Pros/Cons of concave or recessed bullets

[hot chili powder]

Any thoughts on using concave/recessed base bullets (FMJ)....thinking of trying some but never used anything but flat base bullets. These would be for my 9mm CZ Duty, any pros or cons??

 

[LiveLife]

FMJ/RN with hollow base will extend the length of bullet base and will seat the bullet deeper in the case when using the same OAL/COL as flat base bullets. The intent of the hollow base bullets are to better expand the bullet base to seal with the barrel and better engage the rifling with longer bearing surface.

Below comparison picture shows 115 gr FMJ hollow base and flat base bullets from RMR on the left and Berry's 115 gr Thick Plated HB-RN on the right.

 

[Varminterror]

What I have never done, since I don't shoot hollow base ball enough to care, is compare how much actual powder volume is lost, if any, when seating them. In theory, if a flat base and a hollow cavity had the same ogive profile, even though the hollow cavity base is seated deeper than the flat base, there would be just as much bullet volume inside the case as if it were a flat base, since powder can occupy the cavity. So a guy gets a longer bearing surface and a better base obturation to seal against the rifling, and doesn't really lose any powder volume. Pressure would go up according to bearing surface, a bit... Most of my hollow base shooting is done with wadcutters, which is a different animal altogether anyway.

 

[Archie]

Verminterror is correct. A projectile simply has so much volume, regardless of shape. So, seated to the same over all length, it will only take up the same amount of space.

Change the material or alloy of the projectile, OR, change the seating depth and there will be change in the internal volume of the cartridge.

I think the 'hollow-base' or 'concave' base structure should - theoretically - expand and better fill out the bore (grooves) making the powder charge more efficient. (Probably not enough to measure for us regular folks.) This function should - theoretically - aid in accuracy.

The down side is doing this would require one more step in the bullet making process and add cost. Done wrong, it could distort the base of the bullet, fouling up accuracy big time.

 

[H&R Glock]

I agree with the idea of a lead bullet with a hollow base, but have my doubts about the usefullnes of said designs with jacketed bullets. Is there any hard facts proving the jacketed bullets really expand in the hollow region?

 

[LiveLife]

I agree with the idea of a lead bullet with a hollow base, but have my doubts about the usefullnes of said designs with jacketed bullets. Is there any hard facts proving the jacketed bullets really expand in the hollow region?

I guess we need to conduct another myth busting comparison range test to see whether Hollow Base FMJ produces greater accuracy over Flat Base FMJ.

I can volunteer for the range test and also include Berry's HBRN-TP.

 

[H&R Glock]

Berrys, Xtreme, etc etc are soft lead bullets with plating. They are not jacketed bullets. I have no doubt that they expand during firing due to their soft lead makeup.
I'd think a good test would be to fire a jacketed HB bullet into a water trap and use a micrometer to see if there is a difference in the skirt groove diameter and the body diameter??? How would you be able to tell for sure?

 

[hdwhit]

total recoil wrote:
Is there any hard facts proving the jacketed bullets really expand in the hollow region?

I am not aware of any, but measuring the bullet after firing would not necessarily be definitive. The gas filling the hollow base exerts pressure that can be resolved into vectors parallel to the axis of the barrel and perpendicular to the axis of the barrel. If the magnitude of the vector perpendicular to the axis of the barrel is still within the elastic range of the gilding metal/lead alloy composite of the bullet, then the vector perpendicular to the axis of the barrel would push the base into the wall of the barrel, but as soon as the bullet cleared the barrel and the pressure subsided, the base of the bullet would return to its original dimensions.

 

[Walkalong]

I too was worried about the hollow in the Berrys bullet making the bullet unbalanced. but the Berry 124 Gr TP-HBRN and the Berrys 148 Gr HBWC both shoot very well for me. I was recently banging a 16" steel plate at 108 yards with the 124 Gr TP-HBRN loaded to 1300+ FPS in .38 Super. I also retested the new 148 gr HBWC (Anyone else notice they changed it slightly?), and to my great satisfaction it shot very well. I also like to bang the 108 yard plate with them. I like to shoot the 53 yard plate, the 75 yard plate, and the 108 yard plate three times each with a revolver and try not to miss. 53, 75, 108, 53, 75, 108. Can I do it every time? Heck no, I'm not that good. Can I hit them a lot? Yep.

That said, I am far from being Bullseye accurate with pistols, I am just a little above average IMHO. That test would be child's play for Bullseye shooters.

 

[243winxb]

 

[H&R Glock]

I have loaded FMJ flat base and FMJ hollow base bullets for my 9mm's and can see no difference in the accuracy.
I sorta' believed the FMJ hollow base bullets were a sales gimmick as performance for me was underwhelming to say the least. Your range results may differ so keep buying the FMJ HB bullets. Results matter.

 

[Rule3]

I am not aware of any, but measuring the bullet after firing would not necessarily be definitive. The gas filling the hollow base exerts pressure that can be resolved into vectors parallel to the axis of the barrel and perpendicular to the axis of the barrel. If the magnitude of the vector perpendicular to the axis of the barrel is still within the elastic range of the gilding metal/lead alloy composite of the bullet, then the vector perpendicular to the axis of the barrel would push the base into the wall of the barrel, but as soon as the bullet cleared the barrel and the pressure subsided, the base of the bullet would return to its original dimensions.

