Componants are finally all here!!!
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Fiftydriver
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Nope, using his 6 groove.
Kirby Allen(50)
Kirby Allen(50)
Fiftydriver
Official LRH Sponsor
DA,
The barrel for my 338 AM?? If so yes, its already fitted to my receiver. Just have to get it teflon coated and the stock pillar bedded so I can start testing. Right now, up to my ears in customers projects. Guess thats a good thing /ubbthreads/images/graemlins/grin.gif!!
Kirby Allen(50)
The barrel for my 338 AM?? If so yes, its already fitted to my receiver. Just have to get it teflon coated and the stock pillar bedded so I can start testing. Right now, up to my ears in customers projects. Guess thats a good thing /ubbthreads/images/graemlins/grin.gif!!
Kirby Allen(50)
Fiftydriver
Official LRH Sponsor
D-A,
Already ran the 338 AM through some high pressure extraction testing to check for this. Ran her up to where I pierced a primer which was 152.0 gr of H-50BMG over a 300 gr SMK. Extraction was a breeze.
The Pierced primer was as a result of a weak firing pin spring I suspect. I have a replacement from BAT that feels MUCH stiffer. Have yet to install it though.
At 152 gr I was getting some slight extractor marking on the case head so I will consider 150.0 gr top loads with this powder and bullet. Actually right on my prediction, got lucky again.
No chrono testing yet, I was just holding the barrel with my left hand and tripping the trigger with my right. Just wanted to test the extraction of the top end loads before I sent the fired cases off to get FL dies made.
The amount of taper you need for good extraction depends on alot of factors. The main ones I would say are chamber finish and case diameter. The chamber needs to be smooth and free of any flaws obviously for good extraction with a min taper design.
But, the larger diameter a case is, its case baring surface increases dramatically. SO there is more to grip the walls of the chamber.
If you look at a chambering like the Ackley Improved rounds on the '06 case, they will run right at around 8 thou of taper per inch of case body length.
My 257, 6.5 and 270 AM chamberings based on the RUM case have aroughly 6.5 thou of taper per inch of body length, about as square as one should really go with a high pressure chambering with this diameter of a case.
With my 277 and 7mm AM based on the larger diameter 338 Lapua case for instance, I increased the taper per inch to a bit over 7.7 thou which is pushing things a bit. With very top end loads you will get sticky extraction with these two rounds.
THis how ever is by design. Had I designed the chamber for perfect extraction it would have had 8 to 8.5 thou of taper per inch of body. The reason I squared it up to 7.7 was as a safety device. My customers will get into sticky extractions before they reach the limits of the Lapuas case strength.
As these rounds were to be chambered in the Rem 700 receivers, I did not want my customers pushing the Lapua case until the primer pockets lossened up. This would be bad for any factory offered action, yes even the Wby MkV!!
By using this amount of taper, the cases will stick long before the chamber pressures get high enough to loosen the primer pockets on the Lapua case, basically acting as a safety limiter as there will be a very obvious warning sign to reduce your loads!!!
Back to the taper topic though.
Because the 338 Lapua case is larger I increased the taper slightly.
Taking it to the next step, the 338 AM based on the 408 CT case, I increased the body taper to just shy of 8 thou. There are no receivers out there for the 408 CT that can not handle top end loads, at least no receivers that were designed for the 408. As such I wanted to get top performance and the 8 thou taper per inch gives this result.
In comparision to all these, my 224 AM original design has only 6.2 thou of taper per inch of body length!!! You can see I got a bit optomistic here. Should have kept it in the 8 thou range at minimum with this case diameter for easy extraction at all pressure levels.
Soon it will have even more taper then this but thats just to insure easy extraction and it also aids a bit to smoother feeding with this very short case design.
So to answer your question, I would say for no extraction problems at all, I would recommend 8 thou of taper per inch of body length. This would be with a finely polished chamber that is totally free of chambering flaws!!
Just my opinion, I am sure there are many that differ from what I am saying to some degree or another!
Good Shooting!!
Kirby Allen(50)
Already ran the 338 AM through some high pressure extraction testing to check for this. Ran her up to where I pierced a primer which was 152.0 gr of H-50BMG over a 300 gr SMK. Extraction was a breeze.
The Pierced primer was as a result of a weak firing pin spring I suspect. I have a replacement from BAT that feels MUCH stiffer. Have yet to install it though.
At 152 gr I was getting some slight extractor marking on the case head so I will consider 150.0 gr top loads with this powder and bullet. Actually right on my prediction, got lucky again.
No chrono testing yet, I was just holding the barrel with my left hand and tripping the trigger with my right. Just wanted to test the extraction of the top end loads before I sent the fired cases off to get FL dies made.
The amount of taper you need for good extraction depends on alot of factors. The main ones I would say are chamber finish and case diameter. The chamber needs to be smooth and free of any flaws obviously for good extraction with a min taper design.
But, the larger diameter a case is, its case baring surface increases dramatically. SO there is more to grip the walls of the chamber.
If you look at a chambering like the Ackley Improved rounds on the '06 case, they will run right at around 8 thou of taper per inch of case body length.
