Testing the 30XCB

[geargnasher]

OK, I'm back home, thanks everyone for the thoughts and prayers and especially to whoever is responsible for providing dry, safe roads for two solid weeks across three of the larger states in the union and some of the worst mountain passes the US has to offer this time of year. Today will be a rest day. Might actually get to put the Rock Creek barrel on my Pig Gun today. I don't even remember where I was with the XCB, have to study that a bit too and maybe go shooting tomorrow.

Bjorn, if you need anything lube-related just ask. I don't even want to think about the mess I'm likely to find at work Monday, but I'll make time this week to get to the PO if you're in a bind for some known-good bullet grease.

Gear

[RED333]

Glad ya made it back home in good shape.

[btroj]

Some of those passes are just plain scary. I assume you went they Ouray? The road to there from Durango is something I hope to never take again. Did I ever mention I don't like heights?

Glad you and the Mrs made it home safe.

[geargnasher]

Some of those passes are just plain scary. I assume you went they Ouray? The road to there from Durango is something I hope to never take again. Did I ever mention I don't like heights?

Glad you and the Mrs made it home safe.

The "Million Dollar Highway" between Durango and Ouray is one of the bad spots. Did you like how in some places they pave to the edge of the drop-off and still don't quite have enough width to paint the white stripe? I don't recommend taking that two hour trip at 4 a.m. as the 16th and 17th hours of a straight-through trip from central Texas. Not so bad coming back when the urgency to make time was over, it was daytime, and we were at least slightly rested. Having driven that road many times, including on 3" of solid ice and having to drift sideways around the steeper switchbacks to keep momentum up (can't start forward again from a stop or if you lose traction in some places, even with cable chains on the drive wheels), I can really thank the stars that the weather was good this time, especially since Mrs. Geargnasher had to bring back the vehicle her parents originally took up there on vacation in August, together with her mother who doesn't drive much outside of town, all their gear, and one crippled, 122-pound, incontinent dog who had to have his bedding changed every two-three hours. I took their other dog back with me. Did I mention I'm a cat person? We made quite a few trips back and forth to Grand Junction to the hospital, up to Animas Forks and back in heavy mud/snow to fulfill my FIL's last wish of sprinkling a few of his ashes, and overall I put 3200 hard miles on the Sequoia. God bless Toyota Engineering for their excellent, tough four-wheel-drive systems and REAL skid plates. Meanwhile all you dorks are sitting home and not shooting yer stinkin' rifles! Phoey. Do I have to do EVERYTHING?

Gear

[btroj]

Yep, the Million Dollar Highway. Nothing worse than the fear of going over the edge and there isn't even a place to put a cross marking where you died! We met a few RVs pulling a car behind them on that road, that would be some tough driving on that road.

I haven't done anything XCB related ina few weeks. Been getting ready for deer season, that is the big priority now.

In short, yes, I have left the work to you. Maybe after next weekend I will get back to the new rifle. Today was lathe oil change day. It was everything I expected it to be.

[Bjornb]

The "Million Dollar Highway" between Durango and Ouray is one of the bad spots. Did you like how in some places they pave to the edge of the drop-off and still don't quite have enough width to paint the white stripe? I don't recommend taking that two hour trip at 4 a.m. as the 16th and 17th hours of a straight-through trip from central Texas. Not so bad coming back when the urgency to make time was over, it was daytime, and we were at least slightly rested. Having driven that road many times, including on 3" of solid ice and having to drift sideways around the steeper switchbacks to keep momentum up (can't start forward again from a stop or if you lose traction in some places, even with cable chains on the drive wheels), I can really thank the stars that the weather was good this time, especially since Mrs. Geargnasher had to bring back the vehicle her parents originally took up there on vacation in August, together with her mother who doesn't drive much outside of town, all their gear, and one crippled, 122-pound, incontinent dog who had to have his bedding changed every two-three hours. I took their other dog back with me. Did I mention I'm a cat person? We made quite a few trips back and forth to Grand Junction to the hospital, up to Animas Forks and back in heavy mud/snow to fulfill my FIL's last wish of sprinkling a few of his ashes, and overall I put 3200 hard miles on the Sequoia. God bless Toyota Engineering for their excellent, tough four-wheel-drive systems and REAL skid plates. Meanwhile all you dorks are sitting home and not shooting yer stinkin' rifles! Phoey. Do I have to do EVERYTHING?

Gear

Hey I resemble that remark!!!!!!!
No XCB shooting for me since I shipped off Bertha to Goodsteel a week or so ago. The rifle now has a new 30" Shilen Match barrel installed and I'm picking her up on the 20th when I head to Arkansas for some deer hunting. Welcome back Gear.

