30 BR

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mtngun
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30 BR

Postby mtngun » Fri May 13, 2016 6:10 pm

Specs:
-- Kreiger 4-groove barrel
-- 28 1/2" long
-- "MTU" taper to 1" diameter at muzzle
-- 18" twist
-- 0.3318" chamber neck (approximate, it might be a bit more)
-- 1 degree x 3 degree leade (what Dave Kiff calls a "bore riding" throat even though it has nothing to do with bore riding)
-- 0.3095" freebore
-- with this tapered barrel, rifle weighs 14 lb, 14 oz ready to shoot
-- necks turned to 0.0117" thick walls
-- loaded necks OD .3318" - 0.3323"
-- fired necks 0.3323" - 0.3330" (I warned you that the 0.3318" neck diameter was approximate :lol: )

Miller Stability Factor with various wheelweight spitzers:
-- 110 gr., 0.760" long, SF = 1.73
-- 120 gr., 0.810" long, SF = 1.58
-- 130 gr., 0.860" long, SF = 1.45
-- 140 gr., 0.910" long, SF = 1.34
-- 150 gr., 0.965" long, SF = 1.21

Max velocity with H335 (same as WC844) at 96% loading density:
-- 120 gr. = 2802 fps
-- 130 gr. = 2765 fps
-- 140 gr. = 2726 fps
-- 150 gr. = 2686 fps

Today I was merely checking for basic functionality and getting the kinks worked out of my 30BR reloading gear, so no fancy experiments or load tweaks. I picked a powder charge that would deliver 2700+ fps and then tweaked the nose sizing to get the seating depth where I wanted it.

The freebore seemed to be a bit longer than planned, so that very little nose sizing was required
Image

The TPCF (tumbler powder coat plus forceps) bullets were cast with wheelweight alloy and quenched at the 400F curing temperature, making them approximately 18 BHN. The OBPU (oil based polyurethane plus mica) bullets were oven treated at 470F, making them approximately 25 BHN.

The WC844 powder burned very well in this cartridge, with the velocity standard deviation running from 0.38% to 0.53%. This load runs around 45 ksi whereas my 6BR loads run around 25 - 30 ksi and WC844 doesn't burn so well at those lower pressures.

The TPCF coating seemed to be slightly more accurate than OBPU, so TPCF will be my standard coating for GC bullets until something better comes along.
Image

Things To Try Next Time:
-- a harder alloy, reclaimed shot instead of wheelweight
-- 115 gr. and 145 gr. bullets
-- a plain base bullet

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Re: 30 BR

Postby mtngun » Sat May 21, 2016 8:28 pm

OK, after the last range session I mentioned that the 30BR was not "riding the bags" well. The front bag works great since I upgraded to a leather bag, but the rear bag moved 1/4" after every shot. That's not good when you are shooting "free recoil." It also left my shoulder black and blue after only 41 shots. :(

I realize that everyone wants me to try their favorite alloy, lube, bullet design, coating method, etc., and I hope to eventually play with all those variables, but ... one thing at a time. And today that one thing was improving my benchrest technique with the 30BR.

Here's one problem. The rear bag is a very good Protektor bag with 3/8" spacing between the ears. That's not quite enough space for my chubby Richard's Microfit stock. Oh, I can force the stock down into the bag, but it's such a tight fit that there's a lot of friction when it recoils back ... and the friction moves the bag. :(
Image

Here's some suggestions I found on various forums:

-- obviously the bag should fit the stock, or visa versa.
-- place an anti-slip mat between the bag and the bench
-- place sanding screen between the bag and the bench
-- use velcro to keep the bag from moving
-- dampen the bench before setting the bag down (apparently a common practice in competition)
-- apply self-adhesive teflon or UHMW tape to the toe of the stock to reduce friction
-- place a microfiber cloth between the stock and the bag to reduce friction

I debated whether to order a custom bag to fit my chubby stock, or to reshape the stock to fit my bag. Custom bags are expensive and this stock is cheap as benchrest stocks go, so I decided to modify the stock.
Image

The modified stock fit the bag much, much better.

