Higher then expected velocities, .270win - IMR 4350 - Nosler Ballistic Tip 130gr

[Tuxie]

Developing my first load for my TC Dimension 270 barrel, I have imr 4350 on hand so thats why I went that route. 1st stage I'm looking for "velocity nodes" (I know thats not the most correct term) so I can do some condensed OCW work. The velocities I'm seeing lead me to believe my chronograph is off, it was a direct sun day today. Also I did allow my barrel to warm up middle to the end of the shot string, was running short on time. My chrono is a Caldwell ballistic precision. Can I / should I use the data collected below to look for the flat spots in charge weight / muzzle velocity. Or is there some thing in the info collected below that would explain the velocities observed. I forgot to note it on the range day sheet but the bullets are seated 0.02" off the lands. Also I am aware that the first half of my shot string is pretty useless data as I probably would'nt look there for a accurate load but I was curious so I did it anyways.

Tuxie

 

[Straightshooter1]

Developing my first load for my TC Dimension 270 barrel, I have imr 4350 on hand so thats why I went that route. 1 stage I'm looking for "velocity nodes" (I know thats not the most correct term) so I can do some condensed OCW work. The velocities I'm seeing lead me to believe my chronograph is off, it was a direct sun day today. Also I did allow my barrel to warm up middle to the end of the shot string, was running short on time. My chrono is a Caldwell ballistic precision. Can I / should I use the data collected below to look for the flat spots in charge weight / muzzle velocity. Or is there some thing in the info collected below that would explain the velocities observed. I forgot to note it on the range day sheet but the bullets are seated 0.02" off the lands. Also I am aware that the first half of my shot string is pretty useless data as I probably would'nt look there for a accurate load but I was curious so I did it anyways.

Tuxie




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What COAL are those cartridges and the length of your barrel?

Yes, there could very well be an issue with your chrono accuracy. If you can, see if someone at the range or who you might be shooting with has a chrono you can check your velocity with . . . preferably someone with a LabRadar or a MagnetoSpeed.

The extraordinarily high MV's for those powders load could be largely as a result of how close you are to the lands (like, almost touching), which will result in significant pressure spike.

So my thoughts are, it might be a combination of these two things???

 

[HTSmith]

I am anything but an expert, but I spent a lot of time with the 270 Win and those exact bullets when I started out years ago. I can't believe those speed numbers, but whatever was wrong could well be "proportional" (for lack of a better term). Assuming you had no pressure signs, I would focus on the 54.2 Gr. load. In fact the best load in my 270W was 54.0 Gr of IMR450. 20 thousandths off the lands is a good place for a hunting round. 2 thousandths is not IMHO.

 

[Big Mc]

Developing my first load for my TC Dimension 270 barrel, I have imr 4350 on hand so thats why I went that route. 1 stage I'm looking for "velocity nodes" (I know thats not the most correct term) so I can do some condensed OCW work. The velocities I'm seeing lead me to believe my chronograph is off, it was a direct sun day today. Also I did allow my barrel to warm up middle to the end of the shot string, was running short on time. My chrono is a Caldwell ballistic precision. Can I / should I use the data collected below to look for the flat spots in charge weight / muzzle velocity. Or is there some thing in the info collected below that would explain the velocities observed. I forgot to note it on the range day sheet but the bullets are seated 0.02" off the lands. Also I am aware that the first half of my shot string is pretty useless data as I probably would'nt look there for a accurate load but I was curious so I did it anyways.

Tuxie




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Your barrel must be a hummer. I cant get those numbers out of my Sako ,same powder and bullet. Not saying you didnt. But I cant. Tommy Mc 24 inch barrel.

 

[DGP4]

I bought a cheap T/C Compass in .270 WIN on sale for hunting. I have not done much testing , but so far I got 1/2 inch groups at 100 yards with 150 grain Speer Grand Slams over 50.5 grains of 4350. I also tested some 130 grain Grand Slams over 51.5 grains of 4350 and got 1 inch groups at 100 yards. My gun definitely likes the 150 grain bullets better. My Mauser K98 sporter in the same caliber is just the opposite, likes 130 grain bullets way more than the 150 grainers.

 

[Tuxie]

What COAL are those cartridges and the length of your barrel?

