Roskoe

I think what is being inferred here is the general tendency for ball powders to not wear the throat of a rifle out as quickly as extruded powders - all other factors being equal. This phenomenon has been documented by a number of reliable sources, including the American Rifleman staffers.

stubblejumper

To start with throats do not wear out as in wear caused by friction.Rather they burn out due to a combination of pressure and temperature.As to the rate of the throat burning out just what documented tests can you show us for the 300ultramag or any cases of similar bore and case capacity?Just what type of differences are you claiming?Is it 1%,2%,5%?

Roskoe

The process I believe is referred to as "particle erosion", and is most pronounced in the area of the bore immediately ahead of the throat due to higher heat and pressure as the bullet starts to move down the bore. Ball powders generally develop pressure at a lower flame temperature than extruded powders, hence less throat erosion. In the test done a number of years ago by the American Rifleman, the increase in useful barrel life was something like 15 - 20% more in the .308 Winchester if I recall correctly. May not be as much in the .300 Ultra Mag class of cartridge.

Another similar phenomenon is the shorter barrel life one experiences with heavier bullets. I have two .243 Winchesters - both with Krieger barrels - and cut with the same reamer. One has a 12" twist and is used for varmint hunting with mostly 70 grain Nosler Ballistic Tips. The other has an 8" twist and is used exclusively for long range target shooting with various VLD bullets in the 105 to 107 grain range. The 12" twist gun has about 3,000 rounds through it - and shows less throat erosion (through the Hawkeye bore scope) than the 8" twist gun that has less than 2,000 rounds. Reason??

Even though the heavier bullets use less powder to reach full throttle velocities, and the full throttle velocities are lower; the heavier bullet takes longer to get moving down the barrel; exposing the area just ahead of the throat to the forces of particle erosion for a longer period of time.

stubblejumper

To add a few more variables to the equation.First have you any way to measure the pressures developed in each barrel being that pressure is a very important factor in throat erosion? Are both bullets the same distance from the lands in the two rifles?I ask this because the closer the bullet is seated to the lands,the more force necessary to engrave the bullet into the rifling which could cause an additional pressure spike at that point and result in more throat erosion.Are both bullets of the same relative hardness for the same reason?Is the longer bearing surface of the heavier bullet(rather than the extra weight) resulting in the resistance to acceleration that is causing the extra throat erosion?Lastly from my experiences,barrels with a quicker rate of twist generally produce less velocity with the same bullet weight than barrels with a slower rate of twist possibly due to the extra work required to rotate the bullet at a faster rate in the quicker twist barrel.Is the faster rate of twist a contributing factor in this case?Since there are so many differences in this case(unknown pressure developed in each barrel,rate of twist,bearing area of bullet,bullet hardness,bullet to lands distance)i would not be so sure that the difference in throat erosion can be attributed to the heavier bullets used in one barrel.

stubblejumper

Since the powders used in the 308win offer a very different burning rate than those used in the 300ultramag and the case capacities are very different(roughly twice as large in the ultramag case) how do you know that the example you offer would be at all applicable concerning the 300ultramag?

taw

I appreciate the debate, but no one has really given me any suggestions as to what loads I might try ( bullets, powder, how many grains you are shooting in your loads). I would still like that info . Thanks, Tim

mossy33oak

No one????? I thought this posts pretty much summed up what i was shooting.......was there something I missed??? Except maybe that I use Win Mag primers?????

stubblejumper

180gr bullets-92gr to 95gr of reloader 25.

bigcountry

Ok, taw, try that load from Mossy. I gave it to him and it shoots great in my two 300RUM's and Mossys. Seems to be a very dynamic load.

I also have wonderful luck with 89-91gr of Re25 and 180 Barnes TSX.

Lastly for a long distance target load, I shoot 96gr of Retumbo and 190gr Sierra Matchking.

All of these with 215M primer. Remember COL can make a big difference with Barnes bullets. My COL runs anywhere from 3.59" - 3.635". My target load has a COL of 3.68".

taw

I am very sorry mossy33oak you were very helpful and thanks to everyone else who has helped out with some info. Tim