[geargnasher]

Good deal. Tim, do you ever sleep? You must have a waiting list a mile long these days.

I went to stick the barrel on my Pig Gun a little while ago and discovered that one of the locking lugs had galled on the corner due to the locking counterbore in the receiver not being concentric with the bore of the front receiver ring, so there's a little rib of metal on the upper locking lug ramp that gets sheared every time the bolt is cammed home. I'll have to lap the lugs and receiver to clean it up, probably stick the old barrel back on there with a fireformed case in the chamber to keep the bolt head aligned during lapping. I also discovered I don't have a "go" gauge for .308, so I'll just use an FL case like I did with the famous "$29 barrel" that's currently on my XCB. So maybe I'll just shoot the XCB tomorrow! hehehe. I had a plan for what to shoot next but I can't remember what it was. I'll have to check my earlier posts.

Gear

[btroj]

A pound of RE17 followed me home from Cabelas today. That and some new thermal undies. Deer season is looking to be cold, lows in the single digits at least one night. I hate that kind of cold, why can't Eutectic keep it at his place?

I will be interested to see how RE17 does. Is it enough faster than RE19 to make a difference? Time will tell. I just have a bad feeling we are in for a cold, snowy winter and that isn't good for load testing.

Wanna come visit Gear? I bet you would be awesome at shoveling snow!

[Bjornb]

RL17 sits directly above AA4350 on the burn rate chart, so it may very well give good results. It's only 5 places above RL19.
My recent experience with ball powders (WW760/H414 and Superformance) has been good enough that I'll stick with those for now. Both Gear and Larry have also had good results with one or more of these (Larry with Leverevolution).

[geargnasher]

The WC 867 was trying to tell us something, too.

Gear

[Bjornb]

Yeah that's true, but I'm not too sure what it is. It gave good accuracy up to a certain point, and then the groups opened up. Shooters on other forums talk of duplexing this powder. Maybe it's worth trying.

[btroj]

I'm with ya Bjorn. Sometimes you just know the rifle and load are telling you something but you just aren't sure what it is saying. I hate that.
I think RE19 is just a touch too slow. I haven't maxed it out yet but need to. I'm hoping RE17 will be a bit better in the accuracy realm.

Winter is here for real this week. Highs later this week around 30, lows in the teens. Not ideal group shooting weather. It is amazing how much faster mirage shows up in cold, still air. Standing around waiting for a barrel to cool means I get cold, I don't like being cold.

[btroj]

I haven't looked much at a mirage band yet. I've been rather lathey lately.

I would consider moving south except the wife and I both have family here and our heat and humidity in the summer is plenty for me, I don't need more. I also like the people here in Nebraska, the lack of an accent, and we have lots of open spaces and very few people.

[Bjornb]

I haven't looked much at a mirage band yet. I've been rather lathey lately.

I would consider moving south except the wife and I both have family here and our heat and humidity in the summer is plenty for me, I don't need more. I also like the people here in Nebraska, the lack of an accent, and we have lots of open spaces and very few people.

Here in South Florida, with Norwegians and Cubans the accent gets canceled out and sounds like Iowa. They didn't tell ya that?

[btroj]

Florida? Isn't the average age like 90 or something there?

No thanks, I will stay a bit farther north. I would say something about cousins but got chastised for that once.

[Love Life]

I don't think the rule of cousins and sisters applies to Florida.

[btroj]

I don't think the rule of cousins and sisters applies to Florida.

That is good because in some of those retirement villages the cousins are long in the tooth

[detox]

Taper bumping bullet to even out casting imperfections and seat gas check more flush and square should help.

Can Tim make taper bumping die using original XCB reamer? He may need a throating reamer to make one. You will also need a matching nose punch to tap bullet from bump die.

I want to have a custom a .310 diameter throating reamer made to ream throat and to make a taper bump die to match the taper of the Lee 160 Harris design bullet (1.13 degree included angle or .565 degree per side). This would require a throating reamer with about .60 degree per side throat angle. This more gentle throat would also work well with most other cast bullets designs, including the 30 XCB.

I would also like to have made a custom 3r or 5r barrel with 1/14 twist (.300 bore hand lapped with .299 choke last 6" of barrel near muzzle). Some say the last 6" of barrel is very important.

