drilling rifle bullets to improve terminal ballistics

[jackieschmidt]

Why? Why not just buy a bullet for the application?

^^^^^^^

 

[Todd Morley]

Sometimes you can't get the bullet you want. Lots of people seem to like to hunt with Berger target bullets, Sierra Match Kings, and other target bullets, perhaps because they like the high BCs, perhaps because they already have a large supply of the bullets--perhaps even because they like the expansion rate of a target bullet's thicker jacket. (Who knows?) Supposing you're committed (for whatever reason) to hunting with such a target bullet, if the bullet does not have a protective plastic or aluminum tip, you can open it up to improve terminal ballistics. The question is how to do that so you preserve or even enhance accuracy and minimize BC loss.

My trim-then-drill-then-deburr process reduces variation in tip shape (see the attached photo), bullet length, and bullet weight. The deburring also polishes the ogive, which I speculate may restore some of the small difference in BC that I lose to the more open tip. (The difference amounts to < 1/2" vertical at 500 yards.) These bullets are as accurate as the untrimmed originals in my rifles (< 1/2 MOA), but they expand great on nilgai and elk. (I've taken two nilgai at 200 yards each and a cow elk at 600 yards with trimmed and drilled SMKs. All three dropped where they stood and never moved afterwards. Terminal ballistics were authoritative.)

The bullets in the photos are 7mm 183-grain Sierra Match Kings. Actual weight after trimming and drilling averages 182.7 grains, with a very small standard deviation. I've done less aggressive trimming and lost about half that much weight to the process.

Target shooters (like me) sometimes trim target bullets for improved uniformity and hence accuracy. (My trimmer is made for competitive shooters.)



Left, trimmed but not drilled or polished; right, the finished product. Note the effect of polishing the ogive.

 

[chop house]

Right now, I'm trying to work up a load for some 34-grain .20 caliber bullets that aren't up to my usual level of satisfaction in how they shoot. And I bought a box of 5,000. 1/2" MOA is all I have been able to get out of them

I may regrettably be familiar with these bullets. Big open tip, low bc, erratic amounts of core showing in tip?

What I will say is they are 'cheap'. With no support under the thin jacket all my seater stems inflicted some amount of damage to the ogive.

If you break the code let us know...

 

[Todd Morley]

I may regrettably be familiar with these bullets. Big open tip, low bc, erratic amounts of core showing in tip?

What I will say is they are 'cheap'. With no support under the thin jacket all my seater stems inflicted some amount of damage to the ogive.

If you break the code let us know...

If you're seeing different amounts of core showing in the tip, you might improve uniformity by drilling them to a uniform depth. Doesn't sound like you should open up the tips any further (I wouldn't, on 20s). And you might try sorting them by weight, and loading in batches by weight.

 

[AccelR8]

I may regrettably be familiar with these bullets. Big open tip, low bc, erratic amounts of core showing in tip?

What I will say is they are 'cheap'. With no support under the thin jacket all my seater stems inflicted some amount of damage to the ogive.

If you break the code let us know...

Ha I think I have the same ones too. After working with about 75 to 100 of them I was so discouraged the box just takes up space on the shelf now.

 

[searcher]

I may regrettably be familiar with these bullets. Big open tip, low bc, erratic amounts of core showing in tip?

What I will say is they are 'cheap'. With no support under the thin jacket all my seater stems inflicted some amount of damage to the ogive.

If you break the code let us know...

Yes - that sounds like my bullets. And they WERE cheap! I was looking for a super-cheap load for "close-in", high volume shooting at ground squirrels, so as to save some barrel wear on my longer-range rifles. At 1/2" MOA, they are satisfactory for that. Most powders shot them into 1" to 1 1/2" groups. Varmint powder got them to 1/2" or a bit better. My old lot of "T" military powder was a bit better, but I don't want to use that up on varmints. Accurate LT32 was also good - but was almost 60% higher in cost than the Varmint powder - which defeated the purpose of the whole exercise.

 

[Todd Morley]

I loaded the trimmed/drilled SMK 183s for my 280 AI using Ramshot's new Grand powder. Managed 2,925 fps before pressure signs, settled on 2,900 fps, four-shot extreme spread 20 fps, SD 9 fps. Shot under 1/2 MOA. Grand looks like pretty good powder. Not quite RL-26, but whatever is?

