7X300WM- Heavy Bolt Lift only on Fire Formed - Need to Neck Turn?
- By Tikkad
- Reloading Depot
- 9 Replies
Hello all, I have been in the process of researching a build for a new long range hunting rifle for a long time now and after too much contemplation I finally "pulled the trigger". It is a Remington 700 Action that I had a Bartlen 1:8 twist barrel chambered in 7MMX300 Win Mag. The barrel is finished at 26" + the break. I already had the MPA Ultra Lite chassis for it and had a Triggertech trigger installed. The Action was Blueprinted and if you can call it Truing for a Rem 700 it was. The break was timed but the Trigger/Bolt was not.
I am having some problems now though after being incredibly pleased with my initial shooting of right around 0.446" at 100 yards for a 6 round group. ( I load 6 so that I can have a 5 round group with a true called flyer if needed. This one was not needed so I just made the hole a little bit bigger. This was shot during the initial barrel break in and preliminary load development.
The smith that built this rifle uses a different type and manufacturer of brass. (Old Remington I believe- I could not tell you the exact details, but not anything I can get.
It is however a reamer for 300 Win Mag necked down to 7MM.
After having good luck with Lapua 300 Win Mag brass in a true 300 Win Mag I decided to use that.
I am now however thinking that due to the neck thickness of Lapua brass that I may need neck turn this. I have never neck turned before- But I have researched it and have everything I need with the exception of a 7mm Mandrel which is now set to arrive tomorrow.
If you all could weigh it if you think Neck turning is indeed going to help provide a solution and also any input on how/when to do that would be incredibly appreciated.
With little prep the Lapua Virgin Brass shoots well. I am getting some flattened primers but no other signs of pressure except for a heavy bolt lift that is different then what I have experienced as a pressure sign on other guns in previous loads. It is only that last 10 Degrees or so of bolt lift that is at all heavy like it just needs to make that final "snap into place". That's why I made the comment about also possibly needing to have the firing pin/bolt timed? Sorry for my ignorance- But I still have much to learn and want to soak up as much knowledge from the experienced users on here as possible.
The Virgin brass that requires extra effort for that last 10 or so degrees is only on the higher end of my load data.
The real issue was once I went to shoot my now fire formed brass. I have done so twice so far. My last trip to the range yesterday I shot some additional Virgin Brass to continue to work up my stock pile of fire formed brass while also shooting what I was hoping would be working towards my final load development for this rifle. I had trimmed the brass as it had now been fired twice and per the data was needed, but it was properly chamfered and deburred. After experiencing the issue I also closely examined for any "lip" from the trimming process which was not present.
Even though I was still .003 off the lands this now 2X fired brass was somewhat difficult to chamber like what you would experience with a load that was jammed into the lands. No true force was needed, but it was clear that operation was not smooth or proper. Once fired I was getting all "heavy bolt lifts" mostly for that same last 10 degrees.
When I got back to the range I took a few of these pieces of brass to see if my 7mm Berer EOL Elite Hunters would fit by hand back into the fired and not yet re-sized brass. even with what limited force I could give it with my hand I could not get the correct projectile to fit into the case neck past the rear taper where the true bullet diameter of .284 is. (same type/brand/weight/lot bullet that was shot only an hour earlier)
When measuring the inside diameter of the neck with just my calipers I am getting between .2795 and .2815. This does not seem right to me as the bullet that was loaded yesterday morning into this brass was .284 and shot that afternoon before these measurements were taken.
This leads me to believe that the neck on my brass is to thick for my chamber- Is this an accurate assumption?
When I measure with a ball micrometer the neck wall thickness of the brass is reads at different locations on different 2x fired brass of 0.01565" - 0.01605". I did tumble the brass prior to these readings to remove the carbon which I believed would affect these measurements. After seeing the discrepancies I believe my neck tension/consistency would benefit from turning the neck regardless of whether or not this thickness was too great for my chamber.
My real questions are as follows-
Do you believe turning the necks will help/solve this issue of the 10 degrees of heavy bolt lift?
Assuming I will be turning these necks how much do I take off? My original thoughts (though I still need to measure more cases) would be based off the .284 7mm Diameter and subtract narrowest fire formed neck inside diameter IE .2795. Then this measurement of .0045" would be divided by 2 since I would be trimming the neck 360 degrees and the measurement needed is a diameter. So that would mean .00225" Minimum just to get to .284. But would I want to take off a little bit more than the bare minimum? Subtracting .002225 would give me a new neck thickness of .0134" Which I understand to still be a fairly "healthy" neck thickness. Would I be better off going ahead and trimming everything down to and even .013" or even less to prevent this from happening once additional firings of this brass occur? Maybe .0125" for my target neck wall thickness?
