Cast bullet accuracy and trailing edge failure

[303Guy]

It's a segmented high tensile steel tube with an inner steel tube filed with sand. It has a 4140 steel disc at the bottom over and and a 4140 steel sand pot over that - not like any boolit will make it that far! Actually, I used to use water soaked rags as a catch medium to test for boolit performance. Then the boolits did make it into the sand pot.


Like you say, it can be hard to evaluate a recovered boolit due to impact damage.

[DrB]

Yeah, but it could be abstract art. Got a name for that one?

[303Guy]

I'd call it "Boolit Splash".

How it stays together is amazing!

[TRX]

The reason for a little cylinder play in a revolver and a boolit tough enough to pull the cylinder into alignment.

[facepalm] I always wondered if there was some reason the Nagant revolvers had the cylinder slide up and spigot on the back of the barrel. "Gas seal" never made any sense; the 7.62 Nagant cartridge wasn't very powerful, but it was unique to that gun. If they had wanted more velocity, they could simply have loaded it differently.

Though the Nagant cylinder arrangement was more complex than a Colt-style cylinder, the parts were all large and easy to make and fit, unlike the fussy Colt latch mechanism.

The Nagants also did amazingly well in competition, back in the day. Hmm...

[Willbird]

Time + Money + an obnoxious attitude for an objective = accurate results. Most folks give up too soon for one reason or another, either good or bad. My experience has been not obtaining external ideas to get over an unexpected hurdle. The real excuse for many of these projects has been no profit potential for the results.

You are correct in using a "photo" apparatus for measuring the rotation. The boolit would have to be painted with something "hot" that can be read with the existing particle measuring devices. Finding an appropriately short half-life paint would be prohibitive???? Who wants a forever contaminated barrel? ... felix

Dr. Harold Vaughn (In the book Rifle Accuracy Facts) measured bullet rotation by placing a tiny disk shaped magnet in the bullet, in the nose of the bulled like a dig carries a frisbee in his mouth...then fired the bullet through a wound copper coil, and measured the output of the coil.

That book is worth a read and a re read, I need to get another copy.

I think that if the rifling engraving is intact, then we can calculate bullet rpm just like we can say a 1/4-20 threaded bolt must rotate 10 turns to move 1/2" out of a threaded hole.

Bill

[303Guy]

On trailing edge failure, I posted this on my thread;


This being powder kernel peening.

I tried a wad under the patch skirt and had this result. (The one on the right).



Then gearnasher tried it out on the range and had rather interesting results;

... this morning I loaded some of my .45 Colt NEF loads, but this time added some .025" heavy, waxed card stock from a beverage container between the powder and patched boolit base. This cut my 100-yard group size literally in half, with no other discernable effects.

[DrB]

That's an awesome experiment. Thanks 303guy.

[1bluehorse]

Bret, the good Doc is figuring the size of the retro rocket required to compensate for any directional errors during launch. He is finding out compensation is too minuscule to be cost effective. His disclaimer deals with the obscurity of the actual real-time summation of the erroneous vectors (direction and speed) to work with. His discourse is just thinking out loud. ... felix

Uhh, yeh, okay, thanks...

[303Guy]

In the quest to minimize trailing edge damage I tried ball powder as has been suggested to be more cast boolit friendly. Well, preliminary results confirm that.


Ball powder - W748

As opposed to stick powder - Varget/AR2208

[DrB]

The peening or whatever it is on the varget bullet really goes all the way to the edge. What were the loads?

Is there a theory as to why? Single vs double base? I'm also kindof surprised the peening is so heavy all the way to edge, and so coarse. It would be interesting to see a few grains of the powder besides the damaged base of the bullet... Do they roughly match the craters in size?

[303Guy]

The craters do match the powder granules. The charge was 36gr Varget on that worst one. I no longer have that sample but here is a pic of another boolit with the granules placed on top to give some idea. The reason for the impressions actually cutting the boolit edge turns out to be that it was seated just below the neck (an error on my part).



I suspect the shape and hardness of the granules plays a role. Ball powder may have a slower initial burn hence a lower impact or shock against the soft lead. It is likely that ball powder has a self cushioning property due to its shape. I can't help thinking it's the self cushioning effect. Maybe not on its own but partially at least.