While practicing sliding the stock back and forth on the bags, I noticed the bag rocked less if I flipped it around 180 degrees. I had been using the rear bag backwards because the chubby stock fit better that way. Now that the stock had gone on a diet, the bag could be spun back to its intended position.

Velcro, sanding screen, or anti-slip mat? After considering all three I tried an anti-slip mat because it was cheap and easy. It did indeed make it noticeably more difficult to slide the bag on the bench.

I do have some UHMW tape that I can try but that'll have to wait until I re-finish the stock. In the meantime I placed a thin microfiber cloth (the kind that comes with a new scope) between the stock and the bag.
Image

Lastly, I increased the number of rubber bands on my "high tech return to battery system," up to 8 sets of rubber bands.

OK, let's see how it shoots with the new setup. I used exactly the same load as last time, with the powder coated GC bullet. Groups were shot starting on the left and going to the right.

The first group showed some potential. The bag did not move at all. However, the rifle still jumped around more than I cared for -- the 8 rubber bands seemed to make it jump forward on the rebound. You know how you can tell by feel whether or not a shot was good? Well the shots just didn't feel right.

Also my shoulder continued to get slapped despite the extra rubber bands.
Image

The stock does not have a recoil pad because I did not anticipate that the very heavy rifle would need a pad with the puny BR cartridges. But I was wrong. :D "Free recoil" lets the stock get a running start at your shoulder.

So I improvised a recoil pad. That helped a lot.
Image

For the final group (on the far right), I tried gripping the rifle instead of "free recoil." I was experimenting with different grips and one shot went wild that was surely my fault. It reminded me that it's much easier to shoot free recoil provided you can get the rifle to "ride the bags."

Continued in the next post ....

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Re: 30 BR

Postby mtngun » Sat May 21, 2016 8:33 pm

I forgot to mention that while I had the rifle apart to reshape the stock, I tried adjusting the Jewell trigger following the factory instructions, and testing for fire-on-safety-release (never happened) and fire-when-bolt-slammed-hard (did happen). In order to pass the fire-when-bolt-slammed-hard test, the trigger pull ended up being firmer than it was before I adjusted it! :P I didn't have a way to measure the pull but It was enough to shift the crosshairs when the trigger is pulled, I'm guessing 4 - 6 oz. I lived with it for today but will give adjusting the trigger another go before I shoot it again.

The benchrest technique changes in the previous post were mostly for the better except for the added rubber bands, which induced bounce on the rebound. So I dropped the number of rubber bands down to 4, same as I use on the 6BR and 22BR. That provides a little bit of tension but not so much as to make the rifle bouncy.

The improvised recoil pad made the free recoil slap on my shoulder tolerable even with only 4 rubber bands.

So once again I tried free recoil, now with 4 rubber bands and the improvised recoil pad. Same old load except this time the bullets had an almond colored hybrid epoxy-polyester powder coat, rather than the black polyester coat.

Results were an improvement, averaging 1.2" at 2800 fps. The rear bag did move a little bit once in a while with only the 4 rubber bands, but it didn't move that much (a tenth of an inch) or that often. We're making progress. :)

For the final group on the far right, I only had 6 hybrid coat bullets remaining so I finished the group with polyester bullets, which impacted lower than the hybrid bullets. Nonetheless it did not increase the overall group because there was already one low hybrid flyer.
Image

1.2 inches at 2800 fps is respectable, but this slow twist Kreiger should be capable of sub-MOA. My eventual goal with this barrel is 4 consecutive groups averaging less than 1 MOA at 2700+fps, and 4 consecutive groups averaging less than 1.5 MOA at 3000+fps. I'm sure the Kreiger barrel is up to it but it'll take me a while to get there. That's OK, if high velocity cast were easy I'd get bored shooting cast and be forced to take up golf or something.:D

ACTION ITEMS FOR NEXT TIME AND DOWN THE ROAD
-- refinish the stock where I modified it
-- install a recoil pad
-- possibly try UHMW tape on the stock
-- make a system for measuring the trigger pull. It can be as simple as a piece of string or baling wire to hang some weights.
-- try to get the Jewell down to a safe 2 oz, or failing that, start saving my pennies for a Bix & Andy. :(
-- I think the neck tension in today's load was not enough nor was it consistent. It just didn't have enough bullet to grab onto. So try nose-sizing the bullet less such that it has to seat just a little bit deeper.