It is my understanding that is best to turn the necks just after resizing- Is that accurate?
Finally- Based on what I have described- Do you think turning the necks is all that is needed- Or is there anything that stood out to anyone that may mean that I do still need to get the bolt timed?
I am having some problems now though after being incredibly pleased with my initial shooting of right around 0.446" at 100 yards for a 6 round group. ( I load 6 so that I can have a 5 round group with a true called flyer if needed. This one was not needed so I just made the hole a little bit bigger. This was shot during the initial barrel break in and preliminary load development.
The smith that built this rifle uses a different type and manufacturer of brass. (Old Remington I believe- I could not tell you the exact details, but not anything I can get.
It is however a reamer for 300 Win Mag necked down to 7MM.
After having good luck with Lapua 300 Win Mag brass in a true 300 Win Mag I decided to use that.
I am now however thinking that due to the neck thickness of Lapua brass that I may need neck turn this. I have never neck turned before- But I have researched it and have everything I need with the exception of a 7mm Mandrel which is now set to arrive tomorrow.
If you all could weigh it if you think Neck turning is indeed going to help provide a solution and also any input on how/when to do that would be incredibly appreciated.
With little prep the Lapua Virgin Brass shoots well. I am getting some flattened primers but no other signs of pressure except for a heavy bolt lift that is different then what I have experienced as a pressure sign on other guns in previous loads. It is only that last 10 Degrees or so of bolt lift that is at all heavy like it just needs to make that final "snap into place". That's why I made the comment about also possibly needing to have the firing pin/bolt timed? Sorry for my ignorance- But I still have much to learn and want to soak up as much knowledge from the experienced users on here as possible.
The Virgin brass that requires extra effort for that last 10 or so degrees is only on the higher end of my load data.
The real issue was once I went to shoot my now fire formed brass. I have done so twice so far. My last trip to the range yesterday I shot some additional Virgin Brass to continue to work up my stock pile of fire formed brass while also shooting what I was hoping would be working towards my final load development for this rifle. I had trimmed the brass as it had now been fired twice and per the data was needed, but it was properly chamfered and deburred. After experiencing the issue I also closely examined for any "lip" from the trimming process which was not present.
Even though I was still .003 off the lands this now 2X fired brass was somewhat difficult to chamber like what you would experience with a load that was jammed into the lands. No true force was needed, but it was clear that operation was not smooth or proper. Once fired I was getting all "heavy bolt lifts" mostly for that same last 10 degrees.
When I got back to the range I took a few of these pieces of brass to see if my 7mm Berer EOL Elite Hunters would fit by hand back into the fired and not yet re-sized brass. even with what limited force I could give it with my hand I could not get the correct projectile to fit into the case neck past the rear taper where the true bullet diameter of .284 is. (same type/brand/weight/lot bullet that was shot only an hour earlier)
When measuring the inside diameter of the neck with just my calipers I am getting between .2795 and .2815. This does not seem right to me as the bullet that was loaded yesterday morning into this brass was .284 and shot that afternoon before these measurements were taken.
This leads me to believe that the neck on my brass is to thick for my chamber- Is this an accurate assumption?
When I measure with a ball micrometer the neck wall thickness of the brass is reads at different locations on different 2x fired brass of 0.01565" - 0.01605". I did tumble the brass prior to these readings to remove the carbon which I believed would affect these measurements. After seeing the discrepancies I believe my neck tension/consistency would benefit from turning the neck regardless of whether or not this thickness was too great for my chamber.
My real questions are as follows-
Do you believe turning the necks will help/solve this issue of the 10 degrees of heavy bolt lift?
Assuming I will be turning these necks how much do I take off? My original thoughts (though I still need to measure more cases) would be based off the .284 7mm Diameter and subtract narrowest fire formed neck inside diameter IE .2795. Then this measurement of .0045" would be divided by 2 since I would be trimming the neck 360 degrees and the measurement needed is a diameter. So that would mean .00225" Minimum just to get to .284. But would I want to take off a little bit more than the bare minimum? Subtracting .002225 would give me a new neck thickness of .0134" Which I understand to still be a fairly "healthy" neck thickness. Would I be better off going ahead and trimming everything down to and even .013" or even less to prevent this from happening once additional firings of this brass occur? Maybe .0125" for my target neck wall thickness?
It is my understanding that is best to turn the necks just after resizing- Is that accurate?
Finally- Based on what I have described- Do you think turning the necks is all that is needed- Or is there anything that stood out to anyone that may mean that I do still need to get the bolt timed?