[TXGunNut]

Great thread, need to set aside a few weeks to read it along with the reference materials to begin to understand it. My background is sales and marketing, not physics.
I'd like to defend or maybe explain why the gun rags don't print the tech articles that would be helpful or interesting to some of us. Mike V has written about it, I've heard other gun writers talk about it as well. Magazines are owned by corporations that must produce a profit for the shareholders. A large part of the revenue is from advertising. Folks who purchase ads want to reach as many people as possible and they like it when their products are mentioned favorably in the articles. It stands to reason that magazine editors want articles that will interest the widest spectrum of readers. They think those readers want to see the latest products (helps with ads, too) and aren't much interested in the science behind it all. Why put resources into technical articles when the target market probably can't balance a checkbook?
I agree that a magazine such as Handloader should find room for articles on this and other technical subjects but the editors apparently disagree. Could be why the only gun magazine I receive is American Rifleman. I used to subscribe to others but lost interest when the ad pages outnumbered the article pages and the articles often heaped high praise on a product advertised nearby.

[airamb]

I very much agree to Micheal Petrov, I've read the book though.

[303Guy]

I tried a load of 34.8gr W748 under a 194gr patched with printer paper boolit (which was smaller than previous) and the base survived essentially intact. I repeated the test but filling the case with wheat bran. That left a tail ring of the patch on the boolit and base edge flattening with some edge feathering. There was of course an increase in pressure and boolit damage from impact.

The relatively undamaged boolit base - there is peening.

[FirstBrit]

I'd REALLY like to see some checked and pb examples of base cupping. Reality is, and I've never held one of these in my hand and seen what it looks like.

Best regards,
DrB
EDIT 7/12/2011: No one has a load they can suggest that they think will produce cupped base bullets with and without gaschecks? Or just not in .357 Magnum?

Hello DrB

In response to your request I did some testing about 7-8 years back on my S&W Mod. 27 with 180 gr. PB cast bullets from a Magma mould. Basically these tests were to give me some insights into the problems of gas cutting with plain based lead bullets and the influences of alloy hardness and powder burning rate.

Basically 6 loads were tested with 3 alloy strengths BHN 10; 16 and 22.
Series 1 control 5,0 gr. VV 3N37 with 4,4 gr. buffer similar to Buffer Mix # 47 ( Int. Ballistic Products Inc.)
Series 2 control 10,5 gr. VV N-110 with 2,2 gr. buffer.
Series 3 test 4,2 gr. VV N-320
Series 4 test 6,5 gr. VV N-320
Series 5 test 8,0 gr. VV 3N37
Series 6 test 13,0 gr. VV N-110
Hardness of the bullets in the photos is BHN 10, 16 and 22 from left to right.
The idea for the buffered loads was to completely eliminate any gas cutting which did work well. Gas cutting was examined visually and measured in terms of base and front band diameters on the recovered bullets.
My understanding is the maximum strain/stress for these bullets is incurred at P-max. and bullet travel at P-max varied from about 0,175" to 0,540" as predicted by Quick Load software program. Similarly P-max. varied between 19-36k psi.

Based on these limited results I only observed cutting with the buffered loads which as one might expect was more pronounced with the softer alloy. Clear indentation of powder granules was seen in series 6 and nearly all others showed signs of "pimples" or peening with the exception of the harder alloy in both control series.

Some other general observations. Gas cutting was more prevalent with the softer alloy and in the series 4 was so pronounced one can hardly see the groove markings which correlates with rear band diameter of 0,330-0,348".

I am sure these tests are no way conclusive but maybe it will work as a new piece to the overall jisaw puzzle.

Best regards,

Adrian, Germany.

[303Guy]

Thank you for the informative post, FirstBrit. Good to have you with us.

[geargnasher]

DrB, I happened to have a handfull of examples laying on the desk here, just about every single boolit I've recovered that was weaker than the peak PSI of the load cupped it. I don't have any examples of cupped gas check boolits handy, but I've seen it plenty of times there too with hot loads.



Gear

[303Guy]

I do believe I have the solution for my trailing edge damage problem. I increased the powder charge to completely fill the case (AR2209/H4350) and place a card wad under the boolit. I also used a slightly smaller boolit with thicker paper (printer paper).



One can see by the primer that pressure was moderate. I dare say muzzle blast is going to be notice-able with that short barrel even with the suppressor!

I've had the suspicion that it is the powder slamming into the boolit base that has been causing the base cupping, peening and edge feathering. That's what motivated me to take out the air-space altogether. It seems to work, with stick powder anyway.

P.S. For those who don't paper patch, the paper patching allows for full j-word velocities (if not higher) at lower pressure and often with better accuracy - if it's done right.

[popper]

Anybody ever test sizing base first to clean up the edges on a PB CB? Tags from rifling should be the same. Any evidence that dacron filler will reduce base powder peening?

[303Guy]

Any evidence that dacron filler will reduce base powder peening?

Well, it seems like it might even. I got hold of some some filtration medium and it's heavier stuff and takes more to fill the case. Comparing primer flattening between H4227 loads and WW748 loads, there was no boolit base damage or peening at all.



(To compare primers I zoom a photo up on the screen so I can take an accurate measurement then calculate the % flattening. I've done a thread on this).