Yes, there could very well be an issue with your chrono accuracy. If you can, see if someone at the range or who you might be shooting with has a chrono you can check your velocity with . . . preferably someone with a LabRadar or a MagnetoSpeed.

The extraordinarily high MV's for those powders load could be largely as a result of how close you are to the lands (like, almost touching), which will result in significant pressure spike.

So my thoughts are, it might be a combination of these two things???

I'm using CBTO measurements to set my seating depth, using oal guage and comparator body I'm getting a max CBTO on my barrel of 2.8140". I'm then setting seating depth to make my CBTO 2.7940" (well actually on average closer to 2.7945"). This is done on brand new brass for this set of data. Does this seem like a acceptable method of placing bullet 2 hundredths off the lands. I've got less then 3 years of reloading experience.

Secondly, I plan to still use that CW - MV graph to investigate flat spots in the velocity slope. Is this fool hardy?.

 

[Straightshooter1]

I'm using CBTO measurements to set my seating depth, using oal guage and comparator body I'm getting a max CBTO on my barrel of 2.8140". I'm then setting seating depth to make my CBTO 2.7940" (well actually on average closer to 2.7945"). This is done on brand new brass for this set of data. Does this seem like a acceptable method of placing bullet 2 hundredths off the lands. I've got less then 3 years of reloading experience.

Secondly, I plan to still use that CW - MV graph to investigate flat spots in the velocity slope. Is this fool hardy?.

Your method is sound for finding how far you are from "your" lands. But because comparators can vary substantially as well as chamber freebores do, CBTO's simply tells me nothing about the seating depth of your cartridge. This is why I aske for the COAL, as I could then better figure out what your seating depth is (within a reasonable amount, anyway). With a good idea of your actual seating depth and the barrel length, in addition to the other load information you've posted, I can get a better picture of what's involved with those particular velocities.

 

[Tuxie]

Your method is sound for finding how far you are from "your" lands. But because comparators can vary substantially as well as chamber freebores do, CBTO's simply tells me nothing about the seating depth of your cartridge. This is why I aske for the COAL, as I could then better figure out what your seating depth is (within a reasonable amount, anyway). With a good idea of your actual seating depth and the barrel length, in addition to the other load information you've posted, I can get a better picture of what's involved with those particular velocities.

Thanks Straightshooter, I will take some measurements when I get home. It is a 24" barrel, I will have to load a couple more, being careful to copy my exact procedure. It will be same virgin brass, all same components, same methods. Should give a accurate measurement of what the COAL was for those rounds.

 

[Tuxie]

Quick update: Think I probably found the 2 largest contributing factors for the high readings. Firstly I was shooting in the worst light conditions for this chrono, Mid day direct sunlight. Secondly when I set up the chrono on the tripod, I eyeballed it and did'nt take the time to properly level it. I bet it was close but by no means on bubble. Will be interesting to compare my data from this to when I do my OCW testing.

 

[Webster]

Developing my first load for my TC Dimension 270 barrel, I have imr 4350 on hand so thats why I went that route. 1 stage I'm looking for "velocity nodes" (I know thats not the most correct term) so I can do some condensed OCW work. The velocities I'm seeing lead me to believe my chronograph is off, it was a direct sun day today. Also I did allow my barrel to warm up middle to the end of the shot string, was running short on time. My chrono is a Caldwell ballistic precision. Can I / should I use the data collected below to look for the flat spots in charge weight / muzzle velocity. Or is there some thing in the info collected below that would explain the velocities observed. I forgot to note it on the range day sheet but the bullets are seated 0.02" off the lands. Also I am aware that the first half of my shot string is pretty useless data as I probably would'nt look there for a accurate load but I was curious so I did it anyways.

Tuxie




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This subject has been covered many times. The flat spots only occur because ES is being ignored. Even if you plot 5 shots at each load you may see flat spots. I can get an ES of 30 shooting .350" groups with my 6BR GH hunting rifle. Shoot for group size. Small and round. It's 270 Win hunting rifle don't burn up money trying to make it a bench rest rifle.

 

[Tuxie]

This subject has been covered many times. The flat spots only occur because ES is being ignored. Even if you plot 5 shots at each load you may see flat spots. I can get an ES of 30 shooting .350" groups with my 6BR GH hunting rifle. Shoot for group size. Small and round. It's 270 Win hunting rifle don't burn up money trying to make it a bench rest rifle.

