Originally Posted by D.Camilleri
Factory barrels are button rifled. What this means is that a button is drawn through a bored barrel and the button finishes the bore and cuts the rifling. It is my understanding that a button is used for about 10 barrels and then discarded. If the barrel was cut with a new button, the barrel should be very close to spec on the + side and velocity should be fast. If the barrel was the last one cut with the particular button, the dimensions could be on the - side and cause slower velocity. These measurements will be in the .0001's of difference. This is what contributes to fast barrels and slow barrels. The velocity can often vary by as much as 150 fps. The first time I ever read about this was in an issue of shooting times magazine where they were talking about 7mm STW and the difference between fast barrels and slow barrels.
I am not sure if this is your problem or not. I would want to get some velocities from some other loads run through a chrono and then verify the drops with those before coming to any conclusions. As I have stated before, one of my chronos says 3175 with a 215 berger and the other chrono says 3075, but my drops show right at 3000. The drops are the important part. On the other hand, my gun with factory remington 180's shows 3350 accros my slow chrono and my handloads with 180 accubonds match the drops with 3350 as the velocity with 97 grains of H-1000 and seated to magazine length. I seat my bullets to within .010 of the magazine length and they still feed fine. The extra seating length lowers pressure and allows for more powder.
Hey Dave whats up? Its Randy here from Worland. Anyways I do a bit of long range shooting / hunting also. I shoot a 300 rum and 7mag. I have been reading the thread on how possible velocities are off from Chrono readings. I have a bit of news that all of you probably are familiar with but thought I would drop a line anyway. When shooting @ long range and your clicks do not correlate to what drop charts portray them to be the actual B.C. of the bullet varies. I know a couple of summers ago I was shooting 7mm bergers and different lot #'s of ammo would have different B.C. from what is advertised on boxes. The 7mm Berger 168's were shooting around .580-.590 B.C. versus what was advertised on the box .617. With a different lot # they would shoot a tad over .600. Very seldom have I seen Bergers shoot their actual B.C. The Berger 180's seem to be close in the 7mm and come in around .650 and advertised is .659. Jlk bullets have a bit higher B.C. with the same j4 jacket.
I have been shooting the .300 rum for some time on factory barrel and used to shoot 185 bergers with 98.7 grains of retumbo @ 3475 fps. This was also shooting around a .750 group @ 100 yds. I since have made the gun into a Semi Custom and is now getting a Brux Barrel, Wyatt box, HS Stock, Muzzle Break, Cerakote, Timney Trigger, Blue Printed, Flute cut bolt, and Huskemaw scope
. My buddy has the same gun that was built so we will both be running 185's trying to get them dialed in as above.... Sorry for the slight derail of the thread but overall I think all of our goals are to share information and help everyone to shoot & reload as good as we can! Have a great day everyone!