Topic: Individual marks from consecutive manufactured barrels

[afss]

It is a well known fact that firearms examiners are able to differntiate between bullets, fired from consecutive manufactured barrels, and are able to determine from which barrel any bullet was shot.
In the literature, tests and real cases, where consecutive manufactured barrels and bullets fired from them were examined, are well described.
However, in most of those tests & cases, the examiners were able to examine the whole bullet with mosst of the L&G on it intact!
I am looking for cases were only ONE land mark remain, with supposed positive comparison, but with other marks (Lands & Grooves) with distingtive non-resemlence.
If any one of you knows such a case, or cases, or knows about a paper observing this issue, I will be most graitfull for the information.
Thank you,

Lior

[afss]

After reading my request, posted above, I understood I am not clear enough, so I am adding some info to it.
I am interested to know if the examiners, who examined bullets from different barrels, saw similarity between one or more land grooves, even if their final conclusion was that the bullets were fired from different barrels.
Thank you,
Lior

[afss]

Hi Brian,

Maybe my question was not clear, so I will give an example.
Let say we have two barrels made one after the other.
Bullets are fired from both of them. Now you have only two bullets, one from each barrel but you dont know that, and you need to decide wether they were fired from one barrel or two.
You put them on the microscope and this is what you see:
There is a very good resemblence between L1 on bullet 1 and L1 on bullet 2.
You dont find enough individual marks on the rest of the land marks to make any conclusion.
You do find vivid differentiation between the groove marks of the two bullets.
What will be your final conclusion?:
1. There is a positive comparison (because of L1), meaning the two bullets were fired from one barrel.
2. There is a negative comparison (because of GM), meaning the two bullets were fired from two barrels.
3. You dont have enough information to make a conclusive opinion.

Lior

[afss]

Well Brian, thank you for your response. However I am looking for concrete data from tests and/or cases were it was possible to distinguish between two bullets, but still there was high degree of resemblence in one LI or more, made by the fact the two barrels were made consecutively.

[Brian Smelser]

Sorry I could not help.

[winterh]

The discussion does not say if the barrels were rifle or pistol. I will assume we are discussing pistol barrels.
One must ask the question; does the manufacturer outsource parts and if so does he manufacture his own barrels or does someone else. If the latter is the case I will also assume that the barrels were purchased in blank form; to be machined by the user to the specifications for various models and barrel lenghts. as well as caliber. Cost being the determining factor, it is often cheaper to outsource.
Having said that, it would be difficult to keep the cut blanks (those that have been cut to the proper length, say for a 6 in. barrel) to remain together after being cut. Having not yet been finished.
As the barrels have been finished they are placed in bins or racks; to be later fitted and serial numbered to a specific firearm. It is this binning and racking (remember this is an assembly line process)that makes it nearly impossible for two or more barrels, cut from the same blank to be used in two consecutivly numbered weapons.
If one were to walk a barrel blank (keep in mind that they can be as long as 30 in.) through the entire process, keeping the cut sections together, then perhaps a true test result will emerge.
If this isn't done, then all bets are off...HW

[Humpy]

FWIW I have had extensive tours of Ruger, Smith & Wesson, Colt and Rock Island Arsenal and I have never seen barrels arranged in such a way so that they were assembled into a weapon in the order or manufacture. For instance at Ruger you will see hundreds of revolvers fully assembled with no serial numbers.  This is because they are not serial numbered until they are ready to go into a shipping box.  I also worked with guys who worked at Springfield Armory and know their receivers were not serial numbered in order of manufacture.


The closest I ever got to receiving consecutive barrels was I ordered  two 30 cal rifle barrels with a specific contour from same vendor.  I installed both barrels on Winchester Model 70 actions.  I headspaced both barrels to snug on headspace gage and used same chambering reamer on both barrels.


When I barrel a rifle I insert a barrel erosion gage to take a reading on where the throat locates on the gage before first shot is fired and record that in the log I keep on every rifle.


Erosion gages are marked by rings.  The gov't gages have ring separations every .100".  I inserted gages in both rifles and the differences  in the location of the erosion gage stop points was ONE AND ONE HALF RINGS APART ! ! ! !   Obviously this means there was a significant variation in the internal diameter of the barrels.


30 cal barrels (not machineguns) generally show gage advancement of one ring per 1000 rounds fired as the throat is subjected to high heat and pressures on firing and the barrel material is removed and the bullet has to travel further until it contacts the rifling.


This difference in bore diameter show when gaging new barrels on other rifles as well.  For instance you can take a erosion gage for M1 Garand or M14 rifle and gage new barrels and you will find the gages do not locate at the first mark on the gages.


I have  Olympus Series 5 Borescopes (the best)  and other borescopes and my findings in throat wear differences is amazing.  For instance on a new barrel the reamer leaves rings in the throat.  In normal highpower rifle competition shooting 58 to 130 rounds are expended per day once a load is developed and is taken to the range.  On 30 cal barrels the rings in the throat are generally burned away at between  100 and 150 rounds.


Thus the barrel is continually changing through out its life and is becoming for lack of a better term smoother as the continuous rounds pass down it.


Borescope examinations reveal other significant variations.  The amount of bullet contact with the grooves varies greatly barrel to barrel.  On some barrels the groove contact is significant all the way to the muzzle where in others very minimal contact is is apparent.


Note: Borescopes can be had that view straight forward and others view barrel surfaces at different angles up to 90 degrees.  You will see much more surface anomaly with a angled bore scope of at least 30 degree.  On my Olympus borescopes back in 2002 time frame one was $2700.00 and the other was $4700.00.  The smaller the diameter the higher the cost.

[Jim Hamby]

The Brundage/Hamby 10 Consecutive Ruger Barrels has been sent all over the world - now 724 participants from 36 countries: 15 of whom have used some form of imaging. CSAFE - Center for Statistics and Applications in Forensic Evidence - at Iowa State imaged the known and unknown bullets using Sensofar and inter compared all the LEA's against each other. They were able to identify using about 1/2 of a LEA. Article "Algorithmic Approaches to Match Degraded Land Impressions" by Eric Hare, Heike Hofmann & Alicia Carriquiry reports on this research.