K31 and cast, having a problem

[madsenshooter]

My K31 is giving me a hard time with cast bullets. As the barrel gets warmer, or let's say "as I shoot more", the groups get bigger. I'm using the Eagan MX3-30AR which is a very good fit, tapered nose is in the rifling, base is even with the neck/shoulder junction. I'm sizing the bullets .310" and I've noticed the first few shots shave lead off the bullet, and blow it back onto the case neck. I know some are going to think a bedding issue, but it doesn't have any problems with jacketed loads, it's a consistent 1moa rifle. The jacketed groups don't get bigger as I shoot more. I'm neck sizing previously fire formed to the chamber brass, using a collet die to size the neck .001 under bullet diameter. I'm thinking the shaving is causing a bit of a buildup in the throat and accuracy is going out the door with it. I shot three five shot groups today, first group, had a some within an inch of each other, next one a bit bigger and somewhat unpredictable, next one, was even more unpredictable and sometimes off the 6" bull. Load is 22.2gr of 10B101, velocity was 2089fps, ES of 62, SD of 16.8. Alloy was a 23BHN mix that has given me good service in my Krags at over 2160fps. I'm going to size some .308 and see if that makes a difference over the next few days.

[NickSS]

It may be that your bullets are too fat for the K31. My rifle has a groove diameter of ,3075 so your 310 bullet may be shaving led and leaving it in the throat area.

[madsenshooter]

Could be Nick, in fact my groove diameter is even tighter than yours, .3065 and still fairly new. I've got daylight, cleaned the barrel, sized some to .308, loaded em, on my way to the range.

[Bret4207]

Did you find any build up when you cleaned?

[leadman]

If sizing smaller doesn't cure the problem you might try a softer alloy so it will swage to bore size without being shaved off.
I get excellent results with the RCBS 30-150-SP out of 12 BHN alloy and 12grs of Unigue. Slower than your load but holds just over moa.

[HollowPoint]

Although my K31 displayed the same kind of issues with my groups opening up after about five or six rounds, the lead shaving wasn't part of my problem. I size to 309.

In my case the groups opening up after the barrel warmed up seemed to be caused by my stock. It was warped at the very end, which caused it to apply just enough pressure against the muzzle end of the barrel that after a few shots the barrel would (presumably) soften up and succumb to that slight bit of pressure.

The first three shots were real tight clusters at 50 to 100 yards when I did my part correctly. Each shot there after would routinely drift to the right and up from there.

I sanded out the channel of the upper and lower wood so that the barrel was basically free-floating. While I had it apart I also pillar bedded it. This seems to have cured the problem of my groups opening up after the barrel got hot.

Any problems with large groups can now be placed squarely my shoulders; the guy pulling the trigger.

I recently modified my old rifle rest to act as a mechanical-rifle-rest; also built a remote trigger device. In so doing, I'm hoping that it will take more of the human error I contribute to my shooting sessions, out of the equation.

Now if I can just find the time to go to the range more often.

HollowPoint

[madsenshooter]

Thanks for the suggestions, the shaving wasn't the cause. The sized to .308 bullets continued to put em all over the target, even after the barrel cleaning. The bullets didn't shave though. I'm beginning to wonder about this batch of bullets. I mostly use Eagan nose pour molds. I changed alloys, from a lead based babbitt, to something I mixed up using some big ingots of what was supposed to be WW that I'd bought as the base. In retrospect, that's when the problem started, not only my K31 problem, but one of my good Krags went from shooting 1 5/8" consistent groups to 4-5". This was at 2165fps with the same bullet I used in K31, but the accurate ones were cast of a different alloy.

Some of the bullets I've cast with this mix come out banana shaped! You can see that the sunken area was at one point in contact with the mold, then it draws away from it as the alloy cools. I culled out all the visible ones, but have to wonder about what isn't visible now. When I get some time, I'll weigh some of them and edit this post to add any info. I'll see if I can find one of the bananas I haven't melted down and get a good pic.

[canyon-ghost]

That what I'd think, weigh them and see if there isn't a wide swing in weight.

[madsenshooter]

Did that, nothing worth noting. Low of 172.2, high of 172.9 across a sampling of 10 randomly selected. Did the same with 10 that I had ladle cast after adding some tin to the alloy, 8 of them were 171.2, 2 of them were 172.6. Weight difference on the ladle cast ones appears to be mostly on the tip of the nose, the sprue plate had come loose toward the end of casting. The ladle cast ones are sure prettier, no oxides or little pits like the bottom pour cast.

I had thought about being stubborn and loading the ladle cast ones the same as today. But, chances are very good the results would be the same, so I changed my mind, I'll try them slower.

[Larry Gibson]

Madsenshooter

Not sure what burning rate 10B101 but with just 22.2 gr producing 2089 fps it must be a bit on the faster side. You might want to consider that 2089 fps in a 10.5" twist is 143,200 RPM. I know many think that doesn't mean anything but I'd bet if you dropped down to 1900 fps or so with that powder or one with a burning rate up through 4895 the flyers would "fly" to group. If you want to push the Eagan bullet that fast then you might want to try a slower burning powder like RL19, H4350 or AA4350. Just something to consider.