Seriously??

 

[higgite]

If the magnitude of the vector perpendicular to the axis of the barrel is still within the elastic range of the gilding metal/lead alloy composite of the bullet, then the vector perpendicular to the axis of the barrel would push the base into the wall of the barrel, but as soon as the bullet cleared the barrel and the pressure subsided, the base of the bullet would return to its original dimensions.

If that were true, wouldn't the same principle apply to pulled bullets that were over crimped, as in, there would be no visible indication that the bullet had been over crimped?

 

[Holderofthehorns]

Hello, all. New guy here.

I suspect almost identical performance from both.
1. HB has the concave, but, it can't possibly expand beyond the lands and grooves.
2. The HB is jacketed (thicker copper).
3. The Berry's cross section (post 10 above by 243winxb) is thinly plated.

I expect less copper in the plating would allow the softer lead to expand.
And the cup on the FMJ would aid in expansion.
Measuring exit diameters of both could only match the barrel.
A chronograph reading of 10 or so of each, with identical sized brass, seating, crimping, bullet weights and charges may show a difference. But it would take that much sameness to eliminate other effects from the test.

I shoot them both and can't tell the difference.

 

[Schwing]

After a few years and fiddling with all kinds of different bullets I have learned one fact that is true 100% of the time: The same combination of components will always behave differently in different firearms 100% of the time.

I'm being snarky but all of the math and physics while good on paper, will rarely translate into accuracy/reliability for you and your gun.

Now, just to add one more bullet into the mix: How about hollow points and soft points that are poured from the nose?

 

[LiveLife]

After a few years and fiddling with all kinds of different bullets I have learned one fact that is true 100% of the time: The same combination of components will always behave differently in different firearms 100% of the time.

+1. Variance in different firearms/barrels will produce different chamber pressures and muzzle velocities.

I suspect almost identical performance from both.

1. HB has the concave, but, it can't possibly expand beyond the lands and grooves.
2. The HB is jacketed (thicker copper).
3. The Berry's cross section (post 10 above by 243winxb) is thinly plated.

Welcome to THR!

Thickness of gilding metal on jacketed bullets can range .015" - .030" while thickness of copper plating on "thick plated" bullets like Speer TMJ (Total Metal Jacket) is around .015" and Gold Dot HP is about .018" - https://www.thehighroad.org/index.p...ng-at-25-50-yards.808446/page-3#post-10470195

Berry's HBRN-TP copper plating thickness is about .006"-.012" and as shown by 243winxb's picture and I agree with your post that "regular" plated bullets have around .004" thickness copper plating.

 

[LiveLife]

A chronograph reading of 10 or so of each, with identical sized brass, seating, crimping, bullet weights and charges may show a difference. But it would take that much sameness to eliminate other effects from the test.

I shoot them both and can't tell the difference.

Well, there are many, including me who will argue chronograph readings don't necessarily translate to shot group size on target. We have verification from many members that high SD number loads can produce small shot groups.

There are many reloading variables. Even keeping everything the same and simply using mixed range brass will result in enough variance in chamber pressures/muzzle velocities to spread your shot groups.

When we say we can't tell the difference, it may be that reloading variables are overshadowing so much that difference from bullets (which I believe is quite significant to accuracy) are not measurable. If new brass was used to remove the variance from mixed brass, we may see the difference on target.

Then there's shooter input.

I used to test loads at 25 yards while resting my hands on top of a small ice chest to produce 3"-4" average groups during powder workup to 2" groups for more accurate loads. To reduce shooter input, I now use 17" Just Right carbine with 9mm/40S&W/45ACP barrels with scope and bi-pod.

People may blame "flyers" for using mixed brass but when the same loads were fired with the JR carbine, the flyers significantly decreased, which led me to believe it was shooter input not the use of mixed brass.

There are more factors that influence shot group size. These 25 yard 10 shot groups initially shot with adjustable stock produced "scattered" groups -

Using a fixed A2 stock to remove adjustable stock wobble, same load produced smaller shot groups

Using same RMR 115 gr FMJ at 1.130" and mixed brass, simply changing the powder produced very tight one hole group (see center 10 shot group below) - https://www.thehighroad.org/index.p...-and-vectan-ba-9-5-ba-9.817796/#post-10508215

RMR 115 gr FMJ at 1.130" with IMR Target 4.5-4.6 gr (Left), 4.2-4.3 gr (Center) and 4.0-4.1 gr (Right)

With same RMR 115 gr FMJ at 1.130" and IMR Target, changing to thick plated bullet (RMR 115 gr Hardcore Match RN) also produced small group (10 shot group on the right below).

RMR 115 gr Hardcore Match RN at 1.130" with IMR Target 4.0-4.1 gr (Left) and 4.2-4.3 gr (Right)

 

[Holderofthehorns]

Well, there are many, including me who will argue chronograph readings don't necessarily translate to shot group size on target. We have verification from many members that high SD number loads can produce small shot groups.

Agreed. Chronies do offer a general baseline.
If the 2 general baselines differ, then we'll know something "general".
I would also want to remove the human from the shot groups. A sled.
Basically, eliminate any deviation whatsoever, except the Plating vs Jacket.

Well, it seems we are precision, expert guessers. Expert on the guessing, as there is always some issue of variance, like the shooter. Art and science mixed well.