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Measuring Chamber OAL

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 09:35
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Has anyone ever tried this.  After thinking a while and not having a 6.5 Remington magnum modified cartridge for my Hornady OAL gauge, I thought of another way of doing it.  Take a cleaning rod that is small enough to sit flush against the bolt face and with the bolt in the rifle, put the rod in the muzzle all the way to the bolt face.  Make a mark on the rod exactly where the rod exist the muzzle.  Then, take the bullet that you are going to use and after removing the bolt, put it into the chamber and with the rod, push it forward until it sits on the lands and grooves, just as you would with the Hornady gauge.  Then, take the rod and put it into the barrel, while using the Hornady gauge grey piece or another rod or small wooden dowel to hold the bullet in place and slowly pass the rod into the barrel until it meets the bullet.  Then, make a mark on the rod exactly where it exist the muzzle and the difference in marks is your OAL of the chamber of your rifle for that bullet.  And, its free and can be done for any rifle. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 10:07
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Done it.
 
I actually read about it online sometime ago.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 10:16
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I prefer using a already fired case, crimp the case mouth a little so that you can ease a bullet in it. Place a bullet into the case mouth, slowly and softly chamber the round into the chamber, CAREFULLY extract the round and check the OAL. I do this 3 or 4 times to get an accurate measurement.
 
(The bullet has to have just enough tension to hold the bullet, but enough "give" that when you chamber the round, it will slide back into the case mouth when it contacts the rifling.)  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 10:44
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Originally posted by cheaptrick cheaptrick wrote:

I prefer using a already fired case, crimp the case mouth a little so that you can ease a bullet in it. Place a bullet into the case mouth, slowly and softly chamber the round into the chamber, CAREFULLY extract the round and check the OAL. I do this 3 or 4 times to get an accurate measurement.
 
(The bullet has to have just enough tension to hold the bullet, but enough "give" that when you chamber the round, it will slide back into the case mouth when it contacts the rifling.)  


I've done it this way and found it to be pretty accurate. With this method I was finally able to get Trophy Bonded Bear Claws to shoot good out of my 7mag.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 11:10
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       Those methods bring back some memories! They still work fine but I use a Sinclair tool now. Tell ya something else I found out. If you use a comparator to take your measurement of the most accurate cartridge OAL(measuring off of the ogive instead of the tip),and say your rifles accuracy is best at .030 off the lands with a certain bullet,substituting another bullet(even of different weight) at that same comparator cartridge OAL will give you the same accuracy. This has worked with my .25-06(100&115gr),my .300(150&180gr),and other guys rifles I've loaded for. Something else I read years back and has worked for me.
 
til later
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 11:48
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im intrested in trying this with my rifles somebody want to explain it to me in retard talk so i can understand it. also give me a list of things i need to accomplish this task would be nice as well.

Edited by pyro6999 - April/20/2008 at 11:48
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 12:46
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           Basically what your doing is finding a cartridge OAL with the bullet seated a certain distance off of the beginning of the rifling to give you optimum accuracy. The first thing I would do is go to www.sinclairintl.com and order a catalog. This is more than just a catalog as it also gives ALOT of accuracy info and reasons for using the tools you need. As far as what you need in the way of tools:
       --A set of 6" calipers
       --Sinclair hex style bullet comparator(comes in two models)
       --Sinclair bullet seating depth tool
These are the tools I use. There are others out there that will work but these are inexpensive and VERY precise.
 
til later
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 12:46
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Originally posted by 300S&W 300S&W wrote:

       Those methods bring back some memories! They still work fine but I use a Sinclair tool now. Tell ya something else I found out. If you use a comparator to take your measurement of the most accurate cartridge OAL(measuring off of the ogive instead of the tip),and say your rifles accuracy is best at .030 off the lands with a certain bullet,substituting another bullet(even of different weight) at that same comparator cartridge OAL will give you the same accuracy. This has worked with my .25-06(100&115gr),my .300(150&180gr),and other guys rifles I've loaded for. Something else I read years back and has worked for me.
 
til later
 
Your tool is more precise, to be sure.  
 
