Didn't know if I should post this in the reloading forum or in bolt action rifles. I figured bolt action rifles as it's more about the barrels than the actual reloading or the load data.
We get asked the question a lot about tight bore barrels and standard bore barrels, faster, slower, barrel life etc.... This didn't start out as a test but while I was loading ammo up Friday night for my K98k SSR build/rifle that I'm working on it came to me.
The barrel on my K98k is a tight bore barrel where as the barrel on my shop test rifle (Savage 112v) is a standard bore barrel. Both have the same chamber, twist etc....so I chronographed tested both guns Saturday morning.
The test I will call it semi scientific as there are some minor differences but the results where interesting.
Here are a couple of pictures with descriptions:
The set up and the conditions. The distance from the shooting bench to the target/backstop is 114 yards. The range faces N/NE. Chronograph was 15 feet from the bench.
Conditions: Temp. 60F, wind SE at 11mph, humidity 80%, dew point 47 degrees and pressure was 28.89"
The guns and ammo sat outside for approx. 1 hour so they acclimated to the environment from being in the house.
The chronograph is a Oehler 35P with proof screen. Both guns are chambered in 7.5x58mm.
Savage 112v barrel K98k barrel
bore size = .3001" bore = .2991"
goove size = .3080" groove size = .3080"
twist = 11.25 twist = 11.25
finish length = 23" finish length = 23.5"
barrel = stainless steel barrel = chrome moly
Number & style of grooves for both = 5R
Both barrels where installed by myself and chambered with the same chamber reamer. All of the ammo was loaded with the same lot of bullets (175 Sierra Mk), same lot of powder (Varget) and same lot of cases (Win.) and same lot of primers (Fed210m). Bullets are seated .010" off the lands.
The ammo wasn't loaded for max. velocity. I backed off the load as usually I only shoot 155 Lapua's and have never loaded the 175's till this point. Also the K98k rifle action being made in 1941 my intent with that gun is to shoot it and enjoy it and not run max loads thru it.
The load was 47.0gr. of Varget +/- .1 of a grain. Charges where thrown thru a Harrell's BR powder measure and the weight of the charge was checked on two different scales.
The Savage barrel has 160 rounds on it and the K98k barrel has 80 rounds on it. So one barrel doesn't have 3k rounds on it and the other only 200 rounds. So basically both barrels are brand new.
I fired 4 rounds to foul each barrel doing the Savage first and then shooting 4 rounds thru the K98. I don't take chronograph readings with a cold clean barrel/include the very first round fired. Usually the very first round fired is slower than rest because the fouling will kinda act like a lubricant.
I set up the chronograph and then proceeded to clock the loads. I fired one round (recorded the data) to get the barrel back to the same temp. for the most part and cleared the chronograph and then fired 5 rounds. Again I did the Savage first and then the K98. I shot both guns the same way and with the same cadence.
Savage velocites where as follows: 2569, 2578, 2597, 2568, 2574fps.
ES = 29fps, avg. velocity = 2577fps, SD = 11
The K98 are as follows: 2574, 2584, 2574, 2571, 2584fps,
ES = 13, avg. velocity = 2577fps, SD = 6
If I thru in the first warm up round for a total of 6 rounds it came out to be an average of 2582 for the Savage and 2579 for the K98. Only a difference of 3fps.
I had to stop testing at that point as guys showed up in the field behind my backstop (dam snowmobile club putting in trail markers thru the field).
Again I call the test semi scientific. Both barrels where not made from the same material let alone the same lot of steel and different contours. Also the barrel length was different between the two. 23" for the Savage and 23.5". I would've expected a little faster reading from the K98 because of the extra length but it wasn't there. Also again it was a informal test and it wasn't done in a controlled environment/ballistics range and the test should be done with several barrels. Not just one each etc...you should make like 3 or 5 of each when doing tests like this. I feel you get better and more consistent data.
The summary of all of this goes back to what I always say. A tight bore (tops of the lands) doesn't effect the velocity and pressure as much as everyone thinks it does and at least in this case it showed it. Changing the groove size will have a greater impact on pressure and velocities. The next barrel I should do is a .299 bore x .309 groove. Will make the groove size +.001" bigger instead of a .308 groove size.