I am aware of this debate and was'nt looking to have it here. For me personally I have used the 10 shot ladder test to get me quicker into some focused OCW testing. Here I went further down the charge weights then I would normally, but that was for curiosity's sake. I am also very aware that this method does not account for ES / SD which is a valid criticism. But at the end of the day there are very good shooters using this method as a jumping off point to get them to a load with very tight groups with low standard deviation, and there doing it burning less powder then if you only employed the OCW method on its own. The flat spots are the result of how charge weight can effect barrel harmonics. Unfortunately my level of knowledge on barrel harmonics is just that, that it exists.

 

[rickt300]

Out of one of my 270's I get 3110 fps using 53 grains of I4350 which I thought was high. Shot great shows no pressure signs so I still use it. 24 inch barrel, Winchester brass and CCI 250 primers. 130 grain Nosler Partition.

 

[Tuxie]

Out of one of my 270's I get 3110 fps using 53 grains of I4350 which I thought was high. Shot great shows no pressure signs so I still use it. 24 inch barrel, Winchester brass and CCI 250 primers. 130 grain Nosler Partition.

Well thats interesting. As I went up I checked every piece of brass for signs of over pressurization and did'nt get any. I am going to compare when I do some OCW work. I was pretty confident my velocities readings were out to lunch due to improper setup on my chrono, but you never know.

 

[Coyotefurharvester]

What primer? I would load 3 at Nosler start load, seat the bullet to the Nosler oal. Shoot and compare the average to the their data. I have three Dimension barrels, 204,223,22-250 I have not chronographed them, I will this spring.

 

[Tuxie]

What primer? I would load 3 at Nosler start load, seat the bullet to the Nosler oal. Shoot and compare the average to the their data. I have three Dimension barrels, 204,223,22-250 I have not chronographed them, I will this spring.

CCI LR No. 200

 

[Webster]

I am aware of this debate and was'nt looking to have it here. For me personally I have used the 10 shot ladder test to get me quicker into some focused OCW testing. Here I went further down the charge weights then I would normally, but that was for curiosity's sake. I am also very aware that this method does not account for ES / SD which is a valid criticism. But at the end of the day there are very good shooters using this method as a jumping off point to get them to a load with very tight groups with low standard deviation, and there doing it burning less powder then if you only employed the OCW method on its own. The flat spots are the result of how charge weight can effect barrel harmonics. Unfortunately my level of knowledge on barrel harmonics is just that, that it exists.

Your data with computer generated error bars. I eliminated the 2 obvious outlyers. Looks like the calculated ES for all shots is about 25. Personally I would shoot a few 5 shot groups and just stick with what was reasonable for hunting. Didn't include a best fit straight line thru the data, it looks bad. Your still saying there are flat spots that have value. An R squared of .99 means good correlation.

 

[Tuxie]

Your data with computer generated error bars. I eliminated the 2 obvious outlyers. Looks like the calculated ES for all shots is about 25. Personally I would shoot a few 5 shot groups and just stick with what was reasonable for hunting. Didn't include a best fit straight line thru the data, it looks bad. Your still saying there are flat spots that have value. An R squared of .99 means good correlation.
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Very cool Webster, I am printing and placing in my dope book. that is my next step. I did a bunch of measuring pre / post firing, and my COAL measurement which I neglected to take much notice of as I was putting more faith in my CBTO measurements ( Which I neglected to measure my hornady OAL case, vs my virgin brass I was using). I loaded up 5 rounds at 53.6 and if I like the group and get a acceptable SD I might stop there for charge weight, if I don't like it I will move up and down from there. Either way I'm interested in what you and Straightshooter have to say about my COAL measurement as I obviously did screw up a bit. Will post in a separate post.

 

[Tuxie]

Your method is sound for finding how far you are from "your" lands. But because comparators can vary substantially as well as chamber freebores do, CBTO's simply tells me nothing about the seating depth of your cartridge. This is why I aske for the COAL, as I could then better figure out what your seating depth is (within a reasonable amount, anyway). With a good idea of your actual seating depth and the barrel length, in addition to the other load information you've posted, I can get a better picture of what's involved with those particular velocities.