Obviously I would like to experiment with different bullet weights, plain base bullets, different powders, etc., but one thing at a time. :)

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Re: 30 BR

Postby mtngun » Sun May 22, 2016 12:25 pm

A hi-tech trigger pull measuring device. Half inch nuts suspended on a string while the barreled action is held in a vise with the barrel pointing straight up.

Each nut weights 0.57 ounce. The trigger that felt like 5 pounds :evil: when I was shooting yesterday would just barely hold 4 nuts (2.3 ounces) but would definitely not hold 5 nuts (2.8 ounces). Let's split the difference and call it 2.5 ounces.
Image

I tried once again to adjust the trigger following the factory instructions. I learned that if you adjust the trigger with the action laying on its side, it won't be safe with the action pointed straight up, because gravity pulls on the trigger when the action is pointed straight up.

After readjusting as best I could such that it still passed the "slam-the-bolt-closed-as-hard-as-you-can-with-the-action-pointing-straight-up" test, it would support 3 nuts (1.8 ounces) but definitely not 4 nuts (2.3 ounces). Let's split the difference and call it 2 ounces.

I did not attempt a "drop test" but I'm quite sure the trigger would fire when off SAFE if the butt of the rifle were dropped on the ground, thanks to Newton's laws of physics. So don't drop your benchrest rifle on the ground ! :lol:

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Re: 30 BR

Postby mtngun » Sun May 29, 2016 1:01 pm

I'm trying a 1" thick Kick-Eez recoil pad, which according to the internets is the most absorbent recoil pad available. The pad has not been fitted yet because I haven't made up my mind whether to leave it on -- I might simply glue on some 1" thick closed cell foam rubber like the improvised recoil pad in a previous post. The foam rubber is softer and more absorbent than sorbothane.

Note that the bag is made for an angled toe but my toe is straight. Eventually I'll probably get a straight bag to match the stock but good bags are expensive so this mis-matched bag will have to suffice for a while. :roll:
Image

I tried using a dryer sheet -- those sheets you put in your clothes dryer to make your clothes smell nice -- between the stock and the rear bag to reduce friction. It seems to work fine. I got the idea from Lee Martin at SingleActions.com. Pic of Lee's 6PPC.
Image

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Re: 30 BR

Postby mtngun » Sun Jul 24, 2016 8:34 am

Today I tested coatings, using the same load that I used last time.

UPDATE: The bullets referred to as "130 gr. GC" in this post were actually 120 gr., and were different than the true 130 gr. bullets in previous posts. I have so many experiments going on at the same time that I get them mixed up ! :lol:

All of today's bullets were cast with reclaimed shot and oven treated. The uncoated bullets were treated at 470F, while the coated bullets were quenched after their 400F cure, hence the difference in BHN. FYI the BHN numbers are using the 10mm/150kg homemade tester. I also tested the same samples with the 4mm/60 pound homemade tester and it gave 33 BHN for the 470F bullets and 27 BHN for the 400F bullets. For the time being I'll assume that the 10mm test is more reliable.

The hybrid coating was applied in a tumbler. I didn't measure the thickness but based on past experience it's typically 0.0003" - 0.0004" per coat. As you can see this particular powder goes on thin and spotchy when tumbled. It looks ratty but I'm more concerned with how it shoots.
Image

A Caldwell chrono replaces the ProChrono Pal that was executed by an errant gas check from my 6BR. :lol: Today's velocities were higher than last time so as a sanity check I set up my spare chrono behind the Caldwell. The spare chrono averaged 71 fps higher than the Caldwell, so I can't accuse the Caldwell of reading high.
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I may have posted this information before but after minimal nose sizing the bullet is seated with only the GC in the neck, due to the long gentle 1 degree throat. I would prefer to seat it a wee bit deeper but that may require a longer bullet. BTW if the bullet looks crooked that's because it is, because there's not enough bullet inside the case to hold it straight. :lol: However, it straightens itself out when chambered.
Image