I know this will answer some questions and most likely raise more.....
Later, Frank
Bartlein Barrels
We get asked the question a lot about tight bore barrels and standard bore barrels, faster, slower, barrel life etc.... This didn't start out as a test but while I was loading ammo up Friday night for my K98k SSR build/rifle that I'm working on it came to me.
The barrel on my K98k is a tight bore barrel where as the barrel on my shop test rifle (Savage 112v) is a standard bore barrel. Both have the same chamber, twist etc....so I chronographed tested both guns Saturday morning.
The test I will call it semi scientific as there are some minor differences but the results where interesting.
Here are a couple of pictures with descriptions:
The set up and the conditions. The distance from the shooting bench to the target/backstop is 114 yards. The range faces N/NE. Chronograph was 15 feet from the bench.
Conditions: Temp. 60F, wind SE at 11mph, humidity 80%, dew point 47 degrees and pressure was 28.89"
The guns and ammo sat outside for approx. 1 hour so they acclimated to the environment from being in the house.
The chronograph is a Oehler 35P with proof screen. Both guns are chambered in 7.5x58mm.
Savage 112v barrel K98k barrel
bore size = .3001" bore = .2991"
goove size = .3080" groove size = .3080"
twist = 11.25 twist = 11.25
finish length = 23" finish length = 23.5"
barrel = stainless steel barrel = chrome moly
Number & style of grooves for both = 5R
Both barrels where installed by myself and chambered with the same chamber reamer. All of the ammo was loaded with the same lot of bullets (175 Sierra Mk), same lot of powder (Varget) and same lot of cases (Win.) and same lot of primers (Fed210m). Bullets are seated .010" off the lands.
The ammo wasn't loaded for max. velocity. I backed off the load as usually I only shoot 155 Lapua's and have never loaded the 175's till this point. Also the K98k rifle action being made in 1941 my intent with that gun is to shoot it and enjoy it and not run max loads thru it.
The load was 47.0gr. of Varget +/- .1 of a grain. Charges where thrown thru a Harrell's BR powder measure and the weight of the charge was checked on two different scales.
The Savage barrel has 160 rounds on it and the K98k barrel has 80 rounds on it. So one barrel doesn't have 3k rounds on it and the other only 200 rounds. So basically both barrels are brand new.
I fired 4 rounds to foul each barrel doing the Savage first and then shooting 4 rounds thru the K98. I don't take chronograph readings with a cold clean barrel/include the very first round fired. Usually the very first round fired is slower than rest because the fouling will kinda act like a lubricant.
I set up the chronograph and then proceeded to clock the loads. I fired one round (recorded the data) to get the barrel back to the same temp. for the most part and cleared the chronograph and then fired 5 rounds. Again I did the Savage first and then the K98. I shot both guns the same way and with the same cadence.
Savage velocites where as follows: 2569, 2578, 2597, 2568, 2574fps.
ES = 29fps, avg. velocity = 2577fps, SD = 11
The K98 are as follows: 2574, 2584, 2574, 2571, 2584fps,
ES = 13, avg. velocity = 2577fps, SD = 6
If I thru in the first warm up round for a total of 6 rounds it came out to be an average of 2582 for the Savage and 2579 for the K98. Only a difference of 3fps.
I had to stop testing at that point as guys showed up in the field behind my backstop (dam snowmobile club putting in trail markers thru the field).
Again I call the test semi scientific. Both barrels where not made from the same material let alone the same lot of steel and different contours. Also the barrel length was different between the two. 23" for the Savage and 23.5". I would've expected a little faster reading from the K98 because of the extra length but it wasn't there. Also again it was a informal test and it wasn't done in a controlled environment/ballistics range and the test should be done with several barrels. Not just one each etc...you should make like 3 or 5 of each when doing tests like this. I feel you get better and more consistent data.
The summary of all of this goes back to what I always say. A tight bore (tops of the lands) doesn't effect the velocity and pressure as much as everyone thinks it does and at least in this case it showed it. Changing the groove size will have a greater impact on pressure and velocities. The next barrel I should do is a .299 bore x .309 groove. Will make the groove size +.001" bigger instead of a .308 groove size.
I know this will answer some questions and most likely raise more.....
Later, Frank
Bartlein Barrels