 

[D-4297]

As a retired Aerospace Die-maker , I've chuckled as I read this entire topic . Not because of the efforts guys are putting into this ; but because of the sheer futility of it . How many are "indicating" their bullets with a "Tenths" indicator ? How many have checked their lathe spindle to see what the actual "run-out" is ? Are you using the Hardinge Tool-room Lathe ? The "standard" of tool-room precision Lathes ? The probability of improving a bullet BC or aero-capabilities is something bullet manufacturers have been dealing with for decades now , and they still have all sorts of highly skilled machinists and tool-makers working on this , but it just seems to me that some folks have way to much time on their hands . But I do wish you luck in this endeavor .
As someone who "worked" in the Domain of "Tenths" for decades , I am acutely aware of the struggle of duplicating items in this realm .

 

[Todd Morley]

While bullet diameters and jacket thicknesses are measured in tenths of thousandths, bullet lengths can (and routinely do) vary by several thousandths (extreme spread). Meplat trimming (and sometimes subsequent re-pointing) is, or has been, pretty common in benchrest shooting, and tools are sold for it. (I own one.) Meplat trimming reduces variation in bullet length, in my experience, and judging from what I've read in the competitive-shooting literature.

As for the rest, I'm not using a lathe at all. You might read my posts with more care. What I can say is, I have not experienced any degradation in accuracy, just a small decrease in BC (add a half inch of drop at 500 yards) and a big improvement in terminal ballistics when trimming/drilling target bullets. That's the effect that motivates the practice. Do it if you like to hunt with target bullets and you want quicker expansion on impact. Why you might want to hunt with target bullets is another question. What I can tell you is, a lot of people do it--the Berger 215-grain .308 target bullet for long-range elk hunting, especially, and also the SMKs.

 

[TTE]

I have previously posted elsewhere about drilling rifle-bullet tips to improve terminal ballistics

Depends what they are used for. Also depends on what you mean by improved terminal ballistics.

There is not a home drilled bullet on the planet that is acceptable for a Cape Buffalo.

There are already "varmint " bullets and "deep penetrating" bullets .... why would you waste your time drilling anything. If you are off by just a bit with your drill bit, the bullet no longer flies properly.

 

[Todd Morley]

I've addressed these questions in previous posts within this thread, and in the document accompanying my first post.

I am not suggesting the practice at all, let alone for hunting cape buffalo. I am merely reporting my own experience with some of the technicalities of a practice that's at least a century old. (In WWI, soldiers called drilled FMJ bullets "dum dums." It's not my idea.)

 

[Wild Bill IV]

Why? Why not just buy a bullet for the application?

Back in my days, the Mini-14 had a 10 twist while the Colt AR-15 had a 11 or 12 twist. The standard, off the self loads were 55 grain FMJ made for the Colt!!! Knowing that a more rapid twist requires a longer bearing surface bullets, I had to improvize. At that time, my choices were the 60gr Hornaday HP, 63gr Sierra GK semi spitzer, or the Speers 70gr RN. The Hornaday tangent designed was too short a bearing surface. The 63 grouped great, but did not expand on praise dog! The Speers bullets grouped tighter, but were Hot Core design.

Made a collet jig to hold the 70gr bullets in a drill press!!! Drilled down into the bullet until a copper ring formed using a No. 2 center drill. Those bullets grenades on impact!!! Only problem, when shooting past 350, the bullet held together and was so hot, it cauterized the wound. Too much opening caused to much friction at the tip and not enough energy to expand the cup!!!

The Mini was only good out to 300 anyway with the RN bullets!!! Anything beyond that was hit or miss. At least, I got a bullet that torn those dogs to pieces!!! And, I reloaded non drilled bullets to pull dogs out of the hole when all you could see was a nose!!!!

 

[Todd Morley]

Pretty cool story. Wish I had your machinist skills (and, evidently, tools).

 

[Wild Bill IV]

Pretty cool story. Wish I had your machinist skills (and, evidently, tools).