Larry Gibson

[madsenshooter]

10B101 is somewhere around Blue Dot or 2400 in speed. I've got some SPP210, a Swiss made 4198 clone to try, at a bit slower speed, estimating around 1900. Thing that's puzzling me is the fact that I've had the Eagan at 2165 using the SPP210, but that was out of a Krag, and if two variables ain't enough, with a different alloy. Someday Larry, I'm going to start low and work up, instead of starting high and working down! Only 4895 I have is that Russian stuff Bartlett sold some time ago, it doesn't burn worth a hoot at lower pressures. Leaves about as much unburned as something like 860 when the pressure is low. I'll get it working one way or another, at the velocity I want, got a toaster oven, or alternatively, the lead based babbitt I used when I got the higher velocity (with accuracy) in the Krag. That's been my 6x45 alloy too.

[Larry Gibson]

A guy gave me a pound of that russian 4895 'equivelent" to try and said he had a bunch more for sale cheap......I found out why, same as you....not good at lower pressures. Try the 4198 like stuff and start low and work up.....might surprise you.

Larry Gibson

[madsenshooter]

Now that Russian powder does make some good jacketed loads in my 6x45. I got out to try some of the SPP210 loads for my K31 today. Using 26.5gr, I overshot my velocity estimate and got an average of 2005fps. I did get one 1" five shot group out of the three though. After those 3 groups I again went back to the 10B101 this time at an even lower velocity of 1941fps. Again, it was one decent group following by two that were patterns. It could be pressure problems Larry, I've sorta lost track of my alloy composition, maybe it isn't as hard as I think it is, and I haven't seen that little Lee scope for awhile. Since I just overcooked, and thus melted, the batch I was heat-treating, (got my house all heated up for nothing). I guess I'll go back to the lead based babbitt, ladle cast, for future experiments.

[Maven]

madsenshooter, Do you think the poor grouping may also result from poor bedding/expansion as the bbl. heats up? If so, there is a simple "accurizing" fix for the K-31, which won't take more than a few minutes to accomplish IF you have a few small washers on hand (Lowes, Home Depot sells variety packs. The smallest ones are what you need.) Here's the link:

http://www.swissrifles.com/sr/pierre/accurizing.html

The other suggestion is to size those CB's to .309" and seat them as deeply into the case is necessary to allow the bolt to go into battery without battering the bolt closed.

[madsenshooter]

Thanks Maven, I will keep the link in mind, but it's a tack driver with jacketed and continues to be so when things get warm. I think I've just lost track of what's in my alloy and it doesn't take the pressure I'm generating at the velocities I want, you know, slower powder or a harder bullet. I've got the errant alloy in ingots and will set it aside for now. I've got some known stuff that'll give me 2100fps with the powders I wish to use. I prefer fast and medium burners, I like the lack of jet effect from the muzzle and the very low SDs. Have you worked with 860 in the K31?

[NuJudge]

I've been using H4198, with great results: 3 inches at 100 yards, 3 inches also at 200 yards. I'm using the 165gr clone of the Lee Silhouette bullet.

If you don't have that bullet, try that powder.

[Maven]

"Have you worked with 860 in the K31?"

madsen...., Yes I've used quite a lot of it in the K-31 and have been satisfied with it. My loads are typically 46gr. - 49gr. with Win LR Mag. primers and CB's weighing at least 175gr. Of those, the Lee C-309-180R was a good performer, but Saeco #315 was better, a reliable 2 m.o.a. shooter. Btw, my current lot of WC 860 (Wideners) is a bit faster and much cleaner than the Hi Tech version that I got years ago, hence the 46gr. starting charge.

[madsenshooter]

It appears it was my alloy, things went much better today. I was using the Swiss Precision Powder SPP210 that Widener's sells. Not perfect yet, but getting closer. Odd, although there's a difference in water capacity of the cases, I'm getting about the same velocity for a given charge in the K31 as I get from the Krag. The one marked "me" is a shot where I felt a fly land on my arm, flinched just enough to make the striker drop. The 2080 group is 2.3" without the "me" shot, the 2158 is 2.4, both measured at the widest. 2015 showed some promise at an average of 2222fps, but I only had 5 loaded. The blast sounded different, like some of the faster powders I use, as if all the powder (34gr) was being consumed in the barrel. SD with it was 7 vs 14.8 for both SPP210 loads., I'll play with the 2015 some more.

http://castboolits.gunloads.com/imagehosting/thum_12364e6689e63e15f.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=2050)http://castboolits.gunloads.com/imagehosting/thum_12364e6689fe2a6c8.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=2051)

[leadman]

I was wondering about alloy when you sid your boolits looked like bananas. Must be something in their that is shrinking alot when it cools, or is not getting more alloy from the sprue puddle.

[madsenshooter]

Hard to say what's in them leadman, I got them off ebay, they were big ingots that the fellow said he used for ballast in race cars. He packed them 20+ lbs in a small flat rate box. I think he had the resources to get the temp high enough to melt in the zinc ones too. I bought several of them at $1/lb, but they're also good for holding my front rest steady, I won't use anymore of it. I've also switched to ladle casting, should have done that long ago, no more unavoidable oxide pits in my bullets, no more splatters of lead on my pants and shoes from lil drippy. Bullets are slick as snot, more than hard enough at 23BHN, and shiny as chrome.