tight group out of the 39.5gn load of H4350 has won the day. I might mess with bullet jump a little but really, I'm happy. Best not to waste barrel life.

On the topic of barrel life. Common wisdom seems to suggest it's somewhere north of 1500 rounds but under 2200 before it's smoked. Well that's about a year and a half or 2 worth of life. That's from a conventional Enfield rifled gun. I run Columbia River Arms polygonally rifled barrels which have been giving me longer than expected barrel life for years and I used only HBN coated bullets for the last 1000 rounds (it's at north of 1300 rounds now) on my .243AI.

My .243AI still runs like a laser. I only took it off because seating depth was longer than my magazine, but there's plenty of bullet still in the case yet. I could take it another 500+ rounds if I was willing to single feed. Pushing 115's at 3200 can't have been gentle on it and the expectation was that by 1000 rounds it was going to look like 5 miles of rough road down the bore but it's not. It's smooth as glass still and makes tiny 1000 yard groups. So if we take this barrel life thing to mean the point at which the boat tail is up inside the neck of a loaded case when seated equals cooked, my .243AI will have gotten something close to 2000 rounds before its actual death thanks to some combination of the HBN coating and the polygonal rifling.

 

[98Vandal]

I'm in the middle of building a 6 XC and really appreciate the academic rigor you've provided in your post! Additionally, what is the twist rate of your barrel? I'm looking at shooting the heavy bullets (108 gr and above with preference to the 115 gr DTACs) and am moving towards a 1:7.25 twist rate. I appreciate any feedback as this is a continued journey of discovery for me.

 

[wvlapua]

Is your chamber standard 6xc or 6xc2?

 

[98Vandal]

Is your chamber standard 6xc or 6xc2?

Standard 6 XC.

 

[HCICVOGT]

Spamassassin, I have a 6xc I'll share my load data also....
28" Bartlien 1:8 twist 4 groove
6XC CIP chamber
Norma brass
Federal 210M primers
H-4350
Sierra 107gn MK (HBN) coated
COAL 2.720"

I started my powder charge at 37.0gr and worked up to max at 41.3gr. My go to load is 40.8 I have a SD of 9 with .4" groups. Happy loading and good shooting.

 

[spamassassin]

I'm running an 8 twist. Does 115's just fine but I'm probably losing the tiniest bit of BC over not being on a 7.5 twist. No problems to 1000m so far. We're going out to do some work this weekend from 1000-1700 so we'll see how well it does there. I'm on a mostly standard CIP chamber with a custom tight neck. I get the exact same velocity and point of aim from 108 ELD-M's as 115 DTAC's with nearly identical ballistics from H4350 so far. I had that same similarity on my .243AI, 108's and 115's shot same speed and POI. That's been tested on 2 identically chambered rifles.

 

[98Vandal]

I'm up and running with the 6 XC now; I've been getting great results with the 108 gr ELD-Ms with 39.4 grs of H4350 and the bullet seated .020" off the lands. When I shoot the heavier bullets with my current 1:8 twist barrel things go a little sideways.......

 

[98Vandal]

Did some load testing yesterday with RL 16; the results were an improvement over H4350 (1-3% increase in velocity when compared with same charge weight of H4350). Anyone seeing similar results?

 

[spamassassin]

I did IMR 4350. 38.5-~40.5 seems reasonable.

39.5gr seems about optimal from my 25.5" polygonally rifled (Columbia River Arms) barrel and gets ~3020 in real cold, 3050 at room temperature and 3080 at 90F. There were no pressure signs and it made a lot of .5-.7" groups and a couple in the .1-.2 zone. Latest SD's were 6-10fps inside each 5-shot group tested across 50 shots. It really is a honey.

This is with 115 DTAC, Norma LRP brass, F210's and jumping at least .020". Honestly, the way it shoots, I might like the IMR 4350 better. Another 100fps with no excessive pressure? Sign me up!

Chamber is CIP with a snug neck.