Back in those days, I worked in a manufacturing plant and was classified Machinist A (Master because I could set-up and operate any machine in the plant and exceed production quota) and Tool Maker B (Journeyman) while going to school for Engineering. Had access to engine lathes, vertical mills, black diamond drill sharpeners, surface grinders and lappers, horizontal and vertical water cooled grinders, and tool cutters with diamond cups and diamond cut off wheels for carbide tooling! 2nd shifter tool crib operator. The newest machine (brand new) in the plant was a Brown and Sharpes NC (Numerically Controlled) indexing vertical mill (3-axises). The programming was executed using key punch papers tape rolls!!!

 

[Todd Morley]

Pretty neat toys. I wrote my first computer programs in the same era, when computer input and output was on paper tape. Got to college and started on Fortran and punch cards. Wow tech has changed.

 

[Wild Bill IV]

Pretty neat toys. I wrote my first computer programs in the same era, when computer input and output was on paper tape. Got to college and started on Fortran and punch cards. Wow tech has changed.

Fortran IV, the scientific/mathematics programmers language!!! The good old Keys punch cards. You wrote the number on the cards in the order of the programming, just in case you dropped the stack and had to reorder before run time!!
Will never forget that L, M, and N can only be used for REAL WHOLE NUMBER programming Names!!!!!

 

[Todd Morley]

Yeah, we had to write it all out on the oversized green and white paper with the lines of rectangles, one uppercase character per rectangle, before we were allowed to punch the cards. . . .

 

[Tim Slater]

(In WWI, soldiers called drilled FMJ bullets "dum dums." It's not my idea.)

For a historical tangent, the association between hollow points and Dum Dum pre-dates WW1. Dum Dum is a town in India, near Kolkata (then Calcutta), where the British colonial government had a munitions factory. There, in the 1890s, a British officer created what would later be termed the Mk II* (or Mk II Special) cartidge in an effort to increase the lethality of the RNFMJ Mk II .303. The Mk II* was properly a soft point rather than a hollow point, but the name stuck. Following on from this work, the Mk III, IV, and V cartridges were developed which actually had hollow points, but were withdrawn from active service after concerns over their legality.

Interestingly German propaganda in WW1 alleged British soldiers used the magazine cut off to remove the point of Mk VII cartridges (with its wood/aluminium filler) to create a soft point.

 

[Todd Morley]

Tonight I finished trimming and drilling 100 Berger Long Range Hybrid Target 190-grain 7mm bullets. I took a random sample of 30 of the trimmed/drilled bullets and 30 factory bullets, and measured their weights and lengths. Then I did a Levene Test (a statistical test) comparing the standard deviations (a measure of degree of variability) of the two sets of measurements. The SD of the trimmed/drilled bullets was slightly lower, but there was no statistical evidence of a real difference in SD. (In other words, trimming and drilling didn't make the weights either less or more uniform than the factory weights.) For the lengths, there was modest evidence that the trimmed/drilled bullets were ~more~ uniform in length (the SD was lower, but this time the difference was more pronounced).

Trimming and drilling removed on average 0.31 grains of copper at the tip, or about 0.16% of bullet weight. Length decreased on average by 0.038", or about 2.4%. In previous experiments these changes have lowered the BC enough to induce an additional 3/8" of drop at 500 yards, which would amount to a loss of under 5% in the G7 BC, assuming a muzzle velocity of 2,900 fps and typical Rocky Mountain elk-hunting conditions. According to the Berger external-ballistics calculator, the decrease in weight does not measurably affect drop at 500 yards. The combination of decreased weight and BC reduces velocity by about 1% and retained energy by around 2%, at 500 yards.

In summary: if my little experiment represents typical trim/drill results, one can expect (if anything) a slight ~improvement~ in accuracy due to the modest decrease in variability in bullet length (hence variability in SD), as well as improved terminal ballistics, in the sense of expansion consistent with hunting bullets (the main effect a hunter would seek in trimming and drilling). The accuracy-improvement side effect is, for target shooters, the main effect they seek in trimming bullets, so the SD reduction explains the accuracy bump they report. The tradeoff is a small decrease in BC that produces essentially negligible effects out to 500 yards, with effects on velocity and retained energy becoming meaningful well beyond that distance.

 

[Wild Bill IV]

Yeah, we had to write it all out on the oversized green and white paper with the lines of rectangles, one uppercase character per rectangle, before we were allowed to punch the cards. . . .

The good old wide track paper!!!!