[Larry Gibson]

With the original objective being the highest velocity obtainable with acceptable accuracy (2 moa or less) I have about exhausted the possibilities with the 30 XCB cast bullets (WQ’d #2 alloy) in the .308W cartridge in a 14” twist rifle. The .308W cartridge has very close to the same case capacity as the 30 XCB cartridge. Depending on what cases were used to form the 30 XCB it may have a slightly greater capacity. However, the two are going to be close enough in internal ballistics for a valid comparison.

This being the end of my formal testing I have found 1 moa accuracy (10 shot groups at 100 yards) or less to be easily obtainable at 2450 – 2550 fps with several powders but, while the accuracy is nice, those loads do not give the highest velocity and are well under the top end of the RPM Threshold and the capability of the .308W. With a couple of other powders 1 – 1.7 moa accuracy is also consistently easy to obtain at 2600 – 2650 fps. I have several times posted accuracy tests at 100, 200 and 300 yards showing those loads. They also demonstrate very good linear dispersion and are still under the RPM Threshold. The top end of the RPM Threshold (140,000 RPM) is right at 2720 – 2725 fps out of a 14” twist barrel.

So what happens to accuracy and does that accuracy hold linear dispersion at longer ranges when we push to right at the 140,000 RPM level….the ragged edge? That was the objective of my last test. Previous testing showed that only one powder was capable of pushing the 30 XCB bullet very close to that velocity while keeping the psi under 42,000 and maintaining 2 moa or less; LeveRevolution Powder. I had found 43 gr to give 2704 fps with 1.6” accuracy and 44 gr to push 2750 fps with 2.5” accuracy (some bullet holes in the target exhibited signs of instability or wobble/yaw from not yet “going to sleep”) Thus I loaded 30 test rounds with 43.5 gr LvR powder to reach the RPM Threshold at 2720 – 2725 fps. Keeping mind that is an “average” velocity the ES would actually be about 40 fps with the velocities being from around 2700 to 2745 fps for the 10 shot test strings based on my extensive previous testing.

I shot the test strings yesterday afternoon at the LHC range. The temp was 77 and there was a 3 – 5 mph wind from 2 o’clock. Conditions weren’t bad. I shot the 100 yard then 200 yard and lastly the 300 yard targets between 1530 and 1700. The barrel was clean and 3 fouling shots were fired prior to the test. I gave the barrel 2 – 3 minutes between shots to stay relatively cool and let the barrel cool between test strings.

The 100 yard groups accuracy was 2.25”. Looking at the top two and bottom right bullet holes we see signs of instability or woblle/yaw. Was this really instability or was it just wobble/yaw from the bullet not going to sleep yet? Only shooting at 200 and 300 yards would answer that question. The seven nice round bullet holes went into 1.45”. None the less it is obvious that as we approach velocities above 2700 fps with the 30 XCB bullets in the .308W cartridge we are at the ragged edge of obtainable accuracy with velocity and are pushing the RPM Threshold.

At 200 yards things were looking awesome until a flyer, round 7, went high right out of the group giving an overall group size of 4.25”. But was round 7 really a flyer? The 9 shots in the group are at 2.62” which might lead some to believe the theory that some rifles with bullets that “go to sleep” shoot smaller groups at longer range. None of the bullet holes at 200 yards exhibited signs of instability. Either the ones with initial wobble/yaw had “gone to sleep” or in this test string there were none with stability or wobble/yaw issues. Considering that a 4.25” group at 200 yards is essentially linear expansion compared to the 2.25” group at 100 yards we may have just got lucky with random dispersion in the cone of fire with the 9 shots in that group. Shooting at 300 yards would give us that answer.

At 300 yards the group expansion was also essentially linear at 5.95”. None of the bullet holes indicate stability (wobble/yaw) issues and the group is right at 2 moa.

Obviously the larger group at 100 yards was indeed caused by initial wobble/yaw and the bullets were going to sleep somewhere just before or just after the 100 yard range. I’ve no doubt further testing at 200 yards would reveal very close to 2 moa accuracy as indicated by the overall 4.25” group size. The linear expansion was consistent from 100 to 300 yards. Thus we have met the initial objective of pushing the .308W to as high a velocity as we can while maintaining 2 moa or less accuracy. Until a powder comes available to keep the psi low and the time/pressure curve slow within the .308Ws case capacity while boosting velocities above 2725 fps the 14” twist longer barrel we find the feasible top end velocity is right at 2700+ fps at this time.

Larry Gibson

[Bjornb]

You've set the bar high Larry, now I need to duplicate your shooting with the XCB cartridge. I've got LvR powder and a good supply of bullets. Tim will be test firing my rifle with the new barrel in a couple of days.
Great writeup. Stand by for more.