This may have been the first time I've shot the 30BR since adding the recoil pad and reshaping the toe of the stock. The recoil did not bother me this time, the rifle did not jump around on the bags, the rear bag never once moved, and when returned to battery the crosshairs typically had only moved 1/2". That's a vast improvement. :)

All of today's loads used 36.7 gr. WC844, HVR lube, and a CCI #41 primer. However, I'm using a different jug of WC844 than last time, so that may explain today's higher velocities.

Accuracy from best to worst:
-- 1.26" 1-coat hybrid
-- 1.31" 2-coat hybrid
-- 1.40" no coating

Velocity from highest to lowest. Coated bullets usually increase velocity due to higher engraving pressure.
-- 2925 fps 2-coat hybrid
-- 2914 fps 1-coat hybrid
-- 2886 fps no coating

Velocity standard deviation from lowest to highest. Coatings usually reduce velocity variation due to higher engraving pressure.
-- .49% 2-coat hybrid
-- .52% 1-coat hybrid
-- .73% no coating

Average extreme spread for 10 shots, from lowest to highest.
-- 43 fps 2-coat hybrid
-- 45 fps 1-coat hybrid
-- 70 fps no coating
Image

After shooting the 41 rounds (including 1 fouling shot) of uncoated bullets at 2886 fps, the barrel was surprisingly clean. This photo shows the worst fouling I could find, just a little bit of grey wash in the corner of the grooves about 3" from the muzzle.
Image

Conclusions:
-- velocities were higher than I intended, but that's OK because it still shot decent. :)
-- as with previous tests of coated vs. uncoated GC bullets, the coated bullet was a tiny bit more accurate but the difference was not statistically significant. Maybe if you tested 1000 rounds each you could prove a difference. :lol:
-- if nothing else the hybrid coating makes the powder burn better and reduces velocity variation
-- one thin coating works as well as 2 coats, even if the single splotchy coat looks like hell.
-- In general, I'm pleased with the consistency of this combination, but I believe the barrel is capable of doing much better if I can find the right combination.


Things To Try Next Time:

-- heavier bullets, both GC and PB
-- I'm inclined to stick with 1 thin coat of hybrid for GC bullets. It may help a tiny bit and definitely does not hurt.
-- different powders.

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Re: 30 BR

Postby mtngun » Sat Jul 30, 2016 8:40 am

This morning I tested a heavier GC bullet. Nominally 145 gr. but 147 gr. when cast of J.R. reclaimed shot. The usual coating of 1-coat hybrid PC cured for 30 minutes, then quenched.

Besides the new bullet, two things have changed since last time 1) necks had previously had zero clearance, some were even rubbing a bit, so I turned the necks a little more to about 0.011" if I remember right. Now there is about 0.001" clearance with a 0.310" bullet. 2) the nose-sized bullets were making hardest contact in the middle of the bullet when chambered while the front band only made light contact. So I judiciously honed the nose die such than now the front band makes hard contact while the middle of the bullet makes only light contact.
Image

Groups were shot starting on the left and moving to the right.

The first group started out with just enough WC844 to achieve 2700+, but that load had vertical dispersion and excessive velocity variation. Bullets were engraving a little harder than I prefer and that might have contributed to the velocity variation.

For the second group, I nose-sized a wee bit deeper, seated the bullet out a wee bit further, and increased the powder charge to 35.3 gr.. Velocity variation and group size seemed to improve.

For the 3rd and 4th groups, the powder charge was increased to 35.6 gr. Velocity variation was good, and the 3rd group finally cracked the MOA barrier, yet vertical dispersion re-appeared on the fourth group. :cry:
Image

So far it shows no love for this bullet, other than the one lucky group.

