The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > Handloading, Reloading, and Bullet Casting

Reply
 
Thread Tools Search this Thread
Old December 22, 2013, 01:31 AM   #26
1stmar
Senior Member
 
Join Date: March 21, 2012
Location: Connecticut
Posts: 2,378
My notes state 3.165 (includes the 2" for the comparator ) for a hornady 2265(55 gr sp) in 2009. I measured tonight and it was 3.183 or just about .020. Again with a 2265, not the same exact bullet but same model. Assuming no manufacturing changes.
1stmar is offline  
Old December 22, 2013, 11:02 AM   #27
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
The old military .30-06 bore erosion gauge made for M1's and M1903's has a taper of .010" diameter across 1.000" of length across the precision gauging surface. So, for every .001" enlargement of the origin of the rifling touching the gauge, the gauge will go .100" further into the bore; a .003" enlargement means the gauge goes .300" deeper in the bore. They read "0" on new barrels and "3" when the rifling at its origin's opened up .003".

Those 30 caliber barrels were considered worn out for service use when the gauge went in 1.000" and the index was at "10" on its scale. That meant the origin of the rifling had opened up to .310" from its original .300" bore diameter.

I've used one of those gauges to measure the bore erosion on muzzles for several 30 caliber rifles. They barely opened up at all over their life of a few thousand rounds. The Garand barrels' muzzles wore to enlarge them from cleaning with steel rods. Copper wash stopped over half an inch back from the muzzle at about 3000 rounds as well as the gauge showing the crown's bore diameter had opened up almost .002". But accuracy had not degraded as the bullet jackets no longer got wiped off that last half inch of travel on their way out the muzzle.

Last barrel I tracked carefully for muzzle erosion started out with a .2999" bore diameter in a Hart barrel with groove diameter of .3078"; 3000 rounds later the muzzle bore diameter had opened up to .3004"; a total of .0005". The origin of the rifling at its back end starting out at .2999" had opened up about .004": and the bore erosion gauge read "4"; accuracy had dropped off enough to be noticable.

I've known a few folks (one's me) who cut their 30 caliber magnum barrels off at the breech end making a 28" one 24" long then rechambering it for the .308 Win. Accuracy with them was as good as what a new barrel would produce. Whatever enlargement of the muzzle was not enough to be noticed. And the copper wash there was always the same after cleaning from the breech with solid steel rods; it went all the way to the muzzle at the same rate for the number of rounds fired after each cleaning.

Last edited by Bart B.; December 22, 2013 at 11:43 AM.
Bart B. is offline  
Old December 22, 2013, 12:28 PM   #28
1stmar
Senior Member
 
Join Date: March 21, 2012
Location: Connecticut
Posts: 2,378
I went through some of my saved targets. Most recent 10 shot group was .7". I don't have any 10 shot groups from when I first got it but 5 shot groups seemed to not have noticeably changed.
Are the military gauges available somewhere?
I may just rebarrel / bed it and be done with it. Like to get something sub .5 consistently and I just don't think I can get there with this. What should a recut on the breech end cost?
1stmar is offline  
Old December 22, 2013, 01:08 PM   #29
RC20
Senior Member
 
Join Date: April 10, 2008
Location: Alaska
Posts: 7,014
There are a number of sources for the gauges. The Steven Mathews is the least expensive (around $54 or so as I recall). The are abbreviated as TE/MW gauges for Throat Erosion and Muzzle Wear.

They are specific to certain rifles. 1903, M1 and I think the 7.62 Nato chamberings.

We have used the 1903 gauge to check Model of 1917s and it works well.
Its a relative aspect, particularity the TE as how the rear of the receiver over the magazine is formed affects your index. For the 1917 is maybe 1/2 a number off and the relationship has been consistent form one rifle to the next (if the MW is 2, then the TE is 2 or a bit better). I have seen one that was 2.5 for the MW and pushing 4 hard on the TE and thats unusual (I suspect blanks or maybe hot rounds as my theory is its rounds that cause MW and its the hot etching that east up the throat)

However, as long as its 30 caliber and you take measurements while new, you can establish your own baseline for what was normal and see the progression as time goes by. Probably can be done on any 30 caliber.