My 257, 6.5 and 270 AM chamberings based on the RUM case have aroughly 6.5 thou of taper per inch of body length, about as square as one should really go with a high pressure chambering with this diameter of a case.
With my 277 and 7mm AM based on the larger diameter 338 Lapua case for instance, I increased the taper per inch to a bit over 7.7 thou which is pushing things a bit. With very top end loads you will get sticky extraction with these two rounds.
THis how ever is by design. Had I designed the chamber for perfect extraction it would have had 8 to 8.5 thou of taper per inch of body. The reason I squared it up to 7.7 was as a safety device. My customers will get into sticky extractions before they reach the limits of the Lapuas case strength.
As these rounds were to be chambered in the Rem 700 receivers, I did not want my customers pushing the Lapua case until the primer pockets lossened up. This would be bad for any factory offered action, yes even the Wby MkV!!
By using this amount of taper, the cases will stick long before the chamber pressures get high enough to loosen the primer pockets on the Lapua case, basically acting as a safety limiter as there will be a very obvious warning sign to reduce your loads!!!
Back to the taper topic though.
Because the 338 Lapua case is larger I increased the taper slightly.
Taking it to the next step, the 338 AM based on the 408 CT case, I increased the body taper to just shy of 8 thou. There are no receivers out there for the 408 CT that can not handle top end loads, at least no receivers that were designed for the 408. As such I wanted to get top performance and the 8 thou taper per inch gives this result.
In comparision to all these, my 224 AM original design has only 6.2 thou of taper per inch of body length!!! You can see I got a bit optomistic here. Should have kept it in the 8 thou range at minimum with this case diameter for easy extraction at all pressure levels.
Soon it will have even more taper then this but thats just to insure easy extraction and it also aids a bit to smoother feeding with this very short case design.
So to answer your question, I would say for no extraction problems at all, I would recommend 8 thou of taper per inch of body length. This would be with a finely polished chamber that is totally free of chambering flaws!!
Just my opinion, I am sure there are many that differ from what I am saying to some degree or another!
Good Shooting!!
Kirby Allen(50)
Black Diamond 408
Well-Known Member
What Kirby says is right on! My test reamer for the 338 Snipe Tac had .006 per inch taper, it would get sticky before it reached the top loads. I sent the reamer back to be reground to .009 per inch and now it extracts perfectly.
Ackley did lots of testing on chamber finish, he found that a fresh cut chamber would impart less stress on the bolt, the more you polish a chamber the more rearward thrust is created. Just somthing for you guys to mull over, i polish my chambers, "Just what he says"
There is a fine line where extraction and case taper meet, with full loads. With these big cases i suspect it is right around where Kirby has set his. Mine has just a bit more taper, but you couldnt see it if you set the two side by side.
Big-Boomers
Ackley did lots of testing on chamber finish, he found that a fresh cut chamber would impart less stress on the bolt, the more you polish a chamber the more rearward thrust is created. Just somthing for you guys to mull over, i polish my chambers, "Just what he says"
There is a fine line where extraction and case taper meet, with full loads. With these big cases i suspect it is right around where Kirby has set his. Mine has just a bit more taper, but you couldnt see it if you set the two side by side.
Big-Boomers
Fiftydriver
Official LRH Sponsor
The way I figure taper is to take the base diameter, actually the diameter at the bolt face if your looking at a chambering reamer print, take this base diameter and subtract from that the shoulder diameter.
This will give you a certain value, say "X".
Then take "X" and devide it by the length from the bolt face to the body/shoulder junction. This give you the taper per inch of case body length.
For example, here is my 338 AM dimensions:
Base/Bolt face diameter...0.6381"
Shoulder Diameter.........0.6180"
Difference................0.0201"
Case body length..........2.5792"
Total taper(0.0201") divided by case body length(2.5792") equals 0.0078" or 7.8 thou of taper per inch of case body.
I would agree with BD408 the difference in taper between his 338 ST and my 338 AM is meaningless as far as performance potential is concerned.
Good Shooting!!
Kirby Allen (50)
This will give you a certain value, say "X".
Then take "X" and devide it by the length from the bolt face to the body/shoulder junction. This give you the taper per inch of case body length.
For example, here is my 338 AM dimensions:
Base/Bolt face diameter...0.6381"
Shoulder Diameter.........0.6180"
Difference................0.0201"
Case body length..........2.5792"
Total taper(0.0201") divided by case body length(2.5792") equals 0.0078" or 7.8 thou of taper per inch of case body.
I would agree with BD408 the difference in taper between his 338 ST and my 338 AM is meaningless as far as performance potential is concerned.
Good Shooting!!
Kirby Allen (50)
Fiftydriver
Official LRH Sponsor
Did I reply my friend?? I get alot of e-mails, want to make sure I get a reply out to all of them.
Have a good day,
Kirby Allen(50)
Have a good day,
Kirby Allen(50)
Fiftydriver
Official LRH Sponsor
I will, I promise!! Have alot to answer today.
Kirby Allen(50)
Kirby Allen(50)