Sorry Straightshooter, should have got this to you yesterday. My COAL avg on my next 5 rounds (loaded to 53.6 gn) loaded exactly the same way as the previous was 3.3559". Compared to Max SAAMI of 3.3400". The one thing I should have noticed was my Hornady modified case has a OAL of 2.5315, where as my virgin brass OAL was 2.5360.

The following are measurements collected pre / post firing (Unfortunately I don't have the comparator for shoulder length);

OAL: New 2.5360" Fired 2.5330 (approx, noticed the most variance on this dimension)

Shoulder Diameter: New 0.4390" Fired 0.4455

Web Diameter: New 0.4650 Fired 0.4705

Neck OD: New 0.3045 Fired 0.3105

 

[Straightshooter1]

Sorry Straightshooter, should have got this to you yesterday. My COAL avg on my next 5 rounds (loaded to 53.6 gn) loaded exactly the same way as the previous was 3.3559". Compared to Max SAAMI of 3.3400". The one thing I should have noticed was my Hornady modified case has a OAL of 2.5315, where as my virgin brass OAL was 2.5360.

The following are measurements collected pre / post firing (Unfortunately I don't have the comparator for shoulder length);

OAL: New 2.5360" Fired 2.5330 (approx, noticed the most variance on this dimension)

Shoulder Diameter: New 0.4390" Fired 0.4455

Web Diameter: New 0.4650 Fired 0.4705

Neck OD: New 0.3045 Fired 0.3105

Well, looking at all the numbers and some of them are just not adding up. Your loads from 51.0 -55.0 grs of IMR-4350 and these bullets seated .020 off the lands should not be causing any kind of excessive pressure issue that would explain such high velocities. Even if you had a 32" barrel, these would be well above expected velocities. This does lead me to simply think your chrono is not giving you accurate readings. If I were you I'd try to take a couple shots across someone else's chrono and see what it gets, then you'd have a better idea what to look at next, if anything.

You're measurements for your shoulder and web diameter don't look good, in the one shouldn't have such a difference between a new and fired case . . . especially at the web. Number like that tells me there some major pressure going on, and if so, then such pressure could explain those velocities. But, I'd think with pressure that can do those things, you'd have seen a lot of pressure signs include a stiff or hard bolt lift.

I might expect the case web to grow as much a .002, but .0055 is a lot. So, something here just doesn't seem right to me. A lot of expansion at the web like that happen with a lot of pressure. Also, I wouldn't expect the case OAL to be .003 shorter after being fired; usually it's the other way around after sizing.

A lot of mysterious things going on there, and it seems to start with the chrono numbers you've got.

 

[Tuxie]

Well, looking at all the numbers and some of them are just not adding up. Your loads from 51.0 -55.0 grs of IMR-4350 and these bullets seated .020 off the lands should not be causing any kind of excessive pressure issue that would explain such high velocities. Even if you had a 32" barrel, these would be well above expected velocities. This does lead me to simply think your chrono is not giving you accurate readings. If I were you I'd try to take a couple shots across someone else's chrono and see what it gets, then you'd have a better idea what to look at next, if anything.

You're measurements for your shoulder and web diameter don't look good, in the one shouldn't have such a difference between a new and fired case . . . especially at the web. Number like that tells me there some major pressure going on, and if so, then such pressure could explain those velocities. But, I'd think with pressure that can do those things, you'd have seen a lot of pressure signs include a stiff or hard bolt lift.

I might expect the case web to grow as much a .002, but .0055 is a lot. So, something here just doesn't seem right to me. A lot of expansion at the web like that happen with a lot of pressure. Also, I wouldn't expect the case OAL to be .003 shorter after being fired; usually it's the other way around after sizing.

A lot of mysterious things going on there, and it seems to start with the chrono numbers you've got.

I didn't know what to expect on the shoulder and web dimensions. I knew they would expand after being fireformed, but did not know how much would be a normal range. Good info. The OAL brass length was a surprise to me as well, I did'nt know what to make of it, but to be clear these numbers are from brass that has not been resized yet. That will be my next set of dimensions I take, but it won't be till after I fireform all 51 pieces of brass (yes I got a bonus piece, lucky me.). I'll then tumble, resize, remeasure, trim, remeasure.

Edit: Sounds like case shrinkage is a result of a roomy chamber, which is not too surprising in a TC dimension, and I could be miss referencing web diameter and expansion ring diameter.