I have used it on a Sako 30-06 and the MW was spot on and the TE indication was very good using its index so it was not far off.

MW according to my resources is the biggest factor accuracy degradation in that it kicks the bullet off sideways as it leaves the muzzle. Throat erosion has a lot of barrel left to stabilize the bullet and its not abrupt, its still tapered feeding the bullet into the rifling a bit latter but still plenty to stabilize it. Once it gets long enough of course it does de-stabilize (we had a blank fired 1903 that went up past 10 on the gauge and would key hole bullets through a target at 50 yds and the MW was just fine (we did get it to shoot a lot better with 200 gr flat base bullets and at as low a velocity as the books allowed)

Frankly all the theories of how or why the wear occurs while technically interesting are irrelevant to the discussion. The need to measure and assess it and what factor it plays in accuracy reduction is what is relevant.

How good a condition is this rifle I bought (Mil Surplus as well as a target rifle as hunting rifles almost never have enough rounds through them to affect things).

Or a 30 caliber rifle you want to see how its doing and some idea when its the rifle and not you that is affecting its accuracy.
RC20 is offline  
Old December 22, 2013, 02:21 PM   #30
1stmar
Senior Member
 
Join Date: March 21, 2012
Location: Connecticut
Posts: 2,378
Thanks RC20, the rifle referenced in the thread is a Ruger MKII in 22-250. The rifle I'd like the Gauge for is a Ruger MKII in 30-06. The 22-250 has a 26" barrel so if MW is the major contributor to accuracy degradation I could easily cut an inch off and recrown. I'm not sure what the SAMMI specs are for the throat for 22-250 but if the bullet were seated to touch the lands it would probably only be resting in the case by about .020. Really doesn't feel like much. I don't need to seat the bullet to touch the lands, the point I am making is it feels like quite a bit of jump. The bullet (hornady 2265) I don't use anymore, I was only using it for comparison purposes since that was the bullet I used when I first made my measurement.
1stmar is offline  
Old December 22, 2013, 03:52 PM   #31
RC20
Senior Member
 
Join Date: April 10, 2008
Location: Alaska
Posts: 7,014
Given that the gauge would check the Muzzle (MW) pretty well.

There will be a bit of difference as how far the crown was recessed and the profile would change things there a bit but not dramatically.

Receiver end is going to be a bit further off and no idea which way.

If its new then you can take and log both readings and can see the progression.

If not new and you think its had wear then one that has just been used for hunting would give you a good idea.

There is mfg variation. You can actually have a brand new 30 caliber that theoretically reads 1.5 or even 2 for MW and not have been shot. I have not seen that but its possible. More typical is like .5 to 1.5. The TE would be the same if the mfg tolerance was on the large side for that particular barrel. Regardless is the baseline when new or fairly new. We have done probably 20+ of 30-06 with the gauges (which also have a mfg variation!) and if used as an indicator or a guide/baseline check it works well.
RC20 is offline  
Old December 22, 2013, 07:54 PM   #32
1stmar
Senior Member
 
Join Date: March 21, 2012
Location: Connecticut
Posts: 2,378
Do you have a link to the site?
1stmar is offline  
Old December 23, 2013, 12:50 PM   #33
F. Guffey
Senior Member
 
Join Date: July 18, 2008
Posts: 7,249
I made gages, the tapper does not lock me up, and as I have said I have no infatuation with tools, I use tools.

F. Guffey
F. Guffey is offline  
Old December 24, 2013, 12:48 PM   #34
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 8,927
Some folks have used steel taper pins with about .010" taper per inch. Coating one with dark ink (Magic Marker?), gently pushing it into the rifling, removing it then measuring its diameter at the marks made by the rifling. Done this myself on a friend's .270 Win and got good results as confirmed by a hole micrometer measuring bore diameters. They're available at a buck each; good quality, too.
Bart B. is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 12:05 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2021 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Page generated in 0.06691 seconds with 8 queries