The glaring problem with my "spent cartridge" procedure is that bullets will vary in length, even match bullets that are in the same box. This will throw your results off some as well, but this method has served me well.     
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 12:53
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ive got calipers i just dont have the other stuff, im fixing to go to our shop and get myself some cases and some bullets and try cheaps method out and see what i get.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 13:00
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            With a comparator your are eliminating the varying bullet length problem by taking your OAL measurement off of the part of the bullet that does or will make contact with the rifling. Even if you measure your cartridges OAL from base of cartridge to tip of bullet(no need for this as all measurments will be taken with a comparator)and they vary,it will not matter because with a comparator the part that touches the rifling first(ogive)will be in the same place every time. Get the Sinclair catalog as it explains better than I can!
 
til later
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Originally posted by 300S&W 300S&W wrote:

            With a comparator your are eliminating the varying bullet length problem by taking your OAL measurement off of the part of the bullet that does or will make contact with the rifling. Even if you measure your cartridges OAL from base of cartridge to tip of bullet(no need for this as all measurments will be taken with a comparator)and they vary,it will not matter because with a comparator the part that touches the rifling first(ogive)will be in the same place every time. Get the Sinclair catalog as it explains better than I can!
 
til later
You're correct that it will not matter, but you'll lose a portion of  that advantage when you go to seat your bullet with a seating stem that contacts the bullet at any point on the ogive that is different than where the rifling contacts it. If your bullets vary, so will your true bullet jump.  It is certainly a very good method, but not truly precise in absolute terms, if you want to get really technical about it.
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 13:33
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        Honestly haven't had that problem. These comparators are cut with throating reamers to accurately duplicate the throat of a rifle. As long as you keep measuring,with the comparator,the first bullet you are seating until you get that predetermined OAL you got using the comparator the consistancy will be there. 
         RAMPS are done gotta go!!
 
til later
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 14:48
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im noticing that my rifles are all longer than my books consider max oal is that normal?? also now that i have these numbers how much deeper would you guys seat your bullets??

Edited by pyro6999 - April/20/2008 at 15:20
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 16:00
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      The OAL of your cartridge may be limited by the length of the magazine box.  That being said,Sinclair suggests adjusting seating depth in increments of .010" at a time beginning with LIGHTLY touching the rifling(lands),three shots a each depth until you obtain a good group. Then fine tune in increments of .005". We're talking benchrest and maybe varmint rifles here. I don't do this for my hunting loads. I start at .010" off of  the rifling(lands). My .300 shoots both 150s and 180s the best at .030".
       A word of caution here. Don't use loads you have already developed if your going to be moving closer to the rifling as this WILL raise pressures. Reduce the load some. Of course you should do this anytime you alter the cartridge or change components. Also anytime I'm developing loads I use a chronograph and watch as I approach but never go over the highest velocity in my Nosler #4 manual. Erratically low reading may mean somethings amiss also.
     


Edited by 300S&W - April/20/2008 at 16:12
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 16:06
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Originally posted by pyro6999 pyro6999 wrote:

im noticing that my rifles are all longer than my books consider max oal is that normal?? also now that i have these numbers how much deeper would you guys seat your bullets??
 
Yes, that's always the case in factory chambers.  The max OAL shown in reloading manuals is just the SAAMI standard max length that all cartridge manufacturers adhere to to ensure functioning in any rifle. 
 
Most accurate bullet seating depth differs from rifle to rifle, so what works well in my rifle wouldn't necessarily work well in yours.  It's a tuning thing.  At any rate, the max OAL from your manual is not necessarily the max length that will work in your rifle.  Many times the magazine box length is the true limiting factor in how long you can seat your bullets in a factory rifle rather than the throat, so you have to make sure first and foremost that the OAL chosen functions in your magazine.
 