I'll try again this afternoon with some different powders. Unless I find a powder that makes this bullet happy, I may go back to the 130 grainer, or perhaps compromise and try a 135. I think the 130 needs a wee bit more length, particularly a little more inside the neck, but otherwise it was a consistent performer, unlike this 147.

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Re: 30 BR

Postby mtngun » Sat Jul 30, 2016 8:05 pm

... Trying a different powder with the 147 gr. GC. BTW, its BHN was 34.6 with the 10mm / 150kg test, or 27.7 with the 4mm / 60lb test.

This is with WW748.

Left Group: I mis-guessed the powder charge so the velocity was below my self-imposed 2700 fps minimum, plus vertical dispersion was rearing its head.

Right Group: upped the powder charge and seated the bullet a wee bit deeper. The powder density appeared to be right at 100%.
Image

I was out of bullets and out of daylight so that's as far as I got. :| WW748 was no better or worse than WC844. I see no reason to pursue WW748 further, especially since I don't have much of it and it was maxed out on velocity & powder space.

I'm wondering if the 147 grainer's tendency to throw vertical fliers is due to barrel vibes rather than the bullet itself? If so I may need to experiment with higher velocities to find a friendly vibration node.

Next time I'll continue trying different powders, and try upping the velocity in search of a better vibration node.

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Re: 30 BR

Postby mtngun » Thu Aug 04, 2016 10:08 am

My version of a homemade OAL gage for the 30 BR. This is the first time I'd ever made one so I'm not sure that it is the optimal design, but it was the first thing that popped into my head. :lol:

Previously I had been setting COL by how much resistance there was to closing the bolt. Problem with that is, especially in a tight chamber, there are other things besides bullet engraving that can make the bolt resist closing -- if the neck is tight, if the case is too long, if the shoulder has not been set back enough, or if there is a granule of unburned powder in the chamber.

And in fact, I recently discovered that some of my cases were too long, long enough to cause slight resistance when chambered. :( Needless to say that has been corrected.

Some "feel" is required to use the OAL gage, so it is not 100% accurate, nor is it 100% repeatable, yet it's still a big improvement over the "resistance to bolt closing" method.
Image

The gage in use. You screw in the threaded rod while maintaining finger pressure on the "pusher" to keep the dummy round all the way in the chamber. When the threaded rod finally pushes the bullet into contact with the throat, it will try to push the case out of the chamber. I put a mark on the pusher so that I could see when it begins to move. Then I turn the screw out and in a few times to verify the contact spot is repeatable. Remove the assembly and use the depth gage on calipers to measure how deeply the bullet was seated when it made contact. A little math yields the contact OAL.
Image

The "pusher" is slotted so that it can be inserted over the threaded rod.
Image

Now that the contact point has been sorted out, I resumed experimenting with different powders and the 147 gr. GC. Targets were shot from left to right.

1st group: trying WC845 because I have 2 jugs that need something to do. :lol: It's burning rate is halfway between WC844 (H335) and WC846 (BL2C or WW748). The burning rate is about ideal for this cartridge, yet it shot patterns instead of groups. :( This pattern was shot with 0.015" jam.

2nd group: same WC845 load except with 0.004" jump. It still shot a pattern but notice the velocity variation was much improved.

3rd group: LT30, loaded right at the contact point. Velocity variation was very good.

4th group: Increased the charge of LT30, still loaded at the contact point.
Image

Conclusions:
-- no love for WC845.
-- a jam fit seems to increase velocity variation.
-- LT30 shows some promise, but I want to repeat the LT30 load before drawing any conclusion.
-- no conclusions about vibration nodes with this bullet. I need to settle on a powder first and then I'll try different velocities.

I'll continue trying more powders with the 147 grainer as time allows. Here's what's left on my list:
RL7
RL10
H322
IMR4198

And that's basically it -- there aren't very many powders suitable for the 30BR. Benchmark, RL15, H4895, Varget, BLC2, 8208, and N133 were eliminated on Quickload because you can't cram enough powder in the little case to hit my velocity targets.

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Re: 30 BR

Postby mtngun » Thu Aug 04, 2016 7:54 pm

Shooting was interrupted this evening.
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