Barrel Harmonics and bullet weight.

Bill Daniel · December 20, 2010, 10:07 AM

In developing a target load would the use of a bullet of similar shape and identical weight (ie. cheaper) to a SMK 168 gr. bullet produce similar harmonics for the barrel? I have some "Blem" bullets from Midway that appear to be Hornady's A-Max. The are boat tail hollow points with a red synthetic tip. As they are cheap would they make an adequate substitute for the SMK 168 HPBT.
Thanks,
Bill-too cheap for his own good-Daniel

Brian Pfleuger · December 20, 2010, 10:43 AM

Barrel harmonics are largely (entirely?) due to the shock wave create when the primer and powder ignite.

The bigger question would be bullet length and construction. Do they take up the same space when seated to the same OAL? Do they require the same force to initially engrave the rifling? Those variables will effect the pressure, muzzle velocity and barrel timing.

**Unclenick** · December 20, 2010, 01:40 PM

Bill,

There are actually 7 different harmonic modes you can see in animated FEA results at Varmint Al's web site. The two shooters are most concerned with are the pressure wave from ignition that Peezakilla mentioned and that Dan Newberry's method locates sweet spots for, and the vertical deflection from recoil moment that an Audette ladder finds sweet spots for (also shown in FEA animation on Varmint Al's site). Ideally you find a spot where they coincide.

Accuracy load development for rifles always requires tuning. For a given powder burn curve, you are looking to achieve matching barrel time for the two bullets. Once you have an accurate load with one bullet, you will find that loading the other for matching velocity from the same gun using the same powder and primer will usually tune it in. Best seating depth is likely to be different for the two, and that will affect the powder charge needed for a given velocity average.

In your shoes I suspect I would use the Sierra's to tune the loads, then see how the seconds did, rather than the other way around. Tuning takes enough time that I don't want to introduce any extra variables that might fool me. On the other hand, you may find the blemished bullets work great in your gun and that shooting anything else is a waste of money. You're just going to have to try it.

Bill Daniel · December 20, 2010, 02:03 PM

Thanks Fellows!! I will fire form with the "Blems" and search for the perfect load with the SMK's.
BillDaniel

December 20, 2010, 10:07 AM	#1
Bill Daniel Senior Member Join Date: February 10, 2000 Location: Bowling Green, KY. Posts: 518	Barrel Harmonics and bullet weight. In developing a target load would the use of a bullet of similar shape and identical weight (ie. cheaper) to a SMK 168 gr. bullet produce similar harmonics for the barrel? I have some "Blem" bullets from Midway that appear to be Hornady's A-Max. The are boat tail hollow points with a red synthetic tip. As they are cheap would they make an adequate substitute for the SMK 168 HPBT. Thanks, Bill-too cheap for his own good-Daniel

December 20, 2010, 10:43 AM	#2
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,694	Barrel harmonics are largely (entirely?) due to the shock wave create when the primer and powder ignite. The bigger question would be bullet length and construction. Do they take up the same space when seated to the same OAL? Do they require the same force to initially engrave the rifling? Those variables will effect the pressure, muzzle velocity and barrel timing. __________________ https://ecommercearms.com I am the owner/operator! Ask me for custom prices! No sales tax outside CO!

December 20, 2010, 01:40 PM	#3
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,732	Bill, There are actually 7 different harmonic modes you can see in animated FEA results at Varmint Al's web site. The two shooters are most concerned with are the pressure wave from ignition that Peezakilla mentioned and that Dan Newberry's method locates sweet spots for, and the vertical deflection from recoil moment that an Audette ladder finds sweet spots for (also shown in FEA animation on Varmint Al's site). Ideally you find a spot where they coincide. Accuracy load development for rifles always requires tuning. For a given powder burn curve, you are looking to achieve matching barrel time for the two bullets. Once you have an accurate load with one bullet, you will find that loading the other for matching velocity from the same gun using the same powder and primer will usually tune it in. Best seating depth is likely to be different for the two, and that will affect the powder charge needed for a given velocity average. In your shoes I suspect I would use the Sierra's to tune the loads, then see how the seconds did, rather than the other way around. Tuning takes enough time that I don't want to introduce any extra variables that might fool me. On the other hand, you may find the blemished bullets work great in your gun and that shooting anything else is a waste of money. You're just going to have to try it. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

December 20, 2010, 02:03 PM	#4
Bill Daniel Senior Member Join Date: February 10, 2000 Location: Bowling Green, KY. Posts: 518	Barrel harmonics and Bullet weight Thanks Fellows!! I will fire form with the "Blems" and search for the perfect load with the SMK's. BillDaniel