I use the Sinclair comparators 300S&W mentions.  They cost $17.50 each, Sinclair p/n 09-600 (.224, 6mm, .25, 6.5mm, 7mm, .308) and p/n 09-700 (.17, .204, .224, .277, .308, .338)
 
If you're interested, give me a call, and I will explain in detail how to find your max chamber length using either a "dummy round" or seating depth gauge.
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Originally posted by 300S&W 300S&W wrote:

      The OAL of your cartridge may be limited by the length of the magazine box.  That being said,Sinclair suggests adjusting seating depth in increments of .010" at a time beginning with LIGHTLY touching the rifling(lands),three shots a each depth until you obtain a good group. Then fine tune in increments of .005". We're talking benchrest and maybe varmint rifles here. I don't do this for my hunting loads. I start at .010" off of  the rifling(lands). My .300 shoots both 150s and 180s the best at .030".
       A word of caution here. Don't use loads you have already developed if your going to be moving closer to the rifling as this WILL raise pressures. Reduce the load some. Of course you should do this anytime you alter the cartridge or change components.
 
Good advice.  You and I were posting at the same time, so I didn't mean to repeat your point about the magazine box limitation.  I've found best accuracy in my hunting rifles to vary between 0.020" - 0.040" off the lands.
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ok thanks guys i will try some of that, how much do you guess i should back off my loads? 10%  or more/less??
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Originally posted by pyro6999 pyro6999 wrote:

ok thanks guys i will try some of that, how much do you guess i should back off my loads? 10%  or more/less??
 
You have to let your rifle tell you what works best; there is no magic number.  I would start at 0.010" off the lands and work your way back (increasingly shorter) from there in 0.005" increments until you find the "sweet spot."  But again, your magazine box length may limit your OAL to where you can't get anywhere near the lands, so if that's the case, start with the longest length that will reliably function in your magazine box and load individual 10 - 15 round lots at the same seating depth, each lot with the bullets seated deeper in 0.005" increments from there until you find the best accuracy.


Edited by RifleDude - April/20/2008 at 16:26
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i went ahead and figured for backing off .020 off the lands and i have this much difference from what i currently use
22-250- .111" more than i use currently
6.5rem- .272" more than i use currently
.264win-.005" more than i use currently
.280rem-.188 more than i use currently
 
I just ran the numbers and i am some where in the neighborhood of .030 and .050 off the lands right now i ran my max oal and went .040 off the lands and my .264 and .280 would need to be backed out a hair to be .040 off the lands
well here are my numbers
22-250 @ .040 .091"
6.5rem @.040 .252"
.264@ .040 +.015"
.280@ .040 +.04" so i must be in that area now maybe i should shave into the 20-30 area huh?
so should i decrease my powder by say 10% to start or what??


Edited by pyro6999 - April/20/2008 at 16:37
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       No problem!!  I am VERY VERY reluctant about giving advice on load development. I have my own system that has worked FOR ME and the FEW friends I develop loads for over the better part of 25yrs. Just touching on the main concept of it though is that pressure is velocity and vice versa. High air temps,a chronograph,watching for pressure signs,and a reloading manual showing you the velocities they obtained at or below SAAMI set pressure limits are my tools. As I told someone at another forum until we're able to buy a pressure gauge just as we buy any other reload tool,I'll use anything available to me to produce first of all safe and reliable reloads.
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Originally posted by pyro6999 pyro6999 wrote:

i went ahead and figured for backing off .020 off the lands and i have this much difference from what i currently use
22-250- .111" more than i use currently
6.5rem- .272" more than i use currently
.264win-.005" more than i use currently
.280rem-.188 more than i use currently
 
so should i decrease my powder by say 10% to start or what??
 
I don't understand the first part of your post.  How do you know the difference in OAL for those 4 if you haven't yet measured your max OAL to the lands to see what the lengths are for each rifle's chamber?
 
As for the powder charge, you should be o.k. by backing off about 5 grains to start.
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i used marks dummy round method
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/20/2008 at 16:43
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          If you'll notice in your reload manuals the difference between start and max on average is 4grs.  So reduce by 4 grns.
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ok
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well i took my 6.5 rem out and there is no way i can get a 3.095 col into the magazine box about 2.85 is max for the mag box and i am at 2.823 right now my .280 is ok a 3.419 in the box my .264 has a ton of room also my 22-250 has a detachable clip and it looks like about 2.4 is a long as i can go there so i can move out with all my guns but some i cant go a lot more than where i am now.
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