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.Peep out the data below and enjoy. If you have some data you'd like to share, be sure to leave it in a comment and I'll be sure to approve it for publishing.

The 38.5 group was actually fired at the CML dot. FYI.
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 but pressures rise rapidly at the end of the capacity limit.
38.5gn: 2929 average, 13fps SD, .75" group39gn: 2964 average, 15fps SD, .71" group39.5gn: 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 open without a pretty full case. 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. RL-23 is super slow burning.
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 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. The above noted, this is looking like a 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

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 around shot 11.

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 .120 deeper forn my new barrel than Coach's barrel but I can't see 150fps difference from that. This is the polygonal rifling in full effect. Less friction because you're not engraving the bullet, you're swaging then and then twizzlering them, if only ever so slightly.

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 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. This load does suggest it might want just a little more powder.


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. 2900-2950 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 develop a load; much less an expensive one, if one jumps out at me and that H4350 load at 39.5 grains is hard to beat even with stupid tight groups.


A lot of promise in this one. Super stable velocity potential.

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 consistent pressure all the way without a huge spike of pressure in the case itself. My way is easier on brass but harder on barrel throats because there's more grit coming out of the case neck this way. Coach likes his pressure to form in the case, for all the combustion 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 or later in your experimenting. That being the case and the fact that there was no data for IMR-4166 (which is around Varget/IMR-4895 burn speed) we elected to hot-foot bloody educated guess it. I calculated 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 1 full grain too much juice. 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 match 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 is somewhere north of 1700 rounds but under 2100 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 very long barrel life and I use only HBN coated bullets. I got 1300 from my .243AI before it was running bullets beyond mag length but I could easily run it another 500 rounds before the boat tails get sucked up inside the case neck while still maintaining something near .040" jump. Typical life expectancy from a .243AI is around 1000-1300 rounds running them like I was at 3200fps. I'm expecting an honest 2500 before these barrels are burned up.

I'm going to be running a test of barrel life with Modern Spartan Systems Accuracy Oil on these 2 barrels now. One will run the AO treatment throughout its life every 200 rounds. The other will not.


6XC Dimensions

Welp, we've set the second barrel up and tested the 39.5gr H4350 load and it turned in 20 shots with an SD of 12 and 1x 10shot group at .5" and 2 5-shot groups that were from .2 and .45" respectively. We also swapped Coach's scope to one that is calibrated in Mils instead of his usual MOA and went out with my DOPE card and ran 2MOA targets clean from 200-900yrds from both rifles. Same load performance, same units of measure, same skill of shooter, same team. Another regular squad mate now has a 6mm barrel blank from Columbia River Arms and it looks like we might just cut that one with my reamer so we'll have 3 guns that perform identically. A fourth regular squad mate is shooting a .260AI that has identical ballistics to my our 6XC's. We went out last weekend and tested that and we were dead nuts on with each other's elevation DOPE to 1300yrds on 12" targets. His .260 was ever so slightly less susceptible to wind drift but not much.

Our regular match is set up with 50-60 shots on 50-60 targets meaning you only get 1 shot at each. With all of our squad using identically performing setups (and now all being on mils) we'll be able to take exact drop and drift corrections from anyone that misses and apply that to subsequent team members's holds. We're trying to have one of our team be the first to